Abstract
The melting of sea ice floes from the edges (lateral melting) results in open water formation and subsequently increases absorption of solar shortwave energy. However, lateral melt plays a small role in the sea ice mass budget in both hemispheres in most climate models (Keen et al., 2020). This is likely influenced by simple parameterizations of this process in sea ice models that are constrained by limited observations. Here we use a coupled climate model (CESM2.0) to assess the sensitivity of modeled sea ice state to the lateral melt parameterization. The results show that sea ice is sensitive both to the parameters determining the effective lateral melt rate, as well as the nuances in how lateral melting is applied to the ice pack. Increasing the lateral melt rate within the range of reasonable values is largely compensated by decreases in the basal melt rate, but can still result in a significant decrease in sea ice concentration and thickness, particularly in the marginal ice zone. We suggest that it is important to consider the efficiency of melt processes at forming open water, which drives the majority of the ice-albedo feedback. Melt processes are more efficient at forming open water in thinner ice scenarios (as we are likely to see in the future), suggesting the importance of well representing thermodynamic evolution. Revisiting model parameterizations of lateral melting with observations will require finding new ways to represent important physical processes.
Highlights
In both the Arctic and the Antarctic, sea ice forms a heterogeneous cover on the ocean that undergoes strong seasonal changes. 15 A key factor in the annual retreat of sea ice cover is the sea ice-albedo feedback
185 3 Results 3.1 Changes in ice concentration and thickness Figure 3 shows the seasonal cycle of sea ice area, volume, average thickness, average concentration, and thick ice area in the Northern Hemisphere with a constant pre-industrial forcing
The average 195 thickness is somewhat higher July to October in the 10x run compared to the control, while it is significantly reduced in the 100x run (Fig. 3c)
Summary
In both the Arctic and the Antarctic, sea ice forms a heterogeneous cover on the ocean that undergoes strong seasonal changes. 15 A key factor in the annual retreat of sea ice cover is the sea ice-albedo feedback. 15 A key factor in the annual retreat of sea ice cover is the sea ice-albedo feedback. This feedback encompasses a variety of changes in ice mass and surface characteristics (such as the melt of snow and formation of melt ponds), but the largest component of this feedback is typically considered to be the loss of ice-covered area to open water area (Curry et al, 1995). Heat in the upper ocean promotes basal and lateral sea ice melt. All three of these melt processes (surface, basal, and lateral) contribute to open water formation by reducing ice volume with varying effects on ice thickness and area. Vertical melt processes (surface and basal) can only form open water once the ice is very thin, while lateral melt can directly form open water area regardless of ice thickness
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