ALBERT

Description: The South China Sea is the largest marginal sea of southeastern Asia, lying presently under the influences of the Western Pacific Warm Pool and Asian monsoon systems. Sediment cores from this area provide high-resolution records for interpreting millennial- to centennial-scales paleoclimatic changes expressed in the western Pacific. Here we present results of high-resolution paleoceanographic data including planktic foraminifer fauna sea surface temperature (SST) anddepth of thermocline (DOT) estimates along with foraminifer stable isotopes, alkenone SST estimates analyzed froma core takenfrom the southern South China Sea (SCS) near Wan-An Shallow (IMAGES III 1997 cruise core MD97-2151). The intervals of the record presented here cover the past two glacial Terminations (centering at ab. 12,000 and 128,000 yrs B.P.). Our analyses of SST estimates by using planktic foraminifer transfer functions with paralleling measurements of alkenone SST methods all show events of rapid cooling reversals occurrring during the Termination I concurrent with the Younger Dryas (ab. 13-11 kyr B.P.), and Heinrich events reported previously from GISP2 ice core and North Atlantic core studies. Our reconstructions indicate also that theTermination I inthe southern SCS is characterized by a change of monsoon wind systems, with probably much stronger winter monsoon winds in the glacial period. We also found that during the Termination II, there was no such climatic reversal analogous to the Younger Dryas. During oxygen isotope stage 5, our estimates of SST and DOT, and abundances of deep-dwelling planktic foraminifer species all show large-amplitude variations, indicating an instability of monsoon climate during the interglacial period. Our studies also highlight the climatic teleconnections shown by the linkage of the SCS and other regional records for examples from the East China Sea and Chinese loess.

Description: The core samples of mid-ocean-ridge basalts (including Indian and Pacific type) recovered from the Southeast Indian Ridge (SEIR) area near the Australian Antarctic Discordance during Ocean Drilling Program Leg 187 were studied using rock magnetism, mineralogy, and petrography methods. On the basis of thermomagnetic analyses and low-temperature magnetometry, the dominant magnetic carrier in most of the basalt samples (pillow basalts) is characterized as titanomaghemite, which presumably formed by low-temperature oxidation of primary titanomagnetite. Some samples from unaltered massive basalts contain nearly unoxidized titanomagnetite as the main magnetic mineral. A metadiabase sample showing greenschist facies metamorphism contains magnetic minerals dominated by magnetite. The pillow basalts contain titanomaghemite ranging from stable single-domain to pseudosingle-domain (PSD) grains, and the majority are characterized by a single stable component of remanence. The massive basalts show hysteresis features of larger PSD grains and contain a very low coercivity remanence. The values of natural remanent magnetization (NRM) of the samples in this SEIR area are on the same order as those of other oceanic ridge basalts. They show a general decreasing trend of NRM with increasing crust age. However, the values of NRM show no correlation either with the tectonic zonations (Zone A vs. Zone B) or with the mantle provinces (Pacific vs. Indian types).