The Bering Sea Green Belt: shelf‐edge processes and ecosystem production

TLDR

The Bering Sea Green Belt hypothesis is grounded in fragmentary observations of physical and biological features along the continental shelf edge, and although enhanced production at continental margins is a known phenomenon, it has been overlooked in the Bering Sea because of its unusually broad shelf. Intensive tidal mixing, transverse circulation, and eddies in the Bering Slope Current transport nutrients into the euphoric zone at the shelf edge, thereby boosting primary and secondary production and increasing phytoplankton and zooplankton biomass. Observed annual primary production at the shelf edge reaches 175–275 g C m⁻² yr⁻¹—about 60 % higher than the outer shelf and 270 % higher than the oceanic domain—while secondary production is similarly elevated, and the resulting abundance of zooplankton, fishes, and squids attracts large numbers of marine birds and mammals, underscoring sustained primary productivity, intense food‑web exchange, and high transfer efficiency as key drivers of Bering Sea ecosystem production.

Abstract

ABSTRACT The concept of a highly productive habitat, or Green Belt, along the edge of the continental shelf in the Bering Sea is based upon compelling but fragmentary and often anecdotal observations of a variety of physical and biological features acquired from many sources over many years. Enhanced production at continental margins is not a novel concept, but in the case of the Bering Sea its importance has been overlooked during studies of the unusually broad continental shelf. The limited data reported from the vicinity of the shelf edge in the Bering Sea indicate that annual primary production can be as high as 175 to 275 g C m˜ year ‐ , or approximately 60% greater than production in the adjacent outer shelf domain and 270% greater than in the oceanic domain. Estimates of annual secondary production at the eastern shelf edge also average approximately 60% higher than estimates for the outer domain and 260% higher than those for the oceanic domain. Physical processes at the shelf edge, such as intensive tidal mixing and transverse circulation and eddies in the Bering Slope Current, bring nutrients into the euphoric zone and contribute to enhanced primary and secondary production and elevated biomass of phytoplankton and zooplankton. Fishes and squids concentrate in this narrow corridor because of favourable feeding conditions and because of a thermal refuge from cold shelf‐bottom temperatures that can be found at the shelf edge from fall to spring. The abundance of zooplankton, fishes and squids, in turn, attracts large numbers of marine birds and mammals. In aggregate, the observations suggest that sustained primary productivity, intense food web exchange and high transfer efficiency at the shelf edge are important to biomass yield at numerous trophic levels and to ecosystem production of the Bering Sea.