3-d regional circulation models offer the potential for evaluating/estimating the distribution/concentrations and transport of vent-originating chemical species and biota along and off ridges, around and away from active volcanoes, and deposition into their neighboring sediments.

At this stage of measurement availability and model understanding, these models are better suited for forward calculations than inverse calculations. That is to say, given source flux estimates, concentrations and fluxes and deposition patterns can then be estimated; the converse, gaging the value of the heat flux, for example, coming out of any vent or vent field from water column measurements is still some ways off, at least for any flux value accompanied by a precision estimate.

The physical scales of interest in these flux problems vary widely, from flow/transport in an around individual vent chimneys and vent fields, to flow/transport in axial valleys, to flow/transport along and away from ridges or individual active volcanoes. Because the overlying ocean environment is so time variable and source location and fluxes usually so poorly known, the model usage is typically of a process oriented type (e.g. Berdeal et al., 2005) rather than situation directed type. An example of the second is the description of the pathway taken at the EPR by SF6 during the 60 day LADDER experiment (Lavelle et al., 2010). That result required ancillary measurements of currents and hydrography at the site of interest and such measurements are not generally available.

What kinds of problems might yield new insights with existing hydrodynamic models? A longer event plume simulation, as a process model, might look at the conditions or likelihood for the development of multiple megaplumes from a single eruptive event. Imagine a section of ridge of length L being unzipped over time T all during which heat is being added to the ocean at the seafloor. Current models limit T to a very short time interval and simulations to starting plume time scales. Note that problems involving rapidly ascending fluids require the use of models of the non-hydrostatic type.

Diffuse and chronic plume modeling are both ready for further model exploration. No results of 3-d hydrodynamical models for diffuse plumes have yet been published. Some model results for a working group paper of diffuse source distributions of heat, or chemical or perhaps water-column microbial content should now be possible.

The LADDER Project is directed at understanding larval transport between vents sites along the EPR 9-10N segment, and by extension, the transport between ridge segments. The hydrodynamical calculations and physical observations have highlighted new aspects of along-ridge flow and the role of adjacent seamounts in determining time and space scales of larval transport. See ftp://ftp.pmel.noaa.gov/vents/lavelle/animated_cc1plan.gif for an animation of a plume from a steady source at 9°50'N resulting from that modeling work. The methodology developed at EPR might serve as a template for calculations at other ISS sites, at least for transport calculations of a process model sense.