A Possible Hysteresis in the Arctic Ocean due to Release of Subsurface Heat during Sea Ice Retreat
A Possible Hysteresis in the Arctic Ocean due to Release of Subsurface Heat during Sea Ice Retreat
复制标题
由于海冰消退期间地下热量的释放，北冰洋可能出现滞后现象
DOI：
10.1175/jpo-d-22-0131.1
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发表时间：
2023
影响因子：
3.5
通讯作者：
Fine, Elizabeth C.
中科院分区：
文献类型：
--
作者：
Beer, Emma;Eisenman, Ian;Wagner, Till J.;Fine, Elizabeth C.
北冰洋的特点是在温暖和咸的水层之上有一层冰覆盖的寒冷和相对新鲜的水层。据估计，这些深层中储存的热量足以将北极海冰融化许多次，但它们被稳定的盐跃层与表面隔离开来。目前整个北冰洋盐跃层的垂直混合率很小，部分原因是海冰减少了风-海洋动量传递和阻尼内波。然而，最近的观测研究认为，海冰退缩导致混合增强。这可能会产生一种正反馈，即由于海冰退缩而增加的垂直混合会导致先前孤立的地下热量融化更多的海冰。在这里，我们使用一个理想化的气候模型来研究这种反馈的影响。我们发现，一个突然的“临界点”，可以发生在全球变暖，与相关的滞后窗口所界定的鞍结分岔。我们表明，滞后的存在和大小是敏感的模型参数的选择，和滞后发生的参数只有一个有限的范围。在分叉点的临界转变过程中，我们发现只有一小部分储存在深层的热量被释放出来，尽管这仍然足以导致大量的海冰融化。此外，当参数变化时，在热存储的这种变化和滞后水平之间没有明显的关系。
The Arctic Ocean is characterized by an ice-covered layer of cold and relatively fresh water above layers of warmer and saltier water. It is estimated that enough heat is stored in these deeper layers to melt all the Arctic sea ice many times over, but they are isolated from the surface by a stable halocline. Current vertical mixing rates across the Arctic Ocean halocline are small, due in part to sea ice reducing wind–ocean momentum transfer and damping internal waves. However, recent observational studies have argued that sea ice retreat results in enhanced mixing. This could create a positive feedback whereby increased vertical mixing due to sea ice retreat causes the previously isolated subsurface heat to melt more sea ice. Here, we use an idealized climate model to investigate the impacts of such a feedback. We find that an abrupt “tipping point” can occur under global warming, with an associated hysteresis window bounded by saddle-node bifurcations. We show that the presence and magnitude of the hysteresis are sensitive to the choice of model parameters, and the hysteresis occurs for only a limited range of parameters. During the critical transition at the bifurcation point, we find that only a small percentage of the heat stored in the deep layer is released, although this is still enough to lead to substantial sea ice melt. Furthermore, no clear relationship is apparent between this change in heat storage and the level of hysteresis when the parameters are varied.