FISHERY BULLETIN: VOL. 71, NO. 1 



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ipoo METERS BOTTOM SEDIMENTS 



^aORAVEL-SANO ^3 SANDY SILT 



[JS3SAND [IZ]SANO-SILT-CLAY 



CZHSILTY SAND JMlSILT 



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Figure 2. — Distribution of the various types of bottom 

 sediments in the study area. Terminology is based on 

 the classification reported by Shepard (1954) and Emery 

 (1960). 



of glacial erratics. Six major sediment types 

 occur in the area (Figure 2). The terminology 

 used is based on the standard Wentworth par- 

 ticle size classification (Twenhofel and Tyler, 

 1941; and others) and the nomenclature is that 

 of Shepard (1954) and Emery (1960). Three 

 types — sand, silty sand, and sandy silt — are dis- 

 tributed over a rather large area; the other 

 three — gravel-sand, sand-silt-clay, and silt — 

 have limited areal distributions. Sands cover 

 more than half of the area. They occur mainly 

 in shallow water (less than 60 to 80 m), except 

 in the eastern sector and in a narrow (6 km) 

 band parallel to the isobaths just below the outer 

 periphery of the continental shelf. Sands and 

 silts in the vicinity of the shelf break are primar- 

 ily glauconitic. In shallow waters near Nan- 

 tucket and Martha's Vineyard and in the vicinity 

 of Nantucket Shoals, the sands are silt free and 

 occasionally mixed with large quantities of shell. 

 Mixtures of sand and gravel also occur in scat- 

 tered patches in the shallower waters of the 

 northwest sector and in Nantucket Shoals. Li- 

 monitic pellets and sand particles heavily stained 

 with iron oxide are common in the northwest 



sector. Admixtures of silt occur with the sand 

 over most of the remaining area. 



A large (80 by 100 km) area of fine-grained 

 sediments is situated in the southwestern sector. 

 A relatively small circular area of sand-silt-clay 

 near its center is surrounded by an inner band 

 of sandy silt and an outer band of silty sand. 

 Characteristically, the relatively large sand 

 grains throughout the area of fine-textured sed- 

 iments are frosted rounded quartz particles. 

 Pyrite-filled foraminiferal tests occur in the east- 

 ern portion. 



On the continental slope below the sand zone, 

 the dominant sediment component is silt. 



Additional information concerning sediments 

 of this area and references to the geological lit- 

 erature were given by Uchupi (1963), Wigley 

 and Mclntyre (1964), Emery, Merrill, and 

 Trumbull (1965), Emery (1966), Garrison and 

 McMaster (1966), McMaster and Garrison 

 (1966), and Wigley and Emery (1967). 



HYDROGRAPHY 



Within the area the water temperature regime 

 is typically warm-temperate, although the bo- 

 real influence is seasonally significant. Surface 

 temperatures are substantially higher than bot- 

 tom temperatures; off'shore surface waters are 

 somewhat warmer than inshore waters through- 

 out most of the year; temperatures of the entire 

 water column change seasonally and to some ex- 

 tent from year to year. Most pertinent to the 

 subject of this report are bottom water temper- 

 atures and nontidal currents. 



A cell of cold (6.6°C in June 1962) bottom 

 water extends in an east-west band from the 

 New York region eastward to long 70°W (east- 

 ern Nantucket Island). This cell occurs at 

 depths of about 40 to 80 m, which is roughly the 

 midshelf region. At 300 to 600 m the bottom 

 water temperatures are low and nearly constant 

 throughout the year; they generally range be- 

 tween 4° and 7°C. Near the shelf break and 

 upper continental slope the bottom temperatures 

 are substantially higher, but also nearly con- 

 stant; values range near 10° to 12°C through- 

 out the year. Offshore shelf waters, especially 

 in shallow sectors, may range from 3°C in Feb- 



