Carbon Uptake and Seasonal Traits in Antarctic Remineralisation Depth (CUSTARD)

海洋表层是数十亿被称为浮游植物的微小植物的家园，它们利用阳光和二氧化碳在海洋表层产生有机物。当它们死亡时，它们中的许多会下沉，将这些碳带入深海，在那里它可能会被储存数百到数千年，这有助于保持我们今天的气候。一般来说，它们对我们气候的影响大小与它们溶解前下沉的深度有关——下沉越深，储存的碳就越多。这种影响在南大洋北部尤其重要，那里的洋流模式意味着，浅层和深层溶解的差异决定了这些碳是被锁在海洋表面仅仅几年还是几个世纪。这是因为该地区是海洋环流的交汇处。四条海洋“高速公路”从海面到海底，在近5公里深的地方堆叠在一起，将水输送到全球海洋的不同地区。碳被溶解的高速公路决定了它与大气隔绝的时间。出于这个原因，如果我们想了解南大洋北部在调节全球气候方面的作用，我们需要了解海洋表面的碳吸收量有多大，以及下沉的物质是如何溶解的。不幸的是，我们对两者都不太了解；由于天气恶劣，很少有商船通过，南大洋的数据很少。因此，我们关于下沉碳的命运模式和控制这一模式的理论未经检验。因此，我们用来预测该地区未来气候的模型有很大的不确定性。然而，我们现有的证据表明，碳溶解深度的变化是理解这个系统如何运作的关键。在这个项目中，我们将在南大洋的一个偏远地区进行新的观测，使用令人兴奋的机器人车辆和复杂的新型传感器的组合。我们将在南大洋这个重要的高速公路交汇处对海洋吸收了多少碳进行新的观察。我们将研究控制碳吸收及其命运的过程，特别是养分的季节性可用性如何影响浮游植物的组成，浮游植物的组成改变了碳在溶解前的沉降深度。我们将把这些观测结果与一种新的建模方法结合起来，这种方法使我们能够比通常更快地运行气候模型的海洋部分。这使我们能够探索数据中发现的营养物质和浮游植物之间季节性相互作用的后果。特别是，该模型允许我们“标记”碳，这样我们就可以追踪它的去向。通过这种方式，我们可以测量每条高速公路上的下沉碳量，以及这在一年中是如何变化的。结合对养分和下沉碳的季节变化的观察，该模型将使我们能够确定这一重要地区调节碳吸收的关键过程。这将为那些建立英国气候模型的人提供重要的信息，因为该模型正在开发中，为未来（IPCC）关于世界气候状况的高调报告提供输入。

The surface ocean is home to billions of microscopic plants called phytoplankton which produce organic matter in the surface ocean using sunlight and carbon dioxide. When they die many of them sink, taking this carbon into the deep ocean, where it may be stored for hundreds to thousands of years, which helps keep our climate the way it is today. In general terms the size of the effect they have on our climate is linked to how deep they sink before they dissolve - the deeper they sink, the more carbon is stored. This effect is particularly important in the northern part of the Southern Ocean where the pattern of ocean currents means that the difference between shallow and deep dissolution controls whether this carbon is locked away from the surface ocean for just a few years or for centuries. This is because the area is a junction in the ocean circulation. Stacked up on each other from the surface to the seafloor at almost 5km depth are four oceanic 'motorways', taking water to different parts of the global ocean. The motorway that the carbon is dissolved into determines how long it will be kept away from the atmosphere. For this reason, if we want to understand the role of this northern part of the Southern Ocean in regulating global climate we need to understand both how big carbon uptake is at the ocean surface and also how deep sinking material dissolves. Unfortunately we don't understand either well; data are scarce in the Southern Ocean as the weather is poor and few commercial vessels pass through there. Consequently, our theories about the pattern of the fate of sinking carbon and what controls this are untested. As a result the models that we use for predicting future climate have massive uncertainty in this region. However, the evidence that we have suggests that changes in the depth of carbon dissolution are key to understanding how the system works. In this project we will tackle this by making new observations in a remote region of the Southern Ocean using an exciting combination of robotic vehicles and sophisticated new sensors. We will make new observations of how much carbon the ocean takes up in this key motorway junction of the Southern Ocean. We will examine the processes that control the uptake of carbon and its fate, in particular how seasonal availability of nutrients can affect the make-up of the phytoplankton which changes the depth to which carbon sinks before being dissolved. We will combine these observations with a novel modelling approach that allows us to run the ocean part of our climate model much faster than normally. This allows us to explore the consequences of the seasonal interplay between nutrients and phytoplankton found in our data. In particular, the model allows us to 'tag' carbon so that we can trace where it goes. In this way we can measure the amount of sinking carbon ending up on each motorway and how this varies through the year. Together with observations of the seasonal changes in nutrients and sinking carbon the model will allow us to determine the key processes regulating carbon uptake in this important area. This will provide important information to those building the UK's climate model at a time when it is being developed to provide input to a future high profile report (from the IPCC) on the state of the world's climate.