Processes Influencing Carbon Cycling: Observations of the Lower limb of the Antarctic Overturning (PICCOLO)

The vast, remote seas which surround the continent of Antarctica are collectively known as the Southern Ocean. This region with its severe environment of mountainous seas, winter darkness, strong winds, freezing temperatures and ice is unsurprisingly one of the least explored and under-observed parts of the global ocean. However, because of these extremes, it plays a large and still unquantified role in Earth's climate system. In this region, large amounts of heat and carbon dioxide are exchanged between the atmosphere and the ocean.

The physical mechanisms controlling these atmosphere-ocean exchanges are the subject of the NERC ORCHESTRA programme. We propose within PICCOLO to concentrate on the role that chemistry and biology play within those exchanges. In particular, PICCOLO will focus on understanding the mechanisms that transform the carbon contained in the seawater as it rises to the surface near Antarctica, interacts with the atmosphere, ice, phytoplankton and zooplankton inhabiting the near surface, before descending to the ocean depths.

PICCOLO will undertake an ocean research expedition to the region close to Antarctica, as computer models and satellite images show that these are areas crucial for carbon processes. Freezing seawater in these regions releases salt into the water below, making it denser and therefore causing it to sink. Strong winds cause the sea ice to be pushed away from the Antarctic coastline, leaving areas of open water called polynyas. Within the polynyas the water has enough light during the summer to allow phytoplankton to grow, as well as providing dense waters which sink to the deep, driving a giant ocean conveyor belt which has a large impact upon Earth's climate system.

The PICCOLO team will measure the key variables that control the biological and chemical processes in this region including iron, nutrients, phytoplankton and zooplankton. Crucially the team will study the controlling rate terms between different parts of this biological and chemical system. The PICCOLO team will make use of the latest technologies, including autonomous submarines, gliders and floats, to observe these processes in otherwise inaccessible and previously unstudied areas such as under the sea ice. Most ambitiously we will anchor a submarine to the seabed within a polynya and leave it over a winter season to collect data, recovering it the following spring. The PICCOLO team will put instruments on seals which will continuously take data as they dive up and down through the water, sending it back to scientists in real-time via satellite communication links.

This wealth of novel data will be analysed by the PICCOLO team, using state of the art computer models, to test our ideas about how the whole complex set of physical, chemical and biological processes affects carbon. Conceptually we will follow an imaginary parcel of water through the system looking at processes between the atmosphere and ocean, biological processes in the surface layer, exchanges between the upper and lower ocean and the final fate of the carbon.

The PICCOLO hypotheses address the following:

(i) Factors controlling the exchange of carbon dioxide between the ocean and atmosphere and the role of ultra-violet light in controlling the concentration of carbon dioxide in seawater;
(ii) The role of light, iron and nutrients in how carbon is processed by the plankton in the water;
(iii) The mediating processes governing the export of carbon from the upper ocean to depth;
(iv) The processes that take the carbon into the deep ocean on the next stage of its global journey.

Here we summarise the non-academic communities who will benefit from this research project and how they will benefit. Please see the Pathways to Impact attachment for the activities we plan in PICCOLO in order to achieve this impact.

The main beneficiaries of data and knowledge from PICCOLO are:

i) Stakeholders and high level users of the Global Carbon Budget analysis will benefit through an improved product with PICCOLO biogeochemical observations being available for model evaluation and quantification of the ocean carbon sink via high-profile data synthesis products, such as the Global Ocean Data Analysis Project (GLODAP) and the Surface Ocean CO2 Atlas (www.socat.info).

ii) The global earth system modelling community, and the users of such models such as governments, non-governmental organisations (NGOs), and the Intergovernmental Panel for Climate Change (IPCC), will benefit from the mechanistic understanding of carbon uptake processes in the Southern Ocean that PICCOLO will deliver, together with the roadmap for representing such processes in Earth system models. This will deliver a step-change in the quality of the projections undertaken by such models. The Hadley Centre at the UK Met Office will gain insight from PICCOLO, and we will work with them to assess the various NEMO-based models. The results of the project will aid the eventual parameterisation of carbon cycling processes for use in earth system models. The major results of PICCOLO will inform government policy with regard to the uncertainties in sea level rise predictions.

iii) Operational forecasters at global weather/climate services (such as the UK Met Office) and global navies will have free access to the near-real time (within hours of surfacing) temperature and salinity profiles from the Argo floats, gliders and seal tags, for assimilation into their operational forecast models. This will also benefit users of ocean reanalysis products that assimilate the PICCOLO profiles, since our targeted observational campaign location is a data desert.

iv) Those designing the global ocean (and climate) observing systems will benefit from PICCOLO. Our novel observational techniques will allow us to feed into the Southern Ocean Observing System (SOOS) design in order to design effective long-term measuring systems in the most useful locations. We will engage with the SOOS community through the Scientific Committee for Antarctic Research (SCAR).

v) The western and central Weddell Sea is very poorly sampled compared with the rest of this sector and the size of the krill stocks within it will be of interest to the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). The krill fishery in the Southwest Atlantic sector has expanded and there is a clear need for better understanding of the spatial scale of the exploited stocks. ICED (Integrating Climate and Ecosystem Dynamics) is an international multidisciplinary regional programme within the SCOR/Future Earth sponsored IMBER (Integrated Marine Biogeochemistry and Ecosystem Research) project, launched to develop integrated circumpolar analyses of Southern Ocean climate and ecosystem dynamics.

vi) PICCOLO will nurture and train early career scientists, giving them skills to equip them for a productive independent career and to meet national skills shortages.

vii) The general public and young people in particular will gain from PICCOLO outreach. We aim to interest more young people in science and in higher education, raise awareness of global change and polar processes, and attract more people to careers in scientific research. We will target deprived areas such as Great Yarmouth in Norfolk and Plymouth in Devon, where young people's aspirations and achievements are below the national average and where inspiration into education may make a difference.