North Pacific decadal variability in the future

Emanuele Di Lorenzo¹, Jason Furtado¹ and Niklas Schneider²

Recent studies show that decadal climate and ecosystem variations in the North Pacific are largely explained by the first two dominant modes of ocean-atmosphere co-variability evident in sea level pressure and sea surface height. The first co-variability mode tracks changes in the Aleutian Low and is associated in the ocean with the well known Pacific Decadal Oscillation (PDO). The second mode tracks variability in the North Pacific Oscillation (NPO) – a dipole structure in sea level pressure with low pressure over the Bering Sea and high pressure north of Hawaii. The oceanic expression of the NPO is the recently identified North Pacific Gyre Oscillation (NPGO) – a decadal mode of climate variability that reflects changes in strength of the central and eastern branches of the subtropical gyre and of the Kuroshio-Oyashio Extension (KOE). The NPGO is also linked to previously unexplained fluctuations of salinity, nutrient and chlorophyll fluctuations in the Northeast Pacific.

Using a set of ten coupled climate models from the Intergovernmental Panel on Climate Change (IPCC) we (1) assess the degree of realism of the IPCC models to reproduce the first two decadal modes of ocean-atmosphere co-variability in the North Pacific during the twentieth century (1900-2000), (2) explore how decadal variability is projected to change in future scenarios (2001-2100) and (3) discuss strategies for downscaling and regional biophysical model forecasts of climate change.

Community structure, productivity and photosynthetic physiology of phytoplankton in the Oyashio region of the NW subarctic Pacific during spring 2007

Tomonori Isada¹, Ai Hattori¹, Koji Suzuki¹, Mitsuhide Sato² and Ken Furuya²

Despite large diatom blooms occurring in the Oyashio region every spring, our knowledge of factors controlling primary productivity in the region during that season remains incomplete. Therefore, we examined the community structure, productivity and photosynthetic physiology of phytoplankton at a station (42°N, 145°15’E) in the Oyashio region during spring 2007. Chlorophyll a (Chl-a) concentrations in surface waters were consistently high (2-36 mg m-3) and micro-sized phytoplankton accounted for > 83% of the Chl-a levels during our cruise. Diatoms contributed to the surface Chl-a concentrations by > 74%, and the dominant, micro-sized diatoms changed from Thalassiosira species to Chaetoceros species with time. Pico- and nano-sized phytoplankton became significant in phytoplankton biomass in the latter half of the cruise. Interestingly, these tiny cells sometimes showed discontinuous distributions in the water column, indicating the intrusion of different water masses into Oyashio waters. Depth-integrated daily primary production within the euphotic layer ranged between 535 and 3584 mg C m-2 d-1. Although sufficient macronutrients remained in surface waters throughout the study, values of photosynthetic parameters such as Fv/Fm varied temporarily. A non-iron-containing flavoprotein, flavodoxin, which is a diagnostic marker for iron deficiency in situ, was detected in the micro-sized diatoms throughout the cruise. The result indicates that the micro-sized diatoms were stressed by low iron availability.

How effective are Cassin’s auklets as environmental monitors in Central California?

Peter Warzybok¹, Russell W. Bradley¹, Meredith L. Elliott¹, Benjamin L. Saenz^1,2, Nina J. Karnovsky³ and Jaime Jahncke¹

Cassin’s Auklets Ptychoramphus aleuticus are small wing-propelled diving seabirds (Family: Alcidae) of the California Current which forage on macrozooplankton, primarily large euphaussids. For 38 years, PRBO Conservation Science (formerly Point Reyes Bird Observatory) has maintained a continuous annual time series on auklet demography and diet on Southeast Farallon Island, CA, as part of long-term ecological studies of breeding seabirds. During the past 3 years, auklets have suffered unprecedented breeding failure and large declines in breeding population. While it appears that timing of euphaussid availability may be the driving mechanism, causality is still uncertain. There is a strong need to link long-term colony-based studies of marine wildlife to their at-sea foraging behavior to improve understanding of their potential use as monitors of ecosystem status and ‘health’. Using a pilot study with Time Depth Recorders (CEFAS Technology, UK), we examined Cassin’s Auklet foraging behavior to investigate linkages between breeding biology and foraging in the spring/summer of 2008. We assessed foraging effort, depth and duration of diving, physical ocean conditions at foraging sites, and diet of marked birds. We also assessed the effects of auklets carrying TDRs, and dummy devices, by comparing reproductive performance and diet of TDR birds to unmarked birds. TDR deployment was conducted simultaneously with local oceanographic cruises to assess auklet and euphausiid abundance and distribution, to sample physical ocean conditions, and to determine abundance and species composition of zooplankton at predetermined locations.

