Snowball Earth Initiation and the Thermodynamics of Sea Ice
Snowball Earth Initiation and the Thermodynamics of Sea Ice
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DOI：
10.1029/2021ms002734
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发表时间：
2022-08-01
影响因子：
6.8
通讯作者：
Braun, Christoph
中科院分区：
文献类型：
--
作者：
Hoerner, Johannes;Voigt, Aiko;Braun, Christoph
雪球地球是地球远古时期的一种假设状态，在这种状态下，海洋完全或几乎完全被海冰覆盖，这是由失控的冰反照率反馈造成的。在这里，我们讨论了海冰热力学的处理如何影响全球气候模式ICON-A中雪球地球的启动，该模式在理想的板-海洋水行星设置中运行。具体而言，我们通过比较3层Winton和0层Semtner方案，研究了垂直分辨率和冰盐水袋的影响，并研究了限制冰厚度为5 m的影响。更高的垂直分辨率和盐水袋增加了冰的内部储热，这削弱了表面融化，并通过允许冰雪在夏季持续更长时间而增加了全球反照率。两种冰方案的离线模拟证实，内部蓄热会减弱融化棘轮效应。结果是雪球地球的起爆更加容易，雪球起爆的临界二氧化碳增加了50%。限制冰的厚度会阻碍雪球的形成，因为去除多余的冰会产生人工热源。然而，影响很小，关键的二氧化碳只减少了5%。结果表明，海冰厚度限制只起次要作用，冰的内部蓄热是雪球起裂的重要因素，在模拟雪球地球起裂时需要考虑。
Snowball Earth is a hypothesized state in the deep past of Earth in which the ocean was completely or nearly completely covered by sea ice, resulting from a runaway ice-albedo feedback. Here, we address how the treatment of sea-ice thermodynamics affects the initiation of a Snowball Earth in the global climate model ICON-A run in an idealized slab-ocean aquaplanet setup. Specifically, we study the impact of vertical resolution and brine pockets of ice by comparing the 3-layer Winton and a 0-layer Semtner scheme, and we investigate the impact of limiting ice thickness to 5 m. The internal heat storage of ice is increased by higher vertical resolution and brine pockets, which weakens surface melting and increases global albedo by allowing snow and ice to persist longer into the summer season. The internal heat storage weakens the melt-ratchet effect, as is confirmed with offline simulations with the two ice schemes. The result is a substantially easier Snowball Earth initiation and an increase in the critical CO2 for Snowball initiation by 50%. Limiting ice thickness impedes Snowball initiation as the removal of excess ice leads to an artificial heat source. Yet, the impact is minor and critical CO2 is decreased by 5% only. The results show that while the sea-ice thickness limit plays only a minor role, the internal heat storage of ice represents an important factor for Snowball initiation and needs to be taken into account when modeling Snowball Earth initiation.