Turning Up Ocean Temperature & Volume – Underwater Soundscapes in a Changing Climate

Freeman Lauren – lauren.a.freeman3.civ@us.navy.mil

Instagram: @laur.freeman

NUWC Division Newport, NAVSEA, Newport, RI, 02841, United States

Dr. Lauren A. Freeman, Dr. Daniel Duane, Dr. Ian Rooney from NUWC Division Newport and
Dr. Simon E. Freeman from ARPA-E

Popular version of 1aAB1 – Passive Acoustic Monitoring of Biological Soundscapes in a Changing Climate
Presented at the 184 ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0018023

Climate change is impacting our oceans and marine ecosystems across the globe. Passive acoustic monitoring of marine ecosystems has been shown to provide a window into the heartbeat of an ecosystem, its relative health, and even information such as how many whales or fish are present in a given day or month. By studying marine soundscapes, we collate all of the ambient noise at an underwater location and attribute parts of the soundscape to wind and waves, to boats, and to different types of biology. Long term biological soundscape studies allow us to track changes in ecosystems with a single, small, instrument called a hydrophone. I’ve been studying coral reef soundscapes for nearly a decade now, and am starting to have time series long enough to begin to see how climate change affects soundscapes. Some of the most immediate and pronounced impacts of climate change on shallow ocean soundscapes are evident in varying levels of ambient biological sound. We found a ubiquitous trend at research sites in both the tropical Pacific (Hawaii) and sub-tropical Atlantic (Bermuda) that warmer water tends to be associated with higher ambient noise levels. Different frequency bands provide information about different ecological processes (such as fish calls, invertebrate activity, and algal photosynthesis). The response of each of these processes to temperature changes is not uniform, however each type of ambient noise increases in warmer water. At some point, ocean warming and acidification will fundamentally change the ecological structure of a shallow water environment. This would also be reflected in a fundamentally different soundscape, as described by peak frequencies and sound intensity. While I have not monitored the phase shift of an ecosystem at a single site, I have documented and shown that healthy coral reefs with high levels of parrotfish and reef fish have fundamentally different soundscapes, as reflected in their acoustic signature at different frequency bands, than coral reefs that are degraded and overgrown with fleshy macroalgae. This suggests that long term soundscape monitoring could also track these ecological phase shifts under climate stress and other impacts to marine ecosystems such as overfishing.

A healthy coral reef research site in Hawaii with vibrant corals, many reef fish, and copious nooks and crannies for marine invertebrates to make their homes.
Soundscape segmented into three frequency bands capturing fish vocalizations (blue), parrotfish scrapes (red), and invertebrate clicks along with algal photosynthesis bubbles (yellow). All features show an increase in ambient noise level (PSD, y-axis) with increasing ocean temperature at each site studied in Hawaii.

Putting Ocean Acoustics on the stage to address climate change

Kyle M. Becker – kyle.becker1@navy.mil

co-chair, Interagency Working Group on Ocean Sound and Marine Life (IWG-OSML)
Washington, DC 20001
United States

Thomas C Weber – member, IWG-OSML, Washington, DC
Heather Spence – co-chair, IWG-OSML, Washington, DC
Grace C Smarsh – Executive Secretary, IWG-OSML, Washington, DC

Popular version of 1aAB9 – Ocean Acoustics and the UN Decade of Ocean Science for Sustainable Development
Presented at the 184 ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0018031

