Fig. 2: The relationship between Antarctic snow δ¹⁵N_NO3arc and surface mass balance (SMB).

a Map of East Antarctic sites sampled for δ¹⁵N_NO3arc along different scientific and logistic transect routes. Colored circles indicate the locations and δ¹⁵N_NO3arc values of samples included in our field data set, with δ¹⁵N_NO3arc data from the EAIIST (pink) and CHICTABA (yellow) transects newly reported here. The base map SMB data were modeled by MAR¹³ and adjusted for dry site bias (see Methods) with elevation contours from REMA¹¹ overlaid. Preservation of NO₃⁻ is not expected in blue ice zones (gray solid polygons) due to very low or negative SMB and wind scouring⁷⁶. Presently occupied stations in the CONMAP database are shown as labeled triangle icons for spatial reference. b Scatter plot of δ¹⁵N_NO3arc vs. SMB for all sites in the field dataset. The color of the points corresponds to the transects where the samples were collected as shown in a, and the shape of the points corresponds to the sampling method (i.e., snow core, snow pit, or 1-m depth layer). c Scatter plot and linear regression of (1) using all sites in the field dataset. The linear regression (gray solid line) is shown with shaded 95% confidence intervals, and regression parameters are displayed at lower left.