Ocean Observations Below Petermann Gletscher Ice Shelf, Greenland From a Cabled Observatory

Petermann Gletscher in North Greenland features the second largest floating ice shelf by area in the northern hemisphere. In August of 2015 we drilled three holes through the ice shelf and deployed ocean sensors between 5 and 700 m below the glacier-ocean interface. The sensors are controlled by data loggers at the surface that also support a weather station and GPS. All data are transmitted near real-time via a satellite communication link that allowed data downloads and software uploads until February 2016. The system provided gap-free hourly data through the polar night with air temperatures dropping below -48 °C. Mean glacier speeds in winter (Nov.-Feb) were 1180±18 m/year; these values are 12±5% larger than previously reported winter speeds at this location. Hourly ocean observations revealed large bi-monthly pulses within 30 m of the glacier-ocean interface and amplitudes that exceed 1 °C in temperature and 1 psu in salinity. We posit that episodic discharge of glacial meltwater, modulated by the spring-neap tidal cycle thickens the boundary layer under the ice shelf at the location of our measurements. All data are posted at http://ows.udel.edu . A site visit is planned for August 2016 to fix communication failures, retrieve locally stored data, add sensors, and evaluate sustainability of this first cabled observatory on a floating and rapidly melting Greenland glacier.