Meet the Ice Scientists!
November 25, 2014
For 67 years, scientists at McMurdo Station have braved the harsh conditions of coastal Antarctica in the pursuit of knowledge. Year-round, researchers investigate how climate, ice, seawater and Antarctic life change and relate to each other.
According to Stephen Emslie, a marine biologist at UNC Wilmington, while McMurdo’s scientists work, another group just up the coast has some of the answers they’re looking for: a group of penguins.
By tracking the remains of prehistoric colonies of Adelie penguins, Emslie has been able to draw a rough timeline of how the Ross Ice Shelf — one of the most dynamic glacial bodies in the world — has behaved for the last 45,000 years.
Ice shelves are gigantic platforms of ice that reach out over the ocean. They are fed by glaciers and are extremely important to climate scientists because they are in the most immediate danger of breaking up and melting as the planet warms. Ice shelves surround 75% of Antarctica and the Ross Shelf is the biggest.
Scientists know these shelves have advanced and retreated before, but in order to make predictions as to how quickly they will melt in the future, they need to know how quickly they melted when Earth warmed in the past. Their best tool for making these types of measurements involves tracking the ice shelf’s grounding line.
While an ice shelf sits mostly on top of the ocean water, there is always a point where the ice hits the ocean floor, called a grounding line. As an ice shelf advances, the grounding line moves forward, plowing the ocean floor and building up a mound of rocks and sand. Eventually, the ice sheet will reach a stopping point — called a glacial maximum — and begin to retreat, but as it does, that pile of sand and rocks will remain at the glacial maximum. Scientists can look at glacial maxima, determine the age of the rocks inside and confidently say the ice shelf made it out to that point at a specific time.
The trouble is, ice shelves quite literally cover their tracks. Let’s say for example there was a glacial maximum 125,000 years ago 20 miles off the Antarctic coast and another one 25,000 years ago 30 miles off the coast. Each glacial maximum ends with a pile of sand and rocks. The problem is that the new maximum is farther out than the old one, so as the ice shelf makes its way to it’s new maximum, it sweeps up the sand and rock pile from the old one, destroying any record of that maximum. That doesn’t leave scientists with much data about how quickly ice sheets move as climate changes.
This is where the penguins come in. They can serve as a proxy for the Ross Ice Shelf’s movement because of their behavior and the habitat they need to survive.
Scientists frequently use proxies to measure things they can’t get at directly. Oceanographers, for example, use proxies to put together timelines for sea level rise. Salt marshes only occur right around sea level, so if researchers saw salt marsh soil in a core, they would know that sea level was once where that core was taken. They could then carbon date the grass in that marsh layer to figure out how old that marsh was. Enough cores can give a very specific timeline for sea level rise over thousands of years.
Emslie used the remains of ancient penguin colonies in the same way. Adelie penguins nest in Antarctica and look for a few things when picking a spot to do so. They don’t lay their eggs on snow or ice, so they need to have exposed rock and they need access to open water so they can hunt fish and krill. The appearance of penguin colonies, therefore, constrains where the ice shelf was at that time because the penguins won’t nest on the ice shelf and they won’t nest more than a few miles inland of an ice sheet because they need to hunt.
Emslie dug up penguin remains at several points along the Antarctic coast and on a few islands in the Ross Sea. He found egg shells and feathers dating back 45,000 years in the southern Ross Sea. The penguins continued to nest and molt in these locations until about 27,000 years ago. This coincides with a period in which extra sunlight in the Antarctic prevented the ice shelf from advancing north.
But all signs of penguin colonies disappeared from these locations 27,000 years ago, indicating that the ice shelf had begun to push north. Previously, scientists had found the pile of sand and rocks from the last glacial maximum and determined it was 22,000 years old. The distance between the penguin colonies and the rock pile shows the ice shelf advanced at a rate of 50 to 100 meters per year.
Emslie is not sure where the penguins went during this period, but he and his colleagues speculate that as sea level was roughly 80 meters lower then than it is now, the penguins made their colonies in an area that is now currently under water.
About 13,000 years ago, the penguins started to trickle back into the Ross Sea, showing the ice shelf’s retreat. Previous research has shown a dramatic warming period in the Ross Sea between 7,000 and 5,000 years ago, and this time period coincides with a dramatic uptick in the number of penguin colonies.
From here, the penguins’ movement continues to follow changes in the climate. A cold period from 5,000 to 4,000 years ago drove the penguins north while another warming from 4,000 to 3,000 years ago brought the penguins back south into the Ross Sea. The penguins moved north again 2,000 years ago and have remained there ever since.
As much as we might like to, we can’t just ask the penguins how Antarctica’s ice shelves will behave in the future, and while the Adelie penguins’ movements correlate closely to ice shelf behavior, we still have only a very general picture of how the ice shelves behave in response to climate. Emslie’s research, however, does give us a few very important take-homes.
First, while penguin colonies by themselves cannot tell us everything we need to know about ice shelves, they add to a growing body of data that allows scientists to get a perfect picture of how Antarctic ice responds to climate changes.
Second, scientists often make use of microscopic organisms and plants as proxies for geological and climate research, but this study shows that much larger animals, like penguins, can tell us quite a bit about our climate past. This could open up research into other ice shelves using different species as proxies.
Third, the movements of the Adelie penguins clearly illustrate how connected life, geology and climate are. As their planet warmed and cooled, and the Ross Ice Shelf grew and shrank and grew again, the Adelie penguins had to pick up their entire species and move hundreds of miles to find a home. It’s impossible to tell exactly how wildlife will adapt to changes in the Earth’s climate, but this study shows the drastic moves wildlife may have to make to keep up.
Emslie’s study appeared in the journal Geology.
- Daniel Lane
Daniel Lane covers science, engineering, medicine and the environment in North Carolina.