1. Theme 1: Biological uptake and trace element bioavailability
1. How does stoichiometric plasticity connect to trace metal distribution and inventories?
2. How much do we know about the different TE acquisition systems of microorganisms?
3. What ‘modes’ of metal (M) uptake dominate in different natural systems?
4. How important are co-limitations?
5. What are the interactions within an organism for multiple metals?
6. How can molecular tools help us to improve our knowledge?
7. How do we improve our understanding of TE bioavailability?
8. What is the role of TE speciation (redox, organic, and physical) for their uptake and bioavailability (link with Theme 2)?
9. Can we connect entire food-web structure on TE uptake and inventories?
10. Can we capture and understand temporal variations (early stage vs. decline of the bloom) and spatial variations?
11. How available are TE when regenerated (link with Theme 3)?
12. How do we connect large GEOTRACES datasets to their influence on biological pump?
role of zooplankton

2. Theme 1: Biological uptake and trace element bioavailability
1- Bacterial demand? Very poorly modelled… Although very important.
2- Issue of phagotrophy?... Major issue for uptake.
3- What is bioavailability? Do we have new data that can help resolving the question?
2 sub-groups:
Stoichiometry/co-limitation
Uptake/bioavalability

3. Stoichiometry Working Group
Deep chlorophyll maximum iron limitation phenomenon T, I
Cd or other metals (Co) as proxy for sinking POC compare to Th flux(constrained Cd:P) T, I
What does the slope of metal:phosphate mean (d and p)? Spatial variability? T, I
Are biological quotas set by availability or vice versa? Esoteric
Phytoplankton functional groups (PFT): ?
Can we constrain the realized quota, what is the maximum?
Can pigment abundance be converted to estimated metal quotas?
Can quota be estimated from biochemical first principles (Raven-like)? T, I
Present: From model organism specific activities
Future: From metalloproteomics
Do metal-metal interactions influence the dissolved and particulate distribution?
How much stoichiometric distribution is accidental (e.g. Cd and Zn)?
By restoring the model to observations can the gross fluxes from the surface be calculated?
Interesting to look at Fe:NO3- ratios, could also look at vertical gradients to calculate diffusive flux to DCM, scavenging group a bite in DCM for many elements, is decrease in Fe due to biological uptake or scavenging as likely for other elements. Need to consider role of photochemistry in surface.
chlorophyll max minimum in lithogenic elements but not radiogenic isotopes, argues against scavenging but hard to consider biology taking up eg Al, Th,
other metals may come in to Fe transport systems
2. Particles sinking or rate of flux? proxy for single particle? Cd proxy for sinking particle comparison
8. early models don’t model internal cycling, use deficit to calculate flux, can we do this for TE to determine boundary condition?

4. Uptake/bioavailability Working Group
modeling uptake as a function of metal species
Ben Twining found quotas in N. Atlantic relationship of dissolved Fe and quotas not (FeII, L1),
neat to try this
lots of uncertainties in growth and how they are taking up Fe, given uncertainties should be able to bracket order magnitude
estimate max growth rate from culture studies in literature, or use flow cytometery and cell cycle calculations (growth rate lower than Vmax)
lots of previous studies in N. Pacific with historic growth rate data, estimate growth rates from satellite data
caveat: inherent assumption depends on stoichiometry
potentially long chain to go through to get to metal demand, could compare to total demand in models with plankton stoichiometry, gyres not growing at max in models
We can infer this relationship using field data (HPLC, Chla (size-fractionated), nutrient, Community composition, Fe profile, estimated growth rate, primary productivity).
Determine correlation with the different Fe species and particulate Fe species
=> North Pacific, because of high biogenic particles.
=> Can be done for other metals

5. Recommendations Light (PAR)
Flow cytometry-bacteria-largest C pool in ocean
Primary productivity
Size-fractionated Chla
Growth rate
Sequence data can tell us what kinds of bacteria are there, other eukaryotic functional groups that are currently unknown
role of zooplankton and heterotrophic protists
Until which depth?
At the bottom of the DCM and below the euphotic zone (we want bacteria).
Paul Quay on Atlantic transect: productivity? O2//Ar for productivity estimates
phytoplankton are able to be distinguished by broad functional groups in models, bacteria when they are represented (rare) bacteria not distinguished by function, are they playing different roles
do bacteria return trace metals or do they compete for trace metals?—