Shelf-Basin Exchange of Large-Bodied Zooplankton [Copepods] in the Chukchi and Beaufort Seas

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Physical forcing in the North Pacific/Western Arctic region exhibits abrupt regime shifts in which several decades (~25-35 years) of relatively cold, icy (2% above average) conditions are replaced in the span of a year or two by decades of warmer, less icy (3% below average) conditions; these cycles of climate in the region can be traced back at least to the late 1700s. The response of the Chukchi/Beaufort shelf ecosystem to warmer climate could follow two quite different pathways. In one scenario, warm periods would reduce ice cover and could create stronger thermal stratification, less mixing, limited nutrient supply, lower primary production, smaller-sized phytoplankton and smaller, coastal-like zooplankton. In a second scenario, also during warm periods with less ice, increased wind could result in shelf-break upwelling and mixing, enhanced nutrient supply, larger-sized phytoplankton and larger, deep-water zooplankton advectedonto the shelf. Will global change, particularly warming, result in more large-sized zooplankton which support fish, birds, and mammals over the Chukchi and Beaufort shelves and slopes or smaller-sized zooplankton which will diminish the fish, birds, and mammals and favor sedentary benthic organisms?Large-bodied copepods on the Chukchi and Beaufort shelves must be advected there from the slope waters of the Arctic Ocean or Bering Sea; none of them can complete their life cycles on the shelf itself. Therefore, they are tracers of shelf-basin exchanges. The project will seek to understand which large-bodied copepods reach the Chukchi (wide) and Beaufort (narrow) shelves, and the physical forcing (upwelling, intrusions, eddies) that is responsible. Once on the shelves, how do size and reproductive responses of large copepods vary spatially, and what are the roles of physical processes and food supply? These responses define the robustness of the shelf habitat for supporting a pelagic ecosystem. The project will determine which copepods are transported off the shelves and the physical processes (eddies, plumes) associated with that transport. The investigation will integrate these ecosystem measurements with the physical forcing (both observations and models) to understand how advection shapes the food web in the region.