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

地球上一次变暖是在12000多年前。全球变暖结束了上一个冰河时代，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，但一直无法确定是什么导致温室气体浓度增加。最近的研究为海洋中可能影响大气二氧化碳(CO2)上升的地质过程提供了新的线索。利用地球化学方法，科学家们发现有证据表明，二氧化碳是在上一次冰河时代结束时从赤道东太平洋的深海火山岛释放出来的。这一发现很重要，因为赤道东太平洋是海洋中二氧化碳释放到大气中的主要管道之一。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有其他地点在上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了赤道东太平洋。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的二氧化碳浓度。该项目将支持两个机构的一名早期职业研究人员以及本科生和研究生，其中一个是少数族裔/拉美裔服务机构，那里的大多数学生是第一个家庭成员。提出了两个假设来解释最后一次冰川终止期间东赤道和亚热带太平洋(EEP)的大放射性碳(14C)漂移和正二氧化碳异常。一种假说要求将来自以前孤立的深海水库的呼吸代谢碳通过南大洋通风，并通过南极中间水将这些碳平流到低纬度。这一假设得到了热带太平洋东部的ND同位素结果的支持，这些结果记录了Heinrich Staial 1(HS1)和Young Dryas(YD)气候事件期间较低的值，解释为反映了南部来源水域的比例增加。另一种假说要求EEP中的热液系统局部释放地质碳，从而增加了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，该研究记录了与14C大漂移相关的热液金属在EEP海洋沉积物中的积累增加。这两种机制可能都导致了放射性碳异常，并通过EEP上升流系统增加了“旧”碳进入大气的通量。检验每一种假设都需要从EEP以外的地点，特别是从形成中间水域的附近地区获得更多数据。这里的研究人员将通过研究位于从南北向赤道太平洋输送中间水路径的多个地点的通风(14C)和水团(END，Ba/Ca)指标，来测试EEP中“旧”碳的来源。如果这项研究的结果不支持通过中间循环进行旧碳转移，它将增加当地碳库作为EEP中旧碳来源的可能性。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.