Collaborative Research: Sea level induced hydrothermal activity as a trigger for glacial terminations

合作研究：海平面引起的热液活动作为冰川终止的触发因素

• 批准号: 1558641
• 负责人: David Lund
• 金额: $ 28万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558641&HistoricalAwards=false
• 关键词: Collaborative; Research; Sea; level; induced

The last million years of earth's history are characterized the growth and decay of continental ice sheets that covered large portions of North America and Europe. Growth of the ice sheets transferred water from the ocean to the continents and caused sea level to drop by nearly 400 feet. While it has long been known that the pacing of the ice ages is related to changes in the Earth's orbit around the sun, the triggering mechanism for the end ice ages, known as terminations, has yet to be fully explained. Lowering of sea level releases pressure on the global mid-ocean ridge system, a nearly continuous chain of submerged volcanoes that span 30,000 miles of the sea floor. The pressure release should drive enhanced submarine volcanism, which may in turn influence climate by introducing heat and carbon dioxide into the deep ocean. The aim of the proposed work is to assess magmatism along mid-ocean ridges in the eastern South Pacific using geologic archives of volcanic activity. Sediment cores retrieved from the East Pacific Rise (EPR) and Pacific Antarctic Ridge (PAR) will be used to assess hydrothermal plume activity near the ridge crest. Hydrothermal plumes are created through superheating of cold deep ocean water by hot oceanic crust, which is itself heated by magma. Thus, sedimentary archives can be used to assess glacial-interglacial changes in magmatism and test whether enhanced submarine volcanism occurs during glacial terminations. The proposed work will focus on a series of cores from 10°S to 40°S along the EPR and PAR. Preliminary oxygen isotope data indicates that sediments in this region accumulate at a rate sufficient to constrain glacial-interglacial timescales. Hydrothermal activity will be inferred by estimating the flux of Fe, Mn, V, and As to ridge crest sediments. All fluxes will be constrained using the 3He normalization technique. A finding of coherent variations in metal flux at multiple sites would indicate there were regional changes in magmatic activity. Additionally, the timing of anomalous metal fluxes will be compared with climate proxies to assess the feasibility that mid-ocean ridge magmatism acts as a negative feedback on ice sheet size. Finally, a petrologic model will be used to simulate the impact of sea level variations on CO2-bearing melt production in the upper mantle. Simulations of carbon flux from the global mid-ocean ridge system will be used to assess whether variations in carbon flux could have feasibly driven atmospheric CO2 on glacial-interglacial timescales. The proposed work could transform our understanding of the climate system by constraining the interactions between the fluid and solid earth on glacial-interglacial timescales. The broader educational impacts of the proposed work includes the participation of a postdoctoral scholar and two undergraduates at the University of Connecticut, plus an additional undergraduate at Caltech.

地球历史上最后一百万年的特点是覆盖北美和欧洲大部分地区的大陆冰盖的生长和衰退。冰盖的增长将海水从海洋转移到大陆，导致海平面下降了近400英尺。虽然人们早就知道冰河时代的节奏与地球绕太阳轨道的变化有关，但冰河时代结束的触发机制，即所谓的终结，尚未得到充分解释。海平面的下降释放了对全球洋中脊系统的压力，这是一个几乎连续的水下火山链，横跨海底3万英里。压力的释放将推动海底火山活动的增强，这可能反过来通过将热量和二氧化碳引入深海来影响气候。这项工作的目的是利用火山活动的地质档案来评估南太平洋东部洋中脊的岩浆活动。从东太平洋隆起（EPR）和太平洋南极脊（PAR）获取的沉积物岩心将用于评估脊顶附近的热液柱活动。热液柱是由深海冷水被热的海洋地壳过热而形成的，而海洋地壳本身又被岩浆加热。因此，沉积档案可以用来评估冰期-间冰期岩浆活动的变化，并检验在冰川终止期间是否发生了增强的海底火山活动。这项工作将集中在沿着EPR和PAR从10°S到40°S的一系列岩心上。初步的氧同位素数据表明，该地区沉积物的积累速度足以限制冰期-间冰期的时间尺度。热液活动将通过估算铁、锰、钒和砷在脊顶沉积物中的通量来推断。所有的通量都将使用3He归一化技术进行约束。如果在多个地点发现金属通量的连贯变化，则表明岩浆活动存在区域变化。此外，将异常金属通量的时间与气候代用物进行比较，以评估洋中脊岩浆活动对冰盖大小起负反馈作用的可行性。最后，将使用一个岩石学模型来模拟海平面变化对上地幔含二氧化碳熔体产生的影响。来自全球洋中脊系统的碳通量模拟将用于评估碳通量的变化是否可能在冰期-间冰期时间尺度上驱动大气二氧化碳。这项工作可以通过在冰期-间冰期时间尺度上限制流体和固体地球之间的相互作用来改变我们对气候系统的理解。拟议工作的更广泛的教育影响包括一名博士后学者和康涅狄格大学的两名本科生的参与，以及加州理工学院的一名本科生。