Carbonate Turbidity Currents Play an Underappreciated Role in the Global Carbon Cycle

Carbonate turbidity currents play a crucial but underemphasized role in the global carbon cycle through the transport and burial of carbon in the marine environment. Carbonate reef-slope systems transport inorganic carbon (IC) stored in carbonate minerals and organic carbon (OC) from terrestrial and marine sources into the deep sea. Since carbonate sediments and rocks comprise a significant portion of the modern systems and the sedimentary record, understanding IC and carbonate-associated OC transport into the deep sea is vital for quantifying carbon burial in carbonate systems and its effects on climate change, ocean acidification, and deoxygenation. This study presents the first experiments on carbonate turbidity currents that focus on flow dynamics and carbon burial. Using natural carbonate lagoon sediments (sands and muds), four experiments with increasing sediment concentrations (1.1–11%) demonstrate concentration-dependent flow structure, sediment transport, and carbon partitioning. Experimental results show variable distal OC transport, with enrichment of approximately ~45% to 100% in distal location relative to proximal locations, alongside systematic IC depletion of ~15% to 30% from proximal to distal regions across all experiments. Natural records from the western longitudinal transects of the Neogene Great Bahama Bank slope show variable and sequence-dependent OC trends and a consistent proximal-to-distal decrease in IC, indicating high spatial and temporal variability in OC transport. We estimate carbon-burial rates for the Great Bahama Bank over the last 25 million years to be between 0.0059 × 10⁻ 5 to 6.2 × 10⁻ 5 PgC/year (0.0059 × 10⁻ 2 to 6.2 × 10⁻ 2 MtC/year) for OC and 0.09 × 10⁻ 4 to 1.9 × 10⁻ 4 PgC/year (0.09 × 10⁻ 1 to 1.9 × 10⁻ 1 MtC/year) for IC, suggesting that turbidity currents are an important vehicle for carbon redistribution and preservation in deep-sea sediments, which reduces the likelihood of carbonate dissolution and CO₂ release. These findings contribute to our understanding of sediment routing and carbon burial in submarine carbonate environments and highlight the need to reassess the role of carbonate turbidity currents in the long-term carbon cycle.