Close your eyes and picture this: New York State, 20,000 years ago. You’re standing on a flat swath of thick ice as soft snow sifts down from the sky. Look any direction, and there it is: more ice. The surface of the world is quiet, white, and stretching as far as the eye can see.
This was, in fact, what it was like during that era of time – an ice age that American scientists term “the Wisconsin.” Great sheets of ice covered almost one third of the earth’s surface, temperatures were low, and most areas of the northern United States and the world were covered by glaciers. Glaciers are formed in low temperatures when more snow falls than melts, causing the layers to impact on one another and eventually fuse into ice sheets as the pressure of each mounting layer grows. Not only do glaciers provide a fascinating record of past climates, they also shaped many of the landscapes we know today.
What can glaciers tell us about the past?
Window to Past Climates
Scientists have now perfected a method for drilling deep into the glacial ice of Greenland and reaching depths equivalent to 115,000 years ago, when the last major ice age began. As detailed by Elizabeth Kolbert in an article about her own visit to the ice drilling station, the snow that fell on the glacier in the past becomes “a relic of the climate that first formed it. In the Greenland ice there is volcanic ash from Krakatau, lead pollution from ancient Roman smelters, and dust blown in from Mongolia on ice-age winds. Every layer also contains tiny bubbles of trapped air, each of them a sample of a past atmosphere.”
This means that the layers of glacial ice can actually be read as if they were tree rings, or a time capsule. Using what they know about the textures of snow falling in different seasons, scientists can deduce when in time those layers became part of the glaciers. They can also get a rough estimate of the temperature of that time from the isotopic weight of the water comprising the snow.
These temperature variations are wild – what they reveal is that after the onset of an ice age, warm periods of around 10,000 years alternate with dramatic drops down to cold temperatures for up to 90,000 years. Currently, we are in what is known as the Holocene era, an interglacial period of warm temperatures and glacial retreat. But is history bound to repeat itself with another advance of the glaciers?
Discovered primarily in the northern reaches of Siberia and Alaska, the retreating glaciers have unfolded many treasures long entombed within their layers. One of these is the extinct woolly mammoth.
A huge, tusked beast roughly equivalent in size to the elephant, the hairy mammoths once stalked the chilly regions of the world, and were even hunted by ancient humans before a combination of factors, including rising earth temperatures, led to their extinction around 10,000 years ago. Isolated populations survived on Alaska’s St. Paul Island until 6,400 years ago and on Wrangel Island in the Arctic Sea until 4,000 years ago.
The well-preserved mammoth carcasses that have been discovered provide an invaluable glimpse into the characteristics of this long gone species, as well as the characteristics of their time. Scientists have been able to analyze the stomach contents of some of the most well-preserved to see what they were eating, and have discovered mammoths in the ice which were most certainly attacked by humans. Many of these discoveries are 30-40,000 years old, which just goes to show that freezing something means it will last for a very long time.
Extinct animal species aren’t the only ancient creatures to have been buried in the ice. In 1991, two hikers in the Alps stumbled across the remains of a man who died there 5,300 years ago. Although technically not during an ice age, the glacier still preserved a fascinating piece of the historical record in this ancient man.
Nicknamed “Otzi” due to the location of his final resting place, scientists were able to examine the mummy and establish the fabric of his clothing, his occupation as a sheepherder, and even his tattoos! They also cracked the case of his untimely end: Otzi had settled down to a meal, and then been murdered by an arrow that pierced his shoulder. Clearly, someone didn’t want him around, or he had trespassed into unfriendly territory. Although armed with a copper ax and a bow and arrow himself, he was likely taken by surprise.
Dying at the ripe old age of 45, Otzi’s remains showed signs of bad knees and a Lyme disease infection, so he had been struggling with his health for some time. Small consolation, of course.
Quite recently, Canadian scientists were able to revive a sample of moss that had been encased in glacial ice for 400 years. As Teardrop Glacier on Canada’s Ellesmere Island continues to melt, a team of biologists has camped out at its base in order to pull plant samples from its core.
Dated to between 400-600 years old, the moss found in Teardrop Glacier was buried in the ice during the Little Ice Age that stretched from 1550-1850, and especially affected northern climes. Catherine La Farge headed the team, and was able to grow the moss in different petri dishes after grounding up a sample. Moss is part of the bryophyte family, which have survived different climates for millennia because they only need a single cell to survive, and reproduce by cloning that original cell. As this discovery indicates, bryophytes can lie dormant for long periods of time, only to jolt back to life when more favorable growing conditions return.
La Farge is energized by her discovery, and hopes to see what else can be unlocked from the glaciers. “Now we have to think there may be populations of land plants that survived that freezing,” she said. “It makes you wonder what’s under the big ice caps in the Arctic and Antarctic and alpine glaciers.”
Retreats and Advances
Even if you are not standing directly in front of a glacier (though this is highly recommended!), their records may very well be around you. Warm and cool periods of the earth’s climate also correspond to glacial retreats and advances.
When glaciers advance, they flow down-valley. As more and more layers of ice accumulate, an ice sheet forms. Glaciers are violent, even if their movement forward is so slow that it is undetectable to the human eye. As glacial ice advances, it striates the walls of rock that surround it and churns up the earth, often snapping off boulders and carrying them along as souvenirs.
Glacial retreats are equally dramatic, and leave a footprint on the landscape. Illustrating the effects of the Pleistocene and Holocene ice ages, the areas scored by former glaciers are represented by deep, bowl-shaped valleys called cirques. These cirques are often separated by spined ridges known as arêtes. Former glaciers that flowed into the ocean often leave fjords behind as a record of their existence, while land-bound glaciers leave behind a moraine – a field of rock debris. Rock flour, which is created as rocks are pulverized by the intense pressure of the ice, can flow into water and give it a murky look, or, as seen in the glacial lakes of Montana and British Columbia, a stunning, bright green sheen.
Scientific consensus states that the world’s glaciers are in a period of retreat, hastened by the effects of global warming. As they melt—or spectacularly calve into the oceans as large chunks break off and float away—the world’s ocean levels rise and species such as the polar bear that depend on the ice sheets are threatened.
Since they cover 5% of the state, Alaska is one of the best places on earth to see glaciers in action. Remote as it is, Alaska is still much easier for visitors to access than, say, Greenland. From the famed Harding Icefield to Mendenhall Glacier, opportunities abound to see how glaciers impact the landscape, preserve annals of past climates, and freeze jaw-dropping secrets within their depths. It’s only a matter of time before the next amazing discovery is made.