Whole School Seminar 13 November - Dr Tara Jonell
Amplifying climate signals using High Asian mega-lake shorelines
Abstract
Lake basins record critical interactions among all of Earth’s major spheres: the hydrosphere, cryosphere, atmosphere and lithosphere. Lake sediments and shoreline landforms archive timing, duration, and intensity of past climatic variability and environmental impacts over a variety of timescales. More than 1000 lake systems spread across the internally drained Tibetan Plateau today, of which many are only the salty remains of much more expansive paleolakes in the past. This study presents new shoreline ages integrated with quantitative digital topographic analysis and regional geomorphic evidence to reconstruct the sizes and extents of ancient rift lake systems over the last ~41 kyr for the south-central Tibetan Plateau.
This study presents optically stimulated luminescence (OSL) and the first K-feldspar post-infrared infrared (pIRIR) stimulated luminescence ages from two lakes once argued to be part of a Pleistocene Tibetan mega-lake (>66,000 km2). Our new results show that two large but separate paleolake systems developed in the latest Pleistocene-earliest Holocene and no lake larger than ~6460 km2 has existed since at least 41 ka. Early Holocene paleolakes expanded up to 7x modern (+220–335 km3) with two to four-fold greater lake expansion in the west, Findings corroborate earlier investigations, implying dramatic runoff increase and/or evapotranspiration reduction prompted rapid earliest Holocene lake expansion. Spatially variable precipitation, in combination with permafrost degradation, most strongly governed paleolake moisture balance.
The unique relationship between climate and rift topography in shaping water balance and high amplitude (>150 m) lake level fluctuations over 104 yr timescales merits comparison of south Tibetan Plateau lake systems with the highly sensitive amplifier lakes of the East African Rift. Remarkable potential exists to use Tibetan amplifier lake shorelines as direct paleo-“rain gauges”, which may prove essential to quantifying Tibetan Plateau-Asian monsoon boundary conditions under future global warming scenarios and analog paleoclimates.
Biography
Tara Jonell is a geologist working across the fields of geomorphology, geochronology and geochemistry. She is interested in the physical and chemical interactions among erosion, topography, and climate variability in monsoonal landscapes. Her research integrates field and geospatial observations with geochronological and geochemical fingerprints of sediment to understand how, why and when landscapes evolve over millennial to multi-millennial timescales in response to past climate change.
Tara is a Postdoctoral Research Fellow in the School of Earth and Environmental Sciences, The University of Queensland. Prior to this role, she was a Visiting Assistant Professor at the University of Louisiana at Lafayette and Instructor at Louisiana State University. She received her MSc in Geoscience at New Mexico State University and PhD in Geology from Louisiana State University.