Collaborative Research: Investigating the Influences of Hydrothermal and Respired Carbon in Intermediate Waters of the Equatorial Pacific Ocean During the Last Deglaciation

合作研究：调查末次冰消期赤道太平洋中层水域热液和呼吸碳的影响

• 批准号: 2001569
• 负责人: Chandranath Basak
• 金额: $ 25.58万
• 依托单位: University of Delaware
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-08-21 至 2023-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2001569&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; Influences; Hydrothermal

The last time Earth warmed by several degrees centigrade was more than 12 thousand years ago. That global warming ended the last Ice Age and paved the way for human expansion and diversification. Scientists have known for decades that this warming was associated with rising concentrations of greenhouse gases, including both carbon dioxide and methane, but have been unable to pinpoint what caused the greenhouses gases to increase. Recent research has shed new light on geologic processes in the ocean that may have influenced the rise in atmospheric carbon dioxide (CO2). Using geochemical methods, scientists have uncovered evidence that CO2 was released from deep sea volcanic provinces in the eastern equatorial Pacific at the end of the last Ice Age. This discovery is important because the eastern equatorial Pacific is one of the primary conduits through which CO2 from the ocean is released to the atmosphere. In the current project the research team will use similar geochemical methods to investigate whether there were other sites in the ocean where volcanic carbon was released at the end of the last Ice Age and whether ocean currents carried more carbon to the eastern equatorial Pacific as the Earth warmed. The results from this research should help answer one of the Grand Challenges in climate science, what regulated the concentration of atmospheric CO2 during one of Earth's largest climatic changes. The project will support one early career researcher and undergraduate and graduate students at both institutions, one of which is a Minority/Hispanic-Serving Institution where most students are first in family attendees.Two hypotheses have been put forth to explain large radiocarbon (14C) excursions and positive pCO2 anomalies in the Eastern Equatorial and Subtropical Pacific (EEP) during the last glacial termination. One hypothesis calls upon ventilation of respired metabolic carbon from a formerly isolated deep-sea reservoir through the Southern Ocean, and advection of that carbon to low latitudes via Antarctic Intermediate Water. This hypothesis has received support from Nd isotope results from the eastern tropical Pacific that document lower values during the Heinrich Stadial 1(HS1) and the Younger Dryas (YD) climate events, interpreted to reflect an increased proportion of southern sourced waters. The other hypothesis calls upon localized releases of geologic carbon from hydrothermal systems in the EEP that increased carbon flux to the surface ocean. This hypothesis has received additional support from a recent study that documented increased accumulation of hydrothermal metals in the marine sediments of the EEP in association with the large 14C excursions. It is possible that both mechanisms contributed to the radiocarbon anomalies and to an increased flux of "old" carbon to the atmosphere through the EEP upwelling system. Testing each hypothesis requires additional data from sites outside of the EEP and particularly from regions in the vicinity of where intermediate waters are formed. The researchers here will test the origin of the "old" carbon in the EEP by studying ventilation (14C) and water mass (eNd, Ba/Ca) proxies at multiple sites that lay in the path of intermediate waters feeding the equatorial Pacific from the North and South. If results from this study do not support old-carbon transfer via intermediate circulation, it will increase the likelihood of a local carbon reservoir as the source of old carbon in the EEP.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球上一次变暖几摄氏度是在 12000 多年前。全球变暖结束了最后一个冰河时代，为人类扩张和多样化铺平了道路。几十年来，科学家们已经知道，这种变暖与包括二氧化碳和甲烷在内的温室气体浓度上升有关，但一直无法查明导致温室气体增加的原因。最近的研究为可能影响大气二氧化碳（CO2）上升的海洋地质过程提供了新的线索。利用地球化学方法，科学家们发现了二氧化碳在上一个冰河时代末期从赤道东太平洋深海火山区释放出来的证据。这一发现很重要，因为赤道东太平洋是海洋二氧化碳释放到大气中的主要通道之一。在当前的项目中，研究小组将使用类似的地球化学方法来调查海洋中是否还有其他地点在上一个冰河时代末期释放了火山碳，以及洋流是否像地球一样将更多的碳带到了赤道东太平洋。温暖了。这项研究的结果应该有助于回答气候科学的重大挑战之一，即在地球最大的气候变化之一期间，大气二氧化碳浓度的调节因素。该项目将为两个机构的一名早期职业研究员以及本科生和研究生提供支持，其中一个是少数族裔/西班牙裔服务机构，大多数学生是家庭参加者中的第一名。提出了两个假设来解释大量放射性碳 (14C)末次冰期结束期间，东赤道和副热带太平洋（EEP）出现偏移和 pCO2 正异常。一种假设要求将以前孤立的深海水库中的呼吸代谢碳通过南大洋进行通风，并通过南极中层水将这些碳平流到低纬度地区。这一假说得到了东热带太平洋 Nd 同位素结果的支持，该结果记录了 Heinrich Stadial 1 (HS1) 和新仙女木 (YD) 气候事件期间较低的值，解释为反映了南部水源比例的增加。另一种假说认为，EEP 中的热液系统会局部释放地质碳，从而增加流向表层海洋的碳通量。这一假设得到了最近一项研究的进一步支持，该研究记录了 EEP 海洋沉积物中热液金属积累的增加与 14C 的大幅偏移有关。这两种机制都可能导致放射性碳异常，并增加“旧”碳通过 EEP 上升流系统进入大气的通量。检验每个假设需要来自 EEP 以外地点的额外数据，特别是来自中间水域形成地附近区域的数据。这里的研究人员将通过研究多个地点的通风（14C）和水质量（eNd，Ba / Ca）代理来测试EEP中“旧”碳的起源，这些地点位于从赤道太平洋注入中间水域的路径上。北和南。如果这项研究的结果不支持通过中间循环进行旧碳转移，则会增加当地碳库作为 EEP 中旧碳来源的可能性。该奖项反映了 NSF 的法定使命，并被认为值得通过以下方式获得支持：使用基金会的智力价值和更广泛的影响审查标准进行评估。