measurements of surface drift, the latter largely from drift bottle ex- 
periments. A few direct measurements of bottom currents have been 
made from lightships. 
Our knowledge of bottom water circulation along the Atlantic Coast 
may best be summarized by the following four items: 
a. There is an area extending from south of Nantucket 
Shoals westward to the offing of New York from about 30 fathoms to 50 
fathoms which appears to be somewhat isolated from the general circu- 
lation pattern. Following the vernal development of the pycnocline this 
lens of water retains its winter characteristics, remains in the same 
geographic location and does not become modified until the autumn over- 
turn. There appears to be restricted interchange of some of the water 
seaward with slope water. In other words this portion of the continental 
shelf below the pycnocline tends to stagnate for about six months of the 
year. 
b. Observation posts on lightships reveal a mid-summer 
inshore movement of bottom water along the coast from Virginia to New 
Jersey and subsequent upwelling, presumably due to offshore movement 
of surface waters due to wind shear. How far inshore from the light- 
ships this intrusion occurs we do not know. 
The observations also suggest a downwelling during the 
coldest parts of the winter when waters next to the coast chill to low 
temperatures, and subsequent offshore movement when resulting densi- 
ties reach below those of the adjacent offshore waters. This mechanism 
appears to occur in areas farthest from river mouths where the salinity 
inshore is highest. This phenomenon has been observed at Nantucket 
Shoals where the bottom offshore movement was deduced to reach 2 
miles per day (4 cm/sec) and south of Long Island where chilled coastal 
water contributed to the offshore lens of cold water. 
c. The pycnocline develops only very weakly in the coastal 
areas south of Cape Hatteras, allowing greater vertical mixing here 
than to the north where the pyncnocline is better developed. 
d. Bottom flow in the areas seaward from the mouths of 
estuaries can be expected to be shoreward, with intensification of shore- 
ward movement during seasons in which the land drainage into the estu- 
ary is at a maximum. 
Surface circulation. 
The movement of surface waters, summarized below, will be im- 
portant to the distribution of contaminant after diffusion and transport 
from the bottom have brought the contaminant into the surface waters. 
a. At the seaward end of all coastal estuaries the surface 
flow can be expected to be seaward with a tendency toward southerly 
flow along the coast adjacent to the estuary. 
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