Early diagenesis of germanium in sediments of the Antarctic South Atlantic: In search of the missing Ge sink
Pore water and solid-phase geochemistry profiles were obtained from several cores between 41{degree}S and 53{degree}S in the Atlantic sector of the Southern Ocean. Pore water nitrate, manganese, and iron profiles delineate standard redox zones in these sediments, and help characterize those with classic vs. burn-down behaviors. Pore water Si and Ge profiles demonstrate that Ge released during opal dissolution is removed pervasively throughout the uppermost interval of silicate release, and also downwards into the suboxic zone by as yet unidentified precipitation mechanisms. These results indicate that early diagenesis of Ge is uncoupled from that of opal. Solid-phase extractions (Fe, Mn, U, Mo, Ge, Cu, Ni, Co, V, and Cd) in a few cores suggest that anthigenic Ge removal in the suboxic zone is not associated with peaks in authigenic Mn cycling (MnO{sub 2} and related metals) but rather with processes deeper in the sediments, perhaps Fe or U diagenesis. Below the interval of Ge removal, pre water Ge increases linearly with depth by over two orders of magnitude, indicating a deep (below recovery) source of large magnitude. The fraction of opal-derived Ge precipitated authigenically in these sediments ranges from {approximately}1 to 96% and correlates strongly with the detrital fraction as well as the detrital to opal ratio, both of which generally decrease from north to south. The Ge sink observed in these sediments would need to be globally representative to account for the entire missing Ge sink in today's oceanic Ge balance, which seems unlikely. Benthic fluxes of Ge and Si estimated from these pore water profiles and from measurements in three benthic flux chamber experiments at high carbon-rain continental margin sites demonstrate that the Ge/Si rate released from the seafloor in locations with high benthic silicate and carbon fluxes is congruent with Holocene opal dissolution (Ge/Si {approximately} 0.7 x 10{sup {minus}6}). In contrast, Ge/Si flux ratios in areas with low silicate fluxes are Ge-depleted (Ge/Si < 0.5 x 10{sup {minus}6}). The authors speculate that glacial-interglacial changes in oceanic Ge/Si as recorded in diatoms may be due in part to variations in this authigenic Ge sink, perhaps related to shifts in siliceous productivity from open ocean (Antarctic) siliceous oozes during interglacials to areas of higher detrital input (Sub Antarctic, continental margins) and possibly also to generally more reducing conditions in sediments during glacials.
- Research Organization:
- Georgia Inst. of Tech., Atlanta, GA (US)
- OSTI ID:
- 20062608
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 64, Issue 8; Other Information: PBD: Apr 2000; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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