Reply on RC1

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The temperature of the earth is one of the most important climate parameters. Proxy records of past climate changes, in particular temperature, are a fundamental tool for exploring internal climate processes and natural climate forcings. Despite the excellent information provided by ice core records in Antarctica, the temperature variability of the past 2000 years is difficult to evaluate from the low accumulation sites in the Antarctic continent interior. Here we present the results from the Aurora Basin North (ABN) ice core (71&deg; S, 111&deg; E, 2690 m a.s.l.) in the lower part of the East Antarctic plateau where accumulation is substantially higher than other ice core drilling sites on the plateau, and provide unprecedented insight in East Antarctic past temperature variability. We reconstructed the temperature of the last 2000 years using two independent methods: the widely used water stable isotopes (&delta;¹⁸O), and by inverse modelling of borehole temperature and past temperature gradients estimated from the inert gas stable isotopes (&delta;⁴⁰Ar and &delta;¹⁵N). This second reconstruction is based on three independent measurement types: borehole temperature, firn thickness, and firn temperature gradient. The &delta;¹⁸O temperature reconstruction supports stable temperature conditions within 1 &deg;C over the past 2000 years, in agreement with other ice core &delta;¹⁸O records in the region. However, the gas and borehole temperature reconstruction suggest that surface conditions 2 &deg;C cooler than average prevailed in the 1000&ndash;1400 CE period, and support a 20^th century warming of 1 &deg;C. These changes are remarkably consistent with reconstructed Southern Annular Mode (SAM) variability, as it shows colder temperatures during the positive phase of the SAM in the beginning of the last millennium, with rapidly increasing temperature as the SAM changes to the negative phase. The transition to a negative SAM phase after 1400 CE is however not accompanied by a warming in West Antarctica, which suggests an influence of Pacific South American modes, inducing a cooling in West Antarctica while ABN is warming after this time. A precipitation hiatus during cold periods could explain why water isotope temperature reconstruction underestimates the temperature changes. Both reconstructions arguably record climate in their own way, with a focus on atmospheric and hydrologic cycles for water isotopes, as opposed to surface temperature for gases isotopes and borehole. This study demonstrates the importance of using a variety of sources for comprehensive paleoclimate reconstructions.