Preprints
https://doi.org/10.5194/egusphere-2024-598
https://doi.org/10.5194/egusphere-2024-598
13 Mar 2024
 | 13 Mar 2024

Seasonal dynamics and regional distribution patterns of CO2 and CH4 in the north-eastern Baltic Sea

Silvie Lainela, Erik Jacobs, Stella-Theresa Stoicescu, Gregor Rehder, and Urmas Lips

Abstract. Significant research has been carried out in the last decade to describe the CO2 system dynamics in the Baltic Sea. However, there is a lack of knowledge in this field in the NE Baltic Sea, which is the main focus of the present study. We analysed the physical forcing and hydrographic background in the study year (2018) and tried to elucidate the observed patterns of surface water CO2 partial pressure (pCO2) and methane concentrations (cCH4). Surface water pCO2 and cCH4 were calculated from continuous measurements during six monitoring cruises onboard R/V Salme, covering the Northern Baltic Proper (NBP), the Gulf of Finland (GoF) and the Gulf of Riga (GoR) and all seasons in 2018. The general seasonal pCO2 pattern showed oversaturation in autumn-winter and undersaturation in spring-summer in all three areas, but it locally reached the saturation level during the cruises in April, May and August in the GoR and in August in the GoF. cCH4 was oversaturated during the entire study period, and the seasonal course was not well exposed on the background of high variability. Surface water pCO2 and cCH4 distributions showed larger spatial variability in the GoR and GoF than in the NBP for all six cruises. We linked the observed local maxima to river bulges, coastal upwelling events, fronts, and occasions when vertical mixing reached the seabed in shallow areas. Seasonal averaging over the CO2 flux based on our data suggest a weak sink for atmospheric CO2 for all basins, but high variability and the long periods between cruises (temporal gaps in observation) preclude a clear statement.

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Silvie Lainela, Erik Jacobs, Stella-Theresa Stoicescu, Gregor Rehder, and Urmas Lips

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  • RC1: 'Comment on egusphere-2024-598', Anonymous Referee #1, 26 Mar 2024
  • RC2: 'Comment on egusphere-2024-598', Anonymous Referee #2, 29 Mar 2024
Silvie Lainela, Erik Jacobs, Stella-Theresa Stoicescu, Gregor Rehder, and Urmas Lips
Silvie Lainela, Erik Jacobs, Stella-Theresa Stoicescu, Gregor Rehder, and Urmas Lips

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Short summary
We evaluate the variability of carbon dioxide and methane in the surface layer of the north-eastern basins of the Baltic Sea in 2018. We show that the shallower coastal areas have considerably higher spatial variability and seasonal amplitude of surface layer pCO2 and cCH4 than measured in the Baltic Sea offshore areas. Despite this high variability, caused mostly by coastal physical processes, the average annual air-sea CO2 fluxes differed only marginally between the sub-basins.