Sub-seasonal oxygen and carbon isotope variations in shells of modern Radix sp. (Gastropoda) from the Tibetan Plateau: potential of a new archive for palaeoclimatic studies
Sub-seasonal oxygen and carbon isotope variations in shells of modern Radix sp. (Gastropoda) from the Tibetan Plateau: potential of a new archive for palaeoclimatic studies
复制标题
DOI：
10.1016/j.quascirev.2011.12.006
复制
发表时间：
2012-02
影响因子：
4
通讯作者：
L. Taft;U. Wiechert;F. Riedel;M. Weynell;Hucai Zhang
中科院分区：
文献类型：
--
作者：
L. Taft;U. Wiechert;F. Riedel;M. Weynell;Hucai Zhang
测量了东南边缘邦达错湖（北纬 30°29′、东经 97°04′、海拔 4450 m s.l.）和基林错湖（北纬 31°09′、东经 88°17′、公元 4650 年）位于青藏高原中部。沿个体发育螺旋生长，对根壳进行采样，进行高空间分辨率的同位素比分析，为亚季节时间分辨率的同位素记录奠定基础。邦达错贝壳的 δ18O 值相对于 PDB 平均为∼−15.0‰，该模式表现出明显的夏季风降水的开始和进展，表明强烈的“量效应”。该模式反映了相应年份和地区的降水模式，如预期的小（表面积约 0.3 km2）和浅（<5 m）湖泊或栖息地，水停留时间短且湖水蒸发 18 O 富集很少。相比之下，Kyaring Co 栖息地 A 与深（几十米）大（表面积约 660 km2）湖泊相连的板蓝根贝壳的 δ18O 值平均为 ∼−13.0‰，与较高的蒸发速率和较长的水停留时间一致。后者由该栖息地中更多的18O富集水支持。由于栖息地特征相似，Kyaring Co 栖息地 B 的贝壳 δ18O 值几乎与邦达错的贝壳一样低，但这些贝壳的同位素模式表现出较弱的“量效应”。在这两个湖泊系统中，贝壳的 δ13C 值都与氧同位素相关，因为大量同位素轻碳在雨季从山坡冲入湖泊。尽管其他过程影响同位素模式，例如生物生产力（δ13C）或温度（δ18O），与季风信号或板蓝根壳记录中蒸发的影响相比，这些影响较小。与邦达错的贝壳相比，来自嘉林错栖息地 B 的板蓝根贝壳的数量效应总体较弱，这与当前从东南边缘向青藏高原中部逐渐减弱的季风影响一致。因此，腹足动物属的贝壳化石是重建青藏高原气候和环境变化的宝贵档案，并提供有关以前栖息地大小和深度的信息。
Carbon and oxygen isotope ratios have been measured for nine aragonite shells of the gastropod genus Radix from the lake Bangda Co (30°29′N, 97°04′E, 4450 m a.s.l.) at the south-eastern edge and from two characteristic sites at the lake Kyaring Co (31°09′N, 88°17′E, 4650 m a.s.l.) on the central Tibetan Plateau. Radix shells were sampled for isotope ratio analysis with high spatial resolution along the ontogenetic spiral of growth providing the basis of isotope records with a sub-seasonal time-resolution. δ18O values of shells from Bangda Co are on average ∼−15.0‰ relative to PDB and the pattern exhibits a clear onset and progression of the summer monsoon precipitation indicated by a strong “amount effect”. This pattern mirrors the precipitation pattern in the respective year and region as expected for a small (surface area ca 0.3 km2) and shallow (<5 m) lake or habitat with short water residence times and little evaporative18O enrichment of the lake water. In contrast, δ18O values of Radix shells from Kyaring Co habitat A which is connected to the deep (several tens of metres) and big (surface area ca 660 km2) lake, average at ∼−13.0‰ consistent with a higher evaporation rate and longer water residence time. The latter is supported by more18O enriched water in this habitat. The δ18O values of Radix shells from Kyaring Co habitat B are nearly as low as shells from Bangda Co due to the similar habitat characteristic but isotopic patterns of these shells exhibit a weaker “amount effect”. In both lake systems δ13C values of the shells are coupled with oxygen isotopes because a large amount of isotopically light carbon is washed from mountain slopes into the lake during the rainy season. Although other processes influence the isotopic patterns, e.g. biological productivity (δ13C) or temperature (δ18O), these influences are minor compared with the monsoon signal or the effect of evaporation in the Radix shell records. The overall weaker amount effect in Radix shells from Kyaring Co habitat B compared with shells from Bangda Co are consistent with a current decreasing monsoon influence from the south-eastern edge towards the central Tibetan Plateau. Thus, fossil shells of the gastropod genus Radix are a valuable archive for reconstructing climatic and environmental changes on the Tibetan Plateau and provide information about former habitat sizes and depths.