An autonomous buoy system for observing spring freshet plumes under landfast sea ice.

An ice buoy system was developed to measure oceanographic properties of freshwater plumes that occur in Arctic coastal oceans under landfast sea ice during the spring freshet. By implanting such systems into sea ice weeks or months in advance of the freshet event, sensors can be located immediately underneath the sea ice layer in situ at depths that riverine freshwater will occupy later when the freshet arrives. This observing approach is modular, can accommodate a wide range of sensors, is designed intentionally for use in remote regions, and can be readily deployed in any nearshore region that can be accessed by snowmachine. The buoy system incorporates an integral floatation collar that allows it to continue sampling as the coastal ocean becomes progressively ice free in the months after the freshet event. Automated sampling and telemetry via a satellite data network provide near-real-time observations of the timing and character of under-ice freshet plumes. An assessment study was done with an array of these ice buoy systems, outfitted with basic hydrographic and optical sensors and deployed in advance of the 2018 and 2019 freshets in landfast sea ice near the mouths of three coastal rivers in Stefansson Sound, Alaska.