The History of 234Th in Aquatic Ecosystems
Dr. Claudia Benitez-NelsonUniversity of South Carolina
Bhat et al.
Coale & Bruland
NABE
Arabian Sea
Thorium-234
Particle residence times & distribution
“Carbon” Export
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
“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.
“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.
Bhat et al. 1969
Thorium-234 as a tracer of particle dynamics
Kaufman et al. 1981
234Th (dpm L-1)
Suspended Particles (g kg-1)
Santschi et al. 1979
Sediment Resuspension
234ThResidence
Time
Sediment Resuspension
Aller & Cochran1976
Bioturbation and accumulation
Honeyman et al. 1988
Particle Coagulation
Cochran et al. 1993
Coale & Bruland 1987
Particle Export
Infamous Buesseler (1991) Paper….
North Atlantic Bloom Experiment
Buesseler et al. 1992
Particle and “C” Export
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
Buesseler 1998
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….
JGOFS VERTIGO?
MEDFLUX?
MEDFLUX?
3 days(1 sample)
2 hr(1 sample)
2 hr(24 samples)
Guo et al. 2002
Advances in analytical organic chemistry
Geibert and Usbeck 2004
Buesseler et al. 1995
Advances in sampling and measurement
Waples et al. 2003
Lake Michigan!!!
Where do we go from here???