11:50 AM - 12:10 PM
★ [MIS28-04] Glacial to Holocene changes in watermass structure in the western North Pacific
Keywords:watermass structure, LGM, benthic foraminifera, NW Pacific
In the modern North Pacific, no deep water is formed due to well-established halocline. Instead, well-ventilated watermass called North Pacific Intermediate Water (NPIW) at depths of about 300 to 800 m is distributed. The glacial Pacific Ocean had two water masses: well-ventilated and nutrient-depleted glacial North Pacific Intermediate Water (GNPIW) above ~2000 m and less-ventilated and nutrient-enriched deep water below ~2000 m (Keigwin, 1998; Matsumoto et al., 2002). Compared to today, the NPIW volume under glacial conditions was significantly higher extending down to about 2000 m, exhibiting pronounced hydrographic boundary at ~2000 m. The glacial Pacific watermass structure was reconstructed based on stable carbon isotopes of epibenthic foraminifera. However, there are several problems in the North Pacific: (1) poor calcium carbonate preservation particularly during the late Holocene hampers core-top calibration; (2) rare occurrence of epibenthic foraminiferal species (e.g., Cibicidoides wuellerstorfi) in the subarctic Pacific; (3) taxonomy of Cibicidoides sp. in the subarctic Pacific is ambiguous. Core MD01-2420 obtained from the western North Pacific off Japan was with high sedimentation rates (>20 cm/kyr) and no radiocarbon age reversal. Nearly continuous occurrence of Cibicidoides wuellerstorfi was confirmed. In this presentation, we will discuss on the significance and potential of glacial watermass structure reconstruction in the NW Pacific using depth-transect cores near Core MD01-2420.