Global Ocean Heat Content Anomalies and Ocean Heat Uptake based on mapping Argo data using local Gaussian processes

Monthly Ocean Heat Content Anomalies (OHCA) in the top 2000 dbar of the ocean are calculated for 2004–2025, equatorward of 65° latitude, by subtracting the mean OHC over either 2005–2024 or 2005–2025 from the monthly OHC time series. The averaging period used to calculate the mean is indicated in the file name after tw (e.g., tw2005_2024 or tw2005_2025). Yearly OHCA time series are then calculated (one point per year). OHC fields are mapped using locally stationary Gaussian processes (defined over space and time) with data-driven decorrelation scales (Kuusela and Stein, 2018). A linear time trend was included in the estimate of the mean field (along with spatial terms and harmonics for the annual cycle). Mapping is done separately for different vertical sections: 15-20 dbar, 15-300 dbar, 300-700 dbar, 700-1000 dbar, 700-1850 dbar, 1800-1850 dbar. The 15–20 dbar and 1800–1850 dbar sections are used to estimate OHCA for the more sparsely observed 0–15 dbar and 1850–2000 dbar sections, respectively. Different vertical sections are combined to estimate global OHCA time series for 0-2000 dbar, 0-300 dbar, 0-700 dbar, 0-1000 dbar, and 700-2000 dbar (as indicated in the file names). The NetCDF files include the attribute “area,” which gives the corresponding surface area in m² for each estimate. Regions of the ocean that are shallower than 300 m or lack sufficient Argo sampling to support the estimates are not included. Maps of the ocean masks used for the different vertical sections can be found in the .png files (white shading indicates the area used for the horizontal integral); the bathymetry mask by Roemmich and Gilson (included in the file RG_ArgoClim_Temperature_2019.nc at https://sio-argo.ucsd.edu/RG_Climatology.html) is also used to define the ocean mask. Ocean Heat Uptake is calculated from the monthly OHCA and then averaged as described above to produce yearly time series included in the files for the different layers. For the uncertainty at each time point, the standard deviations associated with the OHCA and OHU estimates are included. When plotting a time series, the user may consider, e.g., shading plus/minus 1* or 1.96* standard deviations (corresponding to confidence levels of 68% or 95%, respectively). These standard deviations in the files are estimated using spatially and temporally dependent conditional simulations of monthly gridded anomalies. When combining different layers, the standard deviation of the sum is conservatively estimated as the sum of the standard deviations. Finally, for files starting with ohca_ohu_, OHCA and OHU trends are estimated via least-squares fits over the same period used to calculate, as described above, the time mean removed from the monthly OHC time series. The trends and their uncertainties at the 68% confidence level are reported in the variable metadata. Trend uncertainties are estimated by repeating the least-squares fit for each member of the conditional simulation ensemble described above. Please note that files starting with gcos_ include OHC anomalies (in J/m² and ZJ) and volume-averaged temperature anomalies for the 0–300 dbar, 0–700 dbar, 0–1000 dbar, 700–2000 dbar, and 0–2000 dbar layers. For each layer, the files starting with coverage_ store the water-column thickness at each location where an estimate of the field of interest is available. The thickness is measured downward from the top of the layer, and only contiguous coverage extending from the layer top is included.