Abstract
Abstract. Arctic landfast ice extent and duration are examined from observations, ice assimilations, ocean reanalyses and coupled models. From observations and assimilations, it is shown that in areas where landfast ice conditions last more than 5 months the first-year ice typically grows to more than 2 m and is rarely less than 1 m. The observed spatial distribution of landfast ice closely matches assimilation products but less so for ocean reanalyses and coupled models. Although models generally struggle to represent the landfast ice necessary to emulate the observed import/export of sea ice in regions favourable to landfast ice conditions, some do exhibit both a realistic climatology and a realistic decline of landfast ice extent under an anthropogenic forcing scenario. In these more realistic simulations, projections show that an extensive landfast ice cover should remain for at least 5 months of the year, well into the end of the 21st century. This is in stark contrast with the simulations that have an unrealistic emulation of landfast ice conditions. In these simulations, slow and packed ice conditions shrink markedly over the same period. In all simulations and in areas with landfast ice that lasts more than 5 months, the end-of-winter sea ice thickness remains between 1 and 2 m, well beyond the second half of the century. It is concluded that in the current generation of climate models, projections of winter sea ice conditions in the Canadian Arctic Archipelago and the Laptev Sea are overly sensitive to the representation of landfast ice conditions and that ongoing development in landfast ice parameterization will likely better constrain these projections.
Highlights
Sea ice that is immobile because it is attached to land is termed “landfast”
We have compared the geographical distribution of landfast ice extent and duration in ocean reanalyses and coupled climate models to that in historical ice charts
We have used slow, packed ice in models as a proxy for landfast ice. Using this proxy we find that some current-generation models provide a reasonable representation of landfast ice conditions (e.g. Pan-Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS), Community Earth System Model Large Ensemble (CESM-LE) and GFDL-ESM2G) but others still have a hard time emulating landfast ice in the Canadian Arctic Archipelago (CAA) and even more so in the Laptev Sea
Summary
Sea ice that is immobile because it is attached to land is termed “landfast”. In shallow coastal regions, large pressure ridges can be anchored to the sea floor. Landfast ice is immobile and, its maximum ice thickness is primarily driven by thermodynamics from air temperature and the timing and amount of snowfall during the growth period (Brown and Cote, 1992) Because it isolates thermodynamics from import/export of sea ice, landfast ice is a convenient bellwether of the effect of anthropogenic forcing on the Arctic environment. Since the Sou and Flato (2009) study, several highresolution global ocean and sea ice models have become available, making it possible to study the coupled response of landfast ice to anthropogenic forcing. We provide a more comprehensive investigation into the variability of landfast ice extent and thickness from the current generation of climate models for the Arctic-wide domain and evaluate their response to anthropogenic forcing. We compare the coupled model simulations with our own pan-Arctic ice-ocean simulations
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