本研究分析了採自台灣西南沿海現生種的Anadara granosa(M1、M2)以及恆春晚更新世地層─四溝層上部 (FU)、下部 (FL) 的A. granosa化石，共四個標本的穩定碳、氧同位素及化學元素的組成，來探討年際間的環境變化。
現生標本的δ18O值多落於利用同位素平衡方程式計算出霰石之氧同位素應有的數值範圍(-2.6~-0.3‰)，表示此種貝類殼體與水體氧同位素數值大致可達成同位素平衡。化石標本的主要組成礦物仍為霰石，礦物結晶構造清晰可見，表示未受到成岩作用影響，因此其同位素訊號應能夠代表四溝層沉積時的環境訊號。所有標本的氧同位素數值變化，在貝類生長早期振幅大；後期振幅小，其原因可能是貝類達到成熟生殖期，將部分能量消耗在生殖，導致殼體對於環境訊號的紀錄有所缺失，故本研究未將貝類達成熟生殖期後之數據用在古環境重建之討論中。FU、FL的碳、氧同位素呈現線性正相關，顯示其在四溝層沉積時的生長環境，潟湖水體受到顯著不同程度淡水與海水混合的影響。
化石的δ18O值較現生種的δ18O值整體約高1.5‰，主要是由於冰川效應所影響。年際間氧同位素數值變化扣除最大的溫度效應部份，淡水注入影響水體氧同位素變化量在四溝層下部平均有1.4‰，而在上部四溝層所造成的變化量減少變為1.1‰，表示下部四溝層至上部四溝層沉積過程中，年淡水注入量有些許減少的變化。
Mg/Ca值在二枚貝類 A. granosa 霰石殼體中與δ18O值部份成反相變化，故可能也是溫度的函數。新陳代謝是影響殼體中Sr/Ca含量最主要的因素，Sr/Ca值在各標本中都呈現逐漸降低的趨勢，顯示貝殼成長過程中，新陳代謝速率有逐漸減緩的現象。A. granosa殼體Ba/Ca值應表示水體中營養鹽的多寡，且與Sr/Ca值呈現同相變化，顯示出該貝類的新陳代謝速率可能亦與營養鹽含量有關。
由於四溝層上下層位的δ18O值並無顯著的差異，可推斷當時海退現象應由陸地隆升所造成，並非冰川效應所導致。而下部四溝層的δ13C值較上部四溝層小1.0‰，Ba/Ca含量約大13μmole/mole，顯示陸地隆升使得環境從潟湖環境變化成河口環境，導致營養鹽減少，而間接影響水體中溶解無機碳的同位素數值。若假設當時海水的δ18O值為1.5‰，則當時冬季的海水溫度約為24℃，與現今溫度並無太大差異。

We have analyzed the isotope and element compositions of two modern and two Late Pleistocene Anadara granosa shells to quantitatively characterize the paleoenvironmental change in Szekou Formation, Hengchun area. The δ18O values of modern shells are in good agreement with those calculated values based on available seawater δ18O values and temperature ranges, thus reach apparently isotopic equilibrium. Fossil shells, retaining the originally aragonitic mineralogy, indicate that these shells are not altered by diagenesis.
Excluding data from the period of sexual maturity, average δ18O value of fossil A. granosa is 1.5‰ greater than that of modern species. This difference is probably due to global glaciation effect and is consistent with previous studies. Both fossil specimens show positive linear correlation between δ18O and δ13C values whereas this relationship is not seen for modern samples. This is probably because these fossil shells lived in a lagoon environment whereas modern samples lived in an estuary area where is more opened to seawater. Therefore, samples from Szekou Formation show more significant fresh water-seawater mixing signals than modern ones. Excluding the possible annual temperature variation, the excess -1.4‰ (Lower Szekou Fm.) and -1.1‰ (Upper Szekou Fm.) indicate that the extent of riverine input at Lower Szekou Formation (FL) was little bit greater than that of Upper Szekou Formation (FU).
Episodic minima of Mg/Ca ratios are generally coincide to δ18O maxima. Thus, Mg/Ca ratio may be also varied as a function of temperature in the aragonitic shells. Because the Sr/Ca ratios decrease with tardy metabolism during growth process, metabolic activity of A. granosa should be the major factor controlling Sr/Ca ratio. Ba/Ca ratio is a indicator of nutrition. Sr/Ca and Ba/Ca data show a broadly positively covariant trend demonstrate that metabolism of A. granosa is also related to nutrition.
There is no significant difference in δ18O values between FL and FU. Therefore, the regression occurred from FL to FU was most likely caused by land uplift instead of global ice volume change. Average δ13C value of FL is 1‰ less than that of FU, whereas Ba/Ca ratio of FL is 13μmol/mol greater than that of FU. Land uplift may have changed Szekou depositional environment from lagoon to estuary and caused decrease in nutrient supply. Increase in δ13C of dissolve inorganic carbon of water from FL to FU may be caused by reduced relative biodiversity and need to be further studied. Assuming the δ18O of seawater was 1.5‰, the winter seawater temperature of studied area was about 24℃. The calculated Late Pleistocene seawater temperature is comparable to that of modern observations.

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