Project: Permanence of the recent expansions of the OMZ and denitrification regimes in the eastern tropical North Pacific

NSF abstract:

Oxygen Deficient Zones (ODZs) are regions in the global ocean where concentrations of dissolved oxygen in seawater are very low. Low oxygen concentrations affect rates of denitrification, a microbial process in which nitrate is converted to nitrogen gas. This can lead to significant losses of nitrate from the ocean. Nitrate is an important nutrient in the ocean that supports ocean ecosystems. Ocean warming is likely to expand these ODZs making it imperative we understand the role of the ODZs on the chemistry and biology of these regions. This understanding requires repeated sampling of nutrient and oxygen concentrations through time. The investigator plans to utilize available ship time from an existing grant to sample the Eastern Tropical North Pacific (ETNP) ODZ six times over a two year period during the spring, summer, and winter months. The aim is to determine the permanence and seasonality of the recent expansion of the ODZ in the ETNP, as well as identify the processes responsible for any observed changes. This research will support the University of Washington's Masters in Science for Science Teachers program, which provides a link between researchers, graduate students, and elementary aged youth, and there will be funds provided for two undergraduate students to participate in two research cruises on the R/V Thompson.

This project seeks to answer whether observed increased rates of denitrification in the ODZ of the ETNP are solely due to a growing oxygen deficiency problem or can be attributed to sample timing and seasonality. Additionally, the increased loss of nitrate will be investigated to conclude whether it really is due to increased rates of denitrification in the ODZ or some other cause. Climate model simulations predict a large perturbation to the dissolved oxygen content of the ocean, which could have further consequences than purely oxygen chemistry. This study hopes to answer the question of how climate change impacts on dissolved oxygen will affect denitrification in the ocean, which in turn has a much larger effect on limiting marine productivity.