Increased Stratification and Decreased Lower Trophic Level Productivity in the Oyashio Region of the North Pacific: A 30-Year Retrospective Study |
| |
Authors: | Sanae Chiba Tsuneo Ono Kazuaki Tadokoro Takashi Midorikawa Toshiro Saino |
| |
Institution: | (1) Frontier Research System for Global Change, Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan;(2) Hokkaido National Fisheries Research Institute, Katsurakoi, Kushiro, Hokkaido 085-0802, Japan;(3) Japan Meteorological Agency, Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan;(4) Hydrospheric Atmospheric Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan |
| |
Abstract: | An analysis of the time series data sets collected from the 1960s to 1990s in the Oyashio Water revealed signs of alteration
in the physical, chemical and biological properties of the water column in the western subarctic North Pacific. Wintertime
salinity, phosphate concentration and apparent oxygen utilization (AOU) in the subsurface increased linearly over the 30 years.
At the same time, salinity and phosphate in the surface mixed layer decreased. An increase in the density gradient in the
surface and subsurface suggested that the water column stratification intensified, reducing the vertical exchange of water
properties during the period. The Net Community Production (NCP), estimated from the phosphate consumption from February through
August, also declined. Water column Chl a was approximately halved and diatoms decreased by one order of magnitude in spring, consistent with the multi-decadal decreasing
trend of NCP. Zooplankton biomass was also nearly halved during the same period. In contrast, wintertime Chl a increased by 63% and diatom abundance doubled. Developmental timing became earlier in Neocalanus flemingeri, and spring occurrence of N. plumchrus increased after the 1980s. Reduced vertical water exchange might have limited nutrient supply to the level, decreasing winter-summer
NCP for these three decades. It is speculated that, in the meantime, the earlier stabilization of the surface layer might
have enhanced wintertime diatom production in the Oyashio's light-limited environment. This condition could allow zooplankton
to effectively utilize diatoms from earlier timing, resulting in the apparent early developmental timing and abundance increase.
This revised version was published online in July 2006 with corrections to the Cover Date. |
| |
Keywords: | Oyashio western subarctic North Pacific multi-decadal scale change AOU stratification NCP diatom Neocalanus |
本文献已被 SpringerLink 等数据库收录! |
|