PANGAEA_996907 GEM-2 total ice thickness estimates and MagnaProbe snow and melt pond depth measurements of the ice floe transect during station PS149_25-1 during the PS149 CONTRASTS expedition (July-August 2025) Ringel, Maximilian Harald; Spreen, Gunnar; Krumpen, Thomas; Neudert, Mara GEM-2 total ice thickness estimates and MagnaProbe snow and melt pond depth measurements of the ice floe transect during station PS149_25-1 during the PS149 CONTRASTS expedition (July-August 2025) 2026-09-02 PANGAEA Dataset https://doi.pangaea.de/10.1594/PANGAEA.996907 Earth Science geoscientificInformation Arctic CONTRASTS expedition electromagnetic induction GEM-2 Geophex magnaprobe melt pond depth ocean PS149 RV Polarstern Sea ice Sea ice thickness snow depth 2025-07-31 2025-08-01 Complete 83.7067067 83.738121 17.3996334 18.9907513 AC3 Arctic Amplification unrestricted CC-BY-4.0: Creative Commons Attribution 4.0 International English PANGAEA Data Publisher for Earth & Environmental Science https://www.pangaea.de/ Data Center Contact Michael Diepenbroek info@pangaea.de

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Bremen Bremen 28359 Germany online 2 datasets application/zip Nicolaus, Marcel (2026): The Expedition PS149 of the Research Vessel POLARSTERN to the Arctic Ocean in 2025. Berichte zur Polar- und Meeresforschung = Reports on Polar and Marine Research, 808, 382 pp, https://doi.org/10.57738/BZPM_0808_2026 Ringel, Maximilian Harald; Spreen, Gunnar; Krumpen, Thomas; Neudert, Mara (2026): GEM-2 raw electromagnetic measurements of the ice floe transects during the PS149 CONTRASTS expedition (July-August 2025) [dataset bundled publication]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.996869 Ringel, Maximilian Harald; Spreen, Gunnar; Krumpen, Thomas; Neudert, Mara (2026): GEM-2 total ice thickness estimates co-located with MagnaProbe snow and melt pond depth measurements of the ice floe transects during the PS149 CONTRASTS expedition (July-August 2025) [dataset bundled publication]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.996908

