Category Archives: Earth

Earth, Earth science, oceans

A Lesson in Earth Science

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And Climate Change

Sometimes you can’t keep ahead of the news. Especially in science.  As I was working on the climate change exhibits for California Academy of Sciences earlier this year, I’d keep tabs on research and discoveries in Earth sciences, particularly Earth’s atmosphere and oceans. And, as fast as I’d write up something from peer-reviewed science, there’d be more information and discoveries coming in.  Which is great, but when it comes to climate change, it seems like it might be chronicling drastic change that we neither need nor want.  But, that’s the nature of science research — it reports on what’s happening and tries to find out why it’s happening.If we’re smart, we heed what we see and take action.

Tomorrow there’s a peer-reviewed science paper coming out that I wish had come out earlier, since it would make a striking addition to the exhibits. It states that as Earth’s oceans absorb more carbon dioxide generated by human consumption of fossil fuels and other activities (which warms up oceans and causes them to become more acidic), sounds will travel farther underwater. What’s the big deal, you might ask.  Well, noisier oceans affect marine mammal, for one thing. And, there are likely other effects that reverberate throughout the ocean environment.

Image credit: (c) 2008 MBARI (Base image courtesy of David Fierstein). This illustration shows how increasing carbon dioxide in the atmosphere leads to an increase in the acidity of seawater, which in turn allows sounds (such as whale calls) to travel farther underwater.
Image credit: © 2008 MBARI (Base image courtesy of David Fierstein). This illustration shows how increasing carbon dioxide in the atmosphere leads to an increase in the acidity of seawater, which in turn allows sounds (such as whale calls) to travel farther underwater.

This projected impact on ocean sound is the result of calculations by Keith Hester and his colleagues at the Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing, Calif. Their paper is coming out in tomorrow’s (October 1, 2008) issue of  Geophysical Research Letters, a journal of the American Geophysical Union (AGU).

So, what does it mean? Ocean chemists know that as seawater chemistry changes, its ability to absorb sound changes. As sound moves through seawater, it causes groups of atoms to vibrate, absorbing sounds at specific frequencies. This involves a variety of chemical interactions that are not completely understood.

The overall effect is strongly controlled by the acidity of the seawater. The bottom line is this: the more acidic the seawater, the less low- and mid-frequency sound it absorbs.

As the oceans become more acidic, sounds will travel farther underwater and the level of underwater noise will rise. This change in chemistry will have the greatest effect on sounds below about 3,000 cycles per second (two and one half octaves above “middle C” on a piano).

This range of sound includes many of the underwater noises generated by industrial and military activity, as well as by boats and ships. Such human-generated underwater noise has increased dramatically over the last 50 years, as human activities in the ocean have increased. For marine mammals that also use this range of sounds to communicate, it’s like having your neighborhood go from one of relative quiet to one where the neighbors are blasting their stereos and revving their engines all the time.

The MBARI researchers say that sound already may be traveling 10 percent farther in the oceans than it did a few hundred years ago. However, they predict that by the year 2050, under conservative projections of ocean acidification, sounds could travel as much as 70 percent farther in some ocean areas (particularly in the Atlantic Ocean). This could dramatically improve the ability of marine mammals to communicate over long distances, but, on the down side, it could also increase the amount of background noise that they have to live with.

There are no long-term records of sound absorption over large ocean areas. However, the researchers cite a study off the coast of California which showed an increase in ocean noise between 1960 and 2000 that was not directly attributable to known factors such as ocean winds or ships.

Hester’s research shows how human activities are affecting the Earth in far-reaching and unexpected ways. As the researchers put it in their paper, “The waters in the upper ocean are now undergoing an extraordinary transition in their fundamental chemical state at a rate not seen on Earth for millions of years, and the effects are being felt not only in biological impacts but also on basic geophysical properties, including ocean acoustics.”

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atmosphere, climate change, Earth, global warming

Earth is Where It’s At

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And It’s All We Have… For Now

https://i0.wp.com/nssdc.gsfc.nasa.gov/image/planetary/earth/gal_east-pacific.jpg?resize=474%2C356

Sooner or later, everybody who is interested in space and astronomy gets a look at our planet from “the outside.”  This image, from the Galileo spacecraft during one of its swings around Earth, tells a pretty remarkable story. If you were an incoming alien vessel, you’d see evidence of water. The oceans tell that story, but so do the clouds because they’re made of water vapor. The land masses would tell you that there are places to land on this planet, but at this distance and resolution, you wouldn’t be able to make out plants and animals… or humans and their cities.

If your alien ship had special sensors, it could use spectral analysis to dissect the gases in the atmosphere that blankets the planet. You would find oxygen, nitrogen, plus trace amounts of other gases.  Oh, and carbon dioxide. That’s a biggie. Carbon dioxide (you sometimes see it as CO2) is a by-product of living and geological processed. And, it’s the principal component of the greenhouse gases that we are pumping into our atmosphere from energy generation (driving cars, making electricity, powering manufacturing, etc.). The more greenhouse gases we load into the atmosphere, the warmer our climate is getting. And this is having an effect that future spacecraft will see (and we will have to live with).

As you can see from this picture, our atmosphere looks pretty thin when compared to the vastness of space and the size of our own planet. In fact, if you look at other planetary atmospheres in the solar system, you find them to be thick and heavy (Venus, the gas giants), or thin and possibly even fragile (Mars, Earth, some of the smaller moons of the outer solar system). What we learn about atmospheres is important, since our own planet has the only one that we know of that has harbored (and possibly even helped begin) life.  That makes what we’re doing to it with carbon dioxide a pretty major “experiment.”