Constraining respiration rates of mesopelagic fishes

海洋自然地从大气中去除大量的碳，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的确切工作原理的理解是不完整的。为了避免被送回大气层，碳必须被输出到深海。生物学在碳输出中起着重要作用，但所谓的“生物碳泵”实际上是一组非常复杂的相互作用过程，其中每一个都不完全了解。随着大气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，从而使预测中长期气候未来变得更加困难。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间深处。这些“中层”鱼类在夜间上升到表面沃茨，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。中层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碳的主动移动-但这些鱼类知之甚少，大多数碳循环模型都不包括它们。为了了解鱼类可以移动多少碳，我们需要知道每种鱼呼吸多少碳，以及它如何随着温度变化而变化。这些测量以前是不可能的，但我们的团队已经开发出一种新的方法来估计鱼类的呼吸率从耳石的化学成分。使用这个工具，我们已经表明，目前关于鱼类呼吸量以及它们对温度有多敏感的想法是错误的。在这个项目中，我们将应用这一新的工具，以产生第一次测量现场呼吸率的中层鱼类。我们将研究来自热带、亚热带和低温地区的鱼类，以确保我们的研究结果可以应用于整个大西洋。我们将测量不同体型的中层鱼类呼吸的碳量，以及它们对栖息地水温的敏感程度。利用这些数据，我们将与其他测量中层鱼类全球丰度和体型分布的团队进行联络，以完善中层鱼类呼吸碳总量的估计。这将使海洋生物地球化学建模者能够更好地评估鱼类相对于生物碳泵其他组成部分的相对重要性。我们对野外呼吸速率的热敏感性的测量将测试与鱼类相关的碳运动如何对温度升高作出反应。目前的模型假设呼吸率随着沃茨变暖而迅速增加，这意味着活性碳通量也会增加。然而，我们的试验数据表明，鱼类对温度的敏感性低于假设。这意味着温度升高并不一定会增加鱼类将碳输送到深海的速度。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.