Monosaccharide anhydrides (MA) records of Lake El'gygytgyn sediments (MIS 5e, 6, 7e, 8,11c, 12c)

We freeze-dried and homogenized 44 samples of c. 0.7-1.8 g dry sediment from core PG1351 covering late glacials and interglacials of MIS 8 to MIS 5e, integrating sediment of 1 cm core depth. Temporal resolution of these samples ranges from 140 to 960 years per sample. For the period between 430 and 405 kyrs ago (end of MIS 12 to MIS 11c), 13 samples of 0.5-1.3 g of dry sediment from ICDP core 5011-1 were taken for MA analyses, integrating sediment of 2 cm core depth. Eight of these 13 samples are from the same core depths as were previously analysed for pollen (Melles et al., 2012). Temporal resolution of these samples varies between 200 and 970 years per sample comparable to core PG1351. Across all samples, temporal resolution is 333 ± 273 years per sample, giving centennial- to millennial scale averages.We extracted the polar lipids of all MA samples using a Dionex Accelerated Solvent Extraction system (ASE 350, ThermoFisher Scientific) at 100°C, 103 bar pressure and two extraction cycles (20 min static time) with 100 % methanol, after an ASE cycle with 100 % dichloromethane. For every sample sequence (n=13-18), we extracted a blank ASE cell and included it in all further steps. We added 60 ng of deuterated levoglucosan (C6H3D7O5; dLVG; Th. Geyer GmbH & Co. KG) as internal standard, and filtered the extract over a PTFE filter using acetonitrile and 5 % HPLC-grade water. We analysed the extracts with an Ultimate 3000 RS ultra-high performance liquid chromatograph (U-HPLC) with thermostated autosampler and column oven coupled to a Q Exactive Plus Orbitrap mass spectrometer (Quadrupole-Orbitrap MS; ThermoFisher Scientific) with heated electrospray injection (HESI) probe at GFZ Potsdam, using measurement conditions adapted from earlier studies (Hopmans et al., 2013;Schreuder et al., 2018;Dietze et al., 2019). Briefly, separation was achieved on two Xbridge BEH amide columns in series (2.1 x 150 mm, 3.5 um particle size) fitted with a 50 mm pre-column of the same material (Waters). The compounds were eluted (flow rate 0.2 mL min-1) with 100 % A for 15 minutes, followed by column cleaning with 100 % B for 15 min, and re-equilibration to starting conditions for 25 min. Eluent A was acetonitrile:water:triethylamine (92.5:7.5:0.01) and eluent B acetonitrile:water:triethylamine (70:30:0.01). HESI settings were as follows: sheath gas (N2) pressure 20 (arbitrary units), auxiliary gas (N2) pressure 3 (arbitrary units), auxiliary gas (N2) temperature of 50 ˚C, spray voltage -2.9 kV (negative ion mode), capillary temperature 300 °C, S-Lens 50 V. Detection was achieved by monitoring m/z 150-200 with a resolution of 280,000 ppm. Targeted data dependent MS2 (normalized collision energy 13 V) was performed on any signal within 10 ppm of m/z 161.0445 (calculated exact mass of deprotonated levoglucosan and its isomers) or m/z 168.0884 (calculated exact mass of deprotonated dLVG) with an isolation window of 0.4 m/z. The detection limit was 2.5 pg on column, based on injections of 0.5 to 5000 pg on column of authentic standards of LVG, MAN, and GAL (Santa Cruz Biotechnology) and dLVG.Integrations were performed on mass chromatograms within 3 ppm mass accuracy and corrected for relative response factors to dLVG (1.08 ± 0.10, 0.76 ± 0.10 and 0.24 ± 0.05 for LVG, MAN, and GAL, respectively), according to known authentic standard mixes injected before and after every measurement sequence and supported by characteristic isomer-specific MS² data. All samples were corrected by subtracting the maximum MA concentrations in the blank duplicates of each ASE sequence. To account for biases due to sediment properties and sedimentation rates, MA influxes (mass accumulation rates in ng cm-2 yr-1) were calculated by multiplying the concentrations (ng g-1) with the sample-specific dry bulk densities (Melles et al., 2007;Wennrich et al., 2016), and the sample's sedimentation rates (cm yr-1) using the age-depth models presented by Nowaczyk et al. (2013) for the the PG1351 and the ICDP-5011-1 cores.

