Determination of lead isotopes in a new Greenland deep ice core at the sub-picogram per gram level by thermal ionization mass spectrometry using an improved decontamination method

High-resolution isotopic evidence for a potential Saharan provenance of Greenland glacial dust

“…The final isotopic ratios were obtained after correction for the blanks. The accuracy for the concentrations was better than 10% (95% confidence interval) and the precision was ~0.28% for Pb isotope ratios on a small sample size (tens of picograms of Pb) 26 .…”

“…Each core section (20 cm in length) with a cross section of 4 × 4 cm 2 was mechanically decontaminated using an ultraclean decontamination method that we have developed for isotopic analysis of small volumes of the NEEM ice (see details in ref. 26 ). It involves the chiseling of successive veneers of ice from the outside of the core toward the center to obtain the uncontaminated inner part of the core section, using ultraclean stainless steel chisels or ceramic knives, inside a Class 100 vertical laminar flow clean bench installed inside a cold room at the Korea Polar Research Institute (KOPRI), Korea.…”

“…It involves the chiseling of successive veneers of ice from the outside of the core toward the center to obtain the uncontaminated inner part of the core section, using ultraclean stainless steel chisels or ceramic knives, inside a Class 100 vertical laminar flow clean bench installed inside a cold room at the Korea Polar Research Institute (KOPRI), Korea. This ultraclean decontamination method allowed the determination of Pb and Sr isotopes even in the NEEM ice core sections, which contain only a few tens of picograms of Pb and Sr in a sample weight of ~10 g 26 . The inner core samples were divided into two pieces, each 10 cm long (a sample volume of ~80 mL), and the upper piece was analyzed for this study.…”

“…All sample handling and ultraclean analytical procedures for determining elemental concentrations and isotopic analysis were performed under a Class 10 vertical laminar flow clean bench or booth in clean laboratories (Class 1000) at KOPRI, as described in detail in ref. 26 . The Pb and Ba concentrations and Pb isotopic composition were simultaneously analyzed using a thermal ionization mass spectrometry (TIMS; TRITON, Thermo Scientific) fitted with a 23 cm radius, 90° magnetic sector containing a 21-sample carousel.…”

“… 25 ). In contrast to earlier isotopic tracer studies, particularly those using Nd isotopes for which large samples (>0.5 kg) were required for high precision analysis in Greenland ice 16 , 17 , our Pb and Sr isotopes were determined using a sample weight of ~10 g, allowing for a much higher time resolution in isotopic records related to Greenland dust provenance changes in response to climatic conditions 26 (see Methods).

Figure 1 Changes in Pb, Sr and Ba concentrations, and Pb and Sr isotopic compositions from the NEEM ice core over the past ~31 kyr.

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