Hydrothermal scavenging at the Mid-Atlantic Ridge: radionuclide distributions

Details Hydrothermal scavenging at the Mid-Atlantic Ridge: radionuclide distributions Hydrothermal scavenging at the Mid-Atlantic Ridge: radionuclide distributions

Jul 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991e%26psl.105..170g&link_type=abstract

Earth and Planetary Science Letters, Volume 105, Issue 1-3, p. 170-181.

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Scientific paper

We have carried out a study of U-series radionuclide distributions in the neutrally buoyant plume overlying the TAG hydrothermal vent field at 26°N, Mid-Atlantic Ridge. Limited uptake of U accompanies the formation of Fe-oxyhydroxide particulate material within the hydrothermal plume. The particulate U concentrations are too small for measurable dissolved U anomalies to be produced within the water column at plume height. However, such uptake, followed by deposition in the underlying sediments, could account for ~ 10% of the U enrichment that has been reported previously for metalliferous ridge-crest sediments. Particulate 234Th, 230Th and 228Th activities in the TAG hydrothermal plume represent >=65% of total Th activities typical of the deep ocean. Low dissolved Th activities coincide with the high particulate Th activities, indicating that hydrothermal scavenging strongly affects Th-isotope distributions in the water column close to hydrothermal vents. Much of the scavenging occurs during the initial formation of Fe-rich hydrothermal precipitates but some further scavenging continues as the material is dispersed, away from its source. Distributions of particulate 210Pb and 231Pa activities in the neutrally buoyant plume are also extremely high (7-12 dpm/102 l and 30-160 dpm/106 l, respectively). Like Th, 210Pb and 231Pa show evidence for scavenging within the hydrothermal plume. Total Th activities at plume height are ~ 50% higher than ``background''. This ``focusing'' of Th into the plume is consistent with the entrainment and re-emplacement at plume height of particulate material recycled from beneath the neutrally buoyant plume.

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