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

我们建议从Thwaites-Pine Island冰川系统中获得地质证据，这将表明冰川是否比现在更广泛，如果是的话，是什么时候。我们的目标是：(i)根据现有的地质证据，确定之前的基准线后退-前进周期是否发生在全新世晚期；（ii）确定它们发生在什么样的气候和海平面边界条件下。确定斯韦茨冰川和松岛冰川接地线在过去后退和再前进的条件，对于确定当今接地线的后退是否不可逆转至关重要。我们将采用两种方法来实现这些目标。为了获得过去接地线后退事件的地质证据，我们将对冰下基岩进行宇宙成因核素暴露测年。使用最近在美国开发的用于冰下基岩开采的钻井系统，并在2016-17南极野外季节得到验证，我们将从Thwaites系统中冰层厚度与接地线位置动态相关的地点获得冰下基岩。在这些样品中观察到显著的宇宙生成核素浓度，将为过去与接地线后退有关的变薄事件以及它们的时间和持续时间的限制提供直接、明确的证据。为了重建全新世的相对海平面，我们将在整个松岛湾绘制和确定凸起的海洋和海岸线沉积物的日期。

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.