El Niño–Southern Oscillation signal in a new East Antarctic ice core, Mount Brown South

Abstract

Abstract. Paleoclimate archives, such as high-resolution ice core records, provide a means to investigate past climate variability. Until recently, the Law Dome (Dome Summit South site) ice core record remained one of few millennial-length high-resolution coastal records in East Antarctica. A new ice core drilled in 2017/2018 at Mount Brown South, approximately 1000 km west of Law Dome, provides an additional high-resolution record that will likely span the last millennium in the Indian Ocean sector of East Antarctica. Here, we compare snow accumulation rates and sea salt concentrations in the upper portion (∼ 20 m) of three Mount Brown South ice cores and an updated Law Dome record over the period 1975–2016. Annual sea salt concentrations from the Mount Brown South site record preserve a stronger signal for the El Niño–Southern Oscillation (ENSO; austral winter and spring, r = 0.533, p < 0.001, Multivariate El Niño Index) compared to a previously defined Law Dome record of summer sea salt concentrations (November–February, r = 0.398, p = 0.010, Southern Oscillation Index). The Mount Brown South site record and Law Dome record preserve inverse signals for the ENSO, possibly due to longitudinal variability in meridional transport in the southern Indian Ocean, although further analysis is needed to confirm this. We suggest that ENSO-related sea surface temperature anomalies in the equatorial Pacific drive atmospheric teleconnections in the southern mid-latitudes. These anomalies are associated with a weakening (strengthening) of regional westerly winds to the north of Mount Brown South that correspond to years of low (high) sea salt deposition at Mount Brown South during La Niña (El Niño) events. The extended Mount Brown South annual sea salt record (when complete) may offer a new proxy record for reconstructions of the ENSO over the recent millennium, along with improved understanding of regional atmospheric variability in the southern Indian Ocean, in addition to that derived from Law Dome.

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

“…Analyses of anions and cations were performed using a Thermo-Fisher/Dionex ICS3000 ion chromatograph. A detailed discussion of the discrete chemistry analyses can be found in Crockart et al, (2021).…”

“…Layer thicknesses were combined with an empirical density model to determine annual ice equivalent snow accumulation rates. Further details of the dating procedures and accumulation calculations for the short cores and upper section of MBS-Main can be found in Crockart et al, 2021.…”

“…The mean measured annual accumulation rates for MBS-Alpha, MBS-Charlie and MBS-Main are 0.273 ± 0.06, 0.271 ± 0.07 and 0.284 ± 0.07 m WE yr -1 respectively. Accumulation rates have been converted to water equivalent accumulation from the original Crockart et al (2021) data which is presented as ice equivalent, assuming an ice density of r = 917 kg m -3 . Mean annual accumulation from RACMO2.3p2 slightly underestimates accumulation rates derived from the ice cores, however the annual accumulation from the model is still significantly correlated with ice core accumulation (Table 1), with the exception of MBS-Charlie which has been previously shown to be poorly correlated with accumulation (Crockart et al, 2021).…”

“…In 2017/2018, a series of four ice cores were drilled at this site, including a 295m long main ice core record, which is estimated based on a current age scale in development to extend back 1200 years. Early investigations into the record by Crockart et al, (2021) demonstrated that the ice core preserves an annually resolved climate history that differs from the Law Dome record, with a clear signal of midlatitude Indian Ocean atmospheric variability in annual sea salt concentrations relating to the El Niño-Southern Oscillation.…”

2000 years of annual ice core data from Law Dome, East Antarctica

“…Seasonal sea salt records were originally developed for Vance et al (2013Vance et al ( , 2015 and further used in Crockart et al (2021); Vance et al (2021), as proxies for regional climate. Specifically these records are the summer, and warm and cool season sea salt average concentrations.…”