Response of Eucalanus bungii to oceanographic conditions in the western subarctic Pacific Ocean: Retrospective analysis of the Odate Collections     

Toru Kobari  Kazuaki Tadokoro  Hiroya Sugisaki  Hiroshi Itoh 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2748

To evaluate their response to oceanographic conditions, interannual variations in seasonal abundance of Eucalanus bungii were investigated in zooplankton samples collected from the Oyashio Current system from 1960 to 2002. Large decadal changes were observed in seasonal timing and population age-structure. During the early 1970s and 1990s, E. bungii were abundant until mid-summer, but during the late 1970s and early 1980s, the season of maximum abundance was limited to spring and early summer. From the late 1970s to early 1980s, spring–summer abundance of newly recruited young copepodites (C1–C2) declined significantly, and an even more pronounced decline was observed for the abundance of the late copepodite stages (C3–C5). Monthly population structure showed that young of the year stopped development at C3 during the late 1970s to early 1980s, but molted into late copepodite stages in the other decades. Seasonal weakening of the Aleutian Low Pressure System estimated from North Pacific Index (NPI) was rapid during the late 1970s to early 1980s, and the NPI was positively correlated with phosphate concentrations at sea surface, spring–summer abundance of the young copepodites stages, and the extended duration of the season of high abundance. These results suggest that the decadal decline of copepod abundance originated at the early life stages, and was associated with a shift of atmospheric and oceanographic conditions. As possible biological mechanisms, we propose reduced egg production, lower survival for the portion of the annual cohort with late birth date, and overwintering of the survivors at younger stages.  相似文献   

Nutrient and Plankton Dynamics in the NE and NW Gyres of the Subarctic Pacific Ocean     

Paul J. Harrison  Frank A. Whitney  Atsushi Tsuda  Hiroaki Saito  Kazuaki Tadokoro 《Journal of Oceanography》2004,60(1):93-117

The western subarctic gyre (WSG) and the eastern Alaska Grye (AG) on each side of the subarctic North Pacific, have many similarities. In both gyres, macronutrients are generally high and chl is low, and hence both gyres are High Nitrate, Low Chlorophyll (HNLC) regions. Despite the general similarities between these two gyres, there are many important differences. The time series station established at Stn KNOT on the southwest edge of the WSG and two in situ mesoscale iron enrichment experiments at each of the gyres has provided more information on iron concentrations, the dual role of iron and silicate limitation and seasonal cycles in the gyres. There is more seasonality in many parameters at Stn KNOT than at Stn P. There is an increase in Chl and primary productivity at Stn KNOT in May followed by increased iron limitation in summer. Low DIC:NO₃ ratios and high Si:NO₃ ratios in the WSG, indicate lower calcification and higher diatom production than at Stn P. The sources of iron for these areas are still not clear, but horizontal transport of iron rich coastal water and vertical transport could be important sources at certain times of the year in addition to dust input. Satellite images show that chl-rich coastal waters occasionally extend to the vicinity of Stn KNOT and therefore Stn KNOT may not always represent conditions in the main part of the WSG. This review focuses mainly on a comparison of Stn KNOT and Stn P, two time series stations on the edge of two very large gyres. At present, we have a limited understanding of the temporal and spatial variability within each of these large gyres. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献