Abigail Noble, Marine Chemistry & Geochemistry
Cycling of cobalt, iron, and manganese in McMurdo Sound, AntarcticaI requested funding to work at the WHOI ICP-MS Facility to determine iron and manganese concentrations in seawater and ice samples that I took in McMurdo Sound, Antarctica. A large portion of the analytical work for my thesis involves the measurement of trace metal concentrations in seawater via inductively coupled plasma mass spectrometry (ICP-MS), and time on this instrument is costly.
During November 2009, I deployed to Antarctica for a field study in McMurdo Sound, examining metal fluxes in a pristine coastal area with an isolated but well-ventilated shelf, ice cover, and low dust inputs. Due to weather conditions, we were only able to occupy 3 of the 8 stations proposed. We drilled through the ice to take seawater, ice, and biological samples. I measured cobalt speciation, and total cobalt concentrations using electrochemical methods, sampled for total metals, and have ice core samples that have yet to be analyzed for cobalt, iron, and manganese. I was able to use my COI funding to analyze samples for total dissolved iron, total dissolved manganese, total dissolvable iron, and total dissolvable manganese on the ICP-MS at WHOI using a magnesium hydroxide co-precipitation method (Saito and Schneider 2006). These results were then presented at the EBIC Gordon Conference in June 2010.
My results showed a significant surface input of all three metals, with strong cobalt, iron, and manganese input signals near the volcanic islands. Aside from this strong input signal, all concentrations were relatively constant, and interesting finding given the scavenged behavior of these metals in the open ocean. There was little to no difference between the total dissolved and total dissolvable manganese concentrations, but a significant difference between the total dissolved and total dissolvable iron concentrations. Labile cobalt was detected throughout the water column, a phenomenon that our lab has observed previously in the Ross Sea (Saito et al., in review). These results will be written up as part of my thesis and hopefully eventually published in a peer-reviewed journal. I was able to accomplish this work in 2 days on this ICP-MS. While ice core analyses are still pending, the data that I did acquire was extremely useful and I am grateful to have had the support of the Coastal Ocean Institute to enable this research.