Investigating Australian Monsoon Sensitivity to Large Volcanic Eruptions in the Last Millennium Through Model-Proxy Synthesis

We investigate the response of Australian monsoon precipitation to large volcanic eruptions (> VEI 4) during the last millennium using the Community Earth System Model Last Millennium Ensemble (LME). The LME covers the period 850-2005 CE and consists of 13 individual ensemble members with all transient forcings combined and smaller subsets with single forcing factors, such as volcanic forcing, thereby revealing changes in the Australian summer monsoon system due to discrete volcanic eruptions. Here, we assess relative contributions of forcings to rainfall in northern Australia by analyzing precipitation, moisture transport and sea surface temperature (SST) in the LME in the years following these eruptions.

We focus on the central Australian tropics (northeastern Western Australia), the location of cave KNI-51. Precisely-dated stalagmites from this region have yielded high-resolution reconstructions of the Australian monsoon (via their oxygen isotopes) and are currently being investigated for short-lived rainfall anomalies tied to discrete volcanic eruptions. In the LME simulations, we find that both the VEI and geographic location of large volcanic eruptions influence the hydroclimate over northern Australia, driven by a reduction in moisture transport. This large, but short-lived (< 5 years) hydroclimate response following volcanic eruptions may be hidden in the stalagmite record due to age-model biases (+/- 10 years).

We aim to reconcile this limitation by developing new analytical techniques with LA-ICP-MS and SIMS to interpret signals of sulfur and other trace elements in the stalagmites. The correlation between periods of high sulfur, which are deposited in the stalagmite after large eruptions, and anomalies in the rainfall record allow us to identify hydroclimate extremes induced by volcanic eruptions. The synthesis of KNI-51 stalagmite proxy records and the LME volcanic forcing ensemble members thus offers a promising opportunity to diagnose and understand the hydroclimatic response to volcanic eruptions in a system largely unaffected by El Niño-Southern Oscillation events arising from internal variability.