Methodology:

A total of 64 samples from ponds and lakes were collected on Marion Island during April-May 2011. Altitude, latitude and longitude of the lakes were measured using a GARMIN GPSmap 62s. Water samples were collected from the side of the lakes for chemical analysis. Concentrations of ions and nutrients were measured by atomic absorption spectroscopy (Varian SpectraAA-600) following ISO methods (ISO 7980, 1986; ISO 9964, 1993) and ion chromatography (Dionex ICS-2000) following ISO 10304-1(2007). Temperature, Specific Conductivity, Salinity and pH were measured in the field using a YSI 600 meter. Surface-sediment samples for diatom analysis were taken by hand from the side of each lake at a water depth of c. 20 cm.

Diatom samples were prepared following Van der Werff (1955). Organic matter was removed by adding 37% H2O2 heating to 80°C for about 1h, after which the reaction was completed by addition of KMnO4. Following digestion and centrifugation (3 times 10 minutes at 3500 rpm), the material was diluted with distilled water. Cleaned diatom valves were mounted in Naphrax® and counted and identified on random transects using a Zeiss Axioplan II light microscope with a magnification of 10x100x and immersion oil and an Olympus BX51 microscope equipped with Normarski optics. A minimum of c. 400 diatom valves were counted per slide. Samples MI23, MI57 and MI35 had very low diatom concentrations and counts were restricted to 200, 200 and 100 valves respectively. Diatom identification was based on Van de Vijver et al. (2002) together with more recent publications for a number of species (e.g., Flower et al. (2005); Kulikovskyi et al. (2010); Le Cohu (2005); Lowe et al. (2014); Romero and Van de Vijver (2011); Van de Vijver (2012); Van de Vijver and Cox (2013); Van de Vijver and Gremmen (2006); Van de Vijver et al. (2004, 2011, 2012a, 2012b, 2013); Witkowski et al. (2012); Ziderova et al. (2010, 2012)). Diatom species were expressed as relative abundances (% of total diatom valves per sample).

Bedrock substrate was quantified as lava type for grey lava (1 for older weathered lavas) or black lava (0 for more recent, Holocene age).

Marion_island_diatoms.csv contains diatom relative frequencies for each sample (%) collected on Marion Island. Sample IDs are given using the following naming convention: MIXX where MI refers to Marion Island and XX an arbitrary assigned lake number.

Marion_island_environment.csv contains environment information (concentrations of ions and nutrients) as well as geographical data for each sample collected.

Data collection:

Instrumentation used included:

GPS: GARMIN GPSmap 62s

atomic absorption spectroscopy: Varian SpectraAA-600

ion chromatography: Dionex ICS-2000

conductivity, salinity, pH: YSI 600 meter

microscopy: Zeiss Axioplan II light microscope, Olympus BX51 microscope equipped with Normarski optics.