Abstract

Carbon isotopes of stalagmites are influenced by various factors operating in a cave, like evaporation, vegetation, drip rate and changes in partial pressure of carbon-di-oxide (pCO₂) inside and around a cave system. Consequently, interpretation of δ¹³C record becomes a bit complicated. However, the vegetation changes at a given cave location are generally considered as the dominating factor influencing δ¹³C values of a stalagmite. The δ¹³C records can provide useful information regarding changes in the class of vegetation over a cave due to dissimilar pathways of photosynthesis linking C₃ and C₄ vegetation. Here we present a high-resolution δ¹³C record from a 180 mm long VSPM1 stalagmite collected from the Valmiki cave in Kurnool district of southern India. This study is mainly based on high-resolution δ¹³C measurements of 263 subsamples. The data has been used to infer vegetation and climatic variations for the last deglacial period starting from 15,607 to 13,161 years BP. The StalAge modelling was employed on eight U–Th dates to reconstruct the age model of the stalagmite sample. The stalagmite grew at the rate of 0.07 mm per year with varying growth rate from around 0.03 to 0.8 mm per year. X-ray diffraction analysis reveals absolute aragonite mineralogy of the sample. The record exhibits a weak positive relationship between δ¹³C and δ¹⁸O values. The main factors influencing δ¹³C values were associated with local hydroclimate. The δ¹³C record suggests vital evidence of rapid alterations in vegetation changes from ~15,607 to 13,161 yr BP. A major shift in vegetation activity occurred from 15,607 to 15,105 yr BP with an episode of highly poor vegetation cover around 15,460 yr BP, followed by a gradual decline in vegetation conditions between 15,105 and 14,722 yr BP.

Research highlights

• This study reveals importance of stable carbon isotopes in stalagmites to understand regional hydroclimate and paleo-vegetation changes.

• The δ¹³C record from a stalagmite sample of Valmiki cave located in South India indicates rapid vegetational changes controlled mainly by ISM variability during the last deglacial period.

• Three major phases have been observed; first a wet period from 15,607 to 15,105 yr BP, followed by a dry period between 15,105 and 14,722 yr BP and finally another wet event from 14,722 to 13,161 yr BP.

中文翻译：

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从石笋的碳同位素推断出的印度南部洞穴古植被的 2500 年冰消期记录

摘要

石笋的碳同位素受洞穴中各种因素的影响，例如蒸发、植被、滴速和洞穴系统内部和周围二氧化碳 (pCO ₂ )分压的变化。因此，对δ ¹³ C 记录的解释变得有点复杂。然而，给定洞穴位置的植被变化通常被认为是影响石笋δ ¹³ C 值的主要因素。由于连接 C ₃和 C ₄植被的光合作用途径不同，δ ¹³ C 记录可以提供有关洞穴植被类别变化的有用信息。在这里，我们展示了一个高分辨率的δ ¹³ C 记录来自从印度南部库尔诺尔区 Valmiki 洞穴收集的 180 毫米长 VSPM1 石笋。本研究主要基于对263 个子样本的高分辨率δ ¹³ C 测量。该数据已用于推断从 15,607 年到 13,161 年 BP 的最后一个冰消期的植被和气候变化。在 8 个 U-Th 日期上采用 StalAge 建模来重建石笋样本的年龄模型。石笋以每年 0.07 毫米的速度增长，增长速度从每年 0.03 到 0.8 毫米不等。X 射线衍射分析揭示了样品的绝对文石矿物学。该记录显示δ ¹³ C 和δ ¹⁸之间存在弱正相关关系O 值。影响δ ¹³ C 值的主要因素与当地的水文气候有关。该δ ¹³ C ^记录表明植被变化从大约15607至13,161 BP年快速变化的重要证据。植被活动发生了重大转变，从 15,607 年到 15,105 年 BP，在 15,460 年 BP 左右发生了植被覆盖非常差的事件，随后在 15,105 到 14,722 年 BP 之间植被状况逐渐下降。

研究亮点

• 这项研究揭示了石笋中稳定的碳同位素对了解区域水文气候和古植被变化的重要性。

• 来自印度南部 Valmiki 洞穴石笋样本的δ ¹³ C 记录表明，在最后一个冰消期，主要由 ISM 变异控制的快速植被变化。

• 已观察到三个主要阶段；首先是从 15,607 年到 15,105 年 BP 的湿润期，然后是 15,105 到 14,722 年 BP 之间的干旱期，最后是从 14,722 到 13,161 年 BP 的另一个湿润期。