The Response of the Nordic Seas to Wintertime Sea Ice Retreat

Abstract

The ocean response to wintertime sea-ice retreat is investigated in the coupled climate model HiGEM. We focus on the marginal ice zone and adjacent waters of the Nordic Seas, where the air-sea temperature difference can be large during periods of off-ice winds promoting high heat flux events. Both control and transient climate model ensembles are examined, which allows us to isolate the ocean response due to sea-ice retreat from the response due to climate change. As the wintertime sea-ice edge retreats towards the Greenland coastline, it exposes waters that were previously covered by ice which enhances turbulent heat loss and mechanical mixing, leading to a greater loss of buoyancy and deeper vertical mixing in this location. However, under global warming, the buoyancy loss is inhibited as the atmosphere warms more rapidly than the ocean which reduces the air-sea temperature difference. This occurs most prominently further away from the retreating ice edge, over the Greenland Sea gyre. Over the gyre the upper ocean also warms significantly, resulting in a more stratified water column and, as a consequence, a reduction in the depth of convective mixing. In contrast, closer to the coast the effect of global warming is overshadowed by the effect of the sea-ice retreat, leading to significant changes in ocean temperature and salinity in the vicinity of the marginal ice zone.

North Atlantic overturning and water mass transformation in CMIP6 models

“…Transport of cold, fresh polar waters via the east and west Greenland boundary currents, and the mixing of boundary and interior waters (Tagklis et al, 2020) can also affect the surface densities and hence the stratification and heat loss. Sea ice could also have an important role in restricting heat exchange between the ocean and atmosphere in winter, and through freshwater fluxes from freezing and melting that have a local effect on the stratification and thus on SFWMT (Langehaug et al, 2012;Kostov et al, 2019;Wu et al, 2021). Also subsurface properties could affect SFWMT through changing stratification, and hence deep convection.…”

The Influence of Increased CO2 Concentrations on AMOC Interdecadal Variability Under the LGM Background

“…Further numerical experiments are warranted to validate the robustness of our findings. Additionally, future research that explores the synergy and competition between oceanic and atmospheric processes (Wu et al, 2021) at longer timescales can provide a more comprehensive understanding of AMOC variability in a warming climate. LGM-highCO 2 (shading, unit: W/m 2 , positive values represent heat loss from the ocean).…”

Understanding the Sensitivity of the North Atlantic Subpolar Overturning in Different Resolution Versions of HadGEM3‐GC3.1

“…However, sea ice also influences the dense water formation by insulating the ocean from the atmosphere and regulating air sea interactions during winter. In particular, the sea ice retreat during winter can lead to substantially enhanced turbulent heat loss and mechanical mixing (e.g., modification of the stratification via brine rejection) when warm boundary currents are exposed (Wu et al., 2021). Therefore, given the large surface density fluxes over the boundaries of the Labrador Sea (Figure 4), we address the question of how important the sea ice is for generating large SFWMT in the MM and HH models.…”