Issue n°25 - December 2013
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|In this issue|
This final issue of the IMBER Update newsletter for 2013 focuses on some of the IMBER-related research that has been undertaken in the Asia-Pacific region. The IMBER community in this region is very active, and researchers from China, Japan and Korea (CJK) have been meeting every other year for more than a decade. The CJK symposia started under the auspices of GLOBEC and continue now under IMBER. The 6th such meeting was held in Japan in October. A brief overview of the meeting introduces some of the highlights that were presented, and is followed by eight articles showcasing some of the work that was presented.
An article from one of the working groups of the IMBER Regional Programme, CLIOTOP discusses the recently published special journal issue on the role of squids in pelagic ecosystems. Highlights from the IMBER-endorsed project Materials Transfer at the Continent-Ocean Interface (INCT-TMCOcean) are also included.
From all of us at the IMBER International and Regional Project Offices, best wishes for a very happy and healthy new year.
6th China-Japan-Korea IMBER Symosium (3-4 October 2013, Tokyo, Japan)
Hiroaki Saito1, Hiroshi Ogawa2, Se-Jong Ju3, Liuming Hu4*
1The University of Tokyo, Tokyo, Japan
2Fisheries Research Agency, Yokohama, Japan
3Korea Institute of Ocean Science & Technology, Ansan, South Korea
4IMBER Regional Project Office, ECNU, China.
The biennial China-Japan-Korea (CJK) IMBER Symposium series provides the countries’ scientists with the opportunity to collaborate, and share research achievements and ideas. The 6th in the series was held from 3-4 October 2013 at the University of Tokyo in Japan.
It aimed to:
More than 50 IMBER scientists from China, Japan, Korea, as well as several other countries, participated in the symposium (Fig. 1). In addition to talks, there were many poster presentations (Fig. 2).
The oral presentations were grouped into session themes.
Session 1: The impact of climate change on biogeochemical cycles in the marginal seas and adjacent open oceans
The presentations in this session reported on research relating to nutrients, carbon, trace metals and organic matter dynamics in coastal areas and open oceans. Several focused on the Kuroshio Current, East China Sea and Changjiang River, and discussed the implications of change in physical structure of the ocean and river systems on biogeochemical cycles.
Modelling oceanic nutrient fluxes, Xinyu Guo found a downstream intensification of nutrient transport by the Kuroshio Current. For more detail read the article. Masao Ishii reported on ocean acidification in the western North Pacific subtropical and tropical zones, and noted that acidification is underway in the interior of the subtropical gyre. Click here to learn more about the research.
Sources of NO3 were identified based on δ15N and δ18O values of NO3 in the East China Sea. It was found that their contribution to NO3 dynamics differed depending on the season and year. Read Yu Umezawa’s article. Using 13C & 15N tracer experiments, Xiuqing Ge concluded that the high primary production in summer in Tokyo Bay is controlled mainly by temperature and photosynthetically available radiation (PAR), rather than nutrients.
Session 2: Marine ecosystem responses to anthropogenic activities and natural stressors
Presentations in this session focused on biological responses to anthropogenic activities and natural stressors in the Yellow Sea, East China Sea, East/Japan Sea and North Pacific Ocean. Several presentations discussed the structural and functional responses and changes of marine ecosystems to anthropogenic and natural forcings (ocean warming, high CO2, hypoxia).
Meixun Zhao reported on the East China Sea coastal ecosystems in the past 30 years from biomarker records in the sediment cores. Eunho Ko reported on methodological comparisons (14C uptake method vs. fast repetition rate fluorometery) of primary production measurements in Korean waters.
Hongbin Liu explored predator-prey interactions in planktonic food webs under different food web structures and environmental conditions. Se-Jong Ju used multiple approaches to explore the structural role of Euphausia pacifica in the Yellow Sea. Yasunori Sakurai discussed the negative effect on the survival of Japanese common squid paralarvae, due to ocean warming, which may result in a decrease of the annual squid catch in the future.
Session 3: Modelling the interaction between marine biogeochemistry and food web dynamics.
Presentations in this session included discussions about models used to improve understanding of food web dynamics and biogeochemical cycles.
Eiji Masunaga’s article discusses the influence of internal waves on the movement of sediments in coastal regions. In addition to high resolution survey, the movement of suspended matter was reproduced by a mathematical model. The importance of the vortex structure generated by the breaking of internal waves which influenced the resuspension and cross-margin transport of sediments and nutrients was demonstrated.
Read more about Yoichi Ishikawa’s physical-biogeochemical coupled model, developed to assess the stock of neon flying squid (Ommastrephes bartrami) and forecast future feeding and spawning grounds under the global warming. The model was also used to develop a forecasting procedure of fishing grounds for neon flying squids. Both studies targeted the optimal use of the resource.
Jun Sun discussed the major factors controlling the distribution of coccolithophores in Chinese waters, and estimated their contribution to the carbon cycle.
Session 4: Towards the sustainable use of marine resources and services at the interface of marine and human systems
The studies in this session targeted socio-economic issues, especially relating to the use of marine fisheries resources.
Hiroaki Saito introduced the multidisciplinary research project, Study of Kuroshio Ecosystem Dynamics for Sustainable Fisheries (SKED), that aims to understand the influence of the Kuroshio on the nutrient supply and ecosystem dynamics, and to resolve the “Kuroshio paradox” (high fisheries productivity in the oligotrophic Kuroshio ecosystem). You can read more about SKED here.
Using satellite derived fishing ground and fine-scale model-derived environmental data, Sei-ichi Saitoh developed a method of predicting daily potential fishing zones for the Japanese common squid (Todarodes pacificus). The maps have helped to reduce fuel consumption and make the fishery more effective. Read more about this initiative here.
Takaomi Kaneko examined the social and economic impacts of the Japanese sardine stock collapse in the late 20th century. Four retrospective management options to regulate fishing were suggested, and a detailed analysis of the pros and cons of each option was conducted. Read the article to see if any of the options could perhaps have prevented the collapse.
Presentations mentioned above that are not described in articles in this newsletter can be seen on the IMBER website at:
The full report of this symposium is also available at the above webpage.
Science highlights from the 6th China-Japan-Korea IMBER Symosium
The Kuroshio Paradox and sustainable use of fisheries production: Introduction to SKED (The Study of Kuroshio Ecosystem Dynamics for Sustainable Fisheries)
Tohoku National Fisheries Research Institute, Fisheries Research Agency, Shiogama, Japan
Theme 1: Physical mechanisms controlling the variability in nutrient supply
Theme 2: Phytoplankton species composition and productivity
Theme 3: Ecosystem structure and biogenic elemental cycling
Theme 4: Fisheries and ecosystem interactions
Theme 5: Mathematical model analyses for understanding the ecosystem dynamics and sustainable use of ecosystem services
Theme 1 targets one of the key issues to solving the Kuroshio Paradox. Kuroda et al. (2012) developed a fine scale (~1 km) 3D mathematical model to understand offshore-coastal water interactions, nutrient dynamics and egg/larval transport. Nagai et al (2012) conducted direct observations of the microstructure of the Kuroshio Front and found negative potential vorticity (PV) in the mixed layer south of the Front. The measured turbulent kinetic energy dissipation rates are an order magnitude higher than those predicted by wind-scaling, which is estimated to be elevated by local wind and Ekman buoyancy flux driven by down-front wind. It is estimated that these physical processes play important roles in supporting primary productivity in the Kuroshio region.
Themes 2-4 relate to food-web processes. Nishibe et al. (submitted) found that poecilostomatoid copepods Oncaea spp., which are important prey item for juvenile fish, play an important role in transporting nanophytoplankton primary production to fish. Sapphirina spp. are known to transport picophytoplankton production to fish by feeding on doliolid, gelatinous zooplankton, which feed on pico- and nanophytoplankton (Takahashi et al., 2013). Suzuki et al. (unpublished) found the nano- and picophytoplankton are dominant components of phytoplankton assemblages in the Kuroshio ecosystem, even during phytoplankton blooms. These results suggest that poecilostomatoid copepods are key organisms to solving the Kuroshio Paradox.
Theme 5 uses models such as Ecopath with Ecosim and Multi species virtual population analysis (MSVPA-X). Okunishi et al. (2012) developed a 2D individual-based fish movement model. They are further developing the model to include the predators of small pelagic fish (skipjack tuna) to understand the impact of predators on migration and growth of sardine and anchovy.
Unlike most Japanese funded research projects, SKED has a 10-year life span. MEXT recognised that the usual shorter (3-5 years) terms are often too short to reach the goals of projects, and can prove to be inefficient.
Since spring 2012, SKED has conducted several research cruises relating to Themes 1-4. For more details about SKED and the cruises, please visit the web site http://tnfri.fra.affrc.go.jp/kaiyo/sked/english/index.html
- Kuroda, H., Setou, T., Aoki, K., Takahashi, D., Shimizu, M. and Watanabe, T. 2012. A numerical study of the Kuroshio-induced circulation in Tosa Bay, off the southern coast of Japan. Cont. Shelf Res., 53, 50-62.
- Nagai, T, Tandon, A., Yamazaki, H., Doubell, M. J., Gallager, S. 2012. Direct observations of microscale turbulence and thermohaline structure in the Kuroshio Front. J. Geophys. Res. 117, C08013, doi:10.1029/2011JC007228.
- Okunishi, T., Ito S., Ambe, D., Takasuka, A., Kameda, T., Tadokoro, K., Setou, T., Komatsu, K., Kawabata, A., Kubota, H., Ichikawa, T., Sugisaki, H., Hashioka, T., Yamanaka, Y., Yoshie, N., Watanabe, T. 2012. A modeling approach to evaluate growth and movement for recruitment success of Japanese sardine (Sardinops melanostictus) in the western Pacific. Fisheries Oceanography, 21, 44–57.
- Takahashi, K., Ichikawa, T., Saito, H., Kakehi, S., Sugimoto, Y., Hidaka, K., Hamasaki, K. 2013. Sapphirinid copepods as predators of doliolids: Their role in doliolid mortality and sinking flux. Limnol. Oceanogr. 58, 1972-1984.
Yoichi Ishikawa1,*, Toshiyuki Awaji1,2, Masafumi Kamachi3, Hiromichi Igarashi1, Shiro Nishikawa1, Haruka Nishikawa1, Yoshihisa Hiyoshi1, Yuji Sasaki1, Shuhei Masuda1, Norihisa Usui3, Sei-ichi Saitoh4, Mitso Sakai5, Masaki Seito6, Koji Koyamada2
1Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, Japan.
2Kyoto University, Yoshida-Nihonmatsu-cho, Sakyo-ku, Kyoto, Japan.
3Meteorological Research Institute, Japan Meteorological Agency, 1-1 Nagamine, Tsukuba, Ibaraki,305-0052, Japan.
4Faculty of Fisheries Sciences, Hokkaido University, 3-1-1, Minato, Hakodate, Hokkaido, 041-8611, Japan.
5Hachinohe Station, Tohoku National Fisheries Research Institute, Fisheries Research Agency, 25-259,Asa Shimomekurakubo, Hachinohe, Aomori,031-0841, Japan.
6Fisheries Research Institute, Aomori Prefectural Industrial Technology Research Center, 10, Tsukidomari, Moura, Hiranai-machi, Tsugaru-gun, Aomori, 039-3381, Japan.
