In the Stable Isotope Lab

Post date: Jul 6, 2013 4:44:18 PM

Over this summer, I have been participating in an internship program in the School of Earth Sciences at Stanford. I heard about this program through my soccer coach, who is also the lab manager of a stable isotope lab in the green earth sciences building. Since I knew him already, I went to work in his lab and I came two weeks earlier than most people. As an intern there, I help out whomever needs lab work done, though I am mostly working on a project involving corals (more on that later). Typical lab tasks include washing vials, stuffing filters, weighing samples and standards and I also read articles and a textbook so that I actually understand what I’m working with.

Stuffing filters is a task where one folds a circular filter (made of glass so that it has no carbon) four times and stuffs it into a cap (a cylinder with one end open). This cap is then folded up and pressed into a small disc, after which it is put into an EA or elemental analyzer, hooked up to a mass spectrometer. In combination, these determine how much Carbon and the ratio of C-14 to C-12 isotopes. This is for a project that I know little about with the goal of creating a carbon budget for the ocean. To do this, they look at DIC (dissolved inorganic carbon), organic carbon and dissolved organic carbon.

The project I’m working on involves coral. In coral, everything below the top is dead. This dead part is made of calcium carbonate (CaCO₃) more specifically aragonite (a particular molecular arrangement of calcium and carbonate ions). Little living things at the top called polyps filter feed and are aided in gathering nutrients by small, photosynthesizing symbionts. As they grow, these polyps lay down calcium carbonate with carbon isotope ratios as a function of temperature and salinity. The salinity factor is highly linked to precipitation, so this is why many corals show seasonal variability and the temperature factor usually shows itself in an overarching trend. When we drill into the coral, we take samples every millimeter, which gives us approximately monthly resolution for temperature, and with our 500-year-old coral from Ta’u in American Samoa, that’s a lot of data and a lot of drilling.