|Transport and transformation of Pacific water masses on the eastern Chukchi Sea|
Robert S. Pickart
Observations in the past few decades have shown that the Arctic Ocean is undergoing significant changes due to a rapidly warming climate. The most well-known observation reflecting a changing Arctic is the shrinking of the polar ice cap. Other less obvious but equally important aspects such as the ocean’s ecosystem, chemistry, and physical circulation are changing as well. In order to test and refine our current understanding of the system and to track long term shifts in the Arctic Ocean’s state, it is necessary to establish baseline measurements of key Arctic regions and processes. The Chukchi Sea, a shallow and wide shelf sea just north of the Bering Strait, is a key part of the transport pathway that delivers heat and freshwater from the Pacific Ocean into the western Arctic Ocean. To date there has not been a detailed assessment of the transport pathways and water mass transformation processes in the Chukchi Sea. Utilizing hydrographic and current data collected from several shelf wide surveys of the Chukchi Sea during the past decade (NSF’s Shelf Basin Interaction, NASA’s ICESCAPE, and NSF’s Arctic Observatory Network), I am working on characterizing how Pacific water masses are transported across the Chukchi Sea and trying to understand how physical forcing factors are driving the observed spatial and temporal variability of the flow.
My research focuses primarily on one of the main transport pathways: the swift Alaska Coastal Current (ACC) in the eastern Chukchi Sea. Earlier thinking contends that the ACC is a surface intensified current that mainly advects fresh and buoyant Alaska Coastal Water along the coast. In contrast to this, my study demonstrates that the ACC is weakly baroclinic for significant period of the summer and that it can carry multiple water masses northward at distance up to 100 km from the coast. Furthermore, during early summer the ACC transports warm and dense water masses into Barrow Canyon with the proper density to directly ventilate the upper halocline. The halocline of the western Arctic Ocean separates the deeper warm and salty Atlantic water from the cold and fresh surface mixed layer above it. If weakened, the heat of the Atlantic water may be brought closer to the surface and lessen future sea ice formation. This suggests that shelf processes in the Chukchi Sea may be able to drive long term changes in western Arctic's upper ocean heat budget.