Peat Plant-Wax n-Alkane D/H Ratios Document Early Holocene Arrival of Indian Ocean Monsoon in Southern China
Abstract
Changes in climate are recorded in organic compounds present in the peatlands that developed in temperate northern latitudes after post-glacial continental wetness increased. Peat sequences in China yield evidence of changes in moisture delivery by the Asian monsoon since 15 ka from molecular and isotopic differences in plant-derived peat layers. Proportions of submergent and emergent plants vary in peat bogs as water levels rise and fall in response to changes in precipitation and its temperature-sensitive evaporation. Changes in the water level are recorded in the relative abundances of C23 and C25 submergent-plant n-alkanes and C27, C29, and C31 emergent-plant n-alkanes. Compound-specific D/H analyses of these plant-wax n- alkanes improve our understanding of past changes in delivery of Asian monsoonal precipitation and in temperature. n-Alkane molecular analyses reveal that the warmer climate of the Holocene Climatic Optimum (10.5 to 6 ka) was accompanied by increases in monsoonal precipitation that raised the water level of the Hongyuan bog on the northeast edge of the Tibetan Plateau. At the same time, the climate at Hani in northeast China became less-wet. Comparison of n-alkane delD values from the Hongyuan and Hani bogs reveals that both regions received moisture predominantly from the East Asian Monsoon until ca 10.5 ka. However, after this time, delivery of isotopically light Indian Ocean Monsoon moisture was found to dominate over the Tibetan Plateau, signaling an important change in the Asian monsoon system. Indian Ocean moisture remained dominant at Hongyuan through the late Holocene, although increases in n-alkane delD values indicate that its climate shifted to less wet, implying diminished monsoonal precipitation on the Tibetan Plateau.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMPP24A..05M
- Keywords:
-
- 0454 Isotopic composition and chemistry (1041;
- 4870);
- 0458 Limnology (1845;
- 4239;
- 4942);
- 1055 Organic and biogenic geochemistry;
- 3344 Paleoclimatology (0473;
- 4900)