Like a fox pursued by hounds, the glaciers have left behind innumerable signs of their presence. Instead of tracks and scent, glaciers leave piles of debris (moraines), scour bedrock, polish boulders, dam lakes, and feed silty rivers. The clues are weathered over the thousands of years since the glaciers receded at the end of the last ice age, so the clues can be hard to read, and sometimes seem to provide confusing and conflicting hints. Today’s task was to learn from Professor Meredith Kelly how to read theses clues out of the landscape, and use many of them together like a detective to try to interpret the glacial history of the region.
The weather was sub-optimal, with a stiff breeze and intermittent light drizzle, but certainly not a show stopper. We hiked away from camp, noting that the camp itself was located on a lake floor that clearly had been dammed about 4 feet higher in the not too distant past. Was the lake dammed by a glacial tongue blocking its outflow? As we hiked higher toward the ice margin, we crossed areas scoured to polished bedrock under the mass of the glaciers, and examined deposits of stones, cobbles, dirt and boulders called moraines which mark positions where the edge of the ice sheet was located for a period of time during retreat.
One thing we talked about a lot is how glaciers move. A glacier which has an edge that stays in one place year after year is still moving. The ice is sliding downhill toward the end of the glacier at the same rate that it melts there or is broken off (calved), keeping the edge in one place. By sitting in one place for a long time the moving glacier slowly piles up rocks and dirt in front of it much like a conveyor belt, creating a moraine. A glacier which is retreating actually is still moving forward and dumping rocks out its face. It’s just that the ice at the end of the glacier is melting or calving off faster than more ice flows down to replace it. The glacier never flows backwards. During the end of the last ice age, as the ice was retreating, it paused in many places, building moraines that we can now use to reconstruct de-glaciation.
The most interesting part of the day’s reconstructions was right at the ice edge. Here we found a large, very recently created (in geologic terms) moraine, which is only about 100-200 meters from the current ice edge. The moraine had only a couple plants growing on it, and otherwise looked like a fresh dirt bank in a construction site or mine. Right at the foot of that moraine is tundra which is covered with grass and small shrubs. This tundra has clearly been out of the ice for at least a half dozen centuries to build up enough soil to support this life. It appears that the younger moraine was deposited right on top of it as if pushed there by a giant bulldozer. This newer moraine has been dated to the little ice age, a period after the middle ages until from about 1400-1880 when earth’s climate was slightly cooler than it is now. This is the same cold period thought to have been responsible for the decline and loss of the Viking colonies in Greenland. What this indicates is that the glaciers grew enough during the little ice age to cover areas of tundra which had melted out during the early Holocene, more than 3000 years prior. How much further back the glaciers retreated from their current location during the early Holocene is much more difficult to say, the ice has erased and buried any clues, but there are papers suggesting that the ice was as much as 15 km further back than it is now. This raised all sorts of questions for the group because the ice right now is only a couple hundred meters behind the little ice age moraine, indicating relatively little retreat since that time. Is our current climate change really much smaller than the climate change which occurred during the early Holocene? Generally speaking we understand that the Greenland ice sheet has only just begun to react to the current climate change, and that the mass loss from Greenland has not been a major contributor to sea level rise yet, but still this is an discrepancy in our understanding that all of us hope to further explore when we get back to civilization and decent internet.
The hike also gave us the opportunity to get a wider look at some of the plants, animals, and fungi that grow on the tundra. Simone provided us with a few more descriptions of plants, including a very low ‘cushion plant’ called Dryas which is one of the first plants to colonize a new location. The plant is also one of the few plants which are capable of fixing nitrogen from the atmosphere, a critical process for building amino acids and proteins that all plants an animals depend on, and one which only a handful of plants in the world are capable of. Simone explained that this plant may actually aid colonization by other plants both by creating and protecting a lump of soil under its tight cushion of leaves, and by fixing nitrogen into that lump of soil as it spreads.
In the animal realm, there were bones, antlers, and pieces of hide galore. Enough to keep a hunter like myself glued to the ground, inspecting every piece for clues about the animal’s demise. The quantity of bones and antlers was incredible, many of them years old, including a pair of nice bull carbou antlers almost completely buried in the tundra sod sticking out just enough so that you could wiggle one and see that it was still connected to the other. We decided that two things were likely responsible for this incredible collection of nutrient rich material ignored on the tundra. First, the bones were likely not chewed as they would be in Alaska for example because there are no rodents here. No lemmings at all! An incredible oversight in specie niche it seems. Also, because the bedrock is weathering right now, and we even later found deposits of calcium carbonate on the soil surface, calcium is probably not as limited a nutrient here as in the older, more weathered areas of Alaska and Canada where antlers are prime chewing material for foxes as well.
Finally to the fungi kingdom, we continued to have good luck with the bolete mushrooms, collecting enough for a delectable dinner side as we headed home, across the stream again, now swollen with glacial outflow from the warmth of the day, to cook a warm dinner.