Wide Continental Shelf Research Articles

Obliquely Incident Poincaré Waves on a Sloping Continental Shelf

Abstract An analytical theory of barotropic tides propagating onto a sloping continental shelf from the deep ocean is developed. The plane Poincare waves incident from the deep ocean are obliquely angled, and a full matching of shelf and ocean solutions is implemented. Allowance for a nonzero water depth at the coast requires an additional term, the Bessel function of second kind, in the solution. The full solution is examined for response characteristics for both frictionless tides and for tides affected by a linear bottom friction, and energy dissipation rates are evaluated. Results for narrow continental shelves indicate that a small but nonzero coastal wall depth, in conjunction with the angle of incidence, can play a significant role in modifying the response, while for wider continental shelves both of these features greatly modify the response at resonance.

The Transition on the coastal fringe of Greater Australia

Australia, with its wide continental shelves, is a difficult region for the study of coastal adaptations over the Transition, as so much land was drowned by the post-glacial sealevel rise. What can be discerned has a place in a larger and longer-term pattern of adaptation.

Nephrotoxicity and cyclosporine metabolism in psoriatic patients

The central Great Barrier Reef is situated on a 125 km wide continental shelf with a shallow shelf-break at ca. 70 m. In consequence, the earlier post-glacial reef tract was confined to a narrow fringing belt along the present upper slope and outer shelf. The reef-province only started to assume its modern dimensions after ca. 10 ky B.P., when sea-level stabilised at depths around 28 m. Reef growth since 18 ky B.P. has been controlled by the episodic nature of the post-glacial transgression, being related to shorelines S8 to S1 developed at estimated eustatic depths and ages of 114 m18 ky B.P., 88 m17 ky B.P., 75 m15 ky B.P., 56 m12 ky B.P., 45 m11 ky B.P., 39 m10 ky B.P., 28 m9.5 ky B.P., 23 m9 ky B.P., 9 m7.5 ky B.P. and 0 m6.5 ky B.P. Rates of sea-level rise as high as 12 m ky−1 occurred between stillstands, outpacing coral growth response and resulting in many mid-outer shelf reefs being drowned in situ.

The Role of Natural Prolongation in Relation to Shelf Delimitation beyond 200 Nautical Miles

AbstractIt is common knowledge that the coastal State's right to continental shelf areas emanates from the fundamental conception that "the land dominates the sea". It is, however, by way of the "coastal opening" - the indirect basis of title to shelf areas - that such right manifests itself as the "natural prolongation" into and under the sea of the landmass of the coastal State. Over some 15 years of legal usage natural prolongation assumed a still more abstract character leaving today no trace of its origin as a concept deeply rooted in natural science. The principle of distance was sequentially introduced as the complementary carrier of entitlement to shelf areas. Yet, in case of a wide continental shelf (margin) extending uninterrupted beyond 200 nm from the shoreline, natural prolongation is still considered as the sole carrier of entitlement though in a somewhat figurative sense. It is the role of natural prolongation in relation to the wide shelf and its delimitation between neighbouring States which is the principal subject of the present paper.

Deep water nutrient and oxygen gradients in a modern coastal upwelling zone and their paleoceanographic implications

Dissolved phosphate and oxygen data from the waters at >300 m depth beneath the Peru upwelling system imitate observed onshore/offshore surface productivity data. Positive onshore phosphate gradients and negative onshore oxygen gradients are greater in deeper water (up to 1000 m), reflecting the decreasing degree of horizontal mixing at depth. Mass balance reconstructions of surface productivity, nutrient remineralization, and onshore‐offshore chemical gradients suggest that the lack of wide continental shelves during glacial climates would lead to more pronounced dissolved nutrient and oxygen gradients in the deep water adjacent to continental margins. Horizontal δ13C gradients in sediments beneath highly productive coastal upwelling zones may have been as high as 0.5–1.0‰ per 100 km, suggesting caution in the interpretation of benthic δ13C samples adjacent to continental margins during low sea level stands.