This dataset contains the measurements of snow/SSL (surface scattering layer) depth or melt pond depth as well as the total ice thickness estimates from a walk across the sea ice floe (called long transect) during ice station PS149_25-1 (floe 2b) of the PS149 CONTRASTS expedition. The long transect was traversed across the ice floe to obtain statistically representative distributions of snow/pond depth and ice thickness. The transect was marked with flags at its corner points to ensure that a similar track was measured during repeated visits to the ice floe. A GPS-equipped MagnaProbe was used to measure snow/SSL and melt pond depth, while a Geophex Ltd. GEM2-730 instrument was used to measure total sea ice thickness. Total sea ice thickness refers to the distance between the instrument and the ice–ocean interface. Accordingly, if present, snow/SSL or melt pond depth must be subtracted from this total thickness to obtain the actual sea ice thickness estimate. Since the GEM and MagnaProbe measurements at this station were conducted on two consecutive days, ice floe drift between the surveys would make precise spatiotemporal co-location of the datasets unreliable. Therefore, the measurements are provided as separate datasets without any drift correction. However, both were collected along the same marked transect track. The measurements of all other PS149 ice stations are co-located and available here: https://doi.pangaea.de/10.1594/PANGAEA.996908. ** For all details see the full metadata description at "https://doi.pangaea.de/10.1594/PANGAEA.996907"! ** GEM instrument & data processing: The same frequency set as in the MOSAiC campaign (https://doi.pangaea.de/10.1594/PANGAEA.943666) was used for the GEM measurements: 1.525 kHz, 5.325 kHz, 18.325 kHz, 63.025 kHz, and 93.075 kHz. The ice thickness estimates are derived for all these frequencies from the raw GEM measurements (https://doi.pangaea.de/10.1594/PANGAEA.996869) using an empirical calibration procedure. For this procedure, the GEM was positioned at known heights using the steps of a wooden ladder standing on a flat area of the sea ice floe, where sea ice thickness was measured at five locations below the instrument. Based on these calibration measurements, an exponential function is derived and applied to the transect data to retrieve the total ice thickness. For the calibration, the conductivity of the sea ice plus snow layer was assumed to be 0.05 S m⁻¹, and the conductivity of seawater was set to 2.55 S m⁻¹. Since the calibration was performed on unponded sea ice, the conductivity of melt pond water was not directly accounted for. For the transect the GEM instrument was mounted within a Pulka sledge leading to a height offset of about 0.11m relative to the ground. The processing software to retrieve the total ice thickness from the raw electromagnetic measurements is based on the gem2-seaice-toolbox (https://gitlab.awi.de/sitem/gem2-seaice-toolbox), and its application is detailed in the following tutorial: https://gitlab.awi.de/sitem/gem2-processing-tutorial. The calibration measurements, along with all YAML files used to derive the total ice thickness, is provided with the raw data (https://doi.pangaea.de/10.1594/PANGAEA.996869). Notes: - For the GEM-2-730 data we recommend using the ice thickness derived from the 18.325 kHz in-phase channel for further analysis similar to the GEM processing performed for the MOSAiC campaign (see link above) - If there's no derived sea ice thickness data for a specific channel (e.g. 93.075 kHz quadrature) this means that, for some reason, the sea ice thickness could not be derived for this channel. -- MagnaProbe instrument & processing: The MagnaProbe (produced by Snow-Hydro LLC) instrument measures the depth of the snow and/or surface scattering layer (SSL) on top of the sea ice as well as the depth of melt ponds. The probe consists of a 1.5 m long measuring rod with a flat basket at the lower end. During the measurement, the rod is inserted into the snow, with the basket remaining on the snow surface. The basket was adapted with a flotation made of extruded polystyrene foam. This adaptation allows to measure the depth of melt ponds as the basket floats and stays on top of the water surface. The difference between the sensor tip (ice surface) and the basket (snow/water surface) gives the snow/SSL or melt pond depth. In addition, the GPS position is recorded for each measurement. All measured data is stored in a data logger in the backpack carried by the operator and can be read out later on a PC. MagnaProbe profiles along transects were always measured in conjunction with ice thickness measurements from the GEM (see above). The difference between the GEM measurements and the snow depth measured by the MagnaProbe then gives the actual sea ice thickness. During transect measurements melt ponds were marked in the dataset by a double-measurement, i.e., pushing the button of the MagnaProbe two times at the same location. The MagnaProbe is calibrated for every transect by doing three measurement when the basket is at lowest and highest position, respectively. This calibration is done at the beginning and end of each transect. This transect was performed with magnaprobe-marcel". In a first step, melt pond measurements have to be identified in the dataset. Melt ponds were marked by a double-measurement. Thus, two criteria were used to identify melt ponds: 1) The time difference Δt between two measurements is smaller than a specified threshold value called MPDT and 2) The depth difference Δd between the two measurements is smaller than a specified threshold value called MPDD. MPDT and MPDD were identified for every transect from histogram plots and vary for MPDT between 1.4 s and 3 s and for MPDD between 1 cm and 2.6 cm. The six calibration measurements for the basket in lowest position (three at the beginning, and three at the end of the transect) were averaged and used as reference. The offset of the MagnaProbe is then determined by subtracting the reference value from the length of the metal tip of the MagnaProbe value. The offset is added to all MagnaProbe measurements. Finally. the snow/SSL depth and melt pond depth measurement values were saved as CSV files together with the GPS position and time of each measurement.

https://doi.org/10.57738/BZPM_0808_2026 The Expedition PS149 of the Research Vessel POLARSTERN to the Arctic Ocean in 2025 https://doi.pangaea.de/10.1594/PANGAEA.996869 GEM-2 raw electromagnetic measurements of the ice floe transects during the PS149 CONTRASTS expedition (July-August 2025) https://doi.pangaea.de/10.1594/PANGAEA.996908 GEM-2 total ice thickness estimates co-located with MagnaProbe snow and melt pond depth measurements of the ice floe transects during the PS149 CONTRASTS expedition (July-August 2025) https://gepris.dfg.de/project/268020496 AC3 DIF 9.4 2026-09-02 2026-09-02