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Oceanographic and Meteorological Aspects of the Gulf of California!

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Oceanographic and Meteorological Aspects of the Gulf of California! Oceanographic and Meteorological Aspects of the Gulf of California! GUNNAR 1. RODEN THE PRIMARY OBJECT of the present paper is and it is expected that its importance will to give an adequate description of the cli­ steadily increase in the future, especially as an matic and oceanographic conditions in the additional food source for Mexico. A thor­ Gulf as they are known today . ough knowledge of the physical and chemical Only a few authors have discussed the changes taking place in the Gulf is essential Gulf (Sverdrup, 1940; Osorio Tafall, 1944) to the understanding of its fisheries. and only the geological work was described Moreover, the Gulf is interesting because in detail (Anderson, 1950; Durham, 1950; it represents the only large evaporation basin Natland, 1950; Revelle, 1950; Shephard, of the Pacific Ocean and because it shows 1950). certain differences from other comparable The data used in the present investigation evaporation basins. A final answer to all the are largely taken from the "E. W. Scripps" different problems in the Gulf cannot be expeditions in 1939 (Sverdrup and staff, 1943) expected from the meager data available but and from the publications of the Servicio it is the hope of the author that this paper Mereorologico Mexicano, the U. S. Coast and may stimulate more research in this intriguing Geodetic Survey, and the U. S. Hydrographic area. Office. ACKNOWLEDGEMENTS The data for the Gulf are few and the con­ clusions that can be drawn from them are The author is indebted to Dr. Warren S. necessarily limited and should be taken only Wooster and Dr. Robert S. Arthur for valu­ as a first approximation until more and better able help and suggestions that made this data are at hand. study possible, to Mr. Joseph L. Reid, Jr., The Gulf of California is of considerable Dr. F. Phleger, and Miss June G. Pattullo for interest both scientifically and economically, reading the manuscript, to Mr. Townsend Cromwell for a discussion on a definition of a front, and to Sr. Enrique Avila for advice 1 Contribution of the Scripps Institution of Ocean­ ography, New Series, No. 960. The work reported on on the writing of Spanish place names and herein represents results of research sponsored in part other terms. The author also wishes to express by the Office of Naval Research under contract with his thanks to those who have helped him to the University of California. Manuscript received July 24, 1956. prepare the drawings . 21 22 PACIFIC SCIENCE, Vol. XII, January, 1958 FIG. 1. Bath ymetri c map of the Gulf of Californi a. GENERAL DESCRIPTION AND PREVIO US fluenced by Gulf water (Schott , 1935). This INVESTIGATIONS region will be called the Gulf Entrance, and it has a total surface area of roughly 40,000 The Gulf of California is unique in many krn .t respects. Lying as it does in a predominantly arid region it comprises the only large evapo­ Topographically the Gulf can be divided ration basin ofthe Pacific Ocean . It is roughly into a number of basins, separated from each rectangular in shape and lies between the other by transverse ridges. The deepest basins Mexican states of Baja California to the west have a maximum depth of more than 3000 and of Sonora and Sinaloa to the east. At its m. .and a sill depth below 1500 m. (Geol. southern end the Gulf is in open communica­ Soc. Amer., Mem., 1950). In the northern tion with the ocean. The length of the Gulf part of the Gulf isolated basins are found in is about 1400 km . and the average width which different hydrographic conditions pre­ about 150 km., giving a total surface area of vail (Sverdrup, 1941). These basins seem to roughly 210,000 km.", if the southern boun­ represent deep depressions in an otherwise dary is taken along latitude 23°N . Between quite narrow shelf and are completely isolated this latitude and a line joining Cabo San below 200 to 300 m. Their isolated character Lucas with Cabo Corrientes (Fig. 10) lies a is quite sufficient to explain the hydrographic transition region which occasionally is in- conditions found in them and it is not neces- Gulf of California - RODEN 23 ! .