–Sub-project 2 –
Link between tectonic uplift and environmental changes in East Asia

 
(A) Geochemical and isotopic characterization of the Pliocene red clay formation from       the Chinese Loess Plateau:

1. Geochemical proxies in the loess-paleosol sequences: Late Tertiary to Quaternary loess-paleosol sequences provide invaluable record of the changing environment in continental areas during that time interval. Loess source proxies include quartz morphology, heavy minerals assemblages, oxygen isotope geochemistry of quartz, major and trace elements and Sr-Nd isotopic compositions.

2. Current target area: We have been studying various loess-paleosol sequences in the Chinese Loess Plateau. To executive this subproject, we extended our area of investigation from to the Central Asia loess, with the southern Tajikistan as a key target. The Chashmanigar loess section (38°23'32”N, 69°49'57”E) section was chosen because some detailed stratigraphic and magnetic susceptibility data have been published. To be able to fully compare the magnetic and geochemical data, we use the samples collected by these authors. This section is about 200 m thick and consists of an alternation of loess and paleosol layers (pedocomplex, strictly speaking). The basal age of the section is about 1.77 Ma.

3. Scientific interests: This study is aimed to answer the following questions and to test some hypotheses.

(a) What are the source areas of the Tajik loess? Have these source(s) changed in response to tectonic or climatic events?

(b) What is the most appropriate tracer to be used in unraveling the loess sources(s) and their weathering history?

(c) Are the high mountain regions the ultimate source of the loess material? What is the turnover time required between physical erosion of particles in these areas and incorporation into loess deposits? What the relationship between this time and the mean erosion rate in these areas?

(d) Are the climatic proxies we established on Chinese loess sequences still valid in Central Asia ? Can we go further and be able to reconstruct paleorainfall levels by combining chemical analysis and magnetic susceptibility data?
 

 
 
 
 

黃土標本採自於中亞塔吉克的 Chashmanigar loess section (A 點 )
 
     
(B)Tectonic forcing environmental changes in the South China Sea and Western      Pacific:

1. Dy namic tectonic evolution induced local and global climate changes: The uplift of the Himalayan/Tibetan Plateau has been considered responsible not only for the revolution of the Asian monsoon, but also for late Cenozoic global cooling. The progressive closure of the Central American seaway beginning about 4.6 Ma was suggested to have played a critical role in the development of modern ocean circulation and led to extensive changes in Northern Hemisphere climate.

     
 
 
 


普林蟲( P. obliquiloculata )和杜氏新方球蟲( N. dutertrei )在岩心( a ) MD403 、( b ) OR715 和( c ) MD88 在全新世的相對豐度變化圖。普林蟲銳減事件( PME )發生的時間為圖中陰影部份。箭頭指示普林蟲銳減事件前後的碳十四定年資料點。

 
     
     
2. Objectives in this subproject include:

(a) The onset of Indian and Asian Monsoons.

(b) Paleo-hydrological conditions in the South China Sea and Western Pacific Ocean .

(c) Short-term and long-term variation of Kuroshio, dynamic evolution of Western Pacific Warm Pool (WPWP), and related biogeochemical changes.


3. Current target topics:

(a) Paleo-hydrological condition and Holocene Pulleniatina Minimum Event (PME). Geochemical and biological records of three cores, MD403, OR715 and MD88, suggest that (1) The PME is not restricted to the marginal seas, but widespread in the western North Pacific; (2) the thriving of N. dutertrei during the PME in the Okinawa Trough may be a result of higher availability of food in the absence of P. obliquiloculata ; and (3) No distinctive and consistent anomalies in the paleoceanographic proxies are associated with the PME, implying there were no changes in hydrography and productivity of the surface and subsurface water associated with this event.

(b) Dynamic evolution of the WPWP and Asian Monsoon. Records of foraminiferal Mg/Ca–inferred seas surface temperature and induced seawater d 18 O variation of a marine sediment core, ODP1115B, in the Solomon Sea, Western Pacific, over the past 700 ka suggest that the territory of the WPWP changed significantly at ca. 300-400ka. It might be related to different conditions of Asian Monsoon.
 

     
 
 
 


圖二之一 :海表溫差異圖,圖中包括 ODP806B 與 846 、 ODP806B 與 1115B 、 ODP1115B 與 846 以及 ODP806B 與 MD972140 。其中按照綠色、藍色、紅色以及橙色排列。

 
     
 
 
 


圖二之二: ODP806B, 846 與 1115B 之間溫度差異的示意圖,利用三者之間的溫度差作為三角形之邊長,我們將 ODP806B 與 1115B 和 ODP1115B 與 846 的溫度差異等比例放大兩倍。

 
     
(C)High resolution geochemical analyses on the paleo-climate events since the late      Pleistocene in the South China Sea Rim: Speleothem and coral records

1. Objectives: Speleothem and coral samples in the South China Sea Rim (SCSR) are used for:

(a) to diagnose the WPWP related events, such as East Asian Monsoon, Indian Monsoon, Indian Ocean Dipole, and ENSO and the interaction between climate subsystems in the past 100 years and Holocene; and

(b) to examine whether the D/O cycles were manifested or not in the SCSR in the late Pleistocene.

 

     

採樣地點之位置圖與洞穴中鐘乳石
 
     
2.Current progress topics:

(a) High-resolution records of oxygen/carbon (O/C) isotopes and trace elements in Holocene and Quaternary speleothems. Six speleothem samples were collected from caves in the northern Vietnam . Four Holocene samples have been dated with 20-30-year precision by sector field-ICPMS, Electron Thermo Element II, housed at the Department of Geosciences, NTU. The dates of other two ones are ca. 300 ka. Measurement of O/C isotopes is in progress on Thermo Delta Plus and Thermo MAT 253 at the Department of Geosciences, NTU. A new field trip is proposed in March of 2006 to collect more high-quality samples in the northern Vietnam .

(b) High-precision monthly-resolution records of O/C isotopes and trace metals in living and fossil corals in Taiwan , and central and southern Vietnam . Seawater samples and living Porites coral heads have collected from Nanwan of southern Taiwan , Son Tra Island of central Vietnam and Con Dao Island of southern Vietnam . Several coral, collected in the Sumatran Islands , were requested from Caltech of USA. Analyses of O/C isotopes and trace metals with weekly to monthly resolution are in progress.