The seafloor off greater Los Angeles, California, has been extensively studied for the past century. Terrain analysis of recently compiled multibeam bathymetry reveals the detailed seafloor morphology along the Los Angeles Margin and San Pedro Basin. The terrain analysis uses the multibeam bathymetry to calculate two seafloor indices, a seafloor slope, and a Topographic Position Index. The derived grids along with depth are analyzed in a hierarchical, decision-tree classification to delineate six seafloor provinces—high-relief shelf, low-relief shelf, steep-basin slope, gentle-basin slope, gullies and canyons, and basins. Rock outcrops protrude in places above the generally smooth continental shelf. Gullies incise the steep-basin slopes, and some submarine canyons extend from the coastline to the basin floor. San Pedro Basin is separated from the Santa Monica Basin to the north by a ridge consisting of the Redondo Knoll and the Redondo Submarine Canyon delta. An 865-m-deep sill separates the two basins. Water depths of San Pedro Basin are ~100 m deeper than those in the San Diego Trough to the south, and three passes breach a ridge that separates the San Pedro Basin from the San Diego Trough. Information gained from this study can be used as base maps for such future studies as tectonic reconstructions, identifying sedimentary processes, tracking pollution transport, and defining benthic habitats.

A deep-sea core collected on the continental slope off northern California contains a pollen stratigraphy for the past 20,000 yr that can be correlated to the pollen stratigraphy from the upper section of Clear Lake core CL-73-4. The occurrence in one sequence of pollen, reflecting the local continental paleoclimates, and marine microfossils reflecting the local paleoceanography, allows a comparison of concurrent responses of the local ocean and adjacent continental area to global climate changes. The interpretation of the two data sets gives a complex progression of changes that are probably interrelated, such as upwelling that produced coastal fogs. The changes in climatic and oceanographic environmental conditions that occurred in response to the switch from global glacial to interglacial conditions was not a smooth progression of increasingly moderate regimes; rather, the changes appear to be a complicated series of states that suggests a disequilibrium mode lasting from about 15,000 to 5,000 yr ago.

ABSTRACT Analysis of wide-swath side-scan sonar (GLORIA) data from Eel River Basin shows the basin to have a distinctive surface morphologic and structural expression that documents the influence of interaction between the North American and Gorda Plates during the Quaternary. Elongate, north-trending anticlinal folds and thrust faults occur along and west of the basin axis out to the base of the continental slope. The deformation front defined by these structures increases in age to the west and evolves through a sequence of diapiric deformation in the east, followed by broad anticlinal folding, and finally by large-scale thrust faulting to the west. The deformation front curves inland to the southeast near the southern end of the basin. Young anticlinal folds, cored in places by diapirs, break through the seafloor. Additional information from photos, seismic-reflection profiles, and samples of the anticlinal folds show shale flowage and melange. GLORIA images show halos around rising dome structures, indicating active uplift. Submarine drainage patterns visible on the GLORIA sonographs are controlled by structure; channels and canyons follow fault traces in places and elsewhere are diverted by rising anticlines. Eel River Basin has a high rate of sediment input, and deposits are being deformed both by tectonic compression and by an abundance of slope failures that exceeds most continental margins. Debris slides on the seafloor, in association with growing anticlinal ridges, document recency of these processes.

Abstract The need to expand the search for energy resources in deeper marine environments has intensified the importance of better understanding the nature and origin of continental slope settings and of acquiring a working knowledge of their characteristics. It has been known for a number of years that coarse-grained mass-flow deposits beyond the shelf break can form major petroleum reservoirs (Barbat, 1958), and it is likely that these deep-water environments will continue to be future exploration targets (Hedberg, 1970; Curran et al, 1971; Gardett, 1971; Nagel and Parker, 1971; Yarborough, 1971; Cooke et al, 1972; Schlanger and Combs, 1975; Enos, 1977; Walker, 1978; Wilde et al, 1978). Recently, however, with the concept of plate tectonics, seismic stratigraphy, and advances in seismic-reflection technology, there has emerged a more sophisticated approach to understanding the developments of continental margins. This understanding has placed more emphasis on the geological history and petroleum potential of continental slopes (Burk and Drake, 1974; Weeks, 1974; Bouma et al, 1976; Thompson, 1976; Bloomer, 1977; Schlee et al, 1977; Mattick et al, 1978). This paper presents a practical guide for recognizing continental slope sequences. Criteria are presented that we believe are common, or could be common, to all slopes regardless of whether they are adjacent to active, passive or buttressed continental margins.

Temperature maps of surface water in the North Atlantic for 18,000 B.P. have been reconstructed for the four seasons. Temperatures were estimated by transfer-function analysis of foraminiferal assemblages, and geometric patterns of surface waters were derived from water-mass-related assemblages of Coccolithophorida and Foraminifera. At 18,000 B.P. the Arctic Polar Front, which was characterized by a steep thermal gradient parallel and centered on lat 42°N, marked the fundamental dividing line for all climatic regimens between a northern dynamic zone and a southern area of relative stability. North of lat 42°N the glacial Atlantic was polar in character with wide areas of seasonal pack ice. The Norwegian-Greenland and Labrador Seas had year-round ice cover. The polar sea was dominated by a counterclockwise gyre. Subpolar and transitional surface water masses were squeezed into a narrow band between the polar front and the subtropical gyre, whose geometry differed only slightly from today. Increased upwelling occurred off the west coast of Africa, while the equatorial divergence-Benguela flow increased during Southern Hemisphere winter at 18,000 B.P. The greatest temperature differences between today and 18,000 B.P. are found in a latitudinal band from 42°N to 60°N, with differences in some areas exceeding 10°C. North and south of this maximum anomaly band, temperature differences are smaller. The upwelling region off Africa shows a 6°C anomaly. The subtropical gyre shows no statistically significant anomaly.

