論文 / 著書情報
Article / Book Information
題目(和文)

実験室培養実験に基づく陸生カタツムリ炭酸塩殻の同位体シグナルがもつ環境情報

Title(English)

Environmental implication from isotopic signatures of land snail shellcarbonate based on laboratory culturing experiment

著者(和文)ZHANGNAIZHONG

Author(English)

Naizhong Zhang

出典(和文)

学位:博士（理学）,学位授与機関:東京工業大学,
報告番号:甲第9679号,授与年月日:2014年12月31日,
学位の種別:課程博士,
審査員:吉田 尚弘,大河内 直彦,山田桂太,豊田栄,上野Citation(English)

Degree:,Conferring organization: Tokyo Institute of Technology,
Report number:甲第9679号,
Conferred date:2014/12/31,
Degree Type:Course doctor,Examiner:,,,,

学位種別(和文)

博士論文

Category(English)

Doctoral Thesis

種別(和文)

論文要旨

Type(English)

Summary

Powered by T2R2 (Tokyo Institute Research Repository)雄一郎

（博士課程）Doctoral Program論 文 要 旨ＴＨＥＳＩＳ ＳＵＭＭＡＲＹ

専攻：
Department of

学生氏名：
Student’s Name

化学環境学
Zhang Naizhong

専攻

申請学位（専攻分野）： 博士
Academic Degree Requested

指導教員（主）：Academic Advisor(main)（Science吉田尚弘 教授

Doctor of）

指導教員（副）：Academic Advisor(sub)要旨（英文 800 語程度）
Thesis Summary （approx.800 English Words ）Land snails are strictly local indicators of terrestrial environment and are considered as archive materials instudying the paleo environment, especially in the Quaternary period. Up to now, isotopic tools such as δ13C, δ18O
and clumped isotope thermometry (Δ47) are widely applied in reconstructing the environment conditions such as
paleo-climate changes, shift of vegetation distribution, rainfall amount, and so on. However, the knowledge ofthe relationships between these isotopic signatures and relative environment conditions are still very poor, which
could limit their application in better understanding the paleo environment. Therefore, laboratory cultivation ofland snails under various controlled environment is necessary.
In this study, eight adult land snails of Acusta despecta sieboldiana, which is widely distributed around
Japan and Korea, were collected from Yokohama, Japan. Their offspring were cultured from eggs to adults
around 6–8 months under various controlled environments. Briefly, the snails grew up at three different
temperatures (20 °C, 25 °C, and 30 °C), two kinds of diet (Cabbage, δ13C = -28.4‰; Corn, δ13C = -12.0‰),
three kinds of water (Tap water, δ18O = -8.2‰; Canadian ice water, δ18O = -12.9‰ and Oceanic deionized water,δ18O = -0.1‰), and two kinds of calcium sources (calcium carbonate and calcium phosphate). Finally, shell δ13C,
δ18O and clumped isotope values were measured by isotope ratio mass spectrometry (IRMS, MAT 253 or DeltaXL); organic δ13C and water δ18O values were measured by two different cavity ring-down spectroscopy (CRDS,Picarro), or by IRMS (Delta V).
For carbon isotopic composition (δ13C) of land snail shell carbonate, we confirmed it derives from threesources: diet, atmospheric CO2, and ingested carbonate (limestone). Herein, we consider the influences ofmetabolic rates and temperature on the carbon isotopic composition of the shell carbonate. Based on previousworks and on results obtained in this study, a simple but credible framework is presented for discussion of howeach source and environmental parameter can affect shell carbonate δ 13C values. According to this frameworkand some reasonable assumptions, we have estimated the contributions of different carbon sources for each snail
individual: for cabbage (C3 plant) fed groups, the contributions of diet, atmospheric CO2 and ingested limestone
respectively vary as 66–80%, 16–24%, and 0–13%. For corn (C4 plant) fed groups, because of the possible foodstress (lower consumption ability of C4 plant), the values vary respectively as 56–64%, 18–20%, and 16–26%.
Moreover, we present new evidence that snails have discrimination to choose different plants as food. Therefore,
we suggest that food preferences must be considered adequately when applying δ13C in paleo-environment
studies.
For oxygen isotopic composition (δ18O), we discussed the effectiveness of flux balance model raised by
Balakrishnan and Yapp (2004). However, the complex and variable environmental parameters, such as relativehumidity and ingested water isotope composition, can restrict its application in the modern and paleo studies.
Secondly, we observed a fairly good and common relationship (slop = 0.69; R2 = 0.98) between snail shell δ18O
values and body water δ18O values at various temperatures, suggesting the shell is directly precipitated from thebody fluid. Nevertheless, the deviation of this slope from unity (slope = 1; isotopic-equilibrated precipitation),
indicates that potential non-equilibrated precipitation or vital effect exists. In addition, these relations seem to be
only controlled by the environmental parameter such as temperature and evaporation, rather than the ingested
limestone, input water (e.g. different diet) and growth rate. Thirdly, snails living in some non-optimal conditions(e.g. low temperature) can adapt their biological behaviours to be accustomed to the environment, which willaffect the oxygen isotope compositions in body fluid and shells. Additionally, we observed that evaporation
effect can largely enrich 18O in snail body water, and in further produce a more enriched δ18O values thanexpected values of isotopic equilibrated precipitation.
For the clumped isotope (∆47), we present the first empirical calibration of the clumped isotope
thermometer based on land snails in-laboratory cultured in a temperature range of 20 °C to 30 °C.

