Mineral Dust Influence on the Glacial Nitrate Record from the RICE Ice Core, West Antarctica and Environmental Implications

Abstract. Nitrate (NO₃⁻), an abundant aerosol in polar snow, is a complex environmental proxy to interpret owing to the variety of its sources and its susceptibility to post-depositional processes. During the last glacial period, when the dust level in the Antarctic atmosphere was higher than today by a factor up to ~25, mineral dust appears to have a stabilizing effect on the NO₃⁻ concentration. However, the exact mechanism remains unclear. Here, we present new and highly resolved records of NO₃⁻ and non-sea salt calcium (nssCa²⁺, a proxy for mineral dust) from the Roosevelt Island Climate Evolution (RICE) ice core for the period 26–40 kilo years Before Present (ka BP). This interval includes seven millennial-scale Antarctic Isotope Maxima (AIM) events, against the background of a glacial climate state. We observe a significant correlation between NO₃⁻ and nssCa²⁺ over this period and especially during AIM events. We put our observation into a spatial context by comparing the records to existing data from east Antarctic cores of EPICA Dome C (EDC), Vostok and central Dome Fuji. The data suggest that nssCa²⁺ is contributing to the effective scavenging of NO₃⁻ from the atmosphere through the formation of Ca(NO₃)₂. The geographic pattern implies that the process of Ca(NO₃)₂ formation occurs during the long-distance transport of mineral dust from the mid-latitude source regions by Southern Hemisphere Westerly Winds (SHWW) and most likely over the Southern Ocean. Since NO₃⁻ is dust-bound and the level of dust mobilized through AIM events is mainly regulated by the latitudinal position of SHWW, we suggest that NO₃⁻ may also have the potential to provide insights into paleo-westerly wind pattern during the events.