Major River Mouths Research Articles

Lateralized rhythms of the central and autonomic nervous systems: Implications for stress, adaptation and psychopathology

The levels and trends of organochlorine contaminants were determined along the Spanish Mediterranean coast from 2000 to 2013 using mussel, Mytilus galloprovincialis, as bioindicator species. The highest levels of PCBs and DDTs were found at industrial and urban locations, and at areas under the influence of the mouth of major rivers. Dieldrin and t-NNC were commonly detected, while HCHs, aldrin, isodrin, endrin and HCB were at levels not detectable at many areas. Significant declines on the levels of DDTs were observed at most of the areas studied. Conversely, no trends or weak downtrends for PCBs were observed in the areas more polluted by local sources, and in most areas less polluted, where PCBs inputs may be primarily from the atmosphere. Upward trends for PCBs were found in some areas from the Alborán Sea, probably related to the inputs of PCBs through the Strait of Gibraltar. Background concentrations for PCBs and p,p’-DDE have been calculated for this Mediterranean region.

Lignin geochemistry of North American coastal and continental shelf sediments

The concentrations and composition of lignin in coastal and shelf sediments at five locations along the North American continent—Georges Bank/North Atlantic shelf, northwestern Gulf of Mexico, Southern California, Norton Sound and nearshore Beaufort Sea—have been characterized using alkaline CuO oxidation. Lignin concentrations are generally highest at close proximity to the mouth of major rivers, indicating that deposition of river-borne vascular plant debris is the principal source of lignin to the offshore sediments. Arctic sediments contain the highest concentrations, presumably as a result of an abundant supply of terrestrial organic material and the prevalence of frigid temperatures and surface ice cover during much of the year. Concentrations are lowest in the Georges Bank/North Atlantic sediments, where a dynamic physical environment persists over much of the year and the supply of terrestrial organic matter to the offshore in the form of major rivers is lacking. Stable carbon isotopic compositions show that sediments containing the highest lignin concentrations also contain isotopically-lighter organic matter, consistent with a terrestrial source input. Vanillyl, syringyl and cinnamyl phenol distributions in these offshore sediments are consistent with primary contributions from gymnosperm (predominant) and angiosperm woods and secondary contributions from nonwoody tissues. These estimates may be subject to some uncertainty due to diagenetic alteration of individual lignin phenols. In contrast, p-hydroxyl phenol yields are not strongly correlated with those of the other lignin-derived phenols, suggesting generation from both lignin and non-lignin sources. Elevated acid/aldehyde ratios relative to undegraded plant tissues suggest that the lignin transported to these offshore sediments has undergone some biodegradative oxidation.

Relevance of Contaminated Sediment Studies in the Great Lakes to Pollution Assessment and Control in the Mediterranean Sea

In the Laurentian Great Lakes of North America, pollution status, trends and source identification have benefitted greatly from systematic collection and analyses of lake bottom sediments. Similar systematic surveys, using strict sampling and analytical protocols, might provide the same type of valuable information for the Mediterranean, especially for nearshore areas, off the mouth of major rivers or for entire regional seas such as the Adriatic or Aegean.

The Role of Host Biology, Vector Biology, and Temperature in the Distribution of Trypanoplasma bullocki Infections in the Lower Chesapeake Bay

The hemoflagellate Trypanoplasma bullocki and its leech intermediate host, Calliobdella vivida, were studied concurrently over an 18-mo period. Calliobdella vivida occurred throughout the lower Chesapeake Bay but was most abundant near the mouths of major rivers where salinity ranged between 15 and 22 ppt. Calliobdella vivida produced one generation per year, and aestivated in cocoons. Nine different fishes harbored C. vivida, and leeches fed on an additional five species in the laboratory. Trypanoplasma bullocki infected 35% of 595 C. vivida examined, and also infected 13 species of teleost fishes representing 10 families, although it was most prevalent in flatfishes. The hogchoker, Trinectes maculatus, was infected throughout the year, but infections in summer flounder, Paralichthys dentatus, were only observed during winter. Infections of T. bullocki in migratory fishes were rare and were re- stricted to periods of leech contact during early spring or late fall. Flagellates were rare in blood samples from hogchoker or absent in summer flounder for up to 9 wk after experimental inoculation by syringe or leech at 25 C. Fishes subsequently cooled to 15 C or less developed acute infections. This pattern was the result of host-mediated effects rather than of parasite temperature tolerance.

