Understanding the role of Antarctic sea ice in dense water formation and heat and carbon sequestration: from satellite altimetry to 'big data' analysi

海洋是地球系统中最大的碳库，它储存了人类活动产生的90%以上的多余热量。海洋吸收热量和碳的速度在空间和时间上都有很大的变化，而南大洋是吸收两者的关键区域。然而，我们在预测这种情况未来如何变化方面的技能有限。冰-海洋-大气的相互作用是决定海洋吸收碳和热量速率的关键。南极海冰的形成/输出和绕极西风是南大洋的主要表面强迫，驱动了填充大部分海洋内部的稠密水域的上升流和通风，以及南极底水的形成，而南极底水是全球深海环流的关键组成部分。冰穴——海冰的季节性开口——是形成南极边缘深而稠密的陆架水的另一个主要因素。然而，耦合气候模式对南大洋动力学和环流的模拟很差。即使是最先进的模拟也不能充分地代表冰-海-大气相互作用和生物地球化学过程，而且在这些地区的观测是稀缺和不完整的。方法利用南极海冰引线的卫星全程测高数据，分析冰融区内的海平面，识别密集水形成和循环的指纹。为此，将对来自CryoSat-2（欧洲航天局）和ICESat-2（美国宇航局）极地卫星任务的海面高度和海面高度异常产品进行处理和分析。在第六次耦合模式比对项目（CMIP6）的最新模拟中，将评估驱动南大洋深水形成和环流的过程（如风和海冰动力学）。这将通过建立先进的基于云的计算能力（例如Pangeo）和使用统计工具和机器学习技术来识别和探索冰-海洋-大气过程和相互作用之间的关键关系来实现。这些综合结果将用于确定南极海冰对海洋环流和热量/碳吸收的影响，提高我们对现在和过去趋势的理解，并更熟练地预测这些趋势在未来可能如何变化。2020年，CryoSat-2和ICESat-2的轨道部分对齐，以提供卫星同步测量的独特数据集，并提高南极洲周围海冰测量的准确性。项目工作将包括在NASA进行一次国际访问，在那里正在开发ICESat-2海冰数据。此外，CMIP6模拟档案最近已经可用，并将为政府间气候变化专门委员会（IPCC）的第六次评估报告做出贡献。数值模拟和卫星遥感方面的这些最新进展使这样一个项目特别及时，而处理和解释这些类型的数据产品的能力是国际环境研究中最需要的技能之一。这个博士学位将使学生在一个拥有各种专业知识的国际团队的支持下，熟练掌握这些技术，包括计算机编程和处理“大数据”档案。该学生将在南安普顿的国家海洋学中心工作，并与学生注册的利兹大学、南安普顿大学和英国南极调查局的主管密切合作。将有机会参加南极考察游船。

The ocean is the largest carbon reservoir in the Earth system and it stores over 90% of the excess heat produced by anthropogenic activities. The rate at which both heat and carbon are absorbed by the ocean varies strongly, both in space and time, and the Southern Ocean is a key region for the uptake of both. However, we have limited skills in predicting how this will change in the future. Ice-ocean-atmosphere interactions are key in determining the rates of carbon and heat uptake by the ocean. Antarctic sea ice formation/export and circumpolar westerly winds are the dominant surface forcings in the Southern Ocean, driving the upwelling and ventilation of the dense waters that fill most of the ocean's interior and the formation of Antarctic Bottom Water, a key component of the global abyssal circulation. Polynyas - seasonal openings in the sea ice - are the other main contributors to the formation of deep and dense shelf waters around the Antarctic margins. However, Southern Ocean dynamics and circulation are poorly simulated in coupled climate models. Even state-of-the-art simulations fail to represent both ice-ocean-atmosphere interactions and biogeochemical processes adequately, and observations in these regions are scarce and patchy.MethodsSatellite along-track altimetry data in Antarctic sea ice leads will be used to analyse the ocean's sea level inside polynyas, to identify the fingerprints of dense water formation and circulation. To this end, Sea Surface Height and Sea Height Anomaly products will be processed and analysed from both the CryoSat-2 (European Space Agency) and ICESat-2 (NASA) Polar satellite missions.The representation of processes driving deep water formation and circulation in the Southern Ocean (such as winds and sea ice dynamics) will be assessed in state-of-the-art simulations from the 6th Coupled Model Intercomparison Project (CMIP6). This will be achieved by setting up advanced cloud-based computing capabilities (e.g. Pangeo) and using statistical tools and machine learning techniques to identify and explore the key relationships between ice-ocean-atmosphere processes and interactions.These combined results will be used to determine the effect of Antarctic sea ice on ocean circulation and heat/carbon uptake, improve our understanding of present and past trends, and more skillfully predict how these may change in the future.TrainingThe orbits of CryoSat-2 and ICESat-2 were partially aligned in 2020, to provide a unique dataset of coincident measurements from the satellites and increase the accuracy of sea ice measurements around Antarctica. Project work will include a hosted international visit at NASA, where ICESat-2 sea ice data are being developed. In addition, the CMIP6 archive of simulations has recently become available and will contribute to the 6th assessment report of the Intergovernmental Panel for Climate Change (IPCC).These recent advances in both numerical modelling and satellite remote sensing make such a project especially timely, while the ability to process and interpret these types of data products is among the most in-demand skills in international environmental research. This PhD will enable the student to develop proficiency in these techniques, including computer programming and handling 'big data' archives, with the support of an international team with a diverse range of expertise.The student will be based at the National Oceanography Centre in Southampton and work closely with supervisors based at the University of Leeds, where the student will be registered, the University of Southampton and the British Antarctic Survey. There will be opportunities to participate in Antarctic research cruises.