Collaborative Research: Are Low-Temperature Hydrothermal Vents an Important but Overlooked Source of Stabilized Dissolved Iron to the Ocean?

合作研究：低温热液喷口是否是海洋稳定溶解铁的重要但被忽视的来源？

• 批准号: 1756590
• 负责人: Peter Sedwick
• 金额: $ 24.29万
• 依托单位: Old Dominion University Research Foundation
• 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: 2018-04-01 至 2023-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1756590&HistoricalAwards=false
• 关键词: Collaborative; Research; Low; Temperature; Hydrothermal

Hydrothermal vents are hot springs on the seafloor. They are often thousands of meters below the surface of the ocean along the large volcanic mountain ranges called the mid-ocean ridges. Relatively little is known about these hydrothermal vents because they exist so far from the ocean surface. Instead of lava, these vents emit warm to hot fluids (from several ºC up to 350 ºC) into the ocean, and contain high concentrations of a wide range of dissolved chemicals. One of these chemicals, iron, has been studied extensively by ocean scientists because of its importance as an essential nutrient for the microscopic photosynthetic algae called phytoplankton that grow in surface ocean waters. Scientists once thought that most of the dissolved iron coming out of hydrothermal vent fluids would quickly precipitate (form a solid and sink) near the vents, as a result of chemical reactions between the hot vent fluid and cold seawater, and therefore only small amounts of dissolved iron could be transported from the deep sea mid-ocean ridges to surface waters where phytoplankton grow. However, on a recent scientific expedition over one of the most active mid-ocean ridges called the southern East Pacific Rise (SEPR), scientists discovered that much of the dissolved iron discharged from the SEPR hydrothermal vents was in fact transported thousands of kilometers across the deep ocean. In addition, computer simulations suggest that a substantial amount of this ?hydrothermal iron? is transported as far as the surface waters of the Southern Ocean around Antarctica, where it could support the growth of phytoplankton.Scientists from the University of Washington, Woods Hole Oceanographic Institution and Old Dominion University will return to the SEPR aboard a research ship and make additional measurements to better understand how hydrothermal vents add dissolved iron to the deep ocean. They will use specialized sampling equipment, including unmanned miniature submarines called autonomous underwater vehicles (AUVs), to map the distribution of hydrothermal vents in this region, and collect water samples from both high temperature (250-350 ºC) and low temperature ( 150 ºC) vents. These samples will be analyzed for chemicals that are enriched in the hydrothermal vent fluids, such as iron, manganese and helium-3, which will provide information on the chemical changes that occur as the hydrothermal vent fluids mix with surrounding seawater and are carried away from the SEPR. The scientists will use their observations and chemical analyses to address the following major questions: 1) are there more hydrothermal vents along mid ocean ridges than previously thought? and (2) are low temperature hydrothermal vents especially favorable for stabilizing dissolved iron, and ultimately transporting it to the surface ocean where it supports phytoplankton growth? The project will contribute to the education and training of a graduate student and two senior undergraduate students, and outcomes will be incorporated into high school STEM curricula. The research activities will be communicated via public lectures and media releases, and project results will be disseminated to the scientific community by conference presentations, publications in peer-reviewed scientific journals, and freely available on-line archived data.Along thousands of kilometers of the seafloor volcanic chains known as the mid-ocean ridges, hydrothermal vents discharge hot, acidic, metal-rich fluids into the deep ocean. These submarine hot springs are a major gateway for the exchange of heat and chemicals between the solid earth and the deep ocean, and have received intensive scientific study during the last 40 years. This research has overwhelmingly focused on high temperature (~200-350°C) hydrothermal vents. Lower temperature (150°C) hydrothermal venting has received relatively little attention, although results from recent observational and modeling studies point to the greater abundance of low temperature discharge along the mid-ocean ridges, and its potential importance for the input of elements and chemical compounds into the deep ocean. Among the elements that are enriched in hydrothermal vent fluids, iron has received attention because of its role as an essential nutrient for primary production in the surface ocean. It has long been thought that most of the dissolved iron discharged by hydrothermal vents is lost from solution close to mid-ocean ridge sources, and thus of limited importance for ocean chemistry. But this view has been challenged by recent studies which suggest that chemical stabilization of hydrothermal dissolved iron may facilitate its long-range transport in the deep ocean. In particular, results from the US GEOTRACES program have revealed the lateral transport of a plume of hydrothermal dissolved iron over several thousand kilometers westward from its source region on the southern East Pacific Rise (SEPR).In this project, investigators from the University of Washington, Woods Hole Oceanographic Institution and Old Dominion University will carry out a field research program on the SEPR to test the overarching hypothesis that diffuse low-temperature hydrothermal venting is a major a source of chemically-stabilized dissolved iron to the deep ocean, and hence plays an important but previously overlooked role in the ocean iron cycle. The ship-based field program will use an autonomous underwater vehicle equipped with in-situ optical and chemical sensors to identify plumes of both diffuse (low-temperature) and discrete (high-temperature) hydrothermal discharge along the SEPR. Emissions from multiple sites of both low and high temperature hydrothermal venting will be sampled for shipboard and post-cruise analyses of iron and other trace metals, and the inert hydrothermal "tracer" helium-3. The resulting data will be used to test two specific hypotheses: (1) the population of active hydrothermal discharge sites along mid ocean ridges is greater than previously estimated, (2) low temperature hydrothermal venting is conducive to the chemical stabilization of dissolved iron, thus facilitating its export to the ocean interior and ultimately to surface ocean where it supports primary production by phytoplankton. The information obtained in this research will facilitate inclusion of iron and other trace elements in numerical models of ocean biology and biogeochemistry, which will improve the ability to predict how the ocean will respond to and modulate future climatic and environmental changes.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.

