PNNL

Abstract

In response to greenhouse gas forcing, poleward ocean heat transport (OHT) weakens in the Southern Ocean but increases in the Arctic. The role of ocean circulation changes in the OHT response have been assessed in the literature by decomposing the OHT anomalies into a dynamic (accounting for circulation changes while holding ocean temperature fixed) and a thermodynamic component (accounting for ocean temperature changes while holding the circulation fixed). However, ocean temperature changes are themselves shaped by ocean circulation changes through the redistribution of the existing heat reservoir and subsequent effects on air-sea heat fluxes as sea surface temperatures are modified. Thus, the thermodynamic component of OHT is influenced by changes in ocean circulation, making the dynamic/thermodynamic decomposition unable to isolate the role of circulation changes in OHT anomalies. To address this issue, we use a novel passive-active decomposition to assess the relative contributions of ocean circulation and passive ocean temperature changes to polar OHT anomalies in response to greenhouse gas forcing. We find that ocean circulation changes have a much weaker effect on OHT changes in polar regions than what is inferred using the dynamic/thermodynamic decomposition