Low temperature hydrothermal vent fluxes as traced by radium isotopes

镭同位素追踪的低温热液喷口通量

• 批准号: 1829431
• 负责人: Matthew Charette
• 金额: $ 35.03万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-11-01 至 2023-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1829431&HistoricalAwards=false
• 关键词: Low; temperature; hydrothermal; vent; fluxes

Iron is one of the most abundant elements in fluids released from mid-ocean ridges, yet it has been thought to be mostly removed from seawater near to its hydrothermal vent source. Recent evidence has emerged showing this hydrothermally-derived iron can be transported great distances in the ocean, including toward the sunlit surface layer where it is an essential nutrient for phytoplankton growth. This study will use naturally-occurring radium isotopes, which are also enriched in hydrothermal fluids but are non-reactive compared to iron, as tracers of hydrothermal iron in the deep ocean. With a range of half-lives from days to centuries, radium isotopes can be used as "clocks" to measure the precise rates at which hydrothermal iron is carried by ocean currents toward the ocean interior. Such information can be incorporated into ocean models designed to determine the role of hydrothermal iron on ocean productivity, which has societal relevance due to its role in regulating the carbon dioxide concentrations of Earth's atmosphere. This project will support research opportunities for two students through the Woods Hole Partnership in Education Program, which seeks to increase diversity in ocean and environmental science by inviting college juniors and seniors to gain practical experience through a summer of classroom study and hands-on research activities.A scientist from Woods Hole Oceanographic Institution will quantify rates of iron (Fe) transport above a major ocean spreading center to evaluate the role of hydrothermal venting in supplying this essential micronutrient to the surface ocean. Special attention will be paid to the role of low-temperature hydrothermal Fe fluxes, which are hypothesized to arrive at the seafloor in a stable form that mitigates significant removal during transport. If true, low-temperature fluids may supply a disproportionate amount of the "transportable" dissolved Fe that has not been observed in large-scale deep ocean plumes. Assessment of process rates will be accomplished through concurrent measurements of Fe concentration and speciation and the radium (Ra) "quartet" (224Ra, 223Ra, 228Ra, 226Ra) during an expedition along the southern East Pacific Rise (EPR; 15-18 degrees South). Autonomous underwater vehicle and towed-CTD surveys will be used to identify locations of low- and high-temperature discharge. At selected target areas, the investigators will test the hypotheses that low-temperature hydrothermal inputs have a distinct radium isotopic ratio fingerprint, and that the relative rate of Fe scavenging removal is lower in low-temperature sources. Given their wide ranging half-lives, Ra isotopes have the unique ability to integrate over biogeochemically-relevant time scales of Fe transport in the deep ocean. The combination of concurrent Ra isotope and total dissolved Fe measurements will allow the investigators to quantify Fe residence time for any Fe phase that is transported on large horizontal scales, as has been observed previously along the EPR. Together, Fe loss and transport from Ra measurements will lead to improvements in the predictive capabilities of ocean circulation and biogeochemistry models that assess the importance of hydrothermal Fe in supporting primary productivity and carbon drawdown in overlying surface waters.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.

铁是从中山脊中释放出的液体中最丰富的元素之一，但被认为主要是从海水附近取出的水热通风源。最近出现的证据表明，这种水热衍生的铁可以在海洋中运输较大的距离，包括朝着日光的表面层，这是浮游植物生长的必不可少的营养素。这项研究将使用天然存在的镭同位素，该镭同位素也富含水热流体，但与铁相比是无反应性的，作为深海水热铁的示踪剂。从几天到几个世纪的一半寿命中，辐射的同位素可以用作“时钟”，以测量洋流朝向海洋内部携带的水热铁的确切速率。这些信息可以纳入旨在确定水热铁对海洋生产力的作用的海洋模型，该海洋生产力具有社会相关性，因为它在调节地球大气的二氧化碳浓度中的作用。该项目将通过伍兹孔伙伴关系计划为两名学生提供研究机会，该计划旨在通过邀请大学大三学生和老年人通过课堂研究和动手研究活动来获得实用经验，以增加海洋和环境科学的多样性。 海洋。将特别注意低温水热磁通量的作用，假设这些通量以稳定的形式到达海底，从而减轻运输过程中的大量去除。如果真，低温流体可能会提供不成比例的“可运输”溶解的Fe，而在大型深海羽流中尚未观察到。过程率的评估将通过同时测量FE浓度和物种形成以及辐射（RA）“四重奏”（224ra，223ra，228ra，226ra）在沿南太平洋沿线的一场探险期间（EPR; EPR;南部15-18度）。自动驾驶水下车辆和拖曳CTD调查将用于识别低温排放的位置。在选定的目标区域，研究人员将测试低温水热输入的假设具有不同的同位素比指纹，并且在低温源中，Fe清除液的相对速率较低。鉴于其范围范围的半衰期，RA同位素具有独特的能力，可以在深海中的Fe Transports在生物地球化学上相关的时间尺度。并发RA同位素和总溶解的Fe测量的组合将使研究人员能够在以前在EPR上观察到的任何水平尺度运输的任何Fe相位的FE停留时间。 Together, Fe loss and transport from Ra measurements will lead to improvements in the predictive capabilities of ocean circulation and biogeochemistry models that assess the importance of hydrothermal Fe in supporting primary productivity and carbon drawdown in overlying surface waters.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.