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Evidence for hydrothermal venting in Fe isotope compositions of the deep Pacific Ocean through time

Chu, N-C.; Johnson, C.M.; Beard, B.L.; German, C.R.; Nesbitt, R.W.; Frank, M.; Bohn, U.; Kubik, P.W.; Usui, A.; Graham, I.. 2006 Evidence for hydrothermal venting in Fe isotope compositions of the deep Pacific Ocean through time. Earth and Planetary Science Letters, 245 (1-2). 202-217. 10.1016/j.epsl.2006.02.043

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Abstract/Summary

Temporal variations in Fe isotope compositions at three locations in the Pacific Ocean over the last 10 Ma are inferred from high-resolution analyses of three hydrogenetic ferromanganese crusts. Iron pathways to the central deep Pacific Ocean appear to have remained constant over the past 10 Ma, reflected by a remarkably constant Fe isotope composition, despite large changes in the Fe delivery rates to the surface ocean via dust. These results suggest that the Fe cycle in the deep ocean is decoupled from that in surface waters. By contrast, one ferromanganese crust from the Izu-Bonin (IB) back-arc/marginal basin of the W. Pacific exhibits large δ56Fe variations. In that crust, decreases in δ56Fe values correlate with increases in Mn, Mg, Ni, Cu, Zn, Mo, and V contents, and consistent with periods of intense hydrothermal input and increased growth rates. A second crust located within 100 km of the first IB sample does not record any of these periods of enhanced hydrothermal input. This probably reflects the isolated pathways by which hydrothermally sourced Fe may have migrated in the back arc, highlighting the high degree of provinciality that Fe isotopes may have in the modern (oxic) oceans. Our results demonstrate that despite efficient removal at the source, hydrothermal Fe injected into the deep ocean could account for a significant fraction of the dissolved Fe pool in the deep ocean, and that hydrothermally sourced Fe fluxes to the open ocean may have lower δ56Fe values than those measured so far in situ at hydrothermal vents. Correlation between δ56Fe values and elements enriched in hydrothermal fluids may provide a means for distinguishing hydrothermal Fe from other low-δ56Fe sources to the oceans such as dissolved riverine Fe or porewaters in continental shelf sediments.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.epsl.2006.02.043
ISSN: 0012-821X
Additional Keywords: Fe isotopes; ferromanganese crusts; hydrothermal; Izu-Bonin; Pacific Ocean
Date made live: 08 Mar 2007 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/144693

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