the history of 234 th in aquatic ecosystems dr. claudia benitez-nelson university of south carolina
TRANSCRIPT
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The History of 234Th in Aquatic Ecosystems
Dr. Claudia Benitez-NelsonUniversity of South Carolina
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Bhat et al.
Coale & Bruland
NABE
Arabian Sea
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Thorium-234
Particle residence times & distribution
“Carbon” Export
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Bhat, Krishnaswamy, Lal, Rama, Moore234Th/238U ratios in the Ocean
Earth and Planetary Science Letters 5, 483-491
First Published 234Th data by the Radiochemistry All-Stars:
1969
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“Please excuse the organization of this letter. In order to speed its posting, I was having the first part typed while counting the spikes and while I was writing the last few paragraphs”
Letter from Moore to Swamy, July 31, 1968.
“The AGU Meeting was pretty good, but there has been a lot of trouble in Washington the previous weekend and we were confined to the hotel most of the time. Of course nothing was open around the city and all of the army troops gave a grim atmosphere to a beautiful spring.”
Letter from Moore to Swamy, May 23, 1968.
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“We have added Th-234 spike to millipore filtered seawater and refiltered the water through a 0.45 micron millipore. The retention of Th-234 was less than 5 % of that added on the filter…We also tried to see if live plankton cells pick up Thorium from seawater…initial numbers show the retention (if any) may be very less.”
Letter from Swamy to Moore, August 6, 1968.
“One of the things we must remember in reference to plankton vs. particle uptake of Th-234 is that there are many types of plankton with a wide spectrum of sizes…”
Letter from Moore to Swamy, Sept 6, 1968.
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Bhat et al. 1969
Thorium-234 as a tracer of particle dynamics
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Kaufman et al. 1981
234Th (dpm L-1)
Suspended Particles (g kg-1)
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Santschi et al. 1979
Sediment Resuspension
234ThResidence
Time
Sediment Resuspension
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Aller & Cochran1976
Bioturbation and accumulation
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Honeyman et al. 1988
Particle Coagulation
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Cochran et al. 1993
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Coale & Bruland 1987
Particle Export
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Infamous Buesseler (1991) Paper….
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North Atlantic Bloom Experiment
Buesseler et al. 1992
Particle and “C” Export
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Thorium-234 approach for estimating particle exportThorium-234 approach for estimating particle export
depthdepth(m)(m)
234Th
238U
At Steady State:(238U - 234Th) *Z = 234Th Export (dpm m-2 d-1)
Measure C/234Th on sinking particles --> Carbon Export
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Buesseler 1998
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Three Major Issues:
C/Th ratios and what’s a sinking particle?
Are all “particles” the same?
Temporal and spatial effects?
All ultimately controlled by sampling restraints….
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JGOFS VERTIGO?
MEDFLUX?
MEDFLUX?
3 days(1 sample)
2 hr(1 sample)
2 hr(24 samples)
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Guo et al. 2002
Advances in analytical organic chemistry
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Geibert and Usbeck 2004
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Buesseler et al. 1995
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Advances in sampling and measurement
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Waples et al. 2003
Lake Michigan!!!
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Where do we go from here???