Variable Response in Alpine Tree-Ring Stable Isotopes Following Volcanic Eruptions in the Tropics and Iceland

Abstract

The importance of the stable isotopes in tree rings for the study of the climate variations caused by volcanic eruptions is still unclear. We studied δ18O, δD, δ13C stable isotopes of larch and cembran pine cellulose around four major eruptions with annual resolution, along with a superposed epoch analysis of 34 eruptions with 5-year resolution. Initial analysis of the tropical Tambora (1815 CE) and Samalas (1257 CE) eruptions showed a post-eruption decrease in δ18O values attributed to post-volcanic cooling and increased summer precipitation in Southern Europe, as documented by observations and climate simulations. The post-volcanic cooling was captured by the δD of speleothem fluid inclusion. The δ18O decrease was also observed in the analysis of 34 major tropical eruptions over the last 2000 years. In contrast, the eruptions of c. 750, 756, and 764 CE attributed to Icelandic volcanoes left no significant responses in the cellulose isotopes. Further analysis of all major Icelandic eruptions in the last 2000 years showed no consistent isotopic fingerprints, with the exception of lower post-volcanic δ13C values in larch. In summary, the δ18O values of cellulose can provide relevant information on climatic and hydroclimatic variations following major tropical volcanic eruptions, even when using the 5-year resolution wood samples of the Alpine Tree-Ring Isotope Record database.

Decadal-to-centennial increases of volcanic aerosols from Iceland challenge the concept of a Medieval Quiet Period

“…In contrast to many historic large eruptions, no major summer cooling anomaly is recorded in Northern Hemisphere tree-ring reconstructions in the year following the explosive stratospheric end-phase of the Hrafnkatla episode (i.e., 764 CE) [78][79][80] . The cause for this absence of a summer cooling anomaly is unknown; however, given that the explosive Hrafnkatla event followed a 12-year period of sustained aerosol emissions, increased background aerosol concentrations may have modified the climatic response.…”