High Benthic Transfer Rates with Low Concentrations of Organic Carbon – No Contradiction in the Atacama Trench

Sediments of abyssal plains and in deep-sea trenches have long been considered relatively inactive from a microbiological point of view. High abundances of benthic organisms (Danovaro et al. 2003) and high microbial carbon turnover rates at the seafloor surface (Glud et al. 2013) have already corrected this assumption for some deep-sea ditches. Obviously, partial ocean trenches function as a kind of trap for particulate organic material, which is transported by currents or debris flow from the steep edges into trenches. So far, biogeochemical investigations in deep-sea trenches have only been available for surface sediments. Here we present the first results of deep buried sediments. The samples were collected on a cruise of the RV SONNE in spring 2018 to the Atacama Trench. They prove that even several meters below the seabed the microbial activity can reach an intensity comparable to that known from coastal high production areas. Despite significantly lower total carbon contents in the sediments of the trench, considerable flow rates were observed. We assume that the main original ash for this finding is in the sediment dynamics in the vicinity of the trench. The sediments are characterized by a large number of smaller and more powerful turbidite layers and therefore show very high accumulation rates. Obviously, reactive organic material is buried relatively fast and is therefore preferentially available for anoxic degradation processes.