~ FIG. 1. Bathymetric map of the Gulf of Californi a (continued). sary to assume the existence of a ridge run­ appearance of the water. Their observations ning SSE between Angel de la Guarda and are, however, lost because they had no written Tiburon to account for the differences (Sver­ records: drup, 1941). There are two large islands in the With the coming of the Spaniards, trade Gulf-Angel de la Guarda and Tiburon­ developed between Gulf ports and the Far both with elevations exceeding 1500 m. East (Hakluyt, 1598) and various captains entered the Gulf with lead and line. The first The coast along Baja California is very written records are therefore found in the steep and flanked by numerous islands and ships' logs of the early seafarers. Scientific rocks. OffRio Colorado and northern Sonora exploration began in 1889 when the U. S. the coast is less rugged and possesses a wide Fish Commission steamer "Albatross" (Fig. shelf. Along Sinaloa the shelf narrows again 2) entered the Gulf to make a few hydro­ and disappears at Cabo Corrientes . graphic stations, especially in the northern The Gulf remained scientifically unknown part (Townsend, 1901). The data collected at until fairly recent times. Prior to the coming these stations consisted of temperature and of the conquistadores, the Gulf area was in­ density determinations, the latter being made habited by different Indian tribes who lived with a hydrometer. The results of the expedi­ by fishing and undoubtedly had some local tion (not previously published in this form) knowledge of the currents and the general are shown in Figure 3. 24 PACIFIC SCIENCE, Vol. XII, January, 1958 "E W SCRIPPS " 1939 "E W SCRI PPS "1940 " AL BAT ROSS" 1889 FIG. 2. Stations occupied on previous expeditions. Considerable warming and high salinity for the southern part of the Gulf and deduce were found in shallow bays such as Bahia from them the general circulation in th e Gulf Guaymas and Bahia Concepcion. Upwelling and to correlate the sea surface temperatures was characteristic along the nor thern coast of to the direction of the wind , the orientation Sonora where the temperature was abo ut one of the shore line, and the special climatolog­ % degreelower and thesalinity004 0 lower than ical conditions prevailing in the Gulf. His in the neighborhood offshore; Near the mouth main conclusions were that the temperature of Rio Colorado the salinity varied between ofthe Gulfis independent ofthe temperatu re 35.2 and 35.7% 0, probably due to the ad­ in the adjacent ocean and that the low tem ­ mixture of fresh water. The bottom tempera­ peratures along the east coast in winter are tures in the northern part everywhere exceeded the result of northerly winds that tend to 11"C. and the bottom salinity varied between transport surface water away from th e coast 35.5 and 36.1% 0. and thus produce upwelling. He also observed The next important description of the Gulf correctly that during most of the year the of California was made by Thorade (1909) in circulation is counterclockwise in the Gulf a paper on the California Current. He exam­ and that the water enters the Gulf along the ined a great number of ship logs over many east coast and leaves it alon g the west coast. years and was the first investigator to draw He mentioned that "manifold discontinuities monthly surface temperature charts (Fig. 4) are observed by a. sudden change in tern- Gulf of California- RODEN 25 WIND TEMP. (OC) FIG. 3. Distribution of winds, temperature, and salinity in March , 1889. perature" in the vicinity of Cabo San Lucas, Gulf (Fig. 2) taking temperature, salinity, which might well have been the first descrip­ oxygen, calcium carbonate and plankton ob­ tion of the San Lucas front. servations on each station from the surface to Schott (1935: 208 ) described the Gulf of the bottom (Sverdrup and staff, 1943). These California as part of the Mexican region, a data are still the most complete ever taken region defined roughly as lying between the in the Gulf. Sverdrup's main conclusions were GulfofTehuantepec and Cabo San Lucas and that the Gulf can be subdivided into two extending seaward between the California parts, a northern part and a southern part, Current and the North Equatorial Current. separated from each other by a submarine The Mexican region is characterized by a very ridge which comes to within 200 m. below high surface temperature and very weak cir­ the surface. The water mass to the north is culation. He briefly mentioned the tempera­ largely of local origin and formed by con­ ture -disconrinuity near Cabo San Lucas and vective currents in winter, the water to the drew attention to the frequent hurricanes in south is nearly the same as in the adjacent that region. ocean and only modified slightly at the sur­ In the spring of 1939 the Scripps Institution face by extensive evaporation (Sverdrup, of Oceanography sent an expedition into the 1941). Gulf led by H . u. Sverdrup on the "E . W. In late fall of 1940 the "E. W. Scripps" Scripps." Fifty-three stations were made in the made a second trip to the Gulf. The chief 26 PACIFIC SCIENCE, Vol. XII, January, 1958 16 SEPT. FIG. 4. Sea surface temperature s (0c.) in the Gulf of Californi a. (After Th orade, 1909.) aim was geological (Geol. Soc. Amer., Mem., of the Gulf in order to determine the feasibil ­ 1950) but a few hydrographic stations were ity of a minor guano industry (Osorio Tafall, made (Fig .
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