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

格陵兰冰盖（GrIS）的质量损失在过去二十年中显着增加。除了对海平面上升的影响越来越大外，输入海洋内部的GrIS融水的路径和数量可能对深水的通风和形成以及与气候相关的大西洋纬向翻转环流（AMOC）的强度产生至关重要的影响。在大多数气候和耦合的海洋-海冰模式中，弱对流导致较弱的AMOC和区域性海平面变化。据认为，额外的融水在深水形成区的到来，可以加强密度分层，从而削弱甚至抑制深对流。一些出版物得出结论，GrIS融化已经减缓了世纪的AMOC，而其他人发现，来自GrIS的额外淡水尚未对深水形成产生任何影响。第一阶段的主要结果是，第一次在峡湾外明确识别了GrIS的海底融水（SMW）。SMW组分在混合层以下200 - 300 m处最高，主要局限于格陵兰和加拿大陆坡和陆架。SMW在上层海洋中的强烈稀释以及与丰富的极地淡水相比相对较小的SMW百分比表明SMW还不是LSW形成的主要因素。导致He过剩异常在深水水体中幕式出现的机制尚不确定。根据盐度与SMW的关系，它可能预示着东格陵兰洋流溢出射流事件的发生，其中含有密度大于27.5的SMW含水。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）使用更详细的数据集，量化格陵兰边界流、拉布拉多和Irminger海中GrIS的SMW部分（He，Ne，CFCs，SF6），并应用惰性气体过量法和OMP（2）评估EGC溢出射流起源区域的SMW特征，评估哪些密度等级受到影响，以及与1994年和2015年相比，2018年和2019年是否发现更多溢出射流中的SMW事件（3）使用速度测量值和从瞬态示踪剂CFCs和SF6推断的通风时间计算SMW通量（4）评估LSW的形成以及拉布拉多海和Irminger海其他相关水团的通风变化。分析负责的过程，并估计需要在哪些关键位置上存在多少SMW，以显著影响相关水团的形成和通风。利用该信息，估计SMW信号足够强以满足该标准之前的时间段。

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.