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

点击翻译按钮获取中文摘要

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.