Nagoya University · Earth and Planetary Sciences
Professor Takeshi Nakatsuka's research lab specializes in paleoclimatology and marine biogeochemistry, focusing on reconstructing past climate and oceanographic conditions using stable isotope analysis in tree rings, marine sediments, and water masses. The lab investigates regional climate variability in Asia—particularly the Indian monsoon and North Pacific Ocean systems—through isotopic signatures in cellulose and organic matter. Key research directions include understanding monsoon dynamics, intermediate water formation, and nutrient cycling in marine environments using geochemical proxies such as δ18O, δ13C, and δ15N. The lab also examines the role of physical processes like brine rejection and tidal mixing in shaping marine carbon and nutrient cycles.
Figures are computed from collected data and may differ slightly.
Abstract. We have constructed a regional tree-ring cellulose oxygen isotope (δ18O) record for the northern Indian sub-continent based on two new records from northern India and central Nepal and three published records from northwestern India, western Nepal and Bhutan. The record spans the common interval from 1743 to 2008 CE. Correlation analysis reveals that the record is significantly and negatively correlated with the three regional climatic indices: all India rainfall (AIR; r = −0.5, p <
Dissolved and particulate organic carbon (DOC and POC) were measured in water columns of the Sea of Okhotsk together with other hydrological and chemical properties, including phytoplankton pigments (Chl‐a) and stable carbon isotopic ratios (δ 13 C) of POC. Transects from shelf to slope off the northeast coast of Sakhalin showed the existence of a cold‐water mass in the intermediate layer on the slope area having a density of 26.7–27.0 σθ, which is equivalent to the cold and dense water on the s
Stable carbon and nitrogen isotopic ratios (δ 13 C and δ 15 N) of organic matter were measured in three sediment cores from deep basins of the Bering Sea to investigate past changes in surface nutrient conditions. For surface water reconstructions, hemipelagic layers in the cores were distinguished from turbidite layers (on the basis of their sedimentary structures and 14 C ages) and analyzed for isotopic studies. Although δ 13 C profiles may have been affected by diagenesis, both δ 15 N and δ 1
We found a water mass characterized with enormous turbidity and very low temperature in the intermediate layer of the Sea of Okhotsk in September 1999. In June 2000 and September 1999, the cold and turbid water mass was also located in bottom boundary layer on the northwestern shelf region, where sea ice had rejected large amounts of brine waters in winter. Cold brine waters settled on the bottom of shelf must have entrained sedimentary particles, including newly produced organic matter, due to
Oxygen and carbon isotopic ratios (δ18O and δ13C) were analyzed for cellulose extracted from tree rings of 5 oak trees (Quercus crispula) and 4 fir trees (Abies sachalinensis) standing in a 1 ha plot of a sub-boreal conifer-hardwood mixed forest, northern Japan. The δ18O variations were well correlated between individual trees of Q. crispula (canopy trees) and A. sachalinensis (recently grown-up sub-canopy trees), although A. sachalinensis had about 1 ‰ higher δ18O values than Q. crispula on ave
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