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François Ascani’s Research

Francois Ascani in front of POST building

I am an Assistant Professor in the Department of Marine Science at the University of Hawai`i at Hilo. My expertise is Oceanography and Physical Oceanography but I have also a broad understanding of complex systems and nonlinear science.

I received my PhD in 2008 for a work relative to the dynamics and the modeling of the deep mean east-west current observed below the thermocline (below about 500 m/1500 feet the ocean surface) in the Pacific and Atlantic oceans. I developed a theory suggesting that some of the currents are generated from a dissipated beam of equatorial waves (Ascani et al., J. Phys. Ocean., 2010). One of the key concepts I described is the modification of the potential vorticity of parcels flowing inside the equatorial wave field. I am now working on extending this view of the dynamics of the eddy-driven transport to other components of the general ocean circulation especially the mid-latitude intermediate zonal jets, a.k.a. the “striations”. (see section Eddy-driven Mean Circulation).

I am also interested in the impacts of physical processes on the dynamics of marine ecosystems. One first issue is the effect of mesoscale eddies and submesoscale features and processes on the injection of nitrate from the deep ocean into the euphotic zone. This is particularly relevant to oligotrophic oceans, such as the North Pacific subtropical gyre around Hawai`i, because they are depleted in nitrate over the upper 125 m. It is also relevant to the climate as it concerns the efficiency of the ocean in sequestering atmospheric carbon dioxide, the so-called “biological carbon pump”. Between September 2009 and June 2011, I analyzed float observations, satellite data as well as global and regional high-resolution numerical simulations to explore the issue (see sections Submesoscale Processes, OFES Analysis, HYCOM Analysis). I have written an article that summarizes these efforts (Ascani et al., Deep-Sea Res. II, 2013). This work has prompted me to re-visit the vertical turbulent flux of nitrate using a relatively novel combination of instruments (a microstructure temperature sensor and dissolved oxygen sensor both installed on a Seaglider) as well as to quantify the overall effect played by small-scale turbulence on the efficiency of the biological carbon pump. I am hoping to have soon a funded project to address these issues.

Another theme that I am currently studying with Prof. Kelvin Richards is the impacts of physical processes on simple model of marine ecosystems that contain viruses. Viruses are the most abundant entity of the ocean and contains a large proportion of the genetic diversity of the ocean. Viruses have also an important impact on marine ecosystems: they kill bacteria at a high rate effectively arresting marine plankton blooms, they redistribute genes amongst bacteria and they are engaged in an arms race with their hosts which is responsible in part for the high genetic diversity in the oceans. Long-term goals are to include a parameterization of the effects of viruses in climate models. In parallel, I am also interested in the phage-host dynamics itself; one possible project that I would like to explore is to work with individual-based models that take into account evolutionary mechanisms (see section Microbial Modelling).

Another project is concerned with the migration of loggerhead turtles along the Kuroshio Extension (Northwestern Pacific Ocean). In collaboration with Dr. Melanie Abecassis and Dr. Jeffrey Polovina, we have discovered recently that these turtles spend most of their migrating time along filamentary structures, also known as unstable manifolds in the literature of nonlinear dynamics (see 08.24.2012: Stretching filaments and loggerhead turtle migration along the Kuroshio Extension). This discovery has the potential to impact significantly our understanding of turtles’ behavior in this region and our management of this endangered species.

If you want more information on my work or would like to collaborate, you can contact me at fascani at hawaii dot edu.

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