A 2000-year temperature reconstruction on the East Antarctic plateau from argon-nitrogen and water stable isotopes in the Aurora Basin North ice core

The temperature of the Earth is one of the most important climate parameters. Proxy records of past climate changes, in particular temperature, represent 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 degrees S, 111 degrees E, 2690ma.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 into 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 O-18) and by inverse modelling of borehole temperature and past temperature gradients estimated from the inert gas stable isotopes (delta(40) Ar and delta N-15). This second reconstruction is based on three independent measurement types: borehole temperature, firn thickness, and firn temperature gradient. The delta O-18 temperature reconstruction supports stable temperature conditions within 1 degrees C over the past 2000 years, in agreement with other ice core delta O-18 records in the region. However, the gas and borehole temperature reconstruction suggests that surface conditions 2 degrees C cooler than average prevailed in the 1000-1400 CE period and supports a 20th century warming of 1 degrees C. 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 gas isotopes and boreholes. This study demonstrates the importance of using a variety of sources for comprehensive paleoclimate reconstructions.