Short Name:

Cosmogenic Radionuclides in the WAIS Divide Ice Core

This dataset includes a record of the concentrations of the cosmogenic radionuclides, 10Be (half-life = 1.36 x 10^6 year) and 36Cl (3.0 x 10^5 year), in samples from the West Antarctic Ice Sheet (WAIS) Divide ice core, WDC06A. This work was conducted under the following NSF OPP awards, 0636964, 0839137 (PI Welten) and 0636815, 0839042 (PI Caffee). Radionuclide separations from ice samples were performed in Berkeley and Purdue using procedures described previously (Finkel and Nishiizumi, 1997), while an inter-laboratory comparison study has shown that ice samples processed in both labs produce identical 10Be results within the analytical uncertainties of 2-3% (Woodruff et al. 2013). Measurements of 10Be and 36Cl concentrations were carried out using accelerator mass spectrometry (AMS) at Purdue's PRIME Laboratory (Sharma et al. 2000). The 10Be/Be and 36Cl/Cl ratios of the ice sample were corrected for blank levels and normalized to 10Be and 36Cl AMS standards (Sharma et al. 1990, Nishiizumi 2007). Concentrations of 10Be and 36Cl are reported in atoms per gram ice. The 10Be and 36Cl depth profiles are being used to perfect ice core chronology, based on variations in solar activity which are also observed in the 14C treeing record, and study the possible role of solar activity variations on climate. We will also evaluate the role of wet vs. dry deposition at WAIS Divide by comparing the 10Be dataset with other WD records, such as O-isotopes, Na, and dust. This project includes measurements in 3 types of samples: (1) Decadal resolution 10Be and 36Cl depth profiles in the top 560 m of WAIS Divide ice core. For this depth interval waste samples were collected from the continuous ice core melter system of the McConnell/Edwards group at DRI. Each waste sample collected for 10Be analysis represents 2-4 m of the ice core, equivalent to an average of 12 years of snow accumulation. For 36Cl separation, two adjacent waste samples were combined, representing an average of 24 years of snow accumulation. (2) Annual resolution 10Be in the top 114 m (420 year) of the WD core and between 295-305 m depth. For these records we used dedicated ice samples of 100-300 g per layer. The annual resolution 10Be depth profile provides information on the relationship between solar activity (from the sunspot record) and cosmic-ray variations and allows us to identify short term cosmic-ray spikes such as the one identified at 774/775 AD in the 14C treering record (Miyake et al. 2012). (3) Low-resolution 10Be and 36Cl depth profiles from 1200-2500 m depth in WAIS Divide ice core. For the deep part of the core we used ice samples, representing continuous sections of 2-3 m length (for 10Be) and 4-6 m length (for 36Cl). The resolution of the 10Be samples ranges from ~20 year per sample at ~1200 m depth to ~80 year per sample at ~2500 m depth.

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