Abstract
Abstract Poor age control in Pleistocene sediments of the central Arctic Ocean generates considerable uncertainty in paleoceanographic reconstructions. This problem is rooted in the perplexing magnetic polarity patterns recorded in Arctic marine sediments and the paucity of microfossils capable of providing calibrated biostratigraphic biohorizons or continuous oxygen isotope stratigraphies. Here, we document the occurrence of two key species of calcareous nannofossils in a single marine sediment core from the central Arctic Ocean that provide robust, globally calibrated age constraints for sediments younger than 500 ka. The key species are the coccolithophores Pseudoemiliania lacunosa, which went extinct during marine isotope stage (MIS) 12 (478–424 ka), and Emiliania huxleyi, which evolved during MIS 8 (300–243 ka). This is the first time that P. lacunosa has been described in sediments of the central Arctic Ocean. The sedimentary horizons containing these age-diagnostic species can be traced, through lithostratigraphic correlation, across more than 450 km of the inner Arctic Ocean. They provide the first unequivocal support for proposed Pleistocene chronologies of sediment from this sector of the Arctic, and they constitute a foundation for developing and testing other geochronological tools for dating Arctic marine sediments.
Highlights
Arctic marine sediments can provide valuable paleoceanographic and paleoclimate time series documenting changes to the cryosphere across glacial cycles of the Pleistocene
The key species are the coccolithophores Pseudoemiliania lacunosa, which went extinct during marine isotope stage (MIS) 12 (478–424 ka), and Emiliania huxleyi, which evolved during MIS 8 (300–243 ka)
The occurrence of the calcareous nannofossil Emiliania huxleyi currently provides the most robust constraint on the age of Pleistocene Arctic Ocean sediments (Jakobsson et al, 2001; Backman et al, 2004, 2009), as this taxon evolved during marine isotope stage (MIS) 8 (300–243 ka) in both equatorial and subpolar environmental settings (Thierstein et al, 1977)
Summary
These challenges arise from the sporadic downcore occurrence and limited diversity of microfossil assemblages, which result in few well-dated biostratigraphic datums and prevent the generation of a continuous and interpretable oxygen isotope stratigraphy (Backman et al, 2004) Compounding this problem, there is the complex sequence of high-frequency geomagnetic polarity reversals seen in many Arctic records (Clark, 1970; O’Regan et al, 2008; Xuan et al, 2012), which are difficult to reconcile with the geomagnetic polarity time scale or even with excursions in the Quaternary (Backman et al, 2008; Wiers et al, 2019). The identification of E. huxleyi by Jakobsson et al (2001) (core AO96/12–1PC, collected during the 1996 Arctic Ocean expedition on the icebreaker Oden, 87.0975°N, 144.7728°E; Fig. 1) in sediments previously dated to MIS 15 (621–563 ka) based on paleomagnetic interpretations (Spielhagen et al, 1997) illustrated that polarity reversals in near-surface Arctic sediments did not represent geomagnetic chron and subchron boundaries
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