Palynology on sediment profile Tso Kar in Ladakh

Palynological investigation of a 410 cm long core section from Tso Kar (33°10'N, 78°E, 4527 m a.s.l.), an alpine lake situated in the arid Ladakh area of NW India at the limit of the present-day Indian summer monsoon, was performed in order to reconstruct post-glacial regional vegetation and climate dynamics. The area was covered with alpine desert vegetation from ca. 15.2 to 14 kyr BP (1 kyr=1000 cal. years), reflecting dry and cold conditions. High influx values of long-distance transported Pinus sylvestris type pollen suggest prevailing air flow from the west and northwest. The spread of alpine meadow communities and local aquatic vegetation is a weak sign of climate amelioration after ca. 14 kyr BP. Pollen data (e.g. influx values of Pinus roxburghii type and Quercus) suggest that this was due to a strengthening of the summer monsoon and the reduced activity of westerly winds. The further spread of Artemisia and species-rich meadows occurred in response to improved moisture conditions between ca. 12.9 and 12.5 kyr BP. The subsequent change towards drier desert-steppe vegetation likely indicates more frequent westerly disturbances and associated snowfalls, which favoured the persistence of alpine meadows on edaphically moist sites. The spread of Chenopodiaceae-dominated vegetation associated with an extremely weak monsoon occurred at ca. 12.2-11.8 kyr BP during the Younger Dryas interstadial. A major increase in humidity is inferred from the development of Artemisia-dominated steppe and wet alpine meadows with Gentianaceae after the late glacial/early Holocene transition in response to the strengthening of the summer monsoon. Monsoonal influence reached maximum activity in the Tso Kar region between ca. 10.9 and 9.2 kyr BP. The subsequent development of the alpine meadow, steppe and desert-steppe vegetation points to a moderate reduction in the moisture supply, which can be linked to the weaker summer monsoon and the accompanying enhancement of the winter westerly flow from ca. 9.2 to 4.8 kyr BP. The highest water levels of Tso Kar around 8 kyr BP probably reflect combined effect of both monsoonal and westerly influence in the region. An abrupt shift towards aridity in the Tso Kar region occurred after ca. 4.8 kyr BP, as evidenced by an expansion of Chenopodiaceae-dominated desert-steppe. Low pollen influx values registered ca. 2.8-1.3 kyr BP suggest scarce vegetation cover and unfavourable growing conditions likely associated with a further weakening of the Indian Monsoon.

本研究对位于印度西北部干旱拉达克地区、处于现今印度夏季风边界带的高山湖泊卓卡尔湖（Tso Kar，33°10'N, 78°E，海拔4527 m a.s.l.）的410厘米岩心段开展孢粉学调查，旨在重建冰期后区域植被与气候动态。约15.2至14千年前（kyr BP，1 kyr=1000 cal. years），该区域被高山荒漠植被覆盖，反映出当时寒冷干旱的气候环境。长距离搬运的欧洲赤松（Pinus sylvestris）型花粉通量呈高值，指示当时盛行来自西部与西北部的气流。约14千年前之后，高山草甸群落与本地水生植被的扩张是气候改善的微弱信号。花粉数据（例如长叶松（Pinus roxburghii）型与栎属（Quercus）花粉通量）表明，这一改善源于印度夏季风的增强与西风活动的减弱。约12.9至12.5千年前，蒿属（Artemisia）与物种丰富的草甸进一步扩张，响应于湿度条件的改善。此后向干旱荒漠草原植被的转变，可能指示西风扰动更为频繁且伴随降雪增多，这使得土壤湿润生境中的高山草甸得以存续。以藜科（Chenopodiaceae）为主的植被扩张、伴随季风活动极弱的阶段，发生于新仙女木间冰阶（Younger Dryas）的约12.2-11.8千年前。冰期晚期/全新世早期过渡后，以蒿属为主的草原与伴生龙胆科（Gentianaceae）湿生高山草甸的发育，指示湿度显著升高，这源于印度夏季风的增强。约10.9至9.2千年前，季风影响在卓卡尔湖区域达到最强。约9.2至4.8千年前，高山草甸、草原与荒漠草原的相继发育表明水汽供给适度减少，这与印度夏季风减弱、冬季西风环流增强相关。约8千年前卓卡尔湖的最高水位，可能反映了该区域同时受季风与西风的共同影响。约4.8千年前之后，卓卡尔湖区域突然向干旱环境转变，这一点可由以藜科为主的荒漠草原扩张得到证实。约2.8至1.3千年前记录的低花粉通量，指示植被覆盖稀少且生长条件恶劣，这可能与印度季风的进一步减弱有关。