BPT03-P01

Room:Convention Hall

Time:May 26 18:15-19:30

Intraspecific variation in isotopic composition and trace element concentrations of Pleistocene brachiopods
TAKIZAWA, Mamoru1∗ ; TAKAYANAGI, Hideko1 ; YAMAMOTO, Koshi2 ; SASAKI, Keiichi3 ; IRYU, Yasufumi1
1Graduate School of Science Tohoku University, 2 Graduate School of Environmental Studies Nagoya University, 3 The Facultyof Fine Arts and Informatics Kanazawa Gakuin University
Carbon and oxygen isotope composition (δ 13 CV P DB and δ 18 OV P DB ) in fossil rhynchonelliform brachiopod shells has beenused as a powerful tool to reconstruct paleoenvironmental conditions. Several petrographic and chemical techniques, such astransmitted light microscopy, cathodoluminescence, scanning electron microscope (SEM), and trace element analysis were applied in those studies to select brachiopod shells that have not been diagentically altered and retain their original isotopic andchemical composition. However, there are few references that showed how the isotopic and chemical composition is modified
by several processes operating during meteoric diagenesis. Therefore, we conducted a comparative study of isotopic composition and trace element (Na, Mg, Sr, Mn and Fe) concentrations in modern and fossil brachiopod (Kikaithyris hanzawai ) shells.
The modern and fossil specimens were collected off Amami-o-shima and the Upper Pleistocene Wan Formation in Kikai-jima,respectively. The isotopic profiles of inner shell surface along the maximum growth axis can be divided into three stages thatwere likely to be related to changes in life mode and shell morphology of this species. The trace element concentrations areirregularly varied on the sampling transects. There are some spots on the sampling transects, where Mn and Fe concentrations
are anomalously high. These spots are likely generated by metabolic factor(s) because they are not associated with decreasesin δ 13 CV P DB and δ 18 OV P DB values which are indicative of meteoric diagenesis. Our results suggest that brachiopods withcomplicated shell morphology which may be related to the change in life mode during the growth are not suitable for paleoenvironmental reconstructions based on their isotopic composition. It is also suggested anomalously high Mn and Fe concentrations
cannot be used to identify diagenetically altered portions within brachiopod shells.
Keywords: carbon isotope, oxygen isotope, trace element concentration, brachiopoda, proxy, Pleistocene

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BPT03-P02

Room:Convention Hall

Time:May 26 18:15-19:30

Assessment of skeletal compositions in A. digitifera coral as temperature proxies
SAKATA, Shoko1∗ ; INOUE, Mayuri1 ; TANAKA, Yasuaki2 ; NAKAMURA, Takashi3 ; SAKAI, Kazuhiko2 ;IKEHARA, Minoru4 ; SUZUKI, Atsushi5
1Graduate School of Natural Science and Technology, Okayama University, 2 Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, 3 Faculty of Science, University of the Ryukyus, 4 Center for Advanced Marine Core Research,
Kochi University, 5 Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST)

Introduction
While biogenic carbonates such as foraminifera and coccolithophorid are attractive tools to reconstruct the past environments,
scleractinian corals also provide environmental data around tropical to subtropical region with much higher time resolution. For
example, oxygen isotope ratio (δ 18 O) and strontium-calcium (Sr/Ca) ratio have been used for reconstructing sea surface temperature and salinity by generally using Porites spp. In this study, we investigate the effect of temperature on skeletal δ 18 O andSr/Ca ratio in A. digitifera corals for evaluating temperature proxies for one of paleoceanographic applications.
Materials and Methods
Three colonies of A. digitifera were collected at Sesoko Island, Okinawa, Japan. We reared coral samples in seawater with 5
different temperature settings (18, 21, 24, 27, 30 ℃) and set 2 tanks in each temperature treatment (3 coral nubbins× 3 colonies
in a tank). Calcification rate of coral nubbins was measured by buoyant weight technique every two weeks during the period ofexperiments. Oxygen and carbon isotope ratios (δ 18 O and δ 13 C) were analyzed by a stable isotope ratio mass spectrometer, andthe ratios of trace elements (Sr/Ca, Mg/Ca, U/Ca and Ba/Ca) were measured by an inductively coupled plasma mass spectrometer(ICP-MS).
Results and discussion
Skeletal δ 18 O of corals is often used as a seawater temperature proxy. In this study, a strong negative correlation was foundbetween δ 18 O and water temperature, and the temperature dependency was comparable with that of Porites spp. Thus δ 18 O ofA. digitifera is suggested to be useful as a temperature proxy without clear influence from growth rate. A negative correlation
was also observed between Sr/Ca ratio and temperature, which is compatible with that of Porites spp., although the correlation
was weaker than δ 18 O. But variation of Sr/Ca ratio was not controlled by skeletal growth rate, suggesting that the dominantfactor controlling the skeletal Sr/Ca ratio is water temperature. Thus, skeletal δ 18 O and Sr/Ca ratio of Acropora spp., at least
A. digitifera , can be useful as a proxies for seawater temperature as well as Porites spp., although more investigation would berequired for Sr/Ca-thermometer of Acropora spp.
Keywords: coral skeleton, temperature, proxy1/1

BPT03-P03

Room:Convention Hall

Time:May 26 18:15-19:30

Reliable stable isotopic compositions of individual Uvigerina spp. as sea environmental
proxy
TANAKA, Takashi1 ; ISHIMURA, Toyoho1∗ ; HARADA, Naomi2 ; KIMOTO, Katsunori21

National Institute of Technology, Ibaraki College, 2 JAMSTEC

The stable carbon and oxygen isotopic composition (δ 13 C, δ 18 O) of benthic foraminiferal carbonate shells have been used toreconstruct the past sea environment. Especially, Uvigerina spp. is often used to estimate the sea level changes and deep-sea
circulations. However, it is difficult to analyze the isotopic compositions of individual foraminifera in the traditional analyticalmethod, and thus the reliability of δ 13 C and δ 18 O of individual Uvigerina spp. as sea environmental proxy is still unclear. In
this study, the isotopic compositions of individual U. akitaensis and U. ochotica were analyzed by using the micro-scale isotopic
analytical system.
Surface sediment samples were collected from the four sites in the Sea of Okhotsk during cruise MR06-04 of R/V Mirai(JAMSTEC) in October 2006. Those samples were cut for each 1 cm (0-8cm below the seafloor) and used in this study. Thenthe living (Rose Bengal stained) individuals of U. akitaensis and U. ochotica from samples were analyzed by the micro-scaleisotopic analytical system (Ishimura et al. 2008).
As a result, the isotopic dispersions of Uvigerina spp. indicated about <+/- 0.2 ‰ for both δ 13 C and δ 18 O in all samplingsites. In addition, isotopic values of Uvigerina spp. showed almost constant values in same species regardless of sediment depth,
individual weight, and variation of shell structure. The observed homogeneous isotopic compositions of Uvigerina spp. werecomparable with isotopic homogeneity and dispersions of NBS-19 (international isotopic standard). Therefore, we concluded
that the individual Uvigerina spp. have highly reliable isotopic composition as sea environmental proxy. However, δ 13 C values
represented about 0.7 ‰ differences between U. akitaensis and U. ochotica , thus we have to consider this δ 13 C difference inUvigerina spp. when we reconstruct the past sea environment based on δ 13 C of Uvigerina spp.
Our main conclusion in this study is that the individual Uvigerina spp. have highly reliable stable isotopic compositions as sea
environmental proxy.

Keywords: stable isotope, benthic foraminifera, microscale analysis, Uvigerina

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