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Open Access Publications from the University of California

Publications posted here are typically legacy print or electronic-only publications of value to the Scripps researchers, by non-Scripps authors. Publication here is intended to make these works of value more readily available in an open access environment. Works by Scripps' scientists are published elsewhere on this Repository site.

Cover page of Decapod Crustacea of the Californian and Oregonian Zoogeographic Provinces

Decapod Crustacea of the Californian and Oregonian Zoogeographic Provinces

(2011)

Approximately 280 species of decapod crustaceans live along the west coast of North America between Puget Sound and Magdalena Bay, Baja California, Mexico. Species of the shrimp families Crangonidae, Hippolytidae and Pandalidae and crabs of the Cancridae, Lithodidae, Majidae and Paguridae are particularly abundant. Many of the genera and species either are unique to the North Pacific or are found only along the west coast of North America. Compared to other marine invertebrates, decapods tend to be large and recognizable. Larger crabs, shrimp and lobsters are fished commercially for food or bait. Many species are important in food webs, feeding on small mollusks, worms, crustaceans or detritus and in turn being eaten by fishes, birds, seals or sea lions. Intertidal species have been used in behavioral or physiological research on regeneration, color changes, respiration and symbiotic relationships. Interested visitors to kelp beds and tide pools photograph and observe decapods. One must identify a species in order to study it or label its photograph. Without the needed literature or training in the anatomy of decapod crustaceans, the interested biologist must seek out the few specialists who can identify northeastern Pacific decapods. The fauna of the northeastern Pacific differs greatly at the level of genera from that of tropical regions or the western Atlantic. A person familiar with decapods of other regions may have no idea where to find information on the fauna of the northeastern Pacific, especially if the pertinent literature is in Russian. It is my hope to remedy the lack of a technical guide to decapods of the warm and cold temperate regions of the northeastern Pacific. The format of the text follows that of Shrimps, Lobsters and Crabs of the Atlantic Coast, by A. Williams (1984). The work is focused on nomenclature and natural history of the species. Literature on mariculture, fisheries and physiology is not included. The text is directed to the biologist or advanced university student.

Cover page of Active Electromagnetics At The Mid-Ocean Ridge

Active Electromagnetics At The Mid-Ocean Ridge

(1990)

The 59,000 km long global mid-ocean ridge system is the site of formation of 20 km3 of oceanic crust yearly. Two-thirds of all heat loss from the interior of our planet is through the ocean floors, 40% of this amount is focused through the ridge. Activity involves complex interactions among a number of processes occurring over wide ranges of depths and lateral distances, including melting of the earth's mantle, delivery of the molten rock to a crustal magma chamber, cooling of the magma intrusion by hydrothermal circulation and volcanic eruption, chemical exchange between hot rock surrounding the magma chamber and the overlying seawater, and even the establishment of exotic biological communities near hydrothermal vents at the ridge axis. These features justify the expanding scientific interest in the study of the ridge.

Transient controlled-source electromagnetics (CSEM) is a geophysical exploration technique capable of determining the electrical conductivity beneath fast-spreading segments of the mid-ocean ridge. Geological structure beneath the mid-ocean ridge that is readily accessible to transient CSEM exploration is located at crustal levels and includes the axial magma chamber and its associated zones of partial melt and hydrothermal activity. Seismic images of the top several kilometers beneath the fast spreading East Pacific Rise (EPR) between 9-13°N have already been obtained. Multi-channel reflection profiles place strong constraints on the geometry of the top of the axial magma chamber but refraction data provide only coarse estimates of the sub-surface temperature, distribution of partial melt and porosity, parameters required to distinguish between proposed petrological models of the ridge. Electrical conductivity is a strong indicator of all these critical parameters and therefore CSEM methods are well-suited to improve the estimates and help characterize the ridge environment.

