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

早中新世的年际和轨道尺度气候变率：福尔登玛尔硅藻土的物理、化学和生物研究

• 批准号: 1349659
• 负责人: William D'Andrea
• 金额: $ 24.17万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-04-01 至 2016-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1349659&HistoricalAwards=false
• 关键词: Interannual; Orbital; Scale; Climate; Variability

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.

早中新世的年际和轨道尺度气候变率：Foulden Maar硅藻土的物理、化学和生物学研究[j] .南极地球科学计划（PLR）与沉积地质与古生物学计划（EAR）共同资助。对未来气候的准确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。在湖泊和海洋盆地中积累的沉积物是我们用来研究过去地球气候变化的观测数据的唯一来源。长时间积累的沉积物记录，具有年度分层，并且包含过去气候的自然记录极为罕见，但需要研究全球温度升高下的年际气候变率（例如El Niño-Southern涛动（ENSO）），以及气候系统对地球轨道周期性变化的响应。利用物理和化学沉积学技术的结合，研究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中新世早期温度和水文变化的驱动因素。这项研究将验证一个假设，即赤道太阳能的自然变化导致中纬度气候以大约11000年的速度变化。2)通过发展14个不同千年期的年沉积层厚度记录，记录了中新世早期暖背景状态下不同轨道构型下ENSO变率的性质。这将验证ENSO在全球变暖期间过渡到永久El Niño-like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节ENSO。3)利用化石叶片的气孔密度生成中新世早期极端南极冰川事件期间的大气CO2浓度（pCO2）记录。这将提供重要的数据来检验在这段时间内大气二氧化碳分压在驱动主要气候变化中的作用（或缺乏作用）。新西兰奥塔哥的Foulden Maar硅藻土是一个每年分层的湖泊沉积物序列，它是在10万年的时间里沉积的，也就是2300万年前。这段时期很有趣，因为尽管地球比现在更温暖，但南极冰盖比现在更大，即使没有北半球冰盖。此外，数据表明大气中的二氧化碳分压水平与今天相似。研究人员将利用沉积物中的树叶化石来估算地球过去这个神秘时期的二氧化碳分压，在这个时期，冰盖的行为和全球温度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产量有关，这是一个受气候控制的参数。因此，这些层的厚度可以被测量，并用于检查年际气候变化（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。研究人员将利用沉积物中的有机分子来确定温度和湿度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导致中纬度气候以1.1万年为周期变化的假设。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。这项工作的成果将有助于对地球气候系统、不同气候过程之间的相互作用以及由此产生的对全球气候的影响的基本认识。