CROZEX- CROZet circulation, iron fertilization and EXport production experiment Three cruises on RRS Discovery: Leg November 2004 to mid-Dec Leg 2 - mid-December to late Jan 2005 Leg 3 - benthic cruise not yet scheduled

CROZEX Main objectives and PIs Circulation and mixing (Pollard) Fe source, distribution (Statham) and speciation (Fones) Phyto- (Lucas) and zooplankton (Fielding) biomass and community structure Export flux (Sanders, Lampitt) Benthic response to export (Billett)

P Indivat Basin Antares Ridge

Marion Dufresne core M1 M4 M2 M3

Wide area bathym to show benthic sites

MODELLED CIRCULATION Only OCCAM 1/12 comes close All show N flow just E of CP and E flow at 45°S OCCAM 1/4°OCCAM 1/12°

Niiler float pic Niiler surface drifter map with Crozet 1000m contour and Pollard ACC pathway overlaid

Mixing and source of Fe Sharp spatial onset of bloom at NE corner of Isle de l’Est Mixing and entrainment in lee of island? Source on Antares Ridge?

SWIFS2

SeaWiFS images

Physical objectives & techniques Determine circulation around CP Find and delineate mixing areas, quantify mixing rates Tools: hydrography (CTD, SeaSoar), LADCP, moorings (McLane Moored Profiler = M3, CMs), floats*, models (OGCMs, tides), altimetry *italics = needs funding

Fe objectives 3-D full depth total Fe distribution with respect to water masses - ‘age’ water Identify shallow benthic source and determine pathways to the surface Investigate speciation of iron and Fe complexing ligands close to sediment and changes during dispersion Look in detail at transfer of iron from sediments to water column (PhD)

Fe techniques Towed Fe fish Fe iron analyser (15 minutes per sample) Fe friendly (Ti) rosette and CTD Benthic Boundary Layer Sampler (BBLS) Size fractionation - dissolved and soluble Fe speciation and ligand concentration Ra tracking of water masses (with WHOI) Sediment cores (for PhD)

Phytoplankton objectives Biomass, community structure and distribution associated with the bloom Rate of size-fractionated production Rates of new and regenerated production f-ratio calculation Physiological response to Fe limited and replete regions Detection of phytoplankton Fe limitation

Phytoplankton techniques 6+ samples from every CTD cast for size-fr chl, HPLC, POC/N, particle absorbance, preservation for taxa, cell carbon C fixation (+Si uptake) - daily incubations N uptake and C:N fixation/uptake rates Ammonium regeneration and nitrification P vs E ( 14 C, 15 N) from midday daily CTD FRRF (profiles, underway, lab/incubations) SDS-PAGE samples for flavodoxin

Zooplankton objectives Biomass, distribution and species composition –Microzooplankton and “microbial loop” processes –Mesozooplankton Community (herbivorous) grazing rates Control on primary production as alternative to Fe / nutrients / light? Contribution to export? - eg. via particle transformation, faecal pellet production

Zooplankton techniques 2-4 vertical nets after every CTD cast –preserve for taxonomy, freeze for Carbon –pick for gut fluorescence Daily gut evacuation rate experiment OPC on SeaSoar (mesozooplankton) Up to 8 LHPR tows Flow cytometry & radioisotopes –(“microbial loop”)

Export objectives Quantify the export flux from above the seasonal thermocline Estimate mid-water re-mineralisation Assess detrital quality for benthic community Quantify rain rate to the sea floor Quantify burial rate

Export techniques f-ratio (see phytoplankton) Seasonal euphotic zone nutrient deficits 234 Th and POC from CTD and SAPS (dedicated casts to 1000m every ~2 days) Drifting pelagra traps (~4 day deployments) 3 moored sediment traps at M1, M2, M4 Cores from control and bloom sites

Work on both/all legs Casts for CTD, nutrients etc Zooplankton nets after each CTD Daily incubations (dawn CTD) and PvE (noon with profiled FRRF) Casts with Ti rosette for Fe (~12) Casts for 234 Th followed by SAPS Pelagra trap ~4 day deployments CO2 underway and profiles Occasional benthic trawls Build time series at M1/4 and M2

A possible cruise leg plan - CTDs