On the Role of Atlantic Ocean Millennial Variability in Bolivian Altiplano Lakes Highstands during Heinrich Events of the Last Glacial

The Bolivian Altiplano is today one of the driest high altitude desert of the world with rainfall (about 330 mm/yr) mostly concentrated during austral summer. Yet over the last 130,000 years, this region has experienced abrupt rainfall changes at millennial timescale, which were responsible for the successive formation and disappearance of large lakes. To interpret these abrupt past rainfall changes, previous studies have invoked the modern day impacts of Pacific and Atlantic sea surface temperature variability as observed over the last 30 years. Our research has explored these hypotheses by investigating the detailed links between the observed variability in both oceans and Andean rainfall changes over the 20th century. The results show that the LMDz Atmosphere General Circulation Model nudged with observed sea surface temperatures and sea ice cover is well able to simulate the mean climatology and rare precipitation events of the 20th century over the Andean Altiplano. Furthermore, we are able to attribute specific causes triggering these rainfalls, highlighting the strong influence of the Atlantic Ocean inter-hemispheric thermal contrast. Based on these findings, we designed several idealized experiments to explore the implication of our results for past and future Andean rainfall changes. In particular, we show that the inter-hemispheric sea surface temperature contrast in the Atlantic Ocean during abrupt Heinrich events (North Atlantic cooler than South Atlantic) was the dominant factor that triggered through atmospheric teleconnections increased precipitations over the tropical Andes.