Francesco d'Ovidio

Fluid dynamical niches, biogeography, and biodiversity hotspots

The biogeochemical role of phytoplanktonic organisms strongly varies from one plankton type to another, and their relative abundance and distribution have fundamental consequences at the global and climatological scales. In situ observations find dominant types often associated to specific physical and chemical water properties. However, the mechanisms and spatiotemporal scales by which marine ecosystems are organized are largely not known. We have modeled the spatio-temporal organization of phytoplankton communities by combining multisatellite data, notably high-resolution ocean-color maps of dominant types and altimetry-derived Lagrangian diagnostics of the surface transport. We have found that the phytoplanktonic landscape is organized in (sub-)mesoscale patches (10-100 km) of dominant types separated by physical fronts induced by horizontal stirring. These physical fronts delimit niches supported by water masses of similar history and whose lifetimes are comparable with the timescale of the bloom onset (few weeks),as provided by the local Lyapunov exponent calculation (in the figure, niches of dominant phytoplanktonic types in the Southern Ocean). Currently, we are investigating how this interplay between transport and plankton ecology may contribute to maintain hotspots of planktonic biodiversity and how next-generation high resolution altimetry (SWOT mission) can contribute to understand this phenomenon. In order to study this problem, we are comparing metagenomic and morphological data from the Tara-Oceans expedition, satellite data, and outputs of the MIT Darwin model for constructing global biodiversity indices. We are also studying how fluid dynamical niches affect the behavior of marine predators like sea elephants and frigatebirds.

Exploring fluid dynamical niches in the Southern Ocean: The KEOPS2 campaign

Detection and parameterization of transport structures

Biogeochemical tracers like phytoplankton in the ocean or ozone in the atmosphere are far from being homogeneously distributed. On the contrary, strong contrasts in concentrations are often observed. These contrasts affect both regional and global climate properties and are created by the interplay between tracer dynamics (production/decay) and transport. Turbulent transport in particular is able to create coherent structures (like reservoirs and transport barriers) that during their lifetime organize the distribution of the transported tracers. Nonlinear diagnostics like for instance the calculation of the local Lyapunov exponent provide a method for mapping these coherent structures once the velocity field is known. When applied to atmospheric winds or oceanic surface currents, these diagnostics unveil the presence of fronts where tracer gradients can be expected. For instance, the line defining the so-called ozone hole (the ozone minimum above Antarctica) as well as boundaries of phytoplanktonic rich waters can be both described with this technique. Focusing on oceanic data, we have systematically computed these fronts for the global oceans from satellite-derived geostrophic currents. I'm currently working on other diagnostics capable of providing properties of ecological relevance (for instance, presence and lifetime of segregating structures) from velocity fields and from in situ float experiments (e.g. LATEX campaign). I use the same mathematical tools for parameterizing subgrid transport dynamics in climate-resolving circulation models.

Collective properties in populations of oscillators: dynamical quorum sensing

The phenomenon of synchronization is widespread in both natural and artificial systems, whenever some oscillating units are coupled together. Nonlinear dynamics provide a theoretical framework to deduce general properties of populations of coupled elements that can oscillate. These properties may then be used to understand the emergence of collective behaviors. I focused on the case in which some oscillating units are coupled by a global term that depends on the mean state of the population. This condition greatly simplifies the mathematical analysis and can describe natural situations like the coupling of a population of cells in a strongly turbulent medium. I applied the theoretical findings to two experimental systems: the oscillating metabolism of a population of yeast cells in a stirred reactor and the dynamics of chaotic electronic circuits that share a common signal. In the case of the metabolism of yeast cells, we were able to show that the synchronization of the metabolic oscillations can code in its amplitude and frequency a key ingredient of many properties of multicellular organism: the information about the size of the colony. In this way we could unveil a dynamical quorum sensing mechanism as opposed to the traditional quorum sensing that is coded on a static property (the concentration of a chemical species).

Publication list

J. Le Sommer, F. d'Ovidio, G. Madec, “Parameterization of subgrid stirring in eddy resolving ocean models. Part 1. Theory and diagnostics”, Ocean Modelling, accepted.

A. Despres, G. Riverdin, F. d'Ovidio, “Surface fronts and currents in the Irminger sea”, Ocean Modelling, accepted.

C. Cotté, F. d'Ovidio, A. Chaigneau, M. Lévy, I. Taupier-Letage, C. Guinet, “Scale-dependent interactions of resident Mediterranean whales with marine dynamics” Limnology and Oceanography, in press.

F. d'Ovidio, S. De Monte, S. Alvain, Y. Danonneau, and M. Lévy, “Fluid dynamical niches of phytoplankton types”, Proc. Nat'l Acad. Of Sciences, in press.

