Glacial Melt Field Study Showcases Teledyne ADCPs

LeConte Glacier, one of the most active glaciers in Southeast Alaska.

Global concern about rising sea levels has put increasing loss of glaciers and ice sheets into public attention. The glaciers of Greenland and Alaska that reach the sea have therefore received increased scientific notice. Yet the ways in which warm ocean water interacts with and erodes the face of these glaciers have been largely unobserved. In the summer of 2018, a team of scientists from Oregon State University and University of Alaska deployed an extensive and innovative observational program to study these processes at the face of LeConte Glacier in Southeast Alaska. The target of the project was to measure the plume of sub-glacial discharge ascending the face of this Glacier.

Teledyne RDI ADCPs were installed on moored and moving platforms, and so played two different roles in the study. Upward-looking ADCPs were fitted to several moorings that had a variety of purposes, including recording ascending motions near the face of the glacier and measuring deep horizontal currents. These currents carry warm seawater toward the glacier.

In a second role, ADCPs were mounted on remotely controlled kayaks developed by OSU. These unmanned vehicles were used to deploy moorings in dangerous yet critical locations adjacent to the glacier’s calving ice cliff. The vehicles also performed spatial surveys around the fjord.

During their creep to the sea, glaciers melt at their upper surface. The resulting frigid water drains through the glacier to the underlying rock basement where this meltwater runs seaward below the glacier. This fresh subglacial water, which enters the ocean far below sea level, has two dynamical effects at the glacier’s terminus. First, the meltwater ascends because it is more buoyant than ambient seawater. Turbulent mixing associated with this rising plume entrains warmer seawater that, in turn, enhances melting of the adjacent glacier face.

LeConte Glacier creeps seaward at about 25 m/day. At times, extremely active calving of icebergs more than counters this rate.

Measuring the challenging environment near a calving glacier face required a multifaceted solution. The researchers relied on both unmanned aerial and surface vehicles. Even more impressive, the they used these robotic tools to deploy ADCP moorings from afar— hundreds of meters away. The unmanned surface vessels named ROSE (the Robotic Oceanographic Surface Explorer) come from ongoing engineering work at OSU. These motorized kayaks carry a 300 kHz downlooking ADCP and a profiling CTD system.

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