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？

• 批准号: 1851007
• 负责人: Chris German
• 金额: $ 38.22万
• 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: 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=1851007&HistoricalAwards=false
• 关键词: Collaborative; Research; Hydrothermal; Estuaries; What

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.

就像陆地上的火山一样，横跨海底的洋中脊并不是不断喷发的；然而，地表下存在的岩浆热量可以继续驱动温泉，就像黄石公园“超级火山”火山口内发现的那样。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海洋的各个地方。现在我们的兴趣集中在一种元素上，铁。这是宇宙中每个行星体中最丰富的元素之一，但它在今天的地球海洋中却非常罕见。与此相反，它对地球上几乎所有形式的生命都是必不可少的，从最简单、最古老的微生物菌株到最复杂的动物，包括人类。在地球的海洋中，这种“必需的微量营养物质”的缺乏限制了太平洋南北两极附近阳光照射的海洋表面生命的繁盛，尽管阳光和其他主要营养物质（磷、氮）的供应应该是绰绰多的。我们最新的研究表明，热液羽流释放的铁（来自喷口的浓度比正常海水高100多万倍）可能起主要作用。尽管在热液溶液离开喷口并穿越数千公里的海洋时经历了巨大的稀释，但我们相信，至少有一些深海温泉释放的铁可以在这段旅程中幸存下来，并对地球极地海洋中的生物数量及其从大气中吸收的二氧化碳量产生重大影响。为了研究这个想法，这个项目将研究从热液喷口释放的铁的命运，其长度范围是以前从未研究过的——从海洋的最初1公里到距离喷口100公里。这将填补我们在喷口处发生的事情（由研究潜艇研究）和整个地球海洋盆地发生的海洋化学变化（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一个火山口的物质羽流从胡安·德·富卡山脊火山系统的一些火山口喷发出来后应该逃到哪里。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，从热液羽流最初形成的地方收集样本，直到我们可以跟踪它。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（无论是矿物学还是微生物学）。总之，这将使我们能够追踪铁和其他关键的物理和地球化学示踪剂的命运，这些示踪剂从喷口向下喷出，计算出它们的最终归宿（在水中和沉积物中），以及这些过程发生的速度。我们所做的工作也将有助于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，在那里，人们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，就像在地球上发生的那样。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状物的复杂性质。她将加入我们的游轮，并在游轮结束后与我们的团队一起设计并希望建造一个雕塑，这可能会成为一个大型的、长期的户外装置。国际GEOTRACES计划揭示了铁（Fe）从海底脊向深海无处不在地释放。美国GEOTRACES剖面GP16的结果表明，溶解铁和颗粒（胶体）铁可能持续存在，以至于能够影响南大洋高营养/低叶绿素（HNLC）区域的初级生产力。作为这些局部研究的补充，我们提出了一项详细的过程研究，以阐明热液来源的铁可以在GEOTRACES揭示的规模上跨越海洋的机制。具体来说，虽然热液柱中的“持续”铁在东南太平洋从100公里到4000公里的范围内似乎表现得准保守，但我们也知道，在美国GEOTRACES GP16巡航的南EPR中存在的大部分铁在该站与山脊顶部以外的下一个深海站之间的100公里距离内并没有持续存在。为了填补这一空白，该项目将进行耦合建模和实地研究，以调查距离一个成熟的排放源0- 1,1 -10和10-100公里范围内热液来源的铁的命运。首先，我们将利用Juan de Fuca Ridge的主要奋进部分提供的详细的微测深和长期流计数据来实现最近开发的3D理论羽散模型，该模型可以预测详细的3D弥散轨迹和远离两个长期研究和特征明确的主要奋进区（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哨兵自主水下航行器（AUV）的调查，这些调查将跟随羽流“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）]进行3D调查，这将使我们能够(1)确认（并更好地约束）预测模型；(2)绘制出羽流的形状和轨迹，为我们将从AUV和从痕量金属清洁ctd花环中收集的离散水柱样本提供背景。AUV的采样将使用为CLIO痕量金属清洁水采样器设计的最新一代SUPR采样器。这将足以用于溶解，胶体和颗粒微量金属的样品和收集过滤材料进行逐粒矿物学和生物地球化学分析。该采样计划将通过使用CTD-rosette进行更大体积的羽流采样来支持，以增强我们基于auv的计划，并进行氦同位素分析（跟踪在顺风和羽流之间距离增加的物理羽流稀释程度），并进行互补配体和有机化合物分析，以研究有机络合可能在保护还原态铁[和锰（Mn）中发挥的作用。防止氧化沉淀和从海洋水柱中去除。巡航后，我们的生物地球化学测量和改进的3D物理建模的结合不仅能够提供新的见解，控制铁和锰从热液喷口到海洋的通量的过程，而且这些过程生效的长度尺度。最后，由于我们的三维理论模型包含了速度，我们也预计能够推断出这些过程发生的速率。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。