Inshore Side Research Articles

Acoustic Surveys of Abundance and Distribution of the Japanese Sardine Sardinops melanostictus in the SpawningGrounds off Southern Kyushu, Japan.

Distribution patterns of the spawning population of the Japanese sardine Sardinops melanostictus off southern Kyushu were investigated by the acoustic method in relation to water temperature and the Kuroshio current in three successive winters from 1990 to 1992. Acoustic data were obtained by single-beam 50kHz echo sounders interfaced to digital integrators. Sardine distribution varied during January-March as time advanced. It was closely associated with both water temperature and spawning activity. Maturing sardine stayed on the inshore side of the Kuroshio front while spawning sardine occurred in the higher temperature offshore waters further than the Kuroshio front that appear to have acted as a barrier to distribution previously. The fish abundance in the area of sardine concentration decreased markedly over the 3 years.

The Point Arena eddy: A recurring summer anticyclone in the California Current

The propensity for an anticyclonic eddy (∼100‐ to 200‐km diameter) to develop west of Point Arena during the summer is documented with an analysis of satellite derived sea surface temperature (SST) data and a review of published historical hydrographic data. The satellite data span the period from 1981 through 1989 and the hydrographic data include CalCOFI surveys from 1949–1959 and a few more recent studies. A closed anticyclone was apparent in many of the historical dynamic height maps, while a meander pattern, lacking closed contours, characterized the coincident hydrographic 10‐m temperature maps. A conceptual model of an eddylike perturbation imbedded in a broader equatorward flow is adopted as a working hypothesis. In this simplistic model, the only distinction between an eddy (with closed contours) and a meander (without closed contours) is the relative strength of the eddylike perturbation. This led to a method to detect the eddies in the satellite SST data, which were dominated by meanderlike patterns: A linear trend was subtracted from each image to remove large‐scale SST gradients, leaving an expression of the residual eddylike perturbation. Composite images over select time periods were produced for analysis by computing spatial variance EOFs of the detrended data. With this approach, a warm‐core eddy was evident at Point Arena in summertime satellite SST data from 1981–1985 and 1987–1989 (formation of an eddy in 1986 remains unresolved because the readily available SST data were incomplete). The eddy was bounded on the inshore side by the jet and filament system studied during the 1987 and 1988 Coastal Transition Zone (CTZ) program. Recurrence of this eddy was apparently coupled with the recurring cold filament commonly observed at Point Arena during the summer. The coevolution of the eddy and meandering jet during 1988 was studied with sequential composite empirical orthogonal function (EOF) satellite SST images. These show that a deep anticyclonic meander was present near Cape Mendocino and directed the jet toward shore. In late July 1988 this meander pinched off a new eddy, and the subsequent jet flow was redirected southward and displaced farther offshore. These events account for the transition in the jet observed in the July CTZ hydrographic surveys. The length scale and position of the Point Arena eddy is consistent with a standing wave, phase locked to a prominent cape (in this case, Mendocino). The significance of the apparent splitting off of an eddy in 1988, as well as the apparent preponderance of anticyclones evident in these EOFs, is discussed relative to recent theoretical and numerical model developments.

The nature of the cold filaments in the California Current system

Data from the Coastal Transition Zone (CTZ) experiment are used to describe the velocity fields and water properties associated with cold filaments in the California Current. Combined with previous field surveys and satellite imagery, these show seasonal variability with maximum dynamic height ranges and velocities in summer and minimum values in late winter and early spring. North of Point Arena (between 39°N and 42°N) in spring‐summer the flow field on the outer edge of the cold water has the character of a meandering jet, carrying fresh, nutrient‐poor water from farther north on its offshore side and cold, salty, nutrient‐rich water on its inshore side. At Point Arena in midsummer, the jet often flows offshore and continues south without meandering back onshore as strongly as it does farther north. The flow field south of Point Arena in summer takes on more of the character of a field of mesoscale eddies, although the meandering jet from the north continues to be identifiable. The conceptual model for the May‐July period between 36°N and 42°N is thus of a surface jet that meanders through and interacts with a field of eddies; the eddies are more dominant south of 39°N, where the jet broadens and where multiple jets and filaments are often present. At the surface, the jet often separates biological communities and may appear as a barrier to cross‐jet transport, especially north of Point Arena early in the season (March‐May). However, phytoplankton pigment and nutrients are carried on the inshore flank of the jet, and pigment maxima are sometimes found in the core of the jet. The biological effect of the jet is to define a convoluted, 100 to 400‐km‐wide region next to the coast, within which much of the richer water is contained, and also to carry some of that richer water offshore in meanders along the outer edge of that region.

