Triple oxygen isotopes and clumped isotope thermometry applied to East African water balance over the last 500ky
Abstract
Disentangling local from regional influences is critical for using oxygen isotopes in terrestrial records as indicators of past hydroclimate variability. This is of particular importance for isotopic records from sediment cores recently recovered by the Olorgesailie Drilling Project from the Koora Plain south of outcrops of the Olorgesailie basin in the southern Kenya Rift Valley, where local variations in water balance likely influenced human evolution and migration in eastern Africa. While the Olorgesailie cores are carbonate-rich and extremely well-dated, the basin fluctuated between lacustrine and subaerial conditions over the past 500,000 years, resulting in various modes of carbonate formation. To better constrain the complex climatic and depositional controls on the Olorgesailie carbonate record, we present an approach that combines triple oxygen isotopes (Δ17O) with clumped isotope thermometry [T(Δ47)] and traditional stable oxygen isotopes (δ18O). Carbonate δ18O values average -0.4 ± 1.9‰ (n=141), while T(Δ47) and reconstructed parent water δ18O values range from 14-32°C and -1 to 5‰, respectively (both n=28). The range of Δ17O values is approximately 150 per meg (n = 29), exceeding that reported for freshwater sources today (≤ 80 per meg; Luz and Barkan, 2010; Li et al., 2015). We observe a strong negative correlation between Δ17O and δ18O values, consistent with evaporative enrichment of heavy isotopes in water. Together, these results suggest evaporation within the basin is an important control on the Olorgesailie carbonate δ18O record. This multiproxy approach makes it possible to better distinguish local and regional influences on hydroclimate variability in eastern Africa since 500 ka. With this study, we demonstrate the crucial insight triple oxygen isotopes provide to carbonate δ18O-based hydroclimate records, particularly for those where evaporation is expected to play a significant role on water balance.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMPP31F..06M
- Keywords:
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- 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4924 Geochemical tracers;
- PALEOCEANOGRAPHYDE: 4928 Global climate models;
- PALEOCEANOGRAPHY