Ocean Drilling Program Hole 910A on the Yermak Plateau (80°N, 5°E) at 552 m water depth provides one of the first opportunities for high-resolution studies of Quaternary Arctic Ocean climates. Oxygen and carbon isotopic data based on Neogloboquadrina pachyderma (Sinistrally coiling) from the top 24.5 m at 10 cm sampling resolution provide both stratigraphic age control and a history of middle through late Quaternary surface water environments. The delta18O data reveal oxygen isotope Stages 1 through 16 (and possibly 17), with an amplitude of ~1. Carbon isotopic values in the section from ~19.5 to 24.5 m below seafloor (mbsf) exhibit a series of ~1 fluctuations, followed by a permanent 1 increase at ~19.5 mbsf. Above ~19.5 mbsf, delta13C values are relatively stable, except for large spikes of ~0.5, mainly during inferred interglacials. Significantly, the section from ~19.5 to 24.5 mbsf is a remarkable overconsolidated section," marked by high values for bulk density and sediment strength. The large variations in delta18C below ~19.5 mbsf, and the overconsolidated nature of the section, suggest a fundamentally different sedimentary environment. Possible explanations include (1) episodic grounding of a marine-based ice sheet, perhaps derived from the Barents Sea ice sheet and buttressed by Svalbard, which overcompacted the sediment and strongly influenced surface water chemistry on the Yermak Plateau, and/or (2) coarser grained glacial sedimentation that allowed enhanced compaction during this interval. Oxygen isotopic stratigraphy suggests that overconsolidation ended near the Stage 17/16 boundary (~670 ka), reflecting a major change in state of the Svalbard/Barents Sea ice sheet.
Date of initial receipt: 7 July 1995
Date of acceptance: 1 December 1995
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