Summer upwelling on the Sydney inner continental shelf: The relative roles of local wind forcing and mesoscale eddy encroachment

The inner shelf and surf-zone near Sydney experience several major upwelling events each summer, with a typical event being several days long. Two potential causes of these events are local wind forcing and cross-shelf advection related to the presence of mesoscale eddies over the continental slope. The relative roles of these processes are assessed from cross-shelf temperature transects, weekly hydrographic stations in 50 and 100 m of water, and daily surf-zone temperatures. Local wind forcing affects the vertical motion of the pycnocline over the stratified inner shelf, with typical vertical velocities of about 10 m day −1 for a coast-parallel wind stress of 0.2 N m −2. The hydrographic response lags the wind stress by between 1 and 2 days. About half of the major upwelling events in the surf-zone and over the inner shelf can be identified with periods of strong southward wind stress. Cross-shelf advection associated with the presence of anticyclonic mesoscale eddies near the coast accounts for most of the remaining major upwelling events. The strong southward flow on the inshore side of these eddies results in an onshore mass flux in the bottom boundary layer, which displaces warm surface water seaward over the inner shelf. The currents may also be sufficiently strong for bottom friction to totally homogenize the water column at the 50 m isobath. Both cross-shelf advection and vertical mixing then lead to cooler water in the surf-zone.

Ice erosion of a sea-floor knickpoint at the inner edge of the stamukhi zone, Beaufort Sea, Alaska

In 1981 and 1982, detailed bathymetric and side-scan sonar surveys were made of an area of the sea floor north of Prudhoe Bay, Alaska, to study the changing characteristics of the seabed at the inner boundary of the stamukhi zone, the coast-parallel zone of grounded ice ridges that occurs in water depths between 15 and 50 m in the arctic. The fathograms and sonographs resolved 10-cm features and electronic navigation gave relocations accurate to about 10 m. Year after year an ice boundary develops at the inner edge of the stamukhi zone where major shear and pressure deformation occur in about the same location. Associated with this ice boundary, the bathymetry shows a pronounced break in slope — the knickpoint — on the shelf profile at about 20 m depth. The 2–3 m-high knickpoint is cut in a consolidated gravelly mud of pre-Holocene age. A well-defined gravel and cobble shoal a few meters high usually occurs at the inshore edge of the knickpoint. The sonograph mosaic shows that seaward of the knickpoint, ice gouges saturate the sea floor and are well defined; inshore the gouges are fewer in number and are poorly defined on the records. Few gouges can be traced from the seaward side of the knickpoint across the shoals to the inshore side of the knickpoint. Studies of ice gouging rates in two seabed corridors that cross the stamukhi zone reveal the highest rates of gouging seaward of the knickpoint. We believe that the knickpoint results from ice erosion at the inner boundary of the stamukhi zone. Intensified currents associated with this boundary winnow away fine sediments. Ice bulldozing and currents shape the shoals, which perch atop the knickpoint. The knickpoint helps to limit ice forces on the seabed inshore of the stamukhi zone.

