A Summer of Lake Core Data

By late July I had much of my data together. I had collected and run over 200 samples from three different cores, conducted magnetic susceptibility on three cores, taken photos of five cores and had split over seven cores. It was an exhausting process, but being able to look at the tangible results was very rewarding.

I created graphs for my data in Excel which easily allowed me to manipulate and compare findings between cores. The first lake that I started investigating was Inner Pollen (photo is shown below). My faculty advisor, Nick Balascio, had given me data from two different cores (IND 10D-A and IND 10D-B) that he collected from the same lake in 2010. IND 10D-A was a surface core, meaning the core was less than 50 cm and its main purpose was to preserve the surface-water interface. IND 10D-B was a long core and was extruded, meaning the sediment was divided every centimeter and placed into bags to eventually be dried. When comparing data between all three cores, the first thing I did was to check and make sure that the results were similar between all three cores. For the most part, all of the data for Inner Pollen had the same trends.

When running samples, I also made a point to compare total carbon to organic carbon. To conduct organic carbon tests, I placed about seven milligrams of each sample into silver capsules and then placed them in a plastic tray. The plastic tray was then left in a glass desiccator for six to eight hours with four 10 milliliter beakers. After the elapsed time, all inorganics in the sample would be dissolved by the HCl. The tray was then placed in a drying oven overnight, before being folded and placed into the element analyzer. After comparing the results of the total carbon samples to those of the organic carbon samples, there was very little to no inorganic material in the sediment.

Nick had also sent me carbon isotope data that had yet to be manipulated and organized. I immediately went about organizing the data into graphs and stitching together data from cores that had been split into two. What the data shows is that there is a clear lake transition between depths of 40 and 60 centimeters! The data indicates that all the material below 60 cm was deposited in a marine environment and all the material deposited above 40 cm was deposited in a lake environment. Although we cannot yet determine the time period over which this transition happened, it is super exciting to notice that Inner Pollen was more marine when eustatic sea level was higher.

The way we date lake cores is through carbon dating. Carbon dating is determining the age of terrestrial plant matter based on the amount of Carbon-14 the plant acquired from the atmosphere when it was alive. As soon as the plant dies, the carbon that it contained begins decaying into Nitrogen-14. By comparing the relative amounts of each isotope and knowing the half-life of Carbon-14, the age can be determined. This process involved sifting through sediment to find tiny bits of plant material. It was important that the plants were terrestrial because the source of carbon for land plants is the atmosphere. If aquatic plant material was used, the plants could equilibrate with the carbon in the water which may be much older than the plants themselves, skewing the age.

The summer spent in the lab was a wonderful experience that introduced me to the realities of paleoclimate research. I learned SO much about the different instruments that are used and how to use them. Looking beyond the nitty gritty of how to use the instruments, I learned about why we were using the tools we were, as well as why we were running the tests that we did.

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