GEOTRACES WORKING GROUP 11-12 September 2007ATLANTIC OCEAN TROPICAL-SUBTROPICAL REGION

Chair Bill LandingRaporteur Eric Achterberg

Group members:Bill JenkinsPeter Croot

Peter SedwickSimon UssherWalter Geibert

Armando RamirezPere MasqueTom Church Jana Friedrich

Overall plan

We propose to undertake 2 transects:

Transect one will form part of a dust/Fe plume study cruise (possibly TEI-microbial)

Transect two will be part of a western boundary cruise

Stations are proposed at 2 degrees intervals. Not all stations will be full depth (1800 m).

We will undertake high resolution shallow casts and lower resolution deep casts to characterize deep water masses.

Important research goals are:1. Link atmospheric TEI concentrations to dissolved and particulate TEI

concentrations in the region under the Saharan dust plume.2. Investigate the mechanisms for the maintenance of the tropical Fe

plume, and Fe transport into and out of the plume. Is in-situ generation or lateral advection the most important process?

3. Investigate control of ocean productivity by TEIs4. Characterise chemistry of N Atlantic deep water complex, and observe

Antarctic Bottom Water

ConsiderationsCruise track 1-The dust cruise should take place in a period of year with enhanced atmospheric dust concentrations.-We envisage the deployments of LIDAR on the cruises for ship-board aerosol observations.-UK GEOTRACES proposal will have to be hypothesis driven, with consideration for linking micronutrient distributions and supply-removal to microbial processes and distributions. Consequently such a programme will consider a north-south transect.

Cruise track 2-We will undertake a cross transect in the western basin to characterize deep water masses. -It is envisaged that stations will be occupied in the Amazone river plume and in the Cariaco Basin region (to study isolated suboxic basin system).-Seamounts will be included in the cruise track to study the impact of the nephloid layer on water column TEI concentrations and undertake proxy studies.-Stations over hydrothermal vents on the mid-Atlantic ridge will be included to investigate dissolved and particulate TEI signatures

Links to other Transect-Germans run north-south cruises on 23ºW. Peter Croot is contact person.-Low oxygen studies (1 funded and 1 under review) Peter Croot is contact person. -Extended W transect out of Cape Cod, via Bermuda to Barbados will form ideal link-up transect for our region.-Cruise transect into the Angolan Basin will form ideal link-up for our region.-We will attempt to re-occupy TTO and GEOSECS stations-We envisage that the influence of the Romanche Fracture zone on deep waters will be investigated in other group proposals (Angolan Basin work).

GEOSECS sections

TTO sections