Late Neogene Ice Drainage Changes in Prydz Bay, East Antarctica and the Interaction of Antarctic Ice Sheet Evolution and Climate

During the late Neogene, the Lambert Glacier-Amery Ice Shelf drainage system flowed across Prydz Bay and showed several changes in flow pattern. In the Early Pliocene, the Lambert Glacier ice stream reached the shelf edge and built a trough mouth fan on the upper continental slope. This was associated with an increase in ice discharge from the Princess Elizabeth Land coast into Prydz Bay. The trough mouth fan consists mostly of debris flow deposits derived from the melting out of subglacial debris at the grounding line at the continental shelf edge. The composition of debris changes at around 1.1 Ma BP from material derived from erosion of the Lambert Graben and Prydz Bay Basin to mostly basement derived material. This probably results from a reduction in the depth of erosion and hence the volume of ice in the system. In the trough mouth fan, debris flow intervals are separated by thin mudstone horizons deposited when the ice had retreated from the shelf edge. Age control in an Ocean Drilling Program hole indicates that most of the trough mouth fan was deposited prior to the Brunhes Matuyama Boundary (780 ka BP). This stratigraphy indicates that extreme ice advances in Prydz Bay were rare after the mid Pleistocene, and that ice discharge from Princess Elizabeth Land became more dominant than the Lambert Glacier ice in shelf grounding episodes, since the mid Pleistocene. Mechanisms that might have produced this change are extreme inner shelf erosion and/or decreasing ice accumulation in the interior of East Antarctica. We interpret this pattern as reflecting the increasing elevation of coastal ice through time and the increasing continentality of the interior of the East Antarctic Ice Sheet. The mid Pleistocene change to 100 ka climatic and sea level cycles may also have affected the critical relationship between ice dynamics and the symmetry or asymmetry of the interglacial/glacial climate cycle duration.

晚新近纪（late Neogene）时期，兰伯特冰川-埃默里冰架水系（Lambert Glacier-Amery Ice Shelf drainage system）流经普里兹湾（Prydz Bay），其流态曾发生多次显著变化。上新世早期（Early Pliocene），兰伯特冰川冰流抵达陆架边缘，并在大陆坡上部发育了槽口扇（trough mouth fan），这一沉积过程与伊丽莎白公主地（Princess Elizabeth Land）海岸向普里兹湾的冰体排放量增加密切相关。槽口扇主体由大陆架边缘接地带（grounding line at the continental shelf edge）处冰下碎屑（subglacial debris）熔融卸载形成的碎屑流沉积构成。约1.1 Ma BP时，碎屑组成发生转变：从原本源自兰伯特地堑（Lambert Graben）与普里兹湾盆地（Prydz Bay Basin）侵蚀的物质，逐渐转变为以基底（basement）成因物质为主，这一转变可能源于水系内侵蚀深度的缩减，进而导致系统内冰体体积减小。在槽口扇沉积序列中，碎屑流沉积层被薄泥岩层分隔，这些泥岩形成于冰体从陆架边缘后退的时段。大洋钻探计划（Ocean Drilling Program）钻孔的年代约束数据显示，槽口扇的绝大部分沉积都形成于布容-松山界限（Brunhes-Matuyama Boundary，780 ka BP）之前。该地层记录表明，更新世中期（mid Pleistocene）之后，普里兹湾内的极端冰进事件已十分罕见；且自更新世中期起，在陆架接地事件中，伊丽莎白公主地的冰体补给逐渐取代兰伯特冰川冰流，占据主导地位。可能驱动这一转变的机制包括极端内陆架侵蚀，以及/或东南极冰盖（East Antarctic Ice Sheet）内部的冰积累量下降。我们将这一演化模式解读为：随着时间推移，沿岸冰体高程持续升高，同时东南极冰盖内部的大陆性特征不断增强。此外，更新世中期转变为10万年尺度的气候与海平面旋回，也可能影响了冰体动力学与冰期-间冰期气候周期时长对称性之间的关键关联。