F-24 



of about 40 meters and this depth is shallower than any of 

 the substrates photographed. 



At the equivalent depths, the temperatures in the heads 

 of Oceanographer and Lydonia Canyons tend to be slightly 

 warmer than at locations lying further seaward. The perma- 

 nent thermocline descends to a depth of approximately 100 

 meters where the temperature is about 6°C. The coldest 

 temperatures are 4 C at the depth of 1390 meters in Lydonia 

 Canyon. 



The salinity is uniform at approximately 35 ±0.1 "/o fl- 

 it shows very little variation with depth or position in the 

 canyons. Salinities are highest (35.3 '/oo) on the shallow 

 rim of Baltimore Canyon and lowest on the shelf (34.8 "/oo). 

 This range of values is typical of open marine conditions, 

 and does not reflect any freshwater input. 



Summary and Conclusions 



We interpret the dendritic drainage patterns of the 

 Baltimore, Oceanographer and Lydonia Canyons (believed to be 

 typical of all East Coast submarine canyons) to have been 

 formed in the Quaternary during periods of low sea stands. 

 The dendritic incision would have accompanied the important 

 continental margin regressions such as that experienced with 

 the expansion of the Wisconsin ice sheet between 25,000- 

 11,000 y.B.P. An ancestral dendritic pattern may have 

 originated as far back as the first major cooling in the 

 Late Pliocene at about 3 m.y.B.P. Eustatic sea-level lowerings 



