North-Central Section - 39th Annual Meeting (May 19–20, 2005)

Paper No. 7
Presentation Time: 10:20 AM


KELLY, Megan J.1, EDWARDS, R. Lawrence1, CHENG, Hai2, WANG, Yongjin3 and YUAN, Daoxian4, (1)Department of Geology and Geophysics, Univ. of Minnesota, 310 Pillsbury Dr. SE, Minneapolis, MN 55455, (2)Department of Earth Sciences, University of Minnesota, 310 Pillsbury Dr. SE, Minneapolis, MN 55455, (3)College of Geography Science, Nanjing Normal Univ, Nanjing, 210097, China, (4)Karst Dynamics Laboratory, The Institute of Karst Geology, 40 Qixing Road, Guilin, 541004, China,

Stalagmites from Hulu and Dongge Caves, China, provide a high-resolution U-Th dated Asian Monsoon d18O record between 178 and 91 ka BP, covering much of the penultimate glacial and last interglacial periods. Asian Monsoon (AM) d18O variations are likely related to the intensity of monsoon precipitation, and broadly follow orbitally induced insolation changes across this time period. The d18O record is punctuated by numerous sub-orbital scale climate events, six of which occur between ~178-162 ka BP, and nine between ~155-134 ka BP. These events are similar to last glacial Hulu Cave d18O peaks that are anti-correlated to Greenland Interstadial events, which indicate that wet periods in China correspond to warm Greenland temperatures. Both Hulu and Dongge records contain an extended interval of heavy d18O values between ~136 and 129 ka BP, prior to the abrupt strengthening of the monsoon centered at 129.0 ± 0.9 ka BP which we call AM Termination II. This weak monsoon interval (WMI) allows us to make critical correlations to the atmospheric methane and ice-rafted debris records, providing information regarding the sequence of events surrounding Termination II.

Based upon our correlations, we demonstrate that most of the marine oxygen isotope termination, along with the rise in atmospheric CO2, CH4, and Antarctic temperature, occurs within the WMI, suggesting that the initial phase of deglaciation proceeded while the monsoon was still weak and presumably Greenland was still cold. A similar sequence of events is also seen at Termination I. During the first deglacial phase (initial sea level, CO2, CH4, and Antarctic temperature rise), much of the northern hemisphere was dry, which may have starved the ice sheets of moisture. This effect, combined with CO2 rise and glacial isostatic processes, may have contributed to sea level to rise prior to the monsoon terminations and high northern latitude warming. The second deglacial phase (final CH4 rise, abrupt monsoon strengthening, and Greenland temperature rise) then took place after northern hemisphere insolation began to rise. We conclude that some combination of northern and southern insolation conditions is necessary for forcing glacial terminations, and that this process is much more complex than originally envisioned by Milankovitch.