Chlorophyll specific growth rate and grazing mortality rate of phytoplankton in the shelf water of the Bering Sea in summer

Chlorophyll specific growth rate and grazing mortality rate due to microzooplankton were estimated based on the dilution methods, using surface waters collected at four stations in the continental shelf area of the Bering Sea in summer. Growth rates and grazing mortality rates of phytoplankton communities were ranged between 0.06d^ and 0.56d^ and between 0.04d^ to 0.33d^, respectively. The high growth rate seems to have resulted from continuous supply of nutrients caused by gentle stratification, which is a favorable condition of the water column for phytoplankton growth. Growth and grazing mortality rates were almost the same at one station, where the most typical summer concentration of chlorophyll a was observed (less than 1μgl^), suggesting that the major grazer seems to be microzooplankton in the Bering Sea shelf in summer. On the other hand, the lowest growth rate was obtained in near St. Laurence Island, where higher chlorophyll concentrations more than several μgl^ occurred. In this water passive sinking of cells seems to become one of controlling factor of phytoplankton abundance

APPLICATION OF SATELLITE MICROWAVE REMOTE SENSING DATA TO SIMULATE MIGRATION PATTERN OF ALBACORE TUNA

To simulate migration pattern of albacore tuna in the western North Pacific Ocean during the winter period, a kinesis model driven by high accuracy of sea surface temperature (SST) maps was used. The SST data were derived from the Tropical Rainfall Measuring Mission/TRMM Microwave Imager (TRMM/TMI). Simulations showed that albacore tuna aggregated in areas of thermal preference indicated by contour line of 20°C SST. Results are compared with empirical observation maps of albacore tuna fishing locations determined from longline fishing operation during the same time periods. Albacore tuna distributions along thermal fronts generating from Simulations were fairly consistent with fishing data especially during November-January, although seasonal variations in surface temperature ranges occupied suggest that additional oceanographic factors are involved particularly during February-March. Simulations and empirical data had similar temperature distributions at approximately 18-21°C and one-sample Kolmogorov-Smirnov test reinforced the result performance. These results suggest that kinesis model driven by satellite microwave remote sensing is one of effective mechanisms for describing migration pattern of tuna in the open ocean environment. Keywords: Kinesis model, Microwave remote sensing, SST, Albacore tuna, Migration patter

Albacore (Thunnus alalunga) fishing ground in relation to oceanographic conditions in the western North Pacific Ocean using remotely sensed satellite data

Tuna remote sensingSatellite-based oceanographic data of sea surface temperature (SST), sea surface chlorophyll-a concentration (SSC) and sea surface height anomaly (SSHA) together with catch data were used to investigate the relationship between albacore fishing ground and oceanographic conditions and also to predict potential habitats for albacore in the western North Pacific Ocean. Empirical cumulative distribution function (ECDF) and high catch data analyses were used to calculate preferred ranges of the three oceanographic conditions. Results indicated that highest catch per unit efforts (CPUEs) corresponded with areas of SST 18.5 - 21.5??C, SSC 0.2 - 0.4 mg m-3 and SSHA ???5.0 - 32.2 cm during winter period 1998-2000. We used these ranges to generate a simple prediction map for detecting potential fishing grounds. Statistically, to predict spatial patterns of potential albacore habitats, we applied a combined Generalized Additive Model (GAM)/Generalized Linear Model (GLM). To build our model, we first constructed GAM as an exploratory tool to identify the functional relationships between the environmental variables and CPUE, we then made parameters out of these relationships using GLM to generate a robust prediction tool. The areas of highest CPUEs predicted by the models were consistent with the potential habitats on the simple prediction map and observation data, suggesting that the dynamics of ocean eddies (November 1998 and 2000) and fronts (November 1999) may account for the spatial patterns of highest albacore catch rates predicted in the study area. The results also suggest that multi-spectrum satellite data can provide useful information to characterize and predict potential tuna habitats

Distribution of phytoplankton abundance and physical properties on the southeastern shelf of the Bering Sea in summer

Oceanographic structure, nutrient concentration, and chlorophyll a concentration were surveyed from 55°N to 59°N along 166°W on the southeastern shelf of the Bering Sea during mid to late July of 1994,1995,and 1996. The present results show a consistent trend that, in every year, high chlorophyll a concentration occurred in the outer shelf domain around 55°00\u27N, as well as the coastal shelf domain, and that the concentrations were usually low in the central shelf domain although large yearly variation occurred. The high phytoplankton abundance in the southern outer shelf domain related to relatively high salinity water, which contained more nitrate than the central shelf domain water. It is suggested that the high abundance is maintained by a continuous supply of nutrients caused by interaction between the ocean current from the open water of the North Pacific and the bottom topography in the vicinity of Unimak Pass. On the other hand, alternative high chlorophyll a stock was observed in the coastal shelf domain, where the sea floor depth was about 40m and vertically homogenous water properties occurred. This suggests that the nutrient supply from the bottom maintains the high phytoplankton abundance. In the central shelf domain, chlorophyll a concentrations less than 1.0μg l^ were usually observed between 55°30\u27N and 58°30\u27N in 1995 and 1996. In 1994,however, chlorophyll a concentrations of 1.0 to 2.0 μg l^ were widely distributed. The slightly high concentrations coincided with a weak pycnocline and occurrence of cold bottom water, which contained high nitrate. It is suggested that phytoplankton abundance may be low when the pycnocline is well developed or the cold bottom water does not transport a large amount of nutrients in the central shelf domain of the southeastern Bering Sea

