Authors: S-A Nicholson, D. B Whitt, I. Fer, M.D. du Plessis, A.D Lebéhot, S. Swart, A.J Sutton, P.M.S Monteiro
Accompanying code to the paper "Storms drive outgassing of CO2 in the subpolar Southern Ocean" Nature Communications
Abstract: The subpolar Southern Ocean is a critical region where CO2 outgassing influences the global mean air-sea CO2 flux (FCO2). However, the processes controlling the outgassing remain elusive. We show, using an unprecedented multi-glider dataset combining FCO2 and ocean turbulence, that the air-sea gradient of CO2 (∆pCO2) is modulated by synoptic storm-driven ocean variability (20 µatm, 1-10 days) through two processes. Ekman transport explains 60% of the variability, and entrainment drives strong episodic CO2 outgassing events of 2-4 mol m-2 yr-1. Extrapolation across the subpolar Southern Ocean using a process model shows how ocean fronts spatially modulate synoptic variability in ∆pCO2 (6 µatm2 average) and how spatial variations in stratification influence synoptic entrainment of deeper carbon into the mixed layer (3.5 mol m-2 yr-1 average). These results not only constrain aliased-driven uncertainties in FCO2 but also the effects of synoptic variability on slower seasonal or longer ocean physics-carbon dynamics.
Code requirements
The user will require the following software:
- Python, with the following packages:
- numpy
- xarray
- pandas
- netCDF4
- matplotlib
- scipy
- seaborn
- cmocean
- cartopy
- seaborn
- glidertools
- xesmf
- PyCO2SYS
- seawater
- seaflux
- gsw
Data Sources:
Data generated by Nicholson et al. paper above and used by this code can by retrieved from here from https://doi.org/10.5281/zenodo.5674581.
In this study, we first use a two-month dataset from the Southern Ocean Seasonal Cycle Experiment (SOSCEx) which utilised multiple autonomous platforms to simultaneously observe the coupled atmosphere - ocean system, in high-resolution, in the Atlantic sector of the subpolar Southern Ocean. Corresponding processed data for this experiment used by this study is provided in the folder /Data/SOSCEx_STORM2_Glider_Data.
Using these data we explain how storms influence, through ocean mixed layer physics (advection and mixing), the direction and magnitude of the air-sea CO2 gradient (∆pCO2) and flux (FCO2) over the duration of the experiment. We construct a conceptual ocean mixed layer model that captures the observed synoptic variability of ∆pCO2 in the observations, we estimate the synoptic variability around the entire subpolar Southern Ocean. The relating data for this second step can be found under /Data/Generalisation
Other auxillary source data (not produced in Nicholson et al.) which is required to be downloaded is listed within each notebook and in the main manuscrip text.