Dennis J. McGillicuddy

Objective analysis for coastal regimes

Abstract Statistical interpolation of coastal oceanic fields is addressed within the general framework of Gauss–Markov estimation. Computation of the prior covariance of the field to be estimated is posed as a stochastically-forced differential equation subject to coastal boundary conditions with inhomogeneous, anisotropic parameters. Solution is readily implemented in standard finite element methodology. Examples illustrate the method for idealized one-dimensional situations. Analysis of real biological data from Massachusetts and Cape Cod Bay is shown, using a covariance function derived from velocity and diffusivity fields computed with a hydrodynamic model. The procedure defaults to standard OA methods using distance-based covariance functions, far from boundaries and inhomogeneities.

Interaction between the oceanic mesoscale and the surface mixed layer

Abstract A semianalytic solution to the mutual interaction of a Rossby wave and the surface mixed layer is derived. The presence of the mixed layer causes neither damping nor growth of the interior motions; modal structures and frequencies are simply altered by a small amount. Rossby wave motions perturb the surface boundary layer quite significantly. Vertical transports arising from both the wave itself and its interaction with the Ekman flow cause entrainment and detrainment and create complex remnant layer structures below the mixed layer. The semianalytic solution is used to benchmark a coupled quasigeostrophic and surface boundary layer numerical model. Intricate numerical techniques are required to maintain the fidelity of the mixed layer-remnant layer interface and the structures below it.

The use of mesoscale eddies by juvenile loggerhead sea turtles (Caretta caretta) in the southwestern Atlantic

Marine animals, such as turtles, seabirds and pelagic fishes, are observed to travel and congregate around eddies in the open ocean. Mesoscale eddies, large swirling ocean vortices with radius scales of approximately 50–100 km, provide environmental variability that can structure these populations. In this study, we investigate the use of mesoscale eddies by 24 individual juvenile loggerhead sea turtles (Caretta caretta) in the Brazil-Malvinas Confluence region. The influence of eddies on turtles is assessed by collocating the turtle trajectories to the tracks of mesoscale eddies identified in maps of sea level anomaly. Juvenile loggerhead sea turtles are significantly more likely to be located in the interiors of anticyclones in this region. The distribution of surface drifters in eddy interiors reveals no significant association with the interiors of cyclones or anticyclones, suggesting higher prevalence of turtles in anticyclones is a result of their behavior. In the southern portion of the Brazil-Malvinas Confluence region, turtle swimming speed is significantly slower in the interiors of anticyclones, when compared to the periphery, suggesting that these turtles are possibly feeding on prey items associated with anomalously low near-surface chlorophyll concentrations observed in those features.