Arctic sea ice export as a driver of deglacial climate
Arctic sea ice export as a driver of deglacial climate
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DOI：
10.1130/g47016.1
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发表时间：
2020-04-01
期刊：
影响因子：
5.8
通讯作者：
Bradley, Raymond S.
中科院分区：
文献类型：
--
作者：
Condron, Alan;Joyce, Anthony J.;Bradley, Raymond S.
古气候学中一个广为流传的理论认为，北美冰盖和前冰期湖泊向北欧（格陵兰、挪威和冰岛）海的淡水流量的变化，通过减缓大西洋经向翻转环流（AMOC）的强度，在消冰期（21-8 ka）触发了气候突变的事件。然而，证明这种联系是有问题的，因为气候模型无法产生由短暂的爆发洪水引起的百年到千年的倾覆减少，而海因里希事件1（约16 ka）期间的冰山排放可能发生在气候已经开始降温之后。在这里，一系列数值模式实验的结果表明，在冰川消融之前，北极盆地大部分地区的海冰可能已经达到数十米厚，形成了一个独立于陆地资源的巨大淡水水库。我们的模型显示，冰川消融导致海平面上升，大气环流的变化，以及陆地爆发的洪水导致这些冰通过弗拉姆海峡出口，随后的融化使北欧海变得新鲜，足以削弱AMOC。考虑到北极盆地储存的冰量和模拟输出事件的规模都超过了预估的前冰期阿加西湖（Agassiz Lake）定期排出的融水的体积和通量，我们的结果表明，非陆地淡水来源在造成过去的气候突变中发挥了重要作用。
A widespread theory in paleoclimatology suggests that changes in freshwater discharge to the Nordic (Greenland, Norwegian, and Icelandic) Seas from ice sheets and proglacial lakes over North America played a role in triggering episodes of abrupt climate change during deglaciation (21-8 ka) by slowing the strength of the Atlantic Meridional Overturning circulation (AMOC). Yet, proving this link has been problematic, as climate models are unable to produce centennial-to-millennial-length reductions in overturning from short-lived outburst floods, while periods of iceberg discharge during Heinrich Event 1 (ca. 16 ka) may have occurred after the climate had already begun to cool. Here, results from a series of numerical model experiments are presented to show that prior to deglaciation, sea ice could have become tens of meters thick over large parts of the Arctic Basin, forming an enormous reservoir of freshwater independent from terrestrial sources. Our model then shows that deglacial sea-level rise, changes in atmospheric circulation, and terrestrial outburst floods caused this ice to be exported through Fram Strait, where its subsequent melt freshened the Nordic Seas enough to weaken the AMOC. Given that both the volume of ice stored in the Arctic Basin and the magnitude of the simulated export events exceed estimates of the volumes and fluxes of meltwater periodically discharged from proglacial Lake Agassiz, our results show that non-terrestrial freshwater sources played an important role in causing past abrupt climate change.