Seasonal variability in the abundance and stable carbon-isotopic composition of lipid biomarkers in suspended particulate matter from a stratified equatorial lake (Lake Chala, Kenya/Tanzania): Implications for the sedimentary record
Seasonal variability in the abundance and stable carbon-isotopic composition of lipid biomarkers in suspended particulate matter from a stratified equatorial lake (Lake Chala, Kenya/Tanzania): Implications for the sedimentary record
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DOI：
10.1016/j.quascirev.2018.05.023
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发表时间：
2018-07
影响因子：
4
通讯作者：
L. Bree;F. Peterse;M.T.J. van der Meer;J. Middelburg;A.M.D. Negash;W. Crop;Christine Cocquyt;J. J. Wieringa-J.;D. Verschuren;J. S. S. Damsté-J.-S.-S.-Damsté-2251792131
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作者：
L. Bree;F. Peterse;M.T.J. van der Meer;J. Middelburg;A.M.D. Negash;W. Crop;Christine Cocquyt;J. J. Wieringa-J.;D. Verschuren;J. S. S. Damsté-J.-S.-S.-Damsté-2251792131
我们研究了分布和稳定的碳同位素（δ 13 C）组成的各种脂质生物标志物悬浮颗粒物（SPM）从Chala湖，一个永久分层的火山口湖在赤道东非的水柱，以评估他们的能力，以反映季节性的水柱过程和相关的变化在湖泊的浮游植物群落。这个湖有很大的季节性变化的水柱动态（分层在雨季和旱季混合）与相关的浮游植物演替。我们分析了2013年9月至2015年1月每月在5个深度（0-80 m）收集的SPM中的脂质生物标志物。浮游植物总生物量的季节变化强烈反映在植二烯的浓度，一般光合色素叶绿素的衍生物。2014年6月至12月期间，几种特定生物标志物脂质的盈亏反映了深度混合后浮游植物的明显演替，从长期持续的绿藻水华（由C23：1、C25：1和C27：1正烯烃以及C21和C23正烷烃反映）开始，随后在7月至10月期间硅藻达到峰值（乳石松和等乳石松），然后在10月分层恢复后，真石松（C30和C321，15二醇）。2014年1月至2月水柱浅混合期间C19：1 n-烯烃的峰值丰度可以初步与蓝藻的季节性分布有关。SPM中C28脂肪酸的浓度、季节性变化和低δ 13 C值表明，这种生物标志物是在查拉湖的水柱中产生的，而不是通常认为的维管植物起源。颗粒碳和所有水生生物标志物的δ 13 C特征在混合诱导的高生产力时期变得越来越负（高达16‰），而在这种水华期间预计会富集。这种反向分馏可能归因于化学增强扩散，在高pH值（>9）条件下产生贫HCO 3 −，就像在高生产力时期在查拉湖的上层水层中发生的那样。这一过程的影响可以潜在地解释以前在查拉湖古记录中发现的13 C-贫化碳特征，并且应该在古记录解释高pH值（即碱性）湖泊中水生生物（部分）的有机物δ 13 C值之前加以考虑。
We studied the distribution and stable carbon-isotopic (δ13C) composition of various lipid biomarkers in suspended particulate matter (SPM) from the water column of Lake Chala, a permanently stratified crater lake in equatorial East Africa, to evaluate their capacity to reflect seasonality in water-column processes and associated changes in the lake's phytoplankton community. This lake has large seasonal variation in water-column dynamics (stratified during wet seasons and mixing during dry seasons) with associated phytoplankton succession. We analyzed lipid biomarkers in SPM collected monthly at 5 depths (0–80 m) from September 2013 to January 2015. Seasonal variation in total phytoplankton biovolume is strongly reflected in the concentration of phytadienes, a derivative of the general photosynthetic pigment chlorophyll. The wax and wane of several specific biomarker lipids between June and December 2014 reflect pronounced phytoplankton succession after deep mixing, starting with a long and sustained chlorophyte bloom (reflected by C23:1, C25:1and C27:1n-alkenes, and C21and C23n-alkanes), followed by a peak in diatoms between July and October (loliolide and isololiolide), and then eustigmatophytes (C30and C321,15 diols) once stratification resumes in October. Peak abundance of the C19:1n-alkene during shallow mixing of the water column in January–February 2014 can be tentatively linked to the seasonal distribution of cyanobacteria. The concentration, seasonal variability, and low δ13C values of the C28fatty acid in the SPM suggest that this biomarker is produced in the water column of Lake Chala instead of having the typically assumed vascular plant origin. The δ13C signature of particulate carbon and all aquatic biomarkers become increasingly more negative (by up to 16‰) during mixing-induced episodes of high productivity, whereas enrichment would be expected during such blooms. This reversed fractionation may be attributed to chemically enhanced diffusion, which generates depleted HCO3−under high pH (>9) conditions, as occur in the epilimnion of Lake Chala during periods of high productivity. The influence of this process can potentially explain previously observed13C-depleted carbon signatures in the paleorecord of Lake Chala, and should be considered prior to paleorecord interpretation of organic-matter δ13C values derived (partially) from aquatic organisms in high-pH, i.e. alkaline, lakes.