Volcanic forcing during the Common Era re-evaluated based on new ice core evidence

Assessments of climate sensitivity to projected greenhouse gas concentrations underpin environmental policy decisions, with such assessments primarily based on model simulations of climate during recent centuries and millennia. These simulations depend critically on accurate records of past aerosol forcing from global-scale volcanic eruptions reconstructed from measurements of sulfate deposition in ice cores.New, seasonally resolved, and annual-layer-counted, sulfur records were developed using ice cores extracted from the ice sheets in Greenland (NEEM-2011-S1, TUNU2013) and Antarctica (WAIS Divide). Ice cores were analyzed at the Desert Research Institute with high depth resolution using a continuous ice core melter coupled to two high resolution inductively coupled plasma mass spectrometers (HR-ICPMS) that conjointly also quantify elements distinctive for continental dust, sea salt, biomass burning, and industrial pollutants.We reconstructed volcanic sulfate deposition over Antarctica based on a comprehensive array of existing and new ice core records, synchronized to the annually dated WAIS Divide timescale. This reconstruction for the last 2,000 years is unprecedented in robustness, dating accuracy, length and spatial coverage. While agreement with prior reconstructions is excellent after 1500 C.E., we found a substantially different history of volcanic aerosol deposition prior to 1500 C.E. Combined with a similar detailed reconstruction obtained for the Northern Hemisphere, the Antarctic sulfate record presented here provides the proxy data needed for improvement of volcanic forcing reconstructions that are widely used in climate simulations and to evaluate the relationship between volcanic forcing and climate response as reconstructed from tree ring proxy evidence.