本研究对取自岩芯PG1351的44份干沉积物样品进行冷冻干燥与均质化处理，单份样品干重约0.7~1.8 g，覆盖海洋同位素阶段（Marine Isotope Stage, MIS）8至MIS 5e的晚冰期与间冰期沉积，每份样品均由1cm岩芯深度的沉积物混合制得。该批次样品的时间分辨率为140~960年/样。针对430~405 ka BP（对应海洋同位素阶段12末期至MIS 11c）的沉积时段，我们从ICDP 5011-1岩芯中采集13份干沉积物样品用于生物标志物（Marker Analysis, MA）分析，单份样品干重0.5~1.3 g，每份样品均由2cm岩芯深度的沉积物混合制得。其中8份样品的岩芯深度与此前开展孢粉分析的样品一致（Melles等，2012）。该批次样品的时间分辨率为200~970年/样，与PG1351岩芯样品的时间分辨率相当。所有样品的平均时间分辨率为333±273年/样，对应百年至千年尺度的沉积平均间隔。我们采用戴安加速溶剂萃取系统（Accelerated Solvent Extraction, ASE 350，赛默飞世尔科技）对所有MA分析样品的极性脂类进行提取：先以100%二氯甲烷完成一次ASE循环，随后在100℃、103 bar压力下以100%甲醇进行两次萃取循环（静态萃取时间20 min）。每个样品序列（n=13~18）均设置空白ASE萃取池（无样品），并将空白样品纳入后续所有实验步骤。向提取物中加入60 ng氘代左旋葡聚糖（C6H3D7O5；dLVG；Th. Geyer GmbH & Co. KG）作为内标，随后以乙腈和5%高效液相色谱级水为溶剂，通过聚四氟乙烯（Polytetrafluoroethylene, PTFE）滤膜过滤提取物。采用配备恒温自动进样器与柱温箱的Ultimate 3000 RS超高效液相色谱（Ultra-High Performance Liquid Chromatography, U-HPLC），连接配有加热电喷雾电离（Heated Electrospray Ionization, HESI）探针的Q Exactive Plus Orbitrap四级杆-轨道阱质谱仪（Quadrupole-Orbitrap MS；赛默飞世尔科技），在波茨坦德国地质研究中心（GFZ Potsdam）完成提取物分析，实验参数参照已发表研究（Hopmans等，2013; Schreuder等，2018; Dietze等，2019）进行优化。简要而言，色谱分离采用两根串联的Xbridge BEH酰胺柱（2.1×150 mm，粒径3.5 μm），并搭配50 mm同材质预柱（沃特世，Waters）。以0.2 mL/min的流速进行洗脱：先以100%流动相A运行15 min，随后以100%流动相B冲洗色谱柱15 min，最后以初始流动相体系平衡色谱柱25 min。流动相A为乙腈:水:三乙胺（92.5:7.5:0.01），流动相B为乙腈:水:三乙胺（70:30:0.01）。HESI参数设置如下：鞘气（N2）压力20（任意单位），辅助气（N2）压力3（任意单位），辅助气温度50℃，喷雾电压-2.9 kV（负离子模式），毛细管温度300℃，S-Lens射频电压50 V。检测采用m/z 150~200的质量范围，分辨率为280000 ppm。针对质荷比（m/z）161.0445（去质子化左旋葡聚糖及其异构体的理论精确质量）或m/z 168.0884（去质子化dLVG的理论精确质量）±10 ppm范围内的信号，开展靶向数据依赖型二级质谱（MS²）分析，归一化碰撞能量为13 V，隔离窗口为0.4 m/z。基于0.5~5000 pg柱上进样量的左旋葡聚糖（Levoglucosan, LVG）、甘露糖（Mannose, MAN）、半乳糖（Galactose, GAL）（圣克鲁斯生物技术，Santa Cruz Biotechnology）及dLVG标准品的进样测试，本方法的柱上检测限为2.5 pg。积分操作基于质量色谱图完成，质量准确度控制在3 ppm以内，并根据dLVG的相对响应因子进行校正（LVG、MAN、GAL的相对响应因子分别为1.08±0.10、0.76±0.10和0.24±0.05）；校正依据为每个测量序列前后注入的已知浓度标准品混合溶液，并结合异构体特异性二级质谱数据进行验证。所有样品均通过扣除每个ASE序列空白重复样品的最大MA浓度完成空白校正。为校正沉积物性质与沉积速率带来的偏差，本研究依据Nowaczyk等（2013）提出的PG1351与ICDP-5011-1岩芯年代-深度模型，将样品浓度（ng g⁻¹）与样品专属干容重（Melles等，2007; Wennrich等，2016）、样品沉积速率（cm yr⁻¹）相乘，计算得到MA质量积累速率（mass accumulation rate, MAR，单位为ng cm⁻² yr⁻¹）。