Abstract
Abstract. Based on a composite of several measurement series performed on ice samples stored at −25 °C or −50 °C, we present and discuss the first δO2/N2 record of trapped air from the EPICA Dome C (EDC) ice core covering the period between 300 and 800 ka (thousands of years before present). The samples stored at −25 °C show clear gas loss affecting the precision and mean level of the δO2/N2 record. Two different gas loss corrections are proposed to account for this effect, without altering the spectral properties of the original datasets. Although processes at play remain to be fully understood, previous studies have proposed a link between surface insolation, ice grain properties at close-off, and δO2/N2 in air bubbles, from which orbitally tuned chronologies of the Vostok and Dome Fuji ice core records have been derived over the last four climatic cycles. Here, we show that limitations caused by data quality and resolution, data filtering, and uncertainties in the orbital tuning target limit the precision of this tuning method for EDC. Moreover, our extended record includes two periods of low eccentricity. During these intervals (around 400 ka and 750 ka), the matching between δO2/N2 and the different insolation curves is ambiguous because some local insolation maxima cannot be identified in the δO2/N2 record (and vice versa). Recognizing these limitations, we restrict the use of our δO2/N2 record to show that the EDC3 age scale is generally correct within its published uncertainty (6 kyr) over the 300–800 ka period.
Highlights
While ice core records offer a wealth of paleoclimatic and paleoenvironmental information, uncertainties associated with ice core dating limit their contribution to the understanding of past climate dynamics
Based on a composite of several measurement series performed on ice samples stored at −25 ◦C or −50 ◦C, we present and discuss the first δO2/N2 record of trapped air from the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) ice core covering the period between 300 and 800 ka
Our extended record includes two periods of low eccentricity. During these intervals, the matching between δO2/N2 and the different insolation curves is ambiguous because some local insolation maxima cannot be identified in the δO2/N2 record. Recognizing these limitations, we restrict the use of our δO2/N2 record to show that the EDC3 age scale is generally correct within its published uncertainty (6 kyr) over the 300–800 ka period
Summary
While ice core records offer a wealth of paleoclimatic and paleoenvironmental information, uncertainties associated with ice core dating limit their contribution to the understanding of past climate dynamics. Despite a limited understanding of the physical mechanisms linking local 21 December insolation and δO2/N2 variations in polar ice cores, this approach has been used by Kawamura et al (2007) and Suwa and Bender (2008a) to propose an orbital dating of the Dome F and Vostok ice cores back to 360 and 400 ka, respectively. The validity of the link with local summer insolation has been supported by a similar correspondence observed in the Greenland GISP2 ice core (Suwa and Bender, 2008b) Using their high quality δO2/N2 record on the Dome F ice core and comparison with radiometric dating obtained on speleothem records, Kawamura et al (2007) estimated the dating uncertainty to be as low as 0.8–2.9 kyr. The uncertainties and limitations attached to the use of δO2/N2 as a dating tool for the EDC ice core between 300 and 800 ka are discussed
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