Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....2435w&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #2435
Astronomy and Astrophysics
Astronomy
Scientific paper
ODP Leg 184 drilled 6 sites in the South China Sea, and Site 1143 (9o21.72’N, 113o17.11’E, water depth 2772 m) is the single one from its southern part in a coral reef area. High-resolution (nearly 2.5 k.y. interval) stable isotope analyses of planktonic and benthic foraminifers in the upper 190-m-long core section, in combination with biostratigraphic data, resulted in a 5-myr astronomical timescale or the region (Tian et al., 2002). A distinguished feature in the d13C curves is the occurrence of long-term cycles of 400-500 k.y. superimposed on high- frequent fluctuations, and the d13C sequence is periodically punctuated by carbon isotope maximum events or “d13Cmax”, which are present in all long sequences over the global ocean. As the same cyclicity is also found in carbonate curves, the d13Cmax events must denote major reorganization in carbon reservoir of the global ocean. The occurrence of d13C max is related to the ~400-kyr long eccentricity cycle before the boreal ice-cap developed, but extended to ~500-kyr in the last million years. From late Oligocene to Pliocene, the d13C and d18O covariate at eccentricity bands, but d13C max events mostly lagged the d18O changes; in the last million years, the d13C max events precede major expansions of ice-cap. For example, the major ice-sheet expansion at ca. 430 kyr ago was preceded by a d13C max event and a negative shift. This new finding suggests that disturbance in carbon reservoirs leads to major growth of ice-sheet size and challenges the prevalent concept of Arctic control of glacial cycles (Wang et al., 2003). Because the Earth is now passing again through a d13Cmax episode, it is crucial to understand the causal relationship between the successive d13C changes and ice-sheet growth events.
Cheng Xiande
Tian Junlong
Wang Pei
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