Melt ponds and leads water sampling for biogeochemical parameters during expedition PS122/5 (MOSAiC Leg 5) to the central Arctic in August-September 2020.

Melt ponds water sampling for biogeochemical parameters such as dissolved inorganic carbon (DIC), total alkalinity (TA), oxygen isotopes were examined from August to September 2020. To obtain discrete water samples from the melt ponds and leads, we checked the vertical structure and depth of the meltwater layer from the same hole used for the RINKO Profiler by attaching a conductivity sensor (Cond 315i, WTW GmbH, Germany) to a 2-m-long ruler and inserting the ruler into the lead water until the salinity measured with the Cond 315i increased at the meltwater-seawater interface (Nomura et al., 2024) . Water was pumped up with a peristaltic pump through a 2-m-long PTFE tube (L/S Pump Tubing, Masterflex, USA) at depths corresponding to meltwater (surface), the interface between meltwater and seawater (interface), and seawater (bottom). Salinity was measured at each depth by attaching a Cond 315i conductivity sensor to the bottom of the ruler. The tube intake was likewise attached to the bottom of the ruler. Seawater was subsampled into a 250-mL glass vial (Duran Co., Ltd., Germany) for measurement of dissolved inorganic carbon (DIC) and total alkalinity (TA) and a 50-mL glass, screw-cap, narrow-neck vial (VWR international LLC, Germany) for measurement of the oxygen isotopic ratio (delta18O) of the water. Immediately after subsampling for measurement of DIC and TA, a 6.0% (wt.) mercuric chloride (HgCl2) solution (100 micro L) was added to stop biological activity. Samples for DIC and TA were stored at +4 degreeC on the R/V Polarstern. Samples for delta 18 O were stored at room temperature (20 degreeC). During the discrete water sampling, the CO2 concentration in the water column was measured directly on site by passing the water through an equilibrator Liqui-Cel (G542, S/N: 132462, 3M Company, USA) connected to an infrared gas analyzer (LI-8100A, LI-COR Inc., USA). The analyzer was calibrated with standard gases containing 0.0, 299.3, and 501.3 ppm CO2 before MOSAiC Leg 5. RMS (root means square) noise at 370 ppm with 1 sec signal averaging is <1 ppm (https://www.licor.com/env/products/soil-flux/LI-8100a). The equilibrator was connected in the loop for water sampling (vide supra), and a 2-m-long ruler was inserted into the water and kept at that depth until the CO2 was equilibrated with air (about 1 minute) by monitoring the CO2 values. The CO2 concentration was measured at each depth (i.e., surface, interface, and bottom). At the ROV lead sites, vertical CO2 measurements were made every 0.05 m for detailed profiles. The DIC of water was determined