Episodic Reversal of Autumn Ice Advance Caused by Release of Ocean Heat in the Beaufort Sea

Abstract

High‐resolution measurements of the air‐ice‐ocean system during an October 2015 event in the Beaufort Sea demonstrate how stored ocean heat can be released to temporarily reverse seasonal ice advance. Strong on‐ice winds over a vast fetch caused mixing and release of heat from the upper ocean. This heat was sufficient to melt large areas of thin, newly formed pancake ice; an average of 10 MJ/m2 was lost from the upper ocean in the study area, resulting in ∼3–5 cm pancake sea ice melt. Heat and salt budgets create a consistent picture of the evolving air‐ice‐ocean system during this event, in both a fixed and ice‐following (Lagrangian) reference frame. The heat lost from the upper ocean is large compared with prior observations of ocean heat flux under thick, multiyear Arctic sea ice. In contrast to prior studies, where almost all heat lost goes into ice melt, a significant portion of the ocean heat released in this event goes directly to the atmosphere, while the remainder (∼30–40%) goes into melting sea ice. The magnitude of ocean mixing during this event may have been enhanced by large surface waves, reaching nearly 5 m at the peak, which are becoming increasingly common in the autumn Arctic Ocean. The wave effects are explored by comparing the air‐ice‐ocean evolution observed at short and long fetches, and a common scaling for Langmuir turbulence. After the event, the ocean mixed layer was deeper and cooler, and autumn ice formation resumed.

Effects of an Explosive Polar Cyclone Crossing the Antarctic Marginal Ice Zone

“…In contrast, in the Southern Ocean, we suggest that the storm‐driven wave propagation and oceanic air advection delay consolidation and maintain the mixed frazil‐pancake field, also when ice concentration is close to 100%. This set of observations sheds a new light on sea ice features and their interaction with intense atmospheric events which differs from those previously observed in the Weddell Sea (Doble & Wadhams, ; Valkonen et al, ) and other Arctic cases (Collins et al, ; Itkin et al, ; Smith et al, ). Despite the ice edge moving away from the ice‐tethered buoy over the 20 days period by 200 km, the surface was never consolidated, and the concurrent drift and wave motion were evident (Figures d–f).…”

“…However, these studies had not related larger drift speeds to storm conditions, as demonstrated here. One implication of drift is enhanced ocean heat flux, which was on the lower end of the previous measurements (11 W/m 2 , see Text S3; McPhee et al, ; Ackley et al, ); evidently, this extreme event did not enhance the upwelling of warmer waters, in contrast with what found in the Arctic (Smith et al, ).…”

“…Despite the continued study of extratropical cyclones (Schultz et al, 2018), our understanding of their interactions with sea ice is incomplete. The bulk of the literature has focused on the Arctic and on the impact of cyclones on ice concentration changes (Brümmer et al, 2008;Itkin et al, 2017;Kriegsmann & Brümmer, 2014;Lammert et al, 2009;Rae et al, 2017;Wei et al, 2019), recently including waves (Collins et al, 2015;Smith et al, 2018;Wang et al, 2016). In the Antarctic, where the ocean state and ice conditions are different, waves have been the main focus (Doble & Bidlot, 2013;Kohout et al, 2014).…”

Overview of the Arctic Sea State and Boundary Layer Physics Program

“…Inter‐dependence of these source terms has been indicated in Cheng et al (). This effect is obscured when examining wave heights alone, but can be crucial to questions of mixing (Smith et al, ).…”

Drift of Pancake Ice Floes in the Winter Antarctic Marginal Ice Zone During Polar Cyclones

“…Moreover, Williams et al (2017) found that wave radiation stresses are appreciable only for wave periods < 10 s; the measurements reported here have dominant periods > 15 s. The small floes observed during our measurements, smaller floes than tested by Williams et al (2017), would induce even weaker radiation stresses. Although wave-induced drift is negligible, it is expected that the significant waves measured will have induced turbulence in the water sublayers (Alberello, Onorato, Frascoli, et al, 2019;Smith & Thomson, 2019;Zippel & Thomson, 2016), enhancing mixing and heat fluxes under sea ice (Ackley et al, 2015;Smith et al, 2018). Shen et al (1987) proposed a granular rheology for the MIZ based on momentum transfer through floe-floe collisions.…”