Collaborative research: Arctic Shelf sediment fate - an observational and modeling study of sediment pathways and morphodynamic feedbacks in a changing polar environment

在许多沿海环境中，海岸线侵蚀是海洋沉积物的主要来源。随着时间的推移，这些物质沿着海岸（滋养海滩）和/或近海（形成深水泥块）运输。一些最高的海岸侵蚀率发生在北极，因为含有永久冻土的土地在温暖的海水和海浪的影响下很容易融化。但是一旦这些沉积物进入北冰洋，我们对它们的去向知之甚少。在过去的几十年里，沉积物运输研究一直是海岸管理和地质调查的重要组成部分，但主要集中在温带和热带环境，不受季节性海冰的影响。我们迫切需要将这些研究扩展到北极，以提高我们对沉积物命运的理解，沉积物可以重塑海岸线，改变海底的特征，并将营养物质从陆地转移到海洋。这项研究是及时的，因为与季节性海冰面积减少和波浪能增强有关的海岸侵蚀加速，预计这种趋势将继续下去。本研究旨在确定开放水域季节沿海海洋沉积物的主要路径，预计频繁的风暴会调动最近运送到海底的沉积物。测量将包括颗粒浓度、沉积物在秒到月的时间尺度上的迁移、海底成分和海底岩土特性。这些数据将用于模拟阿拉斯加大陆架如何在数千年的时间尺度上随着海岸线和波浪条件的变化而演变。该项目将由一组具有实地、岩土工程和建模专业知识的研究人员来解决。计划与当地社区建立联系，培训研究生，并通过课程和旨在介绍来自代表性不足群体的学生参与科学研究的项目与北卡罗来纳大学的本科生接触。加速海岸侵蚀是北极地区发生的关键环境变化之一，与海冰面积每年减少导致的波浪气候加剧有关。目前，阿拉斯加北极海岸线的部分地区正经历着世界上最严重的海岸侵蚀。这些速率正在加速，表明进入沿海海洋的沉积物和相关营养物质的来源期增加了。虽然对大陆架动力学的研究为温带和热带纬度的沉积物运输提供了很好的见解，但我们对北极大陆架上沉积物的路径知之甚少。这些偏远的环境一年中有9个月被冰覆盖，经历了独特的过程，如冰压力脊的形成，锚冰生长对海床的干扰，以及破裂时的“卷饼冲刷”。这些过程可能会混淆沉积物积聚的传统海底特征。因此，本项目建议将海底特性测量与风暴季节水柱内泥沙通量的动态测量相结合，以确定泥沙通量的关键机制和途径。野外数据将用于驱动大陆架剖面演化的形态静态和形态动力学模型，以确定波浪传播、侵蚀和大陆架剖面在千年时间尺度上变化之间的反馈。现场包括哈里森湾和邻近的大陆架，接收来自迅速退缩的悬崖和科尔维尔河的沉积物。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。

In many coastal environments, shoreline erosion provides a major source of sediment to the ocean. Over time, this material is transported along the shore (to nourish beaches) and/or offshore (to form deeper-water mud patches). Some of the highest rates of coastal erosion occur in the Arctic because ground containing permafrost thaws easily under the influence of warm ocean water and wave attack. But once that sediment enters the Arctic Ocean, we know very little about where it goes. Studies of sediment transport have been a critical part of coastal management and geologic inquiry for the past several decades but have focused on temperate and tropical environments not impacted by seasonal sea ice. We have a critical need to expand these studies to the Arctic in order to improve our understanding of the fate of sediments, which can re-shape coastlines, change the character of the seabed, and transfer nutrients from land to ocean. This research is timely in light of accelerating coastal erosion associated with reductions in seasonal sea-ice extent and intensifying wave energy, trends which are forecast to continue. This study is designed to determine the primary pathways of sediments in the coastal ocean during the open-water season, when frequent wind storms are expected to mobilize sediments recently delivered to the seabed. Measurements will include particle concentrations, sediment migration on time scales of seconds to months, seabed composition, and seabed geotechnical properties. These data will be used to model how the Alaskan continental shelf may evolve over thousand-year timescales in response to changing shorelines and wave conditions. This project will be tackled by a team of researchers with field, geotechnical, and modeling expertise. Networking with local communities, training of graduate students, and engagement with undergraduates at the University of North Carolina through classes as well as programs aimed at introducing students from underrepresented groups to scientific research are planned.Accelerating coastal erosion is one of the critical environmental changes occurring in the Arctic and is associated with intensifying wave climates driven by annual reductions in sea-ice extent. At present, parts of the Alaskan Arctic coastline are experiencing some of the greatest rates of coastal erosion worldwide. These rates are accelerating, representing an increased source term of sediment and associated nutrients into the coastal ocean. While studies of continental shelf dynamics have provided great insights to sediment transport at temperate and tropical latitudes, we know relatively little about the pathways of sediment on Arctic continental shelves. These remote environments are shrouded by ice for up to nine months of the year and experience unique processes like ice pressure-ridge formation, disturbance of the seabed by anchor-ice growth, and 'strudel scour' during breakup. These processes can confound traditional seabed signatures of sediment accumulation. Thus, this project proposes to pair measurements of seabed properties with dynamic measurements of sediment fluxes within the water column during the storm season to determine the key mechanisms and pathways of sediment flux. Field data will be used to drive morphostatic and morphodynamic models of shelf profile evolution to determine feedbacks between wave propagation, erosion, and changes in the shelf profile over millennial timescales. The field site encompasses Harrison Bay and the adjacent shelf, which receives sediment from rapidly retreating bluffs and the Colville River.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.