:406 OCEANOGRAPHIC OBSERVATIONS, 1960, EAST COAST OF THE UNITED STATES WOODS HOLE, MASS, SPECIAL SCIENTIFIC REPORT-FISHERIES Na406 UNITED STATES DEPARTMENT^FJ^i^^ pisiTANinwILDUFnERvi^ This work was financed by the Bureau of Connmercial Fisheries under Contract No. 14-17-0007-9, with funds made available under the Act of July 1, 1954 (68 Stat. 376), commonly known as the Saltonstall- Kennedy Act. UNITED STATES DEPARTMENT OF THE INTERIOR, Stewart L. Udall, Secretary FISH AND WILDLIFE SERVICE, Clarence F. Pautzke, Commissioner Bureau of Commercial Fisheries, Donald L. McKeman, Director OCEANOGRAPHIC OBSERVATIONS, 1960 EAST COAST OF THE UNITED STATES by C. Godfrey Day Research Associate Woods Hole Oceanographic Institution Woods Hole, Massachusetts Contribution No. 1202 from the Woods Hole Oceanographic Institution United States Fish and Wildlife Service Special Scientific Report--Fisheries No. 406 Washington, D. C. 1963 Frontispiece. Locations along the Atlantic Coast reported herein. CONTENTS Page Introduction 1 Commentary 1 Summary for 1956-60 1 Surface temperature 1 The the rmoc line 3 Bottom water temperature 3 Salinity 3 Meteorological effects 3 The 1960 data: Surface temperature 4 Bottom temperature 4 Mt. Desert Rock Light Station 5 Portland Lights hip 7 Boston Lightship 11 Georges Shoal, Texas Tower §Z 15 Nantucket Shoals, Texas Tower #3 17 Nantucket Lightship 18 Woods Hole, Massachusetts 22 Buzzards Lightship 2 3 Kingston, Rhode Island 25 Ambrose Lightship 26 Texas Tower #4 (off New York) 30 Barnegat Lightship 31 Five Fathom Bank Lightship 35 Winter Quarter Lightship 39 Chesapeake Lightship 43 Diamond Shoals Lightship 47 Frying Pan Shoals Lightship 51 Savannah Lights hip 55 Literature cited - 59 FIGURES Frontispiece. Locations along the Atlantic coast reported herein 1. Normal cycle of temperature at surface and bottom along the string of observation posts for I960 4 2. Mt. Desert Rock Light Station 5 3. Portland Lightship 7 4. Boston Lightship 11 5. Georges Shoal, Texas Tower #2 15 6. Nantucket Shoals, Texas Tower #3 17 7 Nantucket Lightship 18 8. Woods Hole, Massachusetts 22 9. Buzzards Lightship 2 3 10. Kingston, Rhode Island 25 1 1. Ambrose Lightship 26 12. Texas Tower #4 (off New York) 30 13. Barnegat Lightship 31 14. Five Fathom Bank Lightship 35 15. Winter Quarter Lightship 39 16. Chesapeake Lightship 43 17. Diamond Shoals Lightship 47 18. Frying Pan Shoals Lightship 51 1 9 Savannah Light ship 55 OCEANOGRAPHIC OBSERVATIONS, 1960 EAST COAST OF THE UNITED STATES by C. Godfrey Day ABSTRACT Daily water temperature and salinity observations for I960 from eighteen locations along the Atlantic seaboard are tabulated, plotted and discussed for the fifth consecutive year. INTRODUCTION We hope to continue the collection and publication of these data on an annual basis, Through the cooperation of the U.S. Coast and should be glad to include data of a Guard, the Woods Hole Oceanographic Institu- comparable nature from other locations. tion established late in 1955 a series of oceanographic observation posts at a number This work was supported by the Bureau of of lightship stations along the east coast of Commercial Fisheries, U.S. Fish and Wildlife the United States. Additional data have been Service, under Contract No. 14- 17-0007-9 with obtained from independent observers, from the Woods Hole Oceanographic Institution. the Narragansett Marine Laboratory and, courtesy of the U.S. Air Force, from Texas COMMENTARY Towers 2, 3, and 4. Summary for 1956-60 The lightship data have been forwarded on a monthly basis to Woods Hole, where they have Since the present report marks the com- been processed. The bathythermograms have pletion of 5 years of oceanographic observa- been read at several levels and tabulated; tions under this program, a brief description salinities were determined by salinometer. The of results to date is perhaps appropriate. records of air temperature, weather, wind, and clouds were used in studying the other data, Surface Temperature. --Day to day varia- but are not presented here as they are the tions in temperature, sometimes of considera- same as those published in the daily weather ble magnitude, are found at nearly all stations; maps of the U.S. Weather Bureau. these changes are often obscured in the 10- day mean values used for the temperature In addition to tabulating these data, mean profiles in the reports. They are more pro- temperatures for each level for three equal nounced at near- shore stations, where they time periods per month have been determined appear to be the result of tidal action on and plotted, as time-depth profiles for the relatively shallow water which is constantly year at each station where bathythermographs being mixed and subjected to the influence of were used. The one-third monthly mean sur- unmodified continental air. Further offshore, face temperatures have been plotted in com- with the exception of Diamond Shoals, tem- parison with the monthly mean surface tem- perature is naore stable from day to day. perature for the period of record of each station. With only 5 