Aragonite and magnesian calcite fluxes to the deep Sargasso Sea

Abstract

Aragonite and magnesium calcite fluxes were estimated from a 14-month series of sediment trap samples from depths of 500, 1500 and 3200 m in the Sargasso Sea. No significant difference with depth was observed in fluxes of either carbonate phase. At 3200 m, the mean aragonite flux was 2.8 mg m −2 day −1, or 13% of the total CaCO 3 flux. At all depths pteropods were the major source of aragonite, contributing more carbonate than heteropods by a factor of 3–24. Most of the pteropod aragonite occurred in the size fraction >0.5 mm. At 3200 m, more than half of the pteropod mass flux in the size fraction >0.5 mm comprised four species: Styliola subula, Clio pyramidata, Limacina inflata and Cuvierina columnella. The mean magnesian calcite flux at 3200 m was 1.7 mg m −2 day −1, or 8% of the total CaCO 3 flux. The majority of the magnesian calcite (9–12 mole % MgCO 3) occurred in the finest size fraction. <37 μm. Evidence suggests that bryozoans attached to floating Sargassum are the source of this magnesian calcite. The combined fluxes of aragonite and magnesian calcite accounted for 21–25% of the mean annual CaCO 3 flux to 1500 and 3200 m.