Implementation of counted layers for coherent ice core chronology

Abstract

Abstract.A recent coherent chronology has been built for four Antarctic ice cores and the NorthGRIP (NGRIP) Greenland ice core (Antarctic Ice Core Chronology 2012, AICC2012) using a Bayesian approach for ice core dating (Datice). When building the AICC2012 chronology, and in order to prevent any confusion with official ice core chronology, the AICC2012 chronology for NGRIP was forced to fit exactly the GICC05 chronology based on layer counting. However, such a strong tuning did not satisfy the hypothesis of independence of background parameters and observations for the NGRIP core, as required by Datice. We present here the implementation in Datice of a new type of markers that is better suited for constraints deduced from layer counting: the duration constraints. Estimating the global error on chronology due to such markers is not straightforward and implies some assumption on the correlation between individual counting errors for each interval of duration. We validate this new methodological implementation by conducting twin experiments and a posteriori diagnostics on the NGRIP ice core. Several sensitivity tests on marker sampling and correlation between counting errors were performed to provide some guidelines when using such a method for future dating experiments. Finally, using these markers for NGRIP in a five-core dating exercise with Datice leads to new chronologies that do not differ by more than 410 years from AICC2012 for Antarctic ice cores and 150 years from GICC05 for NGRIP over the last 60 000 years.

Quantifying molecular oxygen isotope variations during a Heinrich Stadial

“…Those regions represent the most productive ones and therefore carry a substantial part of the δ 18 O terr signal. Although reconstructed δ 18 O p anomalies fromLewis et al (2010) andPausata et al (2011) studies were estimated differently, they are consistent and common reconstructed δ 18 O p estimates (for Hulu and Songjia Cave) are similar in both www.clim-past.net/11/1527/2015/ Clim. Past, 11, 1527-1551, 2015…”

“…Comparisons of modeled hosing-driven amount-weighted δ 18 O p anomalies with reconstructed δ 18 O of speleothem's calcite during HSs are presented in Table 3 and studies (Table 3, this study; method section of Pausata et al, 2011). The dominant hydrological controls on reconstructed δ 18 O p are site-specific and are described by Lewis et al (2010). Figure 4 demonstrates the ability of the AOGCM LMDZ-iso to reproduce the observed δ 18 O p spatial pattern for most of the sites, particularly in regions strongly affected by ITCZ (and its land extension) variations and hence by changes in the water cycle, regardless of the processes at play.…”

“…Thirteen Heinrich δ 18 O p proxy reconstructions arise fromLewis et al (2010) (n = 11) andPausata et al (2011) (n = 4). They are located in the eastern Mediterranean, and in the regions of the South American monsoon, East Asian monsoon, Indian summer monsoon, North American monsoon and the Australian-Indonesian monsoon.…”

“…Comparison of isotopic proxy records (speleothem's calcite δ 18 O) with annual average modeled amount-weighted δ 18 O p . Note that anomalies fromPausata et al (2011) are calculated from H1 and YD, while anomalies fromLewis et al (2010) arise from all identifiable δ 18 O c excursions.…”

Quantifying molecular oxygen isotope variations during a Heinrich stadial

“…Changes in the O 2 / N 2 ratio can be measured in air trapped in ice cores back to 800 kyr (Bender, 2002;Kawamura et al, 2007;Landais et al, 2012;Lemieux-Dudon et al, 2015). Unfortunately the O 2 / N 2 ratio in ice cores does not provide a direct information on the true atmospheric variations because it is affected by permeation through the ice lattice during bubble formation at pore close-off, roughly 100 m below the ice sheet surface, and by gas loss during ice core storage.…”