A steady state model for buoyant surface plume hydrodynamics in coastal waters

Shallow, surface plumes of buoyant water are frequently discharged into coastal waters by rivers, bays, power plants, and other sources. The most readily observed portion of these plumes is the near field where the initial expansion of plume water occurs, and where there is large contrast between plume and ambient water. In contrast to existing turbulent jet models of such plumes, the present model divides the plume near field into two domains, a frontal domain where turbulent exchange between plume and ambient water is intense, and the remainder of the flow where the dynamics of inviscid, nonlinear gravitational spreading of a shallow buoyant layer dominates. Using this approach, the steady state flow produced by the supercritical outflow of buoyant water from a channel at a coast into ambient water with a uniform alongshore current is modelled. Earth rotation is neglected. Frontal jump conditions developed in an earlier paper are applied to match the flow at the frontal boundary with the remainder of the plume. Numerical solutions for the entire flow are found by the method of characteristics, but much of the flow can be determined by simpler analytic computation. The computed flow fields show that a frontal boundary forms on the upstream or offshore side of the plume where the oncoming ambient current contains the gravitational spreading of the buoyant water. No front forms on the corresponding downstream, inshore side. In the body of the plume the flow simultaneously expands and turns downstream toward alignment with the ambient current. Relatively little change in plume water speed occurs, but the pressure field required for turning the flow downstream results in deepening of the plume interface offshore near the front. This, in turn, concentrates plume volume flux along its offshore side near the front. The maximum angle through which the flow may be turned initially is less than 66°. Outlet channel angles greater than this produce plumes which are separated from the shoreline by ambient water. The model results explain many of the observed features of the Connecticut River plume in Long Island Sound. DOI: 10.1111/j.2153-3490.1982.tb01818.x

Topographically Induced Changes in the Structure of an Inertial Coastal Jet: Application to the Agulhas Current

Abstract Calculations are made of the changes in the structure of an inertial current which can be induced by slow changes in the topography of the continental shelf and slope along which it flows. The particular case of a uniform potential vorticity current over a shelf of uniform slope shows that smooth transitions from subcritical to supercritical flow can occur at a minimum in the shelf width. Long-wave disturbances travel away from such a point. Upstream there is a tendency for a countercurrent to occur at the coast, while downstream there is a tendency for cold water to outcrop on the inshore side of a front. Both these features occur along the path of the Agulhas Current. A method developed for calculating the speed of long-wave disturbances in a flow with a given potential vorticity distribution is applied to sections of the Agulhas Current about 150 km apart. In this distance the shelf width is reduced, and a calculation using a current model with two active layers shows the second mode is very c...

The Argo Abyssal Plain

Eighteen geophysical transects were made in the Argo Abyssal Plain to study the magnetic anomalies, bathymetry and seismic structure. Magnetic anomalies were identified as being the Mesozoic anomalies M-10 to M-25, increasing in age from the Java Trench to the northwest continental shelf of Australia. A new bathymetric map shows that the Argo Abyssal Plain is bounded by the 5600-m contour and reaches a maximum depth of 5730 m against the inshore side of the Exmouth Plateau. Joey Rise was found to limit the Argo Abyssal Plain on the southwest. Continuous seismic profiles, sonobuoy data and seismic data from other cruises permit one to contour the depths to oceanic basement. Numerous diapir-like structures were observed, but their nature and origin is obscure.

Temperature structure across the Kuroshio before and after typhoon Shirley

Two temperature sections across the track of Typhoon Shirley (September 1965) in the vicinity of the Kuroshio are shown. The first is based on observations made less than a week before the storm and the second within two days after its passage. The comparison shows: (1) maximum cooling of more than 3°C directly under the eye of the storm; (2) upwelling of 20–25 m on the seaward side of the eye but very little on the inshore side; (3) a slight increase in the depth of the mixed layer; and (4) some evidence that upwelling continued for at least a day after the storm passed. Heat loss to the atmosphere is estimated at 1000 to 3000 cal/cm 2 . DOI: 10.1111/j.2153-3490.1969.tb00454.x

