Work Description

Readme File for Zhang, Y., C. Gao, S. Zhang, P. Yang, P.A. Meyers, and G. Wang. n-Alkane-based reconstructions of peat accumulation and depositional at four locations around a shallow maar lake in the Changbai Mountains, northeastern China. Journal of Geophysical Research � Biogeosciences. (Submission identification: 2020JG006196) The study focuses on reconstructing the histories of peat deposition using n-alkane biomarkers in peat cores and associated modern plant communities from four sites around Yuanchi Lake, a shallow maar lake in the Changbai Mountains of northeastern China. We find that peat development patterns in the four sites are not concordant although the sites experienced the same paleoclimate histories. We postulate that lava flows and tephra deposits have produced an uneven topography of the volcanogenic lake basin that controls the water depths at the four lake edge locations, thereby leading to differences in peat-forming plant communities and peat deposition among the four sites. Yuanchi Lake (42�01'52"~42�01'58" N?128�26'03"~128�26'10" E; elevation ca. 1280 m asl) partially fills a volcanic crater and has no significant inflow or outflow from surface water or groundwater. Four peat-mud cores were collected around the edges of the lake and were subsampled on-site by slicing into 1 cm intervals. The peat cores were dated at 1 cm intervals by 210Pb analysis (Bao et al., 2010). Peat accumulation rates (PAR, cm/yr) were estimated from the 1 cm depth intervals and the corresponding 210Pb ages. The peat samples were dried at 105 �C and then combusted in a muffle furnace at 550 �C for 4h to determine their loss on ignition (LOI) values. TOC concentrations were estimated from OM content expressed as LOI values by multiplying the LOI by 0.5, and organic carbon accumulation rates (CAR, g C/m2/yr)) were calculated from the TOC concentrations and the PAR values. For n-alkane analyses, air-dried samples (1g) were extracted three times with MeOH/dichloromethane (1:1, v:v) for 15 min in an accelerated solvent extractor. The three extracts were combined after filtration and concentrated using a rotary evaporator. The n-alkanes were isolated using silica gel column chromatography by elution with 20 ml n-hexane. The eluate was concentrated with a N2 stream and transferred to vials for gas chromatography-mass spectrometry (GC-MS) analysis. Identification and quantification of n-alkanes were carried out using a Shimadzu QP5050A GC-MS system equipped with a DB-5MS fused quartz column (30 m � 0.25 mm � 0.25 ?m). The temperature of the ion source was 250 �C, and the ionization energy was 70 eV, with He as carrier gas. GC operating conditions were: 80 �C to 175 �C at 3 �C /min, then heating to 300 �C (held 20 min) at 4 �C /min (Zhang et al., 2014). Data from Bao et al. (2010) are from earlier cores from the sites cored in the present study and consequently their sediment ages differ somewhat and their deeper samples were not analyzed (shown as "NA"). Cited References Bao, K., Yu, X.F., Jia, L., & Wang G.P. (2010). Recent Carbon Accumulation in Changbai Mountain Peatlands, Northeast China. Mountain Research & Development, 30, 33-41. http://dx.doi.org/10.1659/MRD-JOURNAL-D-09-00054.1 Zhang, Y., Liu, X.T., Lin, Q.X., Gao, C.Y., Wang, J. & Wang, G.P. (2014). Vegetation and climate change over the past 800 years in the monsoon margin of northeastern China reconstructed from n-alkanes from the Great Hinggan Mountain ombrotrophic peat bog. Organic Geochemistry, 76, 128-135. http://dx.doi.org/10.1016/ j.orggeochem.2014.07.013