Flexural response of passive margins to deep-sea erosion and slope retreat: Implications for relative sea-level change

Research Article| October 01, 1993 Flexural response of passive margins to deep-sea erosion and slope retreat: Implications for relative sea-level change John P. McGinnis; John P. McGinnis 1Lamont-Doherty Earth Observatory and Department of Geological Sciences, Columbia University, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar Neal W. Driscoll; Neal W. Driscoll 1Lamont-Doherty Earth Observatory and Department of Geological Sciences, Columbia University, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar Garry D. Karner; Garry D. Karner 1Lamont-Doherty Earth Observatory and Department of Geological Sciences, Columbia University, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar William D. Brumbaugh; William D. Brumbaugh 2Conoco, Worldwide Exploration Services, Houston, Texas 77252 Search for other works by this author on: GSW Google Scholar Nick Cameron Nick Cameron 3Conoco (U.K.) Ltd., London W1Y 4NN, England Search for other works by this author on: GSW Google Scholar Geology (1993) 21 (10): 893–896. https://doi.org/10.1130/0091-7613(1993)021<0893:FROPMT>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John P. McGinnis, Neal W. Driscoll, Garry D. Karner, William D. Brumbaugh, Nick Cameron; Flexural response of passive margins to deep-sea erosion and slope retreat: Implications for relative sea-level change. Geology 1993;; 21 (10): 893–896. doi: https://doi.org/10.1130/0091-7613(1993)021<0893:FROPMT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We suggest that the magnitude of the early-late Oligocene eustatic fall, as predicted from sequence stratigraphy, has been overestimated because of flexural rebound along margins that was induced by late Eocene to early Oligocene erosional unloading. The unloading of sediments from a continental margin during periods of deep-sea erosion and slope retreat will be accompanied by some form of flexural rebound. The magnitude and form of this rebound are controlled by (1) the amount of sediment removed from the margin and (2) the strength of the lithosphere at the time of sediment removal. Along margins with narrow continental shelves, this rebound will induce a relative sea-level fall resulting in a basinward shift in the shoreline, and the predicted systems tracts will be similar to those expected for a eustatic fall. In contrast, rebound along wide continental shelves will not alter the position of the shoreline, even though a relative sea-level fall may be recorded across the outer shelf. Deep-sea drilling and seismic reflection data from many margins support the interpretation of a late Eocene to early Oligocene (∼38-34 Ma) deep-sea erosional event best developed along the continental slope and rise. Seismic reflection and drilling data also document a prominent canyon-cutting event across the shelf during the early-late Oligocene (∼32-29 Ma). This event has been interpreted in terms of a large eustatic fall (>150 m). Nevertheless, there appears to be a correlation between late Eocene to early Oligocene deep-sea erosion and the development, or at least enhancement, of unconformities across the shelf during the early-late Oligocene. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Palaeogeographic and geodynamic evolution of the Gondwana continental margins during the Cambrian

SUMMARYDuring the Cambrian, two types of continental margins occurred around Gondwana. The eastern margin (Antarctica, Australia and southern South America) was characterized by a narrow continental shelf with a steep slope separating the shallow water environment from a deep‐oceanic one accompanied by mafidultramafic volcanics. The western margin was characterized by a wider continental shelf, probably passing gradually to an unknown outer basin. This comprised three main domains: the Asiatic shelf, composed of distinct cratonic blocks, presumably separated from each other by deeper‐water/ volcanic intracontinental basins; the European shelf, characterized by the development of shallow intracontinental siliciclastic basins; and the Americanc‐African shelf, morphologically and depositionally uniform. The distinction of these two Gondwana continental margins expresses their different geodynamic behaviour during Cambrian extensional tectonics. In fact, the sedimentary/palaeogeographic evolution, suggests the establishment of an active Pacific‐like margin in the eastern domain, and the tentative establishment of a divergent Atlantic‐like margin, in the westem one.

