Does Arctic sea ice reduction foster shelf–basin exchange?

The recent shift in Arctic ice conditions from prevailing multi‐year ice to first‐year ice will presumably intensify fall–winter sea ice freezing and the associated salt flux to the underlying water column. Here, we conduct a dual modeling study whose results suggest that the predicted catastrophic consequences for the global thermohaline circulation (THC), as a result of the disappearance of Arctic sea ice, may not necessarily occur. In a warmer climate, the substantial fraction of dense water feeding the Greenland–Scotland overflow may form on Arctic shelves and cascade to the deep basin, thus replenishing dense water, which currently forms through open ocean convection in the sub‐Arctic seas. We have used a simplified model for estimating how increased ice production influences shelf–basin exchange associated with dense water cascading. We have carried out case studies in two regions of the Arctic Ocean where cascading was observed in the past. The baseline range of buoyancy‐forcing derived from the columnar ice formation was calculated as part of a 30‐year experiment of the pan‐Arctic coupled ice–ocean general circulation model (GCM). The GCM results indicate that mechanical sea ice divergence associated with lateral advection accounts for a significant part of the interannual variations in sea ice thermal production in the coastal polynya regions. This forcing was then rectified by taking into account sub‐grid processes and used in a regional model with analytically prescribed bottom topography and vertical stratification in order to examine specific cascading conditions in the Pacific and Atlantic sectors of the Arctic Ocean. Our results demonstrate that the consequences of enhanced ice formation depend on geographical location and shelf–basin bathymetry. In the Pacific sector, strong density stratification in slope waters impedes noticeable deepening of shelf‐origin water, even for the strongest forcing applied. In the Atlantic sector, a 1.5× increase of salt flux leads to a threefold increase of shelf‐slope volume flux below the warm core of Atlantic water. This threefold increase would be a sufficient substitute for a similar amount of dense water that currently forms in the Greenland, Iceland, and Norwegian (GIN) seas but is expected to decrease in a warming climate.