Chiho Sukigara

Eddy Resolving Observation of the North Pacific Subtropical Mode Water

AbstractHydrographic data obtained by high-resolution shipboard observations and Argo profiling floats have been analyzed to study the mesoscale structure and circulation of the North Pacific Subtropical Mode Water (STMW). The float data show that in the late winter of 2008, STMW having a temperature of approximately 18.8°, 17.7°, and 16.6°C formed west of 140°E, at 140°–150°E, and east of 150°E, respectively, in the recirculation gyre south of the Kuroshio Extension. After spring, the newly formed STMW gradually shift southward, decreasing in thickness. Simultaneously, the STMWs of 16.6° and 17.7°C are gradually stirred and then mixed in terms of properties. In late fall, they seem to be integrated to form a single group of STMWs having a temperature centered at 17.2°C. Such STMW circulation in 2008 is much more turbulent than that in 2006, which was investigated in a previous study. The difference between the two years is attributed to the more variable state of the Kuroshio Extension in 2008, associate...

Mesoscale eddies control the timing of spring phytoplankton blooms: a case study in the Japan Sea

Satellite Chlorophyll a (CHL) data was used to investigate the influence of mesoscale anticyclonic eddies (AEs) and cyclonic eddies (CEs) on the timing of spring phytoplankton bloom initiation around the Yamato Basin (133-139° E and 35-39.5° N) in the Japan Sea, for the period 2002-2011. The results showed significant differences between AEs and CEs in the timing and initiation mechanism of the spring phytoplankton bloom. Blooms were initiated earlier in CEs which were characterized by shallow mixed-layer depths ( 100 m) but close to the commencement of positive Q0. This suggests that the relaxation of turbulent mixing is crucial for the bloom initiation in AEs.

Comparison of carbon cycle between the western Pacific subarctic and subtropical time-series stations: highlights of the K2S1 project

A comparative study of ecosystems and biogeochemistry at time-series stations in the subarctic gyre (K2) and subtropical region (S1) of the western North Pacific Ocean (K2S1 project) was conducted between 2010 and 2013 to collect essential data about the ecosystem and biological pump in each area and to provide a baseline of information for predicting changes in biologically mediated material cycles in the future. From seasonal chemical and biological observations, general oceanographic settings were verified and annual carbon budgets at both stations were determined. Annual mean of phytoplankton biomass and primary productivity at the oligotrophic station S1 were comparable to that at the eutrophic station K2. Based on chemical/physical observations and numerical simulations, the likely “missing nutrient source” was suggested to include regeneration, meso-scale eddy driven upwelling, meteorological events, and eolian inputs in addition to winter vertical mixing. Time-series observation of carbonate chemistry revealed that ocean acidification (OA) was ongoing at both stations, and that the rate of OA was faster at S1 than at K2 although OA at K2 is more critical for calcifying organisms.