The Red Sea — Gulf of Aden: re-assessment of hydrocarbon potential

The results and conclusions of the UNDP/World Bank Red Sea — Gulf of Aden Regional Hydrocarbons Study Project (June 1989 – January 1992) are summarized. These derive from detailed examination of pooled public sector data provided to the project by the participating bordering states in the region; these included samples and logs from about 56 wells drilled in the two basins (out of a total of 71) and about 30 000 line km of reflection seismic data (selected from 110 000 km available). Well logs were digitized and correlated, and basinwide biostratigraphic, lithostratigraphic and palaeoenvironmental studies, source rock organic richness, quality and maturity studies and sedimentological analyses studies were performed by contracted specialist staff in the UK and France. These were integrated with basinwide seismic structural and isopach mapping for selected regional reflectors/intervals by national task forces in Cairo under project supervision; academically acquired crustal seismic and other geophysical data and oil industry velocity and other borehole data were also integrated for the Red Sea. Modelling utilizing recently acquired geophysical data indicates crustal asymmetry for the Red Sea rift with oceanic crust of pull-apart basin type flooring some portions of offshore Egypt and Sudan on the west and stretched continental crust underlying the eastern Arabian flank. These interpretations furthermore suggest that sinistral strike-slip processes controlled the initial break up of the Arabian plate, shaping the African flank as a sharp plate boundary; similar processes appear to have initially shaped the Somalia flank of the Gulf of Aden rift. Only later did true seafloor spreading propagate; in the eastern Gulf of Aden 10–12 Ma, about <5 Ma in the western Gulf of Aden, Afar and the southern/central Red Sea. Biostratigraphic work shows that deep subsidence and ocean water inundation commenced in the late Middle Oligocene in the Gulf of Aden, in the Late Oligocene in the southern Red Sea and in the Early Miocene in the Central Red Sea/Gulf of Suez. A regional lithostratigraphic nomenclature scheme for the Miocene-Recent syn- and post-rift Red Sea successions keyed to detailed biostratigraphical distribution charts and microfaunal assemblage characteristics was erected, tied to the well documented and understood petroliferous Gulf of Suez basin scheme; this allows facies variations within the basin to be compared and allows consistent interpretation and correlations across the basin to which local informal nomenclature can be related. Pre-rift (pre-Oligocene) marine sediments are present in most of the Gulf of Aden (Jurassic-Eocene) but only incompletely on the basin margins in the Red Sea (Jurassic in the south, Upper Cretaceous — Early Palaeogene in the north). Significant pre-rift oil/gas prone Upper Jurassic, Cretaceous and Palaeogene source rocks occur in Gulf of Aden sub-basins initiated by Late Jurassic — Early Cretaceous tensional tectonics, with maturity levels ranging from early-late to post-mature, whereas early synrift source rocks are generally immature. In the Red Sea good quality pre-rift source rocks outcrop in the north and south but are probably overmature for oil in the basin except in the extreme south (if present). Good syn-, pre- and post-salt and post-rift source levels occur throughout the basin but in the central/southern sectors only the post-salt remains within the oil window because of high geothermal gradients. Both basins are little explored. Attractive pre-rift Jurassic-Eocene exploration plays in rotated fault and horst blocks in predominantly carbonate but subordinate sandstone reservoirs are present in the Gulf of Aden (confirmed by an important undeveloped Eocene light oil discovery in offshore Yemen) with subordinate synrift potential where maturity is established. Relative continental shelf narrowness is economically limiting, but wider sectors occur. In the Red Sea the principal exploration plays are in Miocene synrift, pre- and post-salt successions. Rotated fault blocks occur in the pre-salt, but maturity for oil in the deeper levels is restricted to the northern sector. These levels in the central and southern sectors are overmature except in the southernmost portion but excellent potential exists in the synrift post-salt and early post-rift sequences with a number of attractive play types. Reservoirs for synrift plays are mainly sandstones and potential is confirmed by several undeveloped gas and condensate discoveries and numerous oil seepages throughout the basin; relatively wide continental shelves occur in the south and along much of the eastern flank.

