Acoustic measurements show that the biomass
of zooplankton and mesopelagic fish is redistributed by
mesoscale variability and that the signal extends over several
hundred meters depth. The mechanisms governing this
distribution are not well understood, but influences from
both physical (i.e. redistribution) and biological processes
(i.e. nutrient transport, primary production, active swimming,
etc.) are likely. This study examines how hydrodynamic conditions
and basic vertical swimming behavior act to distribute
biomass in an anticyclonic eddy. Using an eddyresolving
2.3 km-resolution physical ocean model as forcing
for a particle-tracking module, particles representing passively
floating organisms and organisms with vertical swimming
behavior are released within an eddy and monitored for
20 to 30 days. The role of hydrodynamic conditions on the
distribution of biomass is discussed in relation to the acoustic
measurements. Particles released close to the surface tend, in
agreement with the observations, to accumulate around the
edge of the eddy, whereas particles released at depth gradually
become distributed along the isopycnals. After a month
they are displaced several hundreds meters in the vertical
with the deepest particles found close to the eddy center and
the shallowest close to the edge. There is no evidence of aggregation
of particles along the eddy rim in the last simulation.
The model results points towards a physical mechanism
for aggregation at the surface, however biological processes
cannot be ruled out using the current modeling tool.