Annual-to-decadal resolution speleothem records from Zhijin Cave in the central western Guizhou of China: Changes in climate, environment and human activity during the past 1200 years
Abstract
A 12.5-cm long stalagmite (ZJD-21) from Zhijin Cave (26.67°N, 105.77°E) in the central western Guizhou was dated by ICPMS 230Th/U method and 210Pb alpha counting method, revealing a growth history of 1200 years. A total of 490 samples (0.25mm sampling interval) were analyzed for oxygen and carbon isotopes. The δ18O values range from -10.60 to -7.56 permil (PDB) with an average of -9.00 permil, whereas the δ13C values range from -10.70 to -5.76 permil (PDB) with an average of - 8.43 permil. From the same cave, an 8-cm long soda-straw (ZJD-9C) was dated by 210Pb alpha counting method, providing a δ18O and δ13C record over the past 180 years. For the overlapping period, the two speleothem records have similar trends and features. The speleothem δ18O records in this monsoonal region can be used as a wet/dry indicator with lighter values reflecting wetter conditions, and vice versa. The speleothem δ13C records may be used for evaluating the vegetation changes above the cave, with heavier values indicating less vegetation coverage and intensity. The δ18O values of ZJD-21 are mostly heavier than the average value (-9.00 ‰) during AD1050-1270, AD1380-1460 and AD1780-1885, indicating drier climates were prevailing during these periods. Wetter climates were dominated during AD1010-1050, AD1460-1780 and AD1885-1960, reflected by the lighter δ18O values. The δ13C records from Zhijin Cave exhibit three intervals when the δ13C was strongly increased, which may be corresponding to deforestation events from AD1170 to AD1240, from AD1460 to AD1510 and since AD1800. These deforestation events were correlated to the population surges in South Song Dynasty, Ming Dynasty and Late Qing Dynasty in the area. After AD1900, all δ13C values are heavier than -6.6 permil, which indicates that the karst-desertification problem has been seriously developing in this region under human impacts.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMPP11C1407L
- Keywords:
-
- 1000 GEOCHEMISTRY;
- 1041 Stable isotope geochemistry (0454;
- 4870);
- 1616 Climate variability (1635;
- 3305;
- 3309;
- 4215;
- 4513);
- 3344 Paleoclimatology (0473;
- 4900);
- 4215 Climate and interannual variability (1616;
- 1635;
- 3305;
- 3309;
- 4513)