# Ablation provides key macronutrients (nitrogen and phosphorous) to glacier ice algae in NW Greenland

## TL;DR

Nutrients like nitrogen and phosphorus in Greenland ice are present in enough amounts to support glacier algae growth, meaning these nutrients likely do not limit algal activity during the melt season.

## Contribution

The study provides direct measurements of nano-molar concentrations of nitrogen and phosphorus in glacier ice, challenging the assumption that these nutrients limit algal growth.

## Key findings

- Quantifiable concentrations of nitrogen and phosphorus were found in glacier ice samples from NW Greenland.
- Nutrient release during ablation exceeds the nutrient requirements of glacier ice algae.
- These findings suggest that macronutrient availability is not a limiting factor for algal growth on the Greenland Ice Sheet.

## Abstract

Dissolved phosphorus (P) is thought to limit the growth of glacier ice algae, which darken the surface of the Greenland Ice Sheet (GrIS) and enhance surface melt. This contention is largely based on the low-level of P concentrations, which are often below the limit of detection of conventional methods. Here, we propose that low-level nutrient analysis is essential to understand the macronutrient limitation of glacier algal growth on the GrIS. We sample surface (≤5 cm) and shallow (5−10 and ~80−90 cm depth) ice from two sites in NW Greenland and measure the nano-molar concentrations of dissolved nitrogen (N) and P using a custom-built continuous segmented flow analyser. Quantifiable concentrations of these macronutrients are present, along with glacier ice algal abundances comparable to those of the Dark Zone, a zone of biologically enhanced ice sheet melting. Mass balance calculations for each site indicate that N and P released during seasonal ablation exceed the amounts incorporated into glacier ice algal biomass. These results suggest that dissolved macronutrients are unlikely to limit glacier ice algal growth on the Greenland Ice Sheet.

Nitrogen and phosphorus in Greenland ice are present in measurable amounts and exceed algal needs, suggesting these nutrients do not limit glacier ice algae growth during the melt season.