Plio-Plestocene benthic £_18O and grain size records in the South China Sea
Chiu Wei-Yi
Abstract
The benthic £_18O from Site 1143 is highly coherent with the Earth”¦s orbit(ETP) both at the obliquity and precession bands for the last 5 Myr, and at the eccentricity band for the last 2 Myr. A comparison of the benthic £_18O between the Atlantic (ODP 659) and the East and West Pacific (846 and 1143) reveals that the Atlantic-Pacific benthic oxygen isotope difference ratio (”µ£_18OAtl-Pac) displays an increasing trend in three time intervals: (i) 3.6-2.7 Ma, (ii) 2.7-2.1 Ma and (iii) 1.5-0.25 Ma. Each of the intervals begins with a rapid negative shift, and followed by a long period with an increasing trend, corresponding to the growth of the Northern Hemisphere ice sheet.
After 2.5 Ma, obliquity rather than precession had become the dominant force controlling the vertical structure or thermohaline circulation in the paleo-ocean.
The grain-size distributions over the last 1.8 Ma enable a new interpretation of their connections to sea-level variations and East Asian monsoon strength.
End-member modelling indicates that the sediments can be described as a mixture of three end-members. Grain-size variations in the Pleistocene section of the cores indicate a multiple-stage evolution: (i) from 1.8 to 1.25 Ma, the downcore grain-size variations are low but show a correspondence between monsoon rainfall intensity and the fine grain-sized fluvial inputs; (ii) from 1.25 to 0.9 Ma, there is an increase (decrease) in the intermediate (fine) end-member that is associated with the onset of a stronger summer monsoon and modest shelf reworking; (iii) from 0.9 to 0 Ma the grain-size record is dominated by global sea-level variations.
Reference
Tian J., Wang P., Cheng X., Li Q. (2002) Astronomically tuned Plio^Pleistocene benthic £_18O record from South China Sea and Atlantic-Pacifc comparison. Earth and Planetary Science Letters, 203, 1015-1029
Sebastien Boulay, Christophe Colin, Alain Trentesaux, Stephane Clain, Zhifei Liu and Christine Lauer-Leredde (2007) Sedimentary responses to the Pleistocene climatic variations recorded in the South China Sea. Quaternary Research, 68, 162-172