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

CDOM photodegradation CDOM Lower molecular weight DOM Bleached DOM Biological coupling CO 2

POC photodegradation CDOM Lower molecular weight DOM Bleached DOM Biological coupling CO 2 Resuspension and settling POC

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

Photodissolution of deltaic POC Mayer et al 2006

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?

Rate model for photochemical POC loss from sediments: Model as a function of in-water irradiance f(a CDOM, a   a SPM, b b,SPM ) absorption by photodissolution-susceptible particles efficiency of the reaction f(T) a p [m -1 ] = a p * [m 2 g -1 ] x SPM [g m -3 ] SPM: 10 1 – 10 3 [g m -3 ] at surface, can be inverted from R rs (D’Sa et al, Miller & McKee, Walker et al) a p *: ~10 -1 [m 2 g -1, blue ] (Bowers & Binding, Stramski et al) Needs to be determined empirically.

Sample locations Various seasons, March

Absorption measurement methods Integrating sphere (Labsphere, 15 cm diameter, center-mounted 1-cm cuvette). –[SPM] known precisely, high 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 a p * derivation –Particles measured near in situ a p * ( ) = a p ( ) / [SPM]

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

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

Comparison of a p * spectra of isolated seds/SPM (integrating sphere) and in situ SPM (ac9)

Sample group S (error) [nm -1 ] = Field, CDOM (0.2  m filtered ac9) (0.001) Field, particles0.010 (0.002) Lab, freshwater particles0.011 (0.001) Lab, marine particles0.010 (0.001) = Lab, freshwater particles0.010 (0.001) Lab, marine particles0.011 (0.001) Spectral slope calculations (Offset: eg, Bowers & Binding)

Sherman and Waite 1985 Structural features in SPM absorption spectra? Atchafalaya SPM/seds various Fe x O y minerals

Agreement between field (ac9) and lab (integrating sphere) measurements of a p *( ) for mineral-associated POC. a p *( ) increases with mass fraction OC Spectral slopes for all mineral POC are ~ nm -1. Spectral structure at UV-blue wavelengths differs for riverine/marine samples, possibly due to changes in Fe phases. a p * ( ) ~ [m 2 g -1 ] at 412nm while SPM ~ mg/L. a p at the surface determined mostly by SPM concentration  retrieve from R rs Final points

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