In this thesis, a pair of forward modeling computer programs have been developed to design ridge-going experiments and assist interpretation of mid-ocean ridge transient CSEM data sets, as they become available. The programs may also be used to evaluate the transient CSEM technique as it might be applied to investigate other tectonically active regions of the seafloor. One program rapidly computes the theoretical response, as a function of time, of an arbitrary, two dimensional earth to a sudden switch-on of electric current in a line source of electromagnetic energy. The other program is more advanced, requires more computer time, and is referred to as a 2.5-D program because it can handle excitation of the earth by a more realistic, finite source.

The programs solve the forward problem as follows. Electromagnetic boundary value problems based on the governing Maxwell's equations are solved by the finite element method in the Laplace frequency s-domain. The calculated electromagnetic field components are then transformed into the time domain by means of the Gaver-Stehfest algorithm. In the 2.5-D program, Maxwell's equations are additionally Fourier transformed in the direction parallel to the strike of the 2-D conductivity structure, and field components are computed in the along-strike wavenumber q-domain. Following the calculation, inverse transforms are performed to obtain the along-strike spatial variations of the field components. The codes have been validated through comparisons with known analytic solutions in which the earth is modeled as a uniformly conducting half-space. Convergence of the finite element approximation is found to be O(h), where h measures the size of the triangles comprising the finite element mesh. An extrapolation formula is described by which numerical solutions on progressively finer meshes are combined. The formula permits great accuracy to be attained in the computed field components, using relatively coarse meshes.

A numerical study of the performance of an idealized transient CSEM system at the East Pacific Rise has been carried out using the 2-D code. The system consists of an infinite source located 5 km west of the ridge axis, and seafloor magnetic field sensors placed at various distances across the ridge crest. The source is oriented with respect to the strike of the ridge so as to produce only the H-polarization mode of electric current flow. The results indicate that this system can detect the axial magma chamber and the associated zones of hydrothermal activity and partial melt by monitoring two electromagnetic response parameters, the diffusion time T and the response amplitude B max , as a function of transmitter/receiver separation. These response parameters are easily extracted from measured data and are diagnostic of the sub-surface electrical conductivity. The presence of a highly conductive magma chamber slows and attenuates signals diffusing beneath the ridge, increasing T and decreasing Bmax. Hydrothermal circulation in the highly fractured, extrusive basalt layer has the same effect on the data for receivers placed within 3 km of the ridge axis, but very little effect elsewhere. Inferences made from the numerical results suggest that a horizontal electric dipole (HED) of moment 10 4 A•m and receivers sampling the seafloor magnetic field at 10-25 Hz with a sensitivity of 1 pT/s over a time window extending to 10 s are sufficient to detect these crustal targets.

Interpretation of transient CSEM data requires forward modeling using a more realistic, finite source. The 2.5-D code is capable of achieving this. Sample field patterns produced in the vicinity of the ridge by a sudden switch-on of electric current in a horizontal electric dipole (HED) are computed. The patterns illustrate diffusion, in three spatial dimensions and time, of various along-strike electromagnetic field components through typical mid-ocean ridge structures. The results demonstrate the utility of the 2.5-D code, i.e. its potential for interpreting data from a transient CSEM ridge-going experiment.

Cover page of Sedimentation in Submarine Canyons in San Diego County, California, 1984 - 1987

Sedimentation in Submarine Canyons in San Diego County, California, 1984 - 1987

(1988)

Three submarine canyons have an effect on the coast north of San Diego, California. Scripps and La Jolla Canyons extend almost to shore and permanently trap sand at the south end of the Oceanside Littoral Cell. They are also responsible for enhancing the local, long-term shoreline retreat rate as evidenced by the embayed shoreline adjacent to each. Carlsbad Submarine Canyon, in the central portion of the Oceanside Cell, extends shoreward across the Continental Shelf to a water depth of about 100 ft. Littoral sand is not carried to the canyon head at that depth. The effects of wave refraction over Carlsbad Canyon have resulted in a reduction in the local rate of shoreline retreat and produced a slight bulge in the nearby shoreline.

