The Slime Problem in Metal Scavenging
Explore the challenges of Kd variations in metal scavenging and the impact of organic coatings on mineral phases. Learn about the rates of Kon and Koff, the use of mass vs. surface area for characterizing scavenging, and the variability in Kd with environmental factors.
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Presentation Transcript
Do we know Kd? The slime problem Challenge: Phoebe s data shows different Kd for different mineral phases But we know that most particles are covered by organics Some key questions: - what is rate of Kon and Koff for metals, and for organics to mineral phases - how constant are organic coatings with location and particle type? - is mass the best thing to use to characterise scavenging? Should we use surface area and surface charge instead? - are lab surface area measurements relevant to the field? - how much variation is there in Kd and organic coatings with latitude, productivity, O2 levels, etc.? - Mn and Fe oxyhydroxides have similar surface area but very different Kd; different organic coating? Some good news, though: - just adding Mn-oxyhydroxides with high Kd is a step forward (and realised in PISCES now)
Some immediate products: Th isotopes useful for aggregation/disaggregation; extend this to colloid-small particle (Jess/Tom/Paul) Provocative review of organic complexation, exchange, and aggregation/disaggregation model (Kristen/Jess/Tim/Phoebe/ ) We are close to being able to model L1 field in ocean If... L1 field is modelled, and Th gives us particle dynamics we have quantified major aspects of metal scavenging.
Nepheloid layers They are very different from open ocean in terms of particle composition (as well as concentration) Not all layers are the same (at all!) Oxyhydroxides are important (and possibly predictable given overlying productivity flux) Need to target some key locations with range of measurements
