ALBERT

Description: A high-resolution planktonic foraminifer record from a core recovered from the South China Sea (SCS) (Sonne 17938-2: 19°47.2'N, 117° 32.3E; 2840 m; Delta t c. 250-1000 years) shows rapid millennial-scale changes in the western Pacific marginal sea climate during the last 30,000 years. The SCS is the largest western Pacific marginal sea off the southeast Asian continent, the area today dominated by seasonal monsoon changes. Quantitative analyses of planktonic foraminifer faunal abundance data frorn the core indicate large downcore variations in the relative abundances of the dominant taxa since about 30,000 years ago in the isotope stage 3. Further analyses indicate that the abundance of G. inflata, a good indicator species for cold SST (~13°-19°C) and deep MLD (~100-125 m) waters shows abrupt shifts. During stages 2 and 3, the abundance record of G. infiata tends to be punctuated by quasi-periodie short intervals (~2000-3000 yrs) where its abundance reaches 15% or greater, superimposed on generally low (5-10%) background values. This pattern suggests an instability of surface ocean conditions of the SCS during the past 30,000 years. The abrupt abundance changes of G. infiata correlate well with similar climatic changes observed from a GISP2 ice core 8180, and North Atlantic core DSDP 609 N. pachyderma (s.) and lithic grain abundances during 'Heinrich evcnts'. These results suggest that the millennial-scale variability of climate is not peculiar to the Atlantic region. Apparently, the rapid SCS climatic changes during Heinrich events are driven by effective mechanisms, of particularly the effects of shifts in the latitudinal position of the Siberia High Pressure System.

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: We report 150 kyr records of U37K' sea-surface temperature (SST) and carbonate content with 150-200-year sampling resolution from the southern South China Sea (SCS) in the northern margin of the Western Pacific Warm Pool (WPWP) using IMAGES Core MD972151. The glacial/interglacial SST change is about 5 °C for Termination II (23.5 to 28.5°C) and 4°C for Termination I (24 to 28°C). The simultaneous rise of sea level and U37K' SST during Termination I suggests that sea-level change has played an important role in the SCS SST variability by influencing the exchange of tropical ocean warm surface water with the SCS through the Sunda Shelf region (sill depth 30-50 m). When sea-level drop was less than 30 m relative to today's, MD972151 SST was constantly above 27 °C, a situation which occurred during MIS 5e, part of MIS5c and 5a, and over the last 11 kyr. Sea-level change was also the main control on carbonate content in the SCS; this was lower during low sea-level stands due to the dilution effect of enhanced terrigenous inputs. Within the limitations of our age model, millennial-scale SST oscillations (1.5°C over a few hundred years) occurred frequently during the entire glacial period, correlating reasonably well with the Hulu monsoon record from eastern China and the Dansgaard-Oeschger (D-O) cycles recorded for high-latitude regions in the Northern Hemisphere. Such correlations suggest a possible teleconnection between higher latitude atmospheric forcing and low-latitude climate oscillations in the western Pacific tropical region via the Asian monsoon system. Carbonate content also reveals millennial-scale oscillations during the glacial period, with higher content correlated with higher SST. Millennial-scale fluctuations of SST and carbonate contents at this low-latitude SCS provide additional evidence that high-frequency climate changes are global phenomena.