Paper 14 



The anoxic event which began early in the year off New Jersey and 

 Lasted through the spring and summer of 1976 necessitated a 

 detailed analysis of the thermal water column structure, 

 considerino how it ev/olved, was maintainedr and eventually 

 declined. ^Oxygen depletion in the bottom waters over a large 

 area off the coast during the summer had severe effects on the 

 sport and commercial fisheries. The immediate impact included 

 finfish and shellfish mortalities and unusual fish distribution 

 patterns ana concentrations. Likely causes of the oxygen 

 depletion can be traced back to anomalous environmental 

 conditions in January and February of 1976 in the Middle Atlantic 

 Bicht (A rmst ronci/' Paper 17). 



HISTORICAL SUMMARY 



Water temperatures in the Middle Atlantic Bight range from a 

 minimum of <3C in the New York Bight in February to >27C off Cape 

 Hatteras in August (Bumpus et al. 1975). The annual range of 

 surface temperature may be >15C in the Slope Water to >20C in the 

 Shelf i«at er . 



I^inimum winter temperatures are reached in late February or early 

 .^arch and may be as low as 1C. During this coldest season the 

 Shelf Water column is well mixed (isothermal) from surface to 

 bottom and extends out to the Shelf Water/Slope Water front (at 

 aoproximately the 100-m isobath) (Gunnr Paper 18). Irregular 

 warming usually begins in late February or early March, and a 

 t herrr.ocline develops in late April or early May. 



A rather intense thermocline develops during the summer, sealing 

 off the bottom waters and isolating a pool or cell of cold winter 

 water that rests on the bottom surrounded shoreward, seaward, and 

 above by warmer water. As the summer progresses into early fall, 

 this cold cell tends to erode in extent and increase in 

 temperature. This erosion is presumably caused by mixing from 

 above with warmer near surface waters and from a "calving" 

 process, described by Whitcomb (1970), where parcels of this 

 cooler water break off and flow and mix seaward into the Slope 

 water. 



For this rep 



or t all figures have been annotated to show 



SheLf Water/Slope Water front 

 Shelf Water/Slope Water meander 

 North wall of the Gulf Stream 

 Anticyclonic warm core eddy 

 Gulf Stream meander 

 Flow direction 



SSF 



SSFM 



GS 



ACE 



GSM 



e into the page 



© out of the page 



232 



