Lake coring is pretty cool. Like a time capsule waiting to be extracted, the layers of sediment on the bottom of a lake hold clues about the lake’s history. Our core, extracted late last night, is a beauty. Even the engineers and entomologists are able to pick out that there is a major change about 25 cm down in the core. The color of the sediment changes from grey glacial silt to dark brown and black and peaty. Clearly something happened that changed the flow of water from the glaciers into the lake we now work in some time ago. Radiocarbon dating the organic matter just below the interface will tell us just how long ago that was, possibly telling us when the little ice age pushed the glacier back into this valley, once again pouring silt into our pond, which had been cut off from glacial flow sometime in the warmer period of the early Holocene. Also in the core was fossilized insect and plant material which can be used to infer the climate of the region in the past.
One measure of field techniques talked about by scientists, under a variety of different names, is the multiplier. The multiplier is the factor by which you must multiply the amount of time it takes to collect a sample in the field to get how much time it takes to analyze the data back in the office. As an example, the LiDAR work I do on sea ice is about 20… 20 hours sitting in front of a computer for each hour scanning in the field. It is quite possible that lake coring has the highest multiplier of any science I’ve ever participated in. The core only tells its secrets after careful analysis of each layer. You can track isotopic composition of the carbon (for age), nitrogen (for source of organic matter – terrestrial or marine), study fossils under microscope to identify the fly species preserved as indicators of climate, analyze grain size of the sediment to indicate stream inflow rate, filter out black carbon to find past emissions from forest fires and industry, and the list goes on and on. Each of these samples can take hours to prepare and analyze at each of hundreds of levels in the core. The core work for today, however, ended by lunch time, with the core sectioned, photographed and carefully sampled in layers for all of these further analyses.
This afternoon, we did more work over in Vulgaris Valley, trying to date the emergence of the valley from ice at the end of the last ice age. The technique we used, called cosmogenic isotope dating or surface exposure dating can tell us how long a particular rock has been exposed to the atmosphere. The method is pretty clever, and relies on the fact that cosmic rays, which constantly bombard the earth’s atmosphere, penetrate down to the surface at know rates, where they can cause Oxygen – 16 atoms to be converted to Beryllium-10 atoms. By sampling a rock for Beryllium-10, and knowing how much oxygen was part of the rock to begin with, it is possible to estimate how long the rock has been exposed to the atmosphere. This means we want to find boulders which have been continuously exposed since deglaciation… in other words, boulders that stick way up above the surrounding landscape where blowing loess and snow would not come to rest on them. Chipping off pieces of rock from these boulders is super fun, but this science also suffers from a high multiplier. A couple days prep work is required to extract each sample in the lab.
We encountered more of the 5th mammal species present (humans) on our ride home to our campsite near the ice edge (see photo). Back in camp everyone prepared for Professor Kelly’s departure the next day and we all thank her for sharing her knowledge of reading landscapes and smashing chips off boulders with us