Dynamics of ammonium oxidizer activity and nitrous oxide (N20) within and beneath Antarctic sea ice

Abstract

M3STRACT Nitrapynn, an lnh~bitor of NH; oxldlz~ng bactena was used to estlmate the a c t ~ v ~ t y of NH: oxldlzing bacteria in the bottom 1 to 15 cm of annual sea Ice and in the water column at vanous locations In McMurdo Sound and along the Ross Ice Shelf (RIS) N ~ t r a p y r ~ n s~gn~flcantly ~ n h ~ b i t e d dark ' 4 C -H C 0 3 uptake in virtually all sea-ice samples, indlcahng the presence of NH: oxld~zlng bacteria Inorganic carbon futahon by sea ice NH: o x ~ d ~ z e r s was only a small fract~on of that futed by sea-lce photoauto-trophs, both on an hourly and annual b a s ~ s Despite their relative lack of ~mportance to lnorganlc carbon fixation NH: oxidizing bactena may have an important role in the N d y n a m ~ c s w ~ t h l n the b ~ o g e n i c layer of annual sea Ice both In terms of N H ~ utlllzatlon and eventual NO; product~on Inorgamc carbon futatlon in the water column beneath sea ice was generally not i n h ~ b ~ t e d s~gnif~cantly by nitrapynn NH: oxldizer actlvlty was also not detectable in deep water flow~ng beneath (southward) or from under (northward) the RIS N 2 0 (a by-product of NH: oxidation) levels in p e l a g ~ c samples were always near 100 % of saturation w t h respect to the alr above the sea surface corroborating the low levels of NH: ox~dizer activity found In the water column