The History of 234 Th in Aquatic Ecosystems Dr. Claudia Benitez-Nelson University of South Carolina

Bhat et al. Coale & Bruland NABE Arabian Sea

Thorium-234 Particle residence times & distribution “Carbon” Export

Bhat, Krishnaswamy, Lal, Rama, Moore 234 Th/ 238 U ratios in the Ocean Earth and Planetary Science Letters 5, First Published 234 Th 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 Mooreto Swamy, July 31, “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, “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 Thorium-234 as a tracer of particle dynamics

Kaufman et al Th (dpm L -1 ) Suspended Particles (  g kg -1 )

Santschi et al Sediment Resuspension 234 Th Residence Time Sediment Resuspension

Aller & Cochran 1976 Bioturbation and accumulation

Honeyman et al Particle Coagulation

Cochran et al. 1993

Coale & Bruland 1987 Particle Export

Infamous Buesseler (1991) Paper….

North Atlantic Bloom Experiment Buesseler et al Particle and “C” Export

Thorium-234 approach for estimating particle export depth(m) 234 Th 238 U       At Steady State: ( 238 U Th) *Z = 234 Th Export (dpm m -2 d -1 ) Measure C/ 234 Th 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….

JGOFSVERTIGO? MEDFLUX? 3 days (1 sample) 2 hr (1 sample) 2 hr (24 samples)

Guo et al Advances in analytical organic chemistry

Geibert and Usbeck 2004

Buesseler et al. 1995

Advances in sampling and measurement

Waples et al Lake Michigan!!!

Where do we go from here???