Estimates of basal melt from Greenland: a driver for sea level changes

格陵兰冰盖(GRIS)的质量损失在过去20年中显著增加。除了对海平面上升的影响越来越大之外，输入到海洋内部的GRIS熔融水的路径和数量可能对深水的通风和形成产生关键影响，从而对与气候有关的大西洋经向翻转环流(AMOC)的强度产生重要影响。在大多数气候和海-海冰耦合模式中，弱对流导致较弱的AMOC和区域变化的海平面。人们认为，深水形成区的额外熔融水的到来可能会加强密度层结，从而减弱甚至抑制深对流。一些出版物总结说，在20世纪，火山灰岩浆的融化已经减缓了AMOC的速度，而另一些出版物则发现，来自火山灰岩浆的额外淡水还没有对深水的形成产生任何影响。第一阶段的主要成果是，第一次明确地在峡湾外发现了来自GRIS的海底融水(SMW)。SMW组分在混合层以下200-300m的上层最高，主要局限于格陵兰岛和加拿大的斜坡和陆架。SMW在上层海洋中的强烈稀释，以及与极地淡水的丰富程度相比，SMW所占的百分比相对较小，这表明SMW还不是LSW形成的主要参与者。导致深水团超额异常幕式发生的机制尚不清楚。基于盐度-SMW关系，它可能预示着含有含SMW水密度大于27.5的东格陵兰海流溢流事件。然而，这些结果是基于一个小的惰性气体数据集。继续阶段的目标是：(1)使用比目前更详细的数据集(He，Ne，CFCs，SF6)来量化格陵兰边界流、拉布拉多和伊尔明格海中的SMW组分，并通过应用惰性气体过量方法和OMP(2)评估EGC溢出喷流起源区域的SMW特征，评估哪些密度类别受到影响，以及与1994年和2015年相比，2018年和2019年是否发现了更多溢流中SMW的事件(3)使用速度测量和从CFCs和SF6等瞬变示踪剂推断的通风时间计算SMW通量(4)评估拉布拉多和伊明格海LSW的形成和其他相关水团的通风发生了多大程度的变化。分析负责的过程，并估计在哪些关键位置需要存在多少SMW，以显著影响相关水团的形成和通风。利用该信息估计直到SMW信号足够强以满足该标准的时间段。

Mass loss from the Greenland Ice Sheet (GrIS) increased significantly over the past two decades. Besides the growing influence on sea level rise, the pathways and the amount of GrIS melt water imported into the interior of the ocean could have crucial consequences for the ventilation and formation of deep water and hence the strength of the climate-relevant Atlantic meridional overturning circulation (AMOC). In most climate and coupled ocean-sea ice models weak convection leads to a weaker AMOC and a regionally changing sea level. It is thought that the arrival of additional melt water in the deep-water formation region could strengthen the density stratification and thus weaken or even suppress deep convection. Some publications concluded that the GrIS melt has already slowed down the AMOC in the twentieth century, while others found that the additional freshwater from GrIS has not exerted any influence on deep water formation yet. The main result of the first phase is, that for the first time, submarine melt water (SMW) from GrIS was unambiguously identified outside of fjords. SMW fractions are highest in the upper 200 – 300m below the mixed layer and mostly confined at the Greenland and Canadian slope and shelf. The strong dilution of SMW in the upper ocean and the relatively small SMW percentages compared to the abundance of fresh Polar Water indicate that SMW is not a main player for LSW formation yet. The mechanism leading to the episodic occurrence of He excess anomalies in the deep water masses is uncertain. Based on the salinity – SMW relation, it could herald episodic East Greenland Current spill jets events that contains SMW bearing water with densities larger than 27.5. However, these results are based on a small noble gas data set.The objectives for the continuation phase are: (1) Quantify SMW fractions from GrIS in the Greenland boundary current, the Labrador and the Irminger Sea using much more detailed data sets (He, Ne, CFCs, SF6) than was available until now and by applying the noble gas excess method and an OMP (2) Assess the SMW signature in the area of origin of the EGC spill jet, evaluate which density classes are affected and whether more events with SMW in spill jets are found in 2018 and 2019 compared to 1994 and 2015(3) Calculate SMW fluxes using velocity measurements and the ventilation time inferred from transient tracers as CFCs and SF6(4) Assess how much the formation of LSW and the ventilation of other relevant water masses in the Labrador and Irminger Sea changed. Analyze the processes responsible and estimate how much SMW needs to be present on which key locations to significantly influence formation and ventilation of the relevant water masses. With this information estimate the time period until the SMW signal is sufficiently strong to fulfil this criterion.