Sunlight-driven nitrate loss records Antarctic surface mass balance

Abstract Standard proxies for reconstructing surface mass balance (SMB) in Antarctic ice cores are often inaccurate or coarsely resolved when applied to more complicated environments away from dome summits. Here, we propose an alternative SMB proxy based on photolytic fractionation of nitrogen isotopes in nitrate observed at 114 sites throughout East Antarctica. Applying this proxy approach to nitrate in a shallow core drilled at a moderate SMB site (Aurora Basin North), we reconstruct 700 years of SMB changes that agree well with changes estimated from ice core density and upstream surface topography. For the under-sampled transition zones between dome summits and the coast, this proxy can considerably expand our SMB records by providing high-resolution SMBs that better reflect the local environment and are easier to sample than existing techniques.One Sentence Summary: Nitrate isotopes offer a new way to track past and present changes in Antarctic snowfall and ice sheet mass balance.