Project: Collaborative Research: Mesoscale Drivers of Oxygen in the Tropical Pacific

NSF Award Abstract:
The tropical Pacific Ocean is home to rich marine biodiversity and abundant fisheries. It is also the most oxygen-deficient basin in the world, hosting the world’s largest oxygen minimum zones (OMZs). The northern and southern tropical Pacific OMZs are separated by oxygen-rich waters along the equator that provide important habitable space for open ocean fisheries whose feeding behavior is limited by the depth at which oxygen levels decrease below uninhabitable thresholds. Characterizing the processes that control the depth of this low oxygen threshold is important to understanding ecosystem dynamics and to predicting and managing fisheries in this region. The primary goal for this project is to understand the role of regional physical processes in setting the 3-dimensional structure of oxygen in the equatorial Pacific and its changes on seasonal and interannual time scales. The investigators will use a combination of computer models and existing observations to describe the role that regional circulation patterns play in maintaining the volume and oxygen content of the Pacific OMZs. These include global models of ocean circulation and biological and chemical processes controlling the OMZ, as well as models that focus on regional scale features of ocean circulation (such as eddies) and that are informed by observations. The oceanic oxygen cycle integrates physical, biological, and chemical phenomena, making it an ideal curriculum topic for applying Next Generation Science Standards (NGSS) into K-12 classrooms. In this project, the investigators will work closely with NGSS early implementers from the local school districts to introduce this project’s research questions, knowledge, and relevant data and visualization tools into the lesson plans, exposing students and teachers directly to the scientific process.

A major knowledge gap concerns the role of the equatorial current system (ECS) and tropical instability vortices (TIVs) in ventilating the OMZs, and the extent to which oxygen supply by these ventilation pathways is compensated by their effects on nutrient transport, productivity, and respiration rates, motivating the following questions:
1. How does the equatorial current system and its interaction with mesoscale eddies modulate the boundaries and ventilation of the OMZs?
2. What governs the seasonal to interannual variability of OMZ ventilation in this region?
3. Through what physical and biogeochemical mechanisms do TIVs influence equatorial Pacific oxygen?
A central hypothesis for this proposal is that lateral transport by the Equatorial Undercurrent and TIV-mediated fluxes play a dominant role in setting the mean oxygen structure and variability of the upper equatorial Pacific. These questions will be examined using a hierarchy of models of various configurations, including an eddy resolving and coarse global model, an eddy resolving data-assimilating regional model of the tropical Pacific, and Lagrangian analysis. The work is expected to i) elucidate the mechanisms coupling oxygen to ocean circulation and climate variability in the tropical Pacific, ii) inform drivers of OMZ biases in models, and iii) guide observing needs including the on-going Tropical Pacific Observing System (TPOS 2020) efforts and future deployments of biogeochemical (BGC) Argo floats in this region.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.