[CINC] climate change and seawater sound transmission

Mon Jan 12 11:33:01 PST 2009

This is just to share with you 2 interesting articles I recently received from another marine science list.
1) NASA posted an explanation of why it more often uses the term "climate change" instead of "global warming."  Some excerpts below.  Go to the URL to read the full article.2) We have all heard about/read about ocean acidification and about the effects of underwater noise on marine mammals.  But new findings connect these two phenomena in a surprising way.  An article out of the most recent issue of "Ocean Update," the online publication of Sea Web, explains how acidification will change the sound transmission properties of seawater, and what that might mean for marine mammals.

I also recommend checking out the Sea Web site, http://www.seaweb.org/home.php, "a communications-based nonprofit organization that uses social marketing techniques to advance ocean conservation. By raising public awareness, advancing science-based solutions and mobilizing decision-makers around ocean conservation, we are leading voices for a healthy ocean."~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~What's in a Name? Global Warming vs. Climate Change http://www.nasa.gov/topics/earth/features/climate_by_any_other_name.htmlDefinitions Global warming: the increase in Earth’s average surface temperature due to rising levels of greenhouse gases.Climate change: a long-term change in the Earth’s climate, or of a region on Earth. "The Internet is full of references to global warming. The Union of Concerned Scientists website on climate change is titled "Global Warming," just one of many examples. But we don't use global warming much on this website. We use the less appealing "climate change." Why? "... Global warming refers to surface temperature increases, while climate change includes global warming and everything else that increasing greenhouse gas amounts will affect. "... During the late 1980s one more term entered the lexicon, “global change.” This term encompassed many other kinds of change in addition to climate change. When it was approved in 1989, the U.S. climate research program was embedded as a theme area within the U.S. Global Change Research Program. "But global warming became the dominant popular term in June 1988, when NASA scientist James E. Hansen had testified to Congress about climate, specifically referring to global warming. He said: 'global warming has reached a level such that we can ascribe with a high degree of confidence a cause and effect relationship between the greenhouse effect and the observed warming.'   Hansen's testimony was very widely reported in popular and business media, and after that popular use of the term global warming exploded. Global change never gained traction in either the scientific literature or the popular media. "But temperature change itself isn't the most severe effect of changing climate. Changes to precipitation patterns and sea level are likely to have much greater human impact than the higher temperatures alone. For this reason, scientific research on climate change encompasses far more than surface temperature change. So "global climate change" is the more scientifically accurate term. Like the Intergovernmental Panel on Climate Change, we've chosen to emphasize global climate change on this website, and not global warming."~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~2) Ocean Update, Dec. 12, 2008, vol. 13, no. 9http://www.seaweb.org/resources/documents/OU_119_Final.pdf How Can Underwater Sound Impact Marine Mammals? In the early 1950s, gray whales were regularly sighted in the Laguna Guerrero Negro in Baja California. Beginning in 1957, however, barges transported salt from the lagoon, and the mouth of the lagoon was dredged. During the next seven years, censuses revealed declines in the number of whales in the lagoon, and by 1964, no whales were seen there at all. In 1967, the saltworks closed for economic reasons; by 1973, whales began to return, and by the early 1980s more than 100 pairs of mothers and calves used the lagoon. In a paper in the Journal of Mammalogy, Peter Tyack of the Woods Hole Oceanographic Institution argues that, “although it is possible that visual or chemical stimuli from this industrial activity could be sensed by the whales, the dominant stimulus likely was the sounds of shipping and dredging.” Gray whales have several major breeding lagoons in Baja California, and Tyack notes that the temporary loss of one of them did not have an obvious impact on the population’s recovery. However, he observes, “sounds from industrial activity seem to have caused the abandonment of critical habitat from the early 1960s to the early 1970s by a species listed as endangered by the United States.” Tyack writes that anthropogenic sound can affect animals in a number of ways, including interfering with their communications, triggering stress responses or even ultimately damaging hearing. The effects of sound are likely to be significantly greater underwater than in terrestrial environments: sound propagates much better than light in water, and as a result many aquatic animals have evolved to communicate and orient predominantly by sound. Toothed whales have evolved high frequency echolocation systems that can identify prey less than three feet in size from several hundred feet away, while baleen whales in contrast use low frequency sounds to communicate over tens and even hundreds of miles.  