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Anomalous conditions in the south‐eastern Bering Sea, 1997: nutrients, phytoplankton and zooplankton
Author(s) -
Stockwell Dean A.,
Whitledge Terry E.,
Zeeman Stephan I.,
Coyle Kenneth O.,
Napp Jeffrey M.,
Brodeur Richard D.,
Pinchuk Alexei I.,
Hunt George L.
Publication year - 2001
Publication title -
fisheries oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 80
eISSN - 1365-2419
pISSN - 1054-6006
DOI - 10.1046/j.1365-2419.2001.00158.x
Subject(s) - pycnocline , oceanography , emiliania huxleyi , phytoplankton , zooplankton , bloom , water column , diatom , spring bloom , upwelling , continental shelf , environmental science , nutrient , biology , geology , ecology
Anomalies in the regional weather over the south‐eastern Bering Sea during spring and summer of 1997 resulted in significant differences in nutrient availability, phytoplankton species composition, and zooplankton abundance over the continental shelf as compared with measurements in the 1980s. Calm winds and the reduction of cloud cover in spring and summer produced a very shallow mixed layer in which nitrate and silicate were depleted after an April diatom bloom. High submarine light levels allowed subsequent phytoplankton growth below the pycnocline and eventual depletion of nitrate from the water column to depths of 70 m or more. Thus, total new production during 1997 may have exceeded that of previous years when nitrate was not depleted below the pycnocline. A bloom of the coccolithophorid, Emiliania huxleyi , was observed in early July in the warm, nutrient‐depleted waters over the middle and inner shelf. Emiliania huxleyi concentrations reached 4.5 × 10 6 cells L –1 by September, and the bloom persisted through the autumn. There was evidence for increased abundance of some species of copepods in 1997 as compared with data from the middle domain in June 1981. The abundance of adult and juvenile euphausiids in 1997 was statistically similar to values measured in 1980 and 1981. However, near‐surface swarms were rarely observed on the inner shelf in August–September 1997. Lack of euphausiid availability in the upper water column may partially explain the August–September mass mortality of planktivorous short‐tailed shearwaters ( Puffinus tenuirostris ) observed on the inner shelf.