The Acoustic Environment is, collectively, the combination of all sounds within a given area modified by interactions with the environment. This definition includes both the sounds of nature and human use and is used by the US National Park Service as a basis for characterizing, managing, and preserving sound as one of the natural resources within the park system. Thinking in terms of a theatre, the Acoustic Environment is where scenes emerge from the interaction of individual actors (or sources) with all other aspects of the stage (the environment). The audience (or receiver) derives information from a continuous series of actions and interactions that combine to tell a story. In developing the Ocean Decade Research Programme on the Maritime Acoustic Environment (OD-MAE https://tinyurl.com/463uwjk5) we applied the theatre analogy to underwater environments, where acoustic scenes result from the dynamic combination of physical, biological, and chemical processes in the ocean that define the field of oceanography. In the science of Ocean Acoustics, these highly intertwined relationships are reflected in the information available to us through sound and can be used as a means to both differentiate among various ocean regions and tell us something – stories – about processes occurring within the oceans. The use of sound for understanding the natural environment is particularly effective in the oceans because underwater sound travels very efficiently over large distances, allowing us to probe the vast expanses of the globe. As an example of this, the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is capable of monitoring nearly the entire volume of the world’s oceans for underwater nuclear explosions with only eleven underwater acoustic listening stations.

In the context of the UN Decade of Ocean Science for Sustainable Development (oceandecade.org), the OD-MAE program seeks to raise awareness about and support research related to the information available through sound that reflects the regional ocean environment and its state. For example, the noisiest places in the ocean have been found to be in Alaskan and Antarctic fjords where sound energy levels created by the release of trapped air by melting ice exceed that of many other sources, including weather and shipping[1]. Sound energy increases with melt rate as more bubbles are released, providing information about the amount of fresh water being added into the oceans along with other climate indicators.

Representative glacial environment. Image credit: National Park Service

Ambient Sound recorded near Hubbard and Turner Glaciers near Yakutat, AK. Credit: Matthew Zeh, Belmont University and Preston Wilson, Univ. of Texas at Austin

Similarly, in warmer climates, the acoustic environment of coral reefs can provide scientists an indication of a reef system’s health. Healthy reef systems support much more life and as a result more sound is produced by the resident marine life. This is evident when contrasting the sounds recorded at a healthy reef system to those recorded at a location that experienced bleaching owing to increased water temperature and climate change[2].

Representative healthy and degraded reef systems. Image credits NOAA

Sound of representative healthy reef system. Credit: Steve Simpson, University of Bristol, UK

Sound of representative degraded reef system. Credit: Steve Simpson, University of Bristol, UK

As a research program, the OD-MAE seeks to quantify information about the acoustic environment such that we can assess the current state and health of the oceans, from shallow tropical reefs to the very deepest depths of the ocean. Telling the stories of the ocean by listening to it will help provide knowledge and tools for sustainably managing development and even restoring maritime environments[3].


[1] Pettit, E. C., Lee, K. M., Brann, J. P., Nystuen, J. A., Wilson, P. S., and O’Neel, S. (2015), Unusually loud ambient noise in tidewater glacier fjords: A signal of ice melt. Geophys. Res. Lett., 42, 2309– 2316. doi: 10.1002/2014GL062950.
[2] https://artsandculture.google.com/story/can-we-use-sound-to-restore-coral-reefs/ RgUBYCe8v8Ol0Q [last visited 5.3.2023]
[3] Williams, B. R., McAfee, D., and Connell, S. D.. 2021. Repairing recruitment processes with sound technology to accelerate habitat restoration. Ecological Applications 31( 6):e02386. 10.1002/eap.2386

Featured Image Credit: National Park Service

I know what you did last winter: Bowhead whale unusual winter presence in the Beaufort Sea

Nikoletta Diogou – niki.diogou@gmail.com

Twitter: @NikiDiogou
Instagram: @existentialnyquist

University of Victoria
Victoria, BC V5T 4H3

Additional authors: William Halliday, Stan E. Dosso, Xavier Mouy, Andrea Niemi, Stephen Insley

Popular version of 1aAB8 – I know what you did last winter: Bowhead whale anomalous winter acoustic occurrence patterns in the Beaufort Sea, 2018-2020
Presented at the 184 ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0018030

The Arctic is warming at an alarming pace due to climate change. As waters are warming and sea ice is shrinking, the arctic ecosystems are responding with adaptations that we only recently started to observe and strive to understand. Here we present the first evidence of bowhead whales, endemic baleen whales to the Arctic, breaking their annual migration and being detected year-round at their summer grounds.

