The facts & the project
Oceans are an important player in the global carbon cycle. About half of the CO2 released to the atmosphere since the onset of the industrial era (anthropogenic CO2) has accumulated in the oceans. The uptake of CO2 is essential to the equilibrium of Earth’s climate system. It is modulated by processes occurring at mesoscale, such as ocean eddies and their fluctuations. However, given the very high number of core hours necessary for simulating the coupled physical-biogeochemical system at mesoscale, their study was long limited to idealised configurations in terms of size and resolution.
“The recent evolution of national computing resources now allows us running simulation experiments at the scale of the global ocean with coupled ocean biogeochemical general circulation models (OBGCM) at eddy-permitting resolution and for multiple decades”, Marion Gehlen, researcher at CEA, said.
The results
Her work concerns the Southern Ocean which uptakes alone approximating 40% the total ocean sink. In Antarctica, the sink has considerably varied over the past decades, mainly because of atmospheric fluctuations. The strengthening of polar winds favours the upwelling of cold, CO2 rich waters, working against the uptake of anthropogenic CO2. The upwelling intensity is in part counteracted by an increase in eddy activity of the ocean.
In 2015, LSCE (a CEA-CNRS-UVSQ joint research division) completed a 65 year long global simulation at 25 km resolution with the coupled physical biogeochemical model NEMO-PISCES forced by an atmospheric reanalysis. Its analysis is ongoing and will allow quantifying the contribution of mesoscale processes to the variability of uptake and transport of anthropogenic CO2.