Collaborative Research: Hydrothermal Estuaries: What Sets the Hydrothermal Flux of Fe and Mn to the Oceans?

合作研究：热液河口：是什么决定了铁和锰进入海洋的热液通量？

基本信息

批准号：
1851078
负责人：
Jessica Fitzsimmons
金额：
$ 39.96万
依托单位：
Texas A&M University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-06-01 至 2024-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1851078&HistoricalAwards=false
关键词：
Collaborative Research Hydrothermal Estuaries What

项目摘要

Like volcanoes on land, the mid-ocean ridges that cross the ocean floor are not continuously erupting; however, the magmatic heat present just beneath the surface can continue to drive hot springs, just like the ones found within the crater of the "super volcano" at Yellowstone. In our recent work, we have shown that the chemicals released into the oceans from seafloor hot-springs can be dispersed all across the oceans. Now our interest has focused in on one element in particular, iron. This is one of the most abundant elements in every planetary body in the Universe yet it is vanishingly rare in Earth's oceans today. Set against that, it is essential to just about every form of life on Earth from the simplest and most ancient strains of microbes to the most complex animals including humans. In Earth's oceans, the lack of this "essential micro-nutrient" has been found to limit how much life can flourish near both the south and north poles in the Pacific Ocean in the sunlit surface ocean even though the supply of sunlight and other major nutrients (phosphorous, nitrogen) should be more than adequate. Our newest research suggests that iron released from hydrothermal plumes (where the concentrations coming from vents are more than 1 million times higher than normal ocean water) could play a major role. Despite undergoing massive dilution as hydrothermal solutions leave the vents and traverse thousands of kilometers through the oceans, we believe that at least some of the iron released from deep sea hot springs can survive this journey and make a significant impact on how much live exists in Earth's polar oceans and how much CO2 it draws down from the atmosphere. To investigate that idea, this project will study the fate of iron released from a hydrothermal vent over a length scale that hasn't been studied before - from the first 1km through the ocean out to 100km away from the vent-site. This will fill a gap in our knowledge between what happens right at a vent-site (as studied by research submarines) and what happens to ocean chemistry all across Earth's entire ocean basins (as studied by a huge international research project called GEOTRACES). Our work will use a 3D computational model to predict where the plume of material from a vent in the Northeast Pacific Ocean should escape to after it is erupted from some vents at a volcanic system called the Juan de Fuca Ridge. We will then use an advanced autonomous free-swimming robot to search out in the predicted plume area, first to test the accuracy of our predicted model and, second, to collect samples from the hydrothermal plume from where it first forms to as far out as we can follow it. The samples we collect will include both filtered seawater and the particulate material (whether mineralogical or microbiological) that we can extract from the filters. Together, this will allow us to track the fate of the iron and other key physical and geochemical tracers down-plume away from the vents, to work out where it ends up (in the water and in the sediments) and also how fast those processes happen. The work we do will also help plan how to conduct similar robotics-based exploration on future space missions beyond Earth where it has been hypothesized that seafloor events also exist (e.g. Saturn's moon Enceladus) and where, if we are really lucky, we may find that life is hosted based on the energy from seafloor volcanoes, just