The Cooperative Institute for Climate, Ocean, and Ecosystem Studies

I worked under Jessalyn Davis in the Bundy lab at the University of Washington. The Bundy Lab focuses primarily on organic interactions with trace metal cycles, which maintain otherwise unstable forms of metals such as Mn and Fe in the dissolved phase in seawater.  My work focused on organically bound Manganese (III) and its potential mediation of the nitrogen cycle. Mn(III) is important because it is a transition state from Mn(II) and Mn(IV) that can be both oxidized and reduced.

Some researchers, such as Luther et al 1997, have proposed an alternate theoretical pathway of nitrification which could be catalyzed by oxidized Mn in the absence of oxygen. However, this pathway has never been observed in nature, nor has Mn(III)-L been considered as a form of oxidized Mn that could participate in this alternate pathway to N₂. What I did over the summer was analyze an incubation experiment conducted with suboxic porewaters from the northern Gulf of Mexico for Mn(II) and Mn(III)-L concentrations and compare them to their NH4 and NOx concentrations. I reacted the porewater samples with a porphyrin complex, cadmium chlorine, a buffer, and water through a kinetic assay to be able to determine the different concentrations. I analyzed three different pore water treatments, a control, a weakly binding Mn-complex and a strongly binding Mn-complex. My days in the lab involved using clean lab techniques, which required removing my gloves for “dirty” work and having on clean gloves for “clean” work. This was to avoid any contamination because all of my samples had micromolar concentrations of manganese. I would analyze samples by reacting them with the reagents while in the spectrophotometer. This produced an absorbance over time graph which I could use to calculate initial concentrations of Mn(II) and Mn(III)-L. I would also completely reduce each sample and then take an absorbance reading to find out the total manganese. The total manganese would allow me to find Mn(III)-L strong. After running all the samples and processing all the data, I was able to compare the Mn concentrations to their relative N concentrations. Two of my treatments saw no significant change, but the weakly binding Mn complex had interesting trends. It showed a decrease in NH4 and total Mn, but not the expected increase in NOx. This could potentially be due to a step in the nitrogen cycle called anammox where N2 is directly produced, but N2 was not measured so it cannot be proven. There needs to be further research in order to determine what happened and how Mn was possibly involved.

Project Introduction

Research Poster