HR: 1340h
AN: PP23B-1417    [Abstracts]
TI: Holocene Pulleniatina Minimum Event: A Paleoecological Enigma in the Western Pacific
AU: * Lin, Y
EM: r92224205@ntu.edu.tw
AF: National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Wei, K
EM: weiky@ntu.edu.tw
AF: National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Chen, C
EM: b91204044@ntu.edu.tw
AF: National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Shieh, Y
AF: National Taiwan Museum, No.2, Xiangyang Road, Taipei, 100 Taiwan
AU: Mii, H
EM: t44006@cc.ntnu.edu.tw
AF: National Taiwan Normal University, No. 162, Sec.1, HoPing E. Road, Taipei, 106 Taiwan
AU: Chen, Y
EM: ygchen@ccms.ntu.edu.tw
AF: National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AB: During the past decade, paleoceanographers have reported the so-called ��{\it Pulleniatina} Minimum Event (PME)�� at 4.5-3.0 ka from the Okinawa Trough and South China Sea. Several paleoenvironmental and tectonic causes have been invoked to explain the sudden decrease or disappearance of the planktonic foraminifer {\it Pulleniatina obliquiloculata} in such marginal seas. All these interpretations, however, might be misleading because of limited geographic observation and inappropriate proxies. In this study, we report new data from a suite of cores located from the Southern Okinawa Trough to the upper reach of the Kuroshio: MD012403 ($123.2\deg$E, $25.3\deg$N, water depth 1420 m), OR102-3P ($121.3\deg$E, $22.3\deg$N, water depth 1309 m) and MD982188 ($123.5\deg$E, $14.8\deg$N, water depth 730 m). All these three cores witnessed the PME during the period of 5.0 to 3.0 ka. We reconstructed the thermocline hydrography during the past 11 kyr at MD012403 and MD982188 by measuring the oxygen isotope values of the surface-dwelling foraminifer {\it Globigerinoides ruber}, and thermocline-dwelling {\it Globorotalia menardii}, {\it N. dutertrei} and {\it P. obliquiloculata}. No distinct or consistent anomalies can be identified in the $\delta$18O and $\delta$13C values in either core during this period. The reciprocal patterns in relative abundance between {\it P. obliquiloculata} and {\it N. dutertrei} can only be observed in MD012403 (Southern Okinawa Trough) and OR102-3P (off eastern coast of Taiwan). In MD982188 (western Philippine Sea), the relative abundances of {\it N. dutertrei} and {\it Globigerina bulloides} increase only after the PME. Accompanying the lightening $\delta$18O values of {\it N. dutertrei} and {\it P. obliquiloculata}, this faunal change implies a shoaling of the thermocline after 3 ka. These data shed some new lights on the nature of the PME: (1) PME is not a phenomenon restricted in the marginal seas, but widespread at least to the upper reach of the Kuroshio in the margin of the Western Pacific Warm Pool (WPWP). (2) No distinctive anomalies in the planktic isotope values are associated with the PME. This implies that no temperature/salinity changes of the surface waters were involved in this event. (3) The thriving of {\it N. dutertrei} during the PME in the subtropical sites might be a result of regional upwelling when surface waters were better mixed. In other words, {\it P. obliquiloculata} might be better adapted to the well-stratified oligotrophic tropical water than the opportunistic species {\it N. dutertrei}. The inability of using conventional paleoceanographic proxies to characterize this event implies our lack of appropriate understanding of this particular organism, and challenges the validity of our current usage of transfer functions or Modern Analog Technique in the western Pacific. New proxies (such as Mg/Ca ratios of multiple planktic foraminifers) and microfossil census data from a more extensively geographic coverage of the upper reach of the Kuroshio are needed to resolve this PME enigma.
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 4576 Western boundary currents
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting