Zinc, iron and phosphorus co-limitation in the Ocean (ZIPLOc)

浮游植物是生活在阳光充足的表层海洋中的微小植物。浮游植物通过光合作用固定二氧化碳，并利用必要的营养物质，如硝酸盐、磷酸盐和微量金属，如锌和铁，来产生有机物。在这样做的过程中，海洋浮游植物为鱼类和海洋哺乳动物等营养水平较高的物种提供能量，并有助于二氧化碳在大气和海洋之间的分配。超过40%的海洋由被称为亚热带环流的巨大偏远生态系统组成，亚热带环流以温暖的表层水域和极低的营养浓度为典型特征。事实上，浮游植物的活动经常因缺乏营养物质而受到抑制。然而，由于其广阔的面积，副热带涡旋对海洋碳和营养循环的方式有重大影响。这意味着未来亚热带系统活动的任何变化都将对海洋资源以及海洋与气候和地球系统的相互作用产生重要影响。我们目前对未来环流中浮游植物活动将如何应对气候变化的理解是，由于海洋环流的变化，所有必需营养物质的供应将全面减少，导致浮游植物活动下降。然而，这种简化的观点忽略了自然和人为添加到地表水中的氮，这会增加硝酸盐相对于磷酸盐的储量。在亚热带北大西洋，通过固氮而自然增加的氮会导致磷酸盐限制浮游植物的生长。在亚热带北太平洋，最近的观察表明，通过燃烧和化肥增加的人为氮正在导致北太平洋从硝酸盐转向磷酸盐有限的生态系统。持续的人为来源不断向副热带环流系统添加氮意味着，磷的稀缺将在未来几十年成为一个日益严重的问题。目前，浮游植物被认为通过产生酶来适应磷的匮乏，这些酶允许它们从更丰富的溶解有机磷(DOP)池中获取磷。因此，海洋学界通常认为磷酸盐对浮游植物活动的限制并不重要。与这种流行的观点相反，我们的团队发现，浮游植物从DOP中获取磷酸盐的能力可以通过锌的供应来调节。锌是一种微量金属，对浮游植物是必不可少的，但以前从未被证明在控制浮游植物生长方面扮演着如此重要的角色。在亚热带，微量金属铁如何与硝酸盐和磷酸盐相互作用已经引起了很大的关注，但现在显然需要更好地了解锌的作用及其与其他营养循环和浮游植物的相互作用。我们的初步工作表明，通过控制磷酸盐稀缺的影响，锌可能是副热带环流生态系统如何演变的最终仲裁者。我们的目标是结合对北大西洋副热带环流的实地研究，并使用新的技术来测量锌和磷如何控制生物活性。然后，我们将使用最新的建模工具来进一步探索我们在十年时间尺度和其他海洋盆地中的观测结果。北大西洋环流以低磷和低锌为典型特征，因此是了解锌的有效性如何塑造未来亚热带环流生态系统的理想自然实验室。我们雄心勃勃的计划有可能改变我们对亚热带环流生态系统如何应对持续气候变化的理解。我们的团队结合了营养物和浮游植物生物活动的观察和建模方面的世界领先企业，因此在提供这一关键的科学见解方面处于独特的地位。

Phytoplankton are microscopic plants that live in the sunlit surface ocean. Phytoplankton fix carbon dioxide and use essential nutrients such as nitrate, phosphate and trace metals, such as zinc and iron, via photosynthesis, to produce organic matter. In doing so, marine phytoplankton provide energy to higher trophic levels, such as fish and marine mammals, as well as contribute to the distribution of carbon dioxide between the atmosphere and ocean. Over 40% of the ocean consists of vast remote ecosystems known as subtropical gyres, which are typified by warm surface waters and extremely low nutrient concentrations. Indeed, the activity of phytoplankton is often suppressed by the lack of nutrients. However, due to their vast areal extent, subtropical gyres have a significant impact on the way the ocean cycles carbon and nutrients. This means that any future changes in the activity of subtropical systems will have important impacts on marine resources and how the ocean interacts with the climate and the Earth System. Our present understanding of how phytoplankton activity in the gyres will change in the future in response to climate change is that there will be an overall reduction in the supply of all essential nutrients due to changes in ocean circulation, causing a decline in phytoplankton activity. However, this simplified view ignores both the natural and anthropogenic addition of nitrogen to surface waters, which enhance stocks of nitrate relative to phosphate. In the subtropical North Atlantic, the natural addition of nitrogen via nitrogen fixation causes phosphate to limit phytoplankton growth. In the subtropical North Pacific, recent observations show that the addition of anthropogenic nitrogen via combustion and fertilisers are causing the North Pacific to be driven from a nitrate to a phosphate limited ecosystem. The on-going addition of nitrogen to the subtropical gyre systems from continued anthropogenic sources implies that phosphate scarcity will become an increasing problem over the coming decades. At present, phytoplankton are thought to adapt to phosphate scarcity by producing enzymes that allow them to acquire phosphate from the more abundant pools of dissolved organic phosphorus (DOP). As such, the oceanographic community typically assumes phosphate limitation of phytoplankton activity to be unimportant. In contrast to this prevailing view, our team have found that the ability of phytoplankton to acquire phosphate from DOP can be regulated by the supply of zinc. Zinc is a trace metal that is essential for phytoplankton, but has never before been shown to play such a fundamental role in controlling phytoplankton growth. Much attention has been placed on how the trace metal iron interacts with nitrate and phosphate in the subtropics, but there is now an explicit need to better understand the role of zinc and its interaction with other nutrient cycles and phytoplankton. Our initial work suggests that by controlling the impact of phosphate scarcity, zinc may be the ultimate arbiter of how subtropical gyre ecosystems evolve.Our goal is to combine a field study to the subtropical gyre North Atlantic and use novel techniques to measure how zinc and phosphorus control biological activity. We will then use the latest modelling tools to explore our observations further over decadal timescales and other ocean basins. The North Atlantic gyre is typified by low phosphate and zinc and is therefore an ideal natural laboratory in which to understand how zinc availability may shape future subtropical gyre ecosystems. Our ambitious proposal has the potential to produce a step change in our understanding of how subtropical gyre ecosystems respond to ongoing climate change. Our team combines world leaders in the observation and modelling of nutrients and phytoplankton biological activity and is therefore uniquely placed to deliver this crucial scientific insight.