Whither the Chukchi Slope Current?

Abstract

Recent measurements and modeling indicate that roughly half of the Pacific-origin water exiting the Chukchi Sea shelf through Barrow Canyon forms a westward-flowing current known as the Chukchi Slope Current (CSC), yet the trajectory and fate of this current is presently unknown. In this study, through the combined use of shipboard velocity data and information from five profiling floats deployed as quasi-Lagrangian particles, we delve further into the trajectory and the fate of the CSC. During the period of observation, from early September to early October 2018, the CSC progressed far to the north into the Chukchi Borderland. The northward excursion is believed to result from the current negotiating Hanna Canyon on the Chukchi slope, consistent with potential vorticity dynamics. The volume transport of the CSC, calculated using a set of shipboard transects, decreased from approximately 2 Sv (1 Sv ≡ 106 m3 s−1) to near zero over a period of 4 days. This variation can be explained by a concomitant change in the wind stress curl over the Chukchi shelf from positive to negative. After turning northward, the CSC was disrupted and four of the five floats veered offshore, with one of the floats permanently leaving the current. It is hypothesized that the observed disruption was due to an anticyclonic eddy interacting with the CSC, which has been observed previously. These results demonstrate that, at times, the CSC can get entrained into the Beaufort Gyre.

A warm jet in a cold ocean

“…Some water is entrained into eastward or westward boundary currents. For example, sub-surface PSW with the same T-S characteristics as observed here was observed flowing westward in the Chukchi Slope Current 62 . Longer term, both PSW subducted directly from the Barrow Canyon outflow, and the portion subsequently caught up in boundary currents, may be drawn into the central Beaufort Gyre and beneath the main ice pack through a combination of advection by the anti-cyclonic circulation and eddy stirring 63 .…”

“…Meandering warm jets offshore of Barrow Canyon are not unusual 33 , 39 , 40 , 60 . In previous studies, some of that heat leaving the coast near Barrow Canyon seems to be firmly ejected offshore, while some meanders to rejoin one of the boundary currents, and may subsequently leak into the interior by other stirring processes 62 . The subduction and intrathermocline eddy development processes observed here may be a regular occurrence, linking the larger-scale influxes of warm, surface-intensified PSW observed within Barrow Canyon 21 , 29 with discrete intrathermocline eddies and filaments observed within the basin 17 , 18 .…”

Origin and Fate of the Chukchi Slope Current Using a Numerical Model and In‐Situ Data

“…This is consistent with the trajectories of SOLO floats (drogue depth 80–100 m) presented in Boury et al. (2020) which proceeded northward along the eastern edge of the plateau. However, the shipboard sections analyzed by Corlett and Pickart (2017) and near‐surface (25–30 m) drifter trajectories presented by Stabeno et al.…”

“…This indicates that at least part of the water in the slope current ultimately gets entrained into the BG, as hypothesized by Boury et al. (2020). On the other hand, a considerable part of the BC tracer remains on the upper continental slope, verifying the presence of the westward branch of the slope current after passing the Northwind Ridge (Corlett & Pickart, 2017; Stabeno et al., 2018).…”

“…These results suggest two different fates of the slope current. Boury et al (2020) noted that the deeper isobaths of the Chukchi slope west of Northwind Ridge veer more northward than the shallower ones. They argued that if the slope current is located over relatively shallow depths it would continue westward, while in the cases when it is in deeper water it would be more apt to flow northward.…”