The SP19 chronology for the South Pole Ice Core - Part 2: gas chronology, Δage, and smoothing of atmospheric records

Abstract

Abstract. A new ice core drilled at the South Pole provides a 54 000-year paleoenvironmental record including the composition of the past atmosphere. This paper describes the SP19 chronology for the South Pole atmospheric gas record and complements a previous paper (Winski et al., 2019) describing the SP19 ice chronology. The gas chronology is based on a discrete methane (CH4) record with 20- to 190-year resolution. To construct the gas time scale abrupt changes in atmospheric CH4 during the glacial period and centennial CH4 variability during the Holocene were used to synchronize the South Pole gas record with analogous data from the West Antarctic Ice Sheet Divide ice core. Stratigraphic matching based on visual optimization was verified using an automated matching algorithm. The South Pole ice core recovers all expected changes in CH4 based on previous records. Smoothing of the atmospheric record due to gas transport in the firn is evident but relatively minor, despite the deep lock-in depth in the modern South Pole firn column. The new gas chronology, in combination with the existing ice age scale from Winski et al. (2019), allows a model-independent reconstruction of the gas age-ice age difference through the whole record, which will be useful for testing firn densification models.

Antarctic surface temperature and elevation during the Last Glacial Maximum

“…For all sites other than WD, we estimate ∆age empirically by combing ice-phase volcanic matching and gas-phase atmospheric methane (CH 4 ) matching to WD (16). Site ∆age estimates are shown in Fig.…”

“…Synchronization using both volcanic deposits and globally synchronous abrupt atmospheric methane variations, allows us to estimate ∆age empirically for the Antarctic ice cores (10,16). We use an inverse dynamical firn densification-heat transport model (17,18) to reconstruct TS and A histories that optimize the fit to ∆age and δ 15 N data (Fig.…”

Anthropogenic Impacts on Atmospheric Carbonyl Sulfide Since the 19th Century Inferred From Polar Firn Air and Ice Core Measurements

“…The new SPC14 data are on the SP19 chronology (Epifanio et al, 2020). (Bottom) Previously published COS data from the GISP2B and GISP2D ice cores (red circles) from Greenland (Aydin et al, 2007) versus all Antarctic data (black circles) from the top panel.…”

“…Except for the new SPC14 measurements, all data shown here have been published as parts of larger data sets with established chronologies that cover longer periods(Aydin et al, 2002(Aydin et al, , 2008(Aydin et al, , 2014Montzka et al, 2004). The new SPC14 data are on the SP19 chronology(Epifanio et al, 2020). (Bottom) Previously published COS data from the GISP2B and GISP2D ice cores (red circles) from Greenland(Aydin et al, 2007) versus all Antarctic data (black circles) from the top panel.…”

Reconstruction of Temperature, Accumulation Rate, and Layer Thinning From an Ice Core at South Pole, Using a Statistical Inverse Method

“…Here, we present data from a new ice core (SPC14) from the South Pole, East Antarctica, and we use a novel approach to combine multiple data sets to constrain temperature, accumulation‐rate, and ice‐thinning histories. We take advantage of two timescales for SPC14, one for the ice (Winski et al., 2019) and one for the gas enclosed within it (Epifanio et al., 2020), to obtain an empirical measure of the gas‐age ice‐age difference (Δage). We also use high‐resolution measurements of δ 17 O, δ 18 O, and δ D of ice (Steig et al., 2021) to obtain water‐isotope diffusion lengths.…”