Previous research has suggested the presence of anticlockwise and clockwise tidal eddy motion in the western Gulf of Maine (GoM) (Brown and Yu 2006) near one of the major areas of sea scallop recruitment (Figure 1). This eddy motion seems to originate near the coast during both ebb and flood tidal flows respectively; and then translates offshore along the same general path (see the movie on the bottom on this page) toward the center of the Great South Channel in the estern Gulf of Maine. In this MIT Sea Grant-funded research we seek to understand:

(1) how the eddy motion is generated;

(2) how the eddy evolves and decays;

(3) the physics of the 3-D structure on scales of direct relevance to the scallop fisheries biology.

This study is an essential first step in a more comprehensive investigation of how important this tidal eddy phenomena may affect scallop fisheries recruitment in this region.

Research Project:

• Describe the time/space variability of the tidal eddy flow field structure;
• Quantify the time/space variability of the secondary flow in the structure with a particular focus on eddy-induced downwelling/upwelling anomalies;
• Quantify the role and time/space variability of turbulent mixing and dissipative processes in the region;
• Characterize the physical bottom and hydrodynamic settling environment;
• Elucidate the dynamics of the transient tidal motion.

Methodology:

The TTE study consists of (1) hourly CODAR-derived surface current maps; (2) moored and shipboard Acoustic Doppler Current profiles (ADCP) measurements; (3) Shipboard CTD hydrography measurements along a cross-Great South Channel transect; and (4) numerical circulation modeling.

The field program had a May 2008 component during stronger stratification and a November 2008 - January 2009 component during much weaker stratification.

Figure 1: The 2--3 SMAST/industry survey scallop density distribution map for the western Great South Channel region. The large circles represent scallop density of 0.5-7.0 / m^2. Also shown is a schematic of the ocean environment including symbolic ebb tidal flow (arrows), a clockwise transient tidal eddy (ellipse) and a “reference transect” (red line) marking a typical eddy translation path (see below).