The ballast effect of lithogenic matter and its influences on the carbon fluxes in the Indian Ocean

Abstract

Abstract. Data obtained from long-term sediment trap experiments in the Indian Ocean in\nconjunction with satellite observations illustrate the influence of primary\nproduction and the ballast effect on organic carbon flux into the deep sea.\nThey suggest that primary production is the main control on the spatial\nvariability of organic carbon fluxes at most of our study sites in the Indian\nOcean, except at sites influenced by river discharges. At these sites the\nspatial variability of organic carbon flux is influenced by lithogenic matter\ncontent. To quantify the impact of lithogenic matter on the organic carbon\nflux, the densities of the main ballast minerals, their flux rates and\nseawater properties were used to calculate sinking speeds of material\nintercepted by sediment traps. Sinking speeds in combination with\nsatellite-derived export production rates allowed us to compute organic\ncarbon fluxes. Flux calculations imply that lithogenic matter ballast\nincreases organic carbon fluxes at all sampling sites in the Indian Ocean by\nenhancing sinking speeds and reducing the time of organic matter respiration\nin the water column. We calculated that lithogenic matter content in\naggregates and pellets enhances organic carbon flux rates on average by\n45\u2009% and by up to 62\u2009% at trap locations in the river-influenced\nregions of the Indian Ocean. Such a strong lithogenic matter ballast effect\nexplains the fact that organic carbon fluxes are higher in the low-productive\nsouthern Java Sea compared to the high-productive western Arabian Sea. It\nalso implies that land use changes and the associated enhanced transport of\nlithogenic matter from land into the ocean may significantly affect the\n CO2 uptake of the organic carbon pump in the receiving ocean areas.