Geoscience

Influence of Atlantic Circulation on East Asian Monsoon Discovered

The magazine Nature Geoscience published a paper titled “Influence of Atlantic meridional overturning circulation on the East Asian winter monsoon” by Prof. Sun Youbin of the Institute of Earth Environment, CAS and his collaborators on Nov. 27, 2011. They presented records of grain size variations from the northwestern Chinese Loess Plateau, dated using optically stimulated luminescence. The reconstructed millennial-scale variations in the strength of the East Asian winter monsoon over the past 60,000 years are broadly correlated with temperature variations over Greenland and precipitation changes in Eastern Asia. They further investigate the effect of a slow-down of Atlantic meridional overturning circulation on the monsoon system using a coupled climate and find a strengthening winter monsoon circulation over the "Chinese Loess Plateau" and the regions and a reduction in summer monsoon precipitation over East Asia. They conclude that Atlantic meridional overturning circulation is a driver of abrupt change in the East Asian winter and summer monsoon systems, and that the northern westerlies play a role in transmitting this signal from the North Atlantic to the Asian monsoon regions. As highlighted by Nature China, this work suggests that "North Atlantic climate" may have a direct effect on the winter monsoon intensity, dust grain size and summer monsoon precipitation over East Asia. If this is true, rising temperatures in Greenland are likely to bring increasing episodes of natural disasters. The work has been jointly accomplished by the Chinese and American scientists from the Institute of Earth Environment, CAS; Brown University, Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, NOAA's National Climatic Data Center, USA; and Ocean University of China.

Magmatic Fluid Exsolved Proved to be from Magma in Tibet

Li Jinxiang and co-advisors Prof. Qin Kezhang and Asso. Prof. Li Guangming of the Orogenic Belts and Ore-Forming Process Group, Institute of Geology and Geophysics, CAS, found that high-temperature and high-salinity fluid inclusions at Duobuza porphyry copper-gold deposit in Bangongco Belt, Tibet. These fluid inclusions, representing the magmatic-hydrothermal transitional stage, are characterized by the sylvite dissolution between 180 and 360°C and halite dissolution between 240 and 540°C, followed by homogenization through vapor disappearance between 620 and 960°C, and salinity ranging from 34 to 82 wt% NaCl equiv., close to the H2O-NaCl-KCl system. Daughter minerals were identified by SEM as chalcopyrite, hematite, halite, sylvite, rutile, K-feldspar, and Fe-Mn-chloride. They indicate that the fluid is rich in ore-forming elements and of high oxidation state. No coexisting vapor-rich fluid inclusions with similar homogenization temperatures were found, so the brines are interpreted to have formed by direct exsolution from magma rather than trough boiling off of a low-salinity vapor. Estimated minimum pressure of 160 MPa implies approximately 7-km depth. In conclusion, it is suggested that the large size and relatively high ore grade of the Duobuza porphyry copper-gold deposit was favored by direct high-temperature exsolution of highly saline magmatic fluids from an oxidized hydrous granodioritic magma. The fluid transferred sulfur and metals from the crystallising melt into lower-temperature veins where ore minerals precipitated. The research is published in Geofluids (Li et al. High temperature magmatic fluid exsolved from magma at the Duobuza porphyry copper-gold deposit, Northern Tibet. Geofluids, 2011, 11:134-143).