as happens here on Earth. We have a resident artist embedded in our program who has already begun experimenting with the use of air-flow and sound in her sculptures to help communicate the complex nature of these plumes. She will join our cruise, and work with our team post-cruise to design and hopefully build a sculpture that that could potentially result in a large and long-term outdoor installation. The international GEOTRACES program has revealed that iron (Fe) is released ubiquitously from submarine ridges to the deep ocean. Results from US GEOTRACES section GP16 showed that both dissolved and particulate (colloidal) Fe may persist so far as to be able to influence primary productivity in High-Nutrient/Low-Chlorophyll (HNLC) regions of the Southern Ocean. As a complement to these sectional studies, we propose a detailed process study to elucidate the mechanisms by which hydrothermally sourced Fe can persist across the oceans at the scale that GEOTRACES has revealed. Specifically, while the "persistent" Fe in a hydrothermal plume appears to behave quasi-conservatively from 100km to 4000km across the SE Pacific Ocean, it is also known that the majority of the Fe present at the Southern EPR on that US GEOTRACES GP16 cruise did not persist over the 100km separation between that station and the next deep ocean station beyond the ridge crest. To fill that gap, this project will conduct a coupled modelling and field study to investigate the fate of hydrothermally sourced Fe at ranges of 0-1, 1-10 and 10-100km down-plume away from a well established vent-source. To begin, we will use the detailed micro-bathymetry and the long-term current meter data available from the Main Endeavour Segment of the Juan de Fuca Ridge to implement a recently developed 3D theoretical plume dispersion model that can predict both the detailed 3D dispersion trajectory and the rate of flow within the hydrothermal plume away from two long-studied and well characterized Main Endeavour Field (MEF) vents. At sea, we will use that predictive model to guide Sentry autonomous underwater vehicle (AUV) surveys that will follow the plume "down-wind" and "across-plume" to compile a 3D survey using in-situ sensors [optical, redox, conductivity, temperature, depth (CTD)] that will allow us to (1) confirm (and better constrain) the predictive model, and to (2) map out the shape and trajectory of the plume to provide context for discrete water column samples that we will collect - both from the AUV and from a trace metal clean CTD-rosette. Sampling from the AUV will use the latest generation of SUPR samplers designed for the CLIO trace-metal-clean water sampler. This will suffice for samples of dissolved, colloidal and particulate trace metals and collection of filtered material for grain-by-grain mineralogical and biogeochemical analyses. That sampling program will be backed up by larger volume sampling down-plume using a CTD-rosette to augment our AUV-based program with helium isotope analyses (to track extents of physical plume dilution at increasing distances downwind and across plume) and for complementary ligand and organic compound analyses to investigate the role that organic complexation might play in protecting reduced species of Fe [and manganese (Mn), too] against oxidative precipitation and removal from the oceanic water column. Post cruise, our combination of biogeochemical measurements and improved 3D physical modelling will not only be able to provide new insights into the processes that control the fluxes of Fe and Mn to the oceans from hydrothermal venting but also the length scales over which those processes take effect. Finally, because our 3D theoretical model includes velocities, we also anticipate being able to deduce the rates at which these processes occur.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.

