Little Ice Age and Medieval Warm Periods in Eastern China as Read from the Speleothem Records
Abstract
The long-term climatic pace has often been interrupted by short-term abrupt changes. The Little Ice Age and Medieval Warm Period represent the two most important such changes over the last two millennia. Largely due to a dearth of high-resolution climatic records, our knowledge on the spatial extent, duration, and moisture characteristics of these two events is incomplete, and this has hampered our understanding of the driving force causing them as well as the recent global warming trend. Here we present high-resolution climatic records reflected by the δ 18O and δ 13C in three stalagmites from limestone caves in China: S312 from Shihua Cave (about 50 km southwest of Beijing), SF from Buddha Cave (about 80 km south of Xian), and F4 from Fengyu Cave (about 100 km south of Guilin). The chronologies of the stalagmites were determined by lamination counting and by the 210Pb and 230Th (TIMS) methods. S312 (3,600 years old) and F4 (600 years old) have mean growth rates of 0.035 and 0.24 mm/yr, respectively; whereas SF (10,000 years old) has a growth rate of 0.087 mm/yr for the top 1.6 cm and a rate of 0.0163 mm/yr below. We measured δ 18O and δ 13C at a resolution of 1-10 years for the last 1,000 years or so in all three stalagmites. These measurements were extended to the past 4,000 years at lower resolutions in S312 and SF. A total of 1052 pairs of δ 18O and δ 13C data thus obtained forms the basis for our reconstruction of the temperature (using δ 18O as proxy) and moisture (using δ 13C as proxy) variability in eastern China over the last four millennia. From the measured cave-water δ 18O and cave temperature at each location, we calculated the δ 18O values for calcites precipitated under isotopic equilibrium and found them to be similar to the observed δ 18O values in modern stalagmite layers. Measured δ 18O values in S312 and SF average -8.8\permil and -9.1\permil, respectively, reflecting a similar mean temperature of about14°C. The average δ 18O value of F4 is 2.2\permil heavier than those of S312 and SF, indicating an annual mean temperature in Fengyu Cave that is about 5°C warmer than those of the two northern caves. Although the three caves are more than 1000 km apart, their long-term δ 18O records show patterns that are remarkably similar. The records show that in eastern China, the Medieval Warm Period started around 1000 AD and lasted until 1500 AD. A brief cooling during this warm interval occurred around 1150 AD. The Little Ice Age in China started at around 1500 AD and ended in the mid-1800s. Since then, all three locations show a warming trend that has been observed elsewhere in the world. The records of S312 and SF show that for the past 4,000 years, the two locations has had similar temperature variations with five distinct warming trends, but a different moisture variability which is probably more sensitive to local atmospheric circulation changes than temperature. In general, it was relatively dry during the Medieval Warm Period and wet during the Little Ice Age in eastern China. Of the five warming trends, the most recent one is the strongest.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFMPP71C..09L
- Keywords:
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- 1040 Isotopic composition/chemistry;
- 1045 Low-temperature geochemistry;
- 1600 GLOBAL CHANGE (New category);
- 3344 Paleoclimatology;
- 4215 Climate and interannual variability (3309)