The oceanography of the New York Bight

Abstract

The New York Bight consists of the waters lying between Cape May, New Jersey, and Montauk Point, Long Island. A portion of the general southwesterly current known as the Coastal Drift lies in the seaward part of the Bight. Inshore from the Coastal Drift is an area of complex hydrography where the combined outflows of the Hudson River and other rivers enter the sea. In the region where the New Jersey and Long Island coastlines converge, an area 25 nautical miles on each side has been studied at all seasons of the year. This area extends from Sandy Hook southward to a point off Seaside Heights, eastward to 73°15' W longitude, north to the Long Island shore, and westward to Rockaway Inlet. The depth of water in the area averages about 90 feet, except in the innermost part of the Hudson Canyon which runs roughly northwest-southeast across most of the survey area. In the Canyon, depths in excess of 240. feet are found within the limits of the area studied. The hydrographic conditions in the area are in essence similar to those off the mouths of other large rivers. The combined flows of the Hudson and other rivers entering the surveyed area discharge enough fresh water annually to replace about one-half of the total volume of water under the 600 square miles of sea surface extensively surveyed. The salinity within the area is nearly as high as that of adjacent coastal water, however, and the actual quantity of river water within the area at any time rarely exceeds one percent of the total volume of water. Quantitative evaluation of these factors has led to the conclusion that there is an active circulation within the area which rapidly disperses the introduced river effluent. Many surveys of coastal and estuarine waters have been made. Outstanding among these are the survey of the River Tees, (1931, 1935), of the Tamar Estuary, (Hartley and Spooner, 1938; Milne, 1938), and of Alberni Inlet, (Tully, 1949). The general principles of estuarine circulations may be summarized as follows: In order to remove the added river water there must be a non-tidal drift of mixed water in a net seaward direction. When river flow remains constant, a steady state distribution of fresh and salt water throughout the estuary is attained, and at such times the net transport of river water seaward through any complete cross section of the estuary exactly equals the contribution of fresh water from the river during the same interval of time. As the mixture containing the river water moves seaward it gets progressively more saline, as additional sea water is entrained. In order to provide this sea water there must be a counter drift having a net flow in a landward direction. Superimposed on these necessary parts of the circulation are tidal and wind currents. The velocities of the tidal currents are commonly much greater than the velocity of the non-tidal drift, making the latter difficult to measure directly. It can be inferred, however, from the distribution of river water, as derived from the salinity distribution. Using the river water in this way we have evaluated the exchanges of the waters within the New York Bight. Tully (1949) has analyzed the circulation in Alberni Inlet by similar methods. Tidal current measurements made by the Coast and Geodetic Survey at various locations in the northwestern corner of the surveyed area are summarized by Marmer (1935). At Scotland Lightship, which is the location of the stations at the western end of Section A in Figure 1, the total excursion which results from the flood or ebb tidal currents is less than two miles. The currents at Ambrose Lightship, about five miles to the eastward, produce displacements only about half as great. The tidal displacements throughout the rest of the area are presumed to be less than these. The pattern of distribution of properties will be displaced, therefore, a distance less than ±1 mile at various stages of the tide. This distance is small in comparison to the size of the area surveyed, especially when considering the fact that distances between stations ranged from 5 to 8 miles. It was unnecessary, therefore, to attempt to take comparable stations at similar stages of the tide. Other considerations, beside its interesting hydrography, have contributed to the choice of this area for study. Because it is adjacent to centers of dense population and heavy industrial concentration, the New York Bight serves the conflicting purposes of waste disposal and recreation. Sewer effluents and industrial wastes enter the area by way of the rivers. Sewage sludges are barged out and dumped within the region studied. During the period covered by our surveys, The National Lead Company commenced operations to barge and discharge at sea the waste from its titanium plant at Sayreville, New Jersey. Since iron was a major constituent of this waste, analyses for iron in the water were made at each station, and the results have been valuable in checking the rate of the circulation which was computed from the distribution of river effluent. The New York Bight is also used extensively for recreational purposes. Because the area is readily and cheaply accessible by public transportation it must serve the recreational demands of a large part of the population of metropolitan New York. Sport fishing, bathing and boating are the principal recreational activities. Small but valuable commercial fisheries for shellfish and fin-fish also exist. The purpose of this study was to investigate the hydrographic processes in the New York Bight since they have an important bearing on the general problems of coastal oceanography and a knowledge of them should lead to a more successful evaluation and utilization of the area for the diverse purposes it must serve.