Silicon Isotopes in Surface Waters during Summer in the Southern Ocean

Abstract:

This study reports the silicon isotopic composition (δ³⁰Si) of dissolved silicon (DSi) from surface water at the RaTS site in coastal region of the West Antarctic Peninsula (WAP), within Ryder Bay in the Bellingshausen Sea in the Pacific sector. Samples are from the beginning of December 2004 to the middle of February 2005, and from the end of December 2005 to the beginning of March 2006, the end of austral spring through the end of austral summer/beginning of austral autumn over two field seasons. For the most part, for both summers, DSi diminished and δ³⁰Si of DSi increased through time, but this was accomplished during only a few short period of net nutrient drawdown. During these periods, the δ³⁰Si of DSi was strongly negatively correlated to DSi concentrations. Fractionation (expressed in permil as ɛ) determined for the net nutrient drawdown periods was in range of -2.24 to -1.44 ‰ for Open system model and -1.92 to -1.26 ‰ for Closed system model. These results are somewhat higher than previous studies that did not follow changes in δ³⁰Si and DSi over time (but relied more on snapshots like depth profiles) and therefore were more likely to include the effects of mixing of dissolved silicon up into the mixed layer, diminishing the estimate of fractionation. Finally, paleoceanographic studies using silicon isotopes needs to be thoroughly investigated because this method has limitations.