years of record it is not possible to distinguish between normal and unusual de- The one-third monthly means of surface partures from mean conditions. Temperature salinity have been appended to the tempera- regimes differ at various stations according to ture profiles, together with the weekly bottom the hydrographic geography. salinity values. The monthly mean surface water tempera- In the annual cycle, warming and chilling of tures for the year I960 for all stations are surface waters are fairly viniform trends with listed in table 1 for comparison with previous few reversals. The more static conditions of records. summer and winter are subject to abrupt, short-ternn changes; these are more pro- We are particularly indebted to the U.S. nounced during the summer when strong winds Coast Guard personnel aboard participating often partially mix a stratified water column. lightships, and to the personnel of the 12th The short-term wintertime changes are less Weather Squadron, USAF, at the three Texas marked; they result no doubt from changes in Towers reporting and at Otis Air Force Base. air tennperature and from advection. Table 1. —Surface water temperatures F - monthly and annual means, I960 Location . The ThermocIine .--Completely isothermal with only a slight temporal lag. At other water is seldom found at any of the lightship stations further offshore the fluctuations are stations employing the bathythermograph. less extreme and occur later than at the From November through February, bottom inshore stations. water tends to be slightly warmer than surface water since mixing does not keep pace with Monthly mean salinity values between Am- chilling. When vernal warning begins at the brose and Winter Quarter stations increase surface, mixing continues to produce a similar toward the south. Bigelow (1935) drew dia- warming at depth, but again with a lag, so grams of the locations of surface isohalines that a negative gradient is established. The for successive months, based on data from thermocline thus produced is strongest during sections extending offshore across the shelf July and August at a depth between 30 and 60 in this region. While his values increase feet. At stations from Ambrose through Chesa- offshore along a given section, his isohalines peake the temperature gradient is from time curve toward the coast in the Chincoteague to time intensified by advection, possibly region, also showing a southward increase through upwelling, of colder water near the in salinity. bottom. Destruction of the thermocline is directly associated with autumn storms, often Ketchum and Keen (1955) discussed this connected with the passage of hurricanes. phenomenon in a study of the accumulation If such storms occur early in the autumn, the of river water over the shelf in the same thermocline may reappear briefly before the region, concluding that considerable local final overturn. mixing across the shelf must take place. The lightship data tend to confirm this conclusion. Bottom Water Temperature .--Warming and chilling at the bottom are not the steady The annual salinity cycle at the lightship progressions seen at the surface. There are stations reflects the annual precipitation- sharp changes in rate and frequent reversals runoff regime over the east coast. If dynamic in trend. When thermal stratification is pres- gradients from the shore out over the shelf ent, abrupt warming at the bottom is ap- contribute strongly to the circulation patterns, parently the result of wind mixing, as at the there will be large seasonal and year-to-year time of the autumn overturn when bottom values variations in coastal currents. Southwesterly reach their maximum, sometimes rising as movement along shore should be greatest much as 18 F. in 48 hours. Abrupt cooling during April and May at the time of peak appears to be associated with the advection runoff and before the summer southwesterly of colder offshore water. winds become established. During the winter, the dynamic gradient would be weakest. Salinity . --From Ambrose Lightship north- ward, the surface salinity minimum near Meteorological Effects . --The influence of shore occurs in late April or early May, weather on the hydrography of the area of reflecting the peak runoff augmented by snow study has been demonstrated in several in- melt. At Georges Shoals, farther offshore, stances. Bumpus (1960) showed that runoff is the minimum probably appears in late summer a critical factor in inducing the cyclonic move- From Barnegat Lightship southward the salin- ment in the Gulf of Maine, beginning in late ity minima may occur at any time and nnore winter and early spring. The earlier postula- innmediately reflect local precipitation, since tion of Bumpus and Pierce (1955) concerning there is little storage by freezing on the ad- the penetration of Virginian coastal water jacent watersheds. At most stations. Savannah southward past Cape Hatteras has been sub- excepted, the January and February surface stantiated (Bumpus, 1957; Chase, 1959; Day, salinity readings show little year-to-year 1959).