Abstract. Freshwater, in the form of glacial runoff, is hypothesized to play a critical role in centennial to millennial scale climate variability such as the Younger Dryas and Dansgaard-Oeschger Events. Indeed, freshwater injection/hosing experiments with climate models have long shown that freshwater has the capability of generating such abrupt climate transitions. However, the relationship between freshwater and abrupt climate transitions is not straightforward. Large-scale glacial runoff events, such as Meltwater Pulse 1A, are not always temporally proximal to subsequent large-scale cooling. As well, the typical design of hosing experiments tends to artificially amplify the climate response. This study explores the impact that limitations in the representation of runoff in conventional hosing simulations has on our understanding of this relationship and addresses the more fundamental question of where coastally released freshwater is transported when it reaches the ocean. We focus particularly on the prior use of excessive freshwater volumes (often by a factor of 5) and present-day (rather than paleo) ocean gateways, as well as the injection of freshwater directly over sites of deep-water formation (DWF) rather than at runoff locations. We track the routing of glaciologically-constrained freshwater volumes from four different plausible injection locations in a suite of eddy-permitting glacial ocean simulations using MITGCM under both open and closed Bering Strait conditions. Restricting freshwater forcing values to realistic ranges results in less spreading of freshwater across the North Atlantic and indicates that the response of DWF depends strongly on the geographical location of meltwater input. In particular, freshwater released into the Gulf of Mexico has little impact on DWF regions as a result of turbulent mixing by the Gulf Stream. In contrast, freshwater released from the Eurasian Ice sheet or initially into the Arctic is found to have the largest impact on DWF in the North Atlantic and GIN seas. Additional experiments show that when the Bering Strait is open, much like present-day, the Mackenzie River source exhibits twice as much freshening of the Labrador sea as a closed Bering Strait. Finally, our results illustrate that applying a freshwater hosing directly into the North Atlantic with even realistic freshwater amounts still over-estimates the effect of terrestrial runoff on ocean circulation.

中文翻译：

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涡流模拟了上次冰期期间从北半球主要出水口注入的淡水

摘要。据推测，冰川径流形式的淡水在百年至千年尺度的气候变异中起着关键作用，例如Younger Dryas和Dansgaard-Oeschger事件。确实，长期以来使用气候模型进行的淡水注入/居住实验表明，淡水具有产生这种突然的气候转变的能力。但是，淡水和突然的气候变化之间的关系并不简单。诸如冰川融水脉冲1A之类的大规模冰川径流事件在时间上并不总是紧随其后的大规模降温。同样，软管试验的典型设计往往会人为地放大气候响应。这项研究探索了常规管道模拟中径流表示的局限性对我们对这种关系的理解的影响，并解决了一个更根本的问题，即沿海释放的淡水到达海洋时将其输送到何处。我们特别关注先前使用过量淡水（通常是5倍）和当今（而不是古）海洋通道的情况，以及直接在深水形成（DWF）站点上方注入淡水的方法，而不是径流位置。我们使用开放式和封闭式白令海峡条件下的MITGCM，在一套允许涡流的冰川海洋模拟中，追踪了来自四个不同的可能注入位置的受冰川限制的淡水量的路径。将淡水强迫值限制在实际范围内将导致淡水在北大西洋的扩散较少，并表明DWF的响应在很大程度上取决于融水输入的地理位置。特别是，由于墨西哥湾流的湍流混合，释放到墨西哥湾的淡水对DWF地区几乎没有影响。相比之下，发现从欧亚冰盖或最初流入北极的淡水对北大西洋和GIN海的DWF影响最大。其他实验表明，当白令海峡开放时，就像今天一样，麦肯齐河水源对拉布拉多海的新鲜度是封闭的白令海峡的两倍。最后，我们的结果表明，使用淡水 由于墨西哥湾流的湍流混合，释放到墨西哥湾的淡水对DWF地区几乎没有影响。相比之下，发现从欧亚冰盖或最初流入北极的淡水对北大西洋和GIN海的DWF影响最大。其他实验表明，当白令海峡开放时，就像今天一样，麦肯齐河水源对拉布拉多海的新鲜度是封闭的白令海峡的两倍。最后，我们的结果表明，使用淡水 由于墨西哥湾流的湍流混合，释放到墨西哥湾的淡水对DWF地区几乎没有影响。相比之下，发现从欧亚冰盖或最初流入北极的淡水对北大西洋和GIN海的DWF影响最大。其他实验表明，当白令海峡开放时，就像今天一样，麦肯齐河水源对拉布拉多海的新鲜度是封闭的白令海峡的两倍。最后，我们的结果表明，使用淡水 麦肯齐河源头的拉布拉多海新鲜度是封闭白令海峡的两倍。最后，我们的结果表明，使用淡水 麦肯齐河源头的拉布拉多海新鲜度是封闭白令海峡的两倍。最后，我们的结果表明，使用淡水冲水直接进入北大西洋甚至现实的淡水量仍然过高估计地面径流对海洋环流的影响。