DOI: 10.5285/9cd08043-4498-4688-91d8-bb8a867d9024
title: In-situ tracer percolation experiments: conditions, results, and alteration of stable water isotope signatures in the seasonal snow near Ny-Alesund, Svalbard, in March 2023

description: This dataset contains detailed records of in-situ tracer percolation experiments conducted near Ny-Alesund, Svalbard, between 21st and 31st March 2023. For each of the ten snow pits and their respective one to three experiments, we report experiment specifications, temperature monitoring during the experiments, percolation results, and stable water isotope (SWI) signatures after the experiments. The records were obtained by Dorothea Moser as part of an experimental field project ("Wet Fingerprints").

The project was supported by an Arctic Field Grant through the Norwegian Research Council (Project No. 342165, Research in Svalbard RiS ID 12132). Dorothea Elisabeth Moser was supported by BAS Cambridge and the NERC C-CLEAR Doctoral Training Programme (grant no. NE/S007164/1).
description: The following experiment description is based on Moser (2025):

General tracer experiment information:
We conducted in-situ melt experiments that have been designed to mirror short ROS-induced melt events and to trace percolation via visual features corresponding to structural imprint, thermal changes and SWI alteration of the snowpack. 
The melt tracer is based on ultrapure (Milli-Q) water mixed with deuterium oxide (D2O) and blue food dye, following the procedure laid out in Moser (2025), to enable visually and chemically tracing percolation. The percolation tracer of known composition is applied to a defined surface area (40 x 20 cm) of the already assessed snow pit (data available: Moser et al., 2025). The prepared tracer characteristics (volume, temperature, composition) are known before it is evenly distributed onto the snow surface using a sprinkler. 

We documented the specifics for all tracer percolation experiments in the respective snowpit, including: 
Date: DD.MM.YYYY;
Experiment number: consistent across temperature monitoring, percolation depth and SWI results to enable linking of records;
Liquid volume: in millilitres, measured in the NERC Arctic Station lab at the start of the field day;
Liquid temperature: in deg C, measured using a digital thermometer immediately before application in the field;
SWI Tracer ID: system-internal identifier assigned from the fieldwork vial until data processing to enable continuous data tracking;
Tracer d2H and Tracer d18O: the d2H and d18O signature of the tracer liquid, both reported in permil (ppth) against V-SMOW;
Pouring time: is the number of seconds it took to apply the entire tracer liquid to the experiment area. Note: if the pouring time was, e.g., 15 seconds, this corresponds to the first 0.25 decimal minutes of the experiment in the temperature monitoring record.
Thermometer positions: each thermometer is numbered (consistent with the temperature monitoring record in a separate CSV file) and its respective position in the snow pit reported as height above the ground in centimetres.
Note that experiment no. 2 and no. 3 for the snowpit dug on the 25th of March were conducted on 26th March.

Temperature monitoring:
Digital thermometers were placed in regular intervals below the surface, e.g. every 2 cm in the top 10 cm, and used to record snow temperature at regular intervals throughout the percolation observation period. Experiments were concluded when temperatures in the affected snowpack, as reflected by the top thermometer, started to drop, thereby indicating the predominance of refreezing.
In the related CSV file, the first column identifies the experiment number. The second column gives the time since the start of the experiment in decimal minutes. Where values are provided for the 0-minute time step, this shows the temperatures at the start of the experiment. In the subsequent columns, temperature readings are provided for each numbered thermometer at each time-step. The number of thermometers used varies between snowpits, but is consistent within experiments.

Percolation result depths:
Upon completion of the percolation experiment, we used the blue colour of the tracer to measure the average and maximum percolation depth on the snow pit front. These measurements were repeated on two new snow pit fronts that were cut 5 cm and 10 cm into the experiment area to evaluate and ensure representativity. Maximum percolation depth is the greatest depth reached by blue dye during an experiment, and average percolation depth reflects surface melt layer thickness on the respective front. 

The Percolation Results table contains:
Experiment number: given to allow linkage with corresponding "Tracer_Experiments_Info" CSV in the same folder.
For each of the snow pit fronts (0 cm = Front_0, 5 cm = Front_5, 10 cm into the experiment area = Front_10), we provide average and maximum percolation depth. For each, the columns are labelled "Front_X_avg" and "Front_X_max". The estimates are given in centimetres. Note that on 31st March, we added another front cut at 15 cm for the second experiment, so that there are two additional estimates, i.e. columns, in that CSV file.
SWI_Sampling: This column specifies on which of the front cuts the SWI samples were taken. The front naming system is consistent (0 cm = Front_0, 5 cm = Front_5, 10 cm into the experiment area = Front_10). If no SWI sampling was conducted on any front, the cell value is "na".

Stable water isotopes (SWI) after percolation experiments:
Upon completion of each tracer percolation experiment, we assessed the two stable water isotope ratios d18O and d2H, which are abbreviated as d18O and d2H, respectively (7 snow pits, 23rd - 30th March). We sampled in several affected (blue) and unaffected dry (white) parts. Sampling was done by pushing sterilised, dry 50-mL polypropylene centrifuge tubes 5 cm horizontally into the snow pit front, which was freshly cut using a stainless-steel hand saw (STANLEY). The SWI measurements were conducted using a Picarro L2130-i setup based on cavity ring-down spectroscopy located at BAS in June 2023. The Sample ID is a system-internal identifier, which is assigned to the samples from fieldwork until data processing. The Picarro measurements are primarily processed using the LIMS software.
It should be noted that we obtained SWI signatures both before and after tracer percolation experiments to facilitate a comparison of SWI preservation. This is why we named the CSV files, which contain SWI signatures of the specified snow pit after the experiment "SWI_After_Experiments". The corresponding "SWI_Before" data are published in the related dataset. In the SWI-related csv file of each snowpit, we provide the number of the experiment, so that it can be linked to the tracer experiment information in a separate CSV file in the same folder. The column "tracer presence" distinguishes between blue, tracer-affected (value = 1) and white, unaffected (value = 0) samples.

Further:
All measurements made in the field were immediately recorded in a field notebook and digitised upon return to the NERC Arctic Station the same day. All further data processing of the above records was conducted using Microsoft Office Excel 365. Certain measurements were only included after a few experiments, e.g. pouring time and temperature monitoring, and the related cells are filled with "na" where unavailable.
description: General:
Depth measurements: Foldable ruler.
Timekeeping: Stopwatch feature in Clock app (Samsung Galaxy A52s, Android).
Temperature:
Digital Thermometers: Salter 544A HBBKCR and Salter 518 WHCR, 0.1 deg C precision.
SWI:
Polypropylene (BIOFIL) centrifuge tubes.
Picarro L2130-i.

All measurements made in the field were immediately recorded in a field notebook and digitised upon return to the NERC Arctic Station the same day. The Picarro measurements are primarily processed using the LIMS software. All further data processing of the above records was conducted using Microsoft Office Excel 365.
description: The following measures were taken for quality control:
General snow pit setup: We always assessed a snow pit wall that was permanently in the shadow and downwind to prevent artefacts through incoming solar radiation or snow re-deposition.
Percolation depth: Measurements of average and maximum percolation depth were repeated on at least 3 fronts for each experiment to achieve representative results.
Depth readings: percolation estimates and SWI samples taken below the surface after experiments are corrected for surface compaction and reported against the snow surface prior to the experiment.
SWI Sampling: Of each prepared tracer liquid, a small sample was kept and measured for its SWI signatures to ensure comparability in composition.
Empty cells: Where information could not be obtained or has been excluded due to erroneous data points, the cells in the CSV tables are filled with "na".