Centre of Advanced Study, Department of Botany, University of Calcutta, 35, Ballygunge Circular Road, Kolkata 700019, India.
Birbal Sahni Institute of Palaeosciences, 53, University Road, Lucknow 226007, India.
Sci Total Environ. 2021 Jan 1;750:142280. doi: 10.1016/j.scitotenv.2020.142280. Epub 2020 Sep 12.
Past climate reconstructions from palaeoecological records require an understanding of relationships between modern vegetation and climate. Phytoliths are being used widely to reconstruct variations in C3/C4 grasses in the past vegetation and corresponding climate. However, little understanding is available on their relationships with the climate driver(s). Even though, the driver(s) regulating C3/C4 grass distributions vary regionally, while reconstructing the past distributions, a grass phytolith-based climatic index (Ic) has often been found to be used globally without assessing its regional consistency. In the Himalaya, the working potential of Ic has proven to be unsatisfactory when compared to other regions of the globe. To improve the efficacy of Ic, we have identified the redundant grass phytolith morphs and revised it by including four exclusive C3-grass indicator morphotypes (bilobate trapezoidal, bilobate scooped, saddle tall and saddle plateaued) to the existing Ic calculation. Thus, a new climatic index, revised Ic (rIc) is proposed in this article. We have compared the rIc with modern climate variables and a relationship with mean annual temperature (MAT) is established with statistical validation. To assess the working potential of the proposed calibration function in the past temperature reconstructions, we have estimated the late Holocene MAT variations in the Himalaya using rIc. We infer that in the mountainous regions like the Himalaya, even with irregular precipitation distribution, variability in C3/C4 grass distributions and their phytolith spectra seem to be a primary function of temperature. Further, we recommend that rIc can be satisfactorily used to reconstruct past temperature variations in the Himalaya and similar mountainous regions where soil water availability is not a limiting factor.
过去的古生态学记录重建需要了解现代植被与气候之间的关系。植硅体被广泛用于重建过去植被中 C3/C4 草的变化以及相应的气候。然而，对于它们与气候驱动因素之间的关系，人们的了解还很有限。尽管调节 C3/C4 草分布的驱动因素在区域上有所不同，但在重建过去的分布时，基于草植硅体的气候指数 (Ic) 经常被发现被全球使用，而没有评估其区域一致性。在喜马拉雅山，与全球其他地区相比，Ic 的工作潜力被证明并不令人满意。为了提高 Ic 的功效，我们已经确定了冗余的草植硅体形态，并通过将四个独特的 C3 草指示形态（双叶梯形、双叶勺形、鞍形高和鞍形平台）纳入现有的 Ic 计算中，对其进行了修正。因此，本文提出了一个新的气候指数，修正后的 Ic（rIc）。我们比较了 rIc 与现代气候变量的关系，并通过统计验证建立了与年平均温度 (MAT) 的关系。为了评估提议的校准函数在过去温度重建中的工作潜力，我们使用 rIc 估计了喜马拉雅山晚全新世的 MAT 变化。我们推断，在喜马拉雅山等山区，即使降水分布不规则，C3/C4 草的分布及其植硅体光谱的变化似乎主要是温度的函数。此外，我们建议 rIc 可以满意地用于重建喜马拉雅山和类似山区的过去温度变化，在这些地区，土壤水分供应不是一个限制因素。