Aptian-Albian palaeogeography of Neo-Tethyan domain

The Aptian-Albian interval (124.5-97.0 Ma) was a critical time both globally and for the Tethyan domain. In the Tethyan domain it was the time when a united Neo-Tethyan subduction zone became established between the future site of the Alps and Southeast Asia and greatly accelerated the rate of north-south convergence throughout the Tethyan region. A consequent widespread transgression on both Laurasian and Gondwanian margins deposited Orbitolina limestones and associated clastics on wide continental shelf areas. On the sea-floor of the Neo-Tethys ocean, organic-rich siliceous black shales, radiolarites, and turbidites with minor amounts of carbonates were deposited. Siliceous black shales accumulated under euxinic conditions of restricted small ocean basins of the Neo-Tethyan realm and along their margins. These areas received large amounts of organic debris from deltaic areas and coastal plains of the neighbouring continental shelves. Following the establishment of the north-dipping subduction zone, the Laurasian passive margin was largely converted to an active one, fringed by a large number of magmatic arcs that greatly influenced the sedimentation on the margin. Land areas and continental basins were widespread on this margin in northern Tibet, China and Indo-China. This was a consequence of the Late Triassic to Early Jurassic continental collissions and accompanied intracontinental convergence that lasted well into the Cretaceous. A detailed Aptian-Albian facies map and a crude palinspastic palaeogeographic map of the entire Tethyan realm are prepared in order to express the contrasts in sedimentation on Laurasian and gondwanian margins and to show the compatibility of the presented data with the most recent and reliable reconstructions of the major tectonic elements in Tethysides.

Impact of sea‐level rise assessed

Coastal erosion, flooding of low‐lying coastal areas, disruption of ecosystems, probable population relocation, and economic loss are some consequences of projected relative sea‐level rise. The term includes both the rise anticipated to result from global warming and other factors, and the rise from local tectonic subsidence. Some specific sites were discussed at the annual meeting of the American Association for the Advancement of Science, held in Washington, D.C., February 14–19.In comparing the New York City and eastern Mediterranean coasts, Victor Goldsmith of Hunter College, New York, presented a case for stabilization versus retreat of coastal areas, dependent on the geologic terrane and on the degree of development. The 578‐mile New York City coastline is considered “hard,” meaning some sort of cement structure, such as roads, jetties, or piers, separates the water from the coast. It is also an area of many beaches that are not natural, but that have been built up and maintained by the process of sand nourishment over the past 50 years. The Rockaway peninsula, for example, has received more than 12 million cubic yards of sand between 1926 and 1962 in response to the measured sea‐level rise of 30 cm in the last 100 years from downwarping of the wide continental shelf, said Goldsmith. Because land is highly developed and expensive in this area, retreat is not a practical option. Goldsmith suggests that the effects of on‐going sea‐level rise, at rates of about 1 foot per century, can be offset by continued hardening of the New York City coastline and beach nourishment where necessary.

古気候変動史から見た現在

The history of global climate on the earth during these 600 million years is presented based on the oxygen isotope data of fossil shells. The paleoclimatic curves clearly show the cyclic changes with different frequencies, such as, glacial-interglacial cycle of 0.1 Ma and Fischer-Arthur cycle of 32 Ma, and Greenhouse-icehouse cycle of 300 Ma. Today is located in the interglacial period of icehouse state. There are essential differences of the environmental systems and conditions between the greenhouse and icehouse states. The greenhouse state characterized by no continental ice sheets, simple climatic zones, more carbon dioxide in atmosphere, small annual temperature range, warmish and humid poles, high sea level, wide continental shelves, low latitudinal and vertical gradients of seawater temperature, warm oceans, slow circulation of bottom currents, anoxic oceans, abundant marine organisms, black shale deposition of oil raw material, sulfide deposits on oceanic ridges, manganese deposits on continental shelves, active magmatism, first spreading, magnetic quiet and active orogeny. A modern greenhouse warming was also compared with the warming after the “Younger Dryas Event” in the postglacial age.

