A regime change in Arctic sea ice growth

The decline in Arctic sea ice thickness (SIT) is a key indicator response of the cryosphere to anthropogenic climate change. While the drivers of this decline are debated, they involve a competition between the ice-albedo positive feedback that enhances ocean heat content and the thin-ice negative feedback enhancing ice speed and alters dynamic-thermodynamic interactions. To date, pan-Arctic assessments of the dynamic and thermodynamic responses have been limited to the CryoSat-2 era (2010–Present Day).

Here we apply recently developed thickness products to produce novel 30-year records of Arctic sea ice volume (SIV) budget, resolving dynamic and thermodynamic terms. Our residual growth is validated on IMB buoy data and has a slight positive bias of +0.14 m^-1 and a strong seasonal cycle. We identify a step change increase of 1,300 km^-3 in thermodynamic growth, coincident with the pause in volume decline of the winter of 2007/08, representing a regime change in system behaviour where 76\% of seasonal growth is explained by the mean thickness of the surviving sea ice (p<0.001). Furthermore, enhancement in growth is regionalised and strongly correlates with sea ice drift modes. Specifically, we find that cyclonic atmospheric circulation modes associated with a negative Arctic Oscillation promote a dynamically coupled thin-ice feedback by enhancing thermodynamic growth through divergence and advection of SIV. This effect is observed throughout the periphery seas and is variable on inter-annual and decadal timescales. Finally, we investigate the contribution of thickness, concentration and drift to budget term variance. Finding that 87% of volume flux variance is accounted for by SIT anomaly. We highlight the utility of volume budgeting for identifying unphysical spatio-temporal patterns in SIT datasets and provide a new long-term benchmark for constraining sea ice growth in climate model assessments.