Man-Made Oceanography 



137 



high sea level such as at present. Accord- 

 ingly, we might infer that the area contained 

 many animals that now live only farther 

 south off Mexico. Carter (1957fl), Hubbs 

 (personal communication), and others have 

 given evidence that mollusks requiring rela- 

 tively warm water have been present in the 

 region during the past 10,000 years, but this 

 evidence is still far from complete. 



Recently, new methods of paleotempera- 

 ture determination based on the ratio of 

 oxygen isotopes 18 and 16 have been ap- 

 plied to stratigraphy (Urey, Lowenstam, 

 Epstein, and McKinney, 1951). Emiliani 

 (1955) found that cores of the deep sea 

 (about 3000 km southsouthwest of Chart I) 

 contain pelagic foraminiferans whose 0^*/0^^ 

 ratio indicates many periodic variations 

 between about 17 and 20 °C at the depth 

 of growth, 110 meters, which may cor- 

 relate with glacial and interglacial ages of 

 the Pleistocene Epoch. Smaller temper- 

 ature variations were indicated by O'VO^*^ 

 ratios for benthonic foraminiferans that 

 grew in the more uniform bottom water. 

 This technique, when appHed to the more 

 rapidly deposited sediments of the Cali- 

 fornia basins, may provide a more detailed 

 record of the Pleistocene temperatures than 

 is possible from deep-sea cores of the equa- 

 torial regions. If the temperature of growth 

 of benthonic foraminiferans on the floor 

 of each of the basins is determined by 

 Q18/Q16 j-atios at core depths equivalent to, 

 for example, 10,000 years based on radio- 

 carbon dates, it can be assumed that the 

 same temperature would have existed at the 

 basin sill depth. If the temperature for each 

 basin is plotted at the corresponding sill 

 depth, a temperature-depth curve for this part 

 of the Pacific can be constructed for the 

 period 10,000 years ago, or for many other 

 desired times. 



The oxygen isotope method has also been 

 applied to the Lomita marl (Lower Pleisto- 

 cene) of the Los Angeles Basin by Emiliani 

 and Epstein (1953), who found a general 

 upward increase of temperature throughout 

 the part of the formation that was sampled, 

 perhaps indicating a change from glacial to 

 interglacial conditions. The average tem- 

 perature indicated by Miliolidae increased 



from about 16 to 26° C, by Elphidium 14 to 

 18°, and by Cassidulina 12 to 14°. The dif- 

 ferences are probably ascribable to diff'er- 

 ences in habitat of the various forms. 

 Further application of the method to Tertiary 

 strata should do much to remove the uncer- 

 tainties inherent in the biozone method of 

 determining paleotemperatures. 



Important aspects of paleoceanography 

 such as current direction, wave height and 

 direction, and tide range await the develop- 

 ment and use of proper criteria. A begin- 

 ning has been made in the use of flow mark- 

 ings and ripple marks (Natland and Kuenen, 

 1951; Crowell, 1955), but until placed on a 

 regional scale such indicators yield only in- 

 formation related to local slopes and areas 

 of exposure. It is evident that the uncover- 

 ing of knowledge about the ancient seas wiU 

 be the subject of many future studies, par- 

 ticularly so because the more easily observed 

 characteristics of the present ocean are now 

 beginning to be understood. 



Man-Made Oceanography 



It is a well-known fact that shoreline 

 engineering works of man alter local water 

 movements by intercepting longshore cur- 

 rents and by providing lee-side areas of quiet 

 water. Many structures exhibit both effects, 

 but groins at right angles to the shore func- 

 tion better as current deflectors than as 

 protectors for quiet water. The breakwater 

 at Los Angeles Harbor probably intercepts 

 little current because it lies in the lee of the 

 Palos Verdes Hills and within a coastal in- 

 dentation; however, the protection that it 

 offers from waves and some current action 

 has resulted in the accumulation of finer- 

 than-normal sediment in the enclosed area. 

 The Santa Monica breakwater appears to 

 perform both functions because the long- 

 shore current is intercepted and its load of 

 sand is caused to be deposited on the land- 

 ward side, requiring removal at intervals of 

 a few years. Many other examples could 

 be cited including harbor works at Santa 

 Barbara and Redondo Beach. 



Although little known, other works of man 

 are capable of producing currents or of 



