Samuel's Blog

First Blog: Coulometer

I am working with a graduate student (Sverre LeRoy), helping her process the vast amount of lake sediment samples that need to be analyzed from Lago Saramiento in Patagonia. (on the tip of South America). The lab work consists thus far of sampling the cores taken from the lake, grinding the samples into a powder after they have been freeze-dried, and then massing them out for three machines.

The machine that I have been focusing on the most, and that I will likely be working with more over the summer is the coulometer. The most interesting part of the lab work for me so far was trying to figure out how the coulometer works. One morning with another intern working in the lab (Max Blachman), wanted to know the chemistry behind the coulometer but Sverre was unsure so she pointed us to the manual.

The goal with the coulometer is to measure the percentage of carbonate in a particular sample. It does this, as I learned, through the following process: First the sample is dumped in sulfuric acid which will react with any carbonate in the sample to form carbon dioxide gas. The carbon dioxide gas is then passed over a solution containing a chemical that will react to form a blue colored acid in the presence of carbon dioxide. The solution first mentioned is in a voltaic cell, which, when activated produces a base that reacts with the acid to reform the original chemical which is clear and not blue. A spectrophotometer measures the amount of blue in the cell to know when to turn off the current to the cell to stop producing more base. Via this method the amount of carbon is deduced from the amount of current put through the cell.

Hopefully, that makes the process at least somewhat clear. I think the enjoyment came from the puzzle like aspect of the system, having to work to understand what the rather technical manual was trying to say. It should be noted that I had a similar experience reading the first paper that I was given to read on what our analysis of lake sediments can tell us, but that is an explanation for the next blog.

Second Blog: Westerlies

For today’s blog I would like to share my understanding of what the research I am assisting via my internship is trying to assess as well as the mechanism through which such assessment is being executed. Or as is more likely, the rough approximation of such processes.

The final goal is to attempt to analyze the movement of the southern westerly winds (for reasons I will explain in a moment).

To reach our final goal we are analyzing lake sediment from a lake in southern Patagonia, the lake (Lago Saramiento) is large and has no water flowing out of it and only a couple very small streams flowing into it. This means that the water content of the lake is controlled almost entirely by the combination of precipitation and evaporation. Because its catchment is large we can expect the water to be fairly uniform. Now, molecules with lighter isotopes (atoms with fewer neutrons than atoms of the same element) will tend to evaporate more than molecules with heavier elements, thus with no precipitation in our lake we would expect the water to become isotopically heavier over time. The isotope composition of the lake is effectively controlled entirely by precipitation. As organisms in the lake use the water that is available them they will produce sediment that records the isotope composition of the lake at the time the sediment is deposited. We use the record of isotope composition as a proxy record of past precipitation.

For the area that the samples have been taken precipitation has be directly related to the position of the westerly wind belt. Thus the isotope record may be extrapolated to find westerly wind position. (The Westerlies have been shown to move north or south over time).

The reason that we care about westerly movement is that some climate models have the westerly winds moving southward with increased CO₂ levels in the atmosphere, hypothesizing that the Westerlies work to upwell carbon dioxide rich waters of the deep Antarctic Ocean. Carbon dioxide levels being important as a green house gas.