The first objective of the field investigation described in this report was to quantify the rate at which littoral sand was carried to and deposited in the shallow heads of Scripps and La Jolla Canyons between December 1984 and June 1987. The second objective was to establish, for the same period, the rate at which the deposited material was flushed down the axes of the canyons. Littoral sand, once it is flushed to deep water, is unrecoverable. The frequency, magnitude and duration of storms, the characteristics of the local longshore sediment transport regime, and the location and shape of the heads of the canyons control the entrapment rate, how much sand the canyon head can hold before it is flushed out, and the frequency of flushing.

Sand Entrapment Rate. Scripps Canyon has at least 6 shallow-water tributaries that trap sand. The most active four were investigated in this study. La Jolla Canyon has a single, but much larger, O.7-mi long, shallow-water head. Canyon heads filled when sand moved seaward from the littoral zone into nearcoast sediment depressions. Depressions are shallow, relatively steep, saucer-shaped region located above canyon gorges. Gorges are comprised of rock headwalls, rock sidewalls that in some places are vertical or even overhanging, and rocky, seaward-sloping floors.

Sand that had the same size distribution as sediments in the nearby littoral zone was deposited in the depressions. Very fine-grained sands, micas, and organic debris passed over the depressions and were deposited in the gorges. As the prograding deposits in the depressions of Scripps Canyon were funnelled into the narrow (10 to 200-ft wide) gorges, they moved on top of the finer, lower-specific-gravity material. Relatively little passed over the sidewalls. In La Jolla Canyon about equal amounts of sand passed into the gorge over the rim of its wide headwall, and through several chute-like depressions or reentrants that pierce the headwall.

Sumner and South Branches are presently the most active tributaries of Scripps Canyon. The upper boundaries of their depressions are closest to shore and they intercepted more sand than tributaries that began in deeper water. Sumner and South Branches are located near the north end of the tributary system of Scripps Canyon and preferentially filled when longshore sediment transport was to the south. The north re-entrant of La Jolla Canyon was the most active part of that canyon, even though the gorge there is farther from shore than it is elsewhere.

In both canyons a much larger volume of littoral sand was initially deposited in the depressions than in the gorges. The ratio was about 20:1 in Sumner and South Branches.

Over 80 percent of the sand was transported seaward into the canyon heads between November and May during wave storms, probably more the result of storm-induced downwelling than transport in rip currents. Shore-normal transport was dominant. A relatively small quantity of sand entered the canyon heads parallel to shore. Only small amounts of littoral sand were carried into the depressions during the summer and autumn, but large quantities of mica and especially kelp and ,sea grass debris was deposited in the gorges at all times of year. Organic debris was transported by rip currents over the headwalls, and by longshore currents over the sidewalls.

An average of about 29,000 yd3/yr of littoral sand was deposited in the shallow heads of the canyons between December 1984 and June 1987. Only about 1,000 yd3/yr of that was trapped in La Jolla Canyon. In Scripps Canyon an average of about 22,000 yd3/yr was deposited in Sumner Branch; about 2,000 yd3/yr was deposited in South Branch. The long-term rate of littoral sand entrapment in or adjacent to Scripps and La Jolla Canyons appears to be approximately equal to the net longshore sediment transport rate at the south end of the Oceanside Littoral Cell.

