Chesapeake Lightship (Figtire 1J+, Table 14) 



Temperatures showed a minimum, both surface and bottom of less 

 than 1|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 Harch to mid-June warming was in 

 advance of the mean and the 19$6 record. A surface maximum of greater 

 than 76"? 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, 

 wliich in turn was destroyed at the end of the month. This sequence of 

 events created bottoia 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 observ^ed that the 19^6 intrusion followed a period of 

 preponderant strong southerly i-dnds which tended to move surface water 

 offshore and allow this encroachment of colder x^ater at depth. Similar 

 conditions prevailed in 19^7 • VJinds became predominately southerly and 

 southwesterly in mid- June, when the intrusion first appeared; in mid- 

 Augiist northeasterly winds prevailed to pile up surface water and force 

 a retreat of the colder bottoni 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 vjater from 

 the bay flowed seaward and created a weak thermocline to kO 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 19$6. 



85 



