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

格陵兰岛基底融化的估计：海平面变化的驱动因素

• 批准号: 313848278
• 负责人: Dr. Oliver Huhn
• 金额: --
• 依托单位: Abteilung Ozeanographie
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/313848278?language=en
• 关键词: Estimates; basal; melt; Greenland; driver

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.

过去二十年来，格陵兰冰盖（GrIS）的质量损失显着增加。除了对海平面上升的影响越来越大之外，GrIS融水进入海洋内部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经向翻转环流（AMOC）的强度产生至关重要的影响。在大多数气候和海洋-海冰耦合模型中，弱对流会导致 AMOC 减弱和区域性海平面变化。人们认为，额外的融水到达深水形成区会加强密度分层，从而减弱甚至抑制深层对流。一些出版物得出的结论是，GrIS 融化已经减缓了 20 世纪的 AMOC，而另一些出版物则发现，GrIS 带来的额外淡水尚未对深水形成产生任何影响。第一阶段的主要成果是，首次在峡湾外明确识别出来自 GrIS 的海底融水 (SMW)。 SMW 部分最高出现在混合层以下 200 – 300 m 的上部，并且主要局限于格陵兰岛和加拿大的斜坡和陆架。上层海洋中 SMW 的强烈稀释以及与丰富的极地淡水相比 SMW 的百分比相对较小表明 SMW 还不是 LSW 形成的主要参与者。导致深水团偶发性He过量异常的机制尚不清楚。根据盐度与 SMW 的关系，它可能预示着东格陵兰洋流的间歇性溢流射流事件，其中含有密度大于 27.5 的 SMW 水。然而，这些结果基于小型惰性气体数据集。 延续阶段的目标是： (1) 使用比目前可用的更详细的数据集（He、Ne、CFC、SF6）并应用惰性气体过量方法和 OMP，量化格陵兰边界流、拉布拉多和伊尔明格海中 GrIS 的 SMW 分数 (2) 评估 EGC 泄漏源头区域的 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 年是否发现了更多泄漏喷射流中 SMW 事件(3) 使用速度测量值和从瞬态示踪剂（如 CFC 和 SF6）推断的通风时间来计算 SMW 通量(4) 评估拉布拉多海和伊尔明格海中 LSW 的形成和其他相关水团的通风变化了多少。分析负责的过程并估计在哪些关键位置需要存在多少 SMW 才能显着影响相关水团的形成和通风。利用此信息估计 SMW 信号足够强以满足此标准之前的时间段。