With the aim of clarifying and forecasting new links between ocean/climate processes and biogeochemical and fishery environments, a new forecast-analysis system is being developed as part of the national “Research Program on Climate Change Adaptation” (RECCA) supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japan. A description of the program is summarized at: http://www.mext-isacc.jp/eng/.
The main goal of the project is a high-impact application of a 4D-VAR data assimilation system for a physical-biogeochemical coupled model for the stock assessment of neon flying squid (Ommastrephes bartramii) in the North Pacific. This is based on accurate determination of the spawning and feeding grounds, as well as forecasts of potential fishing areas, using a high-resolution model and sophisticated data assimilation system.
The subsurface ocean state was found to be a critical factor in forecasting potential fishing areas. The data assimilation system is therefore, very useful for integrating observation data, such as surface observations from satellite remote sensing, and subsurface profiles from in-situ and/or ARGO float data. In this study, the data assimilation system MOVE/MRI.com (MRI Multivariate Variational Estimation; Usui et al., 2006) developed by the Meteorological Research Institute at the Japan Meteorological Agency, were used. The potential fishing area was estimated from the construction of a habitat suitable index (HSI) model utilising data assimilation products. The results of the data assimilation and HSI model were made available to fishing vessels via the Internet to solicit feedback from fishermen (Fig. 4) (Igarashi et al., 2013). The habitat models were developed further using more complex and sophisticated products with some machine learning techniques, such as neural networking or vector machine support. Visualisation systems were also developed, to assist with the data assimilation products and the construction of the habitat model.
To construct the stock assessment model of neon flying squid, the relationship between variability of the stock and environmental factors, using ocean reanalysis data with biogeochemical parameters (Toyoda et al., 2013) were examined (Nishikawa et al., 2013). As a result, it was determined that the primary production in the spawning area is important for the stock, so that the prediction model of the squid stock could be constructed when the production rates were estimated in the spawning area. For this reason, we constructed a lower trophic level ecosystem model, which is embedded in the atmosphere-ocean coupled data assimilation system for seasonal-interannual predictions (Sugiura et al., 2008). The result of the tri-coupled data assimilation system was then examined to evaluate the predictability of the variability of lower trophic level ecosystem.
The technical know-how obtained could offer the opportunity of optimal fishery stock management and an adaptive, low-cost fishery operation with low CO2 emissions. Those could lead to a sustainable social system through an enhanced Japanese fishery activity and multi-disciplinary decision-making that adapts policy to ocean and climate variations.
- Igarashi, H., T. Awaji, Y. Ishikawa, M. Kamachi, N. Usui, M. Sakai, Y. Kato, S.-I. Saitoh, M. Seito. 2013. Development of a habitat suitability index model for neon flying squid by using 3-D ocean reanalysis product and its practical use. JAMSTEC Report of Research and Development, (in press).
- Nishikawa, H., H. Igarashi, Y. Ishikawa, M. Sakai, Y. Kato, M. Ebina, N. Usui, M. Kamachi, T. Awaji. 2013. Impact of paralarvae and juveniles feeding environment on the neon flying squid (Ommastrephes bartramii) winter-spring cohort stock. Fish. Oceano., (submitted).
- Sugiura, N., T. Awaji, S. Masuda, T. Mochizuki, T. Toyoda, T. Miyama, H. Igarashi and Y. Ishikawa. 2008. Development of a four-dimensional variational coupled data assimilation system for enhanced analysis and prediction of seasonal to interannual climate variations. J. Geophys. Res. 113, C10017, doi:10.1029/2008JC004741.
- Toyoda, T., T. Awaji, S. Masuda, N. Sugiura, H. Igarashi, Y. Sasaki, Y. Hiyoshi, Y. Ishikawa, S.-I. Saitoh, S. Yoon, T. In, M.J., Kishi. 2013. Improved state estimations of lower trophic ecosystems in the global ocean based on a Green’s function approach. Progre. Oceanogr. 119: 90-107, DOI 10.1016/j.pocean.2013.08.008.
- Usui, N., H. Tsujino, Y. Fujii, M. Kamachi. 2006. Short-range prediction experiments of the Kuroshio path variabilities south of Japan. Ocean Dynamics 56: 607-623, DOI 10.1007/s10236-006-0084-z.
Eiji Masunaga1*, Hidekatsu Yamazaki1, Takeyoshi Nagai1, Oliver Fringer2
1Tokyo University of Marine Science and Technology, Tokyo, Japan
2Department of Civil and Environmental Engineering, Stanford University, Stanford, USA
Cross-shelf transport of sediments, nutrients, iron and organic matter from nearshore areas is important for production in offshore sites. Previous studies have pointed out that internal waves propagating along slopes contribute to cross-margin transport and sediment resuspension (e.g. Cacchione et al. 2002; McPhee-Shaw et al. 2006). Lateral mass fluxes due to internal waves are much greater than those caused by vertical settling of material from the ocean surface (Van Weering et al. 2001). The vortex motion, induced by internal waves, largely influences mass fluxes and sediment resuspension along slopes (Venayagamoorthy and Fringer 2006; Van Haren 2009; Masunaga and Yamazaki 2014). However, few studies have documented internal waves propagating along slopes in detail using direct in-situ surveys. In this article, we present our findings on internal waves observed by instruments with high temporal and spatial resolution, and the numerical results obtained using the Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier-Stokes Simulator—SUNTANS (Fringer et al. 2006).
We conducted a field survey in Otsuchi Bay, Iwate Prefecture, Japan, in September 2012. In order to obtain high-resolution data, the YODA Profiler (Masunaga and Yamazaki 2014) was used for the transect observation. The transect line was set along approximately 3500 m, starting from the bay head to offshore. A high-resolution thermistor chain and an Acoustic Doppler Current Profiler (ADCP) were moored in the middle of the transect line (20 m depth).
Temperature data from the transect observation showed that a fine feature in the internal bore wave, accompanied by a low temperature water mass, propagated along the bottom slope into the shallow area (Figs. 5b and c). The isothermal displacement and the propagating speed of the wave along the slope were approximately 20 m and 0.1 ms-1, respectively, based on a comparison between two sequential observations (Figs. 5b and c). High turbidity water was observed at the head of the bore and above the thermocline (the interface of the wave, Figs. 5d and e). High turbidity water intruding into the interior water column from the sloping bottom, the intermediate nepheloid layer (INL), is important for lateral mass fluxes from the bottom boundary into the interior water column (McPhee-Shaw 2006). High turbidity water also appears in the shallow area, likely induced by the turbid outflow from a river. The mouth of Unosumai River is located at the shallowest point of the transect.
Observation data from the ADCP survey showed a shoreward (westward) flow near the bottom, and a weak offshore (eastward) flow above the bottom layer during the bore wave period (Fig. 6a, Time > 62.1). The vertical component of the bore wave showed a strong upward flow at the head of the bore wave and a downward flow behind the head (Fig. 6b). These indicate that the vortex motion was induced by the internal wave. The strong upward current at the bore head reached 0.03 ms-1. High frequency (close to the local buoyancy frequency) upward and downward movements continued after the strong vortex event. These may be due to Kelvin-Helmholtz instability at the interface of the internal wave. Echo intensity data indicated strong vertical resuspension, induced by the vortex motion, at the bore head (Fig. 6c). Resuspended particles followed the ring-like movement of the vortex, to a depth of 8 m above the bottom. The temperature field from the high-resolution thermistor array also indicated the burst-like upward motion and vortex structure at the bore head (Fig. 6d). Although the mooring data showed the vortex structure, the transect observations did not reveal such a feature (Fig. 5c). The horizontal scale of the vortex was approximately 36 m, based on the time scale of the vortex (360 s) and the propagation speed of the bore (0.1 ms-1). The scale of the horizontal resolution of the transect survey (~150 m) is much larger; thus the resolution of the transect survey was not sufficient to detect the small-scale vortex structure.
In order to investigate further the features in the internal waves propagating into Otsuchi Bay, we employed the fully nonlinear, nonhydrostatic model SUNTANS (Fringer et al. 2006) in a two-dimensional domain. The domain size was 10 km long and 80 m deep. The horizontal and vertical grid spacing and the time step were 20 m, 0.8 m and 1 s, respectively. The model was forced by the first mode of internal waves, with M2 tidal frequency, at the ocean boundary. The model revealed a run-up of the internal wave and the vortex motion at the head of the intruding internal wave (Fig. 5f). However, the small vortex motion was not well resolved (Fig. 5g), as the horizontal grid spacing (Δx = 20 m) was too large to capture the details of the vortex. To resolve the vortex, we used a finer resolution domain-length of 320 m, horizontal grid spacing of 0.64 m and vertical grid spacing of 0.22 m. This finer model was forced by the cold water outflow (0.1 ms-1) near the bottom at the deeper boundary. The results showed the finer features of the vortex structure (Figs. 5h and i). The vertical ejection current at the head of the bore wave reached 0.03 ms-1 (Fig. 5k), which is consistent with the observation results shown in Fig. 6b. A comparison of the model’s vortex time series with that of the mooring survey (Figs. 6d and e) corresponded well with the observation results.
Observed and numerical results showed the fine features in the internal bore wave propagating into the shallow bay. Strong sediment resuspension at the bore head and the INL detached from the sloping bottom were observed by the YODA Profiler transect survey. The data indicated that a small vortex, accompanied by a strong current, occurs at the bore head. This study suggests that the vortex induces strong sediment resuspension and contributes to mass fluxes between the sloping bottom and the interior water column.
We thank the crews of the R/V Grand-maillet (University of Tokyo) and the fishing boat Senshu-maru (Shin-Otsuchi Fishery) for their time and help. This study was supported by funding from Tohoku Ecosystem-Associated Marine Science.
- Cacchione, D.A., Pratson, L.F., Ogston, A.S., 2002. The shaping of continental slopes by internal tides. Science, 296, 724–727.
- Fringer, O.B., Gerritsen, M., Street, R.L., 2006. An unstructured-grid, finite-volume, nonhydrostatic, parallel coastal ocean simulator. Ocean Modelling, 14, 139–173.
- Masunaga, E., Yamazaki, H., 2014. A new tow-yo instrument to observe high-resolution phenomena. Journal of Marine Systems 129: 425-436.
- McPhee-Shaw, E., 2006. Boundary–interior exchange: reviewing the idea that internal-wave mixing enhances lateral dispersal near continental margins. Deep Sea Research Part II: Topical Studies in Oceanography, 53(1), 42–59.
- Van Haren, H., 2009. Using high sampling-rate ADCP for observing vigorous processes above sloping [deep] ocean bottoms. Journal of Marine Systems, 77, 418–427.
- Van Weering, T.C.E., De Stigter, H.C., Balzer, W., Epping, E.H.G., Graf, G., Hall, I.R., Helder, W., Khripounoff, A., Lohse, L., McCave, I.N., Thomsen, L, and Vangriesheim, A., 2001. Benthic dynamics and carbon fluxes on the NW European continental margin. Deep Sea Research Part II: Topical Studies in Oceanography, 48(14), 3191–3221.
- Venayagamoorthy, S.K., Fringer, O.B., 2006. Numerical simulations of the interaction of internal waves with a shelf break. Physics of Fluids, 18, 076603/9, DOI:10.1063/1.2221863.
