NO A A PROFESSIONAL PAPER 11 



6. Monthly mean sea-surface temperature at tide sta- 

 tions at Atlantic City, N.J., from NOAA's Na- 

 tional Ocean Survey. 



Since environmental conditions in New York Bight were 

 extensively documented by XWCC cruises in 1975 and 

 1976, the primary comparisons were between these 2 

 years — 1976, a year of anoxic conditions, and 1975, a year 

 without anoxic conditions. Four XWCC stations — 23, 38, 

 69, and 88 (station locations shown in fig. 2-1 of chapter 

 2) — were chosen for comparison, because they were con- 

 sidered representative of the Bight Apex, Hudson Shelf 

 Valley, Long Island shelf, and New Jersey shelf regions, 

 respectively. 



DENSITY (Sigma-/) 



Physical properties in all four areas could be compared 

 in 1975 and 1976, the only 2 years during which all XWCC 

 stations were occupied. Station 23 was occupied several 

 times during 1974, providing a long record. Depth vs. time 

 plots of temperature, salinity, and density or sigma-/ (ct,) 

 were drawn for 1975 and 1976 for each station. Similar 

 plots were drawn for 1974 for station 23. Figure 5-1 shows 

 the CT, plots for station 88. 



From the plots, a gross indication of the strength of the 

 density gradient was computed, using surface-to-bottom 



differences of interpolated (midpoint of month) cr, divided 

 by depth. Ratios of these monthly values were obtained 

 for comparisons between years. Averages within years and 

 stations were then computed from the monthly a, gradients 

 (table 5-1). Monthly ct, gradients less than 0.01 were ex- 

 cluded to eliminate the influence of nonstratified condi- 

 tions on the mean. 



The mean of the 1976/1975 ratios was about the same 

 for all stations, varying between 1.3 and 1.6, indicating 

 that the a, gradient was uniformly stronger during 1976. 

 In contrast, at station 23 the mean ratio between 1976 and 

 1974 was 1 .0, indicating the strength of the pycnocline was 

 comparable in those years. A month-by-month compari- 

 son of 1976/1975 ratios indicates ct, gradients were similar 

 at all stations during July, August, and September, but 

 were significantly greater in 1976 during April, May, and 

 June, with the exception of June at station 88. During 

 April 1975, isopycnic or nearly isopycnic conditions were 

 observed. In April 1976, stratification was apparent at all 

 stations and was most intense at station 23. Stratification 

 was developed by May 1975, apparently about 2 to 4 weeks 

 later than during 1976. Maximum stratification was reached 

 sometime during the summer, varying in time from area 

 to area. Maximum occurred during June or July in 1976, 

 but not until July or August in 1975. After reaching a 

 maximum, the gradient gradually decreased through Sep- 

 tember. 



•Value not used in the computation of the mean of the monthly ratios. 



126 



