Ammonium regeneration in the Scotia-Weddell Confluence area during spring 1988

Abstract

The presence of laige ammonium stocks and the related enhanced quant~ties of microheterotrophs in the Scotla-Weddell Confluence area lndicate the importance of ammonium i e m ~n e r alization processes there Maximal ammonium concentrations in the marglnal ice zone amounted to Inore than 2 pm01 N 1.' and ren~lneralization rates in this zone were consistently hlgher than those measured In the adjacent open ocean and permanently ice-covered zones At one statlon, characterized by a large knll swarm, the remlnerallzation rate was 18 nmol N 1-' h-' rates In the marginal ice zone generally ranged between 5 and 9 nmol N 1-' h-' Protozoan actlv~ty was of predominant importance for the remineralizat~on process only after the k r ~l l event was a very hlgh bacterlal activity observed The presence of krill does not contribute in a direct way to the ammonium pool but probably Initiates the bacterlal breakdown actlvity In algal d e b n s and faecal pellets The increased r e m i n e r a l i ~a t ~o n leads to enhanced availabil~ty of ammonium in the water a n d to decreased f-rat~os for phytoplanktonlc nitrate assimilation Nevertheless, n ~t r a t e uptake represented at least 3 0 3 < of inorganic nltrogen assimilation signif~cantly higher than values measured for oligot~ophic systems This art~cle was submjtted to the editor