Collaborative Research: Kr-86 as a Proxy for Barometric Pressure Variability and Movement of the SH Westerlies during the last Deglaciation

大约一半的人类造成的二氧化碳排放到大气中被海洋吸收，这减少了与这些排放相关的全球变暖量。大部分的碳吸收发生在南极洲周围的南大洋，那里的水从深海来到海面。有多少水被“上井”，从而有多少碳被吸收，被认为取决于南半球主要西风的强度和位置。近几十年来，这些风的模式一直在向南移动，未来的变化可能会影响全球碳循环，并促进从深海到大陆架的相对温暖的水的循环，这有助于加速南极冰融化和海平面上升。因此，了解西风及其在控制大气二氧化碳水平和海水循环中的作用是非常重要的。该奖项支持的工作将研究西风带在过去对自然气候变化的响应。特别令人感兴趣的是最后一次消冰期（2万到1万年前），当时全球气候从冰期气候过渡到目前的暖期。在此期间，大气中的二氧化碳含量从百万分之180上升到百万分之270，一个主要的假设是，二氧化碳含量的上升是由南半球西风带向南移动所驱动的。这项工作的更广泛影响包括对南半球西风带过去的运动及其与大气二氧化碳的联系的看法，这可以指导对未来海洋二氧化碳吸收的预测，具有强大的社会效益；与德国科学家的国际合作；培养博士后科研人员；并延伸到公立学校。这个项目将调查困在南极冰芯中的稀有气体氪-86的丰度是否记录了大气压力的变化，以及这种压力的变化是否可以用来推断过去南半球西风的运动。该项目的基本原理是，南极雪堆（firn）中的空气运动模型表明，压力变化驱动空气运动，扰乱了由气体重力沉降引起的氪-86的正常富集。计算预测氪-86偏离引力平衡反映了压力变化的大小。反过来，大气数据表明，南极洲上空的气压变化与南半球西风的位置有关。南极西部冰原（WAIS）分界冰芯的初步资料显示，在末次冰期到当前暖期的过渡期间，氪-86发生了较大的偏移。研究人员将对冰芯和冷空气样本进行氪-86分析，以确定氪-86偏差是否与压力变化有关，改进来自WAIS分界冰芯的氪同位素记录，利用冷空气模型研究压力变化在冷空气运输中的作用，并研究南极洲的气压变化如何与过去和现在气候中SH西风带的位置/强度联系起来。

Brook 1543267Approximately half of the human caused carbon dioxide emissions to the atmosphere are absorbed by the ocean, which reduces the amount of global warming associated with these emissions. Much of this carbon uptake occurs in the Southern Ocean around Antarctica, where water from the deep ocean comes to the surface. How much water "up-wells," and therefore how much carbon is absorbed, is believed to depend on the strength and location of the major westerly winds in the southern hemisphere. These wind patterns have been shifting southward in recent decades, and future changes could impact the global carbon cycle and promote the circulation of relatively warm water from the deep ocean on to the continental shelf, which contributes to enhanced Antarctic ice melt and sea level rise. Understanding of the westerly winds and their role in controlling atmospheric carbon dioxide levels and the circulation of ocean water is therefore very important. The work supported by this award will study past movement of the SH westerlies in response to natural climate variations. Of particular interest is the last deglaciation (20,000 to 10,000 years ago), when the global climate made a transition from an ice age climate to the current warm period. During this period, atmospheric carbon dioxide rose from about 180 ppm to 270 parts per million, and one leading hypothesis is that the rise in carbon dioxide was driven by a southward movement of the southern hemisphere westerlies. The broader impacts of the work include a perspective on past movement of the southern hemisphere westerlies and their link to atmospheric carbon dioxide, which could guide projections of future oceanic carbon dioxide uptake, with strong societal benefits; international collaboration with German scientists; training of a postdoctoral investigator; and outreach to public schools. This project will investigate whether the abundance of a noble gas, krypton-86, trapped in Antarctic ice cores, records atmospheric pressure variability, and whether or not this pressure variability can be used to infer past movement of the Southern Hemisphere westerly winds. The rationale for the project is that models of air movement in the snow pack (firn) in Antarctica indicate that pressure variations drive air movement that disturbs the normal enrichment in krypton-86 caused by gravitational settling of gases. Calculations predict that the krypton-86 deviation from gravitational equilibrium reflects the magnitude of pressure variations. In turn, atmospheric data show that pressure variability over Antarctica is linked to the position of the southern hemisphere westerly winds. Preliminary data from the West Antarctic Ice Sheet (WAIS) Divide ice core show a large excursion in krypton-86 during the transition from the last ice age to the current warm period. The investigators will perform krypton-86 analysis on ice core and firn air samples to establish whether the Kr-86 deviation is linked to pressure variability, refine the record of krypton isotopes from the WAIS Divide ice core, investigate the role of pressure variability in firn air transport using firn air models, and investigate how barometric pressure variability in Antarctica is linked to the position/strength of the SH westerlies in past and present climates.