Iron limitation in SO waters and DMS emissions to the atmosphereS. 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 iniron-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 thelate phase of the high DMS season

DMS

SO2

DMSO MSA

SO4

Wet Wet

Wet Wet

Dry Dry

DryDry

OH

OH

OHOH, H2O2

O3

OH

OH

NO3

Oxidation pathways of DMS in the atmosphere

Port aux FrançaisDMSaqueous

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 DMSParticulate DMSP in the top 50m

36.1 6.9 nM28.2 2.2 nM

18.6 1.3 nM

Results from cruise ANTARES 2 (Feb. 1994)

During cruise ANTARES 2,particulate DMSP in the Plateauwas twice higher than offshore.

DMSP in the Kerguelen area during late summer

During the KEOPS experimentswe 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 using55Fe-radiolabelled nano- and microphytoplancton.

-determination of the DMSPp-to- 55Fe ratio of phytoplancton DMS(P)d release during grazing = DMSPp/ 55Fe x 55Fe release

The impact of grazing on the release to solution of DMSPpOBEX 2

On-deck incubationof < 0.8µm seawater

Demethylation of DMSPdBact. 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 DMSPd and DMS: OBEX 3

Effect of solar radiation:The experimental protocols are under discussion and will be tested duringthe 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 inhibitorswill be used (Glycine betaine GBT, dimethyldisulfide DMDS)

DMSPd DMS products

products

GBT DMDS