Summer-to-winter record of Greenland moulin water pressure and electrical conductivity revealed by Cryoegg wireless instruments

Subglacial and englacial hydrology is a key driver of ice dynamics in glaciers and ice sheets. Observations of subglacial and englacial water storage, especially in moulins, are extremely challenging, and long-term datasets are consequently limited. The transition from the summer melt season to the winter drainage system shutdown is rarely observed.We studied a glacial moulin on Isunnguata Sermia, West Greenland between July and December 2024 using Cryoegg instruments. Cryoegg is a spherical, wireless device which monitors conditions within the englacial and subglacial environment of glaciers and ice sheets. It provides hourly temperature, pressure, and electrical conductivity (EC) measurements[JH1]  of englacial and subglacial water. Three Cryoeggs were deployed, two at different depths in one moulin and the third in another moulin nearby. We observe the changing hydrology of these moulins, including the transition from summer to winter. In summer, warm sunny days produce diurnal cycles in the pressure and EC measurements, with high pressure and low-EC water being present during the local afternoon and evening. The transition to winter includes evidence of the release of stored (high-EC) water into the drainage system and a gradual transition to a high-pressure, high-EC state as midwinter approaches.