Vertical organic inputs and bio-availability of carbon in an Antarctic coastal sediment

Measurements were made of organic fluxes at a coastal sediment at Signy Island, South Orkney Islands, Antarctica, between December 1990 and March 1992. The deposition rate of organic matter to the sediment was measured at the same time with a maximum sedimentation rate of 306 mg Cm^-2 d^-1. The rates of sedimentary organic input were small during winter ice cover, and the organic content of the sediment declined during this period as available organic matter was depleted. Fresh organic input occurred as soon as the sea-ice melted and ice algal biomass was deposited to the sediment; and was sustained during the spring after ice break-up by continued primary production in the water column. The proportion of available carbon in surface sediments was measured during a seasonal cycle using Pseudomonas aeruginosa as an indicator organism over the 0-1 cm depth horizon. Variations in the amount of organic matter deposited to the sediments and the proportion of available carbon were observed during the seasonal cycle. Seasonal variations of benthic activity in this coastal sediment was regulated by the input and availability of organic matter, and not by seasonal water temperature, which was relatively constant between - 1.8 and 0.5 C.