Abstract:
Oxygen and carbon isotopes of both benthic and planktonic foraminifera
were measured in an IMAGES giant piston core (MD01-2421, 36°01.4'N, 141°46.8'E,
\2224m. water depth, length 45.82m) collected from the area off the east coast
of central Japan, in the northwest Pacific. Paleo-SST at the core site for the
last 144,000 years was calculated from oxygen isotope differences between
benthic and
... planktonic foraminifera, based on an assumption of latitudinal
movements of the oceanic condition similar to the present day.
Samples for oxygen and carbon isotope measurements of foraminiferal tests were
collected at about 15 cm intervals. Each sample was taken using a plastic cube
of 2.2 cm3. The sample was dried with a freeze drier and washed using a 63 um
sieve after ultrasonic cleaning. About 40 individuals for planktonic and 20
specimens for benthic foraminifera were selected with a test size range
between 150 and 250 um for Globigerina bulloides and Bulimina aculeata, and
those between 250 and 355 um for Globorotalia inflata and Uvigerina spp. The
procedure for the isotope measurement is identical to that described by Oba
and Murayama (2004).
Abstract;
Very large sea surface temperature (SST) fluctuations are expected in the
northwest Pacific Ocean between glacial and interglacial periods due to
possible latitudinal migrations of the steep SST front between the Oyashio and
Kuroshio Currents. To reconstruct the SST changes for the past 144,000 years,
we conducted high-resolution oxygen and carbon isotope analysis of both
benthic and planktonic foraminifera from an IMAGES core off central Japan.
Using a newly developed method [Oba, T., Murayama, M., 2004. Sea surface
temperature and salinity changes in the northwest Pacific since the last
glacial maximum. J. Quat. Sci. 19(4), 335-346] for the reconstruction of the
SST, we have found very large (~20°C) SST fluctuations, with minimum SSTs of
3-4°C during Marine Isotope Stage (MIS) 2 and the MIS 6/5e transition, and
with peak SSTs of 22-23°C during early MIS 1 and the MIS 5a/4, 5c/5b and 5e/5d
transitions. The SSTs varied in parallel with changing carbon isotope
differences between Globorotalia inflata and Globigerina bulloides, which
suggests that the SST changes were primarily caused by the latitudinal
displacements of the Kuroshio-Oyashio Currents. We have also found that
northward shifts of the Kuroshio Current lagged up to several thousand years
at these transitions. Strong correlation between the SST shifts and orbital
forcing indicates that the latitudinal displacement of the Kurosho-Oyashio
Currents were influenced by summer insolation at 65N associated with
ENSO-like climatic variability in the tropical Pacific. 