The data

were normalized into the absolute reference frame by the empirical transfer function (ETF) suggested by Denniset al. (2011). The shell clumped isotope data follows a relation to the growth temperatures presented as:
Δ47 = 0.0511 × 106/T2 + 0.1022 (with Δ47 in ‰ and T in K; R2 = 0.73)
The slope is consistent with the published ones digested at 25 °C; and different to those digested at 90 °C.
Besides, our data show a discrepancy (~0.02‰) to those re-calibrated data using two-point secondary transfer
functions (e. g. Ghosh et al., 2006; Dennis and Schrag, 2010), however, the values are consistent with those
directly referenced to the ETFs (e.g., Henkes et al., 2013; Wacker et al., 2014), suggesting the absolute reference
frame based on isotopic equilibrated CO2 gas at various temperatures is effective. Therefore, we encourage morestudies about empirical calibration curves should be carried out based on directly referencing to the absoluteframe. Moreover, we confirmed that land snail shells are precipitated in isotopic equilibrium condition (forclumped isotopes), and the clumped isotope data are not related to the various bulk isotopic sources such as
different food, or water sources, and also has no relation to the ingested carbonate or snail growth rate. Inaddition, we confirmed the size effect reported by Wacker et al. (2013), that is, to those digested in phosphoricacid at 25 °C, the sample size less than 6.5 mg will present more positive data, which sometimes can be as large
as 0.07‰.
In summary, this study permits us to comprehensively understand the relation between isotopic signaturesof land snail shells and their living environment. The next step is to test these relations from studying the living
snails in natural and then try to apply these implications in the Quaternary land snail fossils. All in all, ourresearches prompt the field of paleo environment reconstruction from studying the isotopic composition of landsnail fossils.
備考 : 論文要旨は、和文 2000 字と英文 300 語を 1 部ずつ提出するか、もしくは英文 800 語を 1 部提出してください。
Note : Thesis Summary should be submitted in either a copy of 2000 Japanese Characters and 300 Words (Engｌish) or 1copy of 800
Words (English).
注意：論文要旨は、東工大リサーチリポジトリ（T2R2）にてインターネット公表されますので、公表可能な範囲の内容で作成してください。
Attention: Thesis Summary will be published on Tokyo Tech Research Repository Website (T2R2).