Cross-frontal Exchange

(K. Wishner, J. Ledwell, R. Houghton)


Scotian Shelf Cross-overs

(PC Smith, D. Townsend, D. Mountain)

Time: Oct. 10-12, 2000

10th Cross-frontal Exchange

11th Scotian Shelf Cross-overs

12th Breakouts

Place: Holiday Inn

291 Jones Road

Falmouth, MA

Cross-Frontal Exchange


The role of the tidal front in sustaining the enhanced biological activity on Georges Bank is still a open question. Theoretical calculations suggest that this is a region of cross-bank circulation and enhanced mixing. But to what extent is the front a barrier or conduit for cross-bank exchange? Is the front a locus of enhanced biological productivity, a convergent zone that accumulates biomass, or a modulator for biological activity over the central cap of the Bank. Hopefully data gathered during Phase III will advance our understanding of this system.

Workshop Purpose:

The goals of this workshop are to achieve an overview of the field work in 1999, share results pertinent to specific scientific questions, and to identify and plan future collaborative research

Scotian Shelf Cross-overs


According to the existing paradigm, Browns and Georges Banks support separate groundfish stocks (cod, haddock) with little exchange between the two regions during the critical early life history stages, because of the retentive tendencies (e.g. gyres) inherent in the circulation of each. However, historical evidence suggests strong interannual variability in the “cross-over” of Scotian Shelf water (and biota) from Browns to the northeast peak and southern flank of Georges, especially during the winter/spring spawning period. The primary goal of this project is to observe and quantify Scotian Shelf water cross-overs, and to investigate the dominant forcing mechanism(s) through interpretation of the data and detailed hydrographic modeling.

Workshop Purpose:


Draft Agenda:

Tuesday Oct 10 Cross Frontal Exchange

1) A summary review of the 1999 fieldwork; identify relevant data sets and construct a time-line. (1 hour max., one speaker from each of the major 1999 cross-frontal exchange field efforts.)

2) For the rest of AM and the first half of PM we will have a sequence of discussions on specific topics. Everyone is invited to participate with a brief and relevant contribution not to exceed 3 transparencies.

Suggested topics (to be expanded, contracted, or otherwise modified)

(a) Frontal response to surface forcing.

(b) Secondary circulation at the front.

(c) Eddy mixing (epipycnal) at the front.

(d) Is there vertical migration at the front coupled with the above?

(e) What is the net exchange into or across the front derived from budgets of various scalars? Can we identify sources & sinks and quantify the fluxes?

(f) What are the interactions of various biological components (cod larvae, copepods and their predators and prey) with the physical processes at the front-are different scales or particular processes most important for different components?

3) Second half of PM

Discuss plans for integration of data sets: what is necessary, useful, and possible. One problem is the identification of the frontal location. Is there a simple "marker" (depth of a particular isoline or gradient) that could be used to locate a station with regard to the position of the front at that time?

Wednesday Oct. 11 Scotian-Shelf Crossovers

1) Summary reviews of physical and biological observations, data processing and analysis to date with respect to SSW crossovers(AM)

2) Discussion of planned approaches for modelling and interpreting the preliminary results (AM, PM)

3) Planning for integration of biological and physical data sets. Strategy for modeling the ecosystem. (PM)

Thursday Oct 12 Joint workshop sessions and Breakouts

Prepare plans for synthesis in Phase IV. Identify important or unusual events. What is the relationship (i.e. importance) of cross-over events relative to routine cross-frontal exchange (e.g. tidal) or slope-water interactions? Identify the mix of data and model coordination which is most likely to lead to significant advances in our understanding of the system.