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

GSTDTAP

项目编号	1558990
	Investigating Sources of Excess Carbon and DELTA14C Anomalies During the Last Glacial Termination
	Lowell Stott
主持机构	University of Southern California
项目开始年	2016
	2016-09-15
项目结束日期	2018-08-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	431399(USD)
国家	美国
语种	英语
英文摘要	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.
URL	查看原文
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/70428
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Lowell Stott.Investigating Sources of Excess Carbon and DELTA14C Anomalies During the Last Glacial Termination.2016.