Expanse of the oxygen minimum zone and denitrification in the eastern tropical North Pacific

Abstract

[Author's Abstract] The oxygen concentrations in the eastern tropical North Pacific (ETNP) are quite anomalous; waters ranging from approximately 300 to 1000 meters have very low amounts of oxygen, some even having no oxygen at all. This zone, defined as the oxygen minimum zone or OMZ, has a large impact on the distribution of macro- and microscopic organisms which makes it quite important to define the extent of this water mass in the water column. In order to determine the OMZ’s location in the water column, water samples were collected using a CTD which obtained sealed water containers at various depths for subsequent analysis on the vessel. At very low oxygen concentrations, nitrite concentrations greatly increase, signaling the presence of denitrification. However, the exact oxygen concentration is controversial and has yet to be widely agreed upon. With data from the cruise and the World Ocean Atlas collectively, a value was obtained for the denitrification boundary in the OMZ. The OMZ’s in the ocean are quite small in size, composing only ~1% of the total ocean volume; they are, however, major contributors for oceanic nitrogen loss which makes OMZs highly important to observe and correctly define.