IAN Seminar Series 2013

Abstract

The recent significant decline in Arctic sea ice has captured public interest in the challenges of mitigating and responding to climate changes that seem to be unambiguously underway at high latitudes. Despite the obvious physical differences between ice-covered seas and open water, predicting ecosystem response and biological changes that are likely to result is much more difficult. For example, it is thought that declining sea ice coverage will increase light penetration and increase primary production on arctic continental shelves, which might be globally significant because the continental shelves in the Arctic are the world's largest in extent. However, in comparisons between chlorophyll biomass in the Bering Sea for years with light versus heavy ice coverage, open water conditions do not lead to significantly higher water column chlorophyll biomass possibly because high winds significantly mix phytoplankton in open water and sea ice provides an attachment structure to hold sea ice algae close to the sea surface. The timing of seasonal sea ice retreat is also hypothesized to play a role in structuring the food web with better development of zooplankton populations in some circumstances. The northern Bering and Chukchi continental shelves currently have short, efficient food-chains that deposit organic material synthesized during the brief, but intense production period directly to the shallow sea floor without much exploitation by zooplankton. Specialized apex predators such as walrus, gray whales, bearded seals and diving sea ducks exploit the rich benthos as a food resource, but there is also evidence that fish are becoming more important in structuring the food web and zooplankton may also become more important in intercepting primary production too. The North Pacific Fisheries Management Council has also begun to assess how fisheries should be managed and what the potential conflicts will be for the existing benthic-based food-web as commercial exploitation of Bering Sea fisheries is poised to expand northward. I will present data on what is known about how the Bering and Chukchi Sea food webs and biological systems are changing in response to regime shifts and seasonal sea ice retreat. Our intent is to use these data as a starting point for developing a predictive capability to understand how the arctic biological system will respond to the stresses of climate change.