Late Quaternary Paleoceanography and Climate Dynamics of the Low-latitude Pacific
| Autor: | Pai-Sen Yu, 尤柏森 |
|---|---|
| Rok vydání: | 2010 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 With respect to understandings of late Quaternary paleoclimatic changes and climate dynamics in the tropical oceans, high-resolution / high-quality marine sedimentary cores retrieved from South China Sea (SCS) and eastern equatorial Pacific (EEP) were used to reconstruct paleoceanography of low-latitude Pacific. For archieving detailed and in-deepth information on this issue, our research selected from regional areas SCS/EEP, western Pacific, low-latitude Pacific, and even the global scale. In this thesis, the main objectives include 1) reconstructing SCS oceanographic behaviours affected by the East Asian summer/winter monsoons variations since Marine Isotope Stage (MIS) 6; 2) understanding plausible climate mechanisms that drived orbital time-scales East Asian monsoons variations in the SCS; 3) spatial and temporal patterns of eastern equatorial cold tongue from the last 160 kyrs; and 4) understanding climatic evolution of low-latitude Pacific by comparing marine records with MIS 6-1 and MIS 15-13 time slices, and further investigating possible driving forcings for abnormally warm/humid glacial MIS 14 condition. Planktic foraminifer assemblages and temperature estimations on core MD012394 revealed that changes in monsoon-driven upwelling over the past 135 kyrs. Our results indicated that the relative abundance patterns of Globorotalia inflata and Neogloboquadrina dutertrei + Neogloboquadrina pachyderma R would regarded as hydrographic proxies for East Asian summer and winter monsoon, respectively. In addition, we established planktic foraminifer hydrographic index and SST estimates for these two records and demonstrated that these are useful for indicating the effects of the strength of the East Asain winter monsoons on the SCS surface ocean hydrography. The abundances of G. inflata with abruptly high values were appearred to coincide with Northern Hemisphere summer insolation maxima, particularly at ~11, 33, 59, and 83 kya. The results further supported the view that the strengths of both summer insolation and the East Asian summer monsoon have determined the relative abundance of planktic foraminifer fauna and the SSTs of the western SCS for the last 135 kyr. On the other hand, planktic foraminifer fauna and hydrographic gradient records were relatively high near ~22, 45, 71, 94, and 116 kya, when Northern Hemisphere summer insolation levels were low. The fauna assemblages were primarily indicative of East Asian winter monsoon strength, which was driven by a “cross-equator flow” mechanism. For the EEP region, our Site 1240 record reveals a significantly intensified cold SST condition that may result from enhanced influences from subpolar and/or Eastern Boundary Current (EBC) components into the EEP. However, SST records of ODP Site 1240 revealed no obvious precession cycles in comparison with precession-dominated low-latitudes / SCS-prevailed monsoon regions. This was due to those fairly complicated EEP environments. Thus, our results suggested that high latitude forcings should take into account while investigating climate dynamics of tropical oceans. Furthermore, spatial and temporal SST patterns across the EEP indicated that path of cold tongue possibly oscillated along a meridional variation within 3oN - 6oS over the past 160 kya. In particular, the apparently warm and wet glacial climate conditions of MIS 15-13 were well exemplified in many western Pacific sediment core and East Asian loess and lake records. In order to best understand the specific climate event, the paleoclimatic records reconstructed from this thesis could be compared comparing with other terrestrial records from Chinese loess, lakes in the East Asia, and further our understanding on the validity of the hypotheses on the tropical ocean origins of global climate changes in the late Quaternary. We observed a hemispheric asymetry pattern of the tropical Pacific climate, that is, warming in the west and cooling in the east at MIS 14. We further speculate that a large-scale climatic shifting that may have involved a migration of the Intertropical Convergence Zone and a change of trade wind patterns in the tropical Pacific, was probably responsible for the contrasting surface ocean hydrographies during MIS 14. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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