Organic Carbon Burial Rates in Muddy Temperate Shelf Sea Sediments

Abstract

Muddy continental shelf sediments act as important sinks for atmospheric CO₂ by accumulating organic matter, a small fraction of which is buried and stored as organic carbon (OC) over long timescales. Quantifying long-term OC burial in shelf sediments is critical for understanding their role in climate regulation; however, this remains difficult due to limited age-resolved data and the challenges of determining sediment accumulation rates and temporal changes in OC content. To address this, we quantified age-resolved OC storage over the past two centuries in the upper 50 cm of the Western Irish Sea Mud Belt (WISMB) by measuring depth-resolved OC content and sediment accumulation rates. The OC content (0.15%–1.62%), OC storage (1.30–15.15 gC cm⁻³), and sediment accumulation rates (0.26–0.37 cm yr⁻¹) vary both spatially and temporally, with the highest OC accumulation and burial occurring in muddier, deeper-water sediments. Between 53% and 91% of the OC accumulated in the surface 2 cm over the past 8 years (17.09–39.47 gC m⁻² yr⁻¹), and 60%–68% of the OC accumulated in the upper 10 cm over the past 38 years (21.90–51.13 gC m⁻² yr⁻¹), remains buried for more than 100 years (14.03–33.50 gC m⁻² yr⁻¹). These rates are comparable to those reported for other muddy continental shelf regions, including mud patches, coastal fjords, and glacial troughs.