The Holocene non-tropical coastal and shelf carbonate province of southern Australia

Carbonate-dominant sediments are currently forming and accumulating over the extensive marine shelf of the passive margin of southern Australia. A dearth of continental detritus results from both a very low relief and a predominantly arid climate. The wide continental shelf is bathed by cold upwelling ocean waters that support luxuriant growths of bryozoans and coralline algae, together with sponges, molluscs, asteroids, benthic and some planktonic foraminifera. The open ocean coast is battered by a persistent southwest swell, resulting in erosion of calcrete-encrusted Pleistocene eolianites. Much sediment is reworked and overall shelf sedimentation rates are low. High-energy microtidal beach/dune systems occur between headlands and along the very long ocean beach in the Coorong region. The northern, more arid coastal areas also contain saline lakes that precipitate gypsum from infiltrated sea water, and display marginal facies of aragonite boxwork to fenestral carbonate crusts, with stromatolites and tepee structures. In contrast, the southern, seasonally humid Coorong region, has a predominantly continental groundwater regime where sulphate is rare, and the high summer evaporation precipitates dolomite, magnesite and aragonite muds. Fenestral crusts, breccias, tepees and some stromatolites are also present. St. Vincent and Spencer gulfs both afford some protection from ocean swell, but tidal amplitude and currents increase, and a depth and inundation-related zonation of plants and animals is established. Muddy carbonate sand accumulates on the sea floor below 30 m, where filter-feeding bryozoans, bivalves and sponges dominate. In shallower regions, seagrass meadows contain a rich fauna that results in rapid accumulation of an unsorted muddy bioclastic sand. Mangrove woodlands backed by saline marsh with cyanobacterial mats are common, and accumulate mud-rich and gastropod-bearing sediment. As tidal amplitude and desiccation increase northward into both gulfs, a supratidal zone bare of vegetation (sabkha) becomes the site for deposition of gypsum-rich and fenestral calcitic mud.

Cretaceous paleogeographic maps of Brazil

Thirty-six paleographic maps covering the entire Cretaceous record of Brazil and all the Brazilian basins are prepared for this paper. Each of the paleogeographic maps is accompanied with an explanation text. The evolution of the country is seen in these maps such as: (1) the Early Cretaceous rifting episode; (2) first evidence of epicontinental and marginal seas with the conspicuous evaporite deposits; (3) the Albian-Cenomanian open seas and wide continental shelf; (4) the Turonian-Santonian transgressions, onlap relationships and narrow continental shelves; (5) the Campanian-Maastrichtian onlap-offlap relationships transitional to Tertiary regressive deposits and; (6) the evolution of the non-marine interior basins. Some climatic observations are dealt with during the explanation of the maps.

Sea-level controls on the post-glacial development of the Great Barrier Reef, Queensland

The central Great Barrier Reef is situated on a 125 km wide continental shelf with a shallow shelf-break at ca. 70 m. In consequence, the earlier post-glacial reef tract was confined to a narrow fringing belt along the present upper slope and outer shelf. The reef-province only started to assume its modern dimensions after ca. 10 ky B.P., when sea-level stabilised at depths around 28 m. Reef growth since 18 ky B.P. has been controlled by the episodic nature of the post-glacial transgression, being related to shorelines S8 to S1 developed at estimated eustatic depths and ages of 114 m 18 ky B.P. , 88 m 17 ky B.P. , 75 m 15 ky B.P. , 56 m 12 ky B.P. , 45 m 11 ky B.P. , 39 m 10 ky B.P. , 28 m 9.5 ky B.P. , 23 m 9 ky B.P. , 9 m 7.5 ky B.P. and 0 m 6.5 ky B.P. Rates of sea-level rise as high as 12 m ky −1 occurred between stillstands, outpacing coral growth response and resulting in many mid-outer shelf reefs being drowned in situ.

