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Presents information on the environmental evolution and southwest monsoon changes recorded by lake sediments from Erhai Lake, Yunnan Province, China. Methodology; Environmental condition in Erhai Lake; Characteristics of lakes in Qinghai-Tibetan Plateau.

Abstract: To provide accurate analogues for fossil pollen records from lake cores, we analyzed surface sediments from 42 lakes of Yunnan and southwestern Sichuan Province, China (located between about 1500 and 4600m elevation) for pollen and spores. The pollen analysis reveals that although large amounts of arboreal pollen, such as Pinus, Picea and Abies, Betula, Juglans, deciduous oaks, evergreen oaks, and Rosaceae, from lower elevations are introduced into sub-alpine and alpine lakes by upslope winds, the pollen assemblages of surface lake sediments among and within different vegetation types can still be distinguished by their pollen spectra and indicator species. For example, Alnus is an indicator of the pollen assemblages of lakes among the Pinus yunnanensis forest-Evergreen broadleaved forest or P. yunnanensis forest-Mixed Pinus and Quercus forest. Tsuga and Ericaceae are indicators of the pollen assemblages of lakes in the Picea and Abies forest or the Picea and Abies forest-Alpine (Rhododendron) shrubland. Little pollen from Picea, Abies, Larix and Tsuga is transported downhill in lake sediments, indicating that lake cores near the lower limit of the Picea and Abies forest more correctly reflect climatic changes than lake cores near the tree line (namely the upper limit of the Picea and Abies forest) when using fossil pollen data. Principal component analysis basically separates surface lake samples below and above 3200m a.s.l. However, it does not distinctly distinguish between samples from two different vegetation types above 3200m a.s.l. because percentages of some dominant pollen types, such as Pinus, Picea and Abies, Betula, Juglans, deciduous oaks, evergreen oaks, and Rosaceae, do not markedly change with strong upslope transport. [Copyright &y& Elsevier]

New deglacial pollen and conifer stoma records from Tiancai Lake, northwestern Yunnan Province, southwestern China, an alpine lake in the southwest monsoon region, are presented in this study. Based on these records, the lithology of core TCYL1, and PCA analysis of pollen data between ~21 and 11.5kaBP (calibrated 14C years), the deglacial vegetation and climate changes are discussed in detail. The results show that Tiancai Lake was above the upper limit of Picea/Abies forest (a treeline in the study area) between ~21 and 11.5kaBP, and the climate was colder and drier than that of the Holocene. During this period eight significant vegetation changes are recorded that are considered to be responses to changing temperatures and variations in the southwest monsoon in southwestern China. The Heinrich Event 1 (H1), the Bølling/Allerød warm period (BA) and the Younger Dryas cold event (YD) are all clearly detected in this record. In addition, this study finds that the initial late glacial warming in northwestern Yunnan Province was at ~18.7kaBP, which is coincident with the climate records in monsoonal Central Asia, the Indian Ocean, the tropical and subtropical Pacific Ocean, and Antarctica, and is a response to solar insolation changes. A noted temperature increase between 15.8 and 14.4kaBP occurred at the end of the H1 and before the BA, which indicates a strong pre-Bølling warming. Based on the study, we consider that the hypothesis about a slowdown of the ocean's thermohaline circulation is sufficient to explain these late glacial abrupt events. [ABSTRACT FROM AUTHOR]

Abstract: Reconstructing past changes of the summer monsoon in southwestern China is key to understanding the paleoclimatic dynamics of the Indian summer monsoon (southwest monsoon), a major tropical system with impacts beyond the region. High-resolution pollen and conifer stoma data are presented from a sediment core (Tiancai Lake), located just below treeline in the Hengduan Mountains, northwestern Yunnan Province of China. These data record changes in vegetation and climate for the latest Pleistocene and Holocene (c. the last 12,230 cal. yr BP), and by comparing these results with the pollen records from the nearby Erhai Lake and Lugu Lake, a regional climate history in Yunnan Province can be inferred. During the period of 12,230–11,510 cal. yr BP, open alpine meadow around Tiancai Lake indicates a relatively cold and dry climate, corresponding to the Younger Dryas cold event (YD). Between 11,510 and ∼10,000 cal. yr BP, the vegetation types around Tiancai Lake changed into Picea and Abies forest and alpine Rhododendron shrubland, reflecting increases in the temperature and humidity. From ∼10,000 to 6100 cal. yr BP, Tsuga forest expanded persistently toward Tiancai Lake, indicating further climate changed towards warmer and wetter conditions. Between 6100 and 3410 cal. yr BP, Tsuga forest was the dominant vegetation type nearest to Tiancai Lake, denoting warm and humid climatic conditions, corresponding to the Holocene climatic optimum in the northwestern Yunnan Province. Tsuga forest in mountains around Lugu Lake shrank quickly at 3410 cal. yr BP, reflecting significant decline of humidity. Since 2930 cal. yr BP, Tsuga forest around Tiancai Lake shrank gradually, indicating a fluctuating decrease of temperature. These climatic changes reflect changes of the southwest monsoon, namely, warm and humid climate indicating strong southwest monsoon, cold and dry climate denoting weak southwest monsoon. [Copyright &y& Elsevier]