A high-resolution sampler for nutrient and chlorophyll a profiles of the sea ice platelet layer and underlying water column below fast ice in polar oceans: preliminary results

Abstract

A device (ADONIS) for collecting interstltlal 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 concentratlons at the congelation/platelet Ice Interface Maximum chl a concentration under 2 5 m congelatlon Ice, ranged between 5 20 and 853 pg I-' from 26 October to 3 December 1989 but was only 0 35 pg 1-' under 4 m thick ice wlth a 0 4 m snow cover Ammonlum concentrations In the interstitial water of the platelet Ice layer always exceeded those in the underlylng water column by at least a n order of magnitude with maximum values per proflle ranging from 3 20 to 118 pm01 NH, I ' Concentrations of phosphate nltrate and sil~clc acid In the platelet Ice layer differed only slightly from those in the water column except in the presence of hlgh algal blomass, where they were somewhat depleted but never exhausted By the end of November, ammonium and phosphate at the interface of the congelat~on/platelet Ice layer had incredsed 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 nutnents are apparently replenished by an adequate and efficient water exchange mechanism between platelet layer and underlylng water column ADONIS proved to be a n effect~ve tool with whlch to obtaln hlgh-resolut~on profiles of nutnents and chl a in interstitial waters of the platelet Ice layer and upper water column under congelatlon Ice up to 4 m thickness