Impacts of Sea-ice on the Bering Sea

Spatial Considerations | Bottom-up/Top-down Controls of Zooplankton | Impacts of Sea-ice on Bering Sea

The presence or absence of sea-ice determines the temperature and physical structure of the eastern Bering Sea and the availability of light there. These physical changes to the environment in turn influence the timing, duration, and magnitude of the spring phytoplankton bloom and its fate (Stabeno et al., 1999a; Hunt et al., 2002, 2008; Stabeno & Hunt, 2002). In the late 1990s, the dominant mode of variation was annual between cold conditions (presence of ice and cold integrated temperatures in a well mixed water column) and warm conditions (absence of ice in the southeast, warmer integrated temperatures). In 2000, there was a shift to warm conditions for ~6 years, and, beginning in 2006, a shift back to prolonged cold conditions.

The trophic impacts of these variable ocean conditions were immense. Populations of the large crustacean zooplankter Calanus marshallae crashed during the consecutive warm years of 2000-2006, as did the shelf euphausiid, Thysanoessa raschii (Hunt et al., 2008, 2010, In Press; Coyle et al., 2008). In turn, predators depending on LCZ had diminished energy reserves for winter survival.

Associated with the return of cold conditions was a recovery of LCZ populations, and increased energy stores of young-of-the-year pollock. The broad implication of these results is that zooplankton populations are maintained if there is year-to-year variability in ice cover, but are severely reduced when there is a succession of several warm years.