Emergence of Coherent Clusters in the Ocean

A. D. Kirwan, H. S. Huntley, H. Chang

Research output: Chapter in Book/Report/Conference proceedingChapter


Why does material tend to congregate in long coherent clusters at the surface of the ocean when it is well known that the ocean is dispersive? Here we review some recent research that addresses this question. A standard diagnostic for discerning transport pathways in incompressible 2D flows is the finite time Lyapunov exponent (FTLE). The FTLE can be expressed as the average of two rarely evaluated Lagrangian objects: the dilation and stretch rates. The stretch rate accounts for the ability of fluid shear to change the shape of fluid blobs, and for incompressible fluids it is the FTLE. However, in the real ocean and especially at submesoscales, the horizontal divergence is not negligible. This is quantified by the dilation rate, which is identically zero in 2D incompressible flow. Our analysis demonstrates that the combination of fluid dilation and stretch enhances accumulation of buoyant material along thin clusters in an otherwise dispersing ocean.

Original languageEnglish (US)
Title of host publicationAdvances in Nonlinear Geosciences
PublisherSpringer International Publishing
Number of pages12
ISBN (Electronic)9783319588957
ISBN (Print)9783319588940
StatePublished - Jan 1 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Earth and Planetary Sciences(all)
  • Engineering(all)
  • Mathematics(all)
  • Environmental Science(all)
  • Physics and Astronomy(all)


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