Functioning of the Pelagic Ecosystems of Aquatic Areas Covered with Ice in the Barents and Kara Seas in Winter and Spring

Abstract

The Murmansk Institute of Marine Biology has been performing sea expeditions on board nuclearpowered icebreakers of the Murmansk Marine Shipping Company beginning from February 1996 (Fig. 1). The annual studies consist of the year-round ecosystem monitoring of Arctic seas, including the hydrological, hydrochemical, microbiological, and algal/planktonic survey; netting zooplankton, as well as observations of polar bears, sea mammals, and birds. Vast, unique material has been accumulated during this period; the data obtained have considerably changed the current views on the functions of marine Arctic ecosystems, especially in winter and spring, when observations from ships of non-icebreaker class [1][2][3]. Below, we describe the structural characteristics of pelagic ecosystems of the Barents and Kara Seas in winter and spring.The results of the studies have yielded the pattern of the vertical distribution of hydrological parameters in the sea. We found that distinct gradients of salinity were preserved in zones where sea and estuary waters were mixed even in winter, under a continuous layer of ice. Four main types of waters were distinguished in the aquatic area studied: untransformed and slightly transformed waters of sea origin, intermediate waters of runoff currents, and waters from river-sea barrier zones. The finding of the third type is especially important because substances from the continental runoff are especially intense in such zones.We obtained first data on the quantitative characteristics of bacterioplankton in winter and the ecological factors that determine them. Bacterioplankton associations observed under the conditions of a thick snow and ice cover at temperatures close to the freezing point were characterized as stable communities with complex structure that had a sufficient store of substrates for vital activity.The total biomass of bacterioplankton varied in a range of three orders of magnitude (from 7.8 to 1300 mg/m 3 ), the mean value being 205 mg/m 3 . These values are an order of magnitude higher than those obtained in the same season of earlier years, mainly in the halistic region of the Arctic Ocean and in the Canadian Arctic [4]. Note that the data on the total bacterioplankton biomass in winter are very few, and there are no data at all on some morphological groups.The total amount of bacteria, as estimated by direct count under an epifluorescent microscope, varied from 9.6 × 10 3 to 935 × 10 3 cells/ml (on average, 240 × 10 3 cells/ml). The surface area of bacterioplankton cells (which is the most adequate measure of these organisms) varied from 35 to 3700 mm 2 /l (on average, 1100 mm 2 /l).The spatial distribution of the numbers and biomass of bacterioplankton in winter had the following main characteristics. These parameters were increased in the zones where waters were mixed. These are, first, zones where the continental and freshwater runoffs interact (the Ob'-Yenisei estuary region and the region of the spread of the White Sea runoff current in the southeastern Barents Sea nea...