The role of sea ice and other fresh water in the Arctic circulation

TLDR

Salinity stratification controls high‑latitude ocean vertical circulation, as illustrated by the 1960s–70s North Atlantic anomaly linked to increased Arctic fresh‑water discharge. The study examines how freshwater budgets and storage in the Arctic Ocean and southern convective regions control and could alter northern sea vertical circulation. The authors analyze freshwater budgets and storage in the Arctic Ocean and southern convective regions to assess their influence on vertical circulation. Freshwater input variations from the Arctic via the East Greenland Current can tip Greenland, Iceland, and Labrador Seas between active and halted convection, explaining recent North Atlantic freshening and cooling and underscoring the need for a slight salinity stratification to ventilate the deep ocean.

Abstract

Salinity stratification is critical to the vertical circulation of the high‐latitude ocean. We here examine the control of the vertical circulation in the northern seas, and the potential for altering it, by considering the budgets and storage of fresh water in the Arctic Ocean and in the convective regions to the south. We find that the present‐day Greenland and Iceland seas, and probably also the Labrador Sea, are rather delicately poised with respect to their ability to sustain convection. Small variations in the fresh water supplied to the convective gyres from the Arctic Ocean via the East Greenland Current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past. The North Atlantic salinity anomaly of the 1960s and 1970s is a recent example; it must have had its origin in an increased fresh water discharge from the Arctic Ocean. Similarly, the freshening and cooling of the deep North Atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the Arctic Ocean into the convective gyres. Finally, we note that because of the temperature dependence of compressibility, a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean.