25 Jul 2023
 | 25 Jul 2023
Status: this preprint is currently under review for the journal ESSD.

A regional pCO2 climatology of the Baltic Sea from in situ pCO2 observations and a model-based extrapolation approach

Henry C. Bittig, Erik Jacobs, Thomas Neumann, and Gregor Rehder

Abstract. Ocean surface pCO2 estimates are of great interest for the calculation of air-sea CO2 fluxes, oceanic uptake of anthropogenic CO2, and eventually the Global Carbon Budget. They are accessible from direct observations, which are discrete in space and time and thus always sparse, or from biogeochemical models, which only approximate reality. Here, a combined method for the extrapolation of pCO2 observations is presented that uses (1) model-based patterns of variability from an EOF analysis of variability with (2) observational data to constrain EOF pattern amplitudes in (3) an ensemble approach, which locally adjusts the spatial scale of the mapping to the density of the observations. Thus, data-constrained, gap- and discontinuity-free mapped fields including local error estimates are obtained without the need for or dependence on ancillary data (like, e.g., satellite sea surface temperature maps). This extrapolation approach is generic in that it can be applied to any oceanic or coastal region covered by a suitable model and observations. It is used here to establish a regional pCO2 climatology of the Baltic Sea, largely based on ICOS-DE SOOP Finnmaid surface pCO2 observations between Lübeck-Travemünde (Germany) and Helsinki (Finland). The climatology can serve as improved input for atmosphere-ocean CO2 flux estimation in this coastal environment.

Henry C. Bittig et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on essd-2023-264', Anonymous Referee #1, 07 Sep 2023
  • RC2: 'Comment on essd-2023-264', Anonymous Referee #2, 11 Sep 2023

Henry C. Bittig et al.

Henry C. Bittig et al.


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Short summary
We present a pCO2 climatology of the Baltic Sea using a new approach to extrapolate from individual observations to the entire Baltic Sea. The extrapolation approach uses (a) a model to inform on how data at one location are connected to data at other locations, and (b) very accurate pCO2 observations from 2003–2021 as the base data. The climatology can be used, e.g., to assess uptake and release of CO2 or for identification of extreme events.