HR: 1340h
AN: PP13A-0597    [Abstracts]
TI: Millennial-scale variabilities of subsurface temperature and thermocline depth in the Sea of Okhotsk during the late Quaternary
AU: * Ikehara, M
EM: ikehara@cc.kochi-u.ac.jp
AF: Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku, 783-8502 Japan
AU: Oba, T
EM: oba-tad@ees.hokudai.ac.jp
AF: Graduate School of Environmental Earth Science, Hokkaido University, W5N10, Kita-ku, Sapporo, 060-0810 Japan
AU: Kawamura, K
EM: kawamura@lowtem.hokudai.ac.jp
AF: Institute of Low Temperature Science, Hokkaido University, W8N19, Kita-ku, Sapporo, 060-0819 Japan
AB: The Sea of Okhotsk is characterized by an extended seasonal sea-ice cover and is considered as a possible source area of the North Pacific Intermediate Water (NPIW). Therefore, the reconstruction of past sea surface temperature (SST) and subsurface structures in the Sea of Okhotsk is indispensable for the study of the past variations in the NPIW formation and of the detailed climate changes in the Northwest Pacific. We measured the concentration of alkenones in the Sea of Okhotsk surface sediments to understand the distribution of the marine biomarkers. We also produced the detailed oxygen isotopes of planktonic and benthic foraminifers and alkenone SSTs for a core XP98-PC1 (51ø00'N, 152ø00'E, 1107m water depth) with high sedimentation rate (~10 cm/kyr), which was collected from the slope off Kamchatka Peninsula in the Sea of Okhotsk. Alkenones are detected in the entire Okhotsk Sea including the northwestern continental shelf. The concentrations of alkenones are not shown a systematic distribution pattern in the Sea of Okhotsk. Calculated alkenone SSTs in the Sea of Okhotsk represent summer to autumn SST in the 0-20 m interval, based on the comparison of the modern SST profiles at the each site. The alkenone records indicated that the SSTs were almost constant throughout the Holocene at approximately 8.5øC at the site of core XP98-PC1. Alkenone SSTs are also lowered by 2øC at the early deglaciation and a similar warm SST were detected in the glacial periods in the Okhotsk Sea. Oxygen isotopes of planktonic foraminifera (Grobigerina bulloides and Neogloboquadrina pachyderma), however, showed the short-term fluctuations during the last 70 kyrs. Because the average depth habitat of N. pachyderma was estimated for ~100 m in the southern Okhotsk Sea (Bauch et al., 2002), the planktonic oxygen isotope variabilities were mainly caused by a rapid change in subsurface temperatures due to thermocline depth oscillation. During the Holocene, the subsurface temperature variability may correspond to the Polar Circulation Index (PCI) in the Greenland ice core (GISP2) (Mayewski et al., 1997) and the regional sea level changes (Razjigaeva et al., 2004). Warmer subsurface temperature in the Sea of Okhotsk may correspond to the warmer climate signals of PCI and high sea level stand. Therefore the millennial scale oscillations of subsurface temperature and thermocline depth were periodically occurred in the Sea of Okhotsk.
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting