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>Emission, distribution, and transport of mineral dust in the Southern Hemisphere, and the dust deposition in Antarctica during present-day and the Last Glacial Maximum.
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Emission, distribution, and transport of mineral dust in the Southern Hemisphere, and the dust deposition in Antarctica during present-day and the Last Glacial Maximum.
Mineral dust is an important component of the atmospheric aerosols in the Earth's climate system, but there are relatively few in-depth investigations of the emission, transport, distribution, and deposition of dust aerosols in the Southern Hemisphere (SH). These physical processes are crucial in climate studies, such as in the understanding of the 10--100 times higher dust concentrations in the Antarctic ice cores during the Last Glacial Maximum (LGM) compared with present-day, but are poorly understood. This dissertation conducts an in-depth investigation into the above areas, and addresses the following questions: (1) What are the characteristics of dust emission, distribution, atmospheric burden and deposition in the SH? (2) What are the contributions from the various continental sources? (3) Are there typical meteorological conditions associated with the transport of dust to the high-latitude SH? (4) What are the plausible causes for the observed high dust concentrations in Antarctic ice cores during the LGM?;The methodology consists of three principal steps, using a combination of the Geophysical Fluid Dynamics Laboratory (GFDL) General Circulation Model (GCM) models, a trajectory model (HYSPLIT), and in situ and satellite observations. First, we investigate the dust cycle in the SH and quantify the contributions of the major sources by tagging dust based on its origin, using the GFDL GCM ("AM2.1n"). Second, the transport of the South American Patagonian dust to Antarctica is diagnosed by analyzing the GFDL model results together with results from the trajectory model simulations and using satellite observations. Third, sensitivity experiments are performed using AM2.1n to determine the sensitivity of the source characteristics, circulation, and precipitation on the dust deposition in Antarctic ice cores during the LGM.;The results show that South America, Australia, and Northern Hemisphere are the main sources of the dust atmospheric burden in the SH, with Northern Hemisphere's contributing up to ∼40% over Antarctica. In the case of dust deposition, South America and Australia combine to contribute more than 85% in Antarctica. In the Antarctica, each source dominates half of a hemisphere along 120°E--60°W: the Pacific half is dominated by the Australian dust while the other half is dominated by the South American Patagonian dust. Trajectory analysis indicates that only 13--20% of air masses from Patagonia reach Antarctica, with ¼ of the air masses getting to West Antarctica in 4--5 days and the other ¾ reaching East Antarctica within 7 days. The transport to East Antarctica is driven by the low pressure systems moving eastward in the subpolar low-pressure zone, while southward transport to West Antarctica typically happens when a high pressure system over the Atlantic Ocean blocks depression in the Drake Passage. These two mechanisms are consistent with available satellite observations.;For the LGM climate, the model simulations show that the expansion of source areas and changes in the Antarctic ice accumulation rates together can account for most of the observed increase of dust concentrations in the Vostok, Dome C and Taylor Dome cores, but there is an overestimate of the LGM-to-present ratio in the case of the Byrd core. The source expansion due to the lowering of sea level yields a factor of 2--3 higher contribution than that due to the reduction of continental vegetation. The changes in other climate parameters (e.g., SH precipitation change) are estimated to be relatively less important within the context of this sensitivity study, while the model-simulated LGM surface winds yield a 20--30% reduction rather than an increase in dust deposition in Antarctica. The outcomes of the research provide a fundamental understanding of the emission and distribution of dust in the SH and of the causes for the significant enhancement of the dust deposition in the Antarctic ice cores during the LGM.
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机译：矿物粉尘是地球气候系统中大气气溶胶的重要组成部分，但对南半球（SH）中粉尘气溶胶的排放，运输，分布和沉积的深入研究相对较少。这些物理过程在气候研究中至关重要，例如对于了解“最后一次冰盛期”（LGM）期间南极冰芯中的尘埃浓度要比当今高10--100倍，却知之甚少。本文对上述领域进行了深入的研究，并提出了以下问题：（1）西南地区的粉尘排放，分布，大气负荷和沉积的特征是什么？ （2）来自各个大陆的贡献是什么？ （3）是否有典型的气象条件与尘埃向高纬度SH的传输有关？ （4）在LGM期间观察到南极冰芯中高粉尘浓度的可能原因是什么？;该方法包括三个主要步骤，结合了地球物理流体动力学实验室（GFDL）通用循环模型（GCM）模型，轨迹模型（HYSPLIT），原位和卫星观测。首先，我们使用GFDL GCM（“ AM2.1n”），通过对尘埃的来源进行标记来对SH中的尘埃循环进行调查，并量化主要来源的贡献。其次，通过分析GFDL模型结果，轨迹模型模拟结果以及使用卫星观测结果，诊断了南美巴塔哥尼亚尘埃向南极洲的传输。第三，利用AM2.1n进行敏感性实验，确定南极冰期在南极冰芯的尘埃沉积过程中，气源特征，环流和降水的敏感性。结果表明，南美，澳大利亚和北半球是南半球尘埃大气负担的主要来源，北半球占南极的约40％。就粉尘沉积而言，南美和澳大利亚合计占南极洲的85％以上。在南极洲，沿120°E--60°W的每个源都占半球的一半：太平洋的一半由澳大利亚的尘埃占主导，而另一半则由南美的巴塔哥尼亚尘埃占主导。轨迹分析表明，来自巴塔哥尼亚的气团只有13--20％到达南极洲，其中1/4的气团在4--5天内到达西南极洲，其他3/4的气团在7天内到达南极洲。往南极东部的输送是由在极极低压区中向东移动的低压系统驱动的，而向南极西部的输送通常是在大西洋上空的高压系统阻塞德雷克海峡的低压时发生的。这两种机制与现有的卫星观测结果是一致的。；对于LGM气候，模型模拟表明，源区域的扩展和南极冰蓄积率的变化共同可以解释所观测到的沃斯托克尘埃浓度增加的大部分， Dome C和Taylor Dome核心，但是在Byrd核心的情况下，LGM与现在的比率被高估了。由于海平面降低，源头扩张产生的贡献比大陆植被减少所致的贡献要高出2--3倍。在此敏感性研究的背景下，估计其他气候参数的变化（例如，SH降水变化）的重要性相对较小，而模型模拟的LGM表面风产生的尘埃减少而不是尘埃增加了20--30％沉积在南极洲。研究的结果提供了对南半球上沙尘埃的排放和分布以及南极冰期期间南极冰芯中沙尘沉积显着增加的原因的基本理解。
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