Whales, positioned at the top of the food web, serve as excellent bio-indicators of environmental change and the health of marine ecosystems. There are more than 16,000 bowhead whales in the Bering-Chukchi-Beaufort (BCB) population in the Western Arctic. The BCB bowheads spend their winters in the ice-free Bering Sea, and typically start a journey early each spring of over 6000 km to summer feeding grounds in the Beaufort Sea, returning to the Bering Sea in early fall when ice forms on the Beaufort Sea (Figure 1). But how stable is this journey in our changing climate?

Figure 1. Map showing migration route of BCB bowhead whales and the wider study area.

The Amundsen Gulf (Figure 1), in the Canadian Arctic Archipelago of the Beaufort Sea, is an important summer-feeding area for the BCB whales. However, winter inaccessibility and harsh conditions year-round make long-term observation of marine wildlife here challenging. Passive acoustic monitoring has proven particularly useful for monitoring vocal marine animals such as whales in remote areas, and offers a remarkable opportunity to explore where and when whales are present in the cold darkness of Arctic waters. Figure 2 shows examples of two types of bowhead whale vocalizations (songs and moans) together with other biological and environmental sounds recorded in the Amundsen Gulf.

Figure 2. Examples of spectrograms recorded in the Amundsen Gulf of bowhead whale songs on the left, and bowhead whale moans on the right. Spectrograms are visual representations of sound, indicating the pitch (frequency) and loudness of sounds as a function of time. Spectrograms on the left include bearded seal calls (trills) interfering with the bowhead songs. Spectrograms on the right include other ambient sounds (ice noise) that interfere with the bowhead moans. Image adapted from authors’ original paper.

Examples of characteristic calls of bowhead whales recorded during 2018-2019 in the southern Amundsen Gulf.

In September of 2018 and 2019 we deployed underwater acoustic recorders at five sites in the southern Amundsen Gulf and recorded the ocean sound for two years to detect bowhead whale calls and quantify the whale’s seasonal and geographic distribution. In particular, we looked for any disruptions to their typical migration patterns. And sure enough, there it was.

A combination of automated and manual analysis of the acoustic recordings revealed that bowhead whales were present at all sites, as shown for 3 sites (CB50, CB300 and PP) in Figure 3. Bowhead calls dominated the acoustic data from early spring to early fall, during their summer migration, confirming the importance of the area as a core foraging site for this whale population. But surprisingly, the analysis uncovered a fascinating anomaly in bowhead whale behavior: bowhead calls were detected at each site through the winter of 2018-2019, representing the first clear evidence of bowhead whales overwintering at their summer foraging grounds (Figure 3). This is a significant departure from their usual migratory pattern. However, analysis of the 2019-2020 recordings did not indicate whales over-wintering that year. Hence, it is not yet clear if the over-wintering was a one-time event or the start of a more stable shift in bowhead whale ecology due to climate change. The variability in bowhead acoustic presence between the two years may be partly explained by differences in sea ice coverage and prey density (zooplankton), as summarized in Figure 4.

Figure 3. Number of days with acoustic detections per month for bowhead whales for sites CB50 (blue), CB300 (green), and PP (red) in 2018-2019. The yellow shaded areas represent time periods at each station when the ice concentration was below 20% (“ice-free”), grey areas when ice concentration was 20%-70% (“shoulder season”), and white areas when ice concentration was greater than 70%. Image adapted from authors’ original paper.

Figure 4. Graphical summary of the objectives and major results of the study.

The findings of this study have important implications for understanding how climate change is affecting the Arctic ecosystem, and highlights the need for continued monitoring of Arctic wildlife. Passive acoustic monitoring can provide data on how whale ecology is responding to a changing environment, which can be used to inform conservation efforts to better protect Arctic ecosystems and their inhabitants.