N* variation within the Eastern Tropical North Pacific
MacMillan, Abigal Victoria MacLaine
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[Author's Abstract] N* is a summary parameter used to describe areas of the ocean as either sources or sinks of fixed nitrogen, with positive values denoting nitrogen fixation (a source) and negative values signaling denitrification (a sink). Nitrogen is a major limiting nutrient of biological productivity, so this parameter is useful to differentiate productive regions from decaying regions in the global oceans. I used this parameter to trace water masses by suggesting that the N* signature is a result of the age and source location of different currents. I predict that currents with more productive source locations will have more negative N* values due to increased decomposition of fixed nitrogen caused by breakdown of organic matter by bacteria within the water column. I also predict that older water masses will have more negative N* because the organic matter within the water column would have had more time to be decomposed by these bacteria. By labeling different water masses with separate N* values then levels of mixing could also be identified as a middle number between these end member quantities. I answered these hypotheses using data collected on a cruise of the Eastern Tropical North Pacific (ETNP) in spring 2012 and used this data to provide a more detailed picture of fixed nitrogen breakdown within this region.