Xinyu Guo1,2,*, Xiaohua Zhu2,3
1Center for Marine Environmental Study, Ehime University, Matsuyama 790-8577, Japan
2State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China
3Department of Ocean Science and Engineering, Zhejiang University, Hangzhou 310058, China
Strong western boundary currents carry large quantities of water and heat, as well as a variety of dissolved materials, including nutrients and can have a significant influence on the climate and marine ecosystems. Quantitation of nutrient transport by the western boundary current is an important step to understanding the nutrient element cycle at basin-scale. Pelegrí and Csanady (1991) and Pelegrí et al. (1996) reported a subsurface maximum in nutrient flux (the product of velocity and nutrient concentration) and nitrate transport (integration of flux over a section) in the order of 1000 kmol s-1 in the Gulf Stream, and proposed the presence of a nutrient stream along the Gulf Stream, from upstream to downstream areas.
The Gulf Stream’s North Pacific counterpart, the Kuroshio, is expected to have the same nutrient transport function as the Gulf Stream, from its area of origin east of Luzon Island, where it forms as a northward branch of the westward North Equatorial Current, to the Kuroshio Extension (Fig. 7a). Based on data from four cruises, Chen et al. (1994, 1995) calculated the nutrient flux of a section of the Kuroshio that is east of Taiwan, and reported the presence of a subsurface maximum core at a depth of 500 m. Guo et al. (2012) obtained a long-term averaged nutrient flux at section PN (see Fig. 7b for its location), based on data from 88 cruises from 1987 to 2009, and demonstrated a subsurface maximum core at 400 m depth.
The long-term averaged nitrate transported by the Kuroshio at section PN is 170.8 kmol s-1. This is the only known value for the amount of nutrients transported by the Kuroshio, and is less than that observed in the Gulf Stream. Observations there indicated that the amount of nitrate transported may significantly increase along this stream (Pelegrí and Csanady, 1991; Pelegrí et al., 1996; Williams et al., 2011). Therefore, we also need to investigate the downstream change of nutrient transport by the Kuroshio, 1) to confirm the presence of the “Kuroshio nutrient stream” from its upstream to downstream regions, and 2) to understand the processes responsible for the downstream variations in nutrient transport by the Kuroshio.
Based on absolute geostrophic velocity, which was calculated using repeated hydrographic data from 39 cruises from 2000 to 2009 by the Japan Meteorological Agency and nitrate concentrations measured in the same areas from 1964 to 2009, we obtained the temporally averaged nitrate flux and nitrate transport of four sections across the Kuroshio from the East China Sea (sections PN and TK) to an area south of Japan (sections ASUKA and 137E) (Fig. 7b). In addition, we examined section OK east of the Ryukyu Islands in order to understand how the Ryukyu Current contributes to the transport of nutrients by the Kuroshio south of Japan (Fig. 7b). The details of the calculation and data processing can be found in Guo et al. (2013).
The mean nitrate flux showed a subsurface maximum core with values of 9.6, 10.6, 11.2, 10.5, and 5.7 mol m-2s-1 at sections PN, TK, ASUKA, 137E, and OK, respectively. The depth of the subsurface maximum core changes among these five sections and is approximately 400, 500, 500, 400, and 800 m at sections PN, TK, ASUKA, 137E, and OK, respectively. The mean downstream nitrate transport is 204.8, 165.8, 879.3, 1230.4, and 338.6 kmol s-1 at sections PN, TK, ASUKA, 137E, and OK, respectively (Fig. 7b). The transport of nutrients in these sections suggests the presence of the Kuroshio nutrient stream from its upstream to downstream regions. The deep structure of the Ryukyu Current (section OK) contributes the same order of nitrate transport as does the Kuroshio from the East China Sea (section TK) to the area south of Japan; however, the Ryukyu Current transports only one-fifth of the volume that the Kuroshio transports.
The downstream increase of nitrate transport from section ASUKA-N to section 137E-N has two sources. One is the nitrate carried by the Kuroshio recirculation that enters the area between section 137E-N and section ASUKA-N from its south boundary. The other is the along-stream change of nitrate concentration from section ASUKA-N to section 137E-N, which is caused by diapycnal mixing and biological processes occurring along the Kuroshio between section 137E-N and section ASUKA-N. Assuming a conservation of water mass and nitrate concentration within the area enclosed by section 137E-N, section ASUKA-N, and the south boundary of two sections, we carried out a budget calculation to separate the contributions of Kuroshio recirculation and along-stream change of nitrate concentration to the downstream increase of nitrate transport from section ASUKA-N to section 137E-N (Guo et al., 2013).
The budget calculation suggests that the downstream increase of transported nitrate along the Kuroshio is mainly caused by the recirculation of nitrate into the Kuroshio. This conclusion, however, depends on water depth. In the upper layers (<26.5σθ), the downstream change of nitrate concentration along the Kuroshio and that from the recirculation of nitrate has a significant contribution to the downstream increase of nitrate transport along the Kuroshio. In the deep layers (>26.5σθ), the change in nitrate concentration is small and the Kuroshio recirculation dominates the downstream increase of nitrate transport. This conclusion is also correct for the area enclosed by sections ASUKA-N, TK and OK-W.
Williams et al. (2011) reported that the same downstream intensification of nutrient transport occurred along the Gulf Stream and concluded that the primary cause of the increase in nutrient transport was the recirculation-induced increasing downstream volume transport of the Gulf Stream, while the second cause was the downstream increase of nutrient concentration in the water carried by the denser layers of the Gulf Stream. The importance of recirculation is similar in our results according to the budget calculation for the two areas in the Kuroshio region. However, the downstream increase in nutrient concentration in denser layers is not significant in the Kuroshio main stream and Kuroshio recirculation region.
Pelegrí and Csanady (1991) also reported a downstream increase of nitrate transport along the Gulf Stream and attributed it to the diapycnal mixing that occurred along the Gulf Stream. As the results by Pelegrí and Csanady (1991) are similar to the results of our budget calculations (i.e., nitrate concentration increased in the light layers and decreased in the dense layers), we believe that diapycnal mixing could be an important factor in controlling the change of nitrate along the Kuroshio. Recently, Kaneko et al. (2013) calculated the vertical nitrate flux in the main stream of the Kuroshio from measured nitrate concentrations and the vertical viscosity coefficient estimated from field turbulent measurements. Their results indicated an upward nitrate flux from the depth of 300 m to the surface layer. This measurement supports our result of a downstream increase of nitrate concentration along the light layers of the Kuroshio.
The downstream intensification of the nutrient transport is a common feature in the nutrient streams of the Gulf Stream and the Kuroshio. The recirculation and its contribution to the nutrient transport occur in both streams. A difference between the Gulf Stream and the Kuroshio is the downstream variation of nutrient concentration in the water carried by the two western boundary currents. Therefore, different physical and biogeochemical processes responsible for the change of nitrate concentration must occur in the Kuroshio and Gulf Stream and more effort, including a comparative study for two western boundary currents, is necessary to clarify these processes.
- Chen, C.T.A., Liu, C.T., and Pai, S.C., 1994. Transport of oxygen, nutrients and carbonates by the Kuroshio Current. Chinese Journal of Oceanology and Limnology 12: 220-227.
- Chen, C.T.A., Liu, C.T., and Pai, S.C., 1995. Variations in oxygen, nutrient and carbonate fluxes of the Kuroshio Current. La Mer. 33: 161-176.
- Guo, X., Zhu, X.-H., Wu, Q.-S., and Huang, D., 2012. The Kuroshio nutrient stream and its temporal variation in the East China Sea, J. Geophys. Res. 117, C01026, doi:10.1029/2011JC007292.
- Guo, X., Zhu, X.H., Long, Y., Huang, D., 2013. Spatial variations in the Kuroshio nutrient transport from the East China Sea to south of Japan. Biogeosciences 10: 6403-6417, doi:10.5194/bg-10-6403-2013.
- Kaneko, H., Yasuda, I., Komatsu, K., and Itoh, S., 2013. Observations of vertical turbulent nitrate flux across the Kuroshio, Geophys. Res. Lett. 40: 3123–3127, doi:10.1002/grl.50613.
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Dissemination of potential fishing zone prediction maps of Japanese common squid in the coastal waters of southwestern Hokkaido, Japan
Sei-Ichi Saitoh1,*, Xun Zhang1, Toru Hirawake1, Satoshi Nakada2, Koji Koyamada2, Toshiyuki Awaji3, Yoichi Ishikawa4, and Hiromichi Igarashi4
1Laboratory of Marine Environment and Resource Sensing, Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido, 041-8611, Japan
2Center for the Promotion of Excellence in Higher Education, Kyoto University, Yoshida-Nihonmatsu-Cho, Sakyo-ku, Kyoto, 606-8501, Japan
3Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-Cho, Sakyo-ku, Kyoto, 606-8502, Japan
4Japan Agency for Marine-Earth Science and Technology, Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 3173-25, Japan
The Japanese common squid (Todarodes pacificus) is an important commercially exploited species in the coastal waters of southwestern Hokkaido, Japan (Ministry of Agriculture, Forestry and Fisheries, 2012). Every year from June to December, many squid fishing vessels, all equipped with powerful lights to attract the squid (Kiyofuji et al., 2004), gather in the area to fish. The spatial distribution of the Japanese common squid can vary rapidly with changes in ocean conditions, due to its high sensitivity to environmental conditions (Sakurai et al., 2000 and 2002; Kidokoro et al., 2010; Rosa et al., 2011). Consequently, there can be very large fluctuations in daily catches. Selecting the best area to fish is thus key to successful fishing activities. Understanding of the spatial and temporal distribution of Japanese common squid in this area is, however, still limited, and the application of scientific knowledge of marine species to operational fisheries remains difficult. The objectives of this study were to determine the relationship between squid distribution and environmental conditions, and to promote coastal Japanese common squid fishing through the use of a potential fishing zone (PFZ) prediction map in the coastal waters of southwestern Hokkaido (Fig. 8) developed by the Hakodate Marine Bio-Cluster Project (Saitoh et al., 2011).
A lack of catch data from local fisheries, coupled with limited observed sampling data, make actual fish distributions difficult to asses. The Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS), that detects lights from fishing vessels in the ocean on a nightly basis, was used to obtain the presence or absence of Japanese common squid aggregations (Kiyofuji and Saitoh, 2004). Corresponding environmental factors of bathymetry, model-assimilated daily four-dimensional variational (4D-VAR) environmental data (temperature, salinity, water geostrophic velocity, and eddy kinetic energy) at different depth layers, based on OGCM (the ocean general circulation model developed by Kyoto University) were used to explain squid distribution. A habitat suitability index (HSI) model was applied to determine species-environment associations, and further achieve the prediction using model-assimilated future environmental data.
Many previous studies have suggested that 4D-VAR data is capable of representing the real ocean environment (Sugiura et al., 2008; Ishikawa et al., 2009; Toyoda et al., 2011). The data are stable, without weather constraint or temporal gaps comparing observation data and satellite-derived data, and it provides high-quality future data for predicting potential fishing zones.
The correlation coefficient between squid distribution and various environmental variables in different depth layers was calculated. The selection of variables for building the model was based on these correlation coefficients, and for the area where water depth is lower than the depth with the highest correlation, variables at 20 m were applied. Most of correlation coefficients at the depth layer around 50 m are larger than other depth layers for each variable. This indicates that squid distribution is closely correlated with the environment at depth around 50 m, and presumably that Japanese common squid inhabit areas around 50 m in depth.
