Use of Naturally Occurring Radionuclides as Tracers for Particle
and Carbon Fluxes and Cycling Rates
Michael P. Bacon and J. Kirk Cochran
Goal: To use naturally occurring radionuclides as tracers for
particle (and carbon) fluxes and cycling rates during the EqPac Time
Series cruises. The in situ pumps will be used to sample
suspended and sinking particles and to measure dissolved radionuclides.
Sediment trap samples from moored trap arrays will also be analyzed.
Time Series No. 1: T. Hammar (WHOI),
D. Hirschberg (SUNY)
Time Series No. 2: M. P. Bacon (WHOI),
T. Hammar (WHOI),
D. Hirschberg (SUNY)
Measurement and Sampling information:
Station Depths Sampling Method Analyses
9 N Deepwater column: pump trap Th,Th,Th
1,200 m, 2,200 m, Th,Pb,Po
700 mab + 7 other depths
5 N " " " "
5 S " " " "
12 S " " " "
2 N As above, with " " "
addition of 8
upper 1,000 m
0 " " " "
2 S " " " "
The Bacon pumps have been modified to use a
142-mm adaptation of the Bishop filter sequence: 53 µm
Nitex, 1 µm microquartz, 0.7-µm GF/F. Thus the results should
be comparable to the groups using the Bishop pumps to collect samples (Ku
et al., Murray). The pumps also collect dissolved Th isotopes by
retention on Mn0 absorbers, so each pump sample also will have a
dissolved Th analysis.
Analytical Methods and QA/QC: Pump samples --- Dissolved
Th will be
measured aboard ship by non-destructive gamma spectrometry. The procedure
will follow that of Buesseler et al. (1992a,b). Particulate
Th in the three different size fractions will be analyzed aboard
ship by low-level beta counting.
For the sediment trap samples and all other isotopes on the
pump samples, the sample will be totally dissolved, and Th will be purified by
ion exchange chromatography and then electrodeposited onto stainless steel
for alpha and beta counting (Buesseler et al., 1992b).
Pb and Po will be measured on water samples
collected in a Niskin bottle mounted on the pump frame tripped at the end
of the pump deployment. Analyses will be by Co-APDC precipitation on
board the ship, followed by plating onto silver disks and alpha counting
(Cochran et al., 1983).
Samples to be distributed to others: R. F. Anderson will analyze
some of the pump prefilters for Pa. He will also measure Be
on Be fractions from the pump prefilters. We will share sediment
trap samples with him, but will make sure that an annual composite is
measured in all cases. M. Altabet and R. Francois will measure C and
N isotopes on the prefilters.
Intercalibration: Yield tracers will be exchanged with other
radiochemists. Intercalibration of Th, Pb and Po
analyses will be achieved by analysis of deep water samples from a
mutually agreed on depth. Cochran will distribute a deep-sea sediment
standard for intercalibration of sediment Pb.
- Buesseler, Ken. O., J. Kirk Cochran, Michael P. Bacon, Hugh D.
Livingston, Susan A. Casso, David Hirschberg, Mary C. Hartman and Alan P.
- Determination of thorium isotopes in seawater by
nondestructive and radiochemical procedures. Deep-Sea Research,
- Buesseler, Ken O., Michael P. Bacon, J. Kirk Cochran and Hugh D.
- Carbon and nitrogen export during the JGOFS North
Atlantic Bloom Experiment estimated from Th:U
disequilibria. Deep-Sea Research, 39(7/8): 1115--1137.
- Cochran, J. K., M. P. Bacon, S. Krishnaswami and K. K. Turekian
- Po and Pb distributions in the central and
eastern Indian Ocean. Earth and Planetary Science Letters,