PhD defence: El Niño signatures in Tropical Andean ecosystems

The El Niño-Southern Oscillation (ENSO) in the tropical Pacific is the most prominent interannual climate variation in the world. El Niño episodes are characterized by a periodical increase in sea surface temperature (SSTs) along the western coast of tropical South America. The extreme rainfall associated with El Niño events cause catastrophic floods in Peru and Ecuador. Since the state of trade-wind intensity and SST’s in the Pacific region determine the magnitude, duration and time-intervals of individual ENSO events, it is reasonable to expect that 21st century climate warming would alter ENSO behaviour. In order to understand the impact of climate warming on El Niño and to improve the prediction skill of climate model simulations, it is important to develop long-term ENSO records that extend empirical evidence of El Niño behaviour beyond the scope of instrumental records. In this thesis, biological proxies for climate change, in particular palynology, are introduced, tested and applied for the reconstruction of long-term development of El Niño on centennial, decadal and annual timescales. To this end, biological proxies in sediments from the Tropical Andean lake Laguna Pallcacocha is investigated. The results presented in this thesis illustrate that ENSO plays a key role in the landscape dynamics and species composition of montane forests of the Tropical Andes. Additionally, this thesis shows that land use intensification not only amplifies the impact of ENSO on landscape dynamics, it also results in catastrophic ecological shifts in Andean lakes and the high Andean grasslands. Furthermore, this thesis shows a unique approach to reconstruct the amplitude and frequency of El Niño events on near annual resolution ca. 6000 years ago when the ENSO system evolved into the system we know today.