by coulometry (Johnson et al., 1985; Johnson, 1992) using a home-made CO2 extraction system (Ono et al., 1998) and a coulometer (CM5012, UIC, Inc., Binghamton, NY, USA). The TA of water was determined by titration (Dickson et al., 2007) using a TA analyzer (ATT-05, Kimoto Electric Co., Ltd., Japan). Both DIC and TA measurements were calibrated with reference seawater materials (Batch AR, AU, and AV; KANSO Technos Co., Ltd., Osaka, Japan) traceable to the Certified Reference Material distributed by Prof. A. G. Dickson (Scripps Institution of Oceanography, La Jolla, CA, USA). Oxygen isotope analyses were carried out at the ISOLAB Facility at AWI Potsdam (hdl:10013/sensor.ddc92f54-4c63-492d-81c7-696260694001) with mass spectrometers (DELTA-S Finnigan MAT, USA): hdl:10013/sensor.af148dea-fe65-4c87-9744-50dc4c81f7c9 and hdl:10013/sensor.62e86761-9fae-4f12-9c10-9b245028ea4c employing the equilibration method (details in Meyer et al., 2000). delta 18 O values were given in per mil (permillage) vs. Vienna standard mean ocean water (V-SMOW) as the standard.2020年8月至9月，研究人员针对融池的生物地球化学参数——包括溶解无机碳（dissolved inorganic carbon, DIC）、总碱度（total alkalinity, TA）与氧同位素——开展了水体采样分析。为从融池与冰间水道采集离散水体样本，我们将电导传感器（Cond 315i，德国WTW有限公司）安装于2米长标尺之上，将标尺插入冰间水道水中，直至该传感器测得的盐度在融水-海水界面处出现升高，以此确定融水层的垂直结构与厚度，所用钻孔与RINKO剖面仪（RINKO Profiler）的钻孔一致（Nomura等，2024）。随后使用蠕动泵，通过2米长聚四氟乙烯管（L/S泵管，Masterflex，美国）从对应深度抽取水样：融水层（表层）、融水-海水界面（界面层）与海水层（底层）。每一层的盐度均通过安装在标尺底端的Cond 315i电导传感器测定，该采样管的取水口同样固定于标尺底端。将海水分装至两种采样容器：250毫升玻璃瓶（德国Duran有限公司）用于测定溶解无机碳（DIC）与总碱度（TA），以及50毫升带螺旋盖的窄口玻璃瓶（德国VWR国际有限责任公司）用于测定水体氧同位素比值（δ¹⁸O）。完成DIC与TA取样后，立即向样本中加入6.0%（质量分数）氯化汞（HgCl₂）溶液（100微升）以抑制生物活动。DIC与TA样本在“极星号”科考船（R/V Polarstern）上于+4℃条件下保存，δ¹⁸O样本则于室温（20℃）下保存。在离散水体采样期间，通过将水样流经连接红外气体分析仪（LI-8100A，美国LI-COR公司）的Liqui-Cel平衡器（G542，序列号：132462，美国3M公司），现场直接测定水柱中的CO₂浓度。在MOSAiC第5航次前，已使用浓度分别为0.0、299.3和501.3 ppm的标准CO₂气体对分析仪完成校准。在370 ppm浓度下，采用1秒信号平均时的均方根（root mean square, RMS）噪声小于1 ppm（数据来源：https://www.licor.com/env/products/soil-flux/LI-8100a）。该平衡器接入水样采样环路（如前文所述），将2米长标尺插入水中并固定于目标深度，通过实时监测CO₂值直至其与空气达到平衡（约需1分钟），随后分别在表层、界面层与底层三个深度测定CO₂浓度。在遥控水下机器人（Remotely Operated Vehicle, ROV）冰间水道测点处，以0.05米的间隔开展垂直CO₂剖面的高精度测量。水体溶解无机碳（DIC）采用库仑法测定（Johnson等，1985；Johnson，1992），使用自制CO₂萃取系统（Ono等，1998）与库仑计（CM5012，美国UIC公司，纽约州宾厄姆顿）。总碱度（TA）则采用滴定法测定（Dickson等，2007），使用TA分析仪（ATT-05，日本木村电机株式会社）。DIC与TA的测定结果均采用可追溯至A.G. Dickson教授（美国斯克里普斯海洋研究所，加利福尼亚州拉霍亚）分发的标准参考物质的海水参考材料（批次AR、AU与AV；日本大阪KANSO Technos有限公司）进行校准。氧同位素分析在阿尔弗雷德·魏格纳研究所波茨坦分所ISOLAB实验室（hdl:10013/sensor.ddc92f54-4c63-492d-81c7-696260694001）开展，使用质谱仪（DELTA-S Finnigan MAT，美国）：对应标识为hdl:10013/sensor.af148dea-fe65-4c87-9744-50dc4c81f7c9与hdl:10013/sensor.62e86761-9fae-4f12-9c10-9b245028ea4c，采用平衡法进行分析（详细方法参见Meyer等，2000）。δ¹⁸O值以维也纳标准平均海水（Vienna Standard Mean Ocean Water, V-SMOW）为标准，以千分比（permil）为单位表示。