I finished my work in the lab a couple of weeks ago and definitely enjoyed my time there learning about the applications of chemistry into the field of geology. However, I haven’t been too good about posting, as I’ve had this post drafted for several weeks now. So here it is.
Recently, you may have seen that the fine folks at the Haverford Communications department wrote an article about my internship and I’m going to talk about the sequential iron extraction that was mentioned in the article.
In the Sequential Iron Extraction, we are separating the iron by what mineral phase it is a part of. This allows us to see how much highly-reactive iron (reduced Fe 2+) is present. The ratio of this to the total amount of iron present in the samples, iron tells us whether the ocean was oxic (high in oxygen, like present day) or anoxic. If the ratio is below 0.38, then it is oxic.
If it is anoxic, there are two possible conditions, being euxinic (high in sulfur, similar to the Black Sea today) or ferruginous(iron rich). In this case, we take a ratio of iron as pyrite to highly-reactive iron. We get the amount of pyritic iron from CRS (described in my previous post). If the ratio is below 0.8, then it is ferruginous, which is what we believe data is indicating right now, but we do not have the information about whether it is oxic/anoxic.
This sequential iron extraction has led to “The Case of the Missing Iron”, a tale with a mysterious disappearance of iron from some samples, which is now nowhere to be found.
The extraction method was developed in Simon Poulton’s lab and published in a 2004 paper. There is a specific sequence in which the steps need to be done because later steps also remove the iron associated with the earlier steps. Both Dave and JC, a graduate student in the lab, have run standards in the Poulton lab.
In the procedure, the acetate extraction, requires that it be in a heated water bath, which requires a lot of set-up. Ben Gill, my advisor, had run his own samples to determine if he could just have the samples be spun on a rotator, and found no significant difference. However, Ben, was given the standards to run in Dave’s lab, and was extracting less iron in the acetate step than what Dave and JC had found, even after attempting different methods. Another twist in this tale is that Ben got the same results for the last two steps, meaning that there is some “missing iron” out there. We would usually expect to see the same total amount extracted, with the “missing iron” appearing in a later step.