Ice-ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers
Ice-ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers
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DOI：
10.5194/tc-8-1457-2014
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发表时间：
2014-01-01
期刊：
影响因子：
5.2
通讯作者：
Patton, H.
中科院分区：
文献类型：
--
作者：
Chauche, N.;Hubbard, A.;Patton, H.
来自亚热带的温暖大西洋水(AW)已被确定为格陵兰冰盖(GRIS)海洋部分质量损失的主要驱动因素，但这种水团与潮水冰川崩解锋面相互作用并侵蚀的具体过程经常被模拟和推测，但在很大程度上仍未被观察到。我们提供了一套峡湾盐度、温度、浊度与深度的预测，以及Rink和Store冰川的冰川径流估计，这两个主要的海洋出口在2009年和2010年期间排干了GRIS西段的水。我们描述了存在的主要水体的特征，并解释了它们与各自的崩解锋面的相互作用。我们确定了两种不同的冰-海洋相互作用过程，它们具有不同的空间和时间足迹：(1)均质自由对流融化发生在AW与冰块直接接触的崩解锋面上，以及(2)由冰川下湍急的径流与峡湾水混合而导致的局部上升流驱动融化，该融化发生在崩解锋面的不同注入点处。在整个研究过程中，始终观察到2.8+/-0.2摄氏度的AW与450米以下的两个冰川接触，导致均匀的自由对流潜艇融化到类似200米的深度。在这一底层以上，确定了多种相互作用，主要由冰下淡水排放的速度控制，这导致了局部和离散的上升流羽流。在2010年创纪录的融化年，Store Glacier的崩解面被这些径流驱动的羽流所主导，这导致了高度扭曲的锋面几何结构，其特点是冰下门户处有大片海湾，中间隔着以崩解为主的海角。Rink Glacier比Store深得多，其淹没的冰解面有更大比例暴露在AW下，这导致了均匀、相对平坦的整体正面几何形状。
Warm, subtropical-originating Atlantic water (AW) has been identified as a primary driver of mass loss across the marine sectors of the Greenland Ice Sheet (GrIS), yet the specific processes by which this water mass interacts with and erodes the calving front of tidewater glaciers is frequently modelled and much speculated upon but remains largely unobserved. We present a suite of fjord salinity, temperature, turbidity versus depth casts along with glacial runoff estimation from Rink and Store glaciers, two major marine outlets draining the western sector of the GrIS during 2009 and 2010. We characterise the main water bodies present and interpret their interaction with their respective calving fronts. We identify two distinct processes of ice-ocean interaction which have distinct spatial and temporal footprints: (1) homogenous free convective melting which occurs across the calving front where AW is in direct contact with the ice mass, and (2) localised upwelling-driven melt by turbulent subglacial runoff mixing with fjord water which occurs at distinct injection points across the calving front. Throughout the study, AW at 2.8 +/- 0.2 degrees C was consistently observed in contact with both glaciers below 450 m depth, yielding homogenous, free convective submarine melting up to similar to 200 m depth. Above this bottom layer, multiple interactions are identified, primarily controlled by the rate of subglacial fresh-water discharge which results in localised and discrete upwelling plumes. In the record melt year of 2010, the Store Glacier calving face was dominated by these runoff-driven plumes which led to a highly crenulated frontal geometry characterised by large embayments at the subglacial portals separated by headlands which are dominated by calving. Rink Glacier, which is significantly deeper than Store has a larger proportion of its submerged calving face exposed to AW, which results in a uniform, relatively flat overall frontal geometry.