The first successful deployment of an ice-mounted instrument platform to measure submarine melt rate and boundary layer flow at an active tidewater glacier

We present the first direct observations of submarine melt rate and boundary layer characteristics made from an instrumentation platform mounted underwater into the terminus of Xeitl Sit’ (LeConte Glacier) in southeast Alaska. The instrumentation platform, called a Meltstake, is a remotely deployed robotic platform that drills into a near-vertical submarine ice face, allowing for prolonged stationary measurements in the ice’s reference frame. Three deployments of the Meltstakes were completed at 20 m, 45 m, and 50 m depths, with each deployment lasting approximately two hours. Observations were targeted in the ambient melt region away from the subglacial discharge plume, where the ocean velocity is generally assumed to be quiescent and driven by submarine melt plumes. However, flow along the glacier exhibits broadband variability in both speed and direction. Ocean temperature and salinity within 1 m of the boundary suggest the presence of ambient melt water mixing with fjord water, but no signatures of ambient melt plumes are clearly observed at the deployment locations. Submarine melt rate at the deployment locations is variable in time and exceeds 1-2 m/d. These observations provide an unprecedented look into the boundary layer dynamics driving submarine melt at a near-vertical ice face.