Model validation, based on an independent dataset, showed high predictive accuracy of our HSI model. The area under the curve (AUC) value reached 0.86 (0.9–1.0 excellent; 0.8-0.9 good; 0.7-0.8 fair; 0.6-0.7 poor; 0.5-0.6 fail), which exceeded the previous model (AUC=0.82) that we built using satellite-derived environmental variables. The correlation between the prediction and actual fishing of the present model was also much higher than the previous study using satellite-derived data.
Visible nighttime images obtained during June and early July 2013 from the Day/Night band (DNB) of Visible Infrared Imaging Radiometer Suite (VIIRS) sensor, had better resolution and quality compared to the DMSP/OLS (Schueler et al., 2013), and were used to validate the results. These showed differences in fitness between actual fishing activities and predictions in the Japan Sea and Tsugaru Strait. These differences were suggested to be a consequence of the eastern movement of main fishing grounds from the end of July every year. The PFZ prediction could be further improved with additional DNB data in the model. Predictions were generally consistent with actual fishing locations, and monthly variations also suggested good model accuracy.
With assistance from the local fishery association, our HSI model can be applied to operational fishing activities. Four-day prediction maps were prepared in both colour and gray scale for easy visualization and delivery to local fishermen (Fig. 9). Since July 2013, four-day prediction maps have been sent to the local fishery association and fishermen each morning, together with other useful information about the ocean conditions, to facilitate the selection of fishing positions. Prediction maps are also freely available through the website http://innova01.fish.hokudai.ac.jp/marinegis (in Japanese). The data flow is displayed in Fig. 10 and sample PFZ map on Web-GIS is shown in Fig. 11a and b. Local fishermen have participated actively in the project. Their feedback has shown that the prediction maps are proving to be very useful and have improved fishing efficiency. Their input and cooperation will not only assist in improving the model, but could also promote the development of sustainable use of marine resources and raise awareness of issues of change in fisheries as a result of environmental changes.
This work was supported by “Hakodate Marine Bio Cluster Project” in the knowledge Cluster Program from 2009 and the Grant-in-Aid for the Regional Innovation Strategy Support Program (Global Type) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. This was also supported by the Japan Aerospace Exploration Agency (JAXA) SGLI/GCOM-C Project.
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Fisheries management under species alternation from the perspective of regional economy and food security
Takaomi Kaneko*, Masahito Hirota, Mitsutaku Makino
National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama, Japan
The lack of strong year-classes of chub mackerel (Scomber japonicas), following the sudden decrease of Japanese pilchard (Sardinops melanostictus) in the 1990s, revealed the difficulty of fisheries management under the phenomenon of species alternation. We analyzed this event using retrospective analysis, with the aim of improving management strategies or decisions in the event of future marine fisheries species alternation.
Japanese pilchard stocks increased during the 1980s and annual catches reached 4.48 million tons in 1989 (Fig.12). However, prices for the fish began to decline because of change in the market. Purse seiners, the main beneficiaries of this stock, attempted to compensate for the falling prices by increasing catches. Because the number of vessels was regulated by licenses, they did this by enlarging their ships. The favourable economy in the 1980s provided a further inducement to take out bank loans to build bigger ships. Unfortunately, after having invested money to improve and enlarge their ships, the pilchards virtually disappeared from the ocean. Many purse seiners had overcapitalised and had large debts to repay. Some went out of business, scrapping their ships as part of government buy-back programs. Others shifted their fishing effort to chub mackerel. These had strong year classes during 1992 and 1996, but were severely exploited before they matured. This is considered to have prevented the recovery of the chub mackerel stock in the late 1990s.
In retrospecet, how should the fishery have been managed? Co-management is the main fisheries management strategy used in Japan. It emphasises agreement amongst fishers. It must take into consideration not only the sustainability of the fish stocks, but also the stability of the fishing industry. Thus, an option that would help to improve the stock status but that would be disadvantageous for the purse seiners, would not be acceptable. Using computer simulations, we attempted to find a solution that would conserve the chub mackerel, while ensuring that average purse seining operations did not fall below their break-even point. Results indicated that the chub mackerel stock would recover by the year 2000, if: 1) there were less than 90% of the actual number of vessels fishing in 1992; and 2) the purse seiners preserved the strong year-classes that occur every 5-7 years (Makino and Watanabe, 2010).
How could such conditions have been achieved? We suggested four management options and compared the advantages and disadvantages of each. The options were: 1) Use of public funds by the government to support the scrapping of fishing vessels after the decline of the Japanese pilchard. 2) Government restrictions on the construction of new vessels. 3) A government-imposed per catch landing tax (2 Japanese Yen (JPY) per kg of fish landed) to control investment in new ships. 4) The introduction of an individual transferable quota (ITQ) system by the government to ensure self-regulation of the number of purse seiners.
Option 1 required the government to spend a considerable amount of money, but enabled the fishing industry to fully utilise the Japanese pilchard stock. The advantage of option 2 is that the government would not need to outlay any money, but it would have difficultly persuading the fishers. The merit of option 3 is that government could use the collected landing tax to scrap surplus ships. A disadvantage of the ITQ system (option 4), is that the price of the ITQ is insufficient to compensate all the extra fishers, thus requiring the government to provide the additional funding to scrap the ships.
An Input-Output analysis, to evaluate the impact on the regional economy of applying these options, was conducted. In Japan, the fishing industry is a major contributor to the local economies of several coastal cities. The large volume of fish supplied by purse seiners can significantly affect local economies. In the grand design of fisheries and resource management in Japan (Fig. 13), the local/community policy is one of five principles for ideal fisheries (FRA, 2009). To evaluate the impact of management options on local economies, it is important to take the management of large-scale fisheries, such as purse seiners, into consideration.
The impact on the local economy was estimated as follows. Option 1 would enable the fishing industry to utilise the pelagic stocks maximumally during the 1980s, so the impact on the local economy would be minimal. However, as options 2, 3, and 4 reduce landings, the local economomy would be negatively affected. The estimated impact was about 26.3 (option 2), 34.6 (options 3), and 27.0 (option 4) billiion JPY in the Kanto area. Therefore, the landing tax provides a great advantage to government funding for management, but it would have the highest impact on local economies.
Finally, we evaluated the contribution of the recovery of the chub mackerel to food self-sufficiency in Japan. As Japan is very reliant on imported food, food security is extremely important. The food policy is also included in the five principles for ideal fisheries in Japan (FRA, 2009). Chub mackerel is a very important species in Japanese cuisine, but landings decreased in the 1990s. In addition, the size of the landed mackerel was too small for processing, so many fish processing companies switched to imported Atlantic mackerel (Scomber scombrus). We suggest that if chub mackerel stocks had been preserved during the 1990s, the import of Atlantic mackerel would not have increased as it did. We estimated that if stocks of chub mackerel could have been restored by 2000, then the food self-sufficiency rate for seafood would have improved by 2%.
Desirable management strategies to deal with species alternation largely depend on the use of the limited marine resouces by the Japanese population. If the aim is to use the resource as much as they can, option 1 would be realistic. However, if people do not want any governmental expenditure, options 2 and 3 would be better. What is important is that the management options should be evaluated from multiple perspectives. In particular, the landing of the species such as chub mackerel or Japanese pilchard would greatly affect local economies or food self-sufficiency rates. A variety of options and perspectives should be considered in the management of purse seiners. Our next challenge is to use these results for better management of the next species alternation.
Fisheries Research Agency (2009) The Grand Design of Fisheries and Resources Management in Japan - Final Report
- Makino M. and Watanabe C., 2010. Gyoshu Kotai to Gyogyo no Sogo Sayo (Interaction between fishery and fish alternation). Aquanet (in Japanese)
Masao Ishii1,*, Daisuke Sasano1, Naohiro Kosugi1, Hideyuki Nakano1, Kazutaka Enyo2, Shu Saito2, Toshiya Nakano2, Takashi Midorikawa3, and Hisayuki Y. Inoue4
1Oceanography and Geochemistry Research Department, Meteorological Research Institute, JMA
2Global Environment and Marine Department, JMA
3 Tokyo District Meteorological Observatory, JMA
4 Graduate School of Environmental Science, Hokkaido University
The western North Pacific subtropical and tropical zones contain many coral reef habitats and marine biodiversity hotspots, including the so-called “Coral Triangle” (WWF: http://worldwildlife.org/places/coral-triangle). These zones encompass the coastal regions of several countries including The Philippines, Indonesia and Papua New Guinea, and are home to 76% of the known coral species and more than 2200 species of reef fish. Hundreds of millions of people live in the coastal regions and depend on fishing and other marine resources and services. However, these marine ecosystems have been impacted by human activities through habitat loss, overexploitation, water pollution, eutrophication and coral bleaching. Over the past decade, ocean acidification has been recognized as an additional threat to marine ecosystems (e.g., Doney et al., 2009).
The seasonal variations of NTCO2 superimposed on the long-term increase (+1.10 ±0.07 μmol kg-1 yr-1) as well as variations in SST affect not only pCO2sw but also pH and Ωarag (the saturation index of the calcium carbonate mineral, aragonite). The higher pH (at SST) and lower Ωarag in winter, and the lower pH and the higher Ωarag in summer are superimposed on the long-term trend towards decreasing pH at a rate of -0.0018 ±0.001 yr-1 and that of Ωarag at a rate of -0.011±0.001 yr-1.
In contrast, seasonal variability is not a dominant mode of temporal variability, and the long-term trend of change is clearly visible in the tropical zone at, e.g., 7ºN where the Micronesian islands are located (Fig. 15). However, mean rates of change in ocean CO2 system variables, and thus ocean acidification, in the tropical zone from 1983 – 2012, were slower than in the northern subtropics; +1.37 ± 0.13 μatm yr-1 for pCO2sw, +0.82 ± 0.06 μmol kg-1 yr-1 for NTCO2, -0.0013 ± 0.0001 yr-1 for pH and -0.008 ± 0.001 yr-1 for Ωarag. Midorikawa et al. (2012) indicated that the rates of change in pCO2sw and NTCO2 varied over decadal time-scales. These were consistent with the rate of increase in the atmospheric CO2 concentration for 1984 – 1997, and slowed down significantly from 1999 - 2009. This slower rate of increase of pCO2sw and NTCO2 after the late 1990s was also observed at the Hawaii Ocean Time-series Station ALOHA (Keeling et al., 2004) and in the western equatorial Pacific warm pool (Ishii et al., 2009). Midorikawa et al. (2012) suggested that this reduced rate of increase of pCO2sw and NTCO2 in the surface layer of the tropical zone at 137°E was related to the trend of southward expansion of the subtropical gyre, reported by Qiu and Chen (2012). However, the processes controlling this decrease in the rate of pCO2sw and NTCO2 in these regions are still being actively researched.
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- Ishii, M., Inoue, H. Y., Midorikawa, T., Saito, S., Tokieda, T., Sasano, D., Nakadate, A., Nemoto, K., Metzl, N., Wong, C. S., Feely, R. A., 2009. Spatial variability and decadal trend of the oceanic CO2 in the western equatorial Pacific warm/fresh water. Deep Sea Res., II, 56, 591–606.
