Analysis of Acoustic Scattering Layers In and Around Petermann Fjord, Northwest Greenland

Erin Heffron
Thesis Defense

Master of Science
Earth Sciences, Ocean Mapping

Thursday, Apr. 14, 2022, 11:00am

Mass loss from the Greenland ice sheet has increased rapidly in the last two decades and has contributed significantly to observed sea level rise. The most pronounced change is occurring where ice sheets are grounded below sea level, due to enhanced interaction with warming ocean waters. However, our ability to predict future sea level rise is hampered by our limited knowledge of these glacial systems, including the regional water mass distribution and circulation responsible for that enhanced ocean-ice interaction. The Petermann Expedition of August 2015 encompassed a broad range of data collection in an effort to characterize the Petermann Glacier system, a marine-terminating glacier with a floating ice tongue that has undergone dramatic changes in the last decade. During the expedition, sonars were used to map the water column, generating a continuous dataset over 30 days. This mapping revealed extensive acoustic scattering layers, so called because the components of the layer – typically zooplankton – cause the acoustic energy to scatter much as it does when it encounters the seabed. The layer was observed to change depth in a spatially consistent manner and corresponded to our general, but limited understanding of the complex circulation pattern in the study area. Shipboard insolation data and satellite-derived light attenuation data were used to rule out response to light as the primary reason for changes in the scattering layer depth. Comparison to salinity and temperature measurements were used to demonstrate a pattern in the scattering layer depth distribution related to circulation, confirming that the continuous record provided by acoustics can supplement point observations of temperature and salinity to provide a more complete picture of regional oceanography and the glacial system as a whole.


Erin is a 2004 graduate of Slippery Rock University, where she obtained a B.S. in Environmental Studies. Her undergraduate work had a strong focus in geology and GIS that was supplemented by summer research experience as part of the Slippery Rock University’s Badlands Working Group, and as a research team member on an NSF-REU (National Science Foundation Research Experience for Undergraduates) run by the University of Southern Maine. After graduating she worked at the U.S. Geological Survey in Woods Hole, which marked the start of her ocean mapping experience and education. At U.S.G.S. she contributed to the Stellwagen Bank Sea Floor Mapping Project and National Benthic Habitat Project, collecting/processing data related to the spread of an invasive tunicate species in the Gulf of Maine. From 2006 and until fall of 2015 she was a Product Specialist with QPS, Inc., the marine software company producing the Fledermaus and Qimera applications. She started her master’s work in August 2015; since 2017, she has also been working as an independent contractor providing ocean exploration, ocean mapping and GIS services for multiple organizations and projects including the Ocean Exploration Trust (E/V Nautilus), NOAA Office of Exploration and Research (Okeanos Explorer), and Seabed2030 (seafloor mapping aboard the DSSV Pressure Drop), and has worked on projects analyzing sonar data for indication of seeps with the University of Alaska and processing data for inclusion in the Global Multi-Resolution Topography (GMRT) Synthesis with Lamont-Doherty Earth Observatory.