Integrated method for sockeye salmon stock differentiation in the West Pacific and the Sea of Okhotsk

Anastasia M. Khrustaleva

Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), 17 V. Krasnoselskaya St., Moscow, 107140, Russia

Size structure and age-class composition were analyzed for major sockeye salmon populations from the West Pacific and the Sea of Okhotsk. Microsatellite DNA variation at six microsatellite loci was examined in approximately 720 sockeye salmon sampled in 2003-2005 from the nine stocks on the east and west coasts of Kamchatka, Chukotka, North Kuril Islands, and west coast of the Sea of Okhotsk. A well-defined differentiation of the sockeye salmon stocks by the size population structure (mean size and weight of an individual) and mean frequencies of the year classes was revealed. The differentiation could be associated with various time of sea and freshwater periods of life of sockeye individuals from different lakes and rivers. The microsatellite analysis showed well-defined genetic differentiation among the local populations. Significant differences in allele and genotype frequencies were found. The highest divergence was observed between island populations (North Kuril Islands, Shumshu Island, Bettobu Lake) and continental populations and could be caused by sockeye salmon post-glacial recolonization of Asian habitats. Assignment test of simulated mixed-stock samples showed that six highly polymorphic microsatellite loci would enable relatively accurate individual identification. A new method for sockeye salmon stock differentiation that integrates biological and molecular genetic markers and multivariate statistics has been developed to increase accuracy of sockeye population discrimination.

Distribution and biomass of Benthosema pterotum (Pisces: Myctophidae) in the shelf region of the East China Sea: Mechanisms of population maintenance

Chiyuki Sassa¹, Keisuke Yamamoto², Youichi Tsukamoto¹ and Muneharu Tokimura¹

Benthosema pterotum is a typical pseudoceanic myctophid, widely distributed in the subtropical-tropical slope waters of the Indo-West Pacific. In the East China Sea, they occur in a much shallower shelf region (ca. 30–110 m depth), and undergo a unique diel vertical migration, i.e., occurring in the epipelagic layer at night, and shifting down to the benthopelagic layer during the daytime to form dense aggregations. Therefore, they provide a major prey item for commercially important demersal fishes such as hairtails, croakers, and lizardfishes. Based on data from seasonal bottom trawl surveys during the daytime, dense distributions (>10⁵ individuals per km²) of B. pterotum were mainly observed in the area south of Cheju Island throughout the year, where a persistent cyclonic eddy exists. In this area, the bottom sediments are mainly composed of mud, which are resuspended by the strong tidal current producing waters of high turbidity. Since little sunlight penetrates these depths, the dimly lit conditions in the benthopelagic layer enable B. pterotum to live in such a shallow area. In the area south of Cheju Island, their larvae mainly occur during summer to autumn and are associated with an eddy, which facilitates recruitment into this area. Assuming that (1) the catch efficiency of the trawl is 0.2–0.4, and (2) daytime distribution of B. pterotum is up to 10 m above the bottom, the biomass in the area south of Cheju Island was estimated to range from 8,500 to 40,800 t.

