Iron limitation in SO waters and DMS emissions to the atmosphere S. Belviso (LSCE, Gif-sur-Yvette) DMS increased markedly after deliberated iron fertilisation of SO waters (Boyd et al. 2000) but the origin of the DMS enhancement is unclear SOIREE 0-65m In the patch Outside the patch Scientific background: How important are iron-mediated blooms for DMS production in SO waters? Which biogeochemical processes are involved in DMS production in iron-mediated blooms? The questions to be addressed experimentally during KEOPS:

Monthly distribution of volume weighted mean (VWM) concentration of methanesulfonate (MSA) in rain water samples from Kerguelen Island. Courtesy of Vagelis Baboukas (Univ. of Crete) KEOPS 1 will take place during the late phase of the high DMS season DMS SO 2 DMSOMSA SO 4 Wet Dry OH OH, H 2 O 2 O3O3 OH NO 3 Oxidation pathways of DMS in the atmosphere Port aux Français DMS aqueous Are iron-mediated blooms responsible for DMS production in SO waters in late summer? We will describe with high spatial resolution the sea surface DMS concentration

M2 DMSP is the algal precursor of DMS Particulate DMSP in the top 50m 36.1  6.9 nM 28.2  2.2 nM 18.6  1.3 nM Results from cruise ANTARES 2 (Feb. 1994) During cruise ANTARES 2, particulate DMSP in the Plateau was twice higher than offshore. DMSP in the Kerguelen area during late summer During the KEOPS experiments we will: describe with high spatial resolution the concentration of particulate DMSP in surface waters on the grid and along the transects investigate the factors controlling the availability of particulate DMSP (algal taxonomy, nutritional status and growth limitation of phytoplankton communities) OBEX 1

Microzooplankton and mesozooplankton grazing experiments using 55 Fe-radiolabelled nano- and microphytoplancton. -determination of the DMSPp-to- 55 Fe ratio of phytoplancton DMS(P) d release during grazing = DMSPp/ 55 Fe x 55 Fe release The impact of grazing on the release to solution of DMSPp OBEX 2 On-deck incubation of < 0.8µm seawater Demethylation of DMSPd Bact. Removal of DMS Photochemical removal of DMS dDMS(P) d /dt -determination of gross release rates of DMS(P) d (Christaki et al. 96) DMS(P) d release during grazing = net release + DMS(P) d loss rates

The impact of bacteria and solar radiation on the degradation of DMSP d and DMS : OBEX 3 Effect of solar radiation: The experimental protocols are under discussion and will be tested during the June 2004 workshop in Banyuls/mer in the framework of the UVECO project Bacteria: According to the bacterial production, how much DMSPd is demethylated, how much DMSPd is cleaved to DMS, how much DMS is removed by bacteria? Short incubations of 0.8 µm filtered water (in the dark) where specific inhibitors will be used (Glycine betaine GBT, dimethyldisulfide DMDS) DMSPdDMSproducts GBT DMDS