Oxygen Depletion and Associated Benthic Mortalities 

 in New York Bight, 1976 



Chapter 2. Temporal Development of Physical 



Characteristics 



Robert B. Starr' and Frank W. Steimic- 



' Atlantic Oceanographic and Meteorological Labo- 

 ratories, Environmental Research Laboratories, NOAA, 

 Miami, FL 33149 



' Northeast Fisheries Center, National Marine Fish- 

 eries Service, NOAA, Highlands, NJ 07732 



OBSERVATIONS OF WATER COLUMN 



Environmental conditions in New York Bight waters 

 were observed in 1976 by personnel of the Atlantic Ocean- 

 ographic and Meteorological Laboratories (AOML) on 

 four expanded water-column characterization (XWCC) 

 cruises on NOAA ships George B. Kelez and Researcher 

 (Hazelworth et al. 1977a, 1977b, 1978; Starr at al. 1977) 

 and by personnel of the Sandy Hook Laboratory of the 

 National Marine Fisheries Service (NMFS) on numerous 

 vessels. Locations of XWCC station sites, and the vertical 

 sections described here, are shown in figure 2-1. As many 

 of these sites as possible were occupied on a repeat basis 

 in April, May, June, and September 1976. This sequence 

 of observations defines the physical conditions of the water 

 column and the associated distribution of dissolved oxy- 

 gen. 



Bight waters consist basically of relatively fresh shelf 

 water with warmer, saltier continental slope water sea- 

 ward and quite fresh Hudson-Raritan estuarine water at 

 the Apex. Expanded water-column characterization cruise 

 observations indicate that the spring/summer distribution 

 of dissolved oxygen in bottom waters of the Bight is closely 

 related to the strength and depth of the pycnocline. The 

 pycnocline — that part of the water column where density 

 increases rapidly with depth — is an inverse function of 

 temperature and a direct function of salinity. 



In the Bight in spring and summer, temperature de- 

 creases with depth and salinity increases with depth at a 

 greater rate than during other seasons, causing density to 

 increase rapidly with depth, and the depth of the pycno- 

 cline to increase as spring advances into summer. When 

 the pycnocline is well developed, it becomes a surface of 

 density discontinuity and inhibits vertical mixing. Upper 

 and lower limits of the pycnocline were determined from 

 analyses of vertical density gradients based on density 

 (sigma-r, (j,y values observed at 1-meter intervals of 



3 Sigma-f((T,) is defined as [p(5,0-ljl000, where p(5,/) is the value of 

 seawater density in COS units at standard atmospheric pressure. 



17 



