A device (ADONIS) for collecting interstitial water samples, at closely spaced intervals, from the platelet ice layer and upper water column beneath congelation ice in McMurdo Sound, Antarctica, was designed, developed, and tested. Fourteen profiles of inorganic nutrients and chlorophyll a (chl a) were obtained using ADONIS under fast ice near McMurdo Station. All profiles revealed highest chl a concentrations at the congelation/platelet ice interface. Maximum chl a concentration, under 2.5 m congelation ice, ranged between 5.20 and 853-mu-g l-1 from 26 October to 3 December 1989, but was only 0.35-mu-g l-1 under 4 m thick ice with a 0.4 m snow cover. Ammonium concentrations in the interstitial water of the platelet ice layer always exceeded those in the underlying water column by at least an order of magnitude, with maximum values per profile ranging from 3.20 to 178-mu-mol NH4 l-1. Concentrations of phosphate, nitrate, and silicic acid in the platelet ice layer differed only slightly from those in the water column, except in the presence of high algal biomass, where they were somewhat depleted but never exhausted. By the end of November, ammonium and phosphate at the interface of the congelation/platelet ice layer had increased slightly relative to water column concentrations, indicating that regeneration exceeded uptake. Growth of the sea ice microbial community in the platelet layer does not appear to be nutrient-limited, as nutrients are apparently replenished by an adequate and efficient water exchange mechanism between platelet layer and underlying water column. ADONIS proved to be an effective tool with which to obtain high-resolution profiles of nutrients and chl a in interstitial waters of the platelet ice layer and upper water column under congelation ice up to 4 m thickness.
