An official website of the United States government
Abstract. In the high-latitude Arctic, wintertime sea ice and snowinsulate the relatively warmer ocean from the colder atmosphere. While theclimate warms, wintertime Arctic surface heat fluxes remain dominated by theinsulating effects of snow and sea ice covering the ocean until the sea icethins enough or sea ice concentrations decrease enough to allow for directocean–atmosphere heat fluxes. The Community Earth System Model version 1 LargeEnsemble (CESM1-LE) simulates increases in wintertime conductive heat fluxesin the ice-covered Arctic Ocean by ∼ 7–11 W m−2 bythe mid-21st century, thereby driving an increased warming of theatmosphere. These increased fluxes are due to both thinning sea ice anddecreasing snow on sea ice. The simulations analyzed here use a sub-grid-scaleice thickness distribution. Surface heat flux estimates calculated usinggrid-cell mean values of sea ice thicknesses underestimate mean heat fluxesby ∼16 %–35 % and overestimate changes in conductive heatfluxes by up to ∼36 % in the wintertime Arctic basin evenwhen sea ice concentrations remain above 95 %. These results highlight howwintertime conductive heat fluxes will increase in a warming world evenduring times when sea ice concentrations remain high and that snow and thedistribution of snow significantly impact large-scale calculations ofwintertime surface heat budgets in the Arctic.
more »
« less
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.
more »
« less
- PAR ID:
- 10455240
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 47
- Issue:
- 20
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Precise measurements of Arctic sea ice mass balance are necessary to understand the rapidly changing sea ice cover and its representation in climate models. During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we made repeat point measurements of snow and ice thickness on primarily level first- and second-year ice (FYI, SYI) using ablation stakes and ice thickness gauges. This technique enabled us to distinguish surface and bottom (basal) melt and characterize the importance of oceanic versus atmospheric forcing. We also evaluated the time series of ice growth and melt in the context of other MOSAiC observations and historical mass balance observations from the Surface Heat Budget of the Arctic (SHEBA) campaign and the North Pole Environmental Observatory (NPEO). Despite similar freezing degree days, average ice growth at MOSAiC was greater on FYI (1.67 m) and SYI (1.23 m) than at SHEBA (1.45 m, 0.53 m), due in part to initially thinner ice and snow conditions on MOSAiC. Our estimates of effective snow thermal conductivity, which agree with SHEBA results and other MOSAiC observations, are unlikely to explain the difference. On MOSAiC, FYI grew more and faster than SYI, demonstrating a feedback loop that acts to increase ice production after multi-year ice loss. Surface melt on MOSAiC (mean of 0.50 m) was greater than at NPEO (0.18 m), with considerable spatial variability that correlated with surface albedo variability. Basal melt was relatively small (mean of 0.12 m), and higher than NPEO observations (0.07 m). Finally, we present observations showing that false bottoms reduced basal melt rates in some FYI cases, in agreement with other observations at MOSAiC. These detailed mass balance observations will allow further investigation into connections between the carefully observed surface energy budget, ocean heat fluxes, sea ice, and ecosystem at MOSAiC and during other campaigns.more » « less
-
Abstract The Atlantic multidecadal variability (AMV) and Pacific multidecadal variability (PMV) can influence Arctic sea ice and modulate its trend, but to what extent the AMV and PMV can affect Arctic sea ice and which processes are dominant are not well understood. Here, we analyze the Community Earth System Model, version 1, idealized and time-varying pacemaker ensemble simulations to investigate these issues. These experiments show that the sea ice concentration varies mainly over the marginal Arctic Ocean, while the sea ice thickness variations occur over the entire Arctic Ocean. The internal components of AMV and PMV can enhance or weaken the decadal sea ice loss rates over the marginal Arctic Ocean by more than 50%. The AMV- or PMV-induced anomalous atmospheric energy transport and downward longwave radiation related to low clouds (thermodynamical processes) and sea ice motion (dynamical processes) contribute to the Arctic surface air temperature and sea ice concentration and thickness changes. Anomalous oceanic heat flux is mainly a response to rather than a cause of sea ice variations. The dynamic processes contribute to the winter Arctic sea ice variations as much as the thermodynamic processes, but they contribute less (more) to the summer Arctic sea ice variability than the thermodynamic processes over the marginal Arctic Ocean (parts of the central Arctic Ocean). Sea ice loss enhances air–sea heat fluxes, which cause oceanic heat convergence and warm near-surface air and the lower troposphere, which in turn melt more sea ice.more » « less
-
Abstract. We assess the influence of snow on sea ice in experimentsusing the Community Earth System Model version 2 for a preindustrial and a2xCO2 climate state. In the preindustrial climate, we find that increasingsimulated snow accumulation on sea ice results in thicker sea ice and acooler climate in both hemispheres. The sea ice mass budget response differsfundamentally between the two hemispheres. In the Arctic, increasing snowresults in a decrease in both congelation sea ice growth and surface sea icemelt due to the snow's impact on conductive heat transfer and albedo,respectively. These factors dominate in regions of perennial ice but have asmaller influence in seasonal ice areas. Overall, the mass budget changeslead to a reduced amplitude in the annual cycle of ice thickness. In theAntarctic, with increasing snow, ice growth increases due to snow–iceformation and is balanced by larger basal ice melt, which primarily occursin regions of seasonal ice. In a warmer 2xCO2 climate, the Arctic sea icesensitivity to snow depth is small and reduced relative to that of thepreindustrial climate. In contrast, in the Antarctic, the sensitivity tosnow on sea ice in the 2xCO2 climate is qualitatively similar to thesensitivity in the preindustrial climate. These results underscore theimportance of accurately representing snow accumulation on sea ice incoupled Earth system models due to its impact on a number of competingprocesses and feedbacks that affect the melt and growth of sea ice.more » « less
-
Abstract The Canada Basin (CB) has seen significant sea‐ice loss in recent decades. We use output from the Pan‐Arctic Ice‐Ocean Modeling and Assimilation System to examine the 1979–2023 evolution of seasonal sea‐ice volume (SIV) changes in the CB partitioned into advective and thermodynamic changes. In winter, some years show net convergence into the region that is of comparable magnitude to the SIV change attributed to sea‐ice growth. In summer, melt/ablation dominates the change each year. In both seasons, 44 year trends in seasonal SIV changes are driven primarily by thermodynamic processes. The inferred thermodynamic growth each year is nearly equal to the inferred melt consistent with SIV at the end of the melt season declining more rapidly than SIV at the end of the growth season. Increased melt season atmospheric heating of the ice‐ocean system over 1979–2023, estimated from ERA5 reanalysis, is consistent with the ice‐albedo feedback. In the growth season, net cumulative atmospheric heat release from the ice‐ocean system shows no trend, suggesting increases in inferred thermodynamic ice growth can be attributed to more rapid growth of thinner ice. In each season, cumulative atmospheric heat input exceeds that required for ice melt/growth resulting in a residual that influences ocean heat content (OHC). Seasonal OHC changes, inferred from ocean observations, are equal to approximately one‐third of this residual, although limited ocean observations leave the total heat budget poorly constrained, highlighting a need for more water column observations.more » « less