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Nitrate dynamics of the continental shelf of the East China Sea based on a nitrate dual isotopic composition approach
Faculty of Fisheries, Nagasaki University, Nagasaki, Japan
The East China Sea (ECS), bordered by China, Japan, Korea and Taiwan, is a very productive marginal sea, and serves as a spawning and nursery ground for many species of fish and squid. It is therefore, important to clarify the dynamics of the nutrients supporting the growth of phytoplankton, and subsequently zooplankton, which are the food source for juveniles. Nitrate (NO3) is the dominant component of new dissolved inorganic nitrogen (DIN), and the ECS has multiple sources, such as Kuroshio Subsurface Water (KSSW), Yellow Sea Cold Water Mass (YSCWM), Taiwan Strait Warm Water (TSWW) and Changjiang Diluted Water (CDW) (Fig.16). Nutrient budgets for the shelf areas of the ECS, evaluated by box models (e.g., Zhang et al., 2007), suggested the relative contribution of nutrients by each water mass to the ECS. However, it is not clear which NO3- is actually used for phytoplankton growth on the shelf.
In recent years, stable nitrogen and oxygen isotopes of NO3 (δ15NNO3 and δ18ONO3) have been used to clarify the NO3 dynamics from coastal areas to the open ocean. Both of the heavier isotopes of NO3 (i.e., 15N and 18O) react more slowly in enzyme-mediated reactions, such as NO3 assimilation by phytoplankton and denitrification processes, resulting in a gradual increase in heavier isotopes of the remaining NO3 at a specific ratio and various values in each N pool of the natural environment. Therefore, when δ15N and δ18O values of each NO3 source are distinct from those of other sources, this information can be used to trace the contribution of each NO3 source (e.g., Leichter et al., 2007). Also, when NO3 is taken up by phytoplankton and bacteria following a Rayleigh fractionation model in a closed system, a linear relationship is observed between the log-transformed NO3 concentration (ln[NO3]) and δ15N in NO3 (e.g., Sigman et al., 1999). This provides evidence of actual uptake of NO3 by organisms, and the extent of any deviation from linearity suggests the presence of other biological reactions in the N cycle, such as nitrogen fixation and nitrification (e.g., Sigman et al., 2005; Wankel et al., 2007; Granger et al., 2011). Because isotopic signatures provide time- and space-integrated evidence of multiple biogeochemical processes, this information is helpful for understanding NO3 dynamics on the shelf of the ECS.
From February 2008 to July 2013, eight research cruises were undertaken to investigate the NO3 dynamics on the continental shelf of the ECS, focusing on seasonal, inter-annual and spatial variations (partly in Umezawa et al. 2013). Water samples were collected from different layers, from the bottom to the surface, together with conventional physical and biological parameters, and nutrients and NO3 isotopes were analyzed. Here, we present the results of a transect crossing the ECS continental shelf from east to west (i.e., 31°45.00¢ N, 125°20.00¢ -128°45.00¢ E) in July 2011. Distinct differences in δ15NNO3 and δ18ONO3 in the potential NO3 sources (i.e., 5.5–6.0‰ and 3.5–4.0‰ for KSSW, 6.5–7.5‰ and 5.0–7.0‰ for YSCWM, 8.3‰ and 2.6‰ for Changjiang River (Li et al., 2010), 0.4 ± 2.9‰ and 73.3 ± 9.8‰ for rain water, respectively) were observed, that are potentially useful for tracing the source of NO3. Isotopically heavier δ15NNO3 and δ18ONO3 than those of the potential NO3 sources were observed in the surface and subsurface chlorophyll maximum layers. Most of these values seemed to be plotted along lines which begin from the potential NO3 sources in the 18e:15 e ratio of 1:1. Because this is typical of isotopic fractionation associated with NO3 assimilation by phytoplankton, it is likely that phytoplankton uptake is the primary factor controlling the NO3 isotope values on the continental shelf of the ECS during summer season.
To check the NO3 dynamics, focusing mainly on the source of NO3, that stimulates phytoplankton growth, we plotted their δ15NNO3 as a function of ln[NO3] (Fig. 17). Below the euphotic zone in the Okinawa Trough, δ15NNO3 were almost steady despite a gradual decrease in NO3 concentration, suggesting a simple dilution effect by NO3-depleted Kuroshio Surface Water (KSW). We hypothesized that the fractionation factor associated with NO3 uptake by phytoplankton was the same (e.g., e=3), and that the values on the δ15NNO3-ln[NO3] diagram in the euphotic zone were categorized into different groups. At the relatively deeper chl a maximum in the Okinawa Trough (yellow circle in Fig. 17), δ15NNO3 data points were plotted near the fractionation line, starting from the value of the diluted KSSW (KSW). This suggests that phytoplankton in the subsurface layer at the Okinawa Trough used NO3 originating from the KSSW. At the subsurface chl a maximum, from the mid-shelf to the outer shelf (blue circle in Fig. 17), δ15NNO3 values were plotted near the line starting from YSCWM-derived NO3. In the surface and subsurface water in the mid-shelf area (pink circle in Fig. 17), where lower salinity was observed, δ15NNO3 values were plotted near the fractionation line, starting from the NO3 value typically observed in the lower stream of the Changjiang River.
Despite the use of snapshot sampling, these relationships provided strong evidence that CDW, YSCWM and KSSW-carried NO3 were used by phytoplankton at different locations on the ECS continental shelf. These results corresponded well with the hydrographic characteristics suggested from the T-S diagram. On the other hand, relatively lighter δ15NNO3 than those expected from the fractionation effect during algal uptake might be explained by the contribution of atmospheric N and/or nitrification to NO3 dynamics in the surface and subsurface layers, because the contribution of these processes has been reported in many studies (e.g., Liu et al., 1996; Shiozaki et al. 2011).
Currently, research vessels of the countries surrounding the ECS do not have free access to the area (only to their individual territorial waters). However, good collaboration and communication between researchers has improved understanding of the nutrient dynamics in the ECS.
This study was financially supported by The Study of Kuroshio Ecosystem Dynamics for Sustainable Fisheries project (SKED), funded by the MEXT (Ministry of Education, Culture, Sports, Science and Technology), Japan.
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- Shiozaki, T., Furuya, K., Kurotori, H., Kodama, T., Takeda, S., Endoh, T., Yoshikawa, Y., Ishizaka, J., and Matsuno, T. 2011. Imbalance between vertical nitrate flux and nitrate assimilation on a continental shelf: Implications of nitrification, J. Geophys. Res. 116, C10031, doi:10.1029/2010JC006934.
- Sigman D.M., Altabet M.A., McCorkle D.C., Francois R., Fischer G. 1999. The d15N of nitrate in the Southern Ocean: Consumption of nitrate in surface waters. Global Biogeochemical Cycles 13: 1149-1166.
- Sigman, D. M., Granger, J., DiFiore, P. J., Lehmann, M. M., Ho, R., Cane, G. and van Geen, A. 2005. Coupled nitrogen and oxygen isotope measurements of nitrate along the eastern North Pacific margin, Global Biogeochem. Cycles 19, GB4022, doi:10.1029/2005GB002458.
- Umezawa, Y., Yamaguchi, A., Ishizaka, J., Hasegawa, T., Yoshimizu, C., Tayasu, I., Yoshimura, H., Morii, Y., Aoshima, T., and Yamawaki, N. 2013. Seasonal shifts in the contributions of the Changjiang River and the Kuroshio Current to nitrate dynamics at the continental shelf of the northern East China Sea based on a nitrate dual isotopic composition approach, Biogeosciences Discuss. 10: 10143-10188, doi:10.5194/bgd-10-10143-2013.
- Wankel, S., Kendall, C., Pennington, J. T., Chavez, F. P., and Paytan, A. 2007. Nitrification in the euphotic zone as evidenced by nitrate dual isotopic composition: Observations from Monterey Bay, California. Global Biogeochem. Cycles. 21. GB2009, doi:10.1029/2006GB002723.
- Zhang, J., Liu, S. M., Ren, J. L., Wu, Y., and Zhang, G. L. 2007. Nutrient gradients from the eutrophic Changjiang (Yangtze River) Estuary to the oligotrophic Kuroshio waters and re-evaluation of budgets for the East China Sea Shelf. Prog. Oceanogr. 74: 449-478.
IMBER Research Reports
CLIOTOP supports a Deep Sea Research II volume on the role of squids in pelagic ecosystems
Jock W. Young1, Robert J. Olson2, and Paul G. K.Rodhouse3
1Wealth from Oceans Flagship, CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart, TAS 7000, Australia. firstname.lastname@example.org
2 Inter-American Tropical Tuna Commission, 8901 La Jolla Shores Drive, La Jolla, California 92037, USA.email@example.com
3British Antarctic Survey, High Cross, Madingley Road, Cambridge CB25 9BG, UK.firstname.lastname@example.org
Midtrophic communities play a central role in the structure and function of oceanic ecosystems by linking the biomass of micronekton, particularly myctophid fishes, to oceanic predators. A major component of the midtrophic fauna are squid, which act as prey or predator, but whose role in many communities remains unquantified. Squid have short life spans and fast growth rates, so are among the most sensitive mid-trophic-level organisms to changes in the environment and in the trophic structure in the open ocean. For a number of reasons squid are not well understood: their ability to avoid capture, their complex taxonomy and their minimal retention in predator stomachs, other than their indigestible beaks. Nevertheless, considerable amounts of data have been amassed over the last three decades. These data are now being complemented by new technologies, including tracking (e.g. archival and satellite tags), and advances in biochemical techniques capable of identifying, for example, trophic position.
In 2006 GLOBEC-CLIOTOP (Maury and Lehodey (Eds.), 2005) and the Pelagic Fisheries Research Program (PFRP), University of Hawaii, sponsored a workshop in Honolulu on the role of squids in pelagic ecosystems. The workshop brought together squid ecologists working in diverse ecosystems and oceanographic regions from the Pacific, Atlantic, and Indian Oceans, and a volume of extended abstracts was produced by the CLIOTOP Working Group 3 (Trophic pathways in open ocean ecosystems) (Olson and Young 2007). Much of this information remained unpublished, so we approached Deep Sea Research II as a vehicle for these and other related studies . The resulting volume (Young et al, 2013) has twenty-two peer-reviewed papers covering research areas including squids as prey, squids as predators, the role of squids in ecosystems, their physiology, and climate change.
Some of the findings:
Trophic studies from each of the major oceans underline the importance of squid, particularly ommastrephids, in the diets of fish, seabirds and marine mammals. Important ecological information on the horizontal and vertical distribution of top predators (including sharks, tunas and billfishes) can be gleaned from an understanding of their cephalopod prey.
Squid are major predators in the world’s oceans. Although generally predators of micronekton, they can also be top predators. Large cephalopods in the Atlantic Ocean had similar δ15N isotopic values to those of tunas and billfishes, indicating that these three groups exploited most of their prey from the same trophic levels. Lipid content correlated with satellite-derived sea-surface chlorophyll concentrations, illustrated that diet was closely linked to temporal changes in primary productivity.
