Barrow Canyon in the northeast Chukchi Sea is a critical choke point where Pacific‐origin water, heat, and nutrients enter the interior Arctic. While the flow through the canyon has been monitored for more than 20 years, questions remain regarding the dynamics by which the Pacific‐origin water is fluxed offshore, as well as what drives the variability. In 2018, two high‐resolution shipboard surveys of the canyon were carried out—one in summer and one in fall—to investigate the water mass distribution and velocity structure of the outflow. During the summer survey, high percentages of Pacific water (summer water + winter water) were present seaward of the canyon, associated with strong northward outflow from the canyon and a well‐developed westward‐flowing Chukchi Slope Current (CSC). By contrast, high percentages of Pacific water were confined to the canyon proper and outer Chukchi shelf during the late‐fall survey, at which time the canyon outflow and CSC were considerably weaker. These differences can be attributed to differences in wind forcing during the time period of two surveys. A cyclone‐like circulation was present in the canyon during both surveys, which was also evident in the satellite‐derived sea surface height anomaly field. We argue that this feature corresponds to an arrested topographic Rossby wave, generated as the outflow responds to the deepening bathymetry of the canyon. By applying a self‐organizing map analysis using the satellite altimeter data from 2001 to 2020, we demonstrate that such a cyclone‐like structure is a prevailing aspect of the canyon outflow.
Data from two moorings deployed at 166°W on the northern Chukchi shelf and slope from summer 2002 to fall 2004, as part of the Western Arctic Shelf‐Basin Interactions program, are analyzed to investigate the characteristics and variability of the flow in this region. The depth‐mean velocity at the outer‐shelf mooring is northeastward and bottom‐intensified, while that at the upper‐slope mooring is northwestward and surface‐intensified. This, together with results from a high resolution ocean and sea ice reanalysis, indicates that the outer‐shelf mooring sampled the seaward edge of the Chukchi Shelfbreak Jet, while the upper‐slope mooring sampled the shoreward edge of the Chukchi Slope Current. The coupled variability in velocity at both sites is related to the wind stress curl over the Chukchi Sea shelf, likely via Ekman dynamics and geostrophic set up, analogous to the dynamics of both currents closer to Barrow Canyon near 157°W. Hydrographic signals are analyzed to elucidate the origin of the water masses present at this location. It is argued that the annual appearance of Pacific‐origin warm water at the outer‐shelf (upper‐slope) mooring in late‐fall and winter originates from Herald (Barrow) Canyon some months earlier. Our results constitute the first robust evidence that the westward‐flowing Chukchi Slope Current persists this far west of Barrow Canyon.
more » « less- NSF-PAR ID:
- 10388120
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 128
- Issue:
- 1
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract A high‐resolution regional ocean model together with moored hydrographic and velocity measurements is used to identify the pathways and mechanisms by which Pacific water, modified over the Chukchi shelf, crosses the shelf break into the Canada Basin. Most of the Pacific water flowing into the Arctic Ocean through Bering Strait enters the Canada Basin through Barrow Canyon. Strong advection allows the water to cross the shelf break and exit the shelf. Wind forcing plays little role in this process. Some of the outflowing water from Barrow Canyon flows to the east into the Beaufort Sea; however, approximately 0.4 to 0.5 Sv turns to the west forming the newly identified Chukchi Slope Current. This transport occurs at all times of year, channeling both summer and winter waters from the shelf to the Canada Basin. The model indicates that approximately 75% of this water was exposed to the mixed layer within the Chukchi Sea, while the remaining 25% was able to cross the shelf during the stratified summer before convection commences in late fall. We view the
Sv of the Chukchi Slope Current as replacing Beaufort Gyre water that would have come from the east in the absence of the cross‐topography flow in Barrow Canyon. The weak eastward flow on the Beaufort slope is also consistent with the local disruption of the Beaufort Gyre by the Barrow Canyon outflow. -
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Abstract A regional coupled sea ice‐ocean model and mooring/shipboard measurements are used to investigate the origins, seasonality, and downstream fate of the Chukchi Slope Current (CSC). Three years (2013–2015) of model integration indicates that, in the mean, the model slope current transports ∼0.45 Sv of Pacific water northwestward along the Chukchi continental slope. Only 62% of this water emanates from Barrow Canyon, while the rest (38%) is fed by a westward jet extending from the southern Beaufort Sea. The jet merges with the outflow from the canyon, forming the CSC. Due to these two distinct origins, the slope current in the model has a double velocity core at times. This is consistent with the double‐core structure of the slope current seen in ship‐based observations. Seasonal changes in the volume, heat, and freshwater transports by the slope current appear to be related to the changes in the upstream flows. A tracer diagnostic in the model suggests that the part of the slope current over the upper continental slope continues westward toward the East Siberian Sea, while the portion of the current overlying deeper isobaths flows northward into the Chukchi Borderland, where it ultimately gets entrained into the Beaufort Gyre. Our study provides a detailed and complete picture of the slope current.
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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 ≡ 106m3s−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.
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