Arctic Climate Initiative
Project: An Acoustic System to Observe Glacier-Ocean Interactions in Greenland
Mass loss from the Greenland Ice Sheet more than doubled over the last decade; it presently accounts for a third of global sea-level rise and is projected to increase. This rapid loss was unexpected and unpredicted by ice sheet models. It has been largely attributed to the acceleration and retreat of glaciers in response to ocean warming, consistent with observations of warming waters around Greenland. Yet, the response of glaciers to ocean change is highly non-linear and poorly understood; it is currently absent from climate models and considered a major source of uncertainty for sea-level rise predictions for the 21st century.
Greenland’s glaciers meet the ocean in long, deep fjords that are largely unexplored because they are choked with icebergs and sea-ice for most of the year. Recent pioneering work by Physical Oceanographer Fiammetta Straneo (using ice-breakers, helicopters, snow-mobiles and small vessels) has shown that warm water from the Gulf Stream reaches the fjords and melts the glaciers, but one time snapshots (primarily in summer) do not allow us to quantify the annual melting or its year-to-year variability. To do this, we need year-round measurements from the fjords for many years. Traditional technologies, however, including moorings, gliders and autonomous vehicles, are either inadequate or too costly, given the inaccessibility of the fjords and the threat to instrumentation posed by the deep-reaching (over 200 meters), drifting icebergs.
Dr. Straneo proposes to develop and test a new system that will provide the needed measurements and is 1) safe from icebergs, 2) adequate for long-term deployments, and 3) inexpensive. The system will consist of two independent components, which will be developed and tested in separate phases. The first component involves using non-traditional acoustic measurements from instruments deployed on the seafloor (hundreds of meters beneath the icebergs) to obtain the full-depth heat content of the waters in the fjord and nearby shelf area. These measurements alone will allow us to monitor the amount of warm waters on the shelf and fjord and understand both the process of shelf/fjord exchange as well as the interaction with the glacier.
The second component, to be developed in a subsequent phase, will involve deploying electric instruments on the seafloor to obtain the velocity data in the fjord. The combination of these two components will allow us to estimate the actual transport of heat to the glacier and thus provide an accurate estimate of the melt rate and its variability. These measurements will be combined with satellite-based observations of glacier behavior and larger scale ocean-atmosphere products to understand how glaciers respond to ocean warming. The proposed system builds on existing technologies that will be combined and modified for a new application and a new environment. The acoustic instruments (inverted echo sounders) will be modified to extend their mission length and incorporate WHOI-developed low-power acoustic telemetry that enables data recovery with extensive ice-cover. The system will be compact, can be deployed from a small vessel and can last for up to five years, thus eliminating the costly task of yearly service and enabling monitoring.
Funding of $500,000 is requested to develop and test the first component of the system which will allow us to monitor the amount of warm water present in the fjords and how it varies seasonally and inter-annually. Development of the second component will occur at a later stage after the first has been successfully developed. The proposed system has the potential to enable inexpensive monitoring at the edge of dozens of glaciers in Greenland (and Antarctica where a similar need exists). Such measurements would transform our understanding of ice sheet/ocean interactions and enable their inclusion in models, thus addressing a problem of grave societal concern. The proposed work relies on Dr.Straneo’s experience in working in Greenland’s fjords, which has been funded by WHOI ($500,000) and NSF ($1,000,000). It takes advantage of the existing expertise at WHOI to develop and use acoustic systems and deploy and recover instrumentation in ice-covered regions. Because of the risk associated with developing a system for Greenland’s harsh environment, this project is unlikely to be funded by government agencies.