台灣西南地區現生牡蠣與考古遺址出土牡蠣殼體穩定同位素所反映之水體環境意義

Water environment Inferred from Stable Isotope Compositions of Modern and Archaeological Oyster Shells, Southwest Taiwan

呂香儒(Hsiang-Ju Lu)

指導教授 ： 米泓生博士

國立臺灣師範大學/理學院/地球科學系/碩士(2009年)

摘要

摘要

台灣西南沿海現生牡蠣與台南南關里遺址牡蠣殼體穩定同位素所反映之環境意義
(中華民國九十八年七月)
呂香儒 國立台灣師範大學地球科學研究所
指導教授：米泓生博士

本研究利用養殖於雲林縣金湖漁港潮間帶水域現生長牡蠣（Crassostrea gigas）標本以及水樣標本，探討現生牡蠣殼體氧同位素成份與水體氧同位素數值及其生活水體間之關係。並進一步將現生殼體氧同位素數值與環境之關係，應用於南關里遺址和南關里東遺址牡蠣殼體的氧同位素數值，以了解台灣西南地區環境變遷的情形。標本均由喙部至腹部縱切製成薄片，藉透射光及陰極射線顯微鏡觀察韌帶部殼體的微細構造及保存狀況。
現生牡蠣分別於2008年6、11、12月及2009年3、5月取得，其殼體韌帶部位δ18O數值介於-5.78‰~-0.92‰之間(平均值為-3.90±1.17‰，N=187；1σ)，δ13C數值介於-4.07‰~-0.24‰之間(平均值為-2.15±0.77‰)。不同月份死亡的個體，其氧同位素皆能呈現出輕重不同的變化，符合環境變化的趨勢，從2008年6月至2009年5月的牡蠣氧同位素記錄，可看到完整一年的變化。將不同月份的海水氧同位素與各自月份生長的殼體氧同位素代入氧同位素溫度方程式，可發現計算出的最低溫為19.7°C，與實際海溫的15°C不符，因此推論牡蠣適合生長的環境溫度應高於19°C，低於19°C牡蠣可能會出現停止生長或生長緩慢的現象。
台南科學園區之遺址有兩處，一為南關里遺址，另一為南關里東遺址。南關里遺址年代距今約4100~4700年前，可分為兩個文化層，本研究取自第一文化層的標本有3個，其中保存較好(不發光)的δ18O數值介於-6.91‰~-0.80‰之間(平均值為-3.36±1.65‰，N=83；1σ)，δ13C數值介於-4.08‰~-0.39‰之間(平均值為-1.15±1.35‰)；南關里第二文化層的標本有5個，δ18O數值介於-6.51‰~-0.35‰之間(平均值為-2.89±1.38‰，N=93；1σ)，δ13C數值介於-5.80‰~2.50‰之間(平均值為-1.66±2.07‰)；南關里東遺址年代距今約4200~4700年，標本有3個，δ18O數值介於-7.93‰~-0.37‰之間(平均值為-2.91±1.81‰，N=75；1σ)，δ13C數值介於-5.59‰~-0.56‰之間(平均值為-2.35±1.19‰)。經統計分析，遺址牡蠣較現生牡蠣氧同位素值重1.01‰，顯示距今4100~4700年前溫度較現今低3-5°C，4千多年前呈現較冷的現象。由牡蠣殼體韌帶部氧同位素數值分布可知，考古遺址牡蠣採收季節多為冬天至春天的時候。

關鍵字

穩定同位素 ； 牡蠣 ； 水體環境 ； 考古遺址

並列摘要

ABSTRACT

Water environment Inferred from Stable Isotope Compositions of Modern and Archaeological Oyster Shells, Southwest Taiwan
(July, 2009)
Hsiang-Ju Lu, Department of Earth Sciences, National Taiwan Normal University, Taiwan, Republic of China
Advisor: Dr. Horng-Sheng Mii

The cultivated oysters, Crassostrea gigas, and water samples were collected at Jinhu Fishing Port, Yunlin county in June, November, and December of 2008, and in March and May of 2009. We calibrate the oxygen isotope compositions of modern oyster shells to the temperature, salinity, and oxygen isotope contents of the water they lived in. The archaeological oyster shells were got at Southern Taiwan Science Park. In order to understand climate change in Southwest Taiwan, we analyzed the stable isotope compositions of modern oyster shells compared to those of archaeological oyster shells. The oyster shells were cut from dorsum to abdomen and were made into thin sections. Microstructure of cross- sections of the ligamental area were observed under the microscope with the transmitted light and cathodoluminescence to evaluate the shell preservation.
The oxygen isotope values of the ligamental area of the modern oyster shells are between -5.78‰ and -0.92‰ (-3.90± 1.17‰, N=189; 1σ). The carbon isotope values of the ligamental area of modern oyster shells are between -4.07‰ and -0.24‰ (-2.15± 0.77‰). The δ18O curves of individual modern oyster shells which died in different months can reflect seasonal change and the whole year record, separately. The calculated minimum oxygen isotope temperature is 19.7°C, but whereas the measured minimum temperature is 15°C. Thus, the modern oyster shells may not record the lowest temperature in winter.
Archaeological oyster shells are from two different archaeological sites in Southern Taiwan Science Park. One is Nan Kuang Li (NKL) and the other is Nan Kuang Li East (NKLE) Archaeological Site. The age of Nan Kuang Li Archaeological Site was roughly 4100~ 4700 B. P.. The δ18O values of the three NKL oyster shells from the upper layer are between -6.91‰ and -0.80‰ (-3.36± 1.65‰, N=83; 1σ) and the δ13C values are between -4.08‰ and -0.39‰ (-1.15± 1.35‰). Five shells were took from the lower layer in NKL Archaeological Site. The δ18O values of the well- preserved NKL oyster shells are between -6.51‰ and -0.35‰(-2.89± 1.38‰, N=93; 1σ) and the δ13C values are between -5.80‰ and 2.50‰ (-1.66± 2.07‰). There were three shells from Nan Kuang Li East archaeological site. The δ18O values of the well- preserved NKLE oyster shells are between -7.93‰ and -0.37‰ (-2.91± 1.81‰, N=75; 1σ), and the δ13C values are between -5.59‰ and -0.56‰ (-2.35± 1.19‰). Archaeological oyster shells are 1.01‰ greater than that of the modern oyster shells in δ18O values. It indicates that the climate in 4100~ 4700 a. B. P. was 4 °C less than modern. Based on the δ18O profiles of each archaeological shells, most of the archaeological oysters were collected in winter and spring.

並列關鍵字

Stable isotope ； Oyster ； Water environment ； Archaeological site

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