与陆地上的火山一样，穿过海底的洋中脊也不会持续喷发；然而，地表下方的岩浆热量可以继续驱动温泉，就像在黄石公园的“超级火山”火山口内发现的温泉一样。在我们最近的工作中，我们已经证明，从海底温泉释放到海洋中的化学物质可以分散到整个海洋。现在我们的兴趣集中在一种元素上，特别是铁。这是宇宙中每个行星体中最丰富的元素之一，但在当今地球的海洋中却极其罕见。与此相反，它对地球上几乎所有生命形式都至关重要，从最简单、最古老的微生物菌株到包括人类在内的最复杂的动物。人们发现，在地球海洋中，缺乏这种“必需的微量营养素”会限制太平洋南北极附近阳光照射的表层海洋中生命的繁盛，尽管有阳光和其他主要营养素的供应（磷、氮）应该绰绰有余。我们的最新研究表明，从热液羽流中释放的铁（来自喷口的浓度比正常海水高出 100 万倍以上）可能发挥重要作用。尽管随着热液离开喷口并穿越海洋数千公里而经历了大规模稀释，但我们相信，至少有一些从深海温泉释放的铁能够在这段旅程中幸存下来，并对地球上生命的存在量产生重大影响。极地海洋以及它从大气中吸收了多少二氧化碳。为了研究这个想法，该项目将在以前从未研究过的长度范围内研究从热液喷口释放出的铁的命运——从穿过海洋的最初 1 公里到距喷口地点 100 公里。这将填补我们在喷口发生的情况（由研究潜艇研究）和地球整个海洋盆地的海洋化学发生的情况（由一个名为 GEOTRACES 的大型国际研究项目研究）之间的知识空白。我们的工作将使用 3D 计算模型来预测东北太平洋火山喷口的羽状物质在从胡安德富卡山脊火山系统的一些喷口喷发后应该逃逸到哪里。然后，我们将使用先进的自主自由游泳机器人在预测的羽流区域中进行搜索，首先测试我们预测模型的准确性，其次从热液羽流首次形成的地方收集样本，直到最远的地方。我们可以跟随它。我们收集的样本将包括过滤后的海水和我们可以从过滤器中提取的颗粒物质（无论是矿物的还是微生物的）。总之，这将使我们能够跟踪铁和其他关键物理和地球化学示踪剂从喷口向下羽流的命运，找出它最终的去向（在水中和沉积物中）以及这些过程的速度发生。我们所做的工作还将帮助规划如何在地球以外的未来太空任务中进行类似的基于机器人的探索，假设海底事件也存在（例如土星的卫星土卫二），如果我们真的很幸运，我们可能会发现生命是基于海底火山的能量而存在的，就像地球上发生的那样。我们的项目中有一位常驻艺术家，她已经开始尝试在她的雕塑中使用气流和声音来帮助传达这些羽毛的复杂性质。她将参加我们的巡游，并在巡游结束后与我们的团队合作设计并希望建造一座雕塑，这可能会成为一个大型且长期的户外装置。国际 GEOTRACES 计划显示，铁 (Fe) 无处不在地从海底海脊释放到深海。美国 GEOTRACES GP16 部分的结果表明，溶解铁和颗粒（胶体）铁可能持续存在，足以影响南大洋高营养/低叶绿素 (HNLC) 区域的初级生产力。作为这些截面研究的补充，我们提出了一项详细的过程研究，以阐明热液来源的铁能够以 GEOTRACES 揭示的规模在海洋中持续存在的机制。具体来说，虽然热液羽流中的“持久”铁似乎在太平洋东南部 100 公里到 4000 公里范围内表现出准保守性，但众所周知，美国 GEOTRACES GP16 巡航中 EPR 南部存在的大部分铁不得持续超过该站与山脊顶部以外的下一个深海站之间 100 公里的间隔。为了填补这一空白，该项目将进行耦合建模和现场研究，以调查距成熟喷口源 0-1、1-10 和 10-100 公里羽流范围内热液来源的铁的命运。首先，我们将使用胡安德富卡海岭主奋进段提供的详细微测深和长期海流计数据来实现最近开发的 3D 理论羽流扩散模型，该模型可以预测详细的 3D 扩散轨迹以及远离两个经过长期研究和充分表征的主奋进场 (MEF) 喷口的热液羽流内的流速。在海上，我们将使用该预测模型来指导 Sentry 自主水下航行器 (AUV) 调查，该调查将跟踪羽流“顺风”和“跨羽流”，使用原位传感器 [光学、氧化还原、电导率、温度、深度 (CTD)]，这将使我们能够 (1) 确认（并更好地约束）预测模型，并 (2) 绘制羽流的形状和轨迹，为离散水柱样本提供背景信息我们将收集 - 从 AUV 和微量金属清洁 CTD 玫瑰花结中收集。 AUV 采样将使用专为 CLIO 痕量金属清洁水采样器设计的最新一代 SUPR 采样器。这足以满足溶解、胶体和颗粒痕量金属的样品以及用于逐粒矿物学和生物地球化学分析的过滤材料的收集。该采样计划将得到使用 CTD-rosette 的更大体积的羽流采样的支持，以通过氦同位素分析增强我们基于 AUV 的计划（以跟踪顺风和穿过羽流的距离增加时物理羽流稀释的程度）和补充配体和有机化合物分析，以研究有机络合在保护还原态铁[和锰 (Mn)]免遭氧化沉淀和从海洋水体中去除方面可能发挥的作用。巡航后，我们将生物地球化学测量与改进的 3D 物理模型相结合，不仅能够为控制热液喷发中铁和锰流入海洋的过程提供新的见解，而且还能够为这些过程生效的长度尺度提供新的见解。最后，由于我们的 3D 理论模型包括速度，我们还预计能够推断出这些过程发生的速率。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。