FDU-BTR: A global monthly gridded fCO2 product (1982-2024)

The associated manuscript is currently under review. FDU-BTR is a global monthly gridded reconstruction of surface-ocean CO₂ fugacity (fCO₂) covering January 1982 to December 2024. The dataset contains 516 monthly fields on a regular 1° × 1° latitude–longitude grid. The spatial grid contains 180 latitude points from 89.5° S to 89.5° N and 360 longitude points from 179.5° W to 179.5° E. Monthly fields are referenced to the middle of each month, with temporal coverage from 15 January 1982 to 15 December 2024. Time is stored using the standard calendar as days since 00:00:00 UTC on 1 January 1970. The primary reconstructed variable is: fCO2: monthly surface-ocean CO₂ fugacityUnit: µatmDimensions: time × latitude × longitudeData type: float32 The dataset also provides the individual components and uncertainty diagnostics associated with the Background–Thermal Residual (BTR) reconstruction framework: Background_component: multi-product climatological background; Thermal_component: explicit thermal contribution; Residual_component: residual component beyond the prescribed background and thermal components; fCO2_model_spread: population standard deviation across central-model ensemble members; fCO2_pi67_lower and fCO2_pi67_upper: lower and upper endpoints of the conditional 67% prediction interval; fCO2_pi90_lower and fCO2_pi90_upper: lower and upper endpoints of the conditional 90% prediction interval. The prediction intervals were generated using CatBoost conditional quantile regression with nested spatial-block calibration. The interval endpoints are retained without symmetric re-centering around the central reconstruction. The ensemble-member spread is provided separately from the prediction intervals and should not be interpreted as the same uncertainty quantity. All gridded variables have dimensions of 516 × 180 × 360. The released fields represent the direct monthly 1° reconstruction over the valid product domain. The dataset is distributed in NetCDF format and follows the CF-1.8 and ACDD-1.3 metadata conventions. The product is released under the Creative Commons Attribution 4.0 International license (CC BY 4.0). FDU-BTR is intended primarily for global, basin-scale, and large-scale regional analyses of monthly-to-interannual surface-ocean fCO₂ variability, long-term change, product intercomparison, and air–sea CO₂ exchange. Users are encouraged to consider the accompanying prediction-interval fields when evaluating reconstruction uncertainty in regional applications.