Humification degrees of a lacustrine sedimentary sequence as an indicator of past climatic changes in the last c. 49 000 years in South China

Abstract

Zhong, W., Ma, Q. H., Xue, J. B., Zheng, Y. M., Cai, Y. & Ou, Y. J. 2009: Humification degrees of a lacustrine sedimentary sequence as an indicator of past climatic changes in the last c. 49 000 years in South China. Boreas, 10.1111/j.1502‐3885.2009.00119.x. ISSN 0300‐9483. An 860 cm long sediment core recovered from Dahu Swamp was used to test the potential of the degree of humification (expressed as the corrected absorbance values, HDcab) of lacustrine sediments as an indicator of past climatic changes in South China. The chronological sequence of this core was established using 10 AMS 14C dates and 10 conventional 14C dates and gives the bottom age of c. 48 800 cal. yr BP. Based on comparisons with multiproxy records, such as lithological variation, organic carbon isotope ratio, organic matter content and dry bulk density, we infer that the HDcab record is sensitive to local hydrological variations that are closely related to the East Asian (EA) summer monsoon precipitation. Higher HDcab values would indicate relatively drier conditions, suggesting a weakening of the EA summer monsoon and vice versa. Based on the HDcab, as well as other multiproxies, the climatic history in the last c. 49 000 years in the swamp area shows agreement with the Chinese stalagmite record and with the 25°N summer solar insolation, implying that orbitally induced insolation may have played a role in the last glacial period (LGP) climate in South China. Several millennial‐scale dry phases during the LGP show similarities with the stadials revealed by the ice core record in Greenland and from the Chinese cave stalagmites. Our study demonstrates that the HDcab of lacustrine sediments is a useful proxy of past climatic changes in South China.

Late Quaternary East Asian Summer Monsoon Variability Deduced From Lacustrine Mineral Magnetic Records of Dahu Swamp, Southern China

“…In order to confirm the environmental/climatic interpretations of these magnetic parameters, other sediment proxy records are also provided for comparison, including humification degree (expressed as the corrected absorbance values, HD cab ), total organic matter (TOM), dry bulk density (DD), sediment accumulation rate (SAR, mm/year), and DD‐AR (the accumulation rate of DD, g·cm −2 ·year −1 ). These multiproxy records have all been previously demonstrated to be sensitive to variations in precipitation or effective moisture in Dahu Swamp, with lower TOM and higher HD cab , DD, SAR and DD‐AR values indicating wet conditions, and vice versa (Zhong et al, , ). The interpretation of magnetic parameters (e.g., χ lf and χ ARM /SIRM) as indicators of hydrological changes is supported by their strikingly similar trends with these other climatic proxies (Figure ).…”

“…Shifts between the lacustrine and the peat (organic‐rich mud) sediments suggest notable hydrological variations in this region (Zhou et al, ). In general, the lacustrine sediments indicate expansion of the water body in the basin, suggesting relatively wet conditions, whereas the peat sediments represent shrinkage of the water body, thus implying relatively dry climates (Zhong et al, , ; Zhou et al, ). As such, variation of magnetic parameters in the core sediments could be closely associated with the catchment environment conditions, including rainfall and/or erosion intensity, vegetation coverage, and pedogenic development, which are all fundamentally influenced by hydroclimatic changes.…”

“…The gray dashed line in the bottom indicates the summer insolation (Berger & Loutre, ) at 20°N latitude. DD, TOM, and HD cab are cited from Zhong et al (). Note that vertical axis of χ ARM /SIRM and TOM are reversed.…”

“…The climate became more arid toward the late Holocene, which exhibited synchronous variation with the gradually decreasing insolation. Unfortunately, our records can only record short intervals of the late Holocene due to the intense disturbance by human activities in the top sediments (Zhong et al, , ). But the dry climate during the late Holocene has also been widely reported in various proxy records from southern monsoonal China (Jia et al, ; Wang et al, ; Zhong et al, ).…”

Carbon accumulation in Dahu Swamp in the eastern Nanling Mountains (south China) and its implications for hydroclimatic variability over the past 47 000 years

“…; Zhong et al . , b, , ). The variable sedimentary facies of the swamp would certainly be expected to have caused dramatic changes in the CAR.…”