ALBERT

Description: The contribution of carbonate-producing benthic organisms to the global marine carbon budget has been overlooked, the prevailing view being that calcium carbonate (CaCO3) is predominantly produced by marine plankton. Here, we provide the first estimation of the global contribution of echinoderms to the marine carbon cycle, based on organism-level measurements from species of the five echinoderm classes. Echinoderms global CaCO3 contribution amounts to ~0.861 Pg CaCO3 yr-1 (0.102 Pg C yr-1 of inorganic carbon) as a production rate, and ~2.11 Pg CaCO3 (0.25 Pg C of inorganic carbon) as a standing stock globally. Echinoderm inorganic carbon production (0.102 Pg C yr-1) is less than the global pelagic production (0.4-1.8 Pg C yr-1), and similar to the estimates for carbonate shelves globally (0.02-0.12 Pg C yr-1). Echinoderm CaCO3 production per unit area, is ~27.01 g CaCO3 m-2 yr-1 (3.24 g C m-2 yr-1 as inorganic carbon) on a global scale for all areas, with a standing stock of ~63.34 g CaCO3 m-2 (7.60 g C m-2 as inorganic carbon), and ~7.97 g C m-2 as organic carbon. The shelf production is 77.91 g CaCO3 m-2 yr-1 (9.35 g C m-2 yr-1 as inorganic carbon) in contrast to 2.05 g CaCO3 m-2 yr-1 (0.24 g C m-2 yr-1 as inorganic carbon) for the slope on a global scale. The biogeography of the CaCO3 standing stocks of echinoderms showed strong latitudinal variability. Roughly 80% of the global CaCO3 production from echinoderms occurs between 0 and 800 meters. The shelf and upper slope contribute the most. We provide a global distribution of echinoderm populations in the context of global calcite saturation horizons, since undersaturated waters with respect to mineral phases are surfacing. This shallowing is a direct consequence of ocean acidification, and in some places it may reach the shelf and upper slope permanently. These organism-level data contribute substantially to the assessment of global carbonate inventories, which at present are poorly estimated. Additionally, it is desirable to include these benthic compartments in coupled global biogeochemical models representing the “biological pump”, since at present all efforts have focused on pelagic processes, dominated by coccolithophores.