Collaborative Research: Grazing and Iron Controls of Diatom Blooms in the Arabian Sea

阿拉伯海是重要的全球C和N的预算，因为它的高速率的年度初级生产，其广泛的区域的氧气消耗和反硝化作用，并通过海洋-大气反馈季风风和上升流强度，特别是阿曼上升流，由西南季风驱动的预期强烈响应全球变暖。阿拉伯海的矛盾之处在于，与其他物理动态上升流系统相比，它产生的浮游植物响应非常微弱和延迟。在阿拉伯海，尽管有明显丰富的营养物质、种子资源和有利的水文条件，但大型硅藻的密集繁殖是独一无二的。减弱的响应转移沿海上升流区的碳输出离岸和延迟的主要通量事件，直到西南季风的后期阶段，具有重要意义的西部边界的氧气最小区。这项工作将测试这样的假设：放牧相互作用、铁限制或两者兼而有之，控制着硅藻，更一般地说，控制着阿拉伯海的浮游植物生物量、生产和延迟通量特征。控制食草动物是美国JGOFS计划的一个主要结论，但尚未经过检验。在2007年，其中一名研究人员发现，在西南季风期间，阿拉伯海中部和南部的一大片区域是铁有限的，这与最近的模拟研究一致。铁限制可能会加剧放牧调节，铁和放牧实验的整合是工作计划的核心部分。2010年西南季风期间对阿曼上升流区域的巡航将包括铁和营养盐地球化学、浮游生物群落结构和动态、浮游植物生长和生产的特定分类估计、微型和中型浮游动物的放牧贡献，重点是大型桡足类（Calanoides carinatus，Subeucalanus crassus，Paraeucalanus sewelli），其生活史，丰度和大小与自上而下的调节作用一致。该方法将涉及评估拉格朗日漂流阵列后的净群落变化率，以及同期对浮游植物生长、生产、微型和中型浮游动物摄食的原位研究。船上实验将解决浮游植物的反应，增加铁和硅和繁殖反应的主要大型食草动物的食物供应，他们的能力，调节放牧的影响，微型草食动物和他们的直接和间接影响较低的营养水平。采样方案将解决的丰度，深度分布和脂质含量的主要食草动物在一年中的一个关键时间（8月至9月）时，很少有以前的数据，因为动物准备离开表面沃茨迁移到中层深度。阿拉伯海的放牧控制，如果得到证实，将是一个独特的例子，自上而下的监管一个重要的开放海洋生态系统的碳和氮循环的重要后果。此外，了解铁的可用性的潜在限制效应将使我们能够更好地预测海洋生态和海洋地球化学将如何应对气候和季风强度的变化，影响周围干旱陆地的灰尘通量。该项目旨在了解上升流系统中对生产、碳循环和输出的生态、生物和地球化学限制，以便更好地预测和模拟气候变化的影响。该项目还将为印度和阿曼的海洋学基础设施做出贡献，这两个国家都是美国在印度洋的重要合作伙伴，并将继续开展公共宣传活动，K-12教育，扩大本科教育机会，例如通过MATE计划，以及海洋科学多样性学生的研究生培训。

The Arabian Sea is important in global C and N budgets because of its high rates of annual primary production, its extensive zone of oxygen depletion and denitrification, and its expected strong response to global warming via ocean-atmosphere feedback to monsoon winds and upwelling intensity, especially the Oman Upwelling, driven by the SW Monsoon. The paradox of the Arabian Sea is that it produces a very weak and delayed phytoplankton response compared to other physically dynamic upwelling systems. Thick blooms of large diatoms are uniquely not evident in the Arabian Sea despite apparently abundant nutrients, seed stocks and favorable hydrographic conditions. The subdued response shifts carbon export offshore of the coastal upwelling area and delays major flux events until the latter stages of the SW Monsoon, with important implications for the western boundary of the oxygen minimum zone. This work will test the hypotheses that grazing interactions, iron limitation, or both, control diatoms and, more generally, phytoplankton biomass, production and the delayed flux characteristics of the Arabian Sea. Grazer control was a major, but as yet untested, conclusion of the US JGOFS program. In 2007, one of the investigators found that a large region of the central and southern Arabian Sea was Fe-limited during the SW Monsoon, consistent with recent modeling studies. Iron limitation may exacerbate grazing regulation, and integration of Fe and grazing experiments is a central part of the work plan. A cruise to the Oman upwelling region during the SW Monsoon in 2010 will include iron and nutrient biogeochemistry, plankton community structure and dynamics, taxon-specific estimates of phytoplankton growth and production, grazing contributions of micro- and mesozooplankton, with a focus on large copepods (Calanoides carinatus, Subeucalanus crassus, Paraeucalanus sewelli), whose life histories, abundance and size are consistent with a top-down regulatory role. The approach will involve assessment of net community rates of changes following a Lagrangian drift array and contemporaneous in situ studies of phytoplankton growth, production, micro- and mesozooplankton grazing. Shipboard experiments will address the response of phytoplankton to added Fe and Si and reproductive responses of dominant large grazers to food supply, their ability to modulate the grazing impacts of micro-herbivores and their direct and indirect effects on lower trophic levels. The sampling program will resolve the abundances, depth distribution and lipid contents of major grazers during a critical time of year (August-September) when there is little previous data and as the animals are preparing to leave surface waters for their seasonal diapause migration to mesopelagic depths. Grazing control in the Arabian Sea, if confirmed, will be a unique example of top-down regulation of a significant open-ocean ecosystem with important consequences for carbon and nitrogen cycling. Furthermore, understanding the potential limiting effects of Fe availability will allow us to better anticipate how the ocean ecology and biogeochemistry will respond to changes in climate and monsoon intensity that affect dust fluxes from the surrounding arid landmasses.The most recent IPCC report cites changes in monsoon intensity as a likely impact of the present trend in planetary warming. This project seeks to understand ecological, biological and geochemical constraints on production, carbon cycling and export in the upwelling system so that the effects of climate changes can be better anticipated and modeled. This project will also contribute to the oceanographic infrastructure of India and Oman, both critical US partners in the Indian Ocean, as well as continue ongoing activities in public outreach, K-12 education, broadening undergraduate educational opportunities, for example through the MATE program, and graduate training of diversity students in marine science.