OceanSODA-ETHZ-v2: Surface ocean sea-air CO2 fluxes from 1982 to 2022 (8-day by 0.25° x 0.25°)

Product information

Variables

Each netCDF contains only one variable. The metadata also has a start and end time as well as min/max lat/lon.
The information about the settings used in PyCO2SYS is also included in each file's metadata.

File structure

The file naming structure is <variable>_<decade>_OceanSODAETHZv2.2024rXX.nc. Data are grouped by decade, with each file being about 800 MB. Not all files contain the same number of years (e.g., 1982-1989). The size for each variable (1982-2022) is between 2.5 and 3.5 GB.

Product description

This dataset contains a global gridded dataset of sea-air carbon dioxide fluxes (FCO₂) for subseasonal to decadal studies. The product is available from 1982 through 2022 and is at an 8-daily by 0.25° by 0.25° resolution. FCO2 is calculated using the bulk formulation of flux:

(fCO₂^sea−fCO₂^atm) ⋅ k_w ⋅ K₀ ⋅ (1−ice)

where (fCO₂^sea − fCO₂^atm) is the sea-air difference in fugacity of carbon dioxide, k_w is the gas transfer velocity, K₀ is the solubility of CO2 in seawater, and ice is the sea-ice fraction.

The surface ocean fugacity of carbon dioxide (fCO₂^sea) is calculated using the surface Ocean Carbon dioxide Neural Network (OceanCarbNN). This two-step approach first estimates an 8-day climatology of fCO₂^sea based on climatological drivers. The second step uses the output of the first step as a prior estimate of fCO₂^sea which is then adjusted to a time-varying product. An important novelty of this method is that the first step uses Gradient Boosted Trees (low bias, low variance, but unable to extrapolate) while the second step uses Neural Networks (able to extrapolate, but higher variance). We use 35 ensemble members to make these estimates. The average of the ensemble members is used as the final estimate of fCO₂^sea. Further, the standard deviation of the ensemble members can be scaled (× 5.7) to be used as an analog of the uncertainty.

The atmospheric fugacity of carbon dioxide (fCO₂^atm) is calculated using the NOAA Marine Boundary Layer (MBL) product OR the NOAA CarbonTracker 2022 product (CT), ERA5 sea level pressure. k_w is calculated using the Wanninkhof (2014) formulation, but we adjust the coefficient of gas transfer for the ERA5 wind reanalysis product (0.274) so that the global mean kw = 16.5 cm/hr. K₀ is calculated using the Weiss (1974) formulation.