RAPID: Offshore export of riverine water in the South Atlantic Bight during a strong El Nino event

确定大陆架上河流水的运输途径和离岸输出是重要的，因为低盐度水的输入影响大陆架水文和动力学及其生物地球化学过程。将现成的河水及其所含物质输出到墨西哥湾流中，有可能在北大西洋的大片地区传播它们的特征，并有可能将河流产生的碳从地表隔离到亚热带环流的地下水中。然而，标准的就地取样只允许在相对较小的区域内进行相对低分辨率的观测，因此难以调查低盐度水的分布和出口，因为这些水可能出现在狭窄的细丝中，就地取样很容易错过。将现场数据和漂浮物轨迹与最近开发的算法相结合，以检索该地区的盐度，将允许与正常年份进行比较-该项目在七次研究巡航中收集了大量数据集，以及与过去70多年来最强厄尔尼诺事件之一相关的河流流量极端年份。该项目将通过支持一名研究生和一名本科生来促进教育。该研究项目的研究结果也将在每年夏天由美国国家科学基金会资助的乔治亚州沿海生态系统长期生态研究网站组织的LTER校园计划中传播，其中来自乔治亚州的科学和数学K-12教师沉浸在动手研究活动和沿海过程的讨论中。培训K-12教师将最大限度地向广大受众传播知识，因为每位教师都有机会与来自全州的大量学生互动。作为该项目的一部分生成的所有数据集都将公开提供。该项目将研究目前正在进行的强厄尔尼诺现象期间，南大西洋湾（SAB）浅海和广阔大陆架河水的离岸输出情况，该现象的强度有望与1997/1998年的厄尔尼诺现象相媲美。南澳的河流流量受到厄尔尼诺现象的强烈影响，有记录以来阿尔塔马哈河的最高流量发生在1997/98年的强厄尔尼诺事件期间。2016年初的流量已经比同期的长期平均水平高出两个标准差，这表明2016年春季SAB可能会迎来非常高的河水流量。这提供了一个几十年一次的机会来研究极端条件下的运输途径和控制河流水在大陆架上的离岸出口的机制。该项目的研究人员将利用2016年春季的机会研究巡航，结合现场数据和最近开发的算法，从卫星观测中检索盐度。在Altamaha河口和从大陆架内部延伸到斜坡的跨大陆架横断面上部署的多个地面漂浮器将补充该数据集。2016年，在与厄尔尼诺有关的极端条件下，大陆架上的河水分布和输出将与2014年的分布和输出进行比较，2014年的流量接近历史平均水平，并在该地区的七次研究巡航中收集了大量数据集。在过去两年中，还将评估和比较涡旋和风在河流跨大陆架运输中所起的作用。

The Identification of transport pathways and offshore export of riverine water on continental shelves is important because the input of low salinity water influences shelf hydrography and dynamics, as well as its biogeochemical processes. Off-shelf export of riverine water, and the material it contains, into the Gulf Stream has the potential to spread their signatures over large areas of the North Atlantic, and to potentially sequester riverine-derived carbon away from the surface into subsurface water of the subtropical gyre. However, standard in situ sampling only allows for relatively low resolution observations over relatively small areas, making it difficult to investigate distribution and export of low-salinity water, since those can occur in narrow filaments that are easily missed by in situ sampling. The combination of the in situ data and drifter trajectories with the recently-developed algorithm to retrieve salinity in the region will allow for comparisons between normal years-the project has an extensive data set collected during seven research cruises, and an extreme year in terms of river discharge associated with one of the strongest El Nino events in the last 70+years. This project will promote education by supporting one graduate and one undergraduate student. Findings from this research project will also be disseminated in the LTER Schoolyard Program that is organized every summer by the NSF-funded Georgia Coastal Ecosystem Long-Term Ecological Research site in which science and math K-12 teachers from across the State of Georgia are immersed in hands-on research activities and discussions on coastal processes. Training K-12 teachers will maximize the dissemination of the knowledge to a large audience, since each teacher has the opportunity to interact with a large number of students from across the State. All data sets generated as part of this project will be made publicly available.This project will examine the offshore export of riverine water in the shallow and broad continental shelf of the South Atlantic Bight (SAB) during the strong El Nino currently underway, which is on track to rival the strength of the 1997/1998 event. River discharge in the SAB is strongly influenced by El Ninos, with the highest discharge ever recorded at the Altamaha River having occurred during the strong 1997/98 event. Discharge in early 2016 is already two standard deviations above the long-term average for the same period, indicating that the SAB will likely receive very high river flow during spring 2016. This provides a once-in-many-decades opportunity to investigate transport pathways and the mechanisms controlling the offshore export of riverine water over the shelf under extreme conditions. The project's investigators will take advantage of a research cruise of opportunity in spring 2016 and use a combination of in situ data and a recently-developed algorithm to retrieve salinity from satellite observations. The data set will be complemented by multiple surface drifter deployments at the Altamaha River mouth and along a cross-shelf transect extending from the inner shelf to the slope. The distribution and export of riverine water over the shelf in 2016, under extreme conditions associated with El Nino, will be compared with the distribution and export in 2014, when discharge was near the historical average and an extensive data set was collected during seven research cruises in the region. The role played by eddies and winds on cross-shelf transport of riverine water will also be assessed and compared for the past two years.