近日，英国南极调查局Bradley, Alexander T.及其研究小组的最新研究探明了由于海水入侵导致冰盖接地带融化的临界点。这一研究成果发表在2024年6月25日出版的国际学术期刊《自然—地球科学》上。
据介绍，海洋冰盖对海底在其接地带融化高度敏感，在那里它们在接地冰和浮冰之间过渡。最近发表的关于搁浅区复杂水文的研究表明，温暖的海水可以侵入冰盖下很远的距离，对冰的动力学产生巨大的影响。
研究人员开发了一个模型来捕捉入侵的海水、它引起的融化和由此导致的冰几何变化之间的反馈。研究揭示了接地带动力学对这种反馈的敏感依赖性：随着接地带响应融化而变宽，该区域的温度和流速都增加，进一步加剧了融化。研究发现，海洋温度的升高会导致超过一个临界点，超过这个临界点，海水就会以失控的融化过程无限制地侵入冰盖下面。
此外，这个临界点可能不容易被早期预警指标发现。虽然在实践中不可能预料到完全不受约束的扰动，但这表明了一种导致接地带行为剧烈变化的机制，而这种机制目前尚未被纳入冰盖模型中。该研究组认为现今南极接地带对这一过程的易感性，发现暖水和冷水腔冰架都可能是脆弱的。研究结果强调，冰盖融化的敏感性更强，海平面上升对气候变暖的影响也比之前所了解的要大。
附：英文原文
Title: Tipping point in ice-sheet grounding-zone melting due to ocean water intrusion
Author: Bradley, Alexander T., Hewitt, Ian J.
Issue&Volume: 2024-06-25
Abstract: Marine ice sheets are highly sensitive to submarine melting in their grounding zones, where they transition between grounded and floating ice. Recently published studies of the complex hydrography of grounding zones suggest that warm ocean water can intrude large distances beneath the ice sheet, with dramatic consequences for ice dynamics. Here we develop a model to capture the feedback between intruded ocean water, the melting it induces and the resulting changes in ice geometry. We reveal a sensitive dependence of the grounding-zone dynamics on this feedback: as the grounding zone widens in response to melting, both temperature and flow velocity in the region increase, further enhancing melting. We find that increases in ocean temperature can lead to a tipping point being passed, beyond which ocean water intrudes in an unbounded manner beneath the ice sheet, via a process of runaway melting. Additionally, this tipping point may not be easily detected with early warning indicators. Although completely unbounded intrusions are not expected in practice, this suggests a mechanism for dramatic changes in grounding-zone behaviour, which are not currently included in ice-sheet models. We consider the susceptibility of present-day Antarctic grounding zones to this process, finding that both warm and cold water cavity ice shelves may be vulnerable. Our results point towards a stronger sensitivity of ice-sheet melting, and thus higher sea-level-rise contribution in a warming climate, than has been previously understood.
DOI: 10.1038/s41561-024-01465-7
Source: https://www.nature.com/articles/s41561-024-01465-7