Reconciling substrate specific differences in the carbon isotope excursion marking the Paleocene-Eocene thermal maximum.

协调标志着古新世-始新世热最大值的碳同位素偏移中基质的特定差异。

• 批准号: 1405224
• 负责人: D Kelly
• 金额: $ 31.37万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1405224&HistoricalAwards=false
• 关键词: Reconciling; substrate; specific; differences; carbon

Model predictions and long-range forecasts for future climate change are partly based on studies of geologic records of past global warming events. One such global warming event occurred ~55.8 million years ago and is referred to as the Paleocene-Eocene thermal maximum (PETM). Study of geologic records around the world has shown that surface temperatures warmed 5-8°C, biochemical processes were altered, and the global biosphere was profoundly perturbed during this time. However, the most distinctive hallmark of the PETM is a precipitous decrease in the stable carbon isotope (13C/12C) ratios of terrestrial and marine carbon-bearing materials. This carbon isotope excursion (CIE) has been documented at numerous locations across the globe, and its ubiquity signals the rapid release of massive quantities of isotopically light carbon (12C) into the ocean-atmosphere system. The source of this carbon is still debated, but the most parsimonious explanation invokes the dissociation of massive quantities of sedimentary methane hydrate along continental slopes. The fact that this ancient global warming event is closely linked to a major perturbation to the global carbon cycle uniquely qualifies the PETM as an analogue for future climate change driven by current societal practices.A key piece of evidence for estimating the amount of carbon emitted during the PETM is the magnitude of the CIE, yet it has long been recognized that different carbon-bearing substrates yield different CIE magnitudes. For example, the CIE reported from terrestrial records (soil nodules and land plant remains) is about twice as large as indicated by measurements of marine sediments. This discrepancy is vexing because gases are readily exchanged across the air-sea interface so that the physiochemical state of the surface ocean should equilibrate with the atmosphere on time scales virtually instantaneous by geologic standards. Hence, the magnitude of the CIE in terrestrial and surface-ocean records should be similar, yet this is not borne out by published records. The vast majority of marine PETM records are derived from the stable isotopic compositions of tiny (1 mm) calcite shells grown by planktic foraminifera, an extant group of amoeboid protists with a rich fossil record. The preponderance of planktic foraminiferal shells in deep-sea sediments has made them a preferred substrate for studies using geochemical analyses to reconstruct past ocean/climate change. However, a problem plaguing such records is that post-depositional processes on the seafloor can alter the original chemical compositions of foraminiferal shells, thereby biasing stable isotope records used to reconstruct past climate conditions like those that prevailed during the PETMAt the Wisconsin Secondary Ion Mass Spectrometer (WiscSIMS) laboratory, novel in situ techniques have been developed for measuring stable isotope ratios in tiny (~10 micrometers) targets in calcite samples. This approach permits the identification and analysis of subdomains inside foraminiferal shells that are less affected by chemical alteration and therefore provide a more accurate record of past climatic conditions. Currently, these stable isotope measurements cannot be performed by any other technique. First results from a pilot study indicate that the CIE magnitude recorded within these well-preserved subdomains in planktic foraminiferal shells is actually twice as high as previously reported and thus highly congruous with the CIE magnitude in terrestrial records. This project focuses on obtaining a more accurate measurement of the CIE magnitude. Determining the true magnitude of the CIE is important because it will (1) better constrain the amount of carbon emitted, (2) provide a more realistic testing ground for assessing the viability of proposed sources of the carbon input, (3) improve our ability to gauge climate sensitivity to greenhouse gas forcing, (4) help identify feedback mechanisms within the climate system that either amplify or attenuate global warming, and (5) make it possible to better calibrate biotic (terrestrial and marine) responses to environmental change driven by rapid carbon input. This project will benefit the graduate education of a young female scientist, and provide infrastructure support for the WiscSIMS laboratory where transformative, cutting-edge analytical technologies are being developed.

模型预测和未来气候变化的远程森林部分基于对过去全球变暖事件的地质记录的研究。一项这样的全球变暖事件发生在5580万年前，被称为古新世热最大（PETM）。对世界各地的地质记录的研究表明，在5-8°C，生化过程中变暖的表面温度改变了，并且在此期间全球生物圈受到了深刻的干扰。但是，PETM的最独特标志是稳定的碳同位素（13C/12C）比率降低了陆地和海洋碳碳含量的比率。这种碳同位素偏移（CIE）已在全球众多位置进行了记录，其无处不在的信号标志着大量同位素轻碳（12C）迅速释放到海洋 - 大气系统中。该碳的来源仍在争论中，但最简约的解释是沿连续斜率的大量沉积甲烷水合物的解离。这一古老的全球变暖事件与与全球碳循环的主要扰动密切相关，这使得PETM可以通过当前的社会实践来使PETM作为对未来气候变化的类似物的质量。这是估计PETM发射的碳量的关键证据，但很长很长的碳质量销量，但它已被认识到不同的CIE销量。例如，从地面记录（土壤结节和土地植物保留）中报告的CIE大约是海洋沉积物测量的两倍。这种差异令人沮丧，因为气体很容易在空气接口上交换，因此地面海洋的生理化学状态应等于大气，按时间尺度，按地质标准几乎是瞬时的。因此，在陆地和地表海洋记录中，CIE的大小应该相似，但这并不是出版的记录。绝大多数海洋PETM记录均来自由浮游物有孔虫生长的微小（1 mm）钙壳的稳定同位素组成，这是一群具有丰富化石记录的额外的变形虫生物。深海沉积物中浮游有孔虫壳的优势使它们成为使用地球化学分析的研究的首选底物，以重建过去的海洋/气候变化。但是，困扰此类记录的一个问题是，海底的沉积后过程可以改变有孔虫壳的原始化学成分，从而偏向于重建过去气候条件的稳定同位素记录，例如在佩特玛特（Petmat （〜10微米）钙样品中的靶标。这种方法允许对有孔虫壳内部的子域进行识别和分析，这些子域受化学改变影响较小，因此提供了过去气候条件的更准确记录。当前，这些稳定的同位素测量不能由任何其他技术执行。试点研究的首先结果表明，在这些保存完好的子域中记录的CIE幅度实际上是先前报道的两倍，因此与地面记录中的CIE幅度非常一致。该项目着重于获得CIE幅度的更准确的测量。确定CIE的真实大小很重要，因为它将（1）更好地约束发出的碳量，（2）提供了一个更现实的测试基础，以评估提议的碳输入来源的生存能力，（3）提高我们对气候对温暖的气体强度的气候敏感性的能力，以帮助识别5次的温暖机制，（4）（4）（4）（4）（4）（4）（4）（4）（4）（4）（4）（4）（4）通过快速的碳输入来校准生物（陆生和海洋）对环境变化驱动的反应。该项目将使年轻女科学家的研究生教育受益，并为Wiscsims实验室提供基础设施的支持，并开发了转化，尖端的分析技术。