Gravity data obtained during Chain cruise 73

Abstract

This report presents the results of gravity measurements obtained aboard the Research Vessel CHAIN of the Woods Hole Oceanographic Institution during cruise 7 3, 6 to 26 September 1967. Information on bathymetry and other studies conducted during CHAIN cruise 73 may be found in W.H.O.I. Reference No. 68-50 (Knott, et al., 1968). Gravity measurements were made simultaneously with the Massachusetts Institute of Technology (MIT) vibrating string gravity meter and with LaCoste and Romberg sea gravity meter number S-13. The data presented is a selective composite of information from both meters . The base reference station used for the measurements is at the W. H. 0. I. dock in Woods Hole, Massachusetts. Its gravity value was taken to be 980327. 0 mgal, however, recent ties of this station to national gravity network stations (Anonymous, 1965) in the Boston, Massachusetts area indicate that this reading is high by about 1. 4 mgal. Thermal and electrical difficulties with the MIT meter made port-to-port drift prediction uncertain (Bowin, Wing and Aldrich, in press). Drift rate for this meter was determined on the basis of its continuous averaged differences with the LaCoste and Romberg meter. This method showed the MIT meter drifting with respect to the LaCoste and Romberg meter by+ 1. 611 mgal per day for the cruise period. Drift of the LaCoste and Romberg gravity meter during CHAIN 73 was - 0.026 mgal/day from in-port measurements at beginning and end of cruise. This last drift value is anomalous in sign and magnitude with respect to the meter's over-all drift rate , and was not applied. The accuracy of the sea measurements is estimated to be about ±10 mgal (Bowin, Wing, and Aldrich, in press). Free -air anomaly values were calculated using the 1930 International Gravity Formula. Water depths are in meters corrected according to the tables of Matthews ( 1939). Bouguer anomaly values were calculated using an infinite slab correction and an assumed crustal density of 2. 67 gm/cm3 . A density of 1. 03 gm/cm3 was assumed for sea water.