Physical and Chemical characterization of the aerosol during the cruise

Guieu/Losno/Bonnet/Blain/Gaudichet

1)     Scientific objectives:Determine the particles abundance of the area

Determine the size distribution in order to attempt a IRON FLUX calculation.

Determine the mineralogical composition.

Determine some geochemical tracers (Al, Pb, …) and elements of biogeochemical interest such as Fe and P.

Quantify dissolved iron originating from these particles in the surface seawater

les particules sahariennes (Barbades)

particules collectées au

centre du Pacifique Nord

Particules issues de la pollution

(MaceHead, Irlande)(Al = 6000 ng.m-3)

(Al = 15 ng.m-3)

Moyenne pendant Prosope Al = 600 ng.m-3 avec un échantillon = 2000 ng.m-3

Seasonal distributions of atmospheric Fe fluxes to the global ocean. From model by Gao et al., 2001. (GRL)

Dissolved iron in the surface layer estimated for the eolian input at the global scale. (Bermann-Franck et al., 2001)

Estimation of the Fe deposition to the South Pacific:

Only from model (Gao et al., 2001, GRL)

Lowest predicted values in the South pacific

(along with Antarctic and Arctic)

This recent model used data from stations located mainly on the western S Pacific

No data in the BIOSOPE area

(2)     Methodology and measurements

HOW?

-Aerosol sampling during the transects and clean conditions. Contamination problems are crucial.

-measurements back in the lab on the particulate phase: concentration of elements tracers of the lithogenic origin (Al, Si, Ti), pollution (Pb) and of element of biogeochemical interest for the project (Fe, P). ICP-AES, ICP-MS, XRF.

-Grain size distribution; identification of the particles (clays, soot, glass, biogenic particles). Identification of the clays. Local or remote origin of the soot.

The main goal is to chemically characterize the aerosol in this very remote area

The second objective is to conduct dissolution experiments, in particular to quantify the dissolved iron originating from this poor

atmosphere

HOW?

-very simple protocol to avoid contamination. Analysis back in France: Fe, Si, P, (Cu)

Aerosol (filter)

+

250 ml Filtered seawater/ unfiltered seawater

Clean / dark

Teflon container

6 days

Filtration 0.2 µm

Acidification of the filtrate,

storage. Analysis

back in France

DISSOLUTION EXPERIMENTS: very simple protocol. Has to be done inside the clean container

(3)    Sampling

Multi aerosol sampler

1. Low volume samples: 3 different filters will be performed at the same time, coupled with a Particles Counter. Sampling should be done strictly during clean periods.

2. Water sampling for the dissolution experiment: we will use the ultra-clean high flow rate sampling system: samples from seasurface (no extra time needed from the regular sampling for iron measurement)