ホソトビの回遊と産卵生態に関する研究-III

In the Japan Sea, all kinds of fisheries for flying-fish, Cypselurus opisthopus hiraii ABE, are operated in the inshore areas; drift nets are operated at 10km or so from the shore, surrounding nets in the inshore areas within 2km, and gill nets within 1km from the shore. The change of the fishing method with the approaching proximity of the shore is considered to be dependent on the great changes in the behavior of the flying fish there. The present report deals with the behavior of the fish schools after they descend to the sea bottom at gill net fishing grounds. 1) Coefficient of variation in the flying fish catch with gill net is larger than that of drift net and surrounding net. 2) Since a fish school in the sea bottom is in the nature of a condensed mass, the dif-ference between catches of two adjoining gill nets is large. Generally one school is assumed to be composed of about 2000 fish but occasionally, depending on oceanographic conditions, scores of thousands of fish are also found. 3) More fish are caught at the inshore side of a net than on the offshore side, and in most cases they are caught in masses at about 3m from the sea bottom. 4) Fish schools are considered to be inactive and scarecely move at the sea bottom. They float up to the surface early in the morning to migrate offshore.

Criteria for Recognizing Ancient Barrier Coastlines: ABSTRACT

Worldwide modern barrier coastlines constitute a minor part of the total coastlines of all the continents. The aggregate length of present barrier coastlines in the world is approximately 3,530 mi, distributed as follows: North America, 2,000 mi; Europe, 500 mi; South America, 350 mi; Africa, 300 mi; Australia, 200 mi; and Asia, 200 mi. Barrier islands commonly border coastal plains adjacent to broad continental shelves. They form in areas of abundant sand accumulation where longshore currents are prominent. Sandstone lenses which represent ancient barrier islands would be expected in thick wedges of interfingering terrestrial and marine sandstone, siltstone, and mudstone. Barrier islands of Pleistocene age have been recognized inshore from present End_Page 706------------------------------ coastlines, and drowned Holocene barrier coastline features have been described on the continental shelves. Pre-Holocene linear sandstone bodies resembling barrier islands have been described in ancient rocks of Pennsylvanian, Cretaceous, and Tertiary ages. Probable barrier island sandstone bodies in ancient rocks have been described by previous investigators on the basis of comparison with features of modern analogs: geometry, sedimentary structures within the sand lens, physical properties of the sand, and the nature of associated environments. Recognition criteria used in this report are based partly on previous work and partly on recent studies along the Texas and North Carolina coasts. Barrier islands are linear, have a length to width ratio generally greater than 10:1 and commonly are less than 60 ft thick. Padre Island, Texas, consists of four morphological units that have characteristic sedimentary structures: beach, foredune, barrier flats, and wind tidal flats--though the development of the foredunes and wind tidal flats changes considerably from north to south. Along the North Carolina coast, wind tidal flats are absent, but accretionary beach ridges are locally prominent. Superimposed on the islands of both coasts are storm washovers of hurricane origin that breach the foredunes and channel inlets that cross the island and connect the sea with the lagoon behind the islands. Beaches contain laminae of different thicknesses that dip principally seaward; the san is locally shelly and fine laminae of heavy minerals may be prominent. The foredunes are markedly cross-bedded in an oriented pattern that reflects strongly the predominant wind direction. Barrier flats are underlain by sand which ranges from structureless to highly laminated; vegetal remains are common. Wind tidal-flat sediments that border the lagoon are an interlayered mixture of sand beds containing some fine shell fragments, and laminae of clay and algal remains. Sand is fine grained throughout. However, shell fragments, locally abundant, exhibit greater variability in size, shape, and sorting. Sand which refills channel inlets ranges from horizontally bedded to structureless; this contrasts sharply with the cut-and-fill cross-bedded sand common in stream-channel deposits. The associated lagoon sediments are organic and calcareous mud which interfingers with barrier-island sand; the fauna is less diverse than that of the open sea and unbroken shells are abundant. Tongues of sand--washover deltas and fans which are built by storm flood tides--are prominent local features of the lagoons. Marshes overlying peat are characteristic of the inshore side of the bays along the North Carolina coast. The geometry and alignment of the barrier islands and the close association of the sand in the barrier island with the organic mud of the lagoon are the key factors for the recognition of a barrier coastline. Attendant washover deltas and fans, cross-cutting inlet fill, and associated biota are important supplementary aids. End_of_Article - Last_Page 707------------

