Of Ice Cores & Isotopes

Earth’s atmosphere has a history — not just in terms of temperature and composition, but also in the dynamics of its motions and chemistry. By tracing ultra-rare molecules in the present-day atmosphere and back into the past, Laurence Yeung, Assistant Professor of Earth Science at Rice University and recent Clarke Award recipient, is setting out to trace that dynamic history. “In the same way you'd tag a shark to figure out what its migration patterns are,” he explains, “you can exploit the natural tags that Mother Nature gives us in these stable isotopes.” Stable isotopes are atoms of the same element that differ slightly in mass thanks to an extra neutron or two, and they act as passive tracers in the atmosphere. A heavy isotope’s extra bit of mass can affect the physical and chemical processes it undergoes, concentrating or diluting it with respect to its lighter siblings. As a result, the ratio of these isotopes, like typical oxygen-16 (which has 8 protons and 8 neutrons) to heavier oxygen-17 (8 protons, 9 neutrons) or oxygen-18 (8 protons, 10 neutrons) can hold clues to a given reservoir’s past.

Yeung is at the front lines of the field, pioneering a technique that takes oxygen isotope analysis one step further. Atoms of oxygen-18 (¹⁸O) make up only 0.2% of all of the oxygen atoms on Earth. Even more rare are oxygen molecules (O₂) that contain more than one of these heavy isotopes, and it’s these ¹⁸O-¹⁸O molecules that Yeung and his group are after. By taking measurements of the present-day atmosphere at different altitudes above the surface, and comparing those values to a detailed model of atmospheric chemistry and circulation, the amount of mixing going on between different parts of the atmosphere can be sorted out. “There's a little bit less ¹⁸O-¹⁸O in the troposphere than there is in the stratosphere,” says Yeung. “So when those two reservoirs mix...then you establish some characteristic proportion of stratospheric air vs. tropospheric air.”

These measurements and calculations can be compared against many other methods for getting at the same question, calibrating the ¹⁸O-¹⁸O technique before using it to look at similar quantities in samples of past atmosphere. Where does one come across these secret stashes of ancient air? One key place to look is in the ice deep under the glaciated regions of the Earth, where layers of snow that accumulated and compressed into ice hundreds or even thousands of years ago trapped atmospheric gases in tiny bubbles. “These bubbles end up trapping gases from the ancient atmosphere, and it tells you something about the recent past, up to something like a million years at this point.”

Yeung’s search for ultra-rare oxygen molecules brought him to the National Ice Core Laboratory in Denver, CO, which houses 17 kilometers of precious ice collected from Greenland and Antarctica. Measurements of the oxygen isotopes in the layers of ice themselves, as well as the gases contained in the bubbles, have established a detailed record of past climate, revealing quantities like global temperature and atmospheric composition over the past several hundred thousand years. By extending this research into the ¹⁸O-¹⁸O realm, Yeung hopes to shed light on some of Earth’s dynamical history as well — a subject of great interest today. “There are thermodynamic aspects of climate, things like temperature, chemical composition,” Yeung explains, “but then there are all these dynamical aspects of climate in Earth's atmosphere that aren't nearly as well constrained…How often do the lower and the upper atmosphere overturn, how often do they talk to each other, how rapidly or vigorously do they mix? How strong are storm systems in the past?” These are questions get to the heart of how the atmosphere works as an Earth system, and thanks to these ultra-rare molecules, we have a new promising way of getting answers.
—Podcast & post by Meg Rosenburg
Read the rest of the post . . .

Mountains Made of "Magnetic Honey" Lead to New Insights

What do physicists do when they get stuck on a problem? In the case of magnet mountain growth rates, they chill and stick with it.

Read the rest of the post . . .

Leidenfrost Effect Puts Perpetual Bounce into Hydrogel Beads

Not all great ideas come in the shower. Sometimes inspiration strikes when you're whipping up a stack of pancakes.

Read the rest of the post . . .

Updated Neural Model for Working Memory

Neuroscientists at the Massachusetts Institute of Technology have provided evidence opposing the current model for how working memory operates at the cellular level. The current model says the cellular basis for working memory lies in consistent, sustained activity by brain cells, or neurons. Results from the MIT study, published in the March 17 issue of the scientific journal Neuron, shows the story is more complex, that brain cells involved in working-memory tasks are activated discretely and sporadically.

Read the rest of the post . . .

Biosphere 2

Just outside the town of Oracle, Arizona, nestled between the seemingly endless plains of the Sonaran desert and the cactus-pocked foothills of Mount Lemmon, stands an enormous glass ziggurat: Biosphere 2.


Read the rest of the post . . .

Pi Day: Musings on a Constant

Happy pi day, Physics fans! This 3/14 is a particularly special one, as 3/14/16 is as close as we're going to get to the actual value of pi using our current date format (at least for the next hundred years!) While some here at PhysicsCentral are adherents of the Tau philosophy, there's no reason we can't celebrate again on 6/28! In my book, any excuse to eat pie or pontificate a bit on the nature of transcendental numbers is a good one.

Read the rest of the post . . .

Hail Hydra! Mysterious Sea Creature Revealed to Have Mouth That Functions Like a Pupil

Named after the mythological beast slain by the Greek demigod Heracles, the Hydra is a genus of freshwater animal related to jellyfish and sea anemones, best known for its ability to regenerate whole individuals from parts of another. And until recently, the way it opened its mouth—the animal's only orifice—was a mystery.

Read the rest of the post . . .

Bigger on the Inside? Scientists Trap Light in "Whispering Gallery" Microspheres

In a vacuum, light moves fast enough to travel all the way around the earth in about a tenth of a second. In recent years, though, scientists have found ways to slow and even stop light in its tracks by using new states of matter and other specially engineered materials. Now, researchers in France are reporting that they’ve devised a new way to tackle the challenge, one which circumvents many of the technical difficulties associated with previous techniques.


Read the rest of the post . . .

Physics Brain Teaser: Bee in a Jar

Imagine you've got a jar on a scale, sealed so that no air can escape. Inside this jar, there's a bee hovering in place. Does the scale read more, less, or the same as when the bee is resting at the bottom of the jar?

Read the rest of the post . . .

The Beauty of the Sea Butterfly's "Flight"

Flight has evolved independently at least three times, by three different animal groups: birds, bats, and insects. Now, a team of researchers at Georgia Tech has confirmed that a species of aquatic snail, the "sea butterfly" Limacina helicina, flaps its wing-like appendages the same way that some small insects use their wings to fly.

Image Credit: Russ Hopcroft, Institute of Marine Science, University of Alaska Fairbanks (UAF); and NOAA

Read the rest of the post . . .