Interannual and Orbital-Scale Climate Variability in the Early Miocene: Physical, Chemical and Biological Investigations of the Foulden Maar Diatomite

《中新世早期的年际和轨道尺度的气候变异性：福尔登-玛尔硅藻的物理、化学和生物调查》，作者：William D‘Andrea，EAR-1349659ABSTRACT(南极地球科学计划(PLR)与地质古生物学计划(EAR)共同资助了这笔赠款。准确的未来气候预测需要对地球气候系统及其在过去暖期的行为有一个基本的了解。湖泊和海洋盆地中积累的沉积物是我们研究地球过去深处气候变化的唯一观测数据来源。长期积累、具有年度分层并载有过去气候的自然记录的沉积物记录极为罕见，但对于调查全球变暖情况下的年际气候变异性(例如，厄尔尼诺-南方涛动)以及气候系统对地球轨道周期性变化的反应是必要的。使用物理和化学沉积学技术的组合，调查人员将利用特殊的沉积记录来实现以下目标：1)利用有机地球化学和稳定同位素技术确定亚轨道时间尺度上早中新世温度和水文变化的驱动因素。这项研究将检验这一假设，即赤道太阳能的自然变化会导致中纬度气候的变化，步调大约为11,000年。2)通过发展14个不同的1000年不同周期的年沉积层厚度记录，记录了早中新世温暖背景状态下不同轨道配置下ENSO变化的性质。这将检验ENSO在全球变暖期间转变为永久的类似厄尔尼诺状态的假设，并将有助于确定气候系统在变暖的世界中的行为，以及轨道强迫如何调制ENSO。3)利用化石树叶的气孔密度记录了早中新世南极极端冰川事件的大气二氧化碳浓度(PCO2)。这将为研究大气二氧化碳在推动这一时期的重大气候变化中的作用(或缺乏作用)提供重要数据。新西兰奥塔哥的Foulden Maar硅藻土是一个每年分层的湖泊沉积序列，沉积于2300万年前的10万年前。这段时间很有趣，因为尽管地球比现在温暖，但南极冰盖比现在的大小更大，即使没有北半球冰盖。此外，数据表明，大气中的二氧化碳水平与今天类似。研究人员将使用沉积物中的化石树叶来估计地球过去这段神秘时期的二氧化碳分压，这段时间冰盖和全球温度的行为与现有的二氧化碳分压数据不一致。年沉积层的厚度与湖泊中藻类的生产力有关，这是一个受气候控制的参数。因此，这些层的厚度可以测量并用来检查年际气候变化(特别是ENSO)在这段时间内的表现，以及它是否由于地球轨道的自然变化而发生变化。研究人员将使用沉积物中的有机分子来确定温度和水分在这段时间内是如何变化的，并将检验赤道太阳能的自然变化会导致中纬度气候以11000年为一个周期变化的假设。这些结果将有助于更好地理解影响ENSO动力学的自然强迫机制及其对中纬度气候的影响。拟议工作的成果将有助于从根本上了解地球气候系统、不同气候过程之间的相互作用以及由此对全球气候的影响。

Interannual and Orbital-Scale Climate Variability in the Early Miocene: Physical, Chemical and Biological Investigations of the Foulden Maar DiatomitebyWilliam D'Andrea, Columbia University, EAR-1349659ABSTRACT(The Antarctic Earth Sciences Program (PLR) co-funded the grant with the Seimentary Geology and Paleobiology Program (EAR).Accurate climate projections for the future require a fundamental understanding of Earth's climate system and its behavior during past warm periods. Sediments that have accumulated in lakes and ocean basins are our only source for observational data to examine changes in Earth's climate in the deep past. Sediment records that accumulated over long periods of time, have annual layering and which contain natural recorders of past climate are extremely rare, but are needed to investigate inter-annual climate variability (for example, the El Niño-Southern Oscillation (ENSO)) under warmer global temperature, as well as the response of the climate system to periodic variations in Earth's orbit. Using a combination of physical and chemical sedimentological techniques, the investigators will take advantage of an exceptional sedimentary record to achieve the following goals:1) Determine the drivers of early Miocene temperature and hydrologic change at suborbital timescales using organic geochemical and stable isotopic techniques. The research will test the hypothesis that natural changes in solar energy at the equator cause variations in mid-latitude climate with a pacing of approximately 11,000 years. 2) Document the nature of ENSO variability under different orbital configurations within the warm background state of the early Miocene by developing records of annual sediment layer thickness across fourteen different 1,000-yr periods. This will test the hypothesis that ENSO transitions to a permanent El Niño-like state during periods of global warmth and will help determine how the climate system behaves in a warmer world and how orbital forcing modulates ENSO. 3) Produce a record of atmospheric CO2 concentrations (pCO2) across an extreme Antarctic glaciation event in the early Miocene using stomatal density of fossil leaves. This will provide important data to examine the role (or lack thereof) of atmospheric pCO2 in driving major climate changes during this time period. The Foulden Maar Diatomite in Otago, New Zealand is an annually layered lake-sediment sequence that was deposited during a 100,000-year period, 23 million years ago. This time period is interesting because although the planet was warmer than present, Antarctic Ice Sheets grew larger than their present size, even though there were no Northern Hemisphere Ice Sheets. Furthermore, data suggest that atmospheric pCO2 levels were similar to today. The investigators will use fossil leaves in the sediments to estimate pCO2 across this enigmatic period of Earth's past, a time when the behavior of ice sheets and global temperature is at odds with the existing pCO2 data. The thickness of the annual sediment layers is related to the productivity of algae in the lake, a parameter controlled by climate. The thickness of these layers can therefore be measured and used to examine how inter-annual climate variability (specifically, ENSO) behaved during this time period and whether it changed due to the natural changes in Earth's orbit. The researchers will determine how temperature and moisture changed over this time period using organic molecules in the sediments and will test the hypothesis that natural changes in solar energy at the equator cause variations in mid-latitude climate with an 11,000-year cycle. The results will contribute to a better understanding of the natural forcing mechanisms that impact ENSO dynamics and its influence on mid-latitude climate. The outcomes of the proposed work will contribute to the fundamental understanding of Earth's climate system, interactions among different climatic processes, and the resulting impacts on global climate.