Margaret L. Estapa University of Maine

1. IOPs of suspended sediments in rivers and coastal margins: Towards modeling turbid-water photochemistry from space Margaret L. Estapa University of Maine

2. CDOM photodegradation CO2 CDOM Bleached DOM Lower molecular weight DOM Biological coupling

3. POC photodegradation CO2 POC CDOM Bleached DOM Lower molecular weight DOM Biological coupling Resuspension and settling

4. Louisiana coastline, 4/7/2009. MODIS-Aqua, NASA Atchafalaya R. SPM in large delta-forming rivers Sediments buried @ deltas Keil et al 1997

5. Photodissolution of deltaic POC Mayer et al 2006

6. Beyond the lab, how quickly does photodissolution unload organic carbon from river SPM? Could it account for low organic carbon in buried sediments on deltas?

7. Rate model for photochemical POC loss from sediments: Model as a function of in-water irradiance f(aCDOM, af, aSPM, bb,SPM) absorption by photodissolution-susceptible particles efficiency of the reaction f(T) ap [m-1] = ap*[m2 g-1] x SPM [g m-3] SPM: 101 – 103 [g m-3] at surface, can be inverted from Rrs (D’Sa et al, Miller & McKee, Walker et al) ap*: ~10-1 [m2 g-1, blue l] (Bowers & Binding, Stramski et al) Needs to be determined empirically.

8. Sample locations Various seasons, 2003-2008 March 13-15 2008

9. ap* (l) = ap (l) / [SPM] Absorption measurement methods • Integrating sphere (Labsphere, 15 cm diameter, center-mounted 1-cm cuvette). • [SPM] known precisely, high l resolution, UV data, no scattering correction • Optical effects of isolation & storage? • ac9 (WETLabs,10 cm path) in shipboard clean seawater system. • [SPM] determined from filters, assumptions/corrections in ap* derivation • Particles measured near in situ

10. Mass-specific absorption of discrete samples in integrating sphere (averages, 95% conf. int.) Single marine sample in different media

11. Derivation of ap* from in situ optical measurements 412 nm ac9 total absorption: - Temperature, salinity correction - Spectral scattering correction Pigment absorption, af, removed from ap* following Roesler L&O 1989

12. Comparison of ap* spectra of isolated seds/SPM (integrating sphere) and in situ SPM (ac9)

14. Spectral slope calculations (Offset: eg, Bowers & Binding)

15. Structural features in SPM absorption spectra? various FexOy minerals Atchafalaya SPM/seds Sherman and Waite 1985

16. Final points • Agreement between field (ac9) and lab (integrating sphere) measurements of ap*(l) for mineral-associated POC . • ap*(l) increases with mass fraction OC • Spectral slopes for all mineral POC are ~0.010-0.011 nm-1. Spectral structure at UV-blue wavelengths differs for riverine/marine samples, possibly due to changes in Fe phases. • ap*(l) ~ 0.05-0.1 [m2 g-1]at 412nm while SPM ~ 10-1000 mg/L. ap at the surface determined mostly by SPM concentration retrieve from Rrs

17. Acknowledgements • NASA Earth Systems Science Fellowship (project NNX08AU84H, “Assessing Impacts on Carbon Transport from Land to Ocean: Photochemical Transformations of Particulate Organic Carbon”) • NSF Chemical Oceanography • My advisors Emmanuel Boss and Larry Mayer, and committee member Collin Roesler, for helpful advice and conversations • Mary Jane Perry and Mark Wells for use of lab equipment • Gail Kineke, John Trowbridge, ONR, and crew of the R/V Pelican for ship time • Larry Mayer, Sam Bentley, and Mead Allison for collecting and sharing archived sediment samples • Kathy Hardy and Linda Schick for archived sediment sample processing and analysis