Micromelt sampling of the glacier algal nutrient environment

Abstract

Zygnematophycean "glacier algae" form extensive blooms on ablating glacier surfaces despite the ultra-oligotrophic conditions apparent. Previous work has postulated that this oligotrophic bloom paradox is due to (i) lower nutrient requirements of glacier algae, (ii) efficient uptake and storage of the nutrients available, and/or (iii) ineffective characterisation of the actual nutrient environment that glacier algae experience. We investigate the latter here by directly sampling the thin (∼2 mm) melt water film in which glacier algal cells reside across three glaciers in Svalbard during the 2023 melt season, comparing to outcomes from more typical bulk ice sampling techniques. Micromelt samples generally contained increased concentrations of ammonium (NH4+), nitrate (NO3-), nitrite (NO2-), and phosphate (PO43-), though trends were not uniform, and concentrations remained well within oligotrophic levels. Several major ion species were significantly increased in micromelt fractions as compared to bulk samples, indicating aeolian deposition and marine aerosol influences on the glacier algal environment. In turn, enhanced micromelt dissolved organic carbon concentrations (DOC) indicated likely DOC delivery by glacier algae to the microbial food web from the onset of bloom formation. Taken together, datasets reveal new fine-scale heterogeneity in the glacier algal meltwater environment.

Keywords: Arctic; algal bloom; glacier algae; ice; oligotrophic; supraglacial.

Figure 1.

Glacier sampling sites in Svalbard, satellite photography of Kongsfjord and Ny Ålesund during summer ablation period 2023. (a) Vestre Brøggerbreen (78.914196°N, 11.754798°W) sampled 10 and 21 July 2023. (b) Austre Brøggerbreen (78.897387°N, 11.833194°W) sampled 19 and 25 July 2023. (c) Feiringbreen (79.006498°N, 12.447865°W) sampled 14 and 22 July 2023 (TopoSvalbard—Norsk Polarinstitutt, 2023.).

Figure 2.

Supraglacial sampling method comparison (a) supraglacial sample site demarked by a black square (20 cm h⁻¹ × 20 cm w⁻¹ × ∼2 cm d⁻¹). (b) Set-up of bulk samples (n = 5) and micromelt samples taken using a peristaltic pump and wide bore needle, with the sampled area indicated by gray and black squares, respectively. (c) Traditional bulk sampling collects both ice and water present in the ablating glacier surface via scoop. (d) In situ microscope image of algal cells (indicated by colored arrows) being suctioned up into a needle (white arrow) for liquid-only micromelt sampling, scale bar is 200μm.

Figure 3.

Ancylonema spp. abundance across three glaciers: Austre Brøggerbreen (AB), Feiringbreen (FB), and Vestre Brøggerbreen (VB) over two timepoints (T1, T2) approximately 2 weeks apart. Comparison of (a) bulk sampling method (n = 10) and (b) micromelt sampling method (n = 6–10).

Figure 4.

Comparison of major nutrient concentration within the aqueous geochemistry retrieved by traditional bulk and novel micromelt sampling methods. Supraglacial samples were taken from three Svalbard glaciers during the early ablation period (pooled timepoints, 06/2023): Austre Broggerbreen, Feiringbreen, and Vestre Broggerbreen. (a) DOC, (b) ammonium (NH₄⁺), (c) phosphate (PO₄³⁻), (d) nitrate (NO₃⁻), (e) nitrite (NO₂⁻). n = 10–15 excluding DOC (n_bulk = 6, n_micro= 3). Significant difference between methods determined by Mann Whitney U, thresholds *P < 0.05, **P < 0.01, ***P < 0.001.