Temporal variability in organic carbon fixation, export, sedimentation and utilisation in the Clarion Clipperton Zone

There is interest in biogeochemical cycling and ecosystem functioning in the Clarion Clipperton Zone (CCZ, equatorial Pacific) due to the possibility in the near future of deep sea mining of polymetallic nodules. A set of important processes and ecosystem services relate to the fixation, export and deposition in sediment of organic carbon (C). This is important to understand both as a mechanism for C sequestration, and also as a set of processes which feeds deep sea biological communities. However, due to the remote nature of the CCZ, and the considerable resource required, it has rarely been possible to directly observe the coupling between processes from the sea surface all the way through the water column to the fate of organic C in sediments, nor how those linked processes vary over time or in response to mining disturbance.

Here we present data on C fixation, export, sediment composition and relationships with benthic community biomass. We show clear coupling between surface productivity, export and sinking flux, but that sediment organic C concentrations are not always closely coupled to water column processes. Repeated measurements over a period of ~18 months show inter-annual variability at the seafloor, rather than a stable seasonal pattern. Organic C delivery to the sediment is reflected in the biomass of faunal groups, with different temporal responses in the different groups (macrofauna, metazoan meiofauna and foraminifera) linked to factors such as competition, predation pressure and life cycle differences. Changes in sediment total organic carbon following a mining vehicle test will also be considered.