ORGANIC BIOMARKER-BASED CLIMATE HISTORY OVER THE PAST 16 KA FROM LAGUNA LLAVIUCU, ECUADOR

Global temperature change since the Last Glacial Maximum provides important insights into Earth system responses to climate forcing. Global warming during this period was punctuated by millennial-scale intervals such as the Younger Dryas (YD) and Antarctic Cold Reversal (ACR). However, temperature reconstructions are largely described by ice core isotopes thus geographically biased toward the high latitudes, limiting our understanding of global climate processes and the global footprint of millennial-scale cool events in the low latitude regions. To better understand the impacts of ‘northern’ vs. ‘southern’ modes of temperature changes in tropical Andes, we developed high-resolution temperature and hydroclimate records for the past ~16000 years based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) and leaf wax hydrogen isotopes (δ²H) in a sediment core from Laguna Llaviucu, Ecuador. Our δ²H record shows the tropical Andes experienced a transition from a relatively wet to a dry climate from ~16 to 12 ka, a dry early Holocene, and a long-term trend toward wetter conditions in the late Holocene. Our result is consistent with the notion that austral summer insolation forcing of the South American Summer Monsoon. Interestingly, our hydroclimate reconstruction is remarkably agreeing with oxygen isotope records from a nearby cave, validating the age model of our lake sediment core. Our brGDGT records indicate ~4 °C warming during the glacial termination, punctuated by a ~1.5 °C cold reversal that is concurrent with the ACR. This points to an important influence of meltwater forcing and sea surface temperatures over the tropical Andes during the deglaciation. During the Holocene, our temperature reconstruction is very stable, then shows a gradual warming trend since ~6000 yr BP, which was likely controlled by increasing atmospheric CO₂. We conclude that temperature from the tropical Andes is controlled by radiative forcing from atmospheric greenhouse gases and changes in ocean heat transport by the Atlantic meridional overturning circulation.