Contribution of cryoconite holes in the supraglacial discharge of bioavailable iron in Larsemann Hills, East Antarctica

Supraglacial discharge of limiting micronutrients such as iron (Fe) into high-nutrient low-chlorophyll (HNLC) regions like the Southern Ocean has recently drawn global attention. In this study, we aim to understand the contribution of cryoconite holes (comprising a meltwater column with an underlying layer of sediment) to the discharge of Fe through the glacier runoff. Cryoconite hole meltwater collected from the Larsemann Hills, East Antarctica showed a higher concentration of dissolved Fe (dFe: 71.2 μgL⁻¹) and total Fe extractable from suspended sediments (exFe: 362.1 μgL⁻¹) than in the adjacent streams (dFe: 30.5 μgL⁻¹; exFe: 21.2 μgL⁻¹) and melt pools (dFe: 42.3 μgL⁻¹; exFe: 5.8 μgL⁻¹). Predictive pathways (using PICRUSt2) show that cryoconite hole bacterial communities could acquire Fe and other trace elements using different mechanisms, such as the biosynthesis of siderophores, and transport proteins, therefore influencing the trace metal chemistry in these and other environments that drain cryoconite hole contents. Estimated discharge of dFe (11.4 kg km⁻² a⁻¹) and exFe (57.9 kg km⁻² a⁻¹) within cryoconite holes are 2 and 17 times higher, respectively than the discharge from the adjacent supraglacial streams, indicating that cryoconite holes are an important source of potentially bioavailable Fe to the HNLC region.