Projected Arctic Ocean Warming Accompanied by a Restructuring of the Overturning at the Fram Strait and the Barents Sea Opening

The Arctic Ocean is warming at over twice the rate of the global average, a phenomenon closely linked to enhanced ocean heat transport into the Arctic. The Fram Strait and the Barents Sea Opening play a particularly important role serving as conduits to increased ocean heat transport (OHT) into the Arctic, partially linked to the overturning circulation at the two straits. Here, we analyze the overturning at these Arctic gateways in the Community Earth System Model, version 2, Large Ensemble over years 1920–2100. In particular, we examine the climatological overturning, determine how it changes under climate forcing, and quantify its contribution to the ocean heat transport. We find that during the twentieth century, the overturning is characterized by a net inflow (outflow) at high (low) densities into (out of) the Arctic Ocean. However, beginning in the early twenty-first century, the inflow through both the Fram Strait and the Barents Sea Opening shifts to much lower densities associated with the warming of the inflow, while the outflow maintains its original density until 2070. The lightening of the inflow leads to a sign change in the density-space overturning through the straits in high density classes. Both the Fram Strait inflow and outflow strengthen over the twenty-first century, enhancing the overturning. This overturning pattern change strengthens OHT by 0.05 PW from 1920 to 1930 and from 2090 to 2100, accounting for over half of the total OHT increase over that period. SIGNIFICANCE STATEMENT: The Arctic Ocean is warming over twice as fast as the rest of the world. This phenomenon is closely associated with an increase in the ocean heat transport (OHT) into the Arctic. The Fram Strait and the Barents Sea Opening play a particularly important role in increasing this heat input into the Arctic, partially linked to the overturning circulation at the two straits. Here, we analyze the overturning at these two Arctic gateways in 100 simulations from the same global climate model from 1920 to 2100. We find that during the twentieth century, the overturning is associated with inflow at high densities and outflow at lighter densities. However, over the course of the twenty-first century, the inflow through the two straits lightens greatly, while the outflowing water remains heavy until the later part of the century. This leads to a sign change in the overturning, and the pattern change significantly enhances OHT.