Sulfate sources and oxidation chemistry over the past 230 years from sulfur and oxygen isotopes of sulfate in a West Antarctic ice core

The sulfur and oxygen isotopic composition of sulfate in polar ice cores provides information about atmospheric sulfate sources and formation pathways, which have been impacted regionally by human activity over the past several centuries. We present decadal scale mean ice core measurements of Δ17O, δ34S, Δ33S, and Δ36S of sulfate over the past 230 years from the West Antarctic Ice Sheet (WAIS) Divide deep ice core drill site (WDC05‐A). The low mean δ34S of non–sea‐salt sulfate at WAIS Divide (6.0 ± 0.2‰) relative to East Antarctic coastal and plateau sites may reflect a combination of stronger influence of volcanogenic and/or stratospheric sulfate with low δ34S and the influence of frost flowers on the sea‐salt sulfate‐to‐sodium ratio. Δ33S and Δ36S measurements are all within analytical uncertainty of zero but do not contradict a contribution of stratospheric sources to background sulfate deposition at WAIS Divide. Δ17O of non–sea‐salt sulfate shows a small but significant increase between the late 1700s (1.8‰ ± 0.2‰) and late 1800s (2.6‰ ± 0.2‰), but the influence of stratospheric scale volcanic events on Δ17O in the early 1800s remains uncertain. An isotope mass balance model shows that the lack of change in Δ17O of non–sea‐salt sulfate from the mid‐1800s to early 2000s (2.4‰–2.6‰ ± 0.2‰) is consistent with previous atmospheric chemistry model estimates indicating preindustrial to industrial increases in O3 as high as 50% and decreases in OH of 20% in the southern polar troposphere, as long as H2O2 concentrations also increase by over 50%.