Prediction of nearshore wave heights using a refraction programme

The Dobson wave refraction programme, modified to incorporate bottom frictional attenuation, is being tested for its universal applicability for prediction of nearshore wave heights. An investigation has been undertaken to test the applicability of this programme for the prediction of wave heights over a gently sloping, wide continental shelf. The study has been carried out in the shelf waters off Alleppey, situated along the southwest coast of India. The measured wave height at a nearshore point and the computed wave height at the same point are compared. The application of Spearman's rank correlation and Wilcoxon's matched-pairs signed-ranks test has indicated that there is a high degree of correlation between the measured and predicted heights. Since similar results have been obtained by Bryant (1979) for steep shelf waters of Australia, it may be concluded that the programme can be used in different coastal waters irrespective of the nature of the shelf gradient, but subject to other limitations of the programme.

Geochemical profiles in the central Arctic Ocean: Their relation to freezing and shallow circulation

Temperature, salinity, nutrient, tritium, and oxygen isotope data collected during the Lomonosov Ridge Experiment along a drift track between the Makarov and Fram Basins over the Lomonosov Ridge are presented. The relationship of these quantities to the processes that maintain the halocline, in particular to the production of more saline waters by addition of brines formed during the freezing of seawater, is described. The results support the idea that the wide continental shelves of the Arctic Ocean play an important role in maintaining the halocline. Appendix table is available with entire article on microfiche. Order from the American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document C82‐001; $2.50. Payment must accompany order.

A note on circulation of the East China Sea

The East China Sea lies over a wide continental shelf off the coast of China. Just like its neighbouring areas Bohai Sea and Huanghai Sea, the major part of the East China Sea is of a shallow water area, its mean depth being about 370 m. On the average, the annual discharge of fresh water into Bohai Sea, Huanghai Sea and the East China Sea is about 1.5  8, and among these, about 80~o is discharged into the East China Sea, the Changjiang River alone accounts for about 9 x 10nm3/year. Mixed with this large amount of fresh water the coastal water is of low salinity in this area. This Coastal Water System flows, generally, from north to south. Off the outer margin of the continental shelf, a powerful flow characterized by high temperature and high salinity and known as the Kuroshio moves from south to north, then to NE. Therefore, hydrographically, circulation of the East China Sea and its adjacent seas consists of a mesoscale cyclonic gyre with less saline current on the coastal side, warm and saline Kuroshio on the outer side. The characteristics of these two current systems are verydistinct; and the area these two current systems meet is called "front", where all the interactions (including mixing, diffusion, intrusion, etc.) of these two current-systems (hence two water mass-systems) produce the complicated hydrographic conditions of the East China Sea and its adjacent seas (Bohai Sea and Huanghai Sea). The complicated nature of the coastline and bottom topography, the seasonal variation of the prevailing winds, the changing of the discharge of the fresh water, etc. also contribute much to the distributions and variations of the hydrographic conditions of the East China Sea and its adjacent seas. The fore-mentioned two types of current system and hence two different water systems may further be sub-divided into six original water masses: 1) Coastal Water (of the East China Sea); 2) Huanghai Sea (Cold) Water mass; 3) Kuroshio Surface Water mass; 4) Kuroshio Subsurface Water mass; 5) Kuroshio Intermediate Water mass; and 6) Kuroshio Deep and Bottom Water mass. The Changjiang Diluted Water (mass) may be considered as a special kind of Coastal Water mass (of the East China Sea). Unlike the latter which generally flows from north to south, the Changjiang Diluted Water flows in the summer months from its estuary to NE and heads for the Cheju Island. Huanghai Sea Cold Water mass is located in the central part of Huanghai Sea, only its southern tip extends to the northernmost part of the East China Sea. This water mass, formed locally