However, writes Tyack, the total amount of underwater sound from ship traffic as well as commercial, research and military sources has increased significantly during the past century, and shipping has elevated the global deepwater ambient noise ten- to one hundredfold in the 20Hz to 200Hz band. This is the same frequency that baleen whales use to communicate across vast distances of ocean, a notion of particular concern in the context of populations of many baleen whale species having been decimated by commercial whaling. “If the reduction in these populations of whales increased the typical separation of whales during the breeding season, then this could combine with the reduced range of communication to pose a risk of disrupting breeding behavior, with potential adverse impacts on the recovery of these endangered species,” he writes. In addition to such ambient noise, there is an increasing variety of so-called intentional sound sources, such as depth sounders, sonars used to find fish or human-made objects and air guns used to explore geological strata below the seafloor. Although many of these devices produce sound only intermittently, many of them have higher sound source levels than vessel propulsion systems.  In a separate paper, a team of five authors argues that one such intentional sound source has demonstrably negative impacts on marine mammals.Writing in Marine Pollution Bulletin, Chris Parsons of George Mason University and colleagues catalogue a series of cetacean mass stranding events apparently coincident with nearby use of active sonar by naval vessels. They list, for example, a 2000 stranding in the Bahamas of 16 whales from three species; eight mass strandings of beaked whales associated with military exercises involving active sonar around the Canary Islands; several strandings in Taiwan in February and March 2004 concomitant with joint United States and Philippine naval exercises in the area; and strandings of multiple species on the Outer Banks in North Carolina in January 2005 and of approximately 145 long-finned pilot whales in Queensland, Australia, in October of that year, both incidents apparently related to naval vessels using active sonar in the area. In addition to such stranding events, Parsons and colleagues document other observations of marine mammal behavior apparently related to naval sonar activity, including: significant decreases in northern minke whale sightings rates in western Scotland during periods of naval exercises; changes in vocalizations of long-finned pilot whales during a military exercise involving active sonar in the Ligurian Sea Cetacean Sanctuary; and alterations in singing behavior of male humpback whales when exposed to low frequency sonar sounds. The authors assert that the “probability of these associations occurring by chance is prohibitively low, while the likelihood of undiscovered casualties is very high,” and that “the issue of cetacean strandings and mortalities arising from military exercises and sonar use has progressed well beyond the point of finding a smoking gun.” They criticize government officials, particularly in the United States, for “deliberately obstructing progress in mitigation and making the protection of cetaceans and their environment from sonar more difficult through deliberate and calculated measures, such as legislative changes.” According to a paper in the journal Geophysical Research Letters, the ocean in general will become a noisier place as a result of ocean acidification caused by increased oceanic concentrations of carbon dioxide.  The absorption of sound in the ocean changes with the chemistry of the seawater itself. Although this involves a variety of chemical interactions that are not fully understood, the overall effect is influenced by the acidity of the seawater: the more acidic, the less low- and mid-frequency sound it absorbs and therefore the farther these sounds travel underwater. The ocean has absorbed approximately half the carbon dioxide human activity has released into the atmosphere since the Industrial Revolution. The accumulated total is now estimated to be roughly 530 billion tons, with the total increasing by 1 million tons per hour. The consequent changes in ocean chemistry have lowered the pH of the ocean by about 0.1 points since the mid-1700s, and some scientists estimate that ocean pH will lower by a further 0.2 points by 2050. Keith Hester and colleagues from the Monterey Bay Aquarium Research Institute (MBARI) have calculated that because of its decreased levels of pH, seawater already absorbs low- and midfrequency 12 percent less than in pre-Industrial times; under present projections of increased oceanic carbon dioxide and pH levels, absorption of such sounds could diminish by a total of 40 percent by mid-century.While this decrease in sound absorption would mean that, for example, baleen whale vocalizations would travel across significantly greater distances, the same would be true for anthropogenic sound sources from vessel propulsion to active sonar. Note Hester and colleagues: “It remains to be seen how marine mammals will adapt to an ocean increasingly transparent to sound at low frequencies.”  Sources: Tyack, P.L. 2008. Implications for marine mammals of large-scale changes in the marine acoustic environment. Journal of Mammalogy 89(3): 549-558; Parsons, E.C.M. et al. 2008. Navy sonar and cetaceans: Just how much does the gun need to smoke before we act? Marine Pollution Bulletin 56: 1248-1257; Hester, K.C, et al. 2008. Unanticipated consequences of ocean acidification: A noisier ocean at lower pH. Geophysical Research Letters L19601, doi:10.1029/2008GL034913.  Contacts: Peter L. Tyack, Woods Hole Oceanographic Institution. E-mail: ptyack at whoi.edu Chris Parsons, George Mason University. E-mail: ecm-parsons at earthlink.net Peter G. Brewer, Monterey Bay Aquarium Research Institute. E-mail: brpe at mbari.org
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