Letters

Retraction of an Interpretation

Science  10 Aug 2007:
Vol. 317, Issue 5839, pp. 748b
DOI: 10.1126/science.317.5839.748b

In the Report “Structure of the 8200-year cold event revealed by a speleothem trace element record” (1), we presented a 7762-μm-long ion probe trace element traverse chosen to include the 8200-year event as detected in a previously published laser ablation oxygen isotope study from the same stalagmite (2). The oxygen isotope anomaly was distinct and dropped 8% below baseline values to a low value for the entire Holocene of -12% and was reproducible on a reverse track. However, recent reanalysis of the calcite believed to contain the oxygen isotope anomaly suggests that the anomaly was probably an analytical artifact possibly caused by laser ablation-induced fracturing during the original analysis (3). Consequently, without the original δ18O “marker,” the precise location in the stalagmite of calcite deposited during the 8200-year event is uncertain.

The trace element data in this Report, previously believed to correspond precisely with the entire 8200-year event, are now believed to represent the hydrological and bioproductivity response in western Ireland to a cold/dry event of uncertain provenance and intensity. The U-Th-derived dates of the event correspond approximately with the 8200-year event in Greenland ice cores, but without the additional guidance of the δ18O anomaly, the precise timing in relation to the 8200-year event is now somewhat ambiguous. Unfortunately, it is now unlikely that the approximately 114-year duration ion probe track coincides with the entire 8200-year event (if at all); thus, the ~37-year estimate derived for its duration is probably no longer accurate. However, the trace element data remain robust and are interpreted as reflecting colder and drier conditions in western Ireland, followed by the return to more maritime conditions at the end of the first-order trace element anomaly. Additionally, the novel application of annual trace element cycles to build a high-resolution chronology and reconstruct paleoseasonality remains unchanged.

References

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