Abstract
AbstractSea ice formation processes occur on subgrid scales, and the detailed physics describing the processes are therefore not generally represented in climate models. One likely consequence of this is the premature closing of areas of open water in model simulations, which may result in a misrepresentation of heat and gas exchange between the ocean and atmosphere. This work demonstrates the implementation of a more realistic model of sea ice formation, introducing grease ice as a wind and oceanic stress‐dependent intermediary state between water and new sea ice. We use the fully coupled land‐atmosphere‐ocean‐sea ice model, HadGEM3‐GC3.1 and perform a three‐member ensemble with the new grease ice scheme from 1964 to 2013. Comparing our sea ice results with the existing ensemble without grease ice formation shows an increase in sea ice thickness and volume in the Arctic. In the Antarctic, including grease ice processes results in large local changes to both simulated sea ice concentration and thickness, but no change to the total area or volume.
Highlights
Large‐scale climate models struggle to accurately calculate Arctic sea ice volume (Shu et al, 2015) and thickness (Langehaug et al, 2013; Stroeve et al, 2014) and to capture trends in Antarctic sea ice extent (Turner et al, 2013)
The proximity of this area to the northern ice edge means that if grease ice is produced instead of sea ice, at least some of it is transported to the northern ice edge where it melts without ever having formed sea ice. This reduces the sea ice concentration and thickness in the outer Amundsen Sea in grease ice included (GREASE), relative to STANDARD (Figures 14 and 15). This reduction is roughly equal in magnitude to the increase in the Western Pacific following the implementation of the grease ice scheme, and we do not see the same increase in total sea ice volume in the Antarctic that we see in the Arctic
We have demonstrated a framework whereby grease ice formation and grease ice herding processes can be represented in sea ice formation calculations in a fully coupled global climate model
Summary
Large‐scale climate models struggle to accurately calculate Arctic sea ice volume (Shu et al, 2015) and thickness (Langehaug et al, 2013; Stroeve et al, 2014) and to capture trends in Antarctic sea ice extent (Turner et al, 2013). Sea ice one of the largest known biomes on Earth (Dieckmann & Hellmer, 2010), and high‐latitude biological processes impact on global marine ecosystems and on global climate through interactions between biota incorporated in the sea ice and the atmosphere and ocean (Melnikov et al, 2002; Vancoppenolle et al, 2013) Realistic representation of these processes in ESMs requires grease ice to be represented because, to be incorporated into sea ice, biota are scavenged from the ambient ocean water and first incorporated into grease ice (Gradinger & Ikävalko, 1998), which freezes to become sea ice. A coupled climate model includes wider atmospheric and oceanic processes that are likely to largely determine the volume of sea ice produced in the model, and biases in these are likely to dominate over any biases in the detailed sea ice formation calculations. It is preferable for climate models to include a physically accurate representation of processes where possible because tuning is unlikely to allow for the full range of physically possible responses to changes in other parts of the coupled climate system
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