The WAIS Divide deep ice core WD2014 chronology – Part 2: Annual-layer counting (0–31 ka BP)

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.

Climate driven carbon and microbial signatures through the last ice age

“…Fundamental differences exist, however, between sedimentation processes and aeolian deposition in these environments. Varying amounts of dust in ice attest to both hydro-and lithospheric changes on the continents and long distance transport (Palais and Legrand, 1985;Mahowald et al, 1999;Petit et al, 1999;Sigl et al, 2016). Ion loads in Byrd and WD_3 corroborate these reports, with OM quantity and quality assessments, alongside traditional climate indicators, proving suitable as palaeoecological markers.…”

“…From their study on the vertical profile of microorganisms in ice, Zhang et al (2006) concluded that less dust and microbial species were deposited during warmer periods. The three-fold lower numbers of OTUs and lower dust concentrations in the WD_3 core (Sigl et al, 2016) follow this trend. It is important to note that although both cores were retrieved from West Antarctica (separated by ~161 km), aerosols over ice sheets may differ between locations (Rothlisberger et al, 2000).…”

Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion

“…S1 and S2) show that the glaciochemical anomaly consisted of nine pulses measured between 2,426.97 m and 2,420.04 m depth in the WD core, corresponding to a ∼192-y period from 17.748 ka to 17.556 ka (Fig. 2) on the WD2014 timescale (18). Evidence of this glaciochemical anomaly also has been traced throughout West Antarctica and parts of East Antarctica in ice cores (17) (Fig.…”

“…S1 and S2). WD snow accumulation was relatively high (>100 kg·m −2 ·y −1 ) during this period (18), so the regions of high acidity in the core were well separated from regions of low acidity. Second, consistent with modern observations in which some but not all volcanic eruptions are associated with ozone depletion (26), evaluation of the 100 highest acidity events (annual average concentration >3.0 μeq·L −1 ) in the 10 ka to 25 ka WD record shows that 30% were not associated with bromine depletion and that depletion was not proportional to acidity (SI Appendix, Fig.…”

Deglacial temperature history of West Antarctica

“…Measurements of δD of ice and δ 15 N of trapped N 2 were by laser spectroscopy and mass spectrometry, respectively (15, 47) (SI Ice-Isotopic Data and SI Nitrogen-Isotopic Data). The age-depth relation and annual layer thicknesses were determined by identifying and counting annual layers back to ∼31 ka and by cross-correlations of gas records prior to this time (16,47,53) N(t). Given simultaneous histories of accumulation rate (ḃ(t)) and Ts(t), we calculated firn density profiles using an empirical model (20), recast to use overburden load as a driving variable as in refs.…”