1. Theoretical analysis of the p-ratio S. Bradley Moran, URI OUTLINE Key variables: particle size and density.Key variables: particle size and density. Derivation of p-ratio and sensitivity analysis.Derivation of p-ratio and sensitivity analysis. Summary and recommendations.Summary and recommendations.

2. 1 mm salp euphausiid copepod Courtesy of Alice AlldredgeCourtesy of Debby Steinberg Key variables: particle size and density

4. Some questions regarding POC/ 234 Th ratios and POC flux How should we sample POC/ 234 Th ratios to get an accurate POC export flux? Filtration: what size? Traps: what kind?How should we sample POC/ 234 Th ratios to get an accurate POC export flux? Filtration: what size? Traps: what kind? What is the size-distribution of POC and 234 Th?What is the size-distribution of POC and 234 Th? Are all phases of POC in equilibrium with 234 Th?Are all phases of POC in equilibrium with 234 Th? How are POC/ 234 Th ratios (and hence POC flux) related to changes in particle density, size and hence sinking speed?How are POC/ 234 Th ratios (and hence POC flux) related to changes in particle density, size and hence sinking speed? Given range and variability in POC/ 234 Th ratios, how do we assess the accuracy of POC export flux?Given range and variability in POC/ 234 Th ratios, how do we assess the accuracy of POC export flux?

5. Model derivation of the p-ratio

14. Constant Density w/ Low Flux (LF) and High Flux (HF) p-ratio

16. Variable Density w/ Low Flux (LF) and High Flux (HF) p-ratio

18. Particle Assemblage 1: POC density = 1060 p-ratio

20. Particle Assemblage 2: POC density = 1300 p-ratio

21. Summary The p-ratio is an indicator of the accuracy of 234 Th - derived POC fluxes.The p-ratio is an indicator of the accuracy of 234 Th - derived POC fluxes. For p-ratio (P POC /F POC ) = 1, average sinking speed of POC- and Th-carrying particles must be equal.For p-ratio (P POC /F POC ) = 1, average sinking speed of POC- and Th-carrying particles must be equal. Accurate measurement of POC export flux requires p- ratio = 1 at base of euphotic zone.Accurate measurement of POC export flux requires p- ratio = 1 at base of euphotic zone. p-ratio = 1 does not mean that residence times of POC and 234 Th are equal in the euphotic zone.p-ratio = 1 does not mean that residence times of POC and 234 Th are equal in the euphotic zone.

22. What does all of this mean? Open Ocean:Open Ocean: –Biogenic particles dominate; POC- and Th-carrying particles may have reasonably similar sinking speeds;  p-ratio approaches 1. –However, dust/mineral inputs, org. C remineralization will increase p-ratio. Shelf-Slope:Shelf-Slope: –More inorganic (small, high density) particles that scavenge Th;  p-ratio will increase.

23. Questions to think about How do we best determine the p-ratio?How do we best determine the p-ratio? To what extent do operationally defined sampling methods affect the p-ratio?To what extent do operationally defined sampling methods affect the p-ratio? How much does the p-ratio vary for different oceanic regions (opal, carbonate, lithogenic)?How much does the p-ratio vary for different oceanic regions (opal, carbonate, lithogenic)?

24. Future Work Determine particle size-distributions, densities and sinking speeds of POC- and 234 Th-carrying particles.Determine particle size-distributions, densities and sinking speeds of POC- and 234 Th-carrying particles. Relate measurements of p-ratio to density of size- fractionated particles over range of particle types.Relate measurements of p-ratio to density of size- fractionated particles over range of particle types. Develop models of particle- 234 Th interactions and POC/ 234 Th size-distributions and test against p-ratio.Develop models of particle- 234 Th interactions and POC/ 234 Th size-distributions and test against p-ratio.