Increased diatom dissolution in Prydz Bay, East Antarctica linked to inception of the Prydz Bay gyre

Abstract

Diatom assemblages and abundance in marine sediment cores are utilised as proxies of paleoceanographic conditions. However, diatoms are altered by taphonomic processes, which cause diatom accumulation rates to vary while simultaneously altering assemblages by removing some species from the sedimentary record. Furthermore, these taphonomic processes vary with space and time. Additionally, significant insights into the marine carbon and silicon cycles can be gained by assessing variability in diatom dissolution. Sediment core NBP0101-JPC24 from Prydz Bay, East Antarctica, provides a detailed Holocene record of diatom community shifts in an ecologically significant section of the Antarctic coast. The sedimentary and paleontologic record in JPC24 records the inception of the Prydz Bay gyre during deglaciation, as well as an increase in sea ice and in wind-related turbulence over the last 7000 years. A record of diatom preservation for JPC24 has been established by examining dissolution-induced changes in the morphology of Fragilariopsis curta, a sea-ice-related diatom common in JPC24. Diatom dissolution in NBP0101-JPC24 does not significantly correlate with the relative abundance of any diatom species or ecological species group. However, dissolution is low during the deglacial, prior to the inception of the Prydz Bay gyre and resultant polynya, and increases as the gyre increases in size and strength to present conditions. Circulation in the upper water column associated with the modern persistent gyre causes diatoms and other silt-sized particles to remain in suspension. Prior studies have shown that diatoms exposed to caustic marine water continue to dissolve until they are sequestered in sediments. Once sequestered in the sediments, diatoms will stop dissolving when a chemical equilibrium has been achieved between silicic acid in solution and solid opal. Diatom dissolution, therefore, is seen to be controlled by physical oceanographic factors rather than diatom ecology.