Constraining respiration rates of mesopelagic fishes

海洋自然地从大气中清除了大量的碳，保护我们免受人类碳排放的一些负面影响。然而，我们对这种碳捕获和储存系统是如何工作的理解是不完整的。为了避免排放到大气中，碳必须排放到深海中。生物学在输出碳方面发挥着重要作用，但所谓的“生物碳泵”实际上是一套非常复杂的相互作用过程，每个过程都不完全被理解。随着大气中碳浓度的增加和全球海洋变暖，控制生物碳泵的过程可能会发生变化，这使得预测中长期气候的未来变得更加困难。该项目的目的是研究生物碳泵中最不为人所知的组成部分之一：垂直迁移的鱼类在将碳输送到深海中的作用。大量的小鱼生活在世界海洋的中部深处。这些“中上层”鱼类在夜间上升到水面，消耗碳，然后在白天游回深水，在那里一些碳被呼吸并返回水中。中远洋鱼类是地球上最丰富的脊椎动物，据估计，它们与所有浮游动物一样负责活跃的碳运动，但对这些鱼类的了解非常少，并且不包括在大多数碳循环模型中。为了了解碳鱼可以移动多少，我们需要知道每条鱼呼吸多少碳，以及这是如何随着温度的变化而变化的。这些测量在以前是不可能的，但我们的团队已经开发出一种新的方法，通过耳石的化学成分来估计鱼类的呼吸速率。通过这个工具，我们已经证明了目前关于鱼呼吸多少以及它们对温度有多敏感的想法是错误的。在这个项目中，我们将应用这个新工具来产生中远洋鱼类野外呼吸速率的第一个测量值。我们将研究热带、亚热带和低温地区的鱼类，以确保我们的结果可以应用于整个大西洋。我们将测量不同体型的中上层鱼类呼吸多少碳，以及这对它们所栖息的水温有多敏感。利用这些数据，我们将与其他团队联系，测量中远洋鱼类的全球丰度和体型分布，以精确估计中远洋鱼类呼吸的碳总量。这将使海洋生物地球化学建模者能够更好地评估鱼类与生物碳泵的其他组成部分的相对重要性。我们对野外呼吸速率的热敏性测量将测试与鱼类有关的碳运动如何对温度升高作出反应。目前的模型假设，随着海水变暖，呼吸速率会迅速增加，这意味着活性碳通量也会增加。然而，我们的试验数据表明，鱼类对温度的敏感度低于我们的假设。这意味着温度升高不一定会增加鱼类向深海输送碳的速度。如果我们想更好地预测生物碳泵将如何应对未来的气候变化，解决这些问题是非常重要的。

The oceans naturally remove huge amounts of carbon from the atmosphere, protecting us from some of the negative effects of human carbon emissions. However, our understanding of exactly how this carbon capture and storage system works is incomplete. To avoid being returned to the atmosphere, carbon must be exported to the deep ocean. Biology plays a major role in exporting carbon, but the so called 'biological carbon pump' is in fact a very complicated set of interacting processes each of which is incompletely understood. As atmospheric carbon concentrations increase and the global ocean warms, processes controlling the biological carbon pump may change, making it even harder to predict medium to long term climate futures. The aim of this project is to study one of the least understood components of the biological carbon pump: the role that vertically migrating fishes play in transporting carbon into the deep ocean. A huge volume of small fishes lives in the middle depths of the world's ocean. These 'mesopelagic' fishes rise to surface waters in the night, consuming carbon, then swim back to deep water during the day where some of this carbon is respired and returned to the water. Mesopelagic fishes are the most abundant vertebrates on the planet and it is estimated that they are responsible for as much active movement of carbon as all zooplankton - but these fishes are very poorly known and are not included in most carbon cycle models.To understand how much carbon fish can move, we need to know how much carbon each fish respires, and how this changes as temperature changes. These measurements have not been possible before, but our team has developed a new way to estimate respiration rates of fishes from the chemical composition of ear stones. Using this tool we have shown that current ideas about how much fish respire, and how sensitive they are to temperature are wrong. In this project we will apply this new tool to generate the first measurements of field respiration rates of mesopelagic fishes. We will look at fish from tropical, sub tropical and cool temperature areas to be sure that our results can be applied across the whole Atlantic Ocean.We will measure how much carbon mesopelagic fish of different body sizes respire, and how sensitive this is to the temperature of the water they inhabit. Using these data we will liaise with other teams measuring the global abundance and body size distribution of mesopelagic fishes to refine estimates of the total amount of carbon respired by mesopelagic fishes. This will allow ocean biogeochemical modellers to better assess the relative importance of fish compared to other components of the biological carbon pump. Our measurements of the thermal sensitivity of field respiration rates will test how fish-related carbon movements will respond to increasing temperature. Currently models assume that respiration rates increase quite rapidly as waters warm, implying that the active carbon flux will also increase. However, our pilot data implies that fish are less sensitive to temperature than assumed. This means that increasing temperatures will not necessarily increase the rate at which carbon is transported by fish into the deep ocean. Solving these problems is very important if we want to better predicting how the biological carbon pump will respond to future climate change.