<p> I present a high- resolution record of Southeast Asian Monsoon (SEAM) evolution compiled from δ<sup>18</sup>O measurements conducted on five U-Th dated speleothems from Tham Mai Cave in northern Laos (20.75N, 102.65E), a key site at the interface between the Indian and East Asian monsoon systems. The speleothem oxygen isotope records are tied to robust uranium-series dates and indicate the records span from 0.79 to 13 kyr BP with sub-decadal resolution. During the Holocene, the Tham Mai speleothem δ<sup>18</sup>O records are characterized by lower values during the early to mid-Holocene with increasing values towards the late Holocene. This is similar to trends seen throughout the Asian monsoon region, reflecting the strong insolation control on monsoon strength and ITCZ position. The Younger Dryas is characterized by an abrupt δ<sup> 18</sup>O increase and is synchronous with the even observed in Chinese speleothem records and Greenland ice cores within age uncertainties. This suggests that the SEAM weakened in sync with high-latitude abrupt cooling events.</p><p> Four speleothems from Tham Mai cave grew contemporaneously from 4,300 years BP to 9,000 years BP. These four samples show a similar δ<sup> 18</sup>O pattern, despite a 1.2‰ between sample δ<sup>18 </sup>O variability is observed. A lumped parameter forward model method (KarstFor model) is used to assess to which extent this 1.2‰ discrepancy can be attributed to hydrological variability. Results suggested that this 1.2‰ discrepancy can be generated due to hydrological variability within one cave.</p><p> To better interpret interannual δ<sup>18</sup>O variability in high-resolution oxygen isotope records in the Asian Monsoon region, I utilize existing simulations from a spectrally nudged isotope-enabled general circulation model (IsoGSM) to investigate the climatic controls on δ<sup>18</sup><i> O<sub>p</sub></i> at four cave locations along the Asian monsoon region. Results show that δ<sup>18</sup><i>O<sub>p</sub></i> at the four cave sites reflects large-scale ocean-atmosphere processes, instead of local precipitation amount. Spatial correlation with vertical wind shear indicates that δ<sup>18</sup><i>O<sub>p</sub></i> at all sites is significantly related to monsoon strength and Walker circulation. The spatial correlations with SST and precipitation, suggest that the ENSO likely does play a role and that central Pacific type El Niño events influence precipitation δ<sup>18</sup>O in Oman and northern Laos, in particular.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:10027824 |
| Date | 18 March 2016 |
| Creators | Yang, Hongying |
| Publisher | University of California, Irvine |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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