A nutrient and carbon pump over mid-ocean ridges (RidgeMix)

大洋中脊上的营养物和碳泵 (RidgeMix)

• 批准号: NE/L003406/1
• 负责人: Matthew Palmer
• 金额: $ 16.72万
• 依托单位: NATIONAL OCEANOGRAPHY CENTRE
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2014
• 资助国家: 英国
• 起止时间: 2014 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FL003406%2F1
• 关键词: nutrient; carbon; pump; over; mid

Phytoplankton are aquatic, single-celled plants that lie at the heart of the global cycling of carbon between the atmosphere and the oceans. Like other plants, phytoplankton require sunlight and nutrients to grow and flourish. However, in the ocean sunlight is confined to the upper few tens of metres, while nutrient concentrations are low at the sea surface and greatest at depths of a kilometre or more. The growth of phytoplankton is thus fundamentally dependent on processes that transfer deep nutrients up to the sunlit surface waters.Over the mid latitudes the problem of acquiring nutrients appears to be particularly stark. The winds at mid latitudes provide a widespread downward transport of water, which inhibits the transfer of nutrient-rich deeper waters up into the sunlit, surface waters. Thus, one might expect much of the mid latitude ocean to be a desert due to a lack of nutrients. However, phytoplankton growth in the mid latitude ocean is more than might initially be expected, and is globally very important as it drives about half of the oceans' biological removal of carbon out of the atmosphere. Oceanographers have calculated the amount of nutrient required to support this growth, and the answer agrees with estimates of total nutrient supply based on the concentrations of inert tracers in the surface ocean. However, adding together the known nutrient supplies falls significantly short of this total nutrient requirement. Hence, there is a conundrum as to how the biological growth over the mid latitude ocean is sustained. If we want to understand how carbon is cycled between the atmosphere and oceans, and how it affects our climate, we need to answer this problem.In this proposal, we address the problem of how deep nutrients are transported into the surface waters in mid-latitudes. We propose to test a new view: tides passing over the mid-Atlantic ridge generate enhanced turbulence and mixing, which in turn provides a nutrient supply to the upper thermocline waters. These nutrients are then transported horizontally along density surfaces over the western side of the basin, probably being swept along the Gulf Stream and eventually passing into the winter mixed surface layer. When this surface layer shallows and warms in spring, the nutrients are then available to the phytoplankton. The work plan involves two main components. We will carry out a field programme collecting measurements of the turbulence and nutrient concentrations over and adjacent to the mid-Atlantic ridge. This fieldwork will involve collecting data from a novel long-term moored array of instruments on the ridge along with a focused 5 week research cruise. Our work involves sampling sufficiently quickly to be able to resolve tidal changes in currents and mixing over the ridge: this has never been done before, and we have brought together scientists with expertise in tidal measurements in shallower shelf seas with others who are expert in deep ocean mixing and transports in order to do this. The 2nd component of our work will use computer models of circulation in the Atlantic to explore the wider implications of the fieldwork observations, allowing us to decide whether or not mixing over the mid-Atlantic ridge really does provide enough nutrients to explain the phytoplankton production in the mid-latitude N Atlantic.

浮游植物是水生单细胞植物，位于大气和海洋之间全球碳循环的核心。与其他植物一样，浮游植物需要阳光和营养才能生长和茂盛。然而，在海洋中，阳光仅限于上层几十米，而海面的营养物质浓度较低，在一公里或更深的深处浓度最高。因此，浮游植物的生长从根本上依赖于将深层营养物质转移到阳光照射的表层水域的过程。在中纬度地区，获取营养物质的问题似乎尤为突出。中纬度地区的风提供了广泛的水向下输送，从而抑制了营养丰富的深层水域向上转移到阳光照射的地表水域。因此，人们可能会认为中纬度海洋的大部分地区由于缺乏营养而成为沙漠。然而，中纬度海洋中浮游植物的生长超出了最初的预期，并且在全球范围内非常重要，因为它驱动了大约一半的海洋生物清除大气中的碳。海洋学家计算了支持这种生长所需的养分量，答案与基于表层海洋惰性示踪剂浓度的总养分供应估计值一致。然而，将已知的营养供应加在一起远远低于这一总营养需求。因此，如何维持中纬度海洋上的生物生长是一个难题。如果我们想了解碳如何在大气和海洋之间循环，以及它如何影响我们的气候，我们需要回答这个问题。在这个提案中，我们解决了深层营养物质如何在中层输送到地表水域的问题。纬度。我们建议测试一种新观点：经过大西洋中脊的潮汐会产生增强的湍流和混合，从而为温跃层上部水域提供营养供应。然后，这些营养物质沿着盆地西侧的密度表面水平输送，可能沿着墨西哥湾流扫过，最终进入冬季混合表层。当春季表层变浅并变暖时，浮游植物就可以利用营养物质。该工作计划包括两个主要部分。我们将开展一项实地计划，收集大西洋中脊上方和附近的湍流和营养物浓度的测量结果。这项实地工作将包括从山脊上长期停泊的新型仪器阵列收集数据，以及为期 5 周的重点研究巡航。我们的工作包括足够快地采样，以便能够解决洋流的潮汐变化和海脊上的混合：这是以前从未做过的，我们将具有浅海陆架潮汐测量专业知识的科学家与其他深海潮汐测量专家聚集在一起为此，需要进行海洋混合和运输。我们工作的第二部分将使用大西洋环流的计算机模型来探索实地观测的更广泛影响，使我们能够确定大西洋中部海脊上的混合是否确实提供了足够的营养来解释浮游植物的产生。中纬度北大西洋。