Genesis and Decay of Mesoscale Baroclinic Eddies in the Seasonally Ice-Covered Interior Arctic Ocean

Abstract

Observations of ocean currents in the Arctic interior show a curious, and hitherto unexplained, vertical and temporal distribution of mesoscale activity. A marked seasonal cycle is found close to the surface: strong eddy activity during summer, observed from both satellites and moorings, is followed by very quiet winters. In contrast, subsurface eddies persist all year long within the deeper halocline and below. Informed by baroclinic instability analysis, we explore the origin and evolution of mesoscale eddies in the seasonally ice-covered interior Arctic Ocean. We find that the surface seasonal cycle is controlled by friction with sea ice, dissipating existing eddies and preventing the growth of new ones. In contrast, subsurface eddies, enabled by interior potential vorticity gradients and shielded by a strong stratification at a depth of approximately 50 m, can grow independently of the presence of sea ice. A high-resolution pan-Arctic ocean model confirms that the interior Arctic basin is baroclinically unstable all year long at depth. We address possible implications for the transport of water masses between the margins and the interior of the Arctic basin, and for climate models’ ability to capture the fundamental difference in mesoscale activity between ice-covered and ice-free regions.

Large Mesoscale Eddies in the Western Arctic Ocean From Satellite Altimetry Measurements

“…Altimetry can only detect large eddies with strong SLAs, leaving out several other commonly observed eddy types. Since friction with sea ice can dampen eddy velocities near the surface (e.g., Manley & Hunkins, 1985; Meneghello et al., 2021; Ou & Gordon, 1986), the intrahalocline or sub‐mixed‐layer eddies that can persist under the ice with virtually no surface velocity expressions (Manley & Hunkins, 1985; Zhao et al., 2014) are not visible to altimeters. Furthermore, the eddies in the marginal ice zone are mostly missing in the altimetry data due to their smaller sizes, contamination of altimetry signals by ice, and the inability to find enclosed contours of sea level even in partly ice‐covered areas.…”

“…The properties and dynamics of eddies have been extensively studied in several parts of the study region using CTD and current meter data (D’Asaro, 1988; Manley & Hunkins, 1985; Mathis et al., 2007; Muench et al., 2000; Newton et al., 1974; Scott et al., 2019), Ice‐Tethered Profilers (ITPs) (Timmermans et al., 2008; Zhao et al., 2016), drifters (Mensa et al., 2018), microstructure measurements (Fine et al., 2018; Padman et al., 1990), satellite observations (Kozlov et al., 2019; Watanabe et al., 2012), and modeling (Brannigan et al., 2017; Meneghello et al., 2021; Spall, 2008; Watanabe, 2011). Observations using ITP profilers (Timmermans et al., 2007; Zhao et al., 2014, 2016) were used to obtain statistical eddy properties in the deep and shelf areas of the Beaufort Sea (BS) and study the impact of eddies on the thermohaline structure of the basin.…”

Shelf-Sourced Methane in Surface Seawater at the Eurasian Continental Slope (Arctic Ocean)

“…Though, under the warm surface layer, the CH 4 plumes are sustained by the strong density gradient on the top while the vertical mixing between PML and CHL enabled a downward deepening of the CH 4 plumes (Figure 6A). The ice edge provides favorable conditions for eddy generation as specifically, convection by water cooling in leads generates a vertical dipole structure with a cyclonic eddy in the upper layer and an anticyclonic eddy in the CHL (Manley and Hunkins, 1985;Gupta et al, 2020;Meneghello et al, 2021). Further studies are needed to verify the role of eddies especially their enhanced lateral and vertical mixing capacity between certain water masses at the EES (Zhao et al, 2014;Pnyushkov et al, 2018) to contribute to the deepening of CH 4 plumes into subsurface waters.…”

Reversal of ocean gyres near ice shelves in the Amundsen Sea caused by the interaction of sea ice and wind

“…Regional circulation models have often been used to study ocean gyres (e.g. Meneghello et al, 2021;Regan et al, 2020).…”