How climate model biases skew the distribution of iceberg meltwater
How climate model biases skew the distribution of iceberg meltwater
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DOI：
10.1002/2016gl071645
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发表时间：
2017-04-28
影响因子：
5.2
通讯作者：
Eisenman, Ian
中科院分区：
文献类型：
--
作者：
Wagner, Till J. W.;Eisenman, Ian
预计未来一个世纪，向极地海洋排放的冰山将会增加，这提高了在用于未来预测的全球气候模型（GCM）中准确表示冰山的重要性。在这里，我们通过（i）最先进的 GCM 输出和（ii）观测状态估计，通过循环和温度场强制冰山漂移和衰变模型来分析 GCM 中交互式冰山的前景。研究发现，GCM 的融水扩散范围比观测状态估计的要小，尽管 GCM 存在相当大的高风偏差，这种偏差与大多数当前的 GCM 类似。我们认为，融水扩散的大规模减少主要是由于洋流的局部差异造成的，这可能与 GCM 水平分辨率的粗糙度有关。尽管北极冰山漂移通常由风力强迫主导，但全球气候模型中的高风偏向对融水分布的影响相对较小。我们发现这是由于强风下更快的漂移和更大的风驱动波浪侵蚀之间的补偿效应。这些结果可能对使用支持冰山的 GCM 模拟的大西洋经向翻转环流的未来变化产生影响。 通俗易懂的语言摘要 最近极地冰盖体积的减少凸显了冰盖融水如何影响大规模海洋环流和全球气候这一问题的重要性。例如，有人认为格陵兰岛融水的增加将在未来几十年减缓大西洋经向翻转环流（AMOC）。这种情况发生的可能性取决于融水在海洋表面的释放位置。冰山承载着一半的融水，在北大西洋向赤道输送融水方面发挥着至关重要的作用。我们的结果表明，包括冰山在内的气候模型将低估这种融水向赤道的输送，这对 AMOC 可能产生深远的影响。
The discharge of icebergs into the polar oceans is expected to increase over the coming century, which raises the importance of accurate representations of icebergs in global climate models (GCMs) used for future projections. Here we analyze the prospects for interactive icebergs in GCMs by forcing an iceberg drift and decay model with circulation and temperature fields from (i) state-of-the-art GCM output and (ii) an observational state estimate. The spread of meltwater is found to be smaller for the GCM than for the observational state estimate, despite a substantial high wind bias in the GCM-a bias that is similar to most current GCMs. We argue that this large-scale reduction in the spread of meltwater occurs primarily due to localized differences in ocean currents, which may be related to the coarseness of the horizontal resolution in the GCM. The high wind bias in the GCM is shown to have relatively little impact on the meltwater distribution, despite Arctic iceberg drift typically being dominated by the wind forcing. We find that this is due to compensating effects between faster drift under stronger winds and larger wind-driven wave erosion. These results may have implications for future changes in the Atlantic meridional overturning circulation simulated with iceberg-enabled GCMs.Plain Language Summary Recent reductions in the volume of the polar ice sheets highlight the importance of the question how ice sheet meltwater impacts the large-scale ocean circulation and global climate. For example, it has been argued that increased meltwater from Greenland will slow down the Atlantic meridional overturning circulation (AMOC) in the coming decades. The likelihood of this scenario depends on where the meltwater is released at the ocean surface. Icebergs, which carry up to half of this meltwater, play a crucial role in transporting meltwater equatorward in the North Atlantic. Our results suggest that climate models that include icebergs will underestimate this equatorward transport of meltwater, with potentially far-reaching implications for the AMOC.