Characterization of particulate organic matter in the Lena River delta and adjacent nearshore zone, NE Siberia – Part 2: Lignin-derived phenol compositions

[摘要] The Lena River in central Siberia is one of the major pathways translocatingterrestrial organic matter (OM) from its vast catchment area to the coastalzone of the Laptev Sea and the Arctic Ocean. The permafrost soils of its far south-stretching catchment, which store huge amounts of OM, will most likelyrespond differently to climate warming and remobilize previously frozen OMwith distinct properties specific for the source vegetation and soil. Tocharacterize the material discharged by the Lena River, we analyzed thelignin phenol composition in total suspended matter (TSM) from surface watercollected in spring and summer, surface sediments from Buor Khaya Bayalong with soils from the Lena Delta's first (Holocene) and third terraces(Pleistocene ice complex), and plant samples. Our results show thatlignin-derived cinnamyl : vanillyl (C / V) and syringyl : vanillyl (S / V) ratiosare > 0.14 and 0.25, respectively, in TSM and surface sediments,whereas in delta soils they are > 0.16 and > 0.51,respectively. These lignin compositions are consistent with significantinputs of organic matter from non-woody angiosperm sources mixed withorganic matter derived from woody gymnosperm sources. We applied a simplelinear mixing model based on the C / V and S / V ratios, and the results indicatethe organic matter in delta TSM samples and Buor Khaya Bay surface sedimentscontain comparable contributions from gymnosperm material, which isprimarily derived from the taiga forests south of the delta, and angiospermmaterial typical for tundra vegetation. Considering the small catchment areacovered by tundra (~ 12%), the input is substantial andtundra-derived OM input is likely to increase in a warming Arctic. Thesimilar and high acid to aldehyde ratios of vanillyl and syringyl(Ad / Al_{V, S}) in Lena Delta summer TSM (> 0.7 and > 0.5, respectively) and Buor Khaya Bay surface sediments (> 1.0and > 0.9, respectively) suggest that the OM is highly degradedand Lena River summer TSM could be a possible source of the surfacesediments. The Ad / Al_{V, S} ratios of the first and third delta terraceswere generally lower (mean ratios > 0.4 and > 0.4,respectively) than summer TSM and surface sediments. This implies that TSMcontains additional contributions from a more degraded OM source (southerncatchment and/or finer more degraded particle size). Alternatively, OMdegradation on land after permafrost thawing and subaqueously duringtransport and sedimentation could be considerable. Despite the high naturalheterogeneity of OM stored in delta soils and exported by the Lena River,the catchment-characteristic vegetation is reflected by the lignin biomarkercomposition. Climate-warming-related changes in the Lena River catchment maybe detectable in changing lignin biomarker composition and diageneticalteration.

[学科分类] 地球化学与岩石