Chlorophyll a, particulate organic carbon (POC), particulate organic nitrogen (PON), particulate organic phosphorous (POP) and Surfactants measurements from the central arctic

As part of the MOCCHA 2018 campaign onboard I/B Oden, Sea surface microlayer (SML) and underlying water (ULW) samples were taken from an open lead system in the central arctic. Sampling occured during the autumn freeze-up from 18.08.18 - 08.09.18. Latitude ranged from 88.7644-89.5474 degrees and longitude ranged from 38.1087-45.7652 degrees as the ice pack moved over time, elevevation remained 0. Sea surface microlayer samples were collected using the glass plate technique (Harvey and Burzell, 1972, doi:10.4319/lo.1972.17.1.0156) via rotating glass disks equipped to a catamaran and underlying water samples were collected from 1 meter depth. Seven variables were sampled for; transparent exopolymer particles (TEP), coomassie stainable particles (CSP), surfactants, chlorophyll a, particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate organic phosphorous (POP). Their concentrations are presented here in micrograms per litre. sea surface microlayer (SML) and undrlaying water (ULW) samples were brought back to a wet lab onboard I/B Oden. All samples were stored in their respective states until processing and analysis could be done after the expedition in laboratories of the University of Oldenburg. Transparent exopolymer particles (TEP) were measured by filtering seawater, in triplicates, onto 0.2 µm polycarbonate filters under low vacuum (< 100mmHg) and staining with alcian blue solution (0.02 g alcian blue in 100mL of acetic acid solution of pH 2.5) for 5 s. The 0.2 µm filters collect both large TEP aggregates and smaller colloidal TEP material. Filters were placed in Eppendorf tubes and stored at -18 °C until processing back in the home laboratory. In the laboratory, Alcian blue stain was extracted for 2 h in 80% sulfuric acid, with gentle agitation applied to reduce bubble formation, and analysed using a spectrophotometer (VWR UV-1600PC, precision of 1±0.2%T) following (Passow and Alldredge, 1995, doi:10.4319/lo.1995.40.7.1326.). The stock solution of Alcian blue was calibrated using the xanthan gum (Carl Roth) standard according to Passow and Alldredge (1995). TEP concentrations are shown in relation to xanthan gum equivalence (µg XG eq. L-1). Recent calibration issues noted by Bittar et al. (2018, doi:10.1002/lom3.10268) were not observed in our studies, and thus their new method was not required. Coomassie stainable particles (CSP) were measured by filtering seawater, in triplicates, onto 0.2 µm polycarbonate filters under low vacuum (< 100mmHg) and staining with Coomassie brilliant blue (0.04% in filtered seawater solution with a pH of 7.4) for 30 s. Filters were stored at -18°C until processing back in the home laboratory. In the laboratory, stained filters were placed in glass vials with 10ml of extraction solution (3% SDS in 50% isopropyl alcohol) and gently agitated for 2 hours. Sonication as suggested by Cisternas-Novoa et al. (2014) always resulted in deterioration and consequential contamination by filters, thus only continuous gentle agitation was applied and showed to be sufficient in extracting the stain from the filters into the solution. Extracted stain was then analysed using a spectrophotometer (VWR UV-1600PC, precision of 1±0.2%T) following (Cisternas-Novoa et al., 2014, doi:10.4319/lom.2014.12.604.). Surfactant concentrations were measured using a voltammetry instrument (VA Stand 747, Metrohm, Switzerland) which incorporates a hanging mercury drop electrode (Ćosović, B., and Vojvodić, V. (1998, doi:10.1002/(SICI)1521-4109(199805)10:63.0.CO;2-7) and measures surfactants as bulk concentrations. Under stirring for roughly 30 seconds, surfactants accumulate at the hanging mercury drop electrode at a potential of -0.6 V versus an Ag/AgCl reference electrode. The frequency of the A.C. voltage was 170 Hz and the p-p amplitude was 10 mV. With a sampling rate of 20 mV s-1, the phase-shifted signal of the A.C. current was measured to quantify the amount of surfactants accumulating on the Hg drop. For sample evaluation, 10ml of unfiltered seawater were collected and stored at 4°C in the dark until they could be analysed back in the home laboratory. Each sample was measured three to four times using a standard addition technique involving the non-ionic surfactant Triton X-100 (Sigma Aldrich, Germany) as the standard. Surfactant concentrations are therefore expressed as the equivalent concentration of Triton X-100 addition (µg Teq L-1).