热液喷口是海底的温泉，它们通常位于海底数千米处，沿着被称为大洋中脊的大型火山山脉，人们对这些热液喷口知之甚少，因为它们距离海洋很远。这些喷口不是熔岩，而是将温暖的液体（从几摄氏度到高达 350 摄氏度）排放到海洋中，并含有高浓度的多种溶解化学物质。海洋科学家对这些化学物质主要是铁进行了研究，因为它是生长在表层海水中的称为浮游植物的微小光合藻类的必需营养素，科学家曾经认为大部分溶解的铁来自热液喷口流体。由于热喷口流体和冷海水之间的化学反应，会在喷口附近快速沉淀（形成固体并下沉），因此只能从深海输送少量溶解的铁然而，在最近对最活跃的洋中脊之一（东南太平洋海隆（SEPR））进行的科学考察中，科学家发现大部分溶解的铁从东南太平洋海隆中排出。事实上，热液喷口在深海中输送了数千公里。此外，计算机模拟表明，大量的“热液铁”正在输送至南大洋周围的表层水域。南极洲，在那里它可以支持浮游植物的生长。来自华盛顿大学、伍兹霍尔海洋研究所和奥多明尼恩大学的科学家将乘坐研究船返回 SEPR 并进行额外的测量，以更好地了解热液喷口如何将溶解的铁添加到南极洲他们将使用专门的采样设备，包括称为自主水下航行器（AUV）的无人微型潜艇，绘制该地区热液喷口的分布图，并从两个高处收集水样。高温（250-350 ℃）和低温（150 ℃）喷口将分析这些样品中富含热液喷口流体的化学物质，例如铁、锰和氦-3，这将提供有关化学变化的信息。当热液喷口流体与周围海水混合并被带离SEPR时，科学家们将利用他们的观察和化学分析来解决以下主要问题：1）是否还有更多。沿着大洋中脊的热液喷口比以前想象的要好？（2）低温热液喷口是否特别有利于稳定溶解的铁，并最终将其输送到支持浮游植物生长的表层海洋？一名研究生和两名高年级本科生，研究成果将纳入高中 STEM 课程，研究活动将通过公开讲座和媒体发布进行传达，项目成果将传播给科学界。通过会议演讲、同行评审的科学期刊上的出版物以及免费提供的在线存档数据。沿着被称为大洋中脊的数千公里海底火山链，热液喷口将富含金属的热酸性流体排放到这些海底温泉是固体地球和深海之间热量和化学物质交换的主要门户，在过去 40 年中得到了深入的科学研究。尽管最近的观测和模拟研究结果表明，沿大洋中脊的低温排放量较多，但低温（~200-350°C）热液喷口受到的关注相对较少。 ，及其对于将元素和化合物输入深海的潜在重要性 在热液喷口流体中富含的元素中，铁因其作为地表初级生产的必需营养素的作用而受到关注。长期以来，人们一直认为热液喷口排放的大部分溶解铁是从接近洋中脊源的溶液中流失的，因此对海洋化学的重要性有限，但这一观点受到了最近研究的挑战，这些研究表明：热液溶解铁的化学稳定性可能有助于其在深海中的远距离迁移。特别是，美国GEOTRACES计划的结果揭示了热液溶解铁的羽流从其源区向西数千公里的横向迁移。东南太平洋海隆 (SEPR)。在该项目中，来自华盛顿大学、伍兹霍尔海洋研究所和奥多明尼恩大学的研究人员将在 SEPR 上开展一项实地研究计划，以检验弥漫性低温热液喷发的总体假设是深海化学稳定溶解铁的主要来源，因此在海洋铁循环中发挥着重要但以前被忽视的作用。船基现场项目将使用配备原位光学和技术的自主水下航行器。化学传感器可识别 SEPR 沿线多个低温和高温热液排放点的排放羽流，用于船上和巡航后的铁分析。和其他痕量金属，以及惰性热液“示踪剂”氦 3 所得数据将用于检验两个具体假设：（1）沿大洋的活跃热液排放点的数量。 （2）低温热液喷发有利于溶解铁的化学稳定，从而促进其向海洋内部并最终向表层海洋输出，从而支持浮游植物的初级生产。研究将促进将铁和其他微量元素纳入海洋生物学和生物地球化学的数值模型，这将提高预测海洋将如何响应和调节未来气候和环境变化的能力。该奖项反映了通过使用基金会的智力价值和更广泛的影响审查标准进行评估，NSF 的法定使命被认为值得支持。