Analyses of deep-sea cores from the equatorial Atlantic Ocean suggest strong variation in the intensity of atmospheric and oceanic circulation in response to the waxing and waning of ice sheets during the past 200,000 yr. Comparisons of estimates of paleotemperature, determined by multivariate statistical analysis, between Holocene sediments and sediments from an 18,000 B.P. datum in an equatorial core show only small changes (1° to 2°C) for estimated temperatures for February, but changes of 2° to 10°C for temperature estimates for August. The average “annual” paleotemperatures for this equatorial core agree well with paleotemperatures calculated from oxygen isotope data. By contrast, the zone of upwelling off northwest Africa shows almost a 10°C decrease in temperatures for February 18,000 B.P. but only a 1° to 4°C difference in August. The region between the equator and the upwelling zone shows very little change in sea-surface temperature for the past 200,000 yr. Inferences drawn from estimates of paleotemperatures and faunal analyses suggest that during glacial stages the Intertropical Convergence Zone (ITCZ) was essentially in its interglacial position with seasonal migrations comparable to today's. The difference between glacial and interglacial modes is one of intensity. The glacial mode was more intense than the interglacial mode with the southeast and northeast trade winds strengthening seasonally during the winters of the Southern and Northern Hemisphere respectively.

Intensification of the North and South Equatorial Current systems and trade winds occurred during glacial periods, according to a comparison of late Holocene (interglacial), 18,000 B.P. (glacial), and late Quaternary (0 to 180,000 B.P.) faunal assemblages and sea-surface temperature estimates from the equatorial Atlantic and Caribbean regions. Faster circulation of the North Equatorial Current system in glacial Northern Hemisphere winters (February) is indicated by increased upwelling of cool (15°C) water off northwest Africa and slightly cooler conditions across the northern tropical Atlantic and Caribbean. Intensification of the South Equatorial Current occurred along the Equator during the Southern Hemisphere winter (August). This interpretation is based on the dominance of a cool-equatorial assemblage, which indicated that waters of 16° to 18°C replaced the tropical assemblage that lives today in 24° to 26°C water in this region. The cool influence of the glacial (August) Benguela-South Equatorial Current decreased rapidly westward along the equatorial belt so that the fauna was dominated by the tropical assemblage in the Caribbean. Sea-surface temperatures increased rapidly from east to west in the equatorial belt, so that at long 35°W, the 16°C water had reached ambient temperatures of 24° to 26°C. Both faunal assemblages and temperature estimates of eight late Quaternary Atlantic and Caribbean sediment cores show that the equatorial region experienced three maximum incursions of cool Benguela Current water during the past 150,000 yr—at approximately 135,000 B.P., 73,000 B.P., and 18,000 B.P. Differences of glacial to interglacial sea-surface temperatures range from 5° to 10°C in the eastern equatorial Atlantic to 2° to 3°C in the western Atlantic and the Caribbean. During this time, only two periods with similar faunas and surface temperatures occurred—today and 125,000 B.P. Seasonal temperature contrast (August to February) is three to four times greater in all cores for glacial conditions than for interglacial conditions. The winter temperatures (February to the north of the thermal equator and August south of it) show the greatest changes, and they control the overall temperature pattern. Identical temperature patterns for cores affected by the North and the South Equatorial Currents suggest that the Northern and Southern Hemispheres are generally in phase and that more severe winters control the glacial temperature pattern.

ABSTRACT Deep-sea sediments from the eastern equatorial Atlantic indicate that dissolution of carbonate was greater during the late Pleistocene glacial stages than at present or during the last interglacial stage. Surface (Holocene) carbonate distribution shows a correlation with the 1.9°C potential temperature isotherm which represents the top of Antarctic Bottom Water. A comparison of the surface versus glacial Pleistocene (18,000 YBP) carbonate distribution indicates that the effects of Antarctic Bottom Water were felt 200 to 700 meters shallower during glacial then interglacial conditions. Records of carbonate composition for the past 200,000 years show increases in both carbonate dissolution and terrigenous noncarbonate dilution during glacial stages. Likewise, microscopic examination of the planktonic foraminiferal faunas indicates much greater test fragmentation and destruction and higher percentages of benthonic forams per total foram populations during glacial conditions. The available evidence suggests that Antarctic Bottom Water was the mechanism that produced the increased carbonate dissolution. Therefore, probably either an increase in the production and circulation of Antarctic Bottom Water during glacial stages or the production of a glacial North Atlantic Bottom Water occurred. Regardless of the model used to explain the observations, all of these data suggest that the eastern equatorial Atlantic experienced greater carbonate dissolution during late Pleistocene glacial stages.