Investigation of mechanisms leading to seasonal hypoxia in the Southern Benguela Upwelling System

东大西洋的南部本格拉上升流系统是世界海洋中最肥沃的区域之一，拥有经济上重要的渔场。不幸的是，SBUS的沃茨会发生溶解氧严重耗尽的情况，这种情况也称为季节性缺氧，已经观察到这会导致大量鱼类死亡。 为了更好地了解触发严重缺氧事件的过程，该研究将结合联合收割机现场观察（分析水样中溶解的硝酸盐，亚硝酸盐，铵，可溶性活性磷和亚硝酸盐，以及硝酸盐同位素比率，以确定上升流系统中营养物质的来源和命运）和建模。 这种结合的方法是一个强有力的手段，确定的过程，有助于在SBUS缺氧的发展，从拟议的研究中收集的机制可能会超出SBUS的其他上升流地区，如北方本格拉，加州和秘鲁上升流系统。 关于外联活动，研究生将制作一部关于他们在南非研究的短片。 这部影片可在康涅狄格大学和开普敦大学的网站和YouTube上查阅，将作为向更广泛的受众传播科学的一种手段。作为该项目的一部分，将支助和培训两名研究生。 这些学生将有机会与参与这项研究的南非合作者开普敦大学的Sarah福塞特博士和Jennifer Veitch博士合作。南部本格拉上升流系统（SBUS），南非和纳米比亚的海岸，受到严重的季节性缺氧，已被观察到对野生动物，渔业和国民经济产生灾难性的影响。 康涅狄格大学的研究人员认为，这一地区缺氧事件的倾向与水文前沿近岸大陆架上的营养捕获程度有关。 这反过来又影响了随后的水华的强度，以及当这种有机物质最终在货架底部分解时随之产生的需氧量。 为了证实营养循环在调节缺氧事件中的作用，科学家们将利用观察和定量模拟相结合。 溶解营养素和硝酸盐同位素比率的分析，从水样本收集的季度监测巡航在SBUS将被用来评估营养循环在调节缺氧事件的作用。 与此同时，一个理想化的循环模式的SBUS将开始测试的假设周围近岸营养捕获和事件缺氧。 具体而言，重点将是风的强度和周期性的潜在作用，货架锋面结构和沿岸压力梯度在调制的负担回收养分被困在货架上，其关联缺氧。 最后，SBUS的海洋环流和海洋地球化学将使用现实的后投模型与现实的大气，潮汐和海洋边界条件进行后投模拟的三维环流和水文整个域。这个耦合的物理-地球化学模型将被质疑，以充分调查拟议的营养捕获机制，并确定其在调节缺氧强度的作用，每年之间，并从该预测模型可以developed.This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。

The Southern Benguela Upwelling System (SBUS) in the eastern Atlantic Ocean ranks among the most fertile region in the world ocean, host to economically important fishing grounds. Unfortunately, waters of the SBUS are subject to events wherein dissolved oxygen is severely depleted, a condition also known as seasonal hypoxia, which have been observed to cause substantial fish kills. To gain a better understanding of the processes triggering severe hypoxic events, the study will combine field observations (analyzing water samples for dissolved nitrate, nitrite, ammonium, soluble reactive phosphorus, and silicic acid, as well as nitrate isotopic ratios to identify the origin and fate of nutrients in upwelling systems) and modeling. This combined approach is a powerful means of identifying the processes that contribute to the development of hypoxia in the SBUS and the mechanisms gleaned from the proposed study are likely to extend beyond the SBUS to other upwelling regions, such as the Northern Benguela, California and Peru Upwelling Systems. For outreach activities, graduate students would create a short film on their research in South Africa. This film, made available on the University of Connecticut and the University of Cape Town websites and YouTube, would serve as a means of communicating the science to broader audiences. Two graduate students would be supported and trained as part of this project. These students would have the opportunity to work with the South African collaborators at the University of Cape Town, Drs. Sarah Fawcett and Jennifer Veitch, involved in the study. The Southern Benguela Upwelling System (SBUS), off the coasts of South Africa and Namibia, is subject to severe seasonal hypoxia which has been observed to have catastrophic impacts on wildlife, fisheries, and national economies. Researcher from the University of Connecticut posit that the propensity for hypoxic events in this region is linked to the extent of nutrient trapping on the shelf inshore of the hydrographic fronts. This, in turn, influences the intensity of subsequent blooms, and the consequent oxygen demand when this organic material is ultimately decomposed at the shelf bottom. To confirm the role of nutrient cycling in modulating hypoxic event, the scientists will utilize a combination of observations and quantitative simulations. Analyses of dissolved nutrients and nitrate isotope ratios from water samples collected on quarterly monitoring cruises in the SBUS will be used to assess the role of nutrient cycling in modulating hypoxic events. Concurrently, an idealized circulation model of the SBUS will be initiated to test the hypotheses surrounding inshore nutrient trapping and incident hypoxia. Specifically, the focus will be on the potential roles of wind intensity and periodicity, shelf frontal structure, and the alongshore pressure gradient in modulating the burden of recycled nutrients trapped on the shelf and its association with hypoxia. Finally, the ocean circulation and biogeochemistry of the SBUS will be modeled using a realistic hind-cast model forced with realistic atmospheric, tidal, and ocean boundary conditions to make hind-cast simulations of the 3-D circulation and hydrography throughout the domain. This coupled physical-biogeochemical model would be queried to fully investigate the proposed nutrient trapping mechanism and define its role in modulating the intensity of hypoxia inter-annually and from which a prognostic model can be developed.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.