A 60-year isotopic record from a mid-Holocene fossil giant clam (Tridacna gigas) in the Ryukyu Islands: physiological and paleoclimatic implications
A 60-year isotopic record from a mid-Holocene fossil giant clam (Tridacna gigas) in the Ryukyu Islands: physiological and paleoclimatic implications
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DOI：
10.1016/s0031-0182(04)00358-x
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发表时间：
2004-09
期刊：
影响因子：
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通讯作者：
Tsuyoshi Watanabe;A. Suzuki;H. Kawahata;H. Kan;S. Ogawa
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文献类型：
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作者：
Tsuyoshi Watanabe;A. Suzuki;H. Kawahata;H. Kan;S. Ogawa
我们利用位于日本中部琉球群岛久米岛地质历史最北纬度极限的巨型砗磲化石（距今 6216 年）构建了 60 年稳定同位素记录。稳定氧 (δ18O) 和碳 (δ13C) 同位素分析与内壳层生长线的观察相结合。在内壳层中观察到六十对夏季/冬季生长线，它们保持每日生长增量。在该标本的整个生长历史中，可以清楚地识别出以生长曲线和同位素分布为特征的两个生长阶段。尽管生长速度在 60 年间（包括性成熟开始后）每年变化很大，从 1 毫米/年到 15 毫米/年，但在其生长历史中，没有检测到两种同位素比率的平均值发生显着变化。对化石砗磲δ18O时间序列的光谱分析表明，过去百年在北太平洋观测到的年代际变化在6000年前也存在。我们的研究表明，巨蛤化石是推断年度至十年间气候变化同位素记录的最佳手段之一。砗磲具有壳致密、生长速度快、寿命长、地理地质分布广泛等优点。
We have constructed a 60-year stable isotope record from a14C-dated fossil giant clam, Tridacna gigas (6216 years BP), at its northernmost latitudinal limit in the geological past, on Kume Island, Central Ryukyu Archipelago, Japan. Stable oxygen (δ18O) and carbon (δ13C) isotopic analyses are combined with observations of growth lines seen on the inner shell layer. Sixty pairs of summer/winter growth lines, which preserve daily growth increments were observed in the inner shell layer. Two growth phases, characterized by a growth curve and isotopic profiles, are clearly recognized throughout the growth history of this specimen. No significant shifts in average values of the two isotopic ratios were detected during its growth history, although the growth rate varied widely from 1 to 15 mm/year over 60 years, including after the onset of sexual maturity. Spectral analysis of the fossil Tridacna δ18O time-series implies that decadal variability observed in the North Pacific Ocean during the past hundred years also existed 6000 years ago. Our study implies that fossil giant clams are one of the best means of inferring isotopic records of annual to decadal climate variations. Giant clams have the advantages of a dense shell, high growth rate, long lifespan, and geographically and geologically broad distributions.