Glacial weathering and the hafnium isotope composition of seawater

Publication Type  Journal Article
Year of Publication  2002
Authors  van de Flierdt, T.; Frank, M.; Lee, D. C.; Halliday, A. N.
Journal Title  Earth and Planetary Science Letters
Volume  198
Issue  1-2
Pages  167-175
Journal Date  Apr 30
ISBN Number  0012-821X
Accession Number  ISI:000175733300012
Key Words  hf-177/hf-176; zircon; sea water; geochemistry; ferromanganese composition; fe-mn crusts; atlantic deep-water; north-atlantic; ferromanganese crusts; lu-hf; sedimentary system; residence time; pb isotopes; nd-isotope; ocean

The Hf isotope composition of seawater does not match that expected from dissolution of bulk continental crust. This mismatch is generally considered to be due to retention of unradiogenic Hf in resistant zircons during incomplete weathering of continental crust. During periods of intense glacial weathering. zircons should break down more efficiently. resulting in the release of highly unradiogenic Hf to the oceans. We test this hypothesis by comparing Nd and Hf isotope time series obtained from NW Atlantic ferromanganese crusts. Both isotope systems show a decrease associated with the onset of northern hemisphere glaciation, The observed changes display distinct trajectories in epsilon(Nd)-epsilon(Hf) space. which differ from previously reported arrays of bulk terrestrial material and seawater. Such patterns are consistent with the release of highly unradiogenic Hf from very old zircons, facilitated by enhanced mechanical weathering. (C) 2002 Elsevier Science B.V. All rights reserved.


554JYTimes Cited:15Cited References Count:47

URL  <Go to ISI>://000175733300012
DOI  Pii S0012-821x(02)00521-6