Geochemistry and grain size analysis of the Tangra Yumco lake sediment record

A possible asynchronicity of the spatial and temporal moisture availability on the Tibetan Plateau was controversially discussed in recent years. Here we present the first attempt to systematically investigate possible spatial and temporal variations of moisture availability by examining two lakes, Tangra Yumco and Nam Co, on an east-west-transect on the southern Tibetan Plateau using identical proxies for palaeoenvironmental reconstruction. In this study, an independent record from Tangra Yumco was analyzed applying a multi-proxy approach to reconstruct variations in moisture availability since the Lateglacial. Results were subsequently compared to previously published records from Nam Co and additional records from Tso Moriri (northwestern Himalaya) and Naleng Co (south-eastern Tibetan Plateau). Our results show that Tangra Yumco was at least partially ice-covered prior to 17.1 cal. ka BP. A temperature rise after 17.1 cal. ka BP probably resulted in thawing of the permafrost. At 16.0 cal. ka BP moisture availability increased representing an initial monsoonal intensification. Warmer conditions between 13.0 and 12.4 cal. ka BP and cooler conditions between 12.4 cal. ka BP and the onset of the Holocene reflect the Bølling-Allerød and Younger Dryas. At the onset of the Holocene moisture availability rapidly increased, while moisture was highest prior to 8.5 cal. ka BP concurrently with highest temperatures. After 8.5 cal. ka BP the moisture availability gradually decreased and showed only minor amplitude variations. These findings are well in phase with the records from other large lakes likes Nam Co, Tso Moriri, and Naleng Co revealing a synchronous pattern of moisture availability on the southern Tibetan Plateau.

青藏高原水汽可获得性的时空异步性问题在近年引发了广泛争议。本研究首次尝试系统探究水汽可获得性的潜在时空变化规律：选取青藏高原南部东西断面上的当惹雍错（Tangra Yumco）与纳木错（Nam Co）两个湖泊，采用统一的古环境重建（palaeoenvironmental reconstruction）代用指标（proxy）开展研究。本研究针对当惹雍错的独立记录，运用多代用指标（multi-proxy）方法重建了晚冰期（Lateglacial）以来的水汽可获得性变化序列。随后将本研究结果与已发表的纳木错记录、喜马拉雅西北部的卓莫拉里湖（Tso Moriri）以及青藏高原东南部的纳楞错（Naleng Co）的相关记录进行对比分析。研究结果显示，在距今17.1校准千年BP（cal. ka BP）之前，当惹雍错至少处于部分冰封状态。17.1校准千年BP之后的升温事件可能引发了多年冻土（permafrost）的消融。在16.0校准千年BP时，水汽可获得性显著上升，代表季风强度首次增强。13.0至12.4校准千年BP期间的暖期，以及12.4校准千年BP至全新世（Holocene）起始阶段的冷期，分别对应博林-阿勒罗德暖期（Bølling-Allerød）与新仙女木事件（Younger Dryas）。全新世起始阶段，水汽可获得性迅速提升，并在8.5校准千年BP之前达到峰值，同期对应最高温度阶段。8.5校准千年BP之后，水汽可获得性逐渐降低，仅存在小幅振幅波动。上述研究发现与纳木错、卓莫拉里湖、纳楞错等其他大型湖泊的记录高度吻合，表明青藏高原南部地区的水汽可获得性变化呈现统一的同步模式。