Recent Observations of the Mean Circulation on Georges Bank

Retention of larval haddock Melanogrammus aeglefinus in the Georges Bank region, a gyre-influenced spawning area

“…From the release of surface and bottom drift devices, Bumpus & Lauzier (1965) and Bumpus (1973Bumpus ( , 1976 estimated that surface drift was on the order of 2 to 3 n miles d-l. Bottom drift moved in the same direction as surface water but at a slower Butman et al (1982), the 10 to 40 m depth distribution of most haddock larvae (Miller et al 1965), and the distribution patterns of intermediate and large haddock larvae in Fig. 5, 6 & 7, w e conclude that: (1) the westward displacement of larvae tends to parallel isobaths and, therefore, must be influenced largely by the gyre; (2) the displacement covers a maximum straight line distance of 140 n mile (252 km), thus our transport theory is consistent with mean current velocities presented by Butman et al (1982) and growth rates of young haddock in Bolz & Lough (1983); (3) larvae associated with the outside of the Georges Bank gyre pass south of Great South Channel with most subsequently finding their way onto Nantucket Shoals; (4) larvae associated with the inside of the gyre are caught up in recirculating water and advected north along the eastern side of the channel, thus remaining on Georges Bank. Given the 78 m mean depth where haddock larvae 2 8.3 mm occur, and the large size and relative abundance of larvae in Zones 2 and 3 during May, June, and July (Fig.…”

“…We attribute this marked westward movement in May to a strengthening of the anticyclonic gyre, which reportedly occurs in association with spring warming (Butman et al 1982). We suspect that when the gyre is weak during the March/April period larval transport is influenced largely by the strong semidiurnal rotary tidal currents that Bumpus (1976) described as a distinctive feature of Georges Bank.…”

“…By March the abundance of small larvae increases. Their center of abundance overlies that of eggs, a reflection of sluggish (5 cm S -' ) mean flow conditions along the southern part of the bank (Butman et al 1982). However, the principal concentration of intermediate-sized larvae in March extends further westward, the first indication of an east to west displacement with time (Fig.…”

A finite volume numerical approach for coastal ocean circulation studies: Comparisons with finite difference models

“…[68] Observations have revealed that the nonlinear interaction of tidal currents over the abrupt bottom topography of GB generates a clockwise residual current on GB [Butman et al, 1982;Limeburner and Beardsley, 1996]. This current tends to flow eastward as a jet of $30 cm/s on the northern flank and recirculate westward as a relatively weak, broad current of about 1 -5 cm/s on the southern flank.…”

Talc in the Suspended Matter of the Northwestern Atlantic

“…A sample from the Deer Island sewage outflow off Boston, Massachusetts, did contain traces of talc (Table 1). Talc may be present in the sewage sludge from the New York metropolitan region dumped in New York Bight, but the large amounts of talc relative to other silicates found in the suspended matter, and observations of current directions on the Mid-Atlantic Continental Shelf and on Georges Bank (Butman et al, 1982) argue strongly against sewage disposal as an important source of talc on the outer parts of the Continental Shelf where many of our observations have been made.…”