North Atlantic response to the above‐normal export of sea ice from the Arctic
North Atlantic response to the above‐normal export of sea ice from the Arctic
复制标题
北大西洋对北极海冰异常出口的反应
DOI：
10.1029/2001jc001166
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发表时间：
2003
影响因子：
--
通讯作者：
A. Weaver
中科院分区：
文献类型：
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作者：
O. Saenko;E. Wiebe;A. Weaver
[1]利用全球模式研究了北大西洋北部温盐环流(THC)以及淡水和热量收支对北极超常海冰输出的响应。该模型不受开放边界条件或规定的大气温度和湿度的限制。给出了两组实验：瞬变冰输出和持续超常冰输出。在瞬变情况下，冰出口在1-5年内增加2倍。我们长达一个世纪的模拟并不支持在这样的扰动下模拟的气候可能会切换到新的准平衡的观点。相反，作为对瞬时正冰输出异常的响应，颠覆环流首先减缓，但在扰动消除15-20年后几乎完全恢复。然而，在这种情况下，淡水和热能的预算在长达40年的时间里继续演变。当模拟的北大西洋清新达到与大盐度异常(GSA)相当的量级时，从副热带到亚极地北大西洋的翻转和热量输送强度减少不超过5%。我们表明，为了产生先前报道的倾覆和热量输送减少高达20%，加倍的冰出口必须持续至少5年。这将导致北大西洋变冷，是GSA事件估计的3倍以上。在北极海冰持续高于正常出口的情况下，货柜码头处理费也不会崩溃，至少在这里使用的冰出口增长(1.5-3倍)的范围内不会崩溃。相反，大约15-20年后，颠覆开始恢复。北极海冰持续高于正常水平的输出之所以稳定，似乎是因为有两个过程在15-20年的十年时间尺度上运行。首先，北极和北大西洋之间淡水的内部重新分配(到耦合系统)，与海冰出口的增加有关，使北大西洋更新鲜，北冰洋更咸。如果这种情况持续下去，就会减少以液态形式从北极流向北大西洋的淡水。其次，由于翻转的环流不会崩溃，淡水异常在深水形成区向下传播，从表层海洋中消除了多余的浮力。此外，使用活跃的大气成分对于稳定颠覆环流也很重要。索引术语：4215海洋：一般：气候和年际变化(3309)；4540海洋：物理：冰力学和气/海/冰交换过程；4207海洋：一般：北极和南极海洋学；4255海洋：一般：数值模拟；关键词：北大西洋、北极、海冰、海洋
[1] The response of the thermohaline circulation (THC), as well as the freshwater and heat budgets of the northern North Atlantic, to above-normal sea ice export from the Arctic is examined using a global model. The model is not constrained by either open boundary conditions or prescribed atmospheric air temperature and humidity. Two sets of experiments are presented: the transient and the persistent above-normal ice export. In the transient case, ice export is increased by a factor of 2 for 1–5 years. Our century-long simulations do not support the notion that the simulated climate may switch to a new quasiequilibrium under such perturbations. Rather, in response to the transient positive ice export anomalies the overturning circulation first slows down but then almost completely recovers 15–20 years after the perturbation is removed. However, the budgets of freshwater and heat continue to evolve for up to 40 years in this case. When the simulated North Atlantic freshening reaches a magnitude comparable to that during the Great Salinity Anomaly (GSA), the strength of overturning and heat transport from subtropical to subpolar North Atlantic reduce by no more then 5%. We show that in order to generate a previously reported decrease of overturning and heat transport of as much as 20% the doubled ice export must be sustained for at least 5 years. This would result in a North Atlantic freshening more than 3 times larger than that estimated for the GSA event. In the case of a persistent above-normal export of sea ice from the Arctic the THC also does not collapse, at least within the range of the ice export increase (1.5–3 times) used here. Rather, after about 15–20 years the overturning begins to recover. The stability of the overturning to the persistent above-normal export of sea ice from the Arctic appears to be due to two processes operating on a decadal timescale of 15–20 years. First, the internal (to the coupled system) redistribution of freshwater between the Arctic and North Atlantic, associated with the enhanced export of sea ice, makes the North Atlantic fresher and Arctic Ocean saltier. This, if persistent, decreases the amount of freshwater leaving the Arctic toward the North Atlantic in a liquid form. Second, because the overturning circulation does not collapse, the freshwater anomaly propagates downward within the region of deep water formation, removing the excess of buoyancy from the surface ocean. Also, the use of an active atmospheric component is important for stabilizing the overturning circulation. INDEX TERMS: 4215 Oceanography: General: Climate and interannual variability (3309); 4540 Oceanography: Physical: Ice mechanics and air/sea/ice exchange processes; 4207 Oceanography: General: Arctic and Antarctic oceanography; 4255 Oceanography: General: Numerical modeling; KEYWORDS: North Atlantic, Arctic, sea ice, ocean