The Arctic Subpolar gyre sTate Estimate (ASTE): A Gateway to Understanding Ice-Ocean Dynamics

State estimates like the Arctic Subpolar gyre sTate Estimate (ASTE, Nguyen et al., 2021) are powerful tools that combine observational data and numerical models to reconstruct the ice and ocean’s physical state over time. Unlike sequential data-assimilated reanalysis products, state estimates minimize misfit to a large set of various observations by adjusting model input and parameters rather than altering the model’s physical state, thereby consistently obeying physical laws and ensuring all source and sink terms can be identified. 

In this talk, I will explain the methodology behind a state estimate and present the first release of ASTE, which provides complete estimates of the Arctic sea ice and ocean states spanning 2002-2017 at a spatial resolution of about 15 km. I will highlight how ASTE has informed studies ranging from the analysis of Atlantic Water properties in the Arctic to the characterization of beneficial environmental conditions for high-latitude benthic habitats, and how ASTE’s adjoint model, i.e., the capability of running the model backwards in time to track which processes have influenced a chosen variable, provides a powerful method to unambiguously identify causal connections in the coupled Arctic system.

Towards the next release of ASTE, I will present a study of the impact of tides on Arctic sea ice, based on a higher, 3.5 km resolution version of ASTE that has been run for one full seasonal cycle, in a configuration including and excluding tides. While the study shows an overall decrease in sea ice volume in the presence of tides associated with increased vertical mixing and the upward flux of heat from deeper layers of the Arctic Ocean in line with previous findings, it also reveals an unexpected result, pointing to a new mechanism resulting in delayed sea ice melt in summer.