Transport and thermohaline variability in Barrow Canyon on the Northeastern Chukchi Sea Shelf. Issue 5 (2nd May 2017) - Weingartner, Thomas J.
Abstract: We used a 5 year time series of transport, temperature, and salinity from moorings at the head of Barrow Canyon to describe seasonal variations and construct a 37 year transport hindcast. The latter was developed from summer/winter regressions of transport against Bering‐Chukchi winds. Seasonally, the regressions differ due to baroclinicity, stratification, spatial, and seasonal variations in winds and/or the surface drag coefficients. The climatological annual cycle consists of summer downcanyon (positive and toward the Arctic Ocean) transport of ∼0.45 Sv of warm, freshwaters; fall (October–December) upcanyon transport of ∼−0.1 Sv of cooler, saltier waters; and negligible net winter (January–April) mass transport when shelf waters are saline and near‐freezing. Fall upcanyon transports may modulate shelf freezeup, and negligible winter transports could influence winter water properties. Transport variability is largest in fall and winter. Daily transport probability density functions are negatively skewed in all seasons and seasonal variations in kurtosis are a function of transport event durations. The latter may have consequences for shelf‐basin exchanges. The climatology implies that the Chukchi shelf circulation reorganizes annually: in summer ∼40% of the summer Bering Strait inflow leaves the shelf via Barrow Canyon, but from fall through winter all of it exits via the western Chukchi or Central Channel. We estimate a mean transport of ∼0.2 Sv; ∼50% less than estimates at the mouth of the canyon. Transport discrepancies may be due to inflows from the Beaufort shelf and the Chukchi shelfbreak, with the latter entering the western side of the canyon. Plain Language Summary: Barrow Canyon is a major avenue by which water flows northward from the Pacific Ocean, across the Chukchi Sea, and into the Arctic Ocean. Understanding the water flow through the canyon and its variability deepens our understanding of the Chukchi Sea and its connections to the Arctic Ocean. We used 5 years of direct current measurements to develop transport predictions based on winds. The regressions allow us to hindcast daily Barrow Canyon transports from 1979–2015. The 37‐year hindcast record is used to better understand the annual cycle of transport over the northeastern Chukchi Sea. The results imply that the Chukchi Sea circulation field undergoes a major re‐organization on an annually. In summer the transport is a maximum and towards the Arctic Ocean, however in fall, the transport is weak but from the Arctic Ocean onto the shelf. The mean winter transport is negligible. The results have important implications for water mass formation processes on the Chukchi Sea shelf and on the movement of Pacific Waters into the Arctic Ocean. Key Points: Transport variations are controlled by Chukchi and Bering seas winds, which allow statistically robust transport hindcasts Hindcasts define an climatological annual transport cycle that is downcanyon in summer, upcanyon in fall, and zero in winter Canyon water properties and upcanyon and downcanyon transport event durations vary seasonally