Determining the influence of mesoscale eddies on near-surface currents and phytoplankton populations in the mixed layer

Peter Gaube, Applied Physics Laboratory, University of Washington, Seattle, WA, United States, Alice Della Penna, Organization Not Listed, Washington, DC, United States and Evan Mason, IMEDEA(CSIC-UIB), Department of Marine Technologies and Operational Oceanography, Esporles, Spain
Space-born radiometers used to estimate near-surface phytoplankton community properties measure light reflected from the ocean in the visible spectrum. The depth of penetration of electromagnetic radiation in this frequency range is a function of the opacity of the ocean's surface, ranging from a few tens of centimeters in optically-dense water to many tens of meters in clear water. The physical variability of this near-surface strata is primarily wind-driven and is nearly always entirely constrained to the so called surface mixed layer. Yet, the systematic and persistent influence of geostrophic motions, such as eddies and meanders, which dominate variability below the mixed layer, can be observed in ocean color observations, suggesting that the near-surface wind-driven “slab" is permeable, allowing fluxes of biologically relevant quantities to occur in conjunction with mesoscale modulations of the oceans interior. The interaction of the wind-driven ocean’s surface with its' geostrophically-dominated interior has been a topic of much interest in the field of physical oceanography for decades.

Multiple dynamically-consistent analytical models exist that can be used to inform the interpretation of ocean color data. Here we present the investigation of how the near-surface, wind-driven “permeable slab'' interacts with the geostorophically-dominated interior ocean by analyzing a global acoustic Doppler current profiler (ADCP) database along with global eddy-resolving data assimilating models in conjunction with the trajectories and characteristics of mesoscale eddies and meanders identified in global maps of sea level anomaly. The goal of this project is to establish a mechanistic understanding of when and where mesoscale eddies modulate and effectively trap the near surface mixed layer.