First interpretation of 17O-excess variability over 800,000 years on the East Antarctic Plateau, based on EPICA Dome C deep ice core

Analysis of water isotopes (oxygen and hydrogen) in Antarctic ice cores has enabled reconstruction of Earth’s temperature over the last 800,000 years with the EPICA deep ice core (Dome C) and, soon, over 1.5 million years with the Beyond EPICA deep ice core (Little Dome C). In parallel, differences in fractionation between hydrogen isotopes and oxygen isotopes provided information about the water cycle in the past.

In particular, deuterium excess (dxs = δD − 8 * δ¹⁸O) has been developed to track evaporation and transport conditions from oceanic regions to the ice sheet. However, it is quite challenging to deconvolute source-related and transport-related effects. The ¹⁷O-excess (¹⁷O-excess = ln(δ¹⁷O+1) − 0.528×ln(δ¹⁸O+1)) is a less known second-order parameter, complementary to dxs, also expected to reflect the conditions encountered by the air mass.

Here we present the first long-term record of ¹⁷O-excess (from 41,520 to 800,000 years, with 2,447 data points) based on the analysis of the EPICA deep ice core to better understand the long-term variability of this proxy and its integration into high-latitudes climate variability.

In addition to variations over glacial–interglacial cycles, we observe a significant decrease of the ¹⁷O-excess over the Mid-Brunhes transition ~400,000 years ago. This ¹⁷O-excess record carrying information on the origin of the moisture precipitating in East Antarctica is compared with long-term reconstructions of sea surface temperature, Antarctic circumpolar current strength, and southern westerly winds to disentangle the effects of source changes and isotopic fractionation along transport pathways.

Measuring the ¹⁷O-excess record over such a long period, and compare it with other paleoclimatic records, offers the opportunity of better understanding the variability of this proxy, but also of deepening our understanding of the relationship between climate and water cycle changes at high latitudes.