4:22 PM - 4:37 PM
[MIS16-09] Paleoenvironmental reconstruction of the North Pacific Subtropical Mode Water
at the Last Glacial Maximum based on carbon- and oxygen-isotope composition of
fossil brachiopod Basiliola lucida
Keywords:North Pacific Subtropical Mode Water, Last Glacial Maximum, carbon-isotope composition, oxygen-isotope composition, brachiopod
The North Pacific Subtropical Mode Water (STMW) is distributed along the southern side
of the Kuroshio Current and the Kuroshio Extension in the western North Pacific Ocean. Long-term
oceanographic data along the 137°E meridian south of Japan and profiling float CTD data from the
International Argo Program showed that the STMW is absorbing a large amount of heat and CO2
from the atmosphere to ocean, indicating that the STMW can serve as heat and CO2 reservoir under
recent global warming. Therefore, it is likely that the STMW has acted as an important
positive/negative feedback on climate change at various time scales. However, a little is known
about the behavior and changes in physical properties and chemical composition of the STMW on a
long-term scale because instrumental data recording temporal variations of the STMW is limited to
those after 1900’s. Consequently, proxy records of the past STMW are required to improve and
deepen our knowledge about dynamics of the STMW and the associated feedback effect. It is known
that modern brachiopod Basiliola lucida around the Ryukyu Islands is mainly living in a range of the
STMW, namely on the shelf slope at water depths of 200–300 m and that carbon- and oxygen-
isotope composition of this brachiopod shells is useful to reconstruct the dissolved inorganic carbon
concentration and seawater temperature of the ambient seawater. In this study, we first show an
optimal way to reconstruct secular variations in the physical properties and chemical composition of
the STMW with high accuracy and precision using carbon- and oxygen-isotope composition of
semi-fossil B. lucida shells collected off the Ryukyu Islands. Then, we apply the way to fossil B.
lucida shells dated to the Last Glacial Maximum (LGM). Finally, we will present the B. lucida-based
seawater temperature/salinity and dissolved inorganic carbon concentration of the STMW at the
LGM.
of the Kuroshio Current and the Kuroshio Extension in the western North Pacific Ocean. Long-term
oceanographic data along the 137°E meridian south of Japan and profiling float CTD data from the
International Argo Program showed that the STMW is absorbing a large amount of heat and CO2
from the atmosphere to ocean, indicating that the STMW can serve as heat and CO2 reservoir under
recent global warming. Therefore, it is likely that the STMW has acted as an important
positive/negative feedback on climate change at various time scales. However, a little is known
about the behavior and changes in physical properties and chemical composition of the STMW on a
long-term scale because instrumental data recording temporal variations of the STMW is limited to
those after 1900’s. Consequently, proxy records of the past STMW are required to improve and
deepen our knowledge about dynamics of the STMW and the associated feedback effect. It is known
that modern brachiopod Basiliola lucida around the Ryukyu Islands is mainly living in a range of the
STMW, namely on the shelf slope at water depths of 200–300 m and that carbon- and oxygen-
isotope composition of this brachiopod shells is useful to reconstruct the dissolved inorganic carbon
concentration and seawater temperature of the ambient seawater. In this study, we first show an
optimal way to reconstruct secular variations in the physical properties and chemical composition of
the STMW with high accuracy and precision using carbon- and oxygen-isotope composition of
semi-fossil B. lucida shells collected off the Ryukyu Islands. Then, we apply the way to fossil B.
lucida shells dated to the Last Glacial Maximum (LGM). Finally, we will present the B. lucida-based
seawater temperature/salinity and dissolved inorganic carbon concentration of the STMW at the
LGM.