The science examined the broader role of squid in marine ecosystems, using novel meta-analyses. Squid occupied a large range of trophic levels in marine food webs, reflecting the versatility in their feeding behaviours and trophic connections in the food web. Squid can have a large trophic impact and top-down control on other elements of the food web. One paper synthesized available information for two intrinsic markers (δ15N and δ13C values) in squid for all oceans and several types of ecosystems to obtain a global view of the trophic niches of squid. To compare among systems and oceans, they adjusted squid δ15N values for the isotopic variability of phytoplankton at the base of the food web in the same locations, provided by an ocean circulation-biogeochemistry-isotope model. This was the first study of its kind to use model-generated baseline δ15N values to provide direct comparisons among consumers worldwide and it showed the importance of considering the often-neglected natural baseline variation in stable isotope ratios among ecosystems. Another study showed that squid are major nutrient vectors and play a key role as transient ‘biological pumps’ linking spatially-distinct marine ecosystems. Another explored the impact of increasing anthropogenic noise on oceanic fauna via a series of novel experiments on cephalopod statocysts. Exposed individuals presented lesions on their statocysts consistent with massive acoustic trauma. Perhaps one of the most novel findings was that squid flight may aid migration.
The extraordinary increase in biomass and range of the Humboldt squid, Dosidicus gigas, off North and South America following the 1997-98 El Niño event led to a number of research projects to explore the reasons for the increase. Given its ability to migrate across regions with wide ranges of dissolved oxygen and temperature in the eastern Pacific, a number of studies focused on its physiology.
Under climate change, it seems likely there will be little effect on squids in the Southern Ocean from the relatively small increases in ocean temperatures that are predicted, other than changes in distribution near the limits of their range. Ocean acidification may have a significant impact via effects on statoliths. Reduction in sea ice is likely to have large effects on squids and ecosystems, because of the loss of habitat, especially for krill. Cephalopods are ecological opportunists, and given their potential to evolve fast, predicted changes in the Southern Ocean pelagic ecosystem might enable them to flourish in competition with less ecologically-opportunistic groups. Similarly, tropical and subtropical species are also likely to be potential “winners” as oceans continue to warm.
Given the difficulty of catching cephalopods with research nets etc., other methods to estimate the distribution and abundance of squid species are needed. The recognition that squid predators, such as tunas, are considered efficient samplers underlines the importance of continuing with food web studies. The increasing use of biochemical approaches, such as signature fatty acid analysis, stable isotope analysis, and compound-specific isotope analysis of amino acids, are areas of research where important advances can be made. There is also a continuing need for conventional gut contents analysis, given the prominence of indigestible squid beaks in the stomachs of predators. However, it is the combination of the above techniques where the greatest understanding can be achieved, although reconciling the discrepancies among some of these techniques, particularly those between stomach contents analysis and fatty acid signatures, is needed.
The volume concluded that an holistic approach is needed for predicting effects of global climate change on squid populations and in determining causes of range extensions. Experimental data on effects of ocean acidification are particularly needed. For Humboldt squid, future efforts should be directed to better understanding factors that trigger sudden increases in their abundance, as well as modelling its trophic impacts.
A need was identified for global initiatives to pool data, particularly on the feeding ecology of squids, but also on pelagic food webs generally, where much can be learned from broader comparisons of predator diets.
The Deep Sea Research II volume is a contribution of CLIOTOP Working Group 3 (Trophic pathways in open ocean ecosystems) and grew out of a joint University of Hawaii/ GLOBEC-CLIOTOP initiative. We are grateful to both for their support and funding of the workshop, and to the CLIOTOP Steering Committee for promoting these efforts. We are also grateful to the authors and their research institutes that contributed to the volume. We also thank the many reviewers who read and improved papers in the volume. Finally, we thank the Editor and staff of Deep Sea Research II for their guidance in putting the volume together.
Global Ocean Ecosystem Dynamics – Climate Impacts on Oceanic Top Predators (GLOBEC-CLIOTOP). Currently IMBER-CLIOTOP.
- Olson, R., and Young, J., 2007. The role of squid in open ocean ecosystems. Report of a GLOBEC-CLIOTOP/PFRP workshop,16-17 November 2006, Honolulu, Hawaii, USA. GLOBEC Report Series 24, 106 pp.
- Maury, O. and Lehodey, P. (Eds.). 2005. Climate impacts on oceanic top predators (CLIOTOP). Science Plan and Implementation Strategy. GLOBEC Report Series 18, 42.
- Young J.W., Olson R.J. and Rodhouse, P.G., 2013. The role of squids in pelagic ecosystems, Deep Sea Research II. 95: 3-6. http://dx.doi.org/10.1016/j.dsr2.2013.05.008
Materials Transfer at the Continent-Ocean Interface (INCT-TMCOcean) – an IMBER endorsed project
Luiz Drude de Lacerda
Marine Science Institute, Universidade Federal do Ceará, Fortaleza, 60.165-081, CE, Brazil.
The transfer of material from the continents to the oceans is key to understanding global biogeochemical cycles. In this process, organic matter, nutrients and contaminants undergo physical and chemical changes that eventually result in their accumulation in coastal areas, export and cycling in continental shelf environments and, under certain scenarios, export to the deep sea. The processes involved in such changes, their drivers and the eventual fate of the materials are the focus of the INCT-TMCOcean project. The research is focused along a climate and land use gradient on the Brazilian coast, ranging from the humid sub-tropical urbanized and industrialized southeast (SE), to the semi-arid, tropical, predominantly agricultural northeast (NE). This gradient allows the comparison of processes and their drivers to be assessed under different environmental settings.
INCT-TMCOcean is a research network involving 34 researchers and about 78 postdocs, graduate and undergraduate students from 10 universities, three research institutes and a research company. Four major questions orient the objectives of the project:
To address these questions, the INCT-TMCOcean research network quantifies similarities and dissimilarities of contamination, eutrophication and carrying capacities at different areas along the NE and SE Brazilian coast, integrating and modelling them to construct appropriate scenarios for sustainable utilisation. These include geological, biological and chemical frameworks, as well as anthropogenic nutrient and trace metal emissions. Special attention is given to changes in sediment, nutrients, organic matter and pollutant fluxes from the land downriver to estuaries, where most water-dependent activities (e.g., river damming, agricultural irrigation, urbanisation and aquaculture) occur. Changes in basin morphology, erosion and sedimentation of estuaries are also considered. A hierarchical typology of the major drivers responsible for environmental changes in the studied watersheds was developed to balance management actions to control and minimize impacts. Detailed, comparative, descriptions of the major biogeochemical processes are given, taking into consideration the different geochemical backgrounds, in gradient from the humid SE to the semi-arid NE.
Environmental impacts of global climate change are evaluated using biodiversity proxies of land use changes. These include changing cover and biodiversity of key ecosystems, as well as the spectrum of fisheries and monitoring species identified for the basin. Changes in biogeochemical proxies, together with major lines of research, are used to produce consistent scenarios of sustainable utilisation of coastal zone goods and services in the reality of the Anthropocene.
The project also aims to evaluate the socio-economic impacts of product chains of artisanal fisheries, aquaculture, irrigated agriculture and husbandry due to water use conflicts, soil erosion and waterway sedimentation. Stakeholder participation is encouraged through the organisation of workshops where knowledge generated, and how it can be applied to policy making and sustainable development, is shared. Evaluation of environmental and socio-economic indicators provides information about the income generated and dependence of the local population. This is complemented by a considerable effort to build the human capacity and undertake training at all education levels.
INCT-TMCOcean Science Highlights
1 - Relative contribution of nutrients and trace metals to continental runoff from natural and anthropogenic sources in non-industrialized areas
A comparison of the average relative importance of natural processes and anthropogenic sources,with the total emission of nutrients and metals in 21 estuarine basins in NE Brazil is shown in Fig. 18. In the majority of the basins, notwithstanding their low urban and industrial development, anthropogenic sources are the most important contributor of nutrients (N and P) and some metals (Cu, Zn and Hg).
The condition of most of the estuaries along the NE coast of Brazil is worrisome. Although only a few show obvious environmental impacts such as eutrophication or severe contamination, the large anthropogenic impact is reducing their support capacity and eroding their natural capital, as well as affecting ecological interrelationships and biogeochemical balances. There is no continuous inventorying of the nutrient and metal emissions from these activities and monitoring programs are erratic or non-existent. We hope the results obtained will help local and regional environmental agencies to establish such practices.
Intensive shrimp aquaculture is a relatively new, but important activity in these estuaries. In 1998 there were less than 300 ha of ponds on the NE coast. By 2008, this had increased to nearly 12,000 ha. Production peaked at 90,000 t.yr-1 in 2005, but has now stabilized at 65,000 t.yr-1, with the average productivity around 4,200 t.ha-1. This area accounts for about 93% of the total shrimp farming area, and 96% of the total Brazilian production.
Growth in shrimp farming looks set to continue, due to the abundance of potentially suitable coastal areas for future farming activities, annual export revenues of US$ 240 million, the labour-intensive production chain, advanced technology and constantly growing market. However, notwithstanding its socio-economic importance, intensive shrimp aquaculture may cause significant environmental impacts to coastal ecosystems. Excess fertilizer, aquafeeds and animal excreta enrich effluents with nutrients and organic matter, and erosion of the pond walls by aerators increases the amount of suspended matter. Also, unlike other sources of contaminants (e.g. agriculture, husbandry, waste water and solid waste from urban areas), shrimp farming effluents are released directly into estuaries (Table 1). The activity is currently the most important source of N and P for many estuaries. Little is known, however, about the emission of other pollutants, such as trace metals, that are present as impurities in most consumables used in the activity, especially in aquafeeds.
Table 1. Cu and Hg Emission Factors and annual discharges from shrimp ponds and other anthropogenic sources in the Jaguaribe estuary, a major shrimp farming area in NE Brazil. (n.d. = non-detectable)
This project has demonstrated that, although not as obvious as nutrients, shrimp farming is a potential source of trace metals for estuaries, in particular Cu and Hg, which are natural components of aquafeeds, impurities in fertilizers and active ingredients of algaecides. Cu and Hg emission factors (EFs) range from 386.4 gHg.ha-1.yr-1 for Cu to 0.37 gHg.ha-1.yr-1 for Hg. These EFs are comparable to, and even higher than those from other anthropogenic sources, and we urge environmental authorities around the world to include trace metals in their programs for monitoring emissions from intensive shrimp farming.
Figure 19 shows the Cu balance calculated for a typical intensive shrimp aquaculture activity in the Jaguaribe estuary, where most of shrimp farms (2,640 ha) of Ceará State, NE Brazil are located. The major sources of Cu, as well as other metals, are aquafeeds and chemicals, such as lime and fertilizers, used in the production process. A small fraction of these metals are exported as shrimp biomass and accumulate in bottom sediments. The major part is exported to adjacent estuarine waters. Most is exported as particulate matter, accumulating in sediments of tidal creeks and mangroves.
2 - Changes in environmental proxies due to regional land use and global climate changes
Analysis of remote sensing information, photographs and maps from several studies, and comparisons with pre-anthropogenic era satellite data from various dune fields and estuaries, showed large-scale responses to climate variability and land use change. Selected proxies associated with these environmental changes are the velocity of annual displacement of barchan dunes, and increasing area of mangrove forests. These were quantitatively linked to alterations in the region’s climate, precipitation and fluvial discharges.
The climate in the semi-arid coast of NE Brazil is characterised by a relatively short wet season (4-5 months) and a relatively long dry season (7-8 months), with wind intensity determined by the southern shift of the Intertropical Convergence Zone (ICTZ). Wind power is negatively correlated with precipitation, which in turn is negatively correlated with the difference between sea surface temperatures of the tropical Atlantic Ocean, north and south of the Equator (Fig. 20). The littoral harbours vast sand dune fields, in part constituted by parabolic formations stabilized by vegetation. Another group of dunes, not covered by vegetation, is active and moves freely, forming barchans and transverse dunes. Mobility and stability of these dunes is determined by the wind power; they move during dry periods of high wind power and stabilize in the wet season when wind power is lowest.
