Investigating Sources of Excess Carbon and DELTA14C Anomalies During the Last Glacial Termination

认识到温室气体的变异性在地球最大的气候变化中发挥了主要作用，现在的挑战是发现哪些过程造成了伴随着大气候变化的大气温室气体的变化。 更新世冰期/间冰期循环可以说是地球上最大和最引人注目的气候变化，与大气pCO 2和甲烷的变化有关。但是，经过30年的研究，对于温室气体浓度变化的机制，科学界还没有达成共识。最近的发现揭示了关于地球碳系统的秘密，促使该假说被授予该奖项。该假说认为，在冰川-间冰期循环期间，二氧化碳流入和流出覆盖海洋热液系统的岩石和沉积物的通量随温度而变化。这是因为在冰川作用期间，随着温度的降低，来自热液喷口的二氧化碳和富含二氧化碳的流体的密度比海水高。 密度更大的二氧化碳在岩石和沉积物中积累，直到冰川末端的海洋变暖。当冰川终止期间温度上升时，二氧化碳变得有浮力并被释放到海洋中。 热液系统释放的碳带有明显的地球化学指纹，这些指纹印在海洋沉积物上。该项目将使用地球化学测量来调查这些地球化学信号是否在最后一次冰期到间冰期的过渡中被印在沉积物上。初步证据支持这一假设。这项调查的结果不仅可以让我们了解地质过程如何影响地球过去的气候，还可以让我们了解碳的地质储存对未来海洋温度上升的敏感性。该奖项还将通过为研究生、本科生和高中毕业生提供研究机会，支持他们持续参与南加州大学的STEM培训。来自海洋沉积物的新硼同位素和14 C记录表明，随着大气pCO 2的上升，在末次冰期终止期间，赤道东太平洋的CO2被耗尽到大气中。过量碳的来源和14 C耗尽的CO2通量增加的原因目前尚不清楚。然而，有两种不同的假说被提出来解释冰消历史。一种假说认为，一个形式上孤立的深海水团通过南大洋通风，通风的碳通过中间沃茨输送到热带。另一种假说认为，冰川消退期间，由于海洋变暖，热液库向热带海洋释放地质碳。本研究旨在确定这两个假设中哪一个是正确的。每一种假设的机制都会在滋养赤道太平洋上升流系统的中间沃茨上留下不同的地球化学指纹。所谓的“深海通风假说”预测，向赤道暗流提供碳的源沃茨将具有最低的Delta 14 C特征和最低的[CO 3 =]。或者，如果增加的碳通量在赤道太平洋导致从本地地质来源的碳释放，最耗尽的Delta 14 C值和最低的[CO 3 =]将发生在附近的碳释放的网站。这两种机制将区分与测量的14 C年龄的底栖有孔虫，在Delta 14 C和B/Ca的变化，在[CO 3 =]的变化代理代理的代理。稳定同位素数据（底栖有孔虫δ 13 C和δ 18 O）将增强14 C和B/Ca结果，以表征赤道潜流系统中的中水性质和源水信号的混合。南加州大学的研究人员将使用中等复杂性的地球系统模型（cGENIE）进行这些代理测量并评估结果，该模型能够模拟如果碳从南大洋和/或热液喷口附近的局部来源释放，同位素和[CO 3 =]梯度将如何在太平洋的中间深度发生变化。

Recognizing that greenhouse gas variability played a primary role in Earth's largest climate changes, the challenge now is to discover what processes are responsible for variations in atmospheric greenhouse gases that accompany large climate changes. The Pleistocene glacial/interglacial cycles are arguably some Earth's largest and most dramatic climatic changes associated with variations in atmospheric pCO2 and methane. But after three decades of research there is no scientific consensus on the mechanisms responsible for the variations in greenhouse gas concentrations. Recent discoveries have revealed secretes about the Earth's carbon system that prompted the hypothesis being investigated with this award. The hypothesis argues that the flux of CO2 into and out of rocks and sediments that blanket marine hydrothermal systems varied with temperature during glacial-interglacial cycles. This is because CO2 and CO2-rich fluids from hydrothermal vents become denser than seawater as temperatures cool during glaciations. The denser CO2 accumulates in rocks and sediments until the oceans warm at the glacial terminations. When temperatures rise during a glacial termination, CO2 becomes buoyant and is released into the Ocean. Carbon released from hydrothermal systems carries distinct geochemical fingerprints that are imprinted on marine sediments. This project will use geochemical measurements to investigate whether these geochemical signals were imprinted on sediments at the last glacial-to-interglacial transition. Preliminary evidence supports this hypothesis. The results of this investigation could inform not only our understanding of how geologic processes influenced the Earth's past climate, it could also inform our understanding of how sensitive geologic reservoirs of carbon are to rising ocean temperature in the future. This award will also support ongoing participation in STEM training at the University of Southern California through research opportunities for graduate and undergraduate students and high school seniors.New Boron isotope and 14C records from marine sediments indicate there was a significant increase in the flux of 14C-depleted CO2 from the eastern equatorial Pacific to the atmosphere during the last glacial termination as atmospheric pCO2 was rising. The source of excess carbon and the reason for the increased flux of 14C-depleted CO2 is not currently known. However, two different hypotheses have been put forth to explain the deglacial history. One hypotheses calls upon ventilation of a formally isolated abyssal water mass through the Southern Ocean and transport of the ventilated carbon to the tropics via intermediate waters. An alternative hypothesis calls upon release of geologic carbon into the tropical Ocean from hydrothermal reservoirs in response to ocean warming during the deglaciation. This research seeks to determine which of these two hypotheses is correct. Each of the hypothesized mechanisms would have left a different geochemical fingerprint on the intermediate waters that fed the equatorial Pacific upwelling system. The so-called "abyssal ventilation hypothesis" predicts that the source waters that contributed carbon to the equatorial undercurrent would have had the lowest Delta14C signature and the lowest [CO3=]. Alternatively, if the increased carbon flux in the equatorial Pacific resulted from release of carbon from localized geologic sources, the most depleted Delta14C values and the lowest [CO3=] would have occurred near the sites of carbon release. These two mechanisms will be distinguishable with measurements of 14C ages of benthic foraminifera, a proxy for changes in Delta14C and in B/Ca, a proxy for changes in [CO3=]. Stable isotope data (benthic foraminiferal delta13C and delta18O) will augment the 14C and B/Ca results for characterizing intermediate water properties and mixing of source water signals in the equatorial undercurrent system. Researchers at USC will make these proxy measurements and evaluate the results using an Earth System model of intermediate complexity (cGENIE) that is able to simulate how the isotope and [CO3=] gradients would change at intermediate depths in the Pacific if carbon was released from the Southern Ocean and/or from localized sources near hydrothermal vents.