NSFPLR-NERC: Geological history constraints on the magnitude of grounding line retreat in the Thwaites Glacier system

我们建议从斯韦茨-松岛冰川系统中获得地质证据，以表明冰川是否比现在更小，如果是，什么时候。我们的目标是：(1)确定现有地质证据所表明的以前的接地线退缩-前进周期是否发生在全新世晚期，以及(2)确定它们发生在什么气候和海平面边界条件下。确定Thwaites和Pine Island冰川接地线过去撤退和重新推进的条件，对于确定现在的接地线撤退是否不可逆转至关重要。我们将利用两种方法来实现这些目标。为了获得过去接地线退缩事件的地质证据，我们将对冰下基岩进行宇宙源核素暴露测年。使用美国最近开发的用于冰下基岩恢复的钻探系统，并在2016-17年南极野外考察季节得到验证，我们将从冰层厚度与Thwaites系统中接地线位置动态联系的地点获得冰下基岩。在这些样品中观察到重要的宇宙源核素浓度，将为过去与接地线后退有关的变薄事件提供直接、明确的证据，并限制其时间和持续时间。为了重建全新世的相对海平面，我们将绘制整个松岛湾上升的海洋和海岸线沉积物的地图并确定日期。

We propose to obtain geological evidence from the Thwaites-Pine Island glacier system that will show whether glaciers were less extensive than they are at present, and, if so, when. Our goals are to: (i) determine whether previous grounding-line retreat-advance cycles, as suggested by existing geological evidence, occurred in the late Holocene, and (ii) establish under what climate and sea-level boundary conditions they took place. Determining the conditions under which the Thwaites and Pine Island Glacier grounding lines have retreated and re-advanced in the past is critically relevant to determining whether or not present-day grounding-line retreat is irreversible.We will utilize two approaches to achieve these goals. To obtain geological evidence for past grounding-line retreat episodes, we will apply cosmogenic-nuclide exposure-dating of subglacial bedrock. Using drill systems recently developed in the USA for subglacial bedrock recovery and proven in the 2016-17 Antarctic field season, we will obtain subglacial bedrock from sites where ice thickness is dynamically linked to grounding line position in the Thwaites system. The observation of significant cosmogenic-nuclide concentrations in these samples would provide direct, unambiguous evidence for past episodes of thinning linked to grounding line retreat as well as constraints on their timing and duration. To reconstruct Holocene relative sea level, we will map and date raised marine and shoreline deposits throughout Pine Island Bay.