When barchan dunes move, residual ridges often remain (so-called cuspidate marks indicated by the arrows in Fig. 20). These are formed by vegetation growing along the edge of flooded interdune areas when the water level rises during the rainy period. Each cuspidate mark corresponds to the position of the dune during the wet period in each year. Therefore, variations in the distance between these residual dune ridges could potentially be used to monitor climatic fluctuations in rainfall and wind.
We have shown that there is a correlation between the intensity of ENSO events and the displacement of sand dunes on the coast of Ceará, NE Brazil. Consequently, dune migration could possibly be used to monitor global climate change. A model was developed that simulates the major variations in wind, rainfall and evaporation rates, to examine the potential use of these residual dune ridges to reconstruct past climatic fluctuations, for at least the past 40 years. The model was tested for sensitivity to climatic variability in NE Brazil, and validated against residual dune ridge displacements measured in the field, and from high spatial resolution satellite images. Unfortunately, the results showed that residual dune ridges might not form in particularly dry years, such as during El-Niño events, due to the extreme lowering of the water table. During these events, the distance between adjacent residual dune ridges can correspond to more than one year and, therefore, the correlation between dune displacements and wind power becomes weak or even disappears. Additionally, because of biotic, aeolian and hydrological processes, cuspidate marks may not preserve their initial shape for long periods, making their potential use in reconstructing past climates on a yearly basis or to identify past El Niño events, limited when scaled up to the regional level.
The hydrodynamics of rivers draining the semi-arid NE of Brazil are influenced by climate and regional land use changes. Global climate change causes major impacts, but the effects on fluvial flows are maximized by damming and water withdrawals for human use. An average decrease of 5.3 mm.yr-1 in the annual rainfall of the Ceará State since the late 1960’s has been reported, and confirms results from modelling exercises conducted by the IPCC. Dam construction to provide freshwater for human use has greatly altered the semi-arid watersheds during the last century. These two major drivers have contributed to a general decrease in continental runoff to the ocean, resulting in widespread coastal erosion, increasing saline intrusion and sedimentation of estuaries in NE Brazil.
Mangroves respond rapidly to changes in hydrodynamic and sedimentation-erosion equilibrium and can, therefore, be used to monitor environmental change in estuaries. Thus, a comparative analysis of the semi-arid coastline (using detailed remote sensing information, aerial photographs and maps) and mangrove forests (using detailed mapping) of NE Brazil was undertaken. Images were treated using standard methodology (e.g. GIS, ARCView etc.) to derive graphic scenarios of recent regional changes of the mangrove areas and their eventual correlation with water and material fluxes, as well as changes in the landscape.
Figure 21 provides an example of the expansion of the mangroves in the Pacotí River estuary from 1958 to 2004. The mangrove area increased by about 49%, following the enlargement of river beaches and creation of new fluvial islands. This was due to increased sedimentation, caused by damming of the river, and the 20-fold decrease in river discharge during the rainy season, when most of the sediments that accumulated during the dry season would normally have been moved to the ocean. This situation occurs in most estuaries of the semi-arid coast of NE Brazil.
Comparisons of the expansion of the mangrove areas, with and without human intervention, in 27 river basins along NE Brazil from 1999 to 2006, enabled evaluation of the relative importance of global climate change (no direct human intervention) and regional land use changes (mostly river damming and coastal engineering works) as the major drivers of ecosystem changes. The results strongly suggest that global climate change is a major driver of mangrove expansion. At least 46% of the expansion occurred where there had been no local alteration in land use, although the impact of global change on other areas affected by regional land use drivers cannot be ruled out. Mangrove expansion therefore, is an excellent proxy for the effects of global climate change in the semi-arid coast of NE Brazil.
Other proxies of environmental change on this NE Brazilian coast include beach erosion and changes in river morphology. These processes are accelerating along much of this coast, especially the build up of new islands in lower river courses and estuaries, enlargement of fluvial beaches and loss of beach volume. These are interrelated, complex processes. However, they correlate to a single major driver - decreasing continental runoff.
3 - Oceanography of the continental shelf-deep ocean continuum in the Equatorial Western Atlantic Ocean
Seasonal and inter-annual variability in temperature, salinity and density, so-called state parameters, and their horizontal and vertical distribution in the water column, are fundamental to understanding ocean-atmosphere heat transfer in tropical and equatorial latitudes. In the Equatorial Western Atlantic Ocean, warm, high salinity tropical water (TW) occurs at the surface, over a layer flowing at the pycnocline, with large variability in temperature and salinity of the South Atlantic Central Water (SACW). The SACW is characterized by lower temperatures and salinity. The isopycnal (σθ = 27.1) in tropical regions defines the transition between the SACW and the Intermediate Antarctic Water (AAIW) flowing just below and towards the Equator. The AAIW water mass is relatively cold, oxygen-enriched and low in salinity. It is defined as occurring between the thermo-haline: 3 - 6 oC and 34.2 - 34.6 PSU. Below the AAIW there is the North Atlantic Deep Water (NADW) characterized by lower temperatures (3 - 4 oC) and higher salinity (34.6 to 35.0 PSU). This water mass flows southward between depths of 1,500 m to 3,000 m to approximately 32 oS, where at least part of the current returns to the Equator.
The intrusion of TW on the continental shelf drives a water mass with lower oxygen content towards shallower water. The displacement of this mass may be related to an intensification of the Ekman transport towards the coast, and/or the upwelling of deeper water masses, carried by the heat accumulation in the South Atlantic, enhanced by global climate change. Particularly during the dry season, the TW has a stronger influence on the continental shelf (Fig. 22), most likely due to the space-time variability of the North Brazil Current (NBC), and the role of anticyclonic eddies that meander from the adjacent ocean towards the continental shelf.
In the inner shelf region, a marked presence of the coastal waters (CW) was observed, whereas the continental influence (cw), was restricted to the estuaries, most likely because of the limited ability of the continental runoff to reach the continental shelf. In the middle and outer shelf regions, the TW exerted a stronger influence, most likely because of the existence of space-time variability in the behaviour of the NBC, and the role of anticyclonic eddies that meander along the adjacent ocean towards the continental shelf. Even in low latitudes, the baroclinic adjustment of the NBC may contribute to TW intrusion on the NE continental shelf. This restricting of the continental runoff during the dry season is of major significance to the hydrodynamics and biogeochemistry of estuaries.
Along the shelf-slope continuum we found waters with high salinity and temperatures, from the 20 m isobaths to the breaking of the continental shelf, characterized by high oxygen concentrations, (≥ 6 mg L-1) and always separated by the σθ = 23.5 isopycnal. Beyond this region towards the open ocean, low salinity and temperature waters, which decreased with depth, showed a lower oxygen content. Preliminary results, based on an integration of the vertical distribution of salinity and temperature through a scattered T-S diagram, showed the mixing and stratification of water masses based on the correlation between these variables. The 23.5 isopycnal (σθ) characterizes the Costal Water (CW), extending to a depth of 50 m within the continental shelf. Sub-surface layers with isopycnals of 25 and 26.5 characterize the nucleus of two important water masses associated with the Tropical Water (TW) and the South Atlantic Central Water (SACW). The depth of the two masses is 60 to 120 m for TW, and 150 to 600 m for SACW. Immediately below the SACW, deeper than 700 m, a water mass separated by a isopycnal of 27 characterises the Antarctic Intermediate Water (AAIW), with depths ranging between 700 and 950 m. Below this depth, a water mass characterized by 3 °C < T < 4 °C and 34.5 < S < 35 PSU was observed, which agrees with the thermo-saline indices of the superficial layer of the North Atlantic Deep Water (NADW), at 1,000 m depth. This is corroborated by the oxygen concentrations found in this water mass. Current knowledge of the vertical variability of water masses in the South Atlantic Ocean suggests the presence of NADW between 1,500 m and 3,000 m. Therefore, our results imply that the top layer of the NADW at such shallower depths (~1,000 m). If these results are correct, then the rising of the NADW may be caused by the present heat accumulation in the South Atlantic, and the increasing freshwater inflow in the North Atlantic, due to global climate change. This movement of deep water masses may increase the effects on the continental runoff already observed during the dry season, and therefore enhance its significance on the hydrodynamics and biogeochemistry of estuaries.
4 - The Arctic Paradox
The hydrodynamics and Hg fluxes of the Jaguaribe River estuary have been measured since 2005 during both the dry and rainy seasons. This is the largest watershed in the semi-arid NE Brazil, that discharges into the Equatorial Atlantic Ocean. During rainy periods, water flows to the ocean, with a short residence time in the estuary (0.8 days). During dry periods, seawater limits the fluvial discharge, resulting in a longer residence time (3.1 days) for the water in the estuary. Dissolved (<0.7 µ) and particulate Hg concentrations and fluxes were higher from the river to estuary, than from estuary to sea, with mostly particulate Hg accumulating in the estuary. Particulate Hg export (1.8 to 12.6 mg.s-1) to the ocean occurred in extremely rainy periods while dissolved Hg exports were almost zero during rainy periods, but reached 0.45 mg.s-1 during dry periods (Fig. 23). The hydrodynamics of the Jaguaribe River estuary is essentially dependent on the regional climate and land use changes. The NE Brazilian coast is highly impacted by global climate change, particularly the fluvial flows, that are already significantly affected by damming. A decrease of 5.6 mm.yr-1 in the annual rainfall of the region has been observed since the late 1960’s. The decrease in basin runoff has been further accelerated by the construction of five large (> 106 km3 water storage capacity) and more than 80 small to medium sized reservoirs along the Jaguaribe basin in the past 50 years.
The impacts of global climate change on Hg export to the sea from the semi-arid NE of Brazil, could be correlated with the current situation of the rivers draining into the Arctic Ocean, another region of Earth extremely affected by global change. In the Arctic, increasing continental runoff and reduction of the ice cover in estuaries has resulted in increasing export of Hg to the Arctic Ocean. This has led to increased incorporation of Hg by phytoplankton and increased concentrations in other Arctic biota, as well as higher deposition in shelf sediments. In the semi-arid region of Brazil, because global climate change decreases the freshwater contribution to the estuary and eventually the continental runoff to the sea, it should result in decreased Hg export to the sea. Paradoxically, however, as in the Arctic, high Hg concentrations have been reported in fish from the NE continental shelf off the Jaguaribe River. There have also been increases in Hg and organic matter concomitants in sediment profiles. Reducing continental runoff has thus, increased the residence time of water in the estuary, and flooding of the marginal plains, dominated by mangroves and slack water conditions. During these periods, larger Hg mobilization was simultaneously observed, and resulted in high export of more dissolved bioavailable Hg to the sea.
Based on ongoing observations, greater Hg mobilization is expected when water residence time in the estuary increases, and this may became more frequent as the continental runoff decreases. If this “Arctic Paradox” holds true, this situation will probably deteriorate as global climate change continues to reduce continental runoff in the semi-arid NE Brazil and water withdrawal for human use also increases. Therefore, it is possible that Hg reactivity will increase even more in the estuary and in the adjacent coastal sea, when it is eventually exported there by the ever less frequent freshwater flux peaks. These mechanisms will increase Hg bioavailability in coastal food webs.
