PARTITRICS: PARTIcle Transformation and Respiration Influence on ocean Carbon Storage

海洋中的碳含量是大气中碳含量的50倍。生物过程有助于在与气候有关的时间尺度(数百至数千年)将碳储存在海洋中。海洋浮游植物(漂浮的微型植物)利用上层海洋中的阳光和二氧化碳形成富含碳的身体。当浮游植物死亡时，它们可能会聚集在一起沉入海洋内部，或者它们可能会被浮游动物(微小动物)吃掉，浮游动物会产生快速下沉的粪便颗粒。一旦这些有机碳在水中更深，细菌可能会在这些颗粒上定居并分解它们，或者它们可能会被以它们为食的浮游动物分解。这些过程都会减少到达深海的有机碳的数量，然而，海洋越深，与大气接触的时间就越长。这种“生物碳泵”有助于调节我们的气候，而在海洋中没有生物的情况下，大气中的二氧化碳水平可能几乎是今天的两倍。由于缺乏对颗粒形成和呼吸功能的过程的理解，地球系统模型对生物碳泵有不同的描述，但都相当简单。为政府间气候变化专门委员会报告做出贡献的一系列模型并未就未来气候情景下海洋碳储存的变化幅度或方向达成一致。这意味着我们对未来对海洋碳储量的预测缺乏信心，而模型和观测之间越来越大的差异进一步阻碍了这一预测。在这个项目中，我们将研究在从上层海洋过境的过程中，有多少碳被呼吸，以及以什么方式呼吸。我们将测量颗粒破碎和聚集、微生物呼吸和浮游动物垂直迁移和呼吸的重要过程。我们将使用流程巡航和自动水下航行器来实现这一点。我们试图回答这个问题：有机质是如何通过生物相互作用在中上层转化和呼吸的，这种变化如何随着深度、位置和季节的变化而变化，以及对海洋碳储存的影响是什么？最终目标是对影响内部呼吸速率和深度的重要过程产生新的详细理解，我们将扩大这些过程，以提供开发下一代生物地球化学模型所需的全球解析信息。

The ocean holds fifty times as much carbon as is in the atmosphere. Biological processes contribute to storing carbon in the ocean on climate-relevant timescales (hundreds to thousands of years). Marine phytoplankton (drifting microscopic plants) use sunlight and carbon dioxide in the upper ocean to form their bodies which are rich in carbon. When phytoplankton die they might clump together and sink into the ocean interior, or they could be eaten by zooplankton (tiny animals) which produce fecal pellets that can sink rapidly. Once this organic carbon is deeper in the water, bacteria might colonise the particles and break them down, or they could be broken apart by zooplankton feeding on them. These processes all act to reduce the amount of organic carbon reaching the deep ocean, however the deeper it goes the longer it will remain out of contact with the atmosphere. This "biological carbon pump" helps to regulate our climate, and without biology in the ocean it has been shown that atmospheric carbon dioxide levels could be nearly double what they are today.Earth system models have differing, but all fairly simple, representations of the biological carbon pump due to a lack of understanding of how the processes contributing to particle formation and respiration function. The suite of models that contribute to the Intergovernmental Panel on Climate Change reports do not agree on the magnitude or direction of change for ocean carbon storage under future climate scenarios. This means we have low confidence for our future projections of ocean carbon storage, which is further impeded by a growing discrepancy between models and observations. In this project we will examine how much carbon has been respired during the transit from the upper ocean, and in what ways. We will measure the important processes of particle fragmentation and aggregation, microbial respiration, and zooplankton vertical migration and respiration. We will do this using a process cruise and autonomous underwater vehicles. We seek to answer the question: How is organic matter transformed and respired by biotic interactions in the mesopelagic, how does that vary with depth, location and season, and what are the consequences for ocean carbon storage? The ultimate goal is to generate new detailed understanding of important processes that influence the rate and depth of interior respiration which we will scale up to provide the globally-resolved information needed to develop the next generation of biogeochemical models.