Change of ecosystem services of the Yellow River Delta Wetland, China

Shang Chen, Jian Liu, Tao Xia and Qixiang Wang

Research Center for Marine Ecology, First Institute of Oceanography, SOA, 6 Xianxialing Rd., Qingdao, 266061, PR China

The Yellow River Delta Wetland (YRDW), a coastal reed wetland located in the western Yellow Sea, provides 14 kinds of ecosystem services belonging to 4 groups. Nine of these were evaluated in this study. The YRDW provided ecosystem services worth 2,866 million CNY and 764,900 CNY per km2 in 2006. Among these services, food supply and climate regulation ranked the highest at 633 million CNY each. Second were oxygen production and wastewater purification at 596 and 558 million CNY, respectively. Biodiversity maintenance and raw material supply were third at 230 and 131 million CNY, respectively. Leisure-entertainment, scientific services and disturbance regulation were lowest at 35, 35 and 14 million CNY, respectively. Based on the landscape changes of YRDW from 1992 to 2006, the ecosystem services of YRDW in each year were valuated. The total service value of the YRDW ecosystem was 2,585 million CNY in 1992, 2,136 million CNY in 1996, 2,353 million CNY in 2000, and 2,866 million CNY in 2006. Spatial distribution maps of the YRDW show the service values of the YRDW ecosystem increased in the direction from land to seawater; reed grasslands of 8 landscapes had the highest values of ecosystem services in the 4 single years.

Spatial distribution of Perkinsus olseni in the Manila clam Ruditapes philippinarum along Chinese coast

Yubo Liang, Dongmei Li, Sa Liu, Xingbo Wang, Tao Song, Xing Miao, Guanhua Chen and Guize Liu

National Marine Environmental Monitoring Center, 42 Linghe St., Dalian, 116023, PR China

This is the first report of the spatial distribution of Perkinsus olseni in the Manila clam Ruditapes philippinarum off the coast of China. Histological observations revealed Perkinsus-like organisms in the mantle, gills, digestive tubules, and gonad. Hypnospore formation of the Perkinsus-like organism was confirmed with Ray’s fluid thioglycollate medium assay (RFTM). Genus- and species-specific polymerase chain reaction (PCR) assays and the DNA sequences of the internal transcribed spacer region (ITS) of the Perkinsus sp. isolated from the Manila clam were identical to Perkinsus olseni. Samples were collected from 33 clam populations along the Chinese coast in Yellow Sea, Bohai Sea, Eastern Sea and Southern China Sea, and the prevalence and infection intensity was determined using RFTM and a 2M NaOH digestion technique. The infection intensity averaged 466,532 Perkinsus cells per gram of tissue for the whole coastal water areas, and was 567,659 Perkinsus cells/g tissue in the Bohai Sea; 165,671 Perkinsus cells/g tissue in the Yellow Sea; 516,038 Perkinsus cells/g tissue in the East Sea and 878,385 Perkinsus cells/g tissue in the South China Sea, while the prevalence of Perkinsus ranged from 5.0 to 100.0%.

Japanese IPY activities in the western Arctic Ocean and the Bering Sea

Kohei Mizobata¹, Koji Shimada¹, Sei-ichi Saitoh², Toru Hirawake² and Masahiro Hori³

The Japanese IPY hydrographic surveys were conducted in the western Arctic Ocean and Bering Sea. Observational results describe warming trend and changes in spatial distributions of salinity and nutrients. We will discuss the impacts of sea ice reduction on the marine ecosystem in both seas.

Study of polynya processes in the Bearing Sea using a high resolution dynamic-thermodynamic sea ice model

Hongli Fu, Jinping Zhao and Jie Su

Key Lab of Polar Oceanography and Global Ocean Change, Ocean University of China, Qingdao, 266100, PR China

The circumpolar polynyas are of vital importance for ice production and feedback processes in the atmosphere-ice-ocean system. Thus, they play a crucial role in the Arctic climate as well as the global ocean circulation. A high-resolution dynamic-thermodynamic sea ice model with a horizontal resolution of 5 km has been implemented to investigate polynya processes in the Bering Sea. The model has the same dynamical and thermodynamic process as the Los Alamos National Laboratory CICE model. The data set of Large and Yeager (2004) was used to drive the model. The model performed well in predicting the current polynya conditions in the Bering Sea compared with satellite data and theoretical calculations. The sea-ice concentration in the region of the polynyas is very small, even less than 0.1%. Through appropriately selecting a threshold value of the ice thickness, we calculate the area of every polynya along with their time evolution. The factors of polynya formation are analyzed through sensitivity experiments. Based on these analyses, polynya formation mechanisms are discussed. Our model results suggest that it is possible that polynyas can be represented in future synoptic and climate prediction systems.

