Carbon Uptake and Seasonal Traits of Antarctic Remineralisation Depths (CUSTARD)

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.

CUSTARD will engage fully with the other funded RoSES projects and NERC to ensure CUSTARD's impact plan is integrated with wider impact activities. In addition, CUSTARD will achieve impact in the following areas:

Climate prediction:
International agreements to limit the impact of anthropogenic climate change such as COP21 are based upon accurate and precise predictions of how the earth system will respond to potential scenarios of future greenhouse gas release. Our ability to predict future trajectories of atmospheric CO2 and climate is, in turn, strongly dependent on our ability to develop robust and accurate climate models that can quantitatively demonstrate their skill in reproducing the existing CO2 record. CUSTARD will contribute directly to two aspects of this.
First, CUSTARD will collect ocean CO2 flux data year-round in the chronically under-sampled Southern Ocean. Co-I Bakker is a key member of SOCAT (http://www.socat.info), the standard source of flux data globally and widely used for policy briefings (e.g. Pollution in the open oceans: 2009-2013. Boelens, R. et al., GESAMP reports and Studies 91) and climate model testing (e.g. ESMValTool (v1.0) - A tool for evaluation of Earth System Models in CMIP: Eyring, V., et al., 2016. Geoscientific Model Development 9, doi:10.5194/gmd-9-1747-2016).
Second, CUSTARD will provide mechanistic information on the controls on carbon uptake and redistribution in the Southern Ocean. The new insights generated in CUSTARD into the seasonal variability of production and remineralisation, and the implications for ocean carbon storage will be fed through existing links into ongoing development of UKESM2, the next generation UK Earth System model for the UK's contribution to future IPCC assessments.

Autonomous sensing:
Robotics and autonomous systems were identified by the UK government in 2013 as one of 8 great technologies that will help drive economic growth. This was followed by a large (£10 million) capital investment into the MARS national facility. CUSTARD will thus be of interest to the growing community of AUV and sensors manufacturers and users, including agencies with marine monitoring obligations, e.g. Defra and CEFAS. We will hold a community workshop which will focus on best practice for using autonomous vehicles to derive information on carbon fluxes, which we will host at the NOC. Similar previous events have successfully attracted many representatives of AUV manufacturers, however, we will extend the reach to include stakeholders with a remit for ocean monitoring, such as Defra and CEFAS.

Technology:
A novel dissolved silica sensor developed by NOC's Ocean Technology and Engineering group will be deployed during CUSTARD. This is the first autonomous sensor, suitable for the marine environment, capable of measuring in situ silicate, a key component of ocean biogeochemistry. The successful demonstration of this sensor to provide high quality silicate measurements autonomously over an extended period of time will be exploited to generate interest in commercialisation of the sensor.

Science communication:
The CUSTARD team includes co-I Henson, an experienced and effective communicator to general audiences, having participated in multiple public engagement and schools activities, ranging from on-screen contributions to BBC4 TV series 'The Spectrum of Science', to being a panel member at Royal Institution debates, to lectures at the Cheltenham Science Fair, to exhibiting events aimed at school children such as the Big Bang science fair.
Project staff will also be encouraged to undertake public engagement training, such as through the public engagement courses run by NERC or Sense about Science. In addition, a new public engagement activity will be designed as part of CUSTARD and used during the annual Ocean and Earth day held at NOC (attracts > 3000 visitors) and at other events.