Enhanced carbon export driven by internal tides over the mid-Atlantic ridge (CarTRidge)

大西洋中脊内潮汐推动碳输出增强 (CarTRidge)

• 批准号: NE/X014576/1
• 负责人: Alex Poulton
• 金额: $ 38.03万
• 依托单位: Heriot-Watt University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX014576%2F1
• 关键词: Enhanced; carbon; export; driven; internal

Plankton in the ocean, microscopic plants (phytoplankton) and tiny animals (zooplankton) that eat the plants, are vital to marine life and to Earth's climate. They form the base of food chains that support ocean ecosystems, and remove carbon from the atmosphere and bury it in (or export it to) the ocean depths. It is currently thought that plankton are responsible for removing 6 billion tonnes of carbon from the atmosphere each year; fossil fuel burning releases about 10 billion tonnes of carbon into the atmosphere annually. Without this export of carbon in the ocean, atmospheric CO2 would be twice the current concentration. The importance of plankton to food chains and carbon export depends on the species of plankton. Larger phytoplankton are better at supporting food chains and at exporting carbon because (1) larger phytoplankton sink quicker, removing carbon away from the sea surface and contact with the atmosphere, and (2) larger phytoplankton support larger zooplankton, which are eaten by fish and which also excrete large, fast-sinking faecal pellets which quickly transfer carbon away from the atmosphere.We have discovered a new link between which types of plankton can grow and the tides flowing over a mid-ocean ridge. The ocean is layered, with warmer, less dense layers at the surface and colder, denser layers deeper in the ocean. When tidal currents flow up and down the flanks of a mid-ocean ridge, these layers are pushed up and down, causing waves on the layers called "internal tidal waves". These internal tidal waves reach up to the sun-lit upper ocean, where photosynthesis by the phytoplankton takes place. We think these waves have two important effects. (1) The waves cause mixing between the layers of ocean, bringing nutrients from deep in the ocean up to the phytoplankton; this will help extra phytoplankton growth, but crucially it is also known that extra nutrient supplies allow larger species of phytoplankton to grow. (2) The waves move the phytoplankton up and down; this provides more light to the phytoplankton, because as they are moved upward they get closer to the light at the sea surface and are able to grow more. Thus, we think that the internal tidal waves create more growth of larger plankton over a mid-ocean ridge, which means better food for marine food chains and more carbon exported away from the atmosphere.This new link may explain why ridges support such diverse ecosystems, and it also means that the ocean over ridges is far better at exporting carbon than we previously thought. We have calculated that, for the whole Atlantic Ocean, including the tidal effect of the mid-Atlantic ridge adds about 50% to current estimates of how much carbon the plankton export. This means that current understanding of the ocean's role in Earth's climate, which ignores the ridge-tide effect, significantly underestimates how much CO2 plankton remove from the atmosphere. We need to fix this because our predictions of our future climate depend on having correct descriptions of the processes that govern atmospheric CO2.We will conduct an expedition to the mid-ocean ridge in the S. Atlantic. We will measure the internal tidal waves and the upward mixing of nutrients, and the effect the waves have on light received by phytoplankton. We will measure how fast the phytoplankton and zooplankton grow in response to these waves, how the species of plankton change over the ridge, and how much carbon is exported downward over the ridge compared to the adjacent ocean basin. This will be the first time that internal tidal waves are linked to patterns of carbon export in the ocean: internal tidal waves occur wherever there are ridges or seamounts in the ocean and our results will have important global implications for our understanding of ocean food webs and Earth's climate.

海洋中的浮游生物，微生物（浮游植物）和吃植物的微小动物（浮游动物），对海洋生物和地球气候至关重要。它们构成了支持海洋生态系统的食物链的基础，并从大气中去除碳并将其埋在（或输出到）海洋深处。目前认为，浮游生物每年从大气中清除60亿吨碳;化石燃料燃烧每年向大气中释放约100亿吨碳。如果没有海洋中的碳输出，大气中的二氧化碳浓度将是目前的两倍。浮游生物对食物链和碳输出的重要性取决于浮游生物的种类。较大的浮游植物在支持食物链和输出碳方面更好，因为（1）较大的浮游植物下沉更快，将碳从海面上带走并与大气接触，（2）较大的浮游植物支持较大的浮游动物，这些浮游动物被鱼吃掉，也排泄大量的碳，快速下沉的粪便颗粒，迅速将碳从大气中转移出去。我们发现了哪种浮游生物可以生长与潮汐之间的新联系，海脊。海洋是分层的，在表面有较温暖，密度较低的层，在海洋深处有较冷，密度较高的层。当潮汐流在洋中脊的两侧上下流动时，这些层被上下推动，在这些层上引起称为“内部潮汐波”的波浪。这些内部潮汐波到达阳光照射的上层海洋，浮游植物在那里进行光合作用。我们认为这些波有两个重要的影响。(1)波浪引起海洋各层之间的混合，将海洋深处的营养物质带到浮游植物中;这将有助于额外的浮游植物生长，但重要的是，额外的营养供应也可以让更大的浮游植物生长。(2)波浪使浮游植物上下移动;这为浮游植物提供了更多的光，因为当它们向上移动时，它们更接近海面的光，并且能够生长得更多。因此，我们认为，内部潮汐波在大洋中脊上创造了更多大型浮游生物的生长，这意味着海洋食物链有了更好的食物，更多的碳从大气中输出。这种新的联系可能解释了为什么山脊支持如此多样化的生态系统，也意味着山脊上的海洋在输出碳方面比我们以前想象的要好得多。我们已经计算出，对于整个大西洋，包括大西洋中部海脊的潮汐效应，目前估计的浮游生物输出碳量增加了约50%。这意味着目前对海洋在地球气候中的作用的理解，忽略了山脊潮汐效应，大大低估了浮游生物从大气中吸收的二氧化碳。我们需要解决这个问题，因为我们对未来气候的预测取决于对控制大气二氧化碳的过程的正确描述。大西洋我们将测量内部潮汐波和营养物质的向上混合，以及波浪对浮游植物接收到的光的影响。我们将测量浮游植物和浮游动物响应这些波浪的生长速度，浮游生物的种类在海脊上如何变化，以及与邻近的海洋盆地相比，海脊向下输出了多少碳。这将是第一次将内潮汐波与海洋中的碳输出模式联系起来：内潮汐波发生在海洋中有山脊或海山的地方，我们的研究结果将对我们了解海洋食物网和地球气候产生重要的全球影响。