Volcanically Triggered Ocean Warming Near the Antarctic Peninsula.

Explosive volcanic eruptions are the largest non-anthropogenic perturbations for Earth's climate, because of the injection of sulfate aerosols into the stratosphere. This causes significant radiation imbalances, resulting in surface cooling for most of the globe. However, despite its crucial importance for Antarctic ice sheet mass balance, the response of the Southern Ocean to eruptions has yet to be understood. After the eruption of Mt. Pinatubo in 1991, much of the Southern Ocean cooled; however, off the Antarctic Peninsula a warming of up to 0.8 °C is found in the observations. To understand the physical mechanisms associated with this counter-intuitive response, we combine observational analysis from the Mt. Pinatubo eruption with the Last Millennium Ensemble (850-1850) conducted with the Community Earth System Model. These results show not only that the observed warming off the Peninsula following the Mt. Pinatubo eruption is consistent with the forced response to low-latitude eruptions but further, that this warming is a response to roughly 16% weakening of subsurface Weddell Gyre outflow. These changes are triggered by a southward shift of the Southern Hemisphere polar westerlies (∼2°latitude). Our results suggest that warming induced by future volcanic eruptions may further enhance the vulnerability of the ice shelves off the Antarctic Peninsula.