IMPROVING THE AGE MODEL FOR LAKE TITICACA, BOLIVIA TO RECONSTRUCT TROPICAL CLIMATE VARIABILITY OVER THE PAST CA. 350 KA

The 136-meter continuous drill core obtained from Lake Titicaca in Bolivia provides an invaluable repository of climate change data in tropical South America, spanning the past ca. 350 ka. However, the existing Lake Titicaca chronology is largely unconstrained beyond the limits of radiocarbon dating (ca. 45 ka), relying on a series of four U-Th dates on aragonite between 46 and 48 m (~122 kyr), and orbital tuning (Fritz et al., 2007). Unlike marine records, lacustrine sequences cannot be correlated to global ice volume records by analyzing δ¹⁸O stratigraphy, resulting in a significant challenge in developing accurate age-depth relationships. Older Ar-Ar dating of ash beds has yielded spurious and unconstrained ages and paleomagnetic dating was not possible as the record is strongly affected by diagenesis (Fritz et al., 2007). Similarly, U-Th dates on carbonate beds have yielded significant uncertainties and produced spurious ages in this lake system. In this study, we address these challenges by using new geochronological techniques: optically stimulated luminescence (pIR-IRSL) dating of sediments and zircon double dating of interbedded ash beds. We find strong agreement between different dating approaches throughout most of the record, demonstrating that well-constrained age-depth models for long sedimentary sequences can be achieved using this combination of techniques. We utilize these new geochronologic constraints in a Bayesian sediment modeling approach to generate a continuous age-depth relationship for 350 ka of sedimentation at Lake Titicaca. Our revised chronology was then employed to assess orbital-scale magnetic susceptibility changes, reflecting Andean glacial retreat, at Lake Titicaca. By implementing more robust age constraints through novel dating methodologies, we aim to strengthen the conclusions of previous work and instill increased confidence in utilizing this record for exploring past climate changes beyond radiocarbon dating.