Bathymetry of the Georgia Basin and environs

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This map (Fig. 1, in backpocket) represents a significant advance in bathymetric detail over our previous contouring efforts of the Georgia Basin area (LaBrecque et al., 1981; LaBrecque, 1986). Recently obtained bathymetric soundings from several new sources, most notably the Polar Duke site survey and the updated plotting sheets of the British and Argentine hydrographic offices, have substantially expanded the bathymetric data base for this still relatively underexplored region of the world's oceans (see Fig. 2). In addition, gravity anomalies derived from SEAS AT altimetry data (Haxby et al., 1983; Haxby and LaBrecque, 1986) have provided insight into the morphology of certain bathymetric features that are not as yet fully defined by bathymetric soundings alone (Fig. 3). It should be noted, however, that all of the features shown on the map are at least partly supported by existing bathymetric data; no features are derived from SEASAT data only. One of the difficulties in compiling a bathymetric map of this area is the advanced age of a large part of the data base. A great many of the ship tracks in the western South Atlantic are over 20 yr old and thus, predate the routine use of satellite navigation. As a result, navigation data from these cruises are frequently unreliable. In some cases, the navigation data can be corrected by judiciously correlating track crossings with higher quality navigation from more recent cruises; in places, however, we have discarded whole strings of soundings as too ambiguous for confident manipulation. During the period 1975-1978, the ARA Islas Orcadas (Argentine Naval Hydrographic Service) carried out extensive geophysical surveying in the South Atlantic under a joint program of the Argentine Naval Hydrographic Service and the U.S. National Science Foundation, Division of Polar Programs. The bathymetric data collected during these cruises, along with soundings from Conrad and Vema (Lamont-Doherty Geological Observatory—LDGO), Atlantis II (Woods Hole Oceanographic Institution), Glomar Challenger (Deep Sea Drilling Project), and Polar Duke comprise the predominant portion of the reliable data base in the area. Table 1 lists the data sources used in the compilation of the Figure 1 map. The Polar Duke site survey was conducted in August and September of 1986. Extensive surveys were made of three proposed ODP drill sites, which were subsequently drilled on Leg 114 (Sites 698, 701, and 702). Bathymetry, magnetics, gravity, and single-channel seismic data were acquired. In addition, three cores and four dredges were recovered from seven bottom-sampling stations. The seismic system used a 400-in. water gun and LDGO streamer. The quality of the magnetic, gravity, and seismic data is quite good, but the newly installed 3.5and 12-kHz systems on the site survey vessel did not function properly. As a result, bathymetric data from the cruise have been derived largely from the seismic-reflection data. Using this method, we