The evolution of a shallow front in the Arctic marginal ice zone

Abstract

The high degree of heterogeneity in the ice-ocean-atmosphere system in marginal ice zones leads to a complex set of dynamics which control fluxes of heat and buoyancy in the upper ocean. Strong fronts may occur near the ice edge between the warmer waters of the ice-free regions and the cold, fresh waters near and under the ice. This study presents observations of a well-defined density front located along the ice edge in the Beaufort Sea. The evolution of the front over a ~3-day survey period is captured by multiple cross-front sections measured using an underway conductivity-temperature-depth system, with simultaneous measurements of atmospheric forcing. Synthetic aperture radar images bookending this period show that the ice edge itself underwent concurrent evolution. Prior to the survey, the ice edge was compact and well defined while after the survey it was diffuse and filamented with coherent vortical structures. This transformation might be indicative of the development an active ocean eddy field in the upper ocean mixed layer. Over the course of hours, increasing wind stress is correlated with changes to the lateral buoyancy gradient and frontogenesis. Frontal dynamics appear to vary from typical open-ocean fronts (e.g., here the frontogenesis is linked to an “up-front” wind stress). Convective and shear-driven mixing appear to be unable to describe deepening at the heel of the front. While there was no measurable spatial variation in wind speed, we hypothesize that spatial heterogeneity in the total surface stress input, resulting from varying ice conditions across the marginal ice zone, may be a driver of the observed behaviour.

Stirring of Sea‐Ice Meltwater Enhances Submesoscale Fronts in the Southern Ocean

“…Adding a layer of complexity, von Appen et al (2018) propose that subduction associated with baroclinic instabilities and ML fronts is enhanced due to increased mixing from cabbeling-when two water masses of the same density mix and the resultant water mass is denser. MLEs tend to give rise to increased stratification; however, Brenner et al (2020) could not conclusively show that eddies formed from baroclinic instabilities were a leading factor in setting the ML stratification. Their study suggests that MLEs may not be sufficiently strong in MIZs to impact upper-ocean stratification.…”

“…However, it has been demonstrated by theory and models that submesoscale flows in MIZs interact with horizontal gradients in density to modify ML structure, ESSOAr | https://doi.org/10.1002/essoar.10504395.1 | Non-exclusive | First posted online: Thu, 24 Sep 2020 09:41:41 | This content has not been peer reviewed. manuscript submitted to JGR: Oceans et al, 2016;Lu et al, 2015;Manucharyan & Thompson, 2017), and by observations in the Arctic (Timmermans & Winsor, 2013;Koenig et al, 2020;Brenner et al, 2020) and more recently in the Antarctic (e.g. (Swart et al, 2020;.…”

“…Under winter conditions near the Arctic MIZ, Koenig et al (2020) provide evidence of sustained turbulence by forced symmetric instabilities associated with downfront winds and heat loss from the surface layer, which extract potential vorticity from the water column at submesoscale fronts. Conversely, Brenner et al (2020) found that upfront winds lead to frontogenesis on time scales shorter than Ekman dynamics. The Antarctic MIZ differs from the Arctic in that the Antarctic sea-ice sector experiences strong, event-scale storms (Patoux et al, 2009;Vichi et al, 2019).…”

“…One-dimensional mixing processes associated with local sea-ice melt and vertical mixing have been shown to dominate upper ocean physics in MIZs (Dewey et al, 2017;Smith et al, 2018). However, it has been demonstrated by theory and models that submesoscale flows in MIZs interact with horizontal gradients in density to modify ML structure (Horvat et al, 2016;Lu et al, 2015;Manucharyan & Thompson, 2017), and by observations in the Arctic (Brenner et al, 2020;Koenig et al, 2020;Timmermans & Winsor, 2013) and more recently in the Antarctic (e.g., Swart et al, 2020).…”

Exploring the Pacific Arctic Seasonal Ice Zone With Saildrone USVs

“…Sea ice is known to affect the properties of the seawater around it (e.g., Gallaher et al, 2016;Dewey et al, 2017;Brenner et al, 2020). If the surface marine variables observed in close range of sea ice (say, while ice was visible in the horizontal photos from the vehicles) proved sufficiently distinct from those measured in ice-free water, then they might offer a navigationally useful indicator for the proximity of sea ice.…”