Melt Pond Nutrient Dynamics and Their Relationship With Melt Pond Bottom Ice in the Central Arctic Ocean

Melt pond is a common and important feature of the Arctic in the summer season. Melt ponds provide unique microbial habitats with high light availability, which can promote photosynthesis. Therefore, melt ponds play an important role for nutrient cycling at the ice-ocean interface. However, the changes in nutrient dynamics in and under the sea ice resulting from melt pond formation are poorly understood. To elucidate melt pond nutrient (NO₃⁻, NO₂⁻, NH₄⁺, PO₄³⁻, and Si(OH)₄) dynamics and their relationship with the melt pond bottom ice, which is sea ice right beneath the floor of a melt pond, in the Central Arctic Ocean during late summer, melt pond water and bottom sea-ice samples were collected during the MOSAiC Expedition (2019–2020). Comparison with the dilution line based on winter surface seawater, which is a source of sea ice, suggest that nutrients in the melt ponds are consumed by algae or other organisms, and then remineralized at the pond bottom. Nutrients then percolated downward through the porous bottom ice. Melt pond water was completely exchanged with surrounding seawater (lead or under-ice seawater) and snow derived water. If the surrounding seawater and snow are rich in nutrients, the exchange promotes photosynthesis within the melt pond water and can enhance nutrient accumulation within the pond bottom ice.