Based on direct surface pCO2 observation and a model-based extrapolation technique, we established a regional pCO2 climatology of the Baltic Sea. Observations from June 2003 to Dec. 2021 are obtained from the SOCAT version 2022 data collection and largely based on ICOS DE-SOOP Finnmaid data. The extrapolation technique uses model-based patters of variability to create observational data-constrained, gap- and discontinuity-free mapped fields including local error estimates without the need for or dependence on ancillary data (like, e.g., satellite sea surface temperature maps). Details on the pCO2 climatology and the model-based extrapolation technique are found in Bittig et al. (2023). Here we make the corresponding dataset available with monthly climatological pCO2 value as well as a linear pCO2 time trend for the Baltic Sea domain. Both value and trend are provided with their error estimate and are centered on the 15th of each month. Besides, the long-term trend 2003-2021 in pCO2 as well as its error estimate is given.

Content in Baltic_Sea_pCO2_climato.csv:Month (unitless) Month of the climatology (1..12 = January..December); pCO2, pCO2_1sigma, pCO2_trend, pCO2_trend_1sigma, and number_of_patterns are centered on the 15th of each monthLongitude in degE Longitude of the data pointLatitude in degN Latitude of the data pointpCO2 in μatm Climatological monthly surface CO2 partial pressure in microatmospheres (on the 15th of each month)pCO2_1sigma in μatm Error estimate of pCO2pCO2_trend in μatm d-1 Climatological monthly surface pCO2 trend in microatmospheres per day (on the 15th of each month)pCO2_trend_1sigma in μatm d-1 Error estimate of pCO2_trendnumber_of_patterns (unitless) Average number of spatial variability patterns used in the ensemble mean of the mapping (see Eq. 25 in Bittig et al.)Content in Baltic_Sea_pCO2_long_term_trend.csv:Longitude in degE Longitude of the data pointLatitude in degN Latitude of the data pointpCO2_long_term_trend in μatm yr-1 Long-term surface pCO2 trend (G, Eq. 30 in Bittig et al.) over the 2003-2021 period in microatmospheres per yearpCO2_long_term_trend_1sigma in μatm yr-1 Error estimate of pCO2_long_term_trend