Geometric and oceanographic controls on melting beneath Pine Island Glacier
Geometric and oceanographic controls on melting beneath Pine Island Glacier
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DOI：
10.1002/2013jc009513
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发表时间：
2014-04-01
影响因子：
3.6
通讯作者：
Jenkins, A.
中科院分区：
文献类型：
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作者：
De Rydt, J.;Holland, P. R.;Jenkins, A.
对松岛冰川漂浮部分下方的观测显示，存在一条冰下脊，其高度比周围海底地形高出达300米。在20世纪70年代之前的某个时期，这一地形特征可能一直是稳定的接地线位置，此后便开始了持续的快速接地线后退阶段。结果，在冰下脊后方形成了一个巨大的海洋空洞，这极大地控制着冰架下方的海洋环流，并调节着导致接地线附近冰层融化的海水性质。为了了解在空洞形成的不同阶段融化速率是如何变化的，我们使用一个高分辨率海洋模型，针对一系列合成几何形状来模拟空洞环流。我们发现，冰下脊的高度以及冰下脊与冰架之间的间隙，强烈控制着温暖底层水流入空洞的情况，进而影响融化速率。模型结果表明，在冰层开始变薄时，融水生成量会因几何因素而迅速增加，但一旦冰下脊与冰架之间的间隙超过约200米这一阈值，融化速率对几何形状的敏感度就会降低。这为一种新的冰 - 海耦合反馈提供了证据，该反馈会加剧冰流从基岩高地的初始后退。目前冰下脊与冰架之间的间隙超过200米，我们的研究结果表明，当前观测到的融化速率变化现在受其他因素控制，比如温跃层的深度。
Observations beneath the floating section of Pine Island Glacier have revealed the presence of a subglacial ridge which rises up to 300 m above the surrounding bathymetry. This topographic feature probably served as a steady grounding line position until sometime before the 1970s, when an ongoing phase of rapid grounding line retreat was initiated. As a result, a large ocean cavity has formed behind the ridge, strongly controlling the ocean circulation beneath the ice shelf and modulating the ocean water properties that cause ice melting in the vicinity of the grounding line. In order to understand how melt rates have changed during the various phases of cavity formation, we use a high-resolution ocean model to simulate the cavity circulation for a series of synthetic geometries. We show that the height of the ridge and the gap between the ridge and ice shelf strongly control the inflow of warm bottom waters into the cavity, and hence the melt rates. Model results suggest a rapid geometrically controlled increase of meltwater production at the onset of ice thinning, but a weak sensitivity to geometry once the gap between the ridge and ice shelf has passed a threshold value of about 200 m. This provides evidence for a new, coupled, ice-ocean feedback acting to enhance the initial retreat of an ice stream from a bedrock high. The present gap is over 200 m, and our results suggest that observed variability in melt rates is now controlled by other factors, such as the depth of the thermocline.