Atmospheric Warming Drives Growth in Arctic Sea Ice: A Key Role for Snow

Abstract

A number of feedbacks regulate the response of Arctic sea ice to local atmospheric warming. Using a realistic coupled ocean-sea ice model and its adjoint, we isolate a mechanism by which significant ice growth at the end of the melt season may occur as a lagged response to Arctic atmospheric warming. A series of perturbation simulations informed by adjoint model-derived sensitivity patterns reveal the enhanced ice growth to be accompanied by a reduction of snow thickness on the ice pack. Detailed analysis of ocean-ice-snow heat budgets confirms the essential role of the reduced snow thickness for persistence and delayed overshoot of ice growth. The underlying mechanism is a snow-melt-conductivity feedback, wherein atmosphere-driven snow melt leads to a larger conductive ocean heat loss through the overlying ice layer. Our results highlight the need for accurate observations of snow thickness to constrain climate models and to initialize sea ice forecasts. Plain Language Summary In this study we explore the relationship between Arctic sea ice growth and near-surface air temperature in a modeling framework. By mapping the time-and space-evolving sensitivity of the Arctic ice volume to changes in air temperature, we show that warming at the end of the melting season can lead to thicker ice at the end of the following winter. Warmer air temperatures can melt snow and remove the insulation it provides, exposing the ice surface to subfreezing air temperatures. We show that removal of this insulating snow layer is essential for enhancing sea ice growth later on, by allowing more heat to be conducted up and out of the underlying ocean, supporting seawater freezing. Our results highlight the importance of measuring snow thickness for accurately forecasting Arctic sea ice.

The Arctic Subpolar Gyre sTate Estimate: Description and Assessment of a Data‐Constrained, Dynamically Consistent Ocean‐Sea Ice Estimate for 2002–2017

“…Looking toward the next ASTE_R1 release, we expect the greatest progress will be made by incorporating new model physics. In particular, improving the stability of the sea ice thermodynamic adjoint (Bigdeli et al., 2020) will enable its use in ASTE, providing stronger constraint of air‐ice‐sea exchanges and ocean ventilation. Future efforts will target hydrographic improvements along the Arctic shelf‐basin slope in the eastern Arctic to reduce the ASTE_R1 AW layer warm bias.…”

“…As it is unlikely that widespread observation of 3-D velocity and mixing will be made in the foreseeable future, we anticipate that AW watermass representation in the Eurasian basin will remain an issue for both the next generation of state-of-the-art Arctic Ocean models and the next ASTE release. Although we do not expect large gains from planned changes to the ocean observing system in the near future, we do anticipate improvements in sea ice state, mixed layer representation, and shelf-basin exchanges in the next ASTE release, due to recent improvements to the stability of the adjoint of the sea ice thermodynamics (Bigdeli et al, 2020). This will enable a more complete use of sea ice observations as active contributions to the cost function reduction (Equation 1).…”

The Arctic Subpolar gyre sTate Estimate (ASTE): Description and assessment of a data-constrained, dynamically consistent ocean-sea ice estimate for 2002-2017

“…Looking toward the next ASTE_R1 release, we expect the greatest progress will be made by incorporating new model physics. In particular, improving the stability of the sea ice thermodynamic adjoint (Bigdeli et al, 2020) will enable its use in ASTE, providing stronger constraint of air-ice-sea exchanges and ocean ventilation. Future efforts will target hydrographic improvements along the Arctic shelf-basin slope in the eastern Arctic to reduce the ASTE_R1 AW layer warm bias.…”

Freshwater in the Arctic Ocean 2010–2019

“…Much of the precipitation in the Arctic falls as snow but projections show an increasing amount of rain as the climate warms (Bintanja, 2018). This appears to have been tentatively observed in Greenland, though mostly in southern and western Greenland away from the central Arctic Ocean (Doyle et al, 2015;Haine et al, 2015;Boisvert et al, 2018;Oltmanns et al, 2019), where the consequences of surface melt, surface runoff, and ice dynamics from increased rainfall over the ice sheet have been observed (e.g., Lenaerts et al, 2019).…”