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: 1905505
• 负责人: Chandranath Basak
• 金额: $ 25.58万
• 依托单位: CSUB Auxiliary for Sponsored Programs Administration
• 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: 2019-08-15 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1905505&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.

地球上一次升温几度是在12000多年前。全球变暖结束了最后一个冰河时代，为人类的扩张和多样化铺平了道路。几十年来，科学家们已经知道，这种变暖与温室气体浓度的上升有关，包括二氧化碳和甲烷，但一直无法确定是什么导致了温室气体的增加。最近的研究揭示了海洋中的地质过程可能影响了大气中二氧化碳（CO2）的上升。利用地球化学方法，科学家们发现了证据，证明在最后一个冰河时代结束时，赤道东太平洋的深海火山省释放了二氧化碳。这一发现很重要，因为东赤道太平洋是海洋向大气释放二氧化碳的主要通道之一。在目前的项目中，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方在最后一个冰河时代结束时释放了火山碳，以及随着地球变暖，洋流是否将更多的碳带到赤道东太平洋。这项研究的结果应该有助于回答气候科学中的一个重大挑战，即在地球上最大的气候变化之一期间，是什么调节了大气中二氧化碳的浓度。该项目将支持两所机构的一名早期职业研究人员和本科生和研究生，其中一所是少数民族/西班牙裔服务机构，大多数学生是家庭参与者中的第一名。提出了两个假说来解释末次冰期终止期间赤道东部和亚热带太平洋（EEP）的大量放射性碳（14C）漂移和正pCO2异常。一种假说认为，从以前孤立的深海储层中呼出的代谢碳通过南大洋进行通风，并通过南极中间水将这些碳平流到低纬度地区。这一假设得到了热带太平洋东部Nd同位素结果的支持，该结果在Heinrich Stadial 1（HS1）和Younger Dryas （YD）气候事件期间记录了较低的数值，这被解释为反映了南方水源比例的增加。另一种假说认为，EEP中热液系统的局部地质碳释放增加了流向海洋表面的碳通量。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大规模的14C漂移有关。有可能这两种机制都导致了放射性碳的异常和“老”碳通过EEP上升流系统进入大气的通量增加。要验证每一种假设，都需要从EEP以外的地点，特别是中间水域形成区域附近的地区获得额外的数据。这里的研究人员将通过研究通风（14C）和水质量（eNd, Ba/Ca）代用指标来测试EEP中“老”碳的来源，这些代用指标位于从南北方向流入赤道太平洋的中间水域路径上的多个地点。如果本研究的结果不支持古碳通过中间循环转移，那么它将增加局部碳库作为EEP中古碳来源的可能性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。