iops of suspended sediments in rivers and coastal margins: towards modeling turbid-water...
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IOPs of suspended sediments in rivers and coastal
margins: Towards modeling turbid-water photochemistry
from space
Margaret L. EstapaUniversity of Maine
CDOM photodegradation
CDOM
Lower molecular weight DOM
Bleached DOM
Biological coupling
CO2
POC photodegradation
CDOM
Lower molecular weight DOM
Bleached DOM
Biological coupling
CO2
Resuspension and settling
POC
Atchafalaya R.Atchafalaya R.
Louisiana coastline, 4/7/2009.MODIS-Aqua, NASA
Keil et al 1997
SPM in large delta-forming rivers Sediments
buried @ 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(aCDOM, aaSPM, bb,SPM)
absorption by photodissolution-susceptible particles
efficiency of the reaction f(T)
PDpPD aE
dt
dPOC **0
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 ] (Bowers & Binding, Stramski et al)
Needs to be determined empirically.
Sample locations
-93 -92.5 -92 -91.5 -91 -90.5 -90 -89.5
29
29.5
30
30.5
31
0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
Bottom surficial sedimentsSuspended particulate matterIn situ optical dataIn situ filter stations
Various seasons, 2003-2008
March 13-15 2008
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 ap* derivation– Particles measured near in situ
ap* () = ap () / [SPM]
Single marine sample in different media
300 350 400 450 500 550 600 650 700 750 8000
0.05
0.1
0.15
0.2
0.25
Wavelength [nm]
a p*
[m2 g
-1]
Freshwater samplesMarine samplesDifference
Mass-specific absorption of discrete samples in integrating sphere
300 400 500 600 700 8000
0.05
0.1
0.15
0.2
0.25
MilliQ water5.5 mM CaCl
2
Artificial seawater
(averages, 95% conf. int.)
][*
SPM
aaaa g
p
10 15 20 25 30
1
1.5
2
Salinity [psu]
a g [
m-1
]
ag:S
ag = -0.074 * Salinity + 2.86
Derivation of ap* from in situ optical measurements412 nm
5 10 15 200
500
1000
1500
SPM (gravimetric, mg L-1)
Eco
VS
F s
ign
al (
cou
nts
) Signal = 58.9 * SPM + 93.8
EcoVSF:SPM
ac9 total absorption:
- Temperature, salinity correction
- Spectral scattering correction
Pigment absorption, a, removed from ap* following Roesler L&O 1989
450 500 550 600 650 700
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Wavelength [nm]
a p*
[m2 g
-1]
Comparison of ap* spectra of isolated
seds/SPM (integrating sphere) and in situ SPM (ac9)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
ap* derived from field data (ac9, March '08)
ap* of isolated samples
(integrating sphere, collectedwithin 3 days of field samples)
5 10 15 20 25 30 35
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Organic Carbon [mg-OC g-sed-1]
a p*
(412
) [m
2 g-1
]
ap* (412):OC content
All samples: ap*(412) = 0.0044 * OC - 0.0094, R2 = 0.65, N = 32
Marine only: ap*(412) = 0.0049 * OC - 0.0203, R2 = 0.75, N = 19
Freshwater only (no fit)
Sample groupS (error) [nm-1 ]
= 412-715
Field, CDOM (0.2m filtered ac9) 0.016 (0.001)
Field, particles 0.010 (0.002)
Lab, freshwater particles 0.011 (0.001)
Lab, marine particles 0.010 (0.001)
)715(*)412()( )412( aeaa S
= 300-715
Lab, freshwater particles 0.010 (0.001)
Lab, marine particles 0.011 (0.001)
Spectral slope calculations
(Offset: eg, Bowers & Binding)
Sherman and Waite 1985
Structural features in SPM absorption spectra?
Atchafalaya SPM/sedsAtchafalaya SPM/sedsvarious Fevarious FexxOOyy minerals minerals
300 350 400 450 5000
0.05
0.1
0.15
0.2
0.25
Wavelength [nm]
a p*
[m2 g
-1]
300 350 400 450 500-0.015
-0.01
-0.005
0
0.005
0.01
0.015
Wavelength [nm]
a p*
resi
du
al f
rom
sin
gle
-exp
fit
[m
2 g-1
]
300 350 400 450 500 550 600 650 700 750 8000
0.05
0.1
0.15
0.2
0.25
Wavelength [nm]
a p*
[m2 g
-1]
Freshwater samplesMarine samplesDifference
• Agreement between field (ac9) and lab (integrating sphere) measurements of ap*() for mineral-associated POC .
• ap*() 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*() ~ 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
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