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Impact of Bottom Trawling on CO2 Emissions in the Baltic Sea
Research conducted by the GEOMAR Helmholtz Centre for Ocean Research Kiel reveals that bottom trawling disturbances on the seafloor contribute to significant carbon dioxide (CO2) emissions. The study indicates that the act of dragging trawls across the ocean floor not only releases organic carbon trapped in marine sediments but also exacerbates the oxidation of pyrite, a mineral found in these sediments, which leads to additional CO2 emissions. Published in the journal Communications Earth & Environment, the research underscores the urgent need to protect areas with fine-grained sediments important for carbon storage in the Baltic Sea.
The release of CO2 into the atmosphere can be significantly amplified by the resuspension of seafloor sediments. This disturbance, caused by both human activities like bottom trawling and natural events such as storms, results in the exposure of sediments to oxygen-rich seawater, facilitating a large-scale oxidation of pyrite. This process contributes to CO2 emissions in a manner previously underestimated, revealing it to be a more significant factor than the oxidation of organic materials. This study is noted for providing unprecedented quantitative evidence regarding this phenomenon in the western Baltic Sea.
Kiel Bight: A Critical Carbon Sink at Risk
The focus of this research is on Kiel Bight, a coastal area situated between the German island of Fehmarn and the Danish islands, where various sediment types can be found. It features coarse sandy sediments in shallower regions and fine-grained mud in deeper waters. These muddy sediments play a pivotal role in the Baltic Sea’s carbon cycle due to their rich organic matter content. They are susceptible to changes from both natural forces and human activities including bottom trawling.
Laboratory Experiments Reveal New Insights
To gain insights into sediment resuspension, researchers conducted sediment slurry incubations by collecting samples from varying sites within Kiel Bight. The samples were stirred in laboratory containers filled with seawater to simulate different conditions, including variations in oxygen levels. Over the course of the incubation, the team tracked key chemical parameters such as CO2 levels, pH, nutrient concentrations, and isotopic compositions. These metrics helped uncover the underlying geochemical processes and their implications for the local carbon cycle. The laboratory findings were subsequently integrated into biogeochemical models to evaluate the broader effects of sediment disturbance and oxygenation on carbon dynamics.
Pyrite Oxidation: A Key Factor in CO2 Release
Findings from the research indicate that sediment resuspension results in far greater CO2 emissions than previously understood, particularly due to the oxidation of pyrite. This mineral, prevalent in oxygen-depleted muddy sediments, reacts with seafloor oxygen when disturbed, creating acid that transforms bicarbonate into CO2. This process releases a substantial amount of CO2 into the atmosphere, and modeling indicates that such processes could considerably diminish the carbon uptake capacity of the region, effectively converting these areas from carbon sinks into carbon sources during disturbances.
Protecting Sensitive Seafloor Areas to Preserve CO2 Uptake
“Kiel Bight serves as a vital sink for atmospheric CO2, and our findings reveal that bottom trawling activities greatly undermine this function by enhancing pyrite oxidation and acidification,” explains Kalapurakkal. The implications of this research highlight the critical need to safeguard seafloor zones rich in fine-grained muddy sediments, which are often abundant in pyrite. “Protecting these areas is essential for preserving the CO2 uptake capacity of the Baltic Sea,” adds Kalapurakkal.
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