QGG DENTON, ANDREWS, PORTER GLACIOLOGY AWARD: CONSTRAINING THE TIMING OF DEGLACIAL WARMING IN COSTA RICA

The most recent glacial-interglacial transition, Termination 1 (~19-11.7 ka), was the largest natural global warming event in Earth’s recent history, yet the mechanisms which influenced this climate change are not fully understood. While there are many paleotemperature records from the mid- and high-latitude regions for Termination 1, less is known about the temperature history of the tropical continents, even though the tropics are the main source of heat and energy transported to the poles. Mountain glacier reconstructions provide some of the best indicators of tropical continental temperatures and can help improve our understanding of the spatial pattern of warming during Termination 1.

We are developing a new high-elevation terrestrial temperature record from the tropics by constraining the timing of deglaciation at Cerro Chirripó (3,820 m asl) in the Talamanca Range of Costa Rica and the rate and magnitude of warming during Termination 1. This site is in the humid inner tropics (~10°N-10°S) where temperature is a dominant influence on glacial mass balance. Thus, past glacial extents can be used to infer past temperatures. We are applying ¹⁰Be and ³He surface exposure dating to past glacial extents estimated to range in age from the Last Glacial Maximum (LGM) to late glacial time. Preliminary data include seven new ¹⁰Be ages and nine previously published ages (Cunningham et al., 2019). These data show expanded glaciers at ~21-18 ka and near-deglaciation of at least one valley by ~17 ka. We are currently processing ~10 samples for ³He dating as well as additional samples for ¹⁰Be.

We will use the glacial extent chronologies from multiple valleys to estimate the rate of warming during Termination 1. The preliminary data suggest that warming occurred rapidly, with deglaciation upvalley by ~17 ka and no evidence for subsequent glacial extents on the mountain. We will combine these data with LGM ELA reconstructions from Quesada-Román et al. (2020) and an estimate of the minimum ELAs necessary for glaciers to exist on Cerro Chirripó, which in turn will provide an estimate of the deglacial warming.