Oxygen and hydrogen isotopic ratios from sea ice bottom, false bottom ice, under-ice meltwater layer and surface melt pond samples collected during MOSAiC leg 4 (PS122.4)@en

Oxygen and hydrogen isotopic ratio samples were collected from sea ice and water samples. Coring and sampling were completed at six locations on July 25 for measurement of salinity and stable oxygen isotopic composition to better understand the meltwater sources for under-ice meltwater and false bottoms. Cores were collected using a corer (9 cm inner diameter; Mark II coring system, Kovacs Enterprises, US), and ice samples were collected from the bottom 10 centimeters of the ice core in 5 cm increments (0-5 and 5-10 cm above the bottom) and from the false bottom ice. Under-ice meltwater layer samples and water from directly below the false bottom were collected using a peristaltic pump. In order to minimize contamination from coring activities, under-ice meltwater samples from the meltwater layer in the void space between ice and false bottom were collected prior to coring through the false bottom. Surface melt pond water samples were collected by dipping plastic sample cups (rinsed with milliQ water) in the melt ponds where cores were collected, prior to ice coring. In total, ice samples were collected from six cores –– five of which included false bottoms –– and water samples were collected from four surface melt ponds, three under-ice melt water layers, and seawater beneath false bottoms at four locations. Locations are shown on map (Figure 2) as pink dashes. Ice samples were melted onboard the R/V Polarstern, and salinities of all water and ice samples were measured onboard using a calibrated YSI model 30 probe (salinity is given in PSS-78 scale, unitless). Vials for oxygen isotope composition were shipped to the AlfredWegener Institute (AWI) ISOLAB Facility in Potsdam, Germany, where they were analyzed for stable water isotopes with Finnigan MAT Delta-S mass spectrometers using equilibration techniques. The oxygen isotope composition is given as per mil difference relative to VSMOW (‰, Vienna Standard Mean Ocean Water), with an internal 1 sigma error better than 0.1‰ for delta 18O (Meyer et al., 2000). See attached diagram for a visualization of where the samples were collected.本数据集的氧、氢同位素比值样品采集自海冰及水体样品。研究团队于7月25日在6个采样点位完成钻取与采样工作，旨在测定盐度与稳定氧同位素组成，以深入解析冰下融水层与假底冰（false bottoms）的融水来源。冰芯（ice core）采用内径9 cm的Mark II钻取系统（Kovacs Enterprises，美国）采集；冰样品则从冰芯底部10 cm范围内以5 cm为间隔（距冰底0-5 cm、5-10 cm）以及假底冰中获取。冰下融水层样品以及假底冰正下方的水体样品，通过蠕动泵（peristaltic pump）采集。为最大程度降低钻取作业带来的污染，冰与假底冰之间空隙内的融水层冰下融水样品，需在通过假底冰开展钻取作业前完成采集。冰芯钻取作业前，使用经MilliQ水冲洗后的塑料样品杯，在布设冰芯点位的融水池（melt ponds）中采集表层融池水样品。本次采样共获取6根冰芯（其中5根包含假底冰），并从4个表层融水池、3个冰下融水层以及4个点位的假底冰下方海水中采集水体样品。采样点位以粉色虚线标注于地图（图2）中。冰样品在‘极星号’科考船（R/V Polarstern）上进行融解，所有水体与冰样品的盐度均在船上使用经过校准的YSI 30型盐度探头（YSI model 30 probe）测定，盐度以PSS-78盐度标度（PSS-78 scale）表示，无单位。用于氧同位素分析的样品瓶被运送至德国波茨坦的阿尔弗雷德·魏格纳研究所（Alfred Wegener Institute, AWI）同位素实验室（ISOLAB Facility），采用平衡技术结合Finnigan MAT Delta-S型质谱仪（Finnigan MAT Delta-S mass spectrometers）对样品的稳定水同位素进行分析。氧同位素组成以相对于维也纳标准平均海水（Vienna Standard Mean Ocean Water, VSMOW）的千分偏差（‰）表示，δ¹⁸O（delta 18O）的内部1σ误差优于0.1‰（Meyer等，2000）。采样点位的具体布设情况可参见附件示意图。