Controls on late Holocene and 20th century ice shelf dynamics in northeast Greenland

对格陵兰岛东北部全新世晚期和20世纪冰架动态的控制

• 批准号: 2687334
• 金额: --
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2687334
• 关键词: Controls; late; Holocene; 20th; century

Over the past three decades satellite observations over Greenland and Antarctica have revealed that marine terminating glaciers and ice shelves have been thinning at an accelerating rate in response to both increased air and ocean temperatures. Thinner ice shelves are less able to buttress inland ice, leading to grounding line retreat, increased ice sheet thinning and ultimately, sea-level rise. This process, known as the marine ice sheet instability, has the potential to drive rapid and irreversible ice sheet collapse. Indeed, some ice sheet models indicate that these processes are already underway in Antarctica. In Greenland, several studies have linked recent ice shelf thinning/loss and accelerated ice flow to the incursion of warm Atlantic water. However, understanding the nature and rate of this recent grounding line response to ocean forcing (and other perturbations) requires knowledge of how these processes have evolved over recent centuries. In Antarctica, some changes are known to have started prior to satellite observations, highlighting the need to understand the recent (centennial) history in order to understand the interplay between changing ocean properties and ice sheet dynamics. Such knowledge is essential if we are to accurately predict future ice sheet behaviour as well as the ocean feedbacks in the North Atlantic region. This project will explore the twentieth century evolution of the 79N ice shelf, which currently buttresses the Northeast Greenland ice stream (NEGIS). The NEGIS drains the northeast sector of the Greenland ice Sheet (GrIS) and contains approximately 1.2 m sea-level equivalent (sle). Its future stability is pivotal not only to future mass balance of the GrIS but also the freshwater flux to the northeast Atlantic and specifically, to the North Atlantic Deep Water overturning circulation. Starting in the early 2000s, the ice shelves that front NEGIS (Zachariae Isstrom and 79N) have started to destabilise, but while ZI has disintegrated, 79N has remained relatively stable. Some modelling studies suggest that the 'relative' stability of 79N could continue over the next century, but recent oceanographic observations have shown that ocean heat flux and melt rates maybe increasing. Thus, there is great concern that 79N will be the next ice shelf to disintegrate and if this occurs, it will result in a substantial increase in ice discharge to the ocean.This project will use existing sediment gravity, box and lake sediment cores collected from beneath and adjacent to the 79N ice shelf to reconstruct ice shelf history and Atlantic Water circulation over the last ~200 years. The available material was collected in 2016 and 2017 as part of the NERC project (Greenland in a Warmer Climate) in collaboration with the Alfred Wegener Institute in Germany. Specifically the student will employ a multi-proxy examination of key cores including analyses of sediment properties (physical properties, grain size), geochemical proxies (oxygen, carbon isotopes, XRF, clay mineral) and microfossil content (diatoms, foraminifera) to determine ice shelf presence/absence, changes in ice shelf thickness and water mass characteristics. Foraminiferal and oxygen and carbon stable isotope analyses will be used to investigate the variability in meltwater flux and Atlantic Water adjacent to and beneath the ice shelf. A geochronological framework for changing ice shelf dynamics and incursions of warm water will be determined using radiometric (Pb, Cs) and radiocarbon (C) dating methods. Pb analysis will be critical to establish a chronology twentieth century ice shelf dynamics. Integration of these datasets will enable the processes controlling retreat behaviour to be determined. The successful student will be trained in all aspect of multi-proxy core analyses and wherever possible spend time at key facilities and partner laboratories.In addition, the student will benefit from a large and energetic Polar research communities.

在过去的三十年中，对格陵兰和南极洲的卫星观测结果表明，终止冰川和冰架的海洋终止，以响应升高的空气和海洋温度，以加速的速度变薄。较薄的冰架无法支撑内陆冰，从而导致地面撤退，使冰盖变薄，最终增加海平面上升。这个被称为海洋冰盖不稳定性的过程有可能驱动快速且不可逆转的冰盖崩溃。实际上，一些冰盖模型表明，这些过程已经在南极洲正在进行中。在格陵兰岛，一些研究将最近的冰架稀疏/损失和加速冰流与入侵温暖的大西洋水有关。但是，了解这一最新基础线对海洋强迫（和其他扰动）的响应的性质和速度需要了解这些过程在最近几个世纪的发展。在南极洲，已知有一些变化是在卫星观测之前开始的，突出了需要了解最近（百年）历史以了解不断变化的海洋性能与冰盖动态之间的相互作用的必要性。如果我们要准确预测未来的冰盖行为以及北大西洋地区的海洋反馈，那么这种知识至关重要。该项目将探索79N冰架的20世纪演变，该冰架目前支持东北格陵兰冰流（Negis）。 Negis耗尽了格陵兰冰盖（GRIS）的东北部门，并包含大约1.2 m的海平面等效物（SLE）。它的未来稳定性不仅对格里斯的未来质量平衡至关重要，而且对东北大西洋，特别是北大西洋深水循环的淡水通量至关重要。从2000年代初开始，Negis（Zachariae Isstrom和79n）的冰架开始变得不稳定，但是尽管Zi瓦解了，但79N仍然相对稳定。一些建模研究表明，在下一世纪，79N的“相对”稳定性可能会持续下去，但是最近的海洋学观察结果表明，海洋热通量和熔体速率可能有所增加。因此，非常担心的是，79N将是下一个要分解的冰架，如果发生这种情况，这将导致海洋的冰出排放大幅增加。该项目将使用现有的沉积物重力，盒子和湖泊沉积物核心。在过去的200年中，在79n冰架的下方和附近，重建了冰架历史和大西洋水流。该材料是在2016年和2017年收集的，作为NERC项目（温暖气候中的格陵兰）的一部分，与德国的Alfred Wegener Institute合作。具体而言，学生将对关键核心进行多种检查检查，包括沉积物特性（物理特性，晶粒尺寸），地球化学代理（氧气，碳同位素，XRF，粘土矿物）和微化石含量（二极管，有孔虫）来确定冰确定冰的冰，以确定冰，以确定冰货架的存在/不存在，冰架厚度的变化和水质量特征。有孔虫和氧气和碳稳定的同位素分析将用于研究与冰架相邻和下方的融合水通量和大西洋水的变异性。用于改变冰架动力学和入侵温水的地质框架将使用辐射（PB，CS）和放射性碳（C）约会方法确定。 PB分析对于建立二十世纪冰架动态的年表至关重要。这些数据集的集成将使控制撤退行为的过程能够确定。成功的学生将接受多种核心分析的各个方面的培训，并在可能在关键设施和合作伙伴实验室花费时间的情况下进行培训。此外，该学生将从一个大型且充满活力的极地研究社区中受益。