Methodology:

Snow algae and ice cap surface samples were collected in 50 ml sterile plastic sample tubes at locations across the north-west part of Robert Island's ice cap (South Shetland Islands, maritime Antarctic; 62°22'44.4"S 59°42'1.78"W) between 7 January 2023 and 18 February 2023. Sampling locations were chosen to encompass a range of snow and ice surface types.

50 ml and 15 ml samples were taken from the top 3 cm of snow or ice weathering crust. Samples were transported within 1 - 3 h to the laboratory at the Chilean (INACH) station Luis Risopatrón, Coppermine Cove, on Robert Island for sample processing, cell counts and field microscopy.

Sample tubes were thawed at air temperature (<10 °C) within the research station within 1 - 5 h of sampling. Cell counts were obtained manually by counting auto-fluorescent cells in 2 x 10 µl aliquots from each sample on an Invitrogen Countess 3 FL Automated Cell Counter. The identification of algal cells was based on morphological features observed from the cell counter images. An additional 10 µl aliquot was taken for field microscopy and imaging of the fresh samples using a Dino-lite microscope (Taiwan). Samples for additional microscopy in the UK were prepared by centrifuging a 15 ml aliquot of the sample tube for 2 min at 3,000 rpm, removing the snow-melt supernatant, resuspending the pellet, and transferring it to a 2 ml microfuge tube before being stored at -20 °C. Sample pellets for the metabolomics, pigments, FTIR and total CN were freeze-dried on Robert Island for analysis in the UK. Samples were collected from Robert Island by the RRS Sir David Attenborough (SDA) on 24 February 2023 where they were stored at -20 °C and transported to the UK.

Ancylonema cell counts were obtained manually by identifying Ancylonema cells from the Countess 3 FL output images. Due to the poor resolution of the Countess images it was not possible to calculate individual cell counts of other species groups present. An additional 10 µl aliquot was taken for field microscopy and imaging of the fresh samples using a Dino-lite microscope (Taiwan). Biometric measurement of cell length and width for Ancylonema cells were taken from calibrated Dino-lite imagery (n = 570 cells from 37 samples).

The extent of algae on the Robert Island ice cap was determined within a WorldView 2 satellite image (Maxar Technologies), taken on 6 February 2023, coincident with our fieldwork. Using the methodology outlined in Gray, A., Krolikowski, M., Fretwell, P., Convey, P., Peck, L. S., Mendelova, M., Smith, A. G., Davey, M. P., 2021. Remote Sensing Phenology of Antarctic Green and Red Snow Algae Using WorldView Satellites. Frontiers in Plant Science, 12, 877-877. https://doi.org/10.3389/FPLS.2021.671981/BIBTEX, algal presence on the ice cap was classified based on chlorophyll-a absorbance within each pixel. This was calculated on a per-pixel basis using Equation 3, which describes the scaled integral of WorldView 2's Band 4 versus Band 3 and Band 5, the centres of which are located within and on either shoulder of the chlorophyll absorption feature.

Though this method was originally optimised for detecting algae in snow, it successfully separated every HDRF sample from the background snow or weathering crust, when the equation in Gray et al. 2021 was applied to the collected HDRF spectra. However, an ice cap surface is more complex than a pure snow environment, with snow, weathering crust, glacial ice and different loadings of mineral debris. We do not have enough field spectra from this study to fully deconvolve cell densities based on chlorophyll- a absorption alone. Correlation between the equation in Gray et al. 2021 derived and measured cell densities for the HDRF samples we collected only had an R2 of 0.24. We therefore report a binary presence/absence classification of alg...(7)

Data collection:

Instrumentation:

Automated cell counter Thermo Countess 3.

Freeze drier - HarvestRight Home Pro.

Data quality:

Missing coordinate values are due to coordinates not taken on that field day or location due to weather conditions or battery of GPS unit.