5 - Carbon from a vanished tropical forest biome
The slash-and-burn destruction of Brazil’s Atlantic forest, which once covered over 1.3 million km2 and was one of the largest tropical forest biomes on Earth, is a prime example of unsustainable use of tropical forests. Two groups of the INCT-TMCOcean, in cooperation with the Max Planck Research Group for Marine Geochemistry at the University of Oldenburg, estimated the amount of black carbon generated by the burning of the Atlantic forest (Fig. 24), using historical records of land cover, satellite data and black carbon conversion ratios. It was estimated that before 1973, destruction of the Atlantic forest generated 200–500 million tons of black carbon. The amount of black carbon exported from this relict forest between 1997 and 2008, using measurements of Bezene Polycarboxilic Acid "black carbon" collected from a large river draining the region, and a continuous record of river discharge, showed that dissolved black carbon (DBC) continues to be mobilized from the watershed each year in the rainy season, despite the fact that widespread forest burning ceased in 1973. We estimate that the river exports 2,700 tons of DBC to the ocean each year. Scaling our findings up, we estimate that 50,000–70,000 tons of DBC are exported from the former forest each year. We suggest that an increase in black carbon production on land, could increase the size of the refractory pool of dissolved organic carbon in the deep ocean. The disappearance of the Atlantic forest provides a worst-case scenario for tropical forests worldwide, most of which are being cleared at an increasing rate. The comparably fast mobilization of DBC from soils and its apparent recalcitrance in the deep ocean suggest that an increase of black carbon production on land may alter the size of the refractory dissolved organic matter pool in the deep ocean in the long term.
The original research that resulted in the selected scientific highlights presented here was mostly supported by the National Research Council (CNPq). However, the establishment of a research network provided the necessary framework to increase human and financial resources; and as an output of this successful initiative of promoting scientific research, many other funding agencies in Brazil and abroad helped to support the INCT-TMCOcean activities. We would like to thank, in particular CAPES, from the Ministry of Education, and the local agencies FAPERJ, FUNCAP and FAPESP, for financing researchers from their states. PETRBRAS and EMBRAPA also participated in the research efforts of the network. The host universities and research institutions, in particular the Universidade Federal do Ceará, provided most of the local facilities to carry out the project's objectives. The IRD-France; the Max Planck Institute Germany, IADO-Argentina, IAEA-Monaco, LOICZ and IMBER have been our major international partners, and we would like to thank them for this support. C.R. Rezende and R.V. Marins critically reviewed this manuscript.
All the original research described here, as well as all other INCT-TMCOcean production and activities are available in the project’s website www.inct-tmcocean.com.br .
New Administrative Assistant at the IMBER IPO
|We are delighted to welcome Veslemøy Kjersti Villanger as the new Administrative Assistant at the IMBER International Project Office.|
Deadline for abstract submission for the IMBER Open Science Conference: 31 January 2014
Theme: Future Oceans: Research for marine sustainability, multiple stressors, drivers, challenges and solutions
When and where: 23 - 27 June 2014 in Bergen, Norway
Who should come: Physical, natural and social sciences research communities interested in marine issues in the framework of global change and the transition towards marine sustainability
The IMBER Future Oceans conference will enable marine researchers and research end-users to share their knowledge and experience.
The ultimate goal is to foster collaborative, interdisciplinary marine research that addresses human-natural marine science issues and to provide guidance for decision makers, managers and communities towards marine sustainability.
For more information please visit the IMBER OSC website
We look forward to seeing you in Bergen!
IMBER ClimEco4 Summer School (4-9 August 2014, Shanghai, China)
Delineating the Issues of Climate Change and Impacts to Marine Ecosystems: Bridging the Gap Between Research, Assessment, Policy and Management
The ClimEco4 summer school will continue the IMBER focus on fostering research at the interface of natural and human systems and will bring together participants from both the natural and social sciences. Considerable resources are invested in global environmental change research and in development of policy and management strategies for marine resources. However, a disconnect occurs in the effective transfer of information and knowledge from one community to the other in terms of how to effect changes in the use and management of resources. Indicators provide an approach for characterising and combining information from the natural sciences and the human dimensions of policy and management in a manner that is useful to both communities.
The ClimEco4 summer school will provide training to enable participants to source, analyse and transform data into indicators that can be used to assess the ecological state of a marine ecosystem, the environmental states and trends, benefits to society, and its long term ecosystem sustainability.
Download the summer school flyer:
ClimEco4_flyer.pdf 2.59 MB
For more information about the summer school and how to apply, please go to the ClimEco4 Website
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- Keul N., Langer G., de Nooijer L. J. & Bijma J., 2013. Effect of ocean acidification on the benthic foraminifera Ammonia sp. is caused by a decrease in carbonate ion concentration. Biogeosciences 10, 6185-6198. Article
- Lachkar Z., Effects of upwelling increase on ocean acidification in the California and Canary Current Systems. Geophysical Research Letters. in press. Article
- Le Moigne F. A. C., Boye M., Masson A., Corvaisier R., Grossteffan E., Guéneugues A. & Pondaven P., 2013. Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year. Biogeosciences 10, 281-295. doi:10.5194/bg-10-281-2013. Article
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- Lilly, G. R., Nakken, O., Brattey, J., 2013. A view of the contributions of fisheries and climate variability to contrasting dynamics in two Arcto-boreal Atlantic cod (Gadus morhua) stocks: persistent high productivity in the Barents Sea and collapse on the Newfoundland and Labrador Shelf. Progress in Oceanography 114, 106-125. Article
- Maier C., Bils F., Weinbauer M. G., Watremez P., Peck M. A. & Gattuso J.-P., 2013. Respiration of Mediterranean cold-water corals is not affected by ocean acidification as projected for the end of the century. Biogeosciences 10, 5671-5680. Article
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- Morrison, R.J., Zhang, J., Urban Jr., E.R., Hall, J., Ittekkot, V., Avril, B., Hu, L., Hong h, J.H., Kidwai, S., Lange, C., Lobanov, V., Machiwa, J., San Diego-McGlone, M.L., Oguz, T., Plumley, F.G., Yeemin, T., Zhu, W., Zuo, F., 2013. Developing human capital for successful implementation of international marine scientific research projects. Marine Pollution Bulletin, 77:11-22. Article
- Ottersen, G., L.C. Stige, J.M. Durant, K.-S. Chan, T. Rouyer, K. Drinkwater, and N. Chr. Stenseth. 2013. Temporal shifts in the recruitment dynamics of North Atlantic fish stocks: Effects of spawning stock and temperature. Marine Ecology Progress Series 480: 205-225. doi:10.3354/meps10249 Article
- Palacz, A. P. , St. John, M. A., Brewin, R. J. W., Hirata, T., and Gregg, W.W., 2013. Distribution of phytoplankton functional types in high-nitrate, low-chlorophyll waters in a new diagnostic ecological indicator model. Biogeosciences 10: 7553-7574. Article
- Pérez, F.F., Mercier H., Vázquez-Rodríguez M., Lherminier P., Velo A., Pardo P.C., Rosón G., Rios A.F., 2013. Atlantic Ocean CO2 uptake reduced by weakening of the meridionaloverturning circulation. Nature Geosciences 6, 146–152. Article
- Petitgas, P., A.D. Rijnsdorp, M. Dickey-Collas, G.H. Engelhard, M.A. Peck, J.K. Pinnegar, K.F. Drinkwater, M. Huret and R.D.M. Nash. 2013. Impacts of climate change on the complex life cycles of fish populations. Fisheries Oceanography 22, 121-139. Article
- Planchon F., Cavagna A.-J., Cardinal D., André L. & Dehairs F., 2013. Late summer particulate organic carbon export and twilight zone remineralisation in the Atlantic sector of the Southern Ocean. Biogeosciences 10, 803-820. doi:10.5194/bg-10-803-2013. Article
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- Salihoglu, B., S. Neuer, S. Painting, R. Murtugudde, E. Hofmann, J. Steele, R. Hood, L. Legendre, M. Lomas, J. Wiggert, S. Ito, Z. Lachkar, G. Hunt, K. Drinkwater, and C. Sabine. 2013. Bridging marine ecosystem and biogeochemistry research: Lessons and recommendations from comparative studies. Journal of Marine Systems 109-110: 161-175. Article
- Salt L. A., Thomas H., Prowe A. E. F., Borges A. V., Bozec Y. & de Baar H. J. V., Variability of North Sea pH and CO2 in response to North Atlantic Oscillation forcing. Journal of Geophysical Research: Biogeosciences. DOI: 10.1002/2013JG002306. (in press) Article
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- Theodosi, C. et al., 2013. The significance of atmospheric inputs of major and trace metals to the Black Sea. Journal of Marine Systems 109-110, 94-102. Article
- Wang, W., Murtugudde, R., Hackert, E. and Maranon, E., 2013. Phytoplankton carbon and chlorophyll distributions in the equatorial Pacific and Atlantic: A basin-scale comparative study. Journal of Marine Systems 109-110, 138-148. Article
- Young, J., R. Olson, and P. Rodhouse. 2013. The Role of Squids in Pelagic Ecosystems. Deep Sea Research Part II: Topical Studies in Oceanography 95, 1-224. Article
- 2014 COMPASS Ocean Acidification Communication Workshop (20-22 February 2014, Oahu, Hawaii, USA)
- BERING SEA PROJECT Open Science Meeting (22-23 February 2014, Honolulu, Hawaii, USA)
- 2014 Gulf of Mexico Oil Spill and Ecosystem Science Conference (26-29 January 2014, Mobile, Alabama, US)
- ASLO 2014 Ocean Sciences Meeting (23-28 February 2014, Honolulu, Hawaii, USA)
- EMB 4th Open Forum, Arctic 2050: Towards ecosystem-based management in a changing Arctic Ocean (12 Mar. 2014, Brussels, Belgium)
- 2nd GLP Open Science Meeting (19-21 March 2014, Humboldt University, Berlin)
- Ecosystem Studies of Sub-Arctic Seas (ESSAS) Annual Science Meeting (7-9 April 2014, Denmark)
- PICES FUTURE Open Science Meeting (15-18 April 2014, Kohala Coast, Big Island, Hawaii, U.S.A.)
- IOC-WESTPAC 9th International Scientific Symposium (22-25 April 2014, Nha Trang, Vietnam)
- European Geosciences Union General Assembly 2014 (27 April - 2 May 2014, Vienna, Austria)
- 2014 Salish Sea Ecosystem Conference (30 April - 2 May 2014, Seattle, Washington)
- The 46th international Liège colloquium on ocean dynamics: Low oxygen environments in marine, estuarine and fresh waters (5-9 May 2014, Liège, Belgium)
- IMBER Open Science Conference (23-27 June 2014, Bergen, Norway)
- 2014 OCB Summer Workshop (21-24 July 2014, Woods Hole, MA, USA)
- IMBER ClimEco4 Summer School (4-9 August 2014, Shanghai, China)
- 2nd World Small-Scale Fisheries Congress (21-25 September 2014, Mérida, Mexico)
- 3rd World Conference on Marine Biodiversity (12-16 October 2014, Qingdao, China)
- 2nd International Ocean Research Conference: One Planet One Ocean (17-21 Novemebr 2014, Barcelona, Spain)