Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmpp24a..01q&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #PP24A-01
Mathematics
Logic
0458 Limnology (1845, 4239, 4942), 1051 Sedimentary Geochemistry, 1520 Magnetostratigraphy, 1616 Climate Variability (1635, 3305, 3309, 4215, 4513), 4952 Palynology
Scientific paper
Heqing Basin (100°06'-100°16'E, 26°28'-26°46'N) is situated in southeastern margin of Tibetan Plateau, a geological conjunction zone of three tectonic units separated by Jinshajiang, Honghe and Xiaojinhe-Lijiang fault belts. Modern climate in this region is mainly influenced by Indian monsoon circulation. In Year 2002, a 665.83 m long core was retrieved from the Heqing basin under the support of Chinese Environmental Scientific Drilling program, which permits a high-resolution reconstruction of the Indian monsoon evolution from a continental perspective. The core mainly consists of gray clay, silty clay and silt. Magnetostratographic result generated by both thermal and alternating-field demagnetization methods indicates that the bottom age of the Heqing core is about 2.78 Myr. Multiple proxies (magnetic susceptibility, grain size, CaCO3 content, loss of ignite, pollen concentrations, and major/trace elements) were generated to reconstruct regional climate change and its dynamical links to Indian summer monsoon and solar insolation forcing. The results suggest that during glacial periods, this region is characterized by reduced vegetation cover (e.g., low total pollen concentration) and enhanced physical weathering (e.g., high Rb/Sr ratio), whereas during interglacial times, vegetation cover was extensive and chemical weathering is relatively strong around Heqing basin. Good correlation between variations in proxy indicators from Heqing core and stacked Indian summer monsoon record from Arabian Sea (Clemens and Prell, 2003) indicates that over the last 0.35 Myr, Heqing basin is predominantly influenced by Indian summer monsoon. Unlike Indian monsoon records from the Arabian Sea and Indian Ocean which resolution is relatively low, our high-resolution proxy variations permit a robust understanding of the Indian summer monsoon variations over the last 2.6 Myr. Comparisons of monsoon proxies from land and ocean indicate that solar insolation is the dominant factor controlling the Indian summer monsoon variation, particularly low-latitude radiation difference between northern and southern Hemisphere. However, an evident 100-kyr cycle occurred around 1.2 Myr and became remarkable after 0.5 Myr, implying that global ice volume might have a significant influence on the monsoon records in Heqing basin since at least mid- Pleistocene.
An Zhenghua
Chang Hsuanyeh
Jin Zhensheng
Liu Wende
Liu Xiandong
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