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It is well known that, during the widely used AAA pretreatment (de Vries and Barendsen 1954), alkali treatment is responsible for the incorporation of modern carbon due to the precipitation of atmospheric CO2 as carbonate. Until now, the last step of the experiment, consisting in acid treatment (most of the time with hydrochloric acid) was considered to be sufficient to eliminate all of lab contamination. But wood, peat and sediment present a complex molecular structure. During radiocarbon chemical treatments, functional groups still present in the molecules are likely to form ionic bonds with “modern” carbonates. These new chemical bonds resist a “classical” acid treatment and are responsible for rejuvenation. This short paper presents preliminary results for two common 14C cases: rejuvenation of a 0.4 pMC wood and of an Oxygen Isotope Stage 3 (OIS3) paleosol. For both cases, contamination due to incorporation of modern carbon during chemical treatment is evaluated and an alternative protocol is proposed.

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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

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