Iron limitation in SO waters and DMS emissions to the atmosphere S. Belviso (LSCE, Gif-sur-Yvette)

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

2. Oxidation pathways of DMS in the atmosphere Wet Dry Dry Wet OH, H2O2 SO4 SO2 OH O3 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) NO3 OH OH DMS OH DMSO MSA OH Dry Wet Dry Wet DMS aqueous Port aux Français KEOPS 1 will take place during the late phase of the high DMS season Are iron-mediated blooms responsible for DMS production in SO waters in late summer?We willdescribe with high spatial resolution the sea surface DMS concentration

3. DMSP in the Kerguelen area during late summer Results from cruise ANTARES 2 (Feb. 1994) Particulate DMSP in the top 50m DMSP is the algal precursor of DMS 36.1 ± 6.9 nM 28.2 ± 2.2 nM M2 18.6 ± 1.3 nM 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 During cruise ANTARES 2, particulate DMSP in the Plateau was twice higher than offshore.

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

5. 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) GBT DMDS DMSPd DMS products products The impact of bacteria and solar radiation on the degradation of DMSPd 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