CROZEX- CROZet circulation, iron fertilization and EXport

production experiment

• Three cruises on RRS Discovery:

• Leg 1 - 1 November 2004 to mid-Dec

• Leg 2 - mid-December to late Jan 2005

• Leg 3 - benthic cruise not yet scheduled

CROZEXMain 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 Indi

vat B

asin

Antar

es R

idge

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 (14C, 15N) 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

• 234Th 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 234Th 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