Physics
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996e%26psl.139..351r&link_type=abstract
Earth and Planetary Science Letters, vol. 139, Issue 3-4, pp.351-363
Physics
22
Central Pacific, Th-230, Th-232, Sea Water, Mass Spectroscopy, Particles, Elsevier: Central Pacific, Th-230, Th-232, Sea Water, Mass Spectroscopy, Particles
Scientific paper
232 Th and 230 Th of unfiltered and filtered sea water samples were measured along a depth profile of the central Pacific Ocean using isotopic dilution and thermal ionization mass spectrometry. The 232 Th concentration is rather constant from below 25 m down to over 2000 m (45-60 × 10 6 atom cm -3 ) and it then increases rapidly towards the bottom (119-360 × 10 6 atom cm -3 at 4000 m). The 230 Th concentration increases linearly with depth from 3 × 10 3 atom cm -3 at 25 m to 110 × 10 3 atom cm -3 at 4000 m. The reproducibility of replicate analyses and the regularity of the profiles demonstrate the reliability of the procedure. However, some lack of reproducibility among different samples from the same depth has to be explained by natural variability or by contamination during sample collection. Due to the very low 232 Th concentrations and relatively high 230 Th concentrations, the ratios can be as high as 1.6 × 10 -3 . The ratio of the amount of Th on particles (> 0.2 m) to the amount of Th in solution is significantly higher for 232 Th ( 0.37) than for 230 Th ( 0.18). These data are interpreted in terms of a model that specifically treats particle transport assuming local equilibrium between particles and sea water. The relatively high 230 Th concentrations and ratios measured at 25 m are consistent with a mixed layer of about 100 m. The linear increase in 230 Th with depth implies that the effect of eddy diffusion is negligible for most of the water column over the Th removal time scale. This profile is consistent with transport of 230 Th by reversible uptake on particles settling with a constant velocity. The 232 Th data are inconsistent with this model and they suggest that particles carrying 232 Th experience 70% of mass loss between the surface and 4000 m and must follow different transport rules. This difference in the transport of 230 Th and 232 Th demonstrates the distinctive behavior of these isotopes during particle formation and subsequent remineralization and repackaging in the water column. Different speciation of 230 Th and 232 Th may be explained by their distinctive sources in the ocean (as 230 Th is produced in solution and 232 Th is carried by detrital material) and by their respective packaging mechanisms, which are not yet known.
Chen Jacqueline H.
Roy-Barman Matthieu
Wasserburg Gerald J.
No associations
LandOfFree
230Th-232Th systematics in the central Pacific Ocean: The sources and the fates of thorium does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with 230Th-232Th systematics in the central Pacific Ocean: The sources and the fates of thorium, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and 230Th-232Th systematics in the central Pacific Ocean: The sources and the fates of thorium will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1335721