Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet
Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet
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DOI：
10.1016/j.quascirev.2018.03.013
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发表时间：
2018-06
影响因子：
4
通讯作者：
M. Margold;C. Stokes;C. Clark
中科院分区：
文献类型：
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作者：
M. Margold;C. Stokes;C. Clark
本文从末次冰盛期(LGM)重建了Laurentide冰盖(LIS；包括Innuitian冰盖)的冰川消融过程，重点研究了冰流的时空变化以及与之相关的流型和冰分的变化。我们基于最近对Laurentide冰流的清点，并使用现有的冰缘年代学来制作LIS冰流排水网络的第一个详细的瞬时重建，我们在一系列古地理地图中描绘了这一点。结果表明，LGM的排水网络类似于今天的南极洲。大多数冰流是海洋末端和地形控制的，其中许多在冰川消融后期继续发挥作用，直到冰盖失去海洋边缘。西部和南部有陆地冰缘的冰流更多是瞬变的，冰流方向随着科迪勒兰-劳伦蒂冰鞍区的形成、峰值和坍塌而改变。加拿大大西洋的东南部海洋边缘相对较早地开始消退，该区域的一些冰流在末次冰盖日数日或之后不久停止。相比之下，在波弗特海和巴芬湾流向西北和东北部海洋边缘的冰川似乎在冰川晚期的大部分时间里保持稳定，其中一些冰川继续发挥作用，直到较年轻的仙女座(YD)之后。亚迪影响了冰川消融的动态，但在几个领域，冰盖的反应仍然存在不确定性。我们初步认为这一时期一些主要冰流(如西北边缘的M‘Clintock海峡冰流)的开启，但对于其他与YD时间部分重叠的大冰流，驱动因素不太清楚，更有可能的驱动因素是冰动力过程，而不是气候和地表物质平衡的影响。在YD和冰盖变得仅限于加拿大盾之后，撤退速度明显增加。这种坚硬的底物带来了冰流特征的变化，冰流变得不那么频繁，但产生了更广泛的陆地冰流。在冰盖的最终崩塌中，哈德逊湾及其周围的冰盖几何形状迅速变化，形成了一系列短暂的小冰流。我们的重建表明，在冰川消融的后期，LIS经历了一个由地形控制的冰川排水网络向以较少频繁、宽广的冰流为特征的冰川排水网络的过渡。这些非冰川冰流主要被解释为对局部冰动力强迫(冰川湖泊和海侵海洋中冰锋的漂浮和崩解；由于大量融水到达海床，由于冰盖几何形状的快速变化而脱钩)的反应，而不是从冰盖积累区输送多余质量。在冰盖规模上，随着冰川消融冰盖的缩小，冰流排水网络变得不那么广泛，效率也越来越低，最终消除冰川的主要原因是表面融化。
This paper reconstructs the deglaciation of the Laurentide Ice Sheet (LIS; including the Innuitian Ice Sheet) from the Last Glacial Maximum (LGM), with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides. We build on a recent inventory of Laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the LIS, which we depict in a series of palaeogeographic maps. Results show that the drainage network at the LGM was similar to modern-day Antarctica. The majority of the ice streams were marine terminating and topographically-controlled and many of these continued to function late into the deglaciation, until the ice sheet lost its marine margin. Ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build-up, peak-phase and collapse of the Cordilleran-Laurentide ice saddle. The south-eastern marine margin in Atlantic Canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the LGM. In contrast, the ice streams draining towards the north-western and north-eastern marine margins in the Beaufort Sea and in Baffin Bay appear to have remained stable throughout most of the Late Glacial, and some of them continued to function until after the Younger Dryas (YD). The YD influenced the dynamics of the deglaciation, but there remains uncertainty about the response of the ice sheet in several sectors. We tentatively ascribe the switching-on of some major ice streams during this period (e.g. M'Clintock Channel Ice Stream at the north-west margin), but for other large ice streams whose timing partially overlaps with the YD, the drivers are less clear and ice-dynamical processes, rather than effects of climate and surface mass balance are viewed as more likely drivers. Retreat rates markedly increased after the YD and the ice sheet became limited to the Canadian Shield. This hard-bed substrate brought a change in the character of ice streaming, which became less frequent but generated much broader terrestrial ice streams. The final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around Hudson Bay. Our reconstruction indicates that the LIS underwent a transition from a topographically-controlled ice drainage network at the LGM to an ice drainage network characterised by less frequent, broad ice streams during the later stages of deglaciation. These deglacial ice streams are mostly interpreted as a reaction to localised ice-dynamical forcing (flotation and calving of the ice front in glacial lakes and transgressing sea; basal de-coupling due to large amount of meltwater reaching the bed, debuttressing due to rapid changes in ice sheet geometry) rather than as conveyors of excess mass from the accumulation area of the ice sheet. At an ice sheet scale, the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet, the final elimination of which was mostly driven by surface melt.