Sand Flushing Rate. Once littoral sand passed over the upper edge of the depression it was carried downslope in small surface slumps and by wave-induced bottom oscillations coupled with gravity. In this way a critical slope of about 18 degrees was maintained at the seaward face of the prograding deposit. The normal load created by this deposit increased greatly as its toe prograded onto the steeply-dipping deposit in the gorges of Sumner and South Branches. When the normal load exceeded the internal shear strength of the deposit a massive downslope movement of sediment occurred. The slumps and slides were also controlled, in part, by the decomposition of organic debris that reduced the strength of the deposit near the floor of the gorges. The heads of Scripps Canyon apparently reach a critical volume of sand at which time the deposit is susceptible to failure. In Sumner Branch the critical volume is about 50,000 yd3 while in South Branch it is about 5,000 yd3•

Flushing occurred when storms moved large quantities of sand onto the upper part of the depressions, thereby increasing the normal load. Sumner, South and Shepard Branches flushed on 13 December 1984. Sumner and South Branches filled and again flushed in early spring 1987, so their flushing frequency during the field investigation was O.4/yr. The flushing frequency of other Scripps Canyon tributary valleys is estimated to be O.025+/yr.

Flushing occurs most often in gorges with steeply-sloping floors that fill rapidly because they head close to shore. Wave loading may be a factor in reducing the strength of the deposit during storms.

Cover page of The Tasman Project Of Seafloor Magnetotelluric Exploration

The Tasman Project Of Seafloor Magnetotelluric Exploration

(1988)

The Tasman Project of Seafloor Magnetotelluric Exploration was performed between December 1983 and April 1984 in order to investigate the electrical conductivity structure beneath the Tasman Seafloor and the Australian continental margin. Recordings were made at nine seafloor and nine land sites on a line extending from inland Australia to the Lord Howe Rise in the eastern Tasman Sea. Magnetic field recordings were made at all sites and horizontal electric field recordings at seven of the seafloor sites. In addition, oceanographic recordings were made at several of the seafloor sites, as an additional aim of the project was to provide physical oceanographic information on the Tasman Sea. Data return from the experiment was almost complete and the data quality high. All of the raw recordings have been converted into final magnetic horizontal electric field and ­oceanographic time series.

An analysis of the seafloor magnetotelluric (SFMT) data has been completed. The 'results indicate that geomagnetic induction in the Tasman Sea is a three-dimensional process dependent on the large-scale shape of the Tasman Sea. The seafloor impedances have a dominantly two-dimensional form with the B-pol impedance component (the component perpendicular to the trend of the Tasman Sea) being strongly attenuated near the Australian coastline. Evidence for the three-dimensionality includes large impedance skew-angles and consistent differences between impedances estimated using the SFMT and vertical gradient sounding (VGS) methods. The spatial consistency of these results supports the hypothesis of large-scale geomagnetic induction in the Tasman Sea. The induction arrows calculated for land and seafloor sites near the Australian coast exhibit significant components parallel to the coastline, providing further evidence for a three-­dimensional process.

Evidence suggests that the most appropriate data to analyse using one-dimensional MT techniques are the E-pol impedances from three sites, TP3, TP4 and TP5, in the central Tasman Sea. Inversions were therefore performed on these data using delta-function and minimum-structure inversion algorithms. Delta function inversions were performed in order to investigate the one-dimensionality of the data, the depth of resolution of the and the significance of differences between the conductivity models at the different sites. Minimum-structure inversions were performed in order to produce more physically-realistic conductivity profiles, and to examine which features in the profile are definitely required by the data. In addition to these inversions, the B-pol impedance terms from the seafloor sites were used with the MT anisotropy method to determine the minimum integrated crustal resistance of the Tasman Seafloor, 107 [capital omega].m2. The E-pol impedance terms were used to estimate the depth to the good conductor beneath each site with the MT asymptotic method.

The conductivity models obtained for sites TP3 and TP4 appear to a reliable conductivity profile for the Tasman Sea. The Tasman Sea profile includes a high conducting layer occurring at a depth comparable to that for similar age lithosphere in the Pacific Ocean. The differences between the SFMT and VGS impedance estimates cause some ambiguity regarding the depth to the high conducting layer with the VGS and SFMT impedances estimates suggesting depths of 100 and 200 km respectively. Comparison of the conductivity models with other geophysical results suggests the correct depth lies between 120 and 150 km. At shallow depths the TP4 profile is more conductive than the TP3 profile. The higher conductance at TP4 cannot be explained by differences between the sediment layer at the two sites and is tentatively attributed to thermal effects associated with the source of an active seamount chain located near TP4.

