Robert W. Houghton
Cross-frontal exchange studies at the base of the tidally mixed front using an injected dye tracer
Georges Bank is surrounded by a tidally mixed front. The role of this front in maintaining the high biological productivity on the Bank (Is it a barrier or conduit?) is not fully understood. There is evidence that cross-frontal circulation may be critical for modulating the flux of nutrients and the retention of particles, such as zooplankton and fish larvae, on the Bank both of which contributes to the high productivity of this ecosystem. We propose to use a purposefully injected dye to directly measure the mixing and cross-bank circulation at the foot of the tidal front where on-bank flux is expected to be greatest.
The utility of a fluorescent dye tracer for such studies has recently been demonstrated at the shelfbreak front on the New England Shelf. The ability of the dye to follow a constantly moving frontal boundary makes it a particularly powerful technique for studies on Georges Bank. Since the spreading of the dye patch is referenced to the temperature field that defines the front, the complexity introduced by frontal displacements, irregular bottom topography, and a fluctuating, strong along-bank flow is avoided and the cross-frontal circulation and mixing is unambiguously defined.
The field work will consist of two dye injections in the bottom boundary layer at both the south and north flanks of Georges Bank during mid-May to early June. Each dye patch will be surveyed for 3-4 days using a Scanfish vehicle. To the extent possible this work will be coordinated with other GLOBEC Lagrangian projects.