The early Holocene optimum inferred from a high-resolution pollen record of Huguangyan Maar Lake in southern China

Abstract

A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that (i) pollen percentage of trees and shrubs reached 56% during the early Holocene (11600-7800 cal a BP), of which the pollen percentage of tropical trees reached a maximum at 9500-8000 cal a BP, reflecting a hot and wet environment; (ii) during the mid-Holocene (7800-4200 cal a BP), the pollen percentage of montane coniferous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indicating lower temperature and humidity; (iii) in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500-8000 cal a BP in southern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer monsoon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.

Stalagmite-inferred Holocene precipitation in northern Guizhou Province, China, and asynchronous termination of the Climatic Optimum in the Asian monsoon territory

“…This information does not support the transgressive model described by An et al [1]. High-resolution pollen records from Huguangyan Maar Lake have shown a different time window for the climatic optimum at 9.5-8.0 ka BP in southern China [18]. These conflicting reports could be caused by (1) uncertainties in chronology or sampling resolution and/or (2) different climate responses and feedback processes for different natural biogeochemical archives.…”

“…A total of 479 powdered subsamples (50-100 g each) were drilled for δ 18 O measurements at 1-mm intervals along the central growth axis using a dental drill with a 0.5 mm carbide bit. δ 18 O measurements were performed on a Finnigan MAT-253 mass spectrometer, coupled with an on-line automated preparation system, the Kiel Carbonate Device, at the College of Geography Science, Nanjing Normal University. Replicate measurements of an international standard NBS-19 between every 9 samples showed a long-term reproducibility better than ±0.06‰.…”

“…Fleitmann et al [23] also applied this method to determine transition points of a stalagmite-inferred Holocene Indian Monsoon time series. To understand spatial AM variability during the Holocene Optimum, we applied RAMPFIT to the selected high resolution Holocene δ 18 O records of Qunf Cave [23], Dongge Cave [12], Shigao Cave, Heshang Cave [14] and Sanbao Cave [8] in the Asian Monsoon territory.…”

“…Chinese stalagmite δ 18 O records have been suggested to reflect variations of monsoonal precipitation on orbital and millennial/centennial timescales [8][9][10][11][12][13]. Comparison of the recent 1810-a records from Wanxiang Cave [11] and 750-a records from Dayu Cave [10] with drought/flood indices reconstructed from historical documents indicates that stalagmite  18 O is mainly dominated by monsoonal rainfall.…”

“…Recent studies have led to significant advances in understanding of Asian Monsoon (AM) dynamics during the Holocene [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. However, the timing, duration and transition of the Holocene Optimum are still under debate.…”