Vegetation change in the eastern Pamir Mountains, Tajikistan, inferred from Lake Karakul pollen spectra of the last 28 kyr

Abstract

We present a pollen record for last 28 cal kyr BP from the eastern basin of Lake Karakul, the largest lake in Tajikistan, located in the eastern Pamir Mountains at 3915 m asl, a geographically complex region. The pollen record is dominated by Artemisia and Chenopodiaceae, while other taxa, apart from Poaceae, are present in low quantities and rarely exceed 5% in total. Arboreal pollen occur predominantly from ~28 to ~13 cal kyr BP, but as likely no trees occurred in the high mountain regions of the eastern Pamir during this time due to the high altitude and cold climate, arboreal taxa are attributed to long distance transport, probably by the Westerlies, the dominant atmospheric circulation. Tree pollen influx decreases strongly after ~13 cal kyr BP, allowing the pollen spectra to be interpreted as a regional vegetation signal. We infer that from 27.6 to 19.4 cal kyr BP the eastern Pamir was dominated by dry mountain steppe with low vegetation cover, while from 19.0 to 13.6 cal kyr BP Artemisia values increase and

Hydroclimate in the Pamirs Was Driven by Changes in Precipitation‐Evaporation Seasonality Since the Last Glacial Period

“…31–30, 28–26, and 17–14 kyr BP as a key to understand the occurrences of lake‐level highstands during those intervals. Since vegetation in hyperarid environments reacts sensitively to slight changes in humidity, we suggest that enhanced summer humidity during those intervals caused the higher influx of terrestrial n ‐alkanes, which occurred synchronous to higher pollen counts and a change from alpine desert to steppe vegetation (Heinecke et al, ). While enhanced discharge from glacial meltwater is less likely (glaciers in the Pamirs were still either at a maximum or even expanding in the late MIS 3/early MIS 2 and in the late glacial; Dortch et al, ; Komatsu & Tsukamoto, ), an explanation of the higher lake levels are shifts in the hydrological balance toward higher precipitation and/or lower lake‐water evaporation.…”

“…While the exact origin of those molecules remains unclear, a source from phytoplankton such as eustigmatophytes and chlorophytes and possibly from insects is likely (Aichner et al, ; van Bree et al, ; Zhang et al, ). Occurrence of n ‐alkenes correlate with increased counts of Chironomid remains at 28–26 and 15–14 kyr BP (Heinecke et al, ). Conversely, a much broader range of compounds than observed in the Karakul sediments would be expected with insects as a significant precursor of those compounds (Chikaraishi et al, ; van Bree et al, ).…”

“…31–30 and 28–26 kyr BP). These phases are accompanied by ecological changes within the lake (shift in dominant submerged plants at coring location; occurrence of biomarkers such as alkenones and C 23 , C 25 , and C 27 n ‐alkenes, giving evidence for a change in algal communities) as well as around the lake (change from desert to steppe vegetation; Heinecke et al, ). Unsaturated midchain compounds were discovered in many Tibetan Plateau lakes.…”

“…Recently, a lacustrine archive with a robust chronology spanning a glacial‐interglacial cycle was obtained from Lake Karakul (Mischke et al, ). Inorganic geochemical data, sedimentological, and paleoecological proxies from this record showed large‐scale shifts, possibly driven by insolation, over the past 28 kyr (Heinecke, Epp, et al, ; Heinecke, Mischke, et al, ; Heinecke et al, ). Some of those proxies were interpreted with respect to past lake level changes, but hydrological inferences were tentative.…”

Palynological Evidence of Late Holocene Paleo‐Monsoon in Eastern Pamir

“…The occurrence of the pollen of these taxa potentially enables an evaluation of the influence of air movements associated with the southerly and southwesterly summer monsoon in the western TP (Cour et al, 1999). Fossil Tsuga pollen grains were found in the Holocene sediments of Pumoyum Co , Chen Co (Lu, Wu, et al, 2011;Zhu et al, 2009), Nam Co (Zhu et al, 2015), Selin Co , and Tangra Yumco (Ma et al, 2019) in the central and southeastern TP; at Jharkot (Miehe et al, 2009) and Tso Kar (Demske et al, 2009) along the southern flank of TP; and in Lake Karakul (Heinecke et al, 2018) in Pamir (Figure 3). The area of distribution of Tsuga pollen in Holocene sediments is more westerly than is the case in the TP region today.…”