Dietze, Elisabeth; Karger, Cornelia; Mangelsdorf, Kai (2020): Monosaccharide anhydrides (MA) records of Lake El'gygytgyn sediments (MIS 5e, 6, 7e, 8,11c, 12c) [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.915603

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.