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/X014193/1
• 负责人: Joanne Hopkins
• 金额: $ 78.56万
• 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: 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%2FX014193%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，即以植物为食的微型植物(浮游植物)和微小动物(浮游动物)，对海洋生物和地球气候至关重要。它们构成了支撑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藏在海洋深处(或将其输出到海洋深处)。目前认为，浮游生物每年负责从大气中去除60亿吨碳；化石燃料燃烧每年向大气中释放约100亿吨碳。如果没有海洋中碳的这种输出，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做得更好，因为(1)较大的浮游植物下沉得更快，将碳从海面上移走，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，并分泌快速下沉的大型粪便颗粒，迅速将碳从大气中转移出去。我们发现了一种新的联系，即浮游生物可以生长的类型与大洋中脊上流动的潮汐之间的联系。海洋是分层的，表面有较温暖、密度较低的层，海洋深处有较冷、密度较大的层。当潮流在大洋中脊的两侧上下流动时，这些层就会被向上和向下推，在这些层上产生波，这种波被称为“内潮汐波”。这些内部潮汐波到达阳光充足的上层海洋，浮游植物在那里进行光合作用。我们认为这些浪潮有两个重要的影响。(1)海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；这将有助于额外的浮游植物生长，但关键的是，额外的营养供应也是已知的，允许更大种类的浮游植物生长。(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，它们会更接近海面的光，从而能够生长得更多。因此，我们认为，内部潮汐波在大洋中脊上创造了更多更大的浮游生物生长，这意味着更好的海洋食物链和更多的碳从大气中输出。这种新的联系可能解释了为什么海脊支持如此多样化的生态系统，也意味着海脊上的海洋比我们之前认为的更善于输出碳。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在内，浮游生物出口的碳含量比目前的估计增加了约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脊潮效应，大大低估了浮游生物从大气中清除的二氧化碳的量。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。我们将对南大西洋的大洋中脊进行一次探险。我们将测量内部潮汐波和营养物质的向上混合，以及这些潮汐波对浮游植物接收的光的影响。我们将测量浮游植物和浮游动物对这些海浪的反应有多快，浮游生物物种在海脊上的变化，以及与邻近的洋盆相比，海脊上向下输出了多少碳。这将是第一次将内潮汐波与海洋中碳输出的模式联系起来：内潮汐波发生在海洋中任何有海脊或海山的地方，我们的结果将对我们对海洋食物网和地球气候的理解产生重要的全球影响。