Abstract
Enhanced ocean heat transport into the Arctic is linked to stronger future Arctic warming and polar amplification. To quantify the impact of ocean heat transport on Arctic climate, it is imperative to understand how its magnitude and the associated mechanisms change in other climate states. This paper therefore assesses the ocean heat transport into the Arctic at 70^{circ }hbox {N} for climates forced with a broad range of carbon dioxide concentration levels, ranging from one-fourth to four times modern values. We focused on ocean heat transports through the Arctic entrances (Bering Strait, Canadian Archipelago, and Nordic Seas) and identified relative contributions of volume and temperature to these changes. The results show that ocean heat transport differences across the five climate states are dominated by heat transport changes in the Nordic Seas, although in the warmest climate state heat transport through the Bering Strait plays an almost equally important role. This is primarily caused by changes in horizontal currents owing to anomalous wind responses and to differential advection of thermal anomalies. Changes in sea ice cover play a prominent role by modulating the surface heat fluxes and the impact of wind stresses on ocean currents. The Atlantic meridional overturning circulation and its associated heat transport play a more modest role in the ocean heat transport into the Arctic. The net effect of these changes is that the poleward ocean heat transport at 70^{circ }hbox {N} strongly increases from the coldest climate to the warmest climate state.
Highlights
Arctic amplification, a stronger Arctic than global mean surface temperature trend, is one of the primary patterns of climate change as observed and simulated by climate models (e.g., Manabe and Stouffer 1980; Holland and Bitz 2003)
Transport of dry static energy decreases in a warming climate due to the smaller north–south temperature gradient induced by Arctic amplification, and dominates the net change in atmospheric heat transport (AHT) at 70◦N
We have investigated quasi-equilibrium changes in ocean heat transport toward the Arctic using the stateof-the-art coupled climate model EC-Earth
Summary
A stronger Arctic than global mean surface temperature trend, is one of the primary patterns of climate change as observed and simulated by climate models (e.g., Manabe and Stouffer 1980; Holland and Bitz 2003). (Cheng et al 2013), which plays a key role in the Atlantic ocean heat redistribution by transporting heat northwards from the tropics and subtropics This concurs with a paleoclimate model simulation of the Eocene climate (∼ 50 Ma )—with about four times modern CO2 values—in which the North Atlantic overturning reduces in intensity and depth relative to present-day values (Huber and Sloan 2001). The broad range of atmospheric CO2 concentrations allows us to test the sensitivity of OHT for equilibrium changes to constant CO2 forcings To our knowledge, this is the first time that the OHT to the Arctic under both very high and very low CO2 conditions is systematically analyzed with a stateof-the-art global coupled climate model.
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