Research

• Marine zooplankton ecology
• Deep-sea and mesopelagic biology
• Oxygen minimum zones
• Copepod ecology
• Whale-zooplankton interactions
• Seamounts
• Benthic-pelagic coupling
• Biological-physical interactions
• Biological oceanography

Oxygen minimum zones (OMZs) are among the most extreme oceanic habitats, with oxygen in midwater depths near aerobic life limits. Deoxygenation, the decrease of oceanic oxygen, is one consequence of global warming, and OMZs may expand in future. This may result in ecosystem and economic (fishery) impacts, if animals encounter physiological limits altering their distributions. In the Eastern Tropical North Pacific and Arabian Sea, we have elucidated principles structuring OMZ zooplankton distributions and responses. Zooplankton biomass in the OMZ core (depth zone of lowest oxygen) is much reduced, although diel vertical migration occurs into very hypoxic water. Both the upper and lower oxyclines (strong oxygen gradients) at the OMZ boundaries are locations of intense zooplankton and fish layering. Oxycline layers respond to changes in OMZ thickness (OMZ expansion) with changes in abundance or depth, potentially altering feeding of fish and benthos.

Our current project, with Brad Seibel and Chris Roman, demonstrates substantial submesoscale variability in midwater OMZ oxygen. OMZ zooplankton distributions respond to these extremely small oxygen fluctuations at very low oxygen concentration. At the lower oxycline (~600-800 m), zooplankton layers track precise oxygen values and are forced deeper below an expanded OMZ. Many of these species are living at the limit of their physiological tolerance to low oxygen and may be unable to adapt to future oxygen decreases.