Abstract
Abstract. We present the WD2014 chronology for the upper part (0–2850 m; 31.2 ka BP) of the West Antarctic Ice Sheet (WAIS) Divide (WD) ice core. The chronology is based on counting of annual layers observed in the chemical, dust and electrical conductivity records. These layers are caused by seasonal changes in the source, transport, and deposition of aerosols. The measurements were interpreted manually and with the aid of two automated methods. We validated the chronology by comparing to two high-accuracy, absolutely dated chronologies. For the Holocene, the cosmogenic isotope records of 10Be from WAIS Divide and 14C for IntCal13 demonstrated that WD2014 was consistently accurate to better than 0.5 % of the age. For the glacial period, comparisons to the Hulu Cave chronology demonstrated that WD2014 had an accuracy of better than 1 % of the age at three abrupt climate change events between 27 and 31 ka. WD2014 has consistently younger ages than Greenland ice core chronologies during most of the Holocene. For the Younger Dryas–Preboreal transition (11.595 ka; 24 years younger) and the Bølling–Allerød Warming (14.621 ka; 7 years younger), WD2014 ages are within the combined uncertainties of the timescales. Given its high accuracy, WD2014 can become a reference chronology for the Southern Hemisphere, with synchronization to other chronologies feasible using high-quality proxies of volcanism, solar activity, atmospheric mineral dust, and atmospheric methane concentrations.
Highlights
Polar ice cores are a powerful tool for investigating past changes in the Earth’s climate and are the only direct measure of past concentration of greenhouse gases in the atmosphere (Monnin et al, 2001; Siegenthaler et al, 2005; Marcott et al, 2014)
WD2014 extends to 31.2 ka BP and provides the West Antarctic Ice Sheet (WAIS) Divide ice core with a timescale that has a similar resolution and accuracy to that of the deep Greenland ice cores
Southern Hemisphere forest and grass fires usually peak during a confined burning season following the meteorological dry period driven by seasonal insolation changes (Bowman et al, 2009; Schultz et al, 2008; van der Werf et al, 2010), and aerosols emitted by these fires get transported and deposited on the Antarctic ice sheet (Bisiaux et al, 2012) with peak concentrations in austral autumn
Summary
Polar ice cores are a powerful tool for investigating past changes in the Earth’s climate and are the only direct measure of past concentration of greenhouse gases in the atmosphere (Monnin et al, 2001; Siegenthaler et al, 2005; Marcott et al, 2014). A previous chronology, WDC06A-7 (WAIS Divide Project Members, 2013), was constructed mainly by interpreting the seasonal variations of the electrical properties of the ice and for some sections the ice chemistry (Fig. 1). This chronology, WD2014, supersedes that effort by considering additional, seasonally varying parameters over larger sections. WD2014 extends to 31.2 ka BP (thousands of years before present, with present defined as 1950 CE) and provides the WAIS Divide ice core with a timescale that has a similar resolution and accuracy to that of the deep Greenland ice cores (e.g. the layer-counted Greenland Ice Core Chronology, GICC05). Below 2850 m, WD2014 is dated by stratigraphic matching of methane as described in the companion paper of Buizert et al (2015)
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