Preprints
https://doi.org/10.5194/egusphere-2024-3048
https://doi.org/10.5194/egusphere-2024-3048
23 Oct 2024
 | 23 Oct 2024
Status: this preprint is open for discussion.

Intertidal Regions Regulate Seasonal Coastal Carbonate System Dynamics in the East Frisian Wadden Sea

Julia Meyer, Yoana G. Voynova, Bryce Van Dam, Lara Luitjens, Dagmar Daehne, and Helmuth Thomas

Abstract. Seasonal and regional changes in carbon dynamics in the Wadden Sea, the world's largest intertidal sand and mud flats system, were analyzed to quantify the influence of biogeochemical processes (CaCO3 dissolution and formation, photosynthesis, respiration) on the carbonate system at the land-sea interface. With a focus on the East Frisian Wadden Sea and the highly turbid Ems River estuary, we successfully implemented the proxy of the difference between total alkalinity (TA) and dissolved inorganic carbon (DIC) ([TA-DIC]), as well as the calculated ΔTAexcess, ΔDICexcess and ΔTAP to identify how ongoing biogeochemical processes regulate the carbonate system dynamics and the land-sea interface.

In spring, a phytoplankton bloom with high biological activity was indicated by (a) supersaturated oxygen (up to 180 in % saturation), (b) elevated chlorophyll a (up to 151.7 µg L-1) and (c) low pCO2 (as low as 141.3 µatm). As a result, nitrate (NO3-, 19.29 ± 18.11 µmol kg-1) and DIC (159.4 ± 125.4 µmol kg- 1) decreased, whereas TA slightly increased (9.1 ± 29.2 µmol kg-1) in the intertidal regions from March 2022 to May, most likely through nitrate assimilation. The regression analysis of the differences in NO3 concentrations (ΔNO3) against the differences in DIC (ΔDIC) between March and May 2022 yielded a slope of 6.90 which is close to the Redfield ratio of 6.625 for the C:N ratio of freshly produced phytoplankton biomass.

In summer, high seasonal TA values (up to 2400 µmol kg-1) in the Western part of the East Frisian Wadden Sea, along with positive ΔTAexcess at 73.3 % of all stations, indicated production of TA during this season in the intertidal regions, complemented the DIC dynamics. The increase of TA enhances the coastal ocean’s ability to absorb and store CO2 through buffering, chemical equilibrium, biological calcification and the carbonate pump, and suggests that the intertidal regions can be a source of total alkalinity to the coastal regions during the warm productive seasons. The study highlights the complex relationships of these factors, emphasizing the need for a comprehensive understanding of regional and seasonal variations to better assess the role of coastal systems in carbon cycling, storage and climate regulation.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Julia Meyer, Yoana G. Voynova, Bryce Van Dam, Lara Luitjens, Dagmar Daehne, and Helmuth Thomas

Status: open (until 11 Dec 2024)

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Julia Meyer, Yoana G. Voynova, Bryce Van Dam, Lara Luitjens, Dagmar Daehne, and Helmuth Thomas
Julia Meyer, Yoana G. Voynova, Bryce Van Dam, Lara Luitjens, Dagmar Daehne, and Helmuth Thomas

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Short summary
The study highlights the inter-seasonal variability of the carbonate dynamics of the East Frisian Wadden Sea, the world's largest intertidal area. During spring, increased biological activity leads to lower CO2 and nitrate levels, while total alkalinity (TA) rises slightly. In summer, TA increases, enhancing the ocean's ability to absorb CO2. Our research emphasizes the vital role of these intertidal regions in regulating carbon, contributing to a better understanding of carbon storage.