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.

过去30年来，对格陵兰岛和南极洲的卫星观测表明，由于空气和海洋温度的升高，海洋终止冰川和冰架一直在加速变薄。较薄的冰架不太能够支撑内陆冰，导致接地线后退，冰盖变薄，最终导致海平面上升。这一过程被称为海洋冰盖不稳定性，有可能导致冰盖迅速和不可逆转的崩溃。事实上，一些冰盖模型表明，这些过程已经在南极洲进行。在格陵兰岛，有几项研究将最近的冰架变薄/丧失和冰流加速与大西洋暖流的入侵联系起来。然而，要了解这条最近的接地线对海洋强迫（和其他扰动）的响应的性质和速率，需要了解这些过程在最近几个世纪是如何演变的。在南极洲，已知一些变化在卫星观测之前就已开始，这突出表明需要了解最近（百年）的历史，以便了解不断变化的海洋特性与冰盖动态之间的相互作用。如果我们要准确地预测未来冰盖的行为以及北大西洋区域海洋的反馈，这种知识是必不可少的。该项目将探讨世纪北纬79度冰架的演变，该冰架目前支撑着格陵兰东北部冰流。NEGIS排放格陵兰冰盖（GrIS）的东北部分，包含约1.2米的海平面当量（sle）。其未来的稳定性是至关重要的，不仅未来的质量平衡的GrIS，但也淡水通量的东北大西洋，特别是北大西洋深水翻转环流。从21世纪初开始，NEGIS（Zachariae Istrom和79 N）前面的冰架开始不稳定，但尽管ZI已经解体，79 N仍然保持相对稳定。一些模拟研究表明，79 N的“相对”稳定性可能会持续到下一个世纪，但最近的海洋学观测表明，海洋热通量和融化率可能会增加。因此，人们非常担心79 N将是下一个冰架解体，如果发生这种情况，它将导致大量增加的冰排放到海洋中。本项目将利用现有的沉积物重力，箱和湖泊沉积物芯收集从下面和邻近的79 N冰架重建冰架的历史和大西洋水循环在过去的200年。现有的材料是在2016年和2017年收集的，作为与德国阿尔弗雷德·韦格纳研究所合作的NERC项目（气候变暖中的格陵兰岛）的一部分。具体而言，学生将采用关键核心的多代理检查，包括沉积物特性（物理特性，粒度），地球化学代理（氧，碳同位素，XRF，粘土矿物）和微体化石含量（硅藻，有孔虫）的分析，以确定冰架存在/不存在，冰架厚度和水团特征的变化。有孔虫和氧和碳稳定同位素分析将用于调查冰架附近和冰架下的融水通量和大西洋水的变化。将利用放射性（铅、铯）和放射性碳（C）定年法确定一个不断变化的冰架动态和暖水侵入的地质年代学框架。铅分析将是建立年代学二十世纪冰架动力学的关键。这些数据集的整合将使控制撤退行为的过程得以确定。成功的学生将接受多代理岩心分析各个方面的培训，并在可能的情况下在关键设施和合作伙伴实验室度过一段时间。此外，学生将受益于一个庞大而充满活力的Polar研究社区。