Large-scale carbon storage in the deep-sea through cold-water coral mounds off the Campeche Bank, Gulf of Mexico

Abstract Reef-building cold-water corals form large seabed structures known as coral mounds. As demonstrated in studies from the Northeast Atlantic and Mediterranean Sea, coral mounds accumulate large amounts of carbon(ate). However, beyond the scale of individual mounds, long-term accumulation of both organic (C org ) and inorganic carbon (C inorg ) at the mound province scale remains poorly quantified. In this study, we investigate the Campeche Mound Province, southern Gulf of Mexico, which consists of interconnected coral mound ridges covering an area of > 40 km 2 . Using sediment cores, we reconstruct total carbon (C org and C inorg ) accumulation in the Campeche Mounds over the past ~ 250 kyr. The results show mean total carbon accumulation rates of 0.5–5.6 g C cm −2 kyr −1 . This is three to nine times higher than on the surrounding seafloor. We then upscale obtained carbon concentration data to the entire mound province using high-resolution bathymetry and the CoMMa toolbox, a novel morphometric mapping tool. The total carbon storage of the Campeche Mounds amounts to an estimated 18.5 megatons of carbon that is transferred to the long-term carbon cycle and immobilised for millions of years. For the first time, we present a combination of core-based analysis and spatial mapping. Through accounting for different approaches and time scales, we provide reliable value ranges for carbon accumulation rates in coral mounds. The Campeche Mound Province is not fully mapped and likely much larger, highlighting the substantial, albeit overlooked long-term carbon burial through benthic deep-sea ecosystems in the southern Gulf of Mexico and beyond.