Flow structures with high Lagrangian coherence promote diatom blooms in
oligotrophic waters
Abstract
Diatoms are among the most efficient marine organisms for primary
production and carbon sequestration, absorbing at least 10 billion
tonnes of carbon dioxide every year. Yet, the spatial distributions of
these planktonic organisms remain puzzling and the underlying physical
processes poorly known. Here we investigate what dynamical conditions
are conductive to episodic diatom blooms in oligotrophic waters based on
Lagrangian diagnosis and satellite-derived phytoplankton functional
types and ocean currents. The Lagrangian coherence of the flow is
diagnosed in space and time simultaneously to identify which structures
favor diatom growth. Observations evidence that flow structures with a
high degree of coherence (40 days or longer) in high turbulent kinetic
energy and vorticity sustain high concentrations of diatoms in the
sunlite layers. Our findings show that the integration of Eulerian
kinematic variables into a Lagrangian frame allows revealing new
dynamical aspects of geophysical turbulence and unveil transport
properties having large biological impacts.