Chesapeake Lightship (Figure U4, Table 1) 
Temperatures showed a minimum, both surface and bottom of less 
than )}2°F in mid-February. A month later a false thermocline appeared 
briefly when relatively warm and much fresher Chesapeake Bay water ar= 
rived at the station. Ten days later salinities returned to their pre- 
vious level (ca. 32.0 °/oo) and the water again became isothermal, 
though about 1° warmer. A similar sequence of events occurred in March 
of the previous year. From the end of March to mid-June warming was in 
advance of the mean and the 1956 record. A surface maximum of greater 
than 76°F occurred in July and August and again in mid-September. 
At the end of August the thermocline was destroyed, bringing 
water of greater than 72°F to the bottom. During September, warm water 
of lower salinity from Chesapeake Bay produced a second thermocline, 
which in turn was destroyed at the end of the month. This sequence of 
events created bottom temperatures of greater than 70°F and maintained 
them for a full month. 
The intrusion of cold water at the bottom in July was more pro- 
nounced and of longer duration than was a similar penetration a year 
earlier. Bumpus observed that the 1956 intrusion followed a period of 
preponderant strong southerly winds which tended to move surface water 
offshore and allow this encroachment of colder water at depth. Similar 
conditions prevailed in 1957. Winds became predominately southerly and 
southwesterly in mid-June, when the intrusion first appeared; in mid- 
August northeasterly winds prevailed to pile up surface water and force 
a retreat of the colder bottom water. During the last 10 days of August 
northeasterly winds became even more prevalent and temporarily destroyed 
the thermocline. The first three weeks of September showed winds again 
mostly from southerly quarters, during which time warm fresh water from 
the bay flowed seaward and created a weak thermocline to 0 feet. During 
the last 10 days of September strong northeasterly winds accounted for 
the destruction of the thermocline. 
Salinities, both surface and bottom, while showing the wide 
fluctuations to be expected here, were nevertheless generally higher than 
those of 1956. 
85 