BARRIER BEACH FEATURES OF CALIFORNIA

Remarkable near-continuous examples of barrier beach features are found in many coastal areas, worldwide. The most notable North American examples are the margins of North America along the Atlantic and Gulf of Mexico, where barrier islands are found along more than 60 percent of the coastline. There are, in fact, 280 large-scale individual barrier features, 70 of which are highly developed and 100 more are being developed (Hobson, et al, 1980). These barriers have been built out of the enormous volumes of sediment available from the extensive watersheds of eastern and central North America and, through the ages, appear to have migrated long distances across a wide continental shelf in response to the interplay of waves and tidal currents, eustatic sea level fluctuations and sand supply. Barrier features are less in evidence on the west coast of North America though they are by no means absent. For example, along a 60-mile reach of the Oregon-Washington coast adjacent to the Columbia River mouth, impressive barrier spits have straightened the coast by blocking the bays and headlands. These are black-sand beaches, formed from the large sediment supply of the extensive inland basin of the Columbia (Bascom, 1980; Cooper, 1967), which has the 29thlargest discharge of the world's rivers (Inman and Nordstrom, 1971). The longest spit in this reach is about 19 miles long. The North Pacific coast is a high-energy wave environment, and these spits are continually shifting. Indeed, one of the most outstanding examples of continuing shore movement in North America is found at Cape Shoalwater at the north side of Willapa Bay, Washington where the inlet has migrated about 2.5 miles northward in the last 95 years across homesites, a cemetery and a lighthouse (Terich and Schwartz, 1981; US Corps of Engineers, 1971a).

A Simple Method for Estimating Barotropic Tidal Currents on Continental Margins with Specific Application to the M2Tide off the Atlantic and Pacific Coasts of the United States

Abstract Theory is developed to describe barotropic tidal currents on “smooth” continental shelves, that is, continental shelves with longshore scales much greater than the shelf width. Two models are considered, one in which sea level don not vary significantly across the shelf and the other in which it does. Both models include longshore gradients and friction (parameterized linearly in velocity). The models were tested by calculating the M2 tidal currents off the Atlantic and Pacific coasts of the United States and then comparing the calculated currents to those measured. Results show that theory and observation are in very good agreement as far offshore as 300 km. Along the Atlantic coast, on account of the wide continental shelf, current velocities are typically O(0.10–0.15 m s−1) north of Cape Hatteras and O(0.15–0.28 m s−1) off Savannah, Georgia. Currents rotate anticyclonically and are highly elliptical (ellipticity E ≈ −0.4), with the semi-major axis oriented normal to the coast. Friction is sign...

The effect of continental shelves on tides

Coastal tides are influenced by several factors and one of the most important of these is the character of the adjacent continental shelf. A continental margin theory is derived and used to discuss several different aspects of the effect “smooth” continental shelves have on tides. The main results are as follows. (a) The theory suggests, in accordance with observations, that semi-diurnal tides should be amplified on wide shelves in mid and low latitudes, but that diurnal tides should not be amplified. (b) Continental shelf tidal resonance occurs when the shelf scale ( gα/( ω 2− f 2)( α=shelf bottom slope, ω = tidal frequency) is approximately equal to the shelf width. Theoretical arguments and observation can be used to show that shelf resonance occurs, for example, along sections of the northwest Australian shelf. (c) Given the easily obtained coastal tide, theory shows that tides over the continental shelf and slope can be approximately estimated analytically. Calculations using simple prediction formulae can be made on a hand calculator. Subject to some restrictions, a simple and inexpensive method is thus available for estimating barotropic tides on continental shelves. (d) An appropriate boundary condition for global numerical tidal models, which cannot resolve the continental margin region, is derived. For the diurnal tides, the boundary condition can be well approximated by an impermeable wall condition at the deep-sea continental slope boundary. For the semi-diurnal tides, the impermeable wall condition usually, but not always, suffices; it can break down on wide continental shelves.