Differential Compaction as a Cause of Regional Contemporaneous Faults

Regional contemporaneous faults occur on the inshore sides of major Gulf Coast depocenters and develop as normal faults with major negative displacements on the Gulf, or depocenter, side. Displacement appears to be continuous, first increasing and then decreasing in rate, during the period of rapid sediment accumulation for a particular depocenter. As new depocenters are established higher in the section and gulfward, regional contemporaneous fault zones are established on the inshore sides of the new depocenters. The distribution and characteristics of the faults suggest that they are sediment-related and are caused by large differences in compaction of adjacent sediment masses. A model was constructed to test the hypothesis that differential compaction could cause faulting in unconsolidated sediment. Mud volcanoes were produced during uniform, passive compaction, and faults were produced during forced, differential compaction of clay-water suspensions. Stress analysis indicates that the faults are simple shear failures. The stress field is approximately that of a point-supported beam with distributed loads along part of the length. Differential compaction faults may occur wherever large changes in total compaction of adjacent sediment masses occur, either as a result of change in thickness or of facies change. In the Gulf Coast area they occur on the inshore side of flexures, where both thickening and change from sand to clay facies occur in the offshore direction.

Reptiles and Amphibians of Smith Island, N. C.

Smith Island is of peculiar interest to the biologist as a place for study of an isolated flora and fauna, and as an area of intermingling of temperate and tropical forms. It is a quadrangular land mass roughly 3.5 by 5 miles off the southern coast of North Carolina. The island emerges as a series of low hills from the inshore side of the extensive Frying Pan shoals, opposite the mouth of the Cape Fear River, and is actually composed of a group of irregular islands and tide flats strung like fingers along a broad arching beach on the seaward side. Between the fingers are salt creeks and marshes and large areas of swamp grass. The individual islands bear such local names as Baldhead, Middle Island, and Piney Island. A number of clearly distinct edaphic areas can be described. (See Engels, 1942).1 Behind the broad sand beach which occupies much of the periphery, is a wide zone of dunes. This in turn, breaks sharply into the forests and thickets that cover the interior, in which live oak, loblolly pine, red bay, magnolia, Bermuda mulberry, hickory, holly, wax myrtle, red cedar, dogwood, virginia creeper, wild grape, poisont ivy, and smilax grow in a tangled confusion. Here the land rises to from 30 to 40 feet above the sea, the soil is rich with humus and damp with decaying logs. The forest thins in spots to open brushland, overgrown fields, and small savannas set with palmettos (Sabal palmetto) and cacti (Opuntia drunrmondii). These two latter plants find their most northern distribution on the island. The tropical beauty of the island is most marked in the forested zone, the heavy oaks and tall palmetto palms providing an exotic atmosphere, and the steaming shade beneath them completes the jungle picture. The physical features have been modified to a small extent by cultivation, road-building, ditching, and grazing. At present, only a few fields are being worked, and the human population seldom exceeds a half dozen persons. Semi-feral sheep and pigs are present in some numbers. The physiographic history of the island does not appear to have been studied, but certain clay-like strata seen at low tide allow the speculation that it is older than the more northern off-shore bars described in an excellent paper by Engels (1942). The accessibility in the past to the island through the more or less direct route of the shifting shoals and sand flats extending toward Federal Point is unknown, as is the length of its present isolation. It was expected, in view of the distinct contrast between the flora of the island and the adjacent coast, and of its isolation, that differences would appear between the amphibian and reptilian fauna of the island and the mainland. These expecta. tions were not fulfilled. The interested student is referred to the works of Burt (1938) and Brimley (1939-43) for accounts of the reptiles and amphibians of the adjacent territories.