NO A A PROFESSIONAL PAPER II 



1976 than in any of the previous years represented in the 

 data base (segment A), or the lowest bottom oxygen rec- 

 ords for the entire data base were observed in 1^76. The 

 latter is particularly true for segments Jl. J2. LI. L2, and 

 H where no, or infrequent, bottom oxygen values below 

 2.0 ml/I were observed prior to 1976. However, in each 

 of these segments, numerous values between 0.0 and 2.0 

 ml/1 were observed between J.D. 200 and 270 (July 27 and 

 October 5) in 1976. It is also clear that the 1976 depletion 

 was less severe off Long Island (segments LI, L2) than 

 in the Apex (segment A) and off New Jersey (segments 

 Jl, J2, Ml, M2). Off New Jersey and in the Apex nu- 

 merous values of bottom oxygen were less than 2.0 ml/1 

 as early as J.D. 200; however, the only values less than 

 2.0 ml/I off Long Island were observed about J.D. 270 

 (XWCC cruise 1 1 ) and only one of these was less than 1 .0 

 ml/1. 



Figure 4-3 also gives some idea of the spreading rate 

 of the 1976 oxygen depletion; segments A, Jl, J2, Ml. 

 and M2 have bottom data for the entire year. Assuming 

 that if, and when, low bottom oxygens existed they would 

 have been detected, we can establish the following ap- 

 proximate dates that bottom oxygen levels became critical, 

 that is, less than 2.0 ml/I: 



New York Bight Apex (segment A) mid-June 



Northern New Jersey coast, nearshore mid-June 



(segment Jl) 

 Northern New Jersey coast, offshore mid-June 



(segment J2) 

 Southern New Jersey coast, nearshore early August 



(segment Ml) 

 Southern New Jersey coast, offshore mid-August 



(segment M2) 



This time sequence is essentially the same as that pre- 

 sented in other reports (IDOE Workshop Proceedings 

 1976; Interagency Workshops 1976); however, whether 

 this was simply a discovery sequence of low oxygen oc- 

 currence or a real spreading of the phenomenon has been 

 questioned. Because the data distribution shown here cov- 

 ers the entire year, we can say with some confidence that 

 this is indeed an occurrence sequence rather than a dis- 

 covery sequence. 



Table 4-4 shows how many zero oxygen values (rep- 

 resenting total anoxia) for 1976 actually show up in the 

 data base. Only five such values occur outside segment 

 Ml. Of the 17 in segment Ml, only three were shown to 

 be below the thermocline as defined by the above criteria. 

 Though we use "anoxic" and anoxia" here, the phenom- 

 enon is better described as a severe oxygen depletion. 



Figure 4-3 also shows the theoretical oxygen solubility 

 changes in each segment as a result of temperature 

 changes in bottom water and linear least-squares fits to 

 D.O. versus Julian-day plots wherever sufficient data ex- 

 ist. 



Table 4-4. — Screening of 1976 zero oxygen viiliic:< for 

 New York Bighl 



•■ Limits of area segments shown in figure 1-4 of chapter I 



*• One non-1976 zero value in area segment A. 



' All 14 points are from one data source — a 1977 report bv P. J. 

 Himchak of New Jersey Division of Fish. Game, and Shcllfisheries. 

 Marine Fisheries Section, Nacote Creek Research Station. All 14 samples 

 are for late July or August, list no bathymetric depth, and fail either the 

 temperature or depth test for being below the thermocline. Sample 

 depths vary from 12 to 29 m. 



The oxygen solubility is the theoretical solubility (i.e., 

 maximum concentration) at I atmosphere pressure and 

 was calculated on the basis of mean bottom temperatures 

 (table 4-5) for each month in 1974, 1975, and 1976 as 

 determined from data presented in chapter 5. Since the 

 effect of salinity on oxygen solubility is small, we assumed 

 a mean salinity for Bight bottom waters of 32.75"/|ii, for 

 the solubility calculation. Note that temperature changes 

 in the bottom water are a result of advection and mixing 

 with warmer or colder waters. The solubility curve should 

 not be viewed as a loss in oxygen as bottom water became 

 warmer but rather a change in the maximum theoretical 

 amount of oxygen that the bottom water could contain. 

 As seen in figure 4-3, changes in oxygen solubility re- 

 sulting from temperature changes have a minimal effect 

 on depletion of oxygen in the bottom water. Changes in 

 theoretical maximum oxygen concentration due to tem- 

 perature changes were about I ml/1, whereas observed 

 depletions due to all causes ranged from 4 to 8 ml/I. 



Lines for linear least-squares fits in figure 4-3 were 

 drawn for the time intervals noted only when the condi- 

 tions listed in the figure explanation were fulfilled. These 

 severely limiting conditions prevented drawing many of 

 the lines. Attempts to use more intervals to better define 

 changes in depletion rates with time failed because of poor 

 data distribution. These lines represent depletion rates 

 not utilization rates. The latter are discussed in chapter 

 8. 



An attempt was made to compare 1976 depletion rates 

 (J.D. 100 to 200) in each segment to mean depletion rates 

 for all other years, but this was difficult (table 4-6). Only 



84 



