Reconstructing annual and seasonal climatic responses from volcanic events since A.D. 1270 as recorded in the deuterium signal from the Greenland Ice Sheet Project 2 ice core

A 200 m ice core at the GISP 2 site (Summit, Greenland) provides a 720 year record of volcanic eruptions, identified by pronounced increases in SO 4 2− in relation to the background concentration. Deuterium/hydrogen isotope ratios (δD) measured in the same core provide a proxy climate record (temperature) used to examine the response of the climate system in Greenland to these eruptions. A group of 34 known volcanic events and a subgroup of the six largest volcanic events are isolated and examined. For both groups, significant negative (cooler) isotopic excursions occur beginning the year the volcanic event is detected in the ice core. Cooling is significant for 1 to 2 years. The maximum isotopic excursion averages 4‰ (∼0.7°C) for all 34 events and 10‰ (∼1.8°C) for the subgroup of largest events. For individual events the response in the isotope signal to volcanic events is highly variable but occurs at most 1 year before SO 4 2− is detected in the core. Examination of subannual isotope data suggests that peak winter isotope values are lowered more than peak summer values. We hypothesize that this result is flawed by posted‐positional alteration of the isotopic profile by vapor diffusion. To test this hypothesis, we use numerical deconvolution to account for the smoothing effects of vapor diffusion in the firn. Analysis of the deconvolved data shows greater summer than winter cooling, a result more consistent with instrumental temperature data.