Absorption coefficients of colored dissolved organic matter (CDOM) [ag(λ)] were measured and relationship with salinity was derived in the East China Sea (ECS) during summer when amount of the Changjiang River discharge is large. Low salinity Changjiang Diluted Water (CDW) was observed widely in the shelf region and was considered to be the main origin of CDOM, resulting in a strong relationship between salinity and ag(λ). Error of satellite ag(λ) estimated by the present ocean color algorithm could be corrected by satellite‐retrieved chlorophyll data. Satellite‐retrieved salinity could be predicted with about ±1.0 accuracy from satellite ag(λ) and the relation between salinity and ag(λ). Our study suggests that satellite‐derived ag(λ) can be an indicator of the low salinity CDW during summer.

Enormous quantities of radionuclides were released into the ocean via both atmospheric deposition and direct release as a result of the Fukushima Dai-ichi Nuclear Power Plant (FNPP) accident. This study discusses the southward dispersion of FNPP-derived radioactive cesium (Cs) in subsurface waters. The southernmost point where we found the FNPP-derived (134)Cs (1.5-6.8 Bq m(-3)) was 18 °N, 135 °E, in September 2012. The potential density at the subsurface peaks of (134)Cs (100-500 m) and the increased water column inventories of (137)Cs between 0 and 500 m after the winter of 2011-2012 suggested that the main water mass containing FNPP-derived radioactive Cs was the North Pacific Subtropical Mode Water (NPSTMW), formed as a result of winter convection. We estimated the amount of (134)Cs in core waters of the western part of the NPSTMW to be 0.99 PBq (decay-corrected on 11 March 2011). This accounts for 9.0% of the (134)Cs released from the FNPP, with our estimation revealing that a considerable amount of FNPP-derived radioactive Cs has been transported to the subtropical region by the formation and circulation of the mode water.

No abstract

Interannual variability in somatic growth rate during the larval stage and age at the onset of metamorphosis as a proxy for the development rate of jack mackerel (Trachurus japonicus) were examined in relation to habitat conditions during 2005 to 2010 in the shelf break region of the East China Sea (ECS). Habitat conditions were assessed in the February to March and the April surveys, which corresponded with the early hatching period in the spawning grounds and the main sampling period in the larval nursery grounds, respectively. Relationships between the growth and development rates and juvenile abundances in the near-bottom layer in May to June during the six consecutive survey years were explored. Annual mean growth rates during the late larval stage of pelagic juveniles were faster in years with higher concentrations of Paracalanidae and Oncaeidae copepodites as the main food item for larval T. japonicus in April following the surge of chlorophyll a concentrations. Juvenile abundance in the near-bottom layer was better related to the annual mean growth rate during the late larval stage than to the growth rate during the early larval stage and the development rate. These results suggest that preferred prey conditions due to higher phytoplankton productivity enhance the growth rate during the later larval stage and hence survival during the habitat transition from the surface to the near-bottom layer for T. japonicus in the ECS.

No abstract