Collaborative Research: RAPID: Extreme disturbances/perturbations to coastal deposition systems

该项目将利用2021年8月飓风艾达穿越墨西哥湾北方陆架的机会，研究沿海沉积物中二氧化硅循环的重要方面。在沿海系统中，水柱初级生产力主要由硅藻控制，硅藻是一组浮游植物，它们产生无定形生物硅壳。这种生物成因的二氧化硅可以以其原始的未改变的形式被掩埋，或者经过化学反应将其转化为铝硅酸盐矿物（例如海洋粘土）。后一个过程在包括碳在内的许多元素的全球化学预算中很重要。影响硅是以生物成因二氧化硅的形式埋藏还是转化为硅铝酸盐的因素之一可能是沉积物中的氧含量。风暴混合了海洋沃茨，可以为浅水中的沉积物添加氧气，从而可能改变二氧化硅的平衡。研究人员于2021年8月初，也就是飓风艾达前两周收集了沉积物样本。在风暴后的一年中取样将使他们能够测试风暴是否影响二氧化硅循环。热带和亚热带沿海沉积系统封存了全球25-40%的二氧化硅汇，相对于其面积而言，这是一个不成比例的巨大影响。在墨西哥湾北方，季节性水柱分层可能会影响沉积生物硅的加工和保存限制氧气注入到底栖生物，季节性驱动生物硅埋藏效率。飓风艾达于2021年8月底穿过密西西比三角洲和邻近的路易斯安那州大陆架。2021年8月，飓风艾达在路易斯安那州福尔雄港登陆前13天，研究小组在西南山口（主要的密西西比河支流）和路易斯安那州可可德里之间的顶部三角洲沉积物中的3个地点收集了沉积物岩心;所有地点都经历了艾达的4级飓风条件，最大持续风速为130节（67米/秒）。Ida是一场比2017年的飓风Harvey或Nate强得多的风暴，可能会将氧气引入近海岸区的沉积物中，也许足以将沉积物柱顶部的大部分氧化。研究人员推测，风暴引起的氧化还原和成岩条件的变化最初有利于生物硅的埋藏，而不是自生铝硅酸盐。使用多代理方法，该项目将分析这一重大风暴事件如何改变生物硅埋藏在十个月的过程中。该奖项反映了NSF的法定使命，并已被认为是值得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的支持。

This project will take advantage of the passage of Hurricane Ida across the northern Gulf of Mexico shelf in August, 2021 to study important aspects of the cycling of silica in coastal sediments. In coastal systems, water column primary productivity is dominated by diatoms, a group of phytoplankton which produce a shell of amorphous biogenic silica. This biogenic silica can either be buried in its original unaltered form or undergo chemical reactions that convert it to aluminosilicate minerals (e.g. marine clays). This latter process is important in global chemical budgets for many elements, including carbon. One of the factors that influences whether silicon is buried as biogenic silica or converted to aluminosilicates may be the amount of oxygen in the sediments. Storms mix the ocean waters and can add oxygen to sediments in shallow water, potentially changing the silica balance. The investigators collected sediment samples in early August, 2021, two weeks before Hurricane Ida. Sampling through the year after the storm will allow them to test whether storms affect silica cycling. This project will support an early-career investigator and undergraduate student researchers.Tropical and subtropical coastal deposition systems sequester 25-40% of the global silica sink, a disproportionately large impact relative to their area. In the northern Gulf of Mexico seasonal water column stratification may impact how sedimentary biogenic silica is processed and preserved by limiting oxygen injections into the benthos, seasonally driving biogenic silica burial efficiency. Hurricane Ida moved through the Mississippi Delta and adjacent Louisiana shelf at the end of August 2021. Thirteen days prior to Hurricane Ida’s landfall in Port Fourchon, LA, in August 2021, the team collected sediment cores at 3 sites in the topset delta sediment between the Southwest Pass (major Mississippi River distributary) and Cocodrie, LA; all sites experienced Category 4 hurricane conditions from Ida with maximum sustained winds of 130 knots (67 m/s). Ida, a much stronger storm than either Hurricanes Harvey or Nate in 2017, likely introduced oxygen into the sediment of the proximal coastal zone, perhaps enough to turn most of the top meter or so of the sediment column oxic. The investigators hypothesize that the storm-induced change in redox and diagenetic conditions initially favored burial of biogenic silica rather than an authigenic aluminosilicate. Using a multi-proxy approach, this project will analyze how this major storm event altered biogenic silica burial over the course of ten months.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.