Impact of Ocean Heat Transport on Arctic Sea Ice Variability in the GFDL CM2‐O Model Suite. Issue 3 (7th March 2022) - Decuypère, Marine
Abstract: The impact of horizontal resolution on meridional Ocean Heat Transport (OHT) and sea ice in the Arctic is investigated using the GFDL CM2‐O climate model suite (1°, 1/4°, and 1/10°) in both preindustrial control and climate change simulations. Results show an increase in OHT associated to a decrease in sea ice extent (SIE) in the Arctic on interannual and decadal timescales. This link, however, is not monotonic with spatial resolution. While OHT increases and SIE decreases from the Low to the Medium resolution, the reverse is true from the Medium to the High resolution. Differences in OHT and SIE between the three model configurations mostly arise from the preindustrial state. As the spatial resolution increases, the Irminger Current is favored at the expense of the North Atlantic Drift. This rerouting of water to the Western side of Greenland results in less heat delivered to the Arctic in the High‐resolution configuration than in its Medium counterpart. As a result, the Medium‐resolution configuration is in best agreement with observed SIE and Atlantic OHT. Concurrent with the change in the partitioning in volume is a change in deep convection centers from the Greenland‐Irminger‐Norwegian Seas in the Low resolution to the Labrador Sea in the Medium and High resolutions. Results suggest a coupling between OHT into the Arctic and deep convection in the North Atlantic. Plain Language Summary: The Arctic has experienced a dramatic decrease in its sea ice cover over the past four decades. One of the main drivers of this intense melting is ocean heat transport from lower latitudes into the Arctic. This transport takes place at three main gates linking the North Pacific and Atlantic oceans to the Arctic. Thus, proper representation of ocean currents and the associated heat transport is necessary to make accurate projections of the Arctic pack ice in climate models. Here, we study the response of the Arctic sea ice to an increase in atmospheric carbon dioxide concentration using three configurations of a climate model that differ in their horizontal resolution of the ocean. Changing resolution can affect the strength, pattern, and amount of heat carried by the currents. Our results confirm that the greater the ocean heat transport into the Arctic, the lower the sea ice extent. In contrast with previous studies, however, the ocean heat transport does not systematically increase when refining the ocean horizontal resolution. This result points to the fact that not only the currents strength, but also the pathways are influenced by the ocean horizontal resolution, impacting the penetration of warm Atlantic waters into the Arctic. Key Points: Ocean heat transport into the Arctic does not systematically increase with horizontal resolution in the GFDL CM2‐O model suite The eddy‐permitting and eddy‐rich configurations show a stronger response to climate change than the eddy‐parameterized configuration Flow partitioning in the northern North Atlantic and location of deep convection centers are key to the heat transport into the Arctic