L. Resplendy, M. Lévy, F. d'Ovidio, L. Merlivat, “Evidence for intense submesoscale variability of pCO2 in the northeast Atlantic Ocean”, Global biogeochem. Cycles, 23, GB1017 (2009).

F. d’Ovidio, V. Taillandier, I. Taupier-Letage and L. Mortier, “Lagrangian Validation of the Mediterranean Mean Dynamic Topography by extraction of Tracer Frontal Structures”, Mercator Ocean Quarterly Newsletter, 32: 24 (2009).

F. d'Ovidio, J. Isern-Fontanet, C. López, E. García-Ladona, E. Hernández-García, “Comparison between Eulerian diagnostics and the finite-size Lyapunov exponent computed from altimetry in the Algerian Basin”, Deep Sea Res. I, 56, 15-31 (2009).

E. Shuckburgh, F. d'Ovidio, B. Legras "Local diagnostic of mixing and barrier modulation at the tropopause. Part II: seasonal and interannual variability", J. Atm. Sciences, 66 3695-3706 (2009).

F. d'Ovidio, E. Shuckburgh, B. Legras "Local diagnostic of mixing and barrier modulation at the tropopause. Part I: Lyapunov diffusivity", J. Atm. Sciences, 66 3678-3694 (2009).

S. De Monte*, F. d'Ovidio*, S. Dano, P. G. Sorensen, “Dynamical quorum sensing”, Proc. Natl. Acad. of Sciences, 104, 18377 (2007).

Y. Lehahn, F. d'Ovidio, M. Levy, E. Heifetz, “Stirring of the Northeast Atlantic spring bloom: a Lagrangian analysis based on multi-satellite data”, J. Geophys. Res., 112, C08005 (2007).

I. Gomes Da Silva, S. De Monte, F. d'Ovidio, R. Toral, and C. Mirasso, “Coherent regimes of mutually coupled Chua circuits”, Phys. Rev. E., 73, 036203 (2006).

S. De Monte, F. d'Ovidio, E. Mosekilde, H. Chate', ”Low-dimensional chaos in populations of strongly-coupled noisy maps", Progress of Theoretical Physics, S161, 27-42 (2005).

S. De Monte, F. d'Ovidio, H. Chate', E. Mosekilde, ”Effects of microscopic disorder on the collective dynamics of globally coupled maps”, Physica D, 205, 25-40 (2005).

F. d'Ovidio, H.G. Bohr, P.-A. Lindgaard “Analytical tools for solitons and periodic waves corresponding to phonons on Lennard-Jones lattices in helical proteins”, Phys. Rev. E., 71, 026606 (2005).

F. d'Ovidio, C. López, E. Hernández-García, V. Fernández, “Mixing structures in the Mediterranean sea from Finite-Size Lyapunov Exponents”, Geophys. Res. Lett., 31, L17203 (2004).

S. De Monte, F. d'Ovidio, E. Mosekilde, H. Chaté, ''Noise induced macroscopic bifurcations in globally coupled chaotic units”, Phys. Rev. Lett., 92, 254101 (2004).

J. Aguirre, F. d'Ovidio, and M. Sanjuan, ''Yorke's game of survival'', Phys. Rev. E 69, 016204 (2004).

F. d'Ovidio, H. Bohr, P.-A. Lindgård, ''Solitons on H-bonds in proteins'',J. of Physics: Condensed Matter, 15 S1699-S1707 (2003), cond-mat/0211626.

S. De Monte, F. d'Ovidio, E. Mosekilde, ''Coherent regime of globally coupled dynamical systems'', Phys. Rev. Lett., 90, 054102 (2003) cond-mat/0207701.

M. Maródi, F. d'Ovidio, T. Vicsek, ''Synchronization of oscillators with long range interaction: phase transition and anomalous finite size effects'', Phys. Rev. E., 66, 011109 (2002) cond-mat/0201337.

S. De Monte and F. d'Ovidio, ''Dynamics of order parameters for globally coupled oscillators'', Europhys. Lett., 58, 21-27 (2002).

S. Danø, F. Hynne, S. De Monte, F. d'Ovidio, H. Westerhoff, P. G. Sørensen, ''Synchronization of glycolitic oscillations in intact yeast cells'', Faraday Discuss., 120, 261-276, (2001).

F. d'Ovidio and E. Mosekilde, ''Dynamical system approach to phyllotaxis'', Phys. Rev. E, 61, 354-365 (2000).

F. d'Ovidio, C.A. Andersen, C.N. Ernstsen and E. Mosekilde, ''Bifurcation analysis of spiral growth processes in plants'', Math. Comp. Sim., 1614, 1-16 (1999).