The overall objectives of this project listed above were divided into three work packages (WP). We accomplished the primary goals of each WP, although the final details and analyses sometimes differed somewhat from the original proposed WP due to COVID-19 and a new understanding of nitrate dynamics revealed by our early results. For WP1, we completed isotopic analysis on 1578 individual nitrate samples collected in East Antarctic snow. These include over 500 samples collected by the fellow in Antarctica and over 650 samples archived from 10 years of Antarctic snow monitoring programs. After (1) aggregating our results to produce individual site averages, (2) combining these data with previously reported isotopic data, and (3) identifying snow accumulation rates for each site, we created a standardized dataset of 135 sites. These results greatly increase the number and spatial coverage of nitrate isotope data reported for Antarctica. These data are archived through PANGAEA, and all future data will be similarly archived following FAIR rules. Two subsets of this database are each the subject of a manuscript currently in production with planned submissions in open access journals in the next three months.
We then used this database to complete WP2 by quantifying an empirical model that relates the nitrogen isotopes of nitrate to the local snow accumulation rate. This quantified relationship is the focus of the article “Sunlight-driven nitrate loss records Antarctic surface mass balance” which is currently under revised review at Nature Communications. In this article, we present the findings of WP1 and WP2 along with a newly-derived theoretical framework. We apply our new model to reconstruct 700 years of accumulation history from an ice core taken at Aurora Basin North, Antarctica, and validate our findings with comparative results from ice core density and ground penetrating radar. This paper serves as a summary of the primary accomplishments of SCADI.
WP3 focused on applying our new empirical model to nitrate data from Vostok and Dome C ice cores located on the ultra-dry interior Antarctic Plateau. Our work in WP3 revealed that the archiving process for nitrate in the driest regions of Antarctica has a previously undocumented vertical transportation component that prevents our empirical model from accurately reproducing accumulation rates. Despite the inability to directly convert nitrate isotopes into accumulation histories at these sites, our identification of this undocumented component is critical to properly interpreting the variability of nitrate and other chemical species in ice cores sampled from the ultra-dry regions. This discovery and its ice core science impacts are the focus of a manuscript currently in progress. At wetter sites such as the West Antarctic Ice Sheet Divide, our model accurately reconstructs accumulation variability going back tens of thousands of years, and continuing research aims to further refine the environmental bounds of our model’s application.
