Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

Abstract

The Western Arctic Ocean is a host to major ocean circulation systems, many of which generate eddies that can transport water masses and corresponding tracers over long distances from their formation sites. However, comprehensive observations of critical eddy characteristics are currently not available and are limited to spatially and temporally sparse in situ observations. Here we use high-resolution spaceborne synthetic aperture radar measurements to detect eddies from their surface imprints in ice-free sea surface roughness, and in sea ice patterns throughout marginal ice zones. We provide the first estimate of eddy characteristics extending over the seasonally ice-free and marginal ice zone regions of the Western Arctic Ocean, including their locations, diameters, and monthly distribution. Using available synthetic aperture radar data, we identified over 4,000 open ocean eddies, as well as over 3,500 eddies in marginal ice zones from June to October in 2007, 2011, and 2016. Eddies range in size between 0.5 and 100 km and are frequently found over the shelf and near continental slopes but also present in the deep Canada Basin and over the Chukchi Plateau. We find that cyclonic eddies are twice more frequent compared to anticyclonic eddies at the surface, distinct from the dominating anticyclonic eddies observed at depth by in situ moorings and ice-tethered profilers. Our study supports the notion that eddies are ubiquitous in the Western Arctic Ocean even in the presence of sea ice and emphasizes the need for improved ocean observations and modeling at eddy scales. Plain Language SummaryOcean eddies play an important role in the transport of heat, salt, and pollutants over long distances from their formation sites. However, their observations in the Arctic Ocean are complex due to severe weather and sea ice cover. Here we present results of high-resolution satellite observations over the ice-free ocean and in the marginal ice zones. Detailed eddy characteristics are for the first time presented for the Western Arctic Ocean. These results provide observational evidence that eddies are ubiquitous in this Arctic region even in the presence of sea ice and emphasize the need for improved ocean observations and modeling at eddy scales. Key Points: • First account of eddies in the Western Arctic Ocean is presented based on satellite observations over open ocean and marginal ice zones • Eddies range in size between 0.5 and 100 km and are ubiquitous over deep and shelf regions of the Western Arctic Ocean • Cyclonic eddies are twice more frequent compared to anticyclones

Understanding Arctic Ocean Circulation: A Review of Ocean Dynamics in a Changing Climate

“…Baroclinic eddies are a ubiquitous feature of the Arctic Ocean, which is observed to have a vigorous mesoscale and submesoscale eddy field (e.g., Carpenter & Timmermans, ; Kozlov et al, ; Manley & Hunkins, ; Manucharyan et al, ; Mensa et al, ; Pnyushkov et al, ; Spall et al, ; Timmermans et al, ; Zhao et al, , ). Water‐column kinetic energy in the Arctic's halocline is dominated by eddies (Zhao et al, ), and we expect eddy buoyancy fluxes and along‐isopycnal stirring by eddies to play an important role in the general circulation, as will be shown in section .…”

Eddies in the North Greenland Sea and Fram Strait From Satellite Altimetry, SAR and High‐Resolution Model Data

“…Four of the modes, having the characteristic time scales of less than 3 months, were assembled into the pulsation component. The analysis of ASAR data was performed using a Matlab-based software described in Kozlov et al (2015) and further applied for eddy detection in the Arctic Ocean (Kozlov et al, 2019). The original SAR images were calibrated to normalized radar cross-sectional units, then signal trend in the range direction was removed, and the results were smoothed with the adaptive Wiener filter to reduce the speckle noise (Lim, 1990).…”

“…Eddies are visible in spaceborne SAR images owing to modulation of short-scale sea surface roughness by eddy-induced currents (wave-current interactions), accumulation of slicks or ice floes in the current convergence zones, and due to near-surface wind variation across oceanic fronts (Johannessen et al, 2005;Kozlov et al, 2012Kozlov et al, , 2019Kudryavtsev et al, 2014). The most common method for eddy detection in SAR data is based on visual identification of their surface signatures at relatively small spatial and temporal scales (Atadzhanova et al, 2017;Dokken & Wahl, 1996;Johannessen et al, 1996;Karimova, 2012).…”

“…Following the methodology presented in Kozlov et al (2019), every image was visually inspected at full resolution in search for distinct eddy signatures and identification of their boundaries. Over the ice-free ocean regions, eddy boundaries are manifested mostly in two ways both linked to the formation of the upper ocean convergence zones.…”

Multi-Sensor Observations of Submesoscale Eddies in Coastal Regions

“…The size and location of the anticyclonic eddies in CI gradient parameter fields have little difference from those in HFR-derived current fields because: (1) the Chl-a field aroused by the physical eddy field tends to be weaker than the current field and appears to be shifted by the force of the advection term; (2) the two datasets have different spatial resolutions and different properties (CI and velocity vectors). In addition, our method relies on a single image and gradient information, which is different from other studies about tracer-derived velocity products [46][47][48]. Nevertheless, some limitations do exist in both our method and the CI imagery when compared with HFR imagery.…”