Silica cycling and isotopic composition in northern Marguerite Bay on the rapidly-warming western Antarctic Peninsula

Abstract

The Southern Ocean is a key region for silica (Si) cycling, and the isotopic signatures established here influence the rest of the world's oceans. The climate and ecosystem of the Southern Ocean are changing rapidly, with the potential to impact Si cycling and isotope dynamics. This study examines high-resolution time-series dataset of dissolved Si concentrations and isotopic signatures, particulate Si concentrations and diatom speciation at a coastal site on the western Antarctic Peninsula (WAP), in order to characterise changes in Si cycling with respect to changes occurring in productivity and diatom assemblages. Dissolved and particulate Si phases reflect the dominant control of biological uptake, and combined with isotopic fractionation were consistent with a season of low/intermediate productivity. Biogenic Si is tightly coupled to both chlorophyll and particulate organic carbon at the sampling site, consistent with diatom-dominated phytoplankton assemblages along the WAP. Variability in diatom speciation has a negligible impact on the isotopic signature of dissolved Si in surface waters, although this is unlikely to hold for sediments due to differential dissolution of diatom species. A continued decline in diatom productivity along the WAP would likely result in an increasing unused Si inventory, which can potentially feed back into Si-limited areas, promoting diatom growth and carbon drawdown further afield.