My Research, Part 2
Hi everyone! My name is Heather and I’m studying chromium isotopes in seawater for my PhD. There is only a tiny amount of chromium in seawater, but its isotopes behave in an interesting way when exposed to different levels of oxygen. This behaviour might be useful as an indirect measure of oxygen levels in the oceans or atmosphere, so it is hoped that chromium stored in sediments can be used to find out more about past climates. You can find a more detailed introduction to my research here.
For the past six months I’ve been working on samples taken as part of the Shelf Sea Biogeochemistry (SSB) project. Shelf seas are highly productive and absorb a significant amount of CO2 from the atmosphere, but they are under threat due to anthropogenic disturbance and climate change. We want to know more about them so they can be better managed. In March I was lucky enough to go on an SSB cruise aboard the RRS Discovery.
On my cruise the trace metal team collected samples of seawater, sediments and porewaters in order to study elements such as iron, chromium and radium. We also did some experiments to find out how seawater and sediments interact with each other chemically. Levels of trace metals are so low in seawater that a clean lab with special ventilation and minimal metal components must be used to prevent samples from becoming contaminated.
It was also my job to measure the oxygen and pH levels in different sediment cores collected from the sea floor. These parameters are important to geochemists because other sediment components like metals and organics undergo interesting reactions when oxygen and pH change. This testing took place in a lab which is cooled to the temperature of the sea floor (about 8°C) in order to preserve samples while they are being worked on. I also assisted in extracting pore waters (the water between sediment grains) for trace metal analysis.
During the cruise we acquired some interesting data using spectroscopy and other techniques, but the process of analysing all of the samples collected during this cruise in detail will take months. I am also working my way through samples collected on other cruises from the SSB series. You can find an infographic with more details on how I am extracting chromium isotopic signatures from seawater here.