By Rayna Campbell
The Earth’s history shows a wild mix of climates. Ranging from the toxic CO2-filled atmosphere of the earliest years, to global tropical conditions, to periods of intense and violent volcanic disturbances. In the incredibly short period of time humans have inhabited the earth, the climate has not had much time to change. But if we look back into our history, the last glacial maximum, or “The Ice Age” only occurred about 21,500 years ago (Editors). On the scale of geological time, this is very recent. So recent, in fact, we are still able to look to our paleoecological records and “see” evidence of the changes the environment went through during the presence of these huge ice masses.
On the rocky coasts of lovely Maine in the summer, trips to the seaside provide not only a relaxing retreat from the summer heat, but a wealth of information about glacial movement thousands of years ago. The striations (Fig 1; parallel lines) on the rocks by the sea are evidence of not only a huge mass of ice grinding and eroding the stone, but also the direction it was moving. The movement of glaciers still important today because the materials these massive ice sheets left behind; from small rocks and sedimentary particles to massive boulders, the remnants of the last ice age are scattered throughout the northern hemisphere.
Besides leaving huge boulders scattered about the landscape, glacial recession also contributed a lot of negative space in the form of valleys, long canyons, and other depressions in the surface of the area. These changes in the earth’s surface are a result of the sheer mass of the glacier grinding and eroding the ground beneath it. When enough pressure and friction is exerted on an area over a long enough period of time, we find a deep hollow where the dirt, gravel, stone and bedrock of the earth has been eroded away. Many of these depressions fill with water over time, creating lakes, ponds, or rivers. The Great Lakes surrounding Michigan in the northern continental United States are the largest glacial lakes in the world. Sediment cores have been taken from these lakes to reveal the changes not only within the climate since the last glaciation, but within the local environment, too. Because we are able to detect when these lakes were formed (the end of the last Ice Age), we can relate climate information already known to the new data collected from these and other local cores.
Since the end of the last glacial period, the warming trend of the climate has caused intense and constant reduction of the glacial front. We see these effects as defining characteristics of the landscape. Erosion is one of the most powerful forces in nature, and shapes our coasts, rivers, and canyons. Glaciers have carved out the massive semi-circular bedrock basins to the east of Mt. Katahdin, in Maine. Deposits of gravels and sediments are also spread state-wide as a result of this latest glacial retreat. Perhaps most relevant to our paleoecological interests are the lakes created by the breaking and subsequent melting of glaciers as they provide us with sediment cores which are full of information about the local flora of past years.
If we can detect when glaciers have receded in the past and the environmental and climatic conditions that caused their recession, we can look for trends that reflect these conditions in the paleoecological record. Since the recession of the glacial ice sheet freed up so much land space in the northern hemisphere, a diverse group of plants and animals were able to immigrate to habitats previously hidden under thick ice.
However, it is important to keep in mind the other consequences of melting ice on such a large scale. Even though plenty of ecosystems were revealed, other ecosystems are disturbed. Sea level rise is an issue world-wide. Rising sea levels make their mark on intertidal and arctic habitats, as well as inland habitats. Glacial melt can drastically change the water composition in delicate brackish (salt and freshwater) habitats, whose inhabitants are very sensitive to even minor changes in salinity. When there is an influx of nutrients that may have been previously limited in an environment like an inland lake, we are able to infer many things about the climate at the time through the preserved remnants of organisms and particles.
In conclusion, I find it most humbling to remember the origins of the resources on earth we so often take for granted. The the migration of colossal glaciers across our landscape shaped the geography we’ve become so familiar with. So much of our history, as a species, has depended on the movement and melting of the glaciers. Today, we reflect back on what once was to learn how to better sustain our future, and how the earth and its denizens have adapted in the distant past.
The Editors of Encyclopædia Britannica. “Last Glacial Maximum (climatology).” Encyclopedia Britannica Online. Encyclopedia Britannica, n.d. Web. 27 Mar. 2014.
Friedersdorf, Conor. “What America Looks Like: Yellowstone National Park.” The Atlantic. Atlantic Media Company, 01 July 2011. Web. 27 Mar. 2014.
GNS Science. “Brewster Glacier.” / Soaring Mountains Gallery / Gallery / Landforms / Science Topics / Learning / Home. GNS Science, 2009. Web. 27 Mar. 2014.
Milliman, John D., and J.Paul Liu. Postglacial Sea-level Study: MWP-1A, MWP-1B. Journal of Ocean University of China, 2004.