The global carbon cycle comprises two parts: firstly, the human derived (anthropogenic) flux of about 8 PgCy-1of which the oceans take up about 2 PgCy-1, and the Southern Ocean contributes about 1PgCy-1. Secondly, a very much larger but up to now balanced ocean – atmosphere exchange of natural CO2 of approximately 90GtCy-1.
The steady-state magnitudes of the anthropogenic and natural CO2 fluxes are robustly constrained by the global and regional decadal mean data sets. The science gap lies in the non-steady-state part of these fluxes: both in terms of variability and long-term trends. SOCCO research is focused on understanding and quantifying the non-steady state part of the CO2 variability and trends.
Century-scale trends in atmospheric and ocean CO2 face a dual problem which impacts on global and regional scale mitigation of CO2 emissions to limit climate change risk: not only will the uptake rate of anthropogenic CO2 decrease because of changing CO2 chemistry (Ocean Acidification) and warming but as importantly, climate forcing will begin to alter the ocean physics that controls the much larger natural CO2 flux in the Southern Ocean.
Carbon research in SOCCO approaches these questions along three lines:
- It has established a long-term ship –based CO2 observations system making underway observations in the southeast Atlantic Ocean and the southwest Indian Ocean (Fig. 1). These data are made available to the national (SADCO) and global (CDIAC) databases from where they are then integrated after 2nd level QC into the SOCAT and later ocean acidification databases. Through this SOCCO builds up a data set, which includes a wide range of ancillary variables, to support its own research as well as global community initiatives.
- As part of its scientific focus on fine scale ocean dynamics the CO2 research makes a strong contribution to dedicated experiments which aim to understand the sensitivity of the carbon cycle in and CO2 fluxes to the seasonal and intraseasonal dynamics of upper ocean physics (meso and sub-mesoscale). In this domain we are exploring the use of robotics (surface wave gliders and ocean interior buoyancy gliders) to make observations within these spatial and temporal scale constraints. The Southern Ocean Seasonal Cycle Experiment (SOSCEx) is our platform for these experiments, which target the core hypothesis of the programme: fine scale (carbon) – large scale (climate) links.
- Modelling: in SOCCO we undertake CO2 modelling research in two main areas: firstly, we explore the use of different empirical numerical / machine learning methods to address the need for high precision (< 0.1PgCy-1) CO2 air – sea exchange fluxes in a data sparse system. This part of a global effort to reduce the global uncertainty of CO2 fluxes to ~10% of the mean annual flux necessary to resolve inter-annual variability and long-term trends. Secondly, we use a hierarchy of global and regional coarse (200km) to very high resolution (2km) model runs to test both scale sensitivity research questions for CO2 and the carbon cycle as well as explore the understanding and use of the seasonal cycle as a mode that provides a rigorous test to model outputs.