Controls on sediment geochemistry in the Crozet region

Sediment composition to the north (M10), east (M5), and south (M6) of the Crozet Plateau in the Southern Ocean Polar Frontal Zone (PFZ) reflects the dual control on input from the locally elevated upper water-column export production and the proximity to the volcanic islands. The magnitude of the major sedimentary components (biogenic and lithogenic) has been constrained down core. The major lithogenic input to the three sites is identified as Crozet island basalts based on linear extrapolation of sedimentary major element data to known island basalt domains. High-resolution X-ray scanning of cores identified significant heterogeneity in the distribution of biogenic and lithogenic phases. All sites are characterised by a significant heavy mineral fraction that has been identified by SEM as biogenic barite and a mixed titanium–iron oxide of volcanic origin. There are multiple mass flow or turbidite events in the sediment records at each site that are inferred to be generally associated with sea-level rise during deglaciation. 230Th excess-corrected Holocene mass accumulation rates have been estimated for the sedimentary constituents (calcium carbonate, biogenic silica, lithogenic material, organic carbon, authigenic U, and Ba excess ). The core-top proxy records indicate that there is a significant enhancement of biogenic silica export both north and south of the Plateau and lower values east of the Plateau. Organic carbon export is highest to the north of the Plateau, lower within the High Nutrient Low Chlorophyll (HNLC) waters to the south of the Plateau and indistinguishable from the background PFZ values to the east of the island. The presence of the Crozet Plateau has a significant impact on organic carbon production and export throughout the Holocene, corroborating shipboard and remote observations of enhanced productivity in this region.