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Notes from Transient Upwelling Hot Spots in the Oligotrophic North Pacific by Calil and Richards (2009, submitted to JGR)


In this paper, the authors confirm the result of previous studies on the relationship between surface chlorophyll (SC) spatial structure and temporal variation and Lagrangian structures revealed by the calculation of finite-size Lyapunov exponents (FSLE): “submesoscale chlorophyll patches are often associated with the edges of mesoscale eddies, surface temperature fronts and regions of vigorous horizontal stirring”. They also study the contribution of surface frontogenesis and nonlinear Ekman pumping to vertical upwelling and the formation of SC blooms. Using numerical simulations, they show that large vertical velocities are found near strong gradient fronts (confirming the results of Lapeyre and Klein, 2006? but in a more realistic context?). They also show the vertical velocity field deduced from Q-vector divergence –a diagnostic derived from surface frontogenesis theory– resemble the output one while the vertical velocity field deduced from nonlinear Ekman dynamics is less satisfactory.