Our hydrographic data were processed by 

 computers at the NASA Mississippi Test 

 Facility, Bay St. Louis, Miss. Station profiles 

 of temperature, potential temperature, and 

 density were plotted, and factors of the 

 dynamics of the currents computed. From our 

 study of the data collected in the northwestern 

 Gulf, it is now apparent that the main offshore 

 circulation influences the currents over the 

 western shelf. Also, the exchange of water 

 below 1,000 m. (3,282 ft.) between the eastern 

 and western Gulf exerts a dominating in- 

 fluence on the circulation in the western Gulf. 



We plotted the distribution and abundance of 

 the principal zooplankton taxa in the Gulf, and 

 are studying their relation to the major 

 oceanographic features of the Giilf. 



An intensive oceanographic survey in the 

 vicinity of the Yucatan Strait was planned with 

 the R/V Oregon II to provide "ground truth"-- 

 surface features measured and photographed 

 simultaneously--for photographs that will be 

 taken during the Apollo 7 nnission in October. 

 We selected this area for several reasons: the 

 currents that enter the Gulf through the Strait, 

 the upwelling that extends over the Yucatan 

 shelf, and the supplemental information that 

 was obtained on previous cruises of the R/V 

 Geronimo . We did not achieve all our objectives 

 because of adverse weather, but we did obtain 

 Sonne hydrographic and benthic data that pro- 

 vided additional information on the south- 

 eastern Gulf. 



The analysis of oceanic features seen in 

 photographs taken during manned spaceflights 

 continued to demonstrate that the view from 

 space is valuable to fishery research. Oregon 

 State University and Seaonics International, 

 Inc., made additional studies under contract. 



John R. Grady, Program Leader 



Reconnaissance Survey 



This study is designed to provide informa- 

 tion on sediments throughout the Gulf of Mexico 

 and the oxygen and nutrient content in the 

 overlying waters. In this fiscal year we limited 

 our analyses of water samples to those from 

 the southeastern Gulf. 



Bottom sediments .--We completed the 

 analyses of particle size of marine sediments 

 collected on the Continental Shelf and upper 

 slope east of the Mississippi River Delta in- 

 cluding the Florida and Yucatan Strait during 

 the 1967-68 cruises of the R/V Geronimo . 

 Sediments on the shelf were collected prin- 

 cipally with a van Veen grab, and those on the 

 lower slope were taken with a short, open- 

 barrel, gravity corer of 38-nnm. (1.5-inch) 

 inside diameter. The upper centimeter of the 

 samples was taken for analyses; half was 

 stained with Rose Bengal to identify living 

 organisms. Sediment sizes were treated 



graphically and statistically to provide a 

 means for investigating properties of the 

 bottom sediments and their distribution. 



This year we began analyses of the total 

 organic carbon and carbonate content of the 

 surface sediments. This information will be 

 used to estimate the percentage of organic 

 matter present. Carbon analyses were made 

 by combustion in an induction furnace, and the 

 carbonate was calculated from the difference 

 between the total carbon and the carbon that 

 remained after treatment with a weak acid. 

 Results were obtained and tabulated for sedi- 

 ments east of the Mississippi River. 



We are determining the colors of the sedi- 

 ments by comparing then-i with color chips of 

 the Munsell System. We also are studying the 

 source of color, almost completely biogenic 

 carbonate on the southern Florida Shelf, and 

 its relation to the distribution of sediments 

 and the physical processes now acting in the 

 area. 



We separated the microfauna from sediments 

 (essentially the coarse fraction) collected from 

 the western slope of the Yucatan Strait and 

 sent subsamples to O. L. Bandy at the Uni- 

 versity of Southern California. Identification 

 and frequency distributions of the foraminifera 

 were completed. A nunnber of samples from 

 the deepest water contained ancient shallow- 

 water faunas and lithic debris with a distinct 

 shiny patina mixed in with Recent planktonic 

 and benthic assen-iblages. Shallow- water faunas 

 also were found on the northern Florida Shelf. 

 Specimens of Globorotalia punticulata padana, 

 an index of lower or middle Pliocene, were 

 found in two samples. 



We are preparing for publication a chart of 

 the topography on the commercial shrimping 

 grounds of southern Florida and the distribu- 

 tion of sedinnents in the vicinity of the Dry 

 Tortugas (fig. 22). The bathymetric chart 

 covers about 25, 100 km. (9,700 square nautical 

 miles) and is contoured at 1-m. (3. 3-ft.) inter- 

 vals on a Mercator projection. This map pro- 

 vides a sufficiently detailed base upon which 

 the type and properties of the sediments canbe 

 plotted in their relation to bottom topography. 



Configuration of the bottom was obtained 

 from soundings provided by the USCGS (U.S. 

 Coast and Geodetic Survey) from recent hydro- 

 graphic surveys. Nunnerous enclosed basins 

 and nnounds of irregular shape and minor 

 relief, typical of a limestone bottom, are 

 shoreward east of the 37-m. (122-ft.) isobath. 

 This relict surface that is undergoing little 

 deposition contrasts with the relatively smooth 

 bottom that slopes gently west to the edge of 

 the Shelf. The slope is about 1 m. (3.3 ft.) 

 per mile to a depth of 77 m. (254 ft.), 263 km. 

 (142 nautical miles) west of Cape Sable. 



Knolls or nnoundlike features in a linear 

 north-south arrangement fringe the edge of the 

 shelf. Calcareous algae dredged from their 

 surface indicate that they are reef structures. 



32 



