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

表层海洋是数十亿种被称为浮游植物的微型植物的家园，它们利用阳光和二氧化碳在表层海洋中产生有机物。当他们中的许多人死亡时，他们中的许多人会沉入海底，将这些碳带入深海，在那里可能储存数百年到数千年，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的大小与它们在溶解之前沉入海底的深度有关--它们沉得越深，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，浅溶解和深溶解之间的差异决定了这些碳是在几年内还是在几个世纪内与表层海洋隔离。这是因为该地区是海洋环流的交汇点。从海面到海底近5公里深的四条海洋“高速公路”相互堆叠在一起，将水输送到全球海洋的不同部分。碳被溶解到的高速公路决定了它与大气的距离有多长。因此，如果我们想要了解南大洋北部在调节全球气候方面的作用，我们既需要了解海洋表面的碳吸收有多大，也需要了解下沉物质有多深的溶解。不幸的是，我们对此也不是很了解；南大洋的数据很少，因为天气很差，几乎没有商船通过那里。因此，我们关于碳下沉的命运模式以及是什么控制这一命运的理论未经检验。因此，我们用来预测未来气候的模型在这一地区存在巨大的不确定性。然而，我们所拥有的证据表明，碳溶解深度的变化是理解该系统如何工作的关键。在这个项目中，我们将通过使用机器人车辆和先进的新型传感器的激动人心的组合，在南大洋的一个偏远地区进行新的观测来解决这个问题。我们将对海洋在南大洋这个关键的高速公路交界处吸收多少碳进行新的观测。我们将研究控制碳吸收及其命运的过程，特别是季节性营养物质的可获得性如何影响浮游植物的组成，从而改变碳在被溶解之前的下沉深度。我们将把这些观测与一种新的建模方法结合起来，这种方法允许我们以比平时更快的速度运行我们的气候模型的海洋部分。这使我们能够探索在我们的数据中发现的营养物质和浮游植物之间的季节性相互作用的后果。特别值得一提的是，该模型允许我们对碳进行“标记”，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最终下沉的碳的数量，以及这一数量在一年中的变化情况。结合对营养物质和碳吸收的季节性变化的观察，该模型将使我们能够确定在这一重要领域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信息，因为英国正在开发气候模型，以便为未来一份关于世界气候状况的高调报告(来自IPCC)提供意见。

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.