Oral (POC-P-5217), POC Topic Session

An N-shape thermal front in the western South Yellow Sea in winter

Chuanyu Liu^1,2 and Fan Wang¹

An N-shape sea surface thermal front in the western South Yellow Sea from late October through early March is reported in the present paper based on the Advanced Very High Resolution Radiation (AVHRR) sea surface temperature (SST) data. The front is composed of west and east wings along the northeast-southwestward isobaths with an isobath-crossing middle segment in between. After the front’s generation, the orientation of the middle segment rotates from West-East (W-E) in early November through early December to Northwest-Southeast (NW-SE) in late December through late February, which always crosses the isobaths. Going with the direction of change, this front expands and moves southwestward. Both the surface waters of the colder coastal current and bottom intensified Yellow Sea Warm Current (YSWC) affect the SST distribution through strong advection and vertical mixing, inducing a departure of the front line from the bathymetry. The colder coastal current penetrates into the warmer water modified by the northwestward branch of the YSWC. The N-shape front forms along the borders between the warmer and colder waters. This mechanism is proved primarily by simulation results from the Princeton Ocean Model (POM) with a tide module. Intraseasonal and interannual variations of the front show a close relationship to the wind which is favorable to both the coastal current and the YSWC.

The 1000 km-scale variability of the dynamic height revealed by Argo CTD data at 40ºN in the North Pacific

Masatoshi Sato¹ and Tokihiro Kono²

We analyzed spatial and temporal variability of dynamic height referred to 1000 db and estimated using Argo CTD data every two months from September 2005 to October 2007, with a resolution about 900 km. The local variation in the dynamic height was strong in the Oyashio Extension, off the California coast, and along the Aleutian Islands. In each dynamic-height map, high and low anomalies are seen in rows along the latitudes with wavelengths of about 1000 km in the Oyashio Extension and off the California coast. To clarify the structure of these waves, we separated the variation into wavenumber components greater and less than 0.2×10^-3km^-1 along the parallel of 40ºN. The higher wavenumber components were dominated by the signals of 0.73-1.25×10^-3km^-1, whose amplitudes were large west of 170ºW and east of 140ºW, and small between 170ºW and 140ºW. These high-amplitude signals propagated westward with a phase speed of -1.9 cms^-1, which is almost similar to that of Rossby waves from the linear theory. Similar wavenumber signals and their westward propagation were also clearly seen west of 170ºW in SSH maps of the satellite altimetry (Chelton and Schlax, 1996). East of 140ºW the signals were obscure. This suggests that the SSH cannot always vary coherently with the upper layer thickness in the subarctic.

Upper ocean export of particulate organic carbon in the Bering Sea estimated from thorium-234

Hao Ma^1,2, Mingduan Yin¹, Liqi Chen¹, Jianhua He¹, Wen Yu^1,2 and Shi Zeng²

During the Second Chinese National Arctic Expedition from July to September 2003, depth profiles of dissolved and particulate ²³⁴Th in upper water columns were collected at two stations in the Bering Sea and another one station on the northern mouth of the Bering Strait. Thorium-234 was sampled by using a traditional Fe(OH)₃ co-precipitation technique, which is a reliable approach to ²³⁴Th measurement. We observed ²³⁴Th excess at one station below the euphotic zone, which is possibly due to intensive remineralization of particulate matter. Particulate organic carbon (POC) was estimated from a one-dimensional irreversible steady state model of ²³⁴Th fluxes together with measurements of the POC/²³⁴Th ratio on the suspended particles. The POC export from the euphotic zone varied between 15.39 and 23.38 mmol C m^-2 d^-1. In comparison with observations of other seas, our results suggest that the biological pump would run effectively in summer in the Bering Sea, sub-arctic Pacific Ocean.

