Impact of Horizontal Spatial Resolution on Ocean Heat Transport and Arctic Sea Ice Extent in a Climate Model Suite.

Abstract:

Climate model projections of Arctic sea ice extent (SIE) underestimate the observed rate of decline in the minimum sea ice extent. A recent study links future rapid sea ice extent declines with ocean heat transport (OHT) anomalies through the Barents Sea Opening and the Bering Strait, when the SIE is large enough to cover the continental shelves (Auclair et al., 2018). Moreover, several studies show that high resolution ocean models tend to produce higher Atlantic OHT into the Barents Sea Opening than their coarser resolution counterparts (e.g. Docquier et al., 2019). Since ocean currents are tightly constrained by topography in the Arctic basin, we expect ocean models of different resolutions to show different patterns and intensity in sea ice melting.

To investigate the impact of horizontal resolution on OHT and subsequent sea ice retreat in the Arctic, we use a hierarchy of three global climate models that only differ by their horizontal resolution in the ocean (0.1°, 0.25°, and 1°) and that are run under a pre-industrial and a 1% per year CO2 increase scenario. We find that the rate of decline of the minimum SIE in the medium and high resolution models are in agreement with satellite observations, while that of the low resolution model is much smaller. The medium resolution model presents a significantly higher OHT through all gates as well as a smaller minimum SIE in the pre-industrial simulation. None of the models simulate rapid declines in the September SIE, instead they show a linear decline to a SIE of a similar level to that of the record minimum SIE of 2012 for the medium and high resolution models, and a SIE of the level of the beginning of the satellite era for the low resolution model, after a doubling of CO2. The interannual variability in OHT in the three models is smaller than observations with the low resolution model presenting a weaker variability than the medium and high resolution models. The link between magnitude and variability in OHT through various gates of the Arctic and the decline in sea ice extent is currently being investigated.