Hydrothermal Metal Fluxes over the Cenozoic

热液喷口是水下间歇泉，向海洋中喷发的水与河流中的水一样多。这些喷口可以改变海水的化学成分，在百万年的时间尺度上改变气候。然而，有多少水通过这些喷口循环，或者随着时间的推移它是如何变化的，我们不得而知。在喷发期间，铁和锰等金属从喷口喷发出来，运往深海，并沉积在海洋沉积物中。这些沉积物是地质记录中过去喷发的证据。该项目将收集、扩展、比较和分析在海洋沉积物中发现的多种化学线索。我们的目标是弄清楚这些喷口的流量在数百万年里是如何变化的。最终，该项目将计算热液喷口的金属流量，并绘制地图，显示这些金属现在和过去的储存位置。这些金属如锰、钴、铜和锌的海底分布对现代技术和可再生能源至关重要。此外，该项目还支持涉及地球科学中代表性不足的社区的K-12外联活动。由于整个海洋体积每隔几千年在底层洋壳中循环，全球热液流体流量与全球河流流向海洋的流量相当。热液循环对海水化学平衡、长期气候、生物地球化学循环、古海水成分和俯冲到地幔中的地壳成分有重要影响。尽管很重要，但热液通量受到的限制很少。该项目将汇编、扩充、比较和合成海洋沉积物中热液金属沉积示踪剂，以重建百万年时间尺度上整个盆地热液通量空间分布的变化。以太平洋板块为重点，将比较四种热液沉积示踪剂：来自涂片的铁-锰氧化物丰度、元素浓度的多元模拟、铅同位素和稀土元素模式。该项目测试了一种假设，即从热液喷口追踪金属沉积的海洋沉积物记录可以合并并扩展到海洋盆地，以重建新生代大部分地区现代热液通量的变化。除了估算通量，该项目还将制作现在和过去的热液金属沉积地图，以说明热液羽流从哪里以及远离大洋中脊的距离。这一结果对过去微量营养素(铁)的循环以及对受热液作用影响的新同位素系统增加了限制。鉴于将对锰、钴、铜和锌进行调查，该项目与关键矿物研究有关。该项目支持早期职业科学家和K-12外联活动，涉及在地球科学中代表性不足的社区的人。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。

Hydrothermal vents are underwater geysers that spew about as much water into the ocean as rivers. These vents can change the chemistry of seawater and change the climate on million-year timescales. However, how much water circulates through these vents or how it has changed over time is unknown. During eruptions, metals like iron and manganese are erupted from the vents, transported within the deep ocean, and deposited in the marine sediment. These deposits serve as evidence of past eruptions in the geologic record. This project will gather, expand, compare, and analyze multiple chemical clues found in marine sediments. The goal is to figure out how the flow of these vents has changed over millions of years. Ultimately, the project will calculate the flow of metals from hydrothermal vents and create maps that show where these metals are deposited now and in the past. The seafloor distribution of these metals such as manganese, cobalt, copper, and zinc are critical to modern technology and renewable energy. Additionally, the project supports K-12 outreach activities involving communities underrepresented in the geosciences.With the entire ocean volume cycling through the underlying ocean crust every few thousand years, the global hydrothermal fluid flux is comparable to the global riverine flux to the ocean. Hydrothermal circulation significantly affects the chemical balance of seawater chemistry, long-term climate, biogeochemical cycles, paleo-seawater compositions, and the composition of crust subducted into the mantle. Despite the importance, hydrothermal fluxes are poorly constrained. This project will compile, expand, compare, and synthesize tracers of hydrothermal metal deposition in marine sediment to reconstruct variations in the basin-wide spatial distribution of hydrothermal fluxes over million-year timescales. Focusing on the Pacific Plate, four tracers of hydrothermal deposition will be compared: Fe-Mn oxide abundances from smear slides, multivariate modeling of element concentrations, Pb isotopes, and rare earth element patterns. The project tests the hypothesis that marine sediment records tracing metal deposition from hydrothermal vents can be combined and expanded across ocean basins to reconstruct changes in hydrothermal fluxes for the modern back through much of the Cenozoic. Along with estimating fluxes, the project will produce maps of present and past hydrothermal metal deposition that will illustrate where and how far hydrothermal plumes are transported away from mid-ocean ridges. The outcome has implications for the cycling of micronutrients (iron) in the past as well as adding constraints to novel isotope systems affected by hydrothermalism. Given that Mn, Co, Cu, and Zn will be investigated, the project is pertinent to critical minerals research. The project supports early career scientists and K-12 outreach activities involving people from communities underrepresented in the geosciences as well.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.