Code used in "Storms drive outgassing of CO2 in the subpolar Southern Ocean"

Accompanying code to the manuscript "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 (F_CO2). However, the processes controlling the outgassing remain elusive. We show, using an unprecedented multi-glider dataset combining F_CO2 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 F_CO2 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 and used by this code can be 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 auxiliary source data (not produced in Nicholson et al.) which is required to be downloaded is listed within each notebook and in the main manuscript text.