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???