Review of the oceanography of Long Island Sound 227 



of about one knot in the central and western basins. Many current stations, particu- 

 larly in the eastern part of the Sound, show that the ebb is stronger than the flood in 

 the surface layer, while the reverse is true at the bottom. Thus there is a tendency 

 here, as in many other sounds and estuaries, for the surface layer to move seaward 

 and to be replaced by sahne water flowing in along the bottom. An analysis of the 

 available current stations during the summer season (Riley, 1955 a) indicates that 

 this inflow through the eastern passes is of the order of 15-20 thousand m ' per second. 

 The bottom transport decreases rapidly as it moves west, approaching zero near the 

 western end of the Sound. Clearly the slowing down is due to upwelling of bottom 

 water and admixture with the surface layer, and current measurements demonstrate a 

 corresponding augmentation of the eastward surface transport. The calculated mean 

 rate of upwelling required to satisfy the principle of mass continuity is small, ranging 

 from about 5 cm per month in the central and western part of the Sound to a maximum 

 of 45 cm in the vicinity of the passes. 



It would appear from current stations that about 1,100 m* sec enter the western 

 end of the Sound from New York harbour and flow eastward as part of the surface 

 layer. The latter is further augmented by freshwater drainage, amounting to about 

 300 m^/sec in summer. Thus the surface outflow at the eastern end should exceed the 

 inflow by about 1,400 m^sec, although the statistically derived transport estimates 

 are not accurate enough to demonstrate this. 



Complete current surveys are available only for the summer period. Analyses of 

 salt balance (Riley, 1952 a) indicated a seasonal variation correlated with freshwater 

 drainage. Surface current measurements at Bartlett Reef Lightship in the eastern 

 end of the Sound (Le Lacheur and Sammons, 1932) showed a similar relationship, 

 but farther west, at Cornfield Lightship, the seasonal variation was slight and was 

 not clearly correlated with river outflow. 



The distribution of temperature and salinity has been described by Galtsoff and 

 LoosANOFF (1939) and Riley (1952 a). Surface water temperatures have a seasonal 

 range of roughly 3^ to 19° in the eastern end of the Sound and 0° to 23° in the western 

 portion. The total salinity range is about 23 to 31%„, excluding occasional eddies of 

 fresher water in the immediate vicinity of the rivers. The east-west salinity gradient 

 is ordinarily about 57oo» and there is a seasonal variation of 2 to 4°/„„. 



A two-year series of observations in the central part of the Sound (Riley, 1955 a) 

 at station positions shown in Fig. 1 serves to illustrate general features of the tempera- 

 ture and salinity cycles. There was a small thermocline in spring and summer, and the 

 maximum difference between surface and bottom temperature was about 5 (Fig. 2). 

 A slight salinity gradient was maintained throughout most of the year by the combined 

 eff'ects of freshwater dilution of the surface layer and inflow of saline water along the 

 bottom. Differences in the seasonal cycles from one year to the next show obvious 

 correlations with the meteorological variables included in Fig. 2. 



SEASONAL CYCLES OF PLANKTON AND CHEMICAL FACTORS 



The upper part of Fig. 3 shows the seasonal cycles of surface and bottom phosphate 

 and nitrate as averages of analyses at inshore stations 1, 6, 7, and 8 (Riley and 

 CONOVER, 1955). Chlorophyll analyses included in the figure provide an estimate of 

 the total phytoplankton population, and zooplankton catches obtained by oblique 

 tows with a Clarke-Bumpus sampler are plotted as total displacement volumes. 



