On the Feedback of Ice–Ocean Stress Coupling from Geostrophic Currents in an Anticyclonic Wind Regime over the Beaufort Gyre

Abstract

Based on analysis of observational data it has been suggested that a negative feedback of ice–ocean stress coupling may limit freshwater accumulation in the Beaufort Gyre (BG). In this paper we explore how this feedback can significantly contribute to BG stabilization in an anticyclonic wind regime. We use an ice–ocean model and turn on and off the feedback in simulations to elucidate the role of the feedback. When a persistent anticyclonic wind anomaly is applied over the BG, liquid freshwater content (FWC) increases because of enhanced Ekman downwelling. As a consequence, ocean surface geostrophic currents speed up. However, the spinup of sea ice is weaker than the acceleration of surface geostrophic currents during wintertime, because of strong sea ice internal stress when ice concentration is high and ice is thick. This leads to cyclonic anomalies in the ice–ocean relative velocity and stress over the BG. The resultant seasonal Ekman upwelling anomaly reduces freshwater accumulation by about 1/4 as compared to a simulation with the negative feedback turned off in a control experiment, with a reduction range of 1/10–1/3 in all experiments conducted. We show that the feedback is more effective when the model’s mesoscale eddy diffusivity is smaller or when sea ice internal stress is stronger. Finally, we argue that the ice–ocean stress feedback may become less significant as the Arctic warms and sea ice declines.

Analysis of the Beaufort Gyre Freshwater Content in 2003–2018

“…Note that Ekman transport convergence confined these melt waters in the Beaufort Gyre. Similar conclusions were recently published by Wang et al (), who employed a global coupled ice‐ocean FESOM model with ~4.5‐km grid resolution in the Arctic Ocean to investigate the role of sea ice decline in the Arctic Ocean freshwater content change.…”

“…On the other hand, loss of the freshwater cap (termed a “halocline catastrophe” by Aagaard & Carmack, , and Aagaard, ) allowing deep convection and associated large vertical heat flux could have irreversible consequences for the climate via considerable ice melt and uncertain response of the global climate system. Another important feedback is between the Beaufort Gyre spin‐up, increased eddy activity, and stabilization of halocline properties (e.g., Davis et al, ; Manucharyan & Spall, ; Manucharyan et al, ; Meneghello et al, ; Wang et al, , ; Zhang et al, ; Zhao et al, , ). Furthermore, ecosystems depend crucially on Arctic Ocean freshwater content changes (e.g., Carmack et al, ).…”

Arctic Ocean Response to Greenland Sea Wind Anomalies in a Suite of Model Simulations

“…In the Beaufort Gyre the cyclonic circulation in the AW layer sits beneath the anticyclonic surface layer, so differences in the barotropic stream function, which integrates the two, may be a product of different halocline depths between models (Steiner et al, 2004). In the Beaufort Gyre, differences in the circulation may also be due to differences in vertical mixing or the simulated sea ice cover (not shown), as explained by the "ice-ocean governor" theory of Meneghello et al (2018) and Wang et al (2019). They argue that when wind blows over the ice, the ice drags the ocean, but when the gyre spins up, the geostrophic current catches up with the ice, and the surface stress is reduced.…”

“…In the vertical, it has 47 z levels with 10-m resolution in the upper 100-m depth. This setup has been used in several previous studies with a focus on the Arctic Ocean (Wang et al, 2016a(Wang et al, , 2016b(Wang et al, , 2019.…”

Assessment of the Finite-volumE Sea ice-Ocean Model (FESOM2.0) – Part 1: Description of selected key model elements and comparison to its predecessor version

“…Contour lines highlight the spreading of Antarctic Intermediate Water (< 34.70 psu) northward. and tuning purposes but also for long fully coupled presentday and scenario climate studies Rackow et al, 2016;Wang et al, 2014Wang et al, , 2019aSein et al, 2018) and paleo-applications (Shi et al, 2016) with AWI-CM. Using the coarse reference mesh configuration (∼ 127 K surface vertices, also shown in Fig.…”