Paleoceanography of the Late Cretaceous northwestern Tethys Ocean: Seasonal upwelling or steady thermocline?
Paleoceanography of the Late Cretaceous northwestern Tethys Ocean: Seasonal upwelling or steady thermocline?
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DOI：
10.1371/journal.pone.0238040
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发表时间：
2020-08
期刊：
影响因子：
3.7
通讯作者：
E. Walliser;B. Schöne
中科院分区：
文献类型：
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作者：
E. Walliser;B. Schöne
在这项研究中，我们试图评估在都罗纪晚期-哥尼亚纪早期期间，特提斯洋西缘是否存在季节性上升流或稳定的温跃层。在这个范围内，我们使用了新的和公布的各种生物(双壳类、双壳类、腕足类、鱼类和白足类)的稳定氧同位素(δ18O)数据。新的季节分辨温度估计是基于连续采样的接种剂(Inoceramus sp.)的δ18O记录。和来自意大利北部Scaglia Rossa和奥地利西部Gosau矿床的Rudist(Hippurites Resectus)贝壳。利用反射光、阴极发光(CL)、扫描电子显微镜(SEM)和稳定同位素分析进行成岩筛选。最初保存的δ13C和δ18O值被用来描述双壳类的生活方式，并检测可能具有偏向氧同位素温度重建的重要影响。Inoceridδ18O值首次提供了关于特提斯底栖水温度的信息，平均为14.4±0.6摄氏度，在不到2摄氏度的范围内季节性波动。这种温度状况与图罗纪晚期北部水团的假设温度一致，并支持从北大西洋到特提斯底部存在冷水供应。然而，海底冷却并不影响浅水环境。事实上，基于Rudist的浅水环境温度估计显示，平均年变化范围为11℃，在24至35℃之间(假设季节恒定的δ180w=1.0‰)，这是整个晚白垩世记录到的最热温度之一。因此，我们的发现表明，这两种环境之间存在强烈的热量和食物网络脱钩。不同水体没有季节性的垂直均质，这表明存在稳定的温跃层，因此，与前人假设的该地区存在活跃的沿海上升流形成对比。
In this study we attempted to assess whether seasonal upwelling or a steady thermocline persisted at the western margin of the Tethys Ocean during the late Turonian–early Coniacian interval. For this scope, we employed novel and published stable oxygen isotope (δ18O) data of various organisms (bivalves, bivalves, brachiopods, fish and belemnites). New seasonally resolved temperature estimates were based on the δ18O record of sequentially sampled inoceramid (Inoceramus sp.) and rudist (Hippurites resectus) shells from the Scaglia Rossa and Gosau deposits of northern Italy and western Austria, respectively. Diagenetic screening was performed using reflected light, cathodoluminescence (CL), scanning electron microscopy (SEM) and stable isotope analysis. Originally preserved δ13C and δ18O values were used to characterize the lifestyle of the bivalves and detect vital effects that could have biased oxygen isotope-based temperature reconstructions. Inoceramid δ18O values provide–for the first time–information on temperatures of Tethyan benthic waters, which were, on average, 14.4 ± 0.6 °C and fluctuated seasonally within a range of less than 2 °C. Such a thermal regime is in line with the temperatures postulated for late Turonian boreal water masses and support the existence of a cold water supply from the North Atlantic to the Tethyan bottom. Bottom cooling, however, did not affect the shallow water environment. In fact, the rudist-based temperature estimates for shallow water environment revealed a mean annual range of 11 °C, between 24 and 35 °C (assuming a seasonally constant δ18Ow = 1.0 ‰), which are among the warmest temperatures recorded over the entire Late Cretaceous. Our findings, thus, suggest a strong thermal and food web decoupling between the two environments. The absence of a seasonal vertical homogenization of different water bodies suggests the existence of a steady thermocline and, therefore, contrasts with the presence of an active coastal upwelling in the region as hypothesized by previous authors.