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.

Repeated analyses of the JMC475 Hf standard gave an average ratio 176Hf/177Hf of 0.282139±18 (n=56). All ratios were normalised to their reported JMC475 value of 0.282161±9. Epsilon-Hafnium is calculated with 176Hf/177HfChur = 0.282772.From 1983 until 1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions. At the time it was the most extended data compilation on ferromanganese deposits world wide. Initially published in a proprietary format incompatible with present day standards it was jointly decided by AWI and NOAA to transcribe this legacy data into PANGAEA. This transfer is augmented by a careful checking of the original sources when available and the encoding of ancillary information (sample description, method of analysis..) not present in the NOAA-MMS database.

Supplement to: van de Flierdt, Tina; Frank, Martin; Lee, Der-Chuen; Halliday, Alex N (2002): Glacial weathering and the hafnium isotope composition of seawater. Earth and Planetary Science Letters, 201(3-4), 639-647