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Evidence for a major change in silicon cycling in the subarctic North Pacific at 2.73 Ma
Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Zurich, Switzerland
Leibniz Institute of Marine Sciences at University of Kiel (IFM-GEOMAR), Kiel, Germany
Department of Earth Sciences, Oxford University, Oxford, UK
The initiation of Northern Hemisphere glaciation in the subarctic North Pacific at ∼2.73 Ma was marked by an abrupt cessation of high opaline accumulation, considered to result from an increased stratification of the water column that should have led to higher utilization of nutrients in the surface ocean. We present a new stable Si isotope-based record of Si utilization that is hard to reconcile with this model. A drop in 30Si/28Si by 0.4‰ at 2.73 Ma is coincident with an increase in bulk N isotope composition. The contrasting utilization records cannot have been both caused by a hydrographic change alone. Excluding a change in the Si:N export ratio, these results either imply a relative increase in silicic acid supplied to the surface waters or a change in its Si isotope composition. While it is impossible to distinguish between these two possibilities, both imply a regional or global change in the Si biogeochemical cycle, potentially caused by an enhanced storage of Si in the underlying deep waters of the Pacific.
Received 24 October 2007; accepted 16 October 2008; published 27 December 2008.
Citation: (2008), Evidence for a major change in silicon cycling in the subarctic North Pacific at 2.73 Ma, Paleoceanography, 23, PA4219, doi:10.1029/2007PA001563.
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