Carbonate clumped isotope evidence for latitudinal seawater temperature gradients and the oxygen isotope composition of Early Cretaceous seas
Carbonate clumped isotope evidence for latitudinal seawater temperature gradients and the oxygen isotope composition of Early Cretaceous seas
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DOI：
10.1016/j.palaeo.2020.109777
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发表时间：
2020-08
期刊：
影响因子：
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通讯作者：
G. Price;D. Bajnai;J. Fiebig
中科院分区：
文献类型：
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作者：
G. Price;D. Bajnai;J. Fiebig
在这项研究中，我们研究了早白垩纪（Valanginian，约1.35亿年前）从亚热带到北纬古纬度的气候。结合亚北极、北方和亚热带蛭石化石（软体动物：头足纲）的碳酸盐团块同位素和氧同位素数据，提供了新的古温度估算以及对海水氧同位素组成的约束。我们的蛭石数据显示温暖的高纬度海洋温度（约22°C）和温暖的亚热带温度（约31°C）。用tex86公布的数据补充我们基于团块同位素的温度估计，结果是对纬度温度梯度的保守重建，与现代条件相比降低了。我们发现，当考虑到高二氧化碳水平时，建模工作接近于重现热带温度。然而，温暖的极地温度意味着数据模型的差异仍然存在。早白垩世海水氧同位素值呈现现代剖面，比通常假设的要积极得多（最高可达1.5‰SMOW）。根据我们的研究结果，如果不考虑白垩纪海水的正δ18O值，碳酸盐δ18O测温将低估温度，特别是在中热带纬度地区。
In this study, we investigated Early Cretaceous (Valanginian, ca. 135 million years ago) climate from subtropical to boreal palaeolatitudes. Combined carbonate clumped isotope and oxygen isotope data derived from sub-arctic, boreal, and sub-tropical fossil belemnite rostra (Mollusca: Cephalopoda) provide new palaeotemperature estimates as well as a constraint on the oxygen isotope composition of seawater. Our belemnite data reveal balmy high-latitude marine temperatures (ca. 22 °C) and warm sub-tropical temperatures (ca. 31 °C). Supplementing our clumped isotope-based temperature estimates with published TEX86data results in a conservative reconstruction of a latitudinal temperature gradient that is reduced compared to modern conditions. We find that modelling efforts are close to reproducing tropical temperatures when highpCO2levels are considered. Warm polar temperatures imply, however, that data-model discrepancies remain. Early Cretaceous seawater oxygen isotope values show a modern profile and are much more positive (up to 1.5‰ SMOW) than typically assumed. Based on our findings, if the positive Cretaceous seawater δ18O values are not considered, carbonateδ18O thermometry would underestimate temperatures, most acute at middle and tropical latitudes.