Chlorophyll dispersal by eddy‐eddy interactions in the Gulf of Mexico

Abstract

[1] A Lagrangian analysis of the transport and dispersal of plumes observed in satellitederived ocean color images was conducted using a data-assimilating model of the Gulf of Mexico. The interaction between pervasive cyclonic and anticyclonic eddies in the Gulf generated advective paths that connect remote shelf regions. These paths aligned remarkably well with the plume events recorded with the chlorophyll-a ocean color product from SeaWiFS. Two such events were studied. In one event material was transported in a thin strip between the northern wall of the Loop Current and an adjacent cyclone, connecting the eastern Campheche shelf (off the Yucatan Peninsula) and South Florida shelves. The other event began off the Louisiana shelf break as a small plume traced by chlorophyll and then developed into a long and thin feature which meandered to the shelf break off the northern Yucatan Peninsula, moving between a large anticyclone and several adjacent cyclones. These results indicate that inter-eddy advection plays a crucial role in developing the ocean color patterns observed in the satellite ocean color data.

Hyperbolicity in temperature and flow fields during the formation of a Loop Current ring

“…Their analysis was purely kinematic and thus did not provide any criteria on how close these features might be. Toner et al (2003) used the neighborhood trait of distinguished hyperbolic trajectories and stagnation points to find material lines governing the evolution of chlorophyll patterns in the eastern Gulf of Mexico. Thus, there is prior observational confirmation of the close proximity of these features.…”

Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

“…Turbid and nutrient rich freshwater from major rivers and the associated high chlorophyll coastal waters have a strong impact on the coastal ocean color variability in the GoM (Muller-Karger et al, 1991;Gilbes et al, 1996;Jolliff et al, 2003;Toner et al, 2003;Martinez-Lopez and Zavala-Hidalgo, 2009;Nababan et al, 2011), especially in regions surrounding the Mississippi River delta, the shelf break off Veracruz, and the Bay of Campeche. Analyses of gulf-wide, long-term satellite sea surface Temperature (SST hereafter) and ocean color data provide evidence that the GoM waters have two characteristic states: (1) a winter mixing period characterized by annual maxima of surface pigment concentration, and (2) a thermally stratified period characterized by the annual minimum of surface pigment concentration (Jolliff et al, 2008).…”

“…Associated with the LC and its eddies, are many smaller cyclonic and anticyclonic eddies. Confluence of along-shelf currents introduced by local wind stress and wind stress curl, together with interactions between eddies and shelf/slope circulation, can effectively transport highchlorophyll shelf waters into the deep GoM (e.g., MullerKarger et al, 1991;Toner et al, 2003;. These transport processes therefore play a crucial role in changing temporal and spatial distributions of biogeochemical properties in the GoM, and subsequently the regional marine ecosystem dynamics.…”

On the use of a simple primary productivity model to assess the skill of a physical ocean model

“…On the other hand, Figure 4 shows an ocean color digital image provided for August 24 th , 1998 (day 235, courtesy of M. Toner of the Naval Oceanographic Office, NOO; see also Kuznetsov et al 2002, Toner et al 2003, Elliott 1982. The image is overlaid on modeled integrated 10-day drifters trajectories (the dots denote release points), calculated integrating currents obtained from the operational model of the GoM (see again Kantha 2005), i.e.…”

“…Thus, where it may be difficult to discern temperature contrasts, it may still be possible to detect chlorophyll concentration contrasts. In the Gulf of Mexico case, for instance, it is often easier to detect the Loop Current and eddy fronts because of the small but discernible contrast in phytoplankton biomass and hence chlorophyll concentrations between Gulf water masses and the nutrient-poor Caribbean water masses entering the Gulf through the Yucatan Channel, even during summer (Toner et al 2003). Color imagery also constitutes an independent data set for model skill assessment since chlorophyll data from color sensors are not routinely assimilated into ocean circulation models.…”