Page 12 - WINTER2019

The Underwater Sounds of Glaciers
The underwater sounds of glaciers are a powerful remote sensing tool for monitoring changing conditions in polar regions.
Introduction and Motivation
The stability of major ice sheets in polar regions are linked to sea level rise and the input of fresh meltwater into sensitive regions of the thermohaline circulation system (the oceanic salt and heat conveyor belt), two critical issues related to global change. Estimates of the future contributions to sea level rise from the melting of glaciers in Greenland alone range from 0.3 m to 3 m for the year 2100 (Berwyn, 2018). Moreover, the recent acceleration of mass loss from the Greenland ice sheet (GrIS), which quadrupled from 1992–2001 to 2002–2011 (Figure 1), led to a global mean sea level rise of 7-8 mm between 1992 and 2011 (Shepherd et al., 2012). Global glacier melt (small glaciers, ice caps, and ice sheets) currently contributes almost 1 mm/yr to the total sea level rise (Zemp et al., 2019). In addition to con- tributing to sea level rise, the freshening of surface waters affects global-scale heat transport by weakening the Atlantic meridional overturning circulation (Bamber et al., 2012). For these and other reasons, understanding the mass loss of glaciers is an important problem.
Here we focus on studying the behavior of tidewater glaciers using the various sounds they make in the ocean as they flow, melt, and break apart. However, before discussing the acoustics, we present some preliminaries about the glaciers them- selves to introduce terminology and describe the processes that generate noise. Tidewater glaciers are valley glaciers flowing from their accumulation zones in the snowfields to the ocean over a journey that can take hundreds to thousands of years. Tidewater glaciers may flow short distances from local high mountain peaks (such as
Grant B. Deane
Email:
gdeane@ucsd.edu
Oskar Glowacki
Email:
oglowacki@ucsd.edu
M. Dale Stokes
Email:
dstokes@ucsd.edu
Address:
Marine Physical Laboratory Scripps Institution of Oceanography University of California, San Diego (UCSD) Code 0206 La Jolla, California 92093-0206 USA
Erin C. Pettit
Address:
Geology and Geophysics College of Earth, Ocean, and Atmospheric Sciences Oregon State University Weniger 533 Corvallis, Oregon 97331 USA
Email:
pettiter@oregonstate.edu
12 | Acoustics Today | Winter 2019 | volume 15, issue 4 ©2019 Acoustical Society of America. All rights reserved. https://doi.org/10.1121/AT.2019.15.4.12
Figure 1. Cumulative ice mass loss (and sea level equivalent [SLE]) from Greenland derived as annual averages from 18 recent studies. Gt, gigatonnes. Reproduced from IPCC (2013, Figure 4.15). See main text and Appendix 4.A of IPCC (2013) for details.