Do metalliferous sediments record mid-ocean ridge hydrothermal activity? Constraining the roles of iron oxidation rate and 230Th scavenging

含金属沉积物是否记录了洋中脊热液活动？

• 批准号: 2030343
• 负责人: David Lund
• 金额: $ 44.28万
• 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: 2020
• 资助国家: 美国
• 起止时间: 2020-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2030343&HistoricalAwards=false
• 关键词: Do; metalliferous; sediments; record; mid

Do metalliferous sediments record mid-ocean ridge hydrothermal activity?High-temperature vents at mid-ocean ridges are an important source of heat and dissolved metals to the ocean interior. As discharging hydrothermal vent fluids mix with bottom waters, chemical reactions create metal-rich particles. These particles are carried up from the vents by warm (buoyant) hydrothermal plumes that spread into the surrounding seawater. The plumes carry the particles away from the vents, and the particles fall to the seafloor along ridge axes and ridge flanks. As a result, mid-ocean ridges are blanketed with metal-rich sediments, which reflect the combined influence of hydrothermal activity, particle formation, plume transport, and sedimentary processes. Recent studies show that metal fluxes to ridge crest sediments vary on glacial-interglacial timescales. This suggests that climate-linked changes in global sea level may modulate seafloor hydrothermal activity. However, the metal flux records may be biased by other processes. Such biases would complicate efforts to understand the impact of climate on seafloor hydrothermal activity. The project would evaluate: 1) the influence of iron oxidation rate on metal fluxes to mid-ocean ridge sediments, and 2) whether scavenging of thorium (Th) from seawater by hydrothermal particles precludes the use of the radioisotope 230Th as a constant flux proxy in ridge settings. The proposed work could transform understanding of how climate and sea level influence hydrothermal output from mid-ocean ridges. The education-related broader impacts of the project include the training and mentoring of a Ph.D. student and an undergraduate researcher.Ridge-crest metal flux records from the Southern East Pacific Rise (SEPR), Mid-Atlantic Ridge, and Juan de Fuca Ridge indicate that hydrothermal sedimentation increased during the last deglaciation (~10-20 kyr BP). In addition, results from the SEPR also show that deglacial fluxes of 230Th to ridge crest sediments were 2-3x higher than the water column production rate. Although sea level-driven changes in hydrothermal activity are the simplest explanation of the results, variations in the oxidation rate of reduced iron may have modulated the metal flux signal. The proposed study will test the oxidation rate hypothesis using transects of metal flux records from the SEPR. If enhanced Fe(II) oxidation caused higher fluxes near the ridge axis, then corresponding deficits should be found at off-axis locations. Greater hydrothermal output, on the other hand, should yield greater fluxes on both the ridge crest and flanks. The study will also constrain oxidation rate changes using benthic foraminiferal B/Ca as a proxy for deep Pacific carbonate ion concentration. The B/Ca results will fill a key gap in existing records and improve our understanding of carbon cycling during the deglaciation. Finally, the study will use 3He-normalized 230Th fluxes to assess whether 230Th can be used to study sediment fluxes near mid-ocean ridges, a key region for paleoceanographic studies. The study will lay the necessary groundwork for evaluating how sea level influences hydrothermal output from mid-ocean ridges. The project will support the training of a Ph.D. student and an undergraduate researcher, including informal and formal guidance to develop teaching skills, professional networking, and grant proposal writing skills.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.

金属沉积物是否记录了海脊中脊的水热活动？中山脊的高温通风孔是海洋内部的热量来源和溶解金属的重要来源。当排放热液排气流体与底部水混合时，化学反应会产生富含金属的颗粒。这些颗粒是通过温暖的（浮力）水热羽来从通风孔中延伸的，这些羽流散布到周围的海水中。羽毛将颗粒从通风孔移开，颗粒沿着山脊轴和山脊侧面掉落到海底。结果，中海脊覆盖了金属丰富的沉积物，这反映了水热活动，颗粒形成，羽流和沉积过程的综合影响。最近的研究表明，在冰川冰上时间尺度上，金属通向山脊波峰沉积物的金属通量各不相同。这表明全球海平面的气候变化可能会调节海底水热活动。但是，金属通量记录可能会受到其他过程的偏见。这种偏见会使人们努力理解气候对海底水热活动的影响变得复杂。该项目将评估：1）铁氧化速率对金属通量对中山脊沉积物的影响，以及2）水热颗粒从海水中清除ther（Th）是否排除了放射性同位素230th作为频繁的磁带代理的使用。拟议的工作可以改变人们对气候和海平面如何影响中山脊的水热产量的理解。该项目与教育有关的更广泛影响包括培训和指导博士学位。学生和本科生研究人员。从东太平洋南部崛起（SEPR），中大西洋山脊和胡安·德·富卡山脊的ridge-Crest金属通量记录表明，在最后一次脱脂期间（〜10-20 kir bp），热液沉积增加了。此外，SEPR的结果还表明，第230到山脊的冰川通量比水柱生产速率高2-3倍。尽管海平面驱动的水热活性的变化是结果的最简单解释，但减少铁的氧化速率的变化可能已调节金属通量信号。拟议的研究将使用SEPR的金属通量记录的样带检验氧化速率假设。如果增强的Fe（II）氧化导致山脊轴附近较高的通量，则应在离轴位置发现相应的缺陷。另一方面，更大的热液输出应在山脊波峰和侧面产生更大的通量。该研究还将使用底栖有孔虫B/CA作为深太平洋碳酸盐离子浓度的替代量来限制氧化速率的变化。 B/CA结果将填补现有记录中的关键空白，并提高我们对脱胶过程中碳循环的理解。最后，这项研究将使用3HE归一化的第230通量来评估是否可以使用第230次使用中山脊附近的沉积物通量，这是古海洋学研究的关键区域。该研究将为评估海平面如何影响海脊中的水热产量提供必要的基础。该项目将支持博士学位的培训。学生和本科研究人员，包括非正式和正式的指导，以发展教学技能，专业网络和赠款提案写作技巧。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的评估评估的评估来支持的。