The conductivity profile obtained for the third site, TP5, in the Central Tasman is probably only geophysically accurate at depths greater than 200 km. The deep structure at this site is more resistive than at sites TP4 and TP3 to the east, a result supported by the asymptotic-method results for sites near TP5. Confirmation of the conductivity results for the Tasman Sea will be provided by the application of three-dimensional modelling methods. In particular, thin-sheet modelling should indicate the accuracy of the assumptions made during the ID analyses described in this thesis.

In addition to information on the sub-oceanic conductivity structure, the Tasman Project has provided valuable information in other areas. Induction arrows at the land and seafloor sites are currently being analysed for information on the electrical conductivity structure of the Australian continental margin. Physical oceanographic information on processes including tides, eddies, and internal waves has been obtained, and information is also available on geomagnetic source-fields in the Tasman Sea region.

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Cover page of Biology of the White Shark, a Symposium

Biology of the White Shark, a Symposium

(1985)

Sixteen papers were presented during the symposium and asterisks denote the names of authors who have contributed to this volume. Leonard Compagno began with an overview of white shark biology and anatomy followed by Shelton Applegate and Luis Espinosa who presented two papers dealing with the fossil history of the white shark and implications concerning the habits and present status of the recent species. Peter Klimley* and Wes Pratt* and Jack Casey* presented papers on the distribution of white sharks along the California coast and in the western North Atlantic, respectively. Leighton Taylor* presented a paper on historical and contemporary records of white sharks in Hawaii. Three papers dealing with white shark physiology were presented by Frank Carey* (body temperature and capacity for activity), Scott Emery* (hematology, cardiac and gill morphology), and Joel Cohen* and Samuel Gruber* (visual system with emphasis on retinal structure)followed by Gregor Cailliet* who presented information on age and growth. Richard Huddleston presented a paper on stomach and spiral-valve contents of juvenile white sharks. The behavior of white sharks was detailed in four papers presented by John McCosker* (attack behavior and predator/prey strategies), Timothy Tricas* (feeding ethology), Donald Nelson (telemetry of white shark behavior), and David Ainley* (white shark/pinniped interactions at the Farallon Islands). Robert Lea* presented an update on shark attacks off California and Oregon. Bernard Zahuranec offered the concluding remarks. Eleven of the 16 contributed papers appear in this volume.

Cover page of A Surface Recovery Technique for Deep Moored Vertical Arrays

A Surface Recovery Technique for Deep Moored Vertical Arrays

(1981)

A surface recovery technique was developed for the retrieval of a vertically oriented array which had been anchored at a depth of 4550 meters. The array was severed within 100 meters of the bottom in order to retrieve two faulty anchor releases as well as the scientific instrumentation.

Cover page of San Diego Marine Life Refuge, San Diego County

San Diego Marine Life Refuge, San Diego County

(1980)

The San Diego Marine Life Refuge Area of Special Biological Significance (SDMLR-ASBS) is located in La Jolla Bay, adjacent to Scripps Institute of Oceanography, La Jolla, San Diego County. The SDMLR-ASBS is part of the San Diego-La Jolla Underwater Park. The park has a total surface area of 5,977 acres while the surface area of the SDMLR-ASBS is approximately 92 acres. The SDMLR-ASBS includes three distinct habitats: a broad, sandy shelf; a concrete pier piling system; and an intertidal mudstone reef complex of dikes, boulders, and ledges. Therefore, the SDMLR-ASBS contains organisms representative of a sandy substrate and a rock reef, while the pier exhibits a limited rocky biota. This SDMLR-ASBS is immediately north of the San Diego-La Jolla Ecological Reserve ASBS, with which it shares many of the same species and organisms.