Nitrogen (N) is an essential element of life that organisms need to make DNA and proteins. Unlike other essential elements such as phosphorous, nitrogen takes many different forms (NH4+, N2O, NO, NO2-, NO3, N2) which are constantly cycling in the recently revised oceanic nitrogen cycle. One group in the Archaeal domain of life, ammonium-oxidizing Archaea (AOA), has recently been discovered to be a key player in the oceanic nitrogen cycle. In this cycle, Archaea oxidize ammonium (NH4+) into nitrite (NO2-) in a process called nitrification. We hypothesized that different abiotic factors such as copper, light, and temperature regulate the physiology and depth distribution of the AOA. To test our hypothesis, we conducted 15NH4+-oxidation experiments in July 2012 aboard the R/V Clifford A. Barnes in Hood Canal, Washington. Samples of seawater were filled in bottles, spiked with 15NH4+, and incubated for 10 hours. We measured the oxidation of the 15N isotope using mass spectrometry, and compared the rates for control treatments to rates for treatments amended by copper (Cu), light, and other factors. 15NH4+-oxidation rates were consistently low at the surface, increased until 30-40 m, and decreased to 115 m depth. Our experiments clearly showed light inhibition of 15NH4+-oxidation, but the data did not clearly determine whether sunlight-produced peroxides inhibited AOA. Copper additions in Cu-deplete regions increased nitrification, possibly because the key enzyme in ammonium oxidation (amoA) is Cu-dependent. TETA, a chelator that binds Cu, did not show any effect when added during incubations. All together our results suggest that Archaea are Cu-limited, but may store Cu in small amounts. This project is part of a larger interdisciplinary effort to understand the oceanic microbes and the impacts they have on biodiversity and greenhouse gases such as N2O and CO2. Future studies in 2013 will extend these experiments to the open ocean.