Description: The West Antarctic Peninsula (WAP) is a highly productive shelf region during austral summer, supporting a rich ecosystem that has a significant impact on carbon sequestration. This ecosystem is heterogeneous, and characterised by biological "hotspots" fuelled largely by diatom production. The specific mechanisms determining the location and extent of these hotspots are not fully understood. Sedimentary enrichment of silicic acid (DSi) relative to other nutrients along the WAP, suggest that nutrient transfer across the sediment-water interface could have an impact on algal community composition. Here we combine reaction-transport modelling with porewater profiles of DSi concentration and stable silicon isotopic composition, biogenic silica content (BSi) and diatom abundances from sediment cores collected along the WAP, to assess the DSi flux and the processes that release this key nutrient from the WAP sediment into the overlying waters. We estimate a DSi diffusive flux of 2.67- 10**10 ± 2.75- 10**9 mol/yr for the WAP continental shelf area, which is lower than that previously estimated for the open Southern Ocean. Porewater isotopic compositions suggest that DSi concentrations are supplied primarily by BSi dissolution and respond to authigenic phase formation. Reaction-transport modelling highlights the highly dynamic environment of core-top sediments and the strong impact of surface productivity on sedimentary processes and the early diagenetic release of DSi. Both observations and modelling suggest a strong pelagic influence on benthic environment with the silicon benthic fluxes highly variable on different temporal and spatial scales, and thus sensitive to sea ice dynamics and climate change.

Description: The supply of nutrients to the low-latitude thermocline is largely controlled by intermediate-depth waters formed at the surface in the high southern latitudes. Silicic acid is an essential macronutrient for diatoms, which are responsible for a significant portion of marine carbon export production. Changes in ocean circulation, such as those observed during the last deglaciation, would influence the nutrient composition of the thermocline and, therefore, the relative abundance of diatoms in the low latitudes. Here we present the first record of the silicic acid content of the Atlantic over the last glacial cycle. Our results show that at intermediate depths of the South Atlantic, the silicic acid concentration was the same at the Last Glacial Maximum (LGM) as it is today, overprinted by high silicic acid pulses that coincided with abrupt changes in ocean and atmospheric circulation during Heinrich Stadials and the Younger Dryas. We suggest these pulses were caused by changes in intermediate water formation resulting from shifts in the subpolar hydrological cycle, with fundamental implications for the nutrient supply to the Atlantic.