Transport and thermohaline variability in Barrow Canyon on the Northeastern Chukchi Sea Shelf

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.

Flow Patterns in the Eastern Chukchi Sea: 2010–2015

“…Part of this difference can be seen in the seasonal magnitudes—in January–April both our estimate and Weingartner et al () indicated weak transport while in October–December our estimates were weakly positive, while theirs were weakly negative. The largest differences were in the summer months—our estimate of ∼0.7 Sv is more in agreement with Gong and Pickart () composite hydrographic estimate of 0.8 ± 0.2 Sv, than the Weingartner et al () estimate of 0.45 Sv. The discrepancies can be attributed to a variety of factors ranging from high interannual variability to failure to capture all parts of the Alaskan Coastal Current (ACC) flow, or an over‐estimation of flow seaward of C3.…”

“…Our annual transport estimate of 0.4 Sv at Icy Cape is similar to the 0.45 Sv estimated by Itoh et al () at the mouth of Barrow Canyon. It is, however, stronger than the annual estimate by Weingartner et al (). Part of this difference can be seen in the seasonal magnitudes—in January–April both our estimate and Weingartner et al () indicated weak transport while in October–December our estimates were weakly positive, while theirs were weakly negative.…”

“…It is, however, stronger than the annual estimate by Weingartner et al (). Part of this difference can be seen in the seasonal magnitudes—in January–April both our estimate and Weingartner et al () indicated weak transport while in October–December our estimates were weakly positive, while theirs were weakly negative. The largest differences were in the summer months—our estimate of ∼0.7 Sv is more in agreement with Gong and Pickart () composite hydrographic estimate of 0.8 ± 0.2 Sv, than the Weingartner et al () estimate of 0.45 Sv.…”

Winter Water Formation in Coastal Polynyas of the Eastern Chukchi Shelf: Pacific and Atlantic Influences

“…In Barrow Canyon, persistent northeastward flow intensifies in summer and slows down in winter (Aagaard & Roach, ; Itoh et al, ; Weingartner et al, ; Weingartner et al, ). Recently, Weingartner et al () constructed a 37‐year hindcast of the mean daily transport at the head of Barrow Canyon, and they showed the annual net transport cycle that comprises down‐canyon transport of ~0.45 Sv in summer (May–September), up‐canyon transport of ~0.1 Sv in fall (October–December), and a little more than zero in winter (January–April). Table summarizes water mass/type definitions used in this study.…”

“…Warm, saline Atlantic Water (AW, S > 34.0) is centered at 300–400 m water depths in the Canada Basin (e.g., Jackson et al, ), below ~200 m in the Beaufort slope (e.g., Nikolopoulos et al, ), and below ~150 m in Barrow Canyon (e.g., Itoh et al, ). From late fall to winter, prevailing northeasterly winds inhibit northeastward transport of PWW in Barrow Canyon and bring AW upwelling into Barrow Canyon (Aagaard & Roach, ; Woodgate, Aagaard, & Weingartner, ) and onto the eastern Chukchi shelf (Hirano et al, ; Ladd et al, ; Weingartner et al, ). In this way, Barrow Canyon is an important bathymetric feature as a gateway of Pacific‐origin water into the Canada Basin and conversely of Atlantic‐origin water onto the Chukchi shelf.…”