The northern European shelf as an increasing net sink for CO 2

• Published in: Biogeosciences
• Main Authors: M. Becker, A. Olsen, P. Landschützer, A. Omar, G. Rehder, C. Rödenbeck, I. Skjelvan
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Barents Sea
• Online Access: https://doi.org/10.5194/bg-18-1127-2021; https://doaj.org/article/4914831d8d954b568652d6ff314bff0a

We developed a simple method to refine existing open-ocean maps and extend them towards different coastal seas. Using a multi-linear regression we produced monthly maps of surface ocean f CO 2 in the northern European coastal seas (the North Sea, the Baltic Sea, the Norwegian Coast and the Barents Sea) covering a time period from 1998 to 2016. A comparison with gridded Surface Ocean CO 2 Atlas (SOCAT) v5 data revealed mean biases and standard deviations of 0 ± 26 µatm in the North Sea, 0 ± 16 µatm along the Norwegian Coast, 0 ± 19 µatm in the Barents Sea and 2 ± 42 µatm in the Baltic Sea. We used these maps to investigate trends in f CO 2 , pH and air–sea CO 2 flux. The surface ocean f CO 2 trends are smaller than the atmospheric trend in most of the studied regions. The only exception to this is the western part of the North Sea, where sea surface f CO 2 increases by 2 µatm yr −1 , which is similar to the atmospheric trend. The Baltic Sea does not show a significant trend. Here, the variability was much larger than the expected trends. Consistently, the pH trends were smaller than expected for an increase in f CO 2 in pace with the rise of atmospheric CO 2 levels. The calculated air–sea CO 2 fluxes revealed that most regions were net sinks for CO 2 . Only the southern North Sea and the Baltic Sea emitted CO 2 to the atmosphere. Especially in the northern regions the sink strength increased during the studied period.