Behavior of a low salinity water mass during summer in the South Sea of Korea using in-situ observations

In-Seong Han¹, Takeshi Matsuno², Tomoharu Senjyu², Young-Sang Suh¹ and Ki-Tack Seong¹

A low salinity water mass (LSWM) <28 psu originated by Changjian Diluted Water frequently approaches Jeju Island and the South Sea of Korea during summer. This LSWM occasionally flows into the East/Japan Sea through Korea Strait and damages coastal fishing grounds and farms around Jeju Island. The National Fisheries Research and Development Institute (NFRDI) has conducted serial oceanographic investigations in the northern East China Sea since 1995 and the South Sea of Korea since 1961. NFRDI also operates a real-time observation system, which continuously measures surface temperature and salinity across Jeju Strait using an instrumented ferryboat since 2006. Temperature and salinity sensors also are moored at fisheries set-nets around Jeju Island and Korea Strait by Kyushu University (KU) since 2004. NFRDI and KU deployed 7 satellite-tracked surface drift buoys around the northern East China Sea in August 2007. These observations show the behavior of LSWM around Jeju Island and the South Sea of Korea in summer. From results in 2006 and 2007, LSWM, which appeared about 175 km west of Jeju Island, approached the west coast of Jeju Island about 8-9 days later. Then, it flowed into the East/Japan Sea through Jeju Strait about 10-12 days later. Salinity concentration in the LSWM continuously increased from ~25 psu west of Jeju Island to ~32 psu at Korea Strait, and its drift velocity was usually ~20-30 cm/s northeastward. This information will aid prediction of the behavior of LSWM around the South Sea of Korea.

Ensemble adjustment Kalman filter study for Argo data

Xunqiang, Yin, Fangli Qiao, Yongzeng Yang and Changshui Xia

First Institute of Oceanography, 6 Xian-Xia-Ling Rd., Qingdao, 266061, PR China

An ensemble adjustment Kalman filter system is developed to assimilate Argo data into the North-West Pacific MASNUM wave-circulation coupled model which is based on the Princeton Ocean Model (POM). This model was recoded in FORTRAN-90 style and some new data types were defined to improve the efficiency of system designing and execution. This system is arranged for parallel computing by using UNIX shell scripts, and is easier for a single model running separately with the required information exchanged through input/output files.

Two experiments are carried out to check the performance of the system: one assimilates the simulated ‘Argo’ data and the other one assimilates the real Argo data in 2005. The first experiment shows that the assimilation system performs well. The comparison with the satellite-derived sea surface temperature (SST) shows that modeled SST errors are reduced after assimilating; at the same time, the spatial correlation between the simulated SST anomalies and the satellite data is improved because of Argo assimilation. Furthermore, the temporal evolution/trend of SST becomes much better than those results without data assimilation. All these results suggest that this system is potentially capable of reconstructing oceanic data sets which are of high quality, and temporally and spatially continuous.

Toward a data-assimilation system for marginal seas in the SEA-WP region

Yasumasa Miyazawa^1,2, Yoshikazu Sasai¹ and Kazuo Nadaoka²

The South East Asia and West Pacific (SEA-WP) region is a significant reservoir of the world’s richest marine biodiversity, but is deteriorating in its coastal ecosystems owing to various environmental threats. To provide a proper conservation strategy, we have started a study that aims at clarifying regional reef connectivity in the SEA-WP region and thereby identifying important candidate areas to be properly managed as Marine Protected Areas (MPAs), on the basis of numerical simulations on larval dispersal, molecular biological analysis on meta-population dynamics and others. To provide realistic ocean currents for the simulation of larval dispersal, we have developed high-resolution ocean general circulation models in the SEA-WP region. The data assimilation has potentials for farther improvement of the model skills by combination of both the model and observation. Since the SEA-WP region includes shallow marginal-seas, it is important to modify the traditional data assimilation technique that has been developed mainly for use in deep open ocean. We conducted sensitivity experiments of adjustable parameters included in a data assimilation system, JCOPE2 (Miyazawa et al., 2008), in the marginal sea (the East China Sea) and open ocean (Kuroshio Extension and Kuroshio-Oyashio Mixed Water region). We found that the assimilation of sea surface height anomaly is effective in the Kuroshio Extension but not so in the East China Sea. We also found that use of sea surface temperature is useful in the East China Sea.