Japan Tsunami Current Flows Observed by HF Radars on Two Continents

Quantitative real-time observations of a tsunami have been limited to deep-water, pressure-sensor observations of changes in the sea surface elevation and observations of sea level fluctuations at the coast, which are essentially point measurements. Constrained by these data, models have been used for predictions and warning of the arrival of a tsunami, but to date no detailed verification of flow patterns nor area measurements have been possible. Here we present unique HF-radar area observations of the tsunami signal seen in current velocities as the wave train approaches the coast. Networks of coastal HF-radars are now routinely observing surface currents in many countries and we report clear results from five HF radar sites spanning a distance of 8,200 km on two continents following the magnitude 9.0 earthquake off Sendai, Japan, on 11 March 2011. We confirm the tsunami signal with three different methodologies and compare the currents observed with coastal sea level fluctuations at tide gauges. The distance offshore at which the tsunami can be detected, and hence the warning time provided, depends on the bathymetry: the wider the shallow continental shelf, the greater this time. Data from these and other radars around the Pacific rim can be used to further develop radar as an important tool to aid in tsunami observation and warning as well as post-processing comparisons between observation and model predictions

An attempt of dissemination of potential fishing zones prediction map of Japanese common squid in the coastal water, southwestern Hokkaido, Japan

Accurate prediction of potential fishing zones is regarded as one of the most immediate and effective approaches in operational fisheries. It helps fishermen reduce their cost on fuel and also decrease the uncertainty of their fish catches. To predict potential fishing zones of Japanese common squid, we derived fishing positions from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS), combine with bathymetry and model-derived environmental factors from the 4D-VAR data assimilation system and fitted using habitat suitability index (HSI) model. Validations with an independent DMSP/OLS dataset showed better performance of the model in figuring out the squid aggregations than our previous model established with satellite-derived environmental data. Nighttime visible images during June and early July of 2013 derived from Day/Night band (DNB) of Visible Infrared Imaging Radiometer Suite (VIIRS) sensor with a better resolution and quality compared to DMSP/OLS, were also applied for validation and results showed differences of fitness between actual fishing activities and predictions in Japan Sea and Tsugaru Strait

A modeling study of seasonal variations of sea ice and plankton in the Bering and Chukchi Seas during 2007–2008

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97464/1/jgrc20061.pd

Fluorescence, pigment and microscopic characterization of Bering Sea phytoplankton community structure and photosynthetic competency in the presence of a Cold Pool during summer

Spectral fluorescence measurements of phytoplankton chlorophyll a (Chl a), phytoplankton phycobilipigments and variable fluorescence (Fv/Fm), are utilized with High Performance Liquid Chromatography (HPLC) estimates of phytoplankton pigments and microscopic cells counts to construct a comprehensive picture of summer-time phytoplankton communities and their photosynthetic competency in the eastern Bering Sea shelf. Although the Bering Sea was ice-free during our study, the exceptionally cold winter that preceded the summer of 2008 when our cruise took place, facilitated the formation of a “Cold Pool” (<2 °C) and its entrapment at depth in the northern middle shelf. The presence of a strong pycnocline over the entire middle and outer shelves restricted inorganic nutrient fluxes into the surface waters resulting in phytoplankton populations that were photo-physiologically stressed due to nutrient limitation. Elevated Chl a concentrations recorded in the Green Belt along the shelf edge of the Bering Sea, were due to Phaeocystis pouchetii and nano-sized cryptophytes. Although inorganic nutrients were not limiting in the Green Belt, Fv/Fm values were low in all probability due to iron limitation. Phytoplankton communities in the low biomass surface waters of the middle shelf were comprised of prasinophytes, haptophytes, cryptophytes and diatoms. In the northern part of the middle shelf, a sinking bloom made up of the centric diatoms Chaeotoceros socialis, Thalassiosira nordenskioeldii and Porosira glacialis was located above the Cold Pool. The high biomass associated with this senescent bloom and its accretion above the pycnocline, suggests that the Cold Pool acts as a barrier, preventing sinking phytoplankton from reaching the bottom where they can become available to benthic organisms. We further posit that if summer-time storms are not energetic enough and the Cold Pool is not eroded, its presence facilitates the transfer of the large spring phytoplankton bloom to the pelagic ecosystem