Climatology of the Mount Brown South ice core site in East Antarctica: implications for the interpretation of a water isotope record

Abstract

Abstract. Water stable isotope records from ice cores (δ18O and δD) are a critical tool for constraining long-term temperature variability in the high-latitudes. However, precipitation in Antarctica consists of semi-continuous small events and intermittent extreme events. In regions of high-accumulation, this can bias ice core records towards recording the synoptic climate conditions present during extreme precipitation events. In this study we utilise a combination of ice core data, re-analysis products and models to understand how precipitation intermittency impacts the temperature records preserved in an ice core from Mount Brown South in East Antarctica. Extreme precipitation events represent only the largest 10 % of all precipitation events, but they account for 44 % of the total annual snowfall at this site leading to an over-representation of these events in the ice core record. Extreme precipitation events are associated with high-pressure systems in the mid-latitudes which cause increased transport of warm and moist air from the southern Indian Ocean to the ice core site. Warm temperatures associated with these events result in a +2.8 °C warm bias in the mean annual temperature when weighted by daily precipitation, and water isotopes in the Mount Brown South ice core are shown to be significantly correlated with local temperature when this precipitation-induced temperature bias is included. The Mount Brown South water isotope record spans more than 1000 years and will provide a valuable regional reconstruction of long-term temperature and hydroclimate variability in the data-sparse southern Indian Ocean region.

An annually resolved chronology for the Mount Brown South ice cores, East Antarctica

“…For simplicity in this study we will hereafter refer to the 2017/2018 ice cores as 'MBS' unless comparing to the earlier drilling effort. Crockart et al (2021) and Jackson et al (2022) found the snowfall accumulation regime at MBS to follow a seasonal cycle of higher precipitation during the polar winter (March-October), and lower precipitation during December/January. Variability between accumulation records across the site was present, due to the prevailing easterlies and resulting surface features (Figure 1), which in some cases were found to be of equivalent height to the satellite era mean annual accumulation rate of 0.3 metres ice equivalent (m.i.e.)…”

“…Coastal East Antarctica is subject to maritime moisture intrusions which result in intense precipitation events occurring over hours to days, a subset of which reach thresholds to be classified as atmospheric rivers (Gorodetskaya et al, 2014;Turner et al, 2019;Wille et al, 2021). At MBS, intense precipitation events on average account for 44% of annual accumulation (Jackson et al, 2022). These events are strongly related to mid-latitude blocking in the southern Indian Ocean to the northeast of MBS, which channels warm and moist maritime air masses to the site (Jackson et al, 2022;Pohl et al, 2021;Udy et al, 2021Udy et al, , 2022.…”

“…At MBS, intense precipitation events on average account for 44% of annual accumulation (Jackson et al, 2022). These events are strongly related to mid-latitude blocking in the southern Indian Ocean to the northeast of MBS, which channels warm and moist maritime air masses to the site (Jackson et al, 2022;Pohl et al, 2021;Udy et al, 2021Udy et al, , 2022.…”

“…Given the seasonal cycle of accumulation at MBS displays higher accumulation during the polar winter (March/April to November), this suggests a relationship between accumulation and wind speed. For a deeper analysis of variability in isotopic ratios, temperature and wind direction, see Jackson et al (2022). No particular differences in wind speed and direction were observed between different reanalysis products (e.g.…”

Spatiotemporal variability of extreme precipitation events and associated atmospheric processes over Dronning Maud Land, East Antarctica

“…When compared to interior sites, the coastal regions experience smaller temperature anomalies during EPEs due to frequent synoptic cyclone landfall and advection of warm airmasses. The high-temperature anomalies during EPEs can cause a significant warm bias in the ice-core records (Jackson et al, 2022;Servettaz et al, 2020), and reconstruction of ice-core isotope data will overestimate reconstructed temperature, if this warm bias is not taken into account (Noone & Simmonds, 1998;Servettaz et al, 2020).…”