Sone T.,Marine Works Japan |
Kano A.,Kyushu University |
Kashiwagi K.,University of Toyama |
Mori T.,Kyushu University |
And 3 more authors.
Island Arc | Year: 2015
The Holocene stalagmite FG01 collected at the Fukugaguchi Cave in Itoigawa, central Japan provides a unique high-resolution record of the East Asian winter monsoon. Because of the climate conditions on the Japan Sea side of the Japanese islands, the volume of precipitation during the winter is strongly reflected in the stalagmite δ18O signal. Examination of the carbon isotopes and the Mg/Ca ratio of FG01 provided additional information on the Holocene climate in Itoigawa, which is characterized by two different modes separated at 6.4 ka. Dripwater composition and the correlation between the δ13C and Mg/Ca data of FG01 indicate the importance of prior calcite precipitation (PCP), a process that selectively eliminated 12C and calcium ions from infiltrating water from CO2 degassing and calcite precipitation. In an earlier period (10.0-6.4 ka), an increase in soil pCO2 associated with warming and wetting climate trends was a critical factor that enhanced PCP, and resulted in an increasing trend in the Mg/Ca and δ13C data and a negative correlation between the δ13C and δ18O profiles. A distinct peak in the δ13C age profile at 6.8 ka could be a response to an increase of approximately 10% in C4 plants in the recharge area. At 6.4 ka, the climate mode changed to another, and correlation between δ18O and δ13C became positive. In addition, a millennial-scale variation in δ18O and pulsed changes in δ13C and Mg/Ca became distinct. Assuming that δ18O and PCP were controlled by moisture in the later period, the volume of precipitation was high during 6.0-5.2, 4.4-4.0, and 3.0-2.0 ka. In contrast, the driest interval in Itoigawa was during 0.2-0.4 ka, and broadly corresponds to the Little Ice Age. © Wiley Publishing Asia Pty Ltd.
Asakawa K.,Japan Agency for Marine - Earth Science and Technology |
Ishihara Y.,Japan Agency for Marine - Earth Science and Technology |
Takahashi Y.,Japan Agency for Marine - Earth Science and Technology |
Sugiyama T.,Marine Works Japan |
Araya A.,University of Tokyo
MTS/IEEE Seattle, OCEANS 2010 | Year: 2010
In order to develop a new optical method to measure the refractive index of seawater having longterm stability, we propose to use a heterodyne Michelson interferometer. We made a prototype, and measured the difference of refractive index of pure water and 3 ‰ saline water in order to evaluate the possibility of the proposed method. The result coincided with the theoretically expected value within an accuracy of ±1.6×10-5. In this paper we present the outline and the results of basic experiments, and discuss the feasibility of the proposed method. ©2010 IEEE.
Inagaki F.,Japan Agency for Marine - Earth Science and Technology |
Hinrichs K.-U.,University of Bremen |
Kubo Y.,Japan Agency for Marine - Earth Science and Technology |
Bowles M.W.,University of Bremen |
And 50 more authors.
Science | Year: 2015
Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ∼40° to 60°C sediment associated with lignite coal beds at ∼1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was indicated by the isotopic compositions of methane and carbon dioxide, biomarkers, cultivation data, and gas compositions. Concentrations of indigenous microbial cells below 1.5 km ranged from <10 to ∼104 cells cm-3. Peak concentrations occurred in lignite layers, where communities differed markedly from shallower subseafloor communities and instead resembled organotrophic communities in forest soils. This suggests that terrigenous sediments retain indigenous community members tens of millions of years after burial in the seabed.
Kitamura A.,University of Shizuoka |
Kobayashi K.,University of Shizuoka |
Tamaki C.,University of Shizuoka |
Yamamoto N.,Marine Works Japan |
And 3 more authors.
Paleontological Research | Year: 2013
The aragonitic micro-bivalve Carditella iejimensis, which is less than 3.5 mm in height and length, inhabits the sediment surface in a submarine cave off the Okinawa Islands, Japan. To evaluate the use of this species as a quantitative paleoceanographic proxy, we analyzed the δ18O values of 50 living C. iejimensis specimens collected from the Daidokutsu submarine cave (ca. 30 m water depth). Results show that most individuals (96%) preserve δ18O values corresponding to the mean annual temperature and δ18O of seawater. The mean δ 18Oshell of the 50 specimens was-1.10 ± 0.18‰. These results, when applied to fossil shell δ18O records from Daidokutsu cave, indicate that its mean annual surface water temperature is about 1°C higher than temperatures during the Medieval Warm Period and the Middle Holocene Climatic Optimum, and that the recent warming is likely exceptional during the past 7000 years. © by the Palaeontological Society of Japan.
Nomaki H.,Japan Agency for Marine - Earth Science and Technology |
Chikaraishi Y.,Japan Agency for Marine - Earth Science and Technology |
Tsuchiya M.,Japan Agency for Marine - Earth Science and Technology |
Toyofuku T.,Japan Agency for Marine - Earth Science and Technology |
And 5 more authors.
Limnology and Oceanography | Year: 2015
We evaluated nitrate utilization by benthic foraminifera at the redox boundary around the sediment-water interface by examining the stable nitrogen isotopic composition (δ15N, ‰ vs. AIR) of amino acids. Five foraminiferal species collected from bathyal Sagami Bay (water depth, 1430 m) in three different sampling seasons were analyzed by determining the δ15N values of amino acids from whole cells and those in test (shell) proteins remaining after H2O2 treatment. The δ15N values of phenylalanine fell within a narrow range (typically 1-3 ‰) in the test proteins of all five species, but the whole-cell d δ15N values of phenylalanine were substantially different from those of the test proteins in two species, Globobulimina affinis (by 6.3 ‰)and Uvigerina akitaensis (by 4.5 ‰). These differences in the δ15N values of amino acids suggest that these species utilize nitrate in their cells probably for nitrate respiration (i.e., denitrification) to adapt to oxygen-depleted environments, as was previously observed in the shallow water benthic foraminifera Ammonia sp. Apparent trophic positions determined using the δ15N values of amino acids also differed between whole cells and tests in G. affinis, U. akitaensis,and Ammonia sp., perhaps because they have different microbial associations, as observed by cellular ultrastructural analysis. These differences in nitrate utilization and microbial associations among benthic foraminifera suggest that foraminifera adapt in diverse ways to conditions in dysoxic to anoxic sediments. © 2015 Association for the Sciences of Limnology and Oceanography.