ORIGINAL RESEARCH article
Front. Earth Sci.
Sec. Marine Geoscience
Volume 13 - 2025 | doi: 10.3389/feart.2025.1593031
This article is part of the Research TopicNew Challenges for Baltic Sea Earth System ResearchView all articles
Early diagenesis in anoxic sediments of the Gulf of Gdańsk (southern Baltic Sea): Implications for porewater chemistry and benthic flux of carbonate alkalinity
Provisionally accepted
Katarzyna Łukawska-Matuszewska1*
Maciej Dwornik2- 1Faculty of Oceanography and Geography, University of Gdańsk, Gdańsk, Poland
- 2Faculty of Geology, Geophysics and Environmental Protection, AGH University of Krakow, Krakow, Poland
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Being a measure of acid-neutralizing capacity, alkalinity determines CO2 uptake from the atmosphere and the pH of seawater. However, the alkalinity budget in the Baltic Sea is still poorly understood. According to recent modeling studies, anaerobic processes in sediments are an important internal source of alkalinity in the Baltic Sea. Nevertheless, determining the role of sediments in alkalinity enhancement is difficult due to the high variability of environmental conditions and, consequently, biogeochemical processes. Here we describe the geochemistry of different types of anoxic sediments from the Gulf of Gdańskmethanic, methanic with freshwater seepage, and methane-free, emphasizing dissolved inorganic carbon, methane, and sulfate. We estimate the benthic flux of carbonate alkalinity (JCA) and the rate of sulfate reduction (SRR) due to the dissimilatory sulfate reduction (DSR) and anaerobic methane oxidation with sulfate (SO4 2--AOM), the main alkalinityproducing processes. We show that the role of anaerobic sediments as a source of alkalinity can vary significantly, depending on the benthic conditions. The concentration and release of carbonate alkalinity (CA) from sediments depends on the SRR, type of the process producing CA (DSR, SO4 2--AOM), as well as the depth of sulfate-methane transition (SMT) in the sediment. The estimated SRR are from 0.1 to 26 nmol cm -3 d -1 . The range of JCA obtained in the present study varies from 1037 to 2084 µmol m 2 d -1 . Assuming the complete oxidation of sulfide released from the sediment to the bottom water, the net flux of CA (J*CA) in the study area is 943-2064 µmol m 2 d -1 with the highest values for sediment dominated with SO4 2--AOM with fresh groundwater seepage, shallow SMT and high SRR in the subsurface sediment layer. Our results may be useful for further studies to determine the role of sediments as an internal source of alkalinity to close its budget in the Baltic Sea.
Keywords: Alkalinity, anoxic diagenesis, microbial activity, Anaerobic methane oxidation, sulfate reduction, marine sediment
Received: 13 Mar 2025; Accepted: 30 Apr 2025.
Copyright: © 2025 Łukawska-Matuszewska and Dwornik. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Katarzyna Łukawska-Matuszewska, Faculty of Oceanography and Geography, University of Gdańsk, Gdańsk, Poland
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