Neotectonic Activity of Atlantic Inner Continental Margin: ABSTRACT

A consistent pattern of neotectonic activity along the inner edge of the Atlantic continental margin is emerging from new data on earthquake activity, contemporary vertical movement and geologic structure. Seismic activity, as shown by both historic and instrumental data, is concentrated in embayments on the Atlantic coastal margin. These are the Southeast Georgia, Salisbury, and Raritan Bay embayments and all major bays and mouths of major rivers in New England. Present-day subsidence is indicated to be taking place at most of these embayments from studies of releveling and tidal-gauge data, Pleistocene and Holocene shorelines, position of historic construction relative to sea level, and archaeological studies. Releveling studies indicate Passamaquoddy Bay, Maine-New Brunswick, is subsiding at a rate of 9 mm per year relative to Bangor, Maine. The embayments appear to have developed as irregularities on the general downwarp of the continental margin by early Tertiary. Many of the embayments occur over older grabens, which may help control their position. The offshore Blake Spur fracture zone trends toward and is aligned with the earthquake activity at Charleston, South Carolina. This fracture zone may also help to control the spacing of the embayments. End_Page 1658------------------------------ The neotectonic activity along the inner continental margin and seismic activity along extensional faults inland from it strongly suggest that slight rifting is still occurring from the opening of the Atlantic. The present downwarping at the continental edge is now concentrated in irregularities, embayments, that possibly developed by sagging over basement structures. End_of_Article - Last_Page 1659------------

Preliminary sonobuoy study of rapidly accumulating shelf sediments

Sonobuoy records with smoothly curved travel time data are found most commonly near rapidly outbuilding shelves and near the mouths of major rivers. It is judged that the smooth increase of velocity with depth is most likely where sediments are young and have accumulated rapidly. These sonobuoy records are amenable to analytical techniques for determining velocity gradients in shelf sediments. These methods are simpler and more accurate than those used in deep water (if the source and receiver are at the surface). Also, sea floor sound velocity can be determined by measuring the critical angle of reflection from sea floor multiples, which form an energetic and clearly defined wedge of closely spaced multiples slightly later than the simple sea floor reflection. Velocity inversion techniques applied to the travel time data provide accurate velocity‐depth information. These techniques show that shelves with sections of rapidly accumulating sediments are ideal for the measurement of detailed velocity characteristics. A method is proposed for measuring in situ attenuation on shelves where the velocity increases smoothly with depth. The method takes advantage of the apparent lack of prominent reflectors in rapidly accumulating sediment bodies and uses the decay in amplitude observed between first‐arrival refractions and their simple multiples. In this proposed technique, the first‐arrival refractions are considered to be the ‘source.’ Simple ray theory shows that maximum focusing occurs in the shallow curved path arrivals at a velocity cusp. The velocity cusps can form in shallow water (less than about 100 m) only when the velocity contrast at the sea floor is nonexistent or slightly positive.

The Influence of Upwelling on Suspended Matter and Shelf Sediments off Southeastern Brazil

ABSTRACT Surface waters off southeastern Brazil contain very little terrigenous material in suspension, even off the mouths of major rivers. As a result of the low rate of supply of terrigenous sediment, calcarenites and live algal reefs are widespread on the middle and outer continental shelf. Upwelling near the coast and over offshore banks, is associated with elevated amounts of suspensates, which are mainly planktonic and non-skeletal, and reach concentrations of 0.5 to 1.0 mg/l. Beneath the biologically productive upwelled surface waters there is remarkably little sedimentation of this organic matter. Also, although phosphorite deposits are usually associated with upwelling centers, there are no phosphatic sediments off southeastern Brazil. The absence of both organogenic sediment and pho phorite differentiates this coast from the areas of upwelling in the eastern Atlantic, and probably results from the high degree of oxygenation of upwelled water, which contains up to 6 ml/l of dissolved oxygen (more than three times as much as found in upwelling centers off northwest Africa, for example). Phosphorite and organically enriched sediment would be absent from paleo-upwelling centers of similar type, but these centers might be recognized through local enhancements of organic matter in the silt and clay fraction of marine sediments.

Suspended Matter and Other Properties of Surface Waters of the Northeastern Atlantic Ocean

ABSTRACT Samples of suspended matter in surface waters were collected at 1534 stations off the west coast of Africa during two geophysical cruises of 1972 and 1973. Many positive correlations exist with respect to auxiliary measurements of winds, temperature, salinity, currents, chlorophyll, phytoplankton, zooplankton-nekton, dustfall, and proximity to major river mouths. Some of the relationships can be expressed in terms of oceanic zones. The most concentrated suspended matter (total, organic, and inorganic) occurs above the continental shelf north of Latitude 7°N, where the high concentration of organic matter is due to coastal upwelling (indicated by relatively low temperatures and salinities, and high chlorophyll and phytoplankton concentrations). The high concentration of inorganic m tter also present along the coasts is due to contributions by major rivers and heavy dustfall. Secondary concentrations of organic matter and the presence of related parameters typify open-ocean belts of divergence at the equator and south of the Sub-Tropical Convergence (south of Lat. 35°S).

The structure and origin of the large submarine canyons of the Bering Sea

Three exceptionally large and long submarine canyons — Bering, Pribilof, and Zhemchug — incise the continental slope underlying the southeastern Bering Sea. Bering Canyon, the world's longest known slope valley, is approximately 400 km long and has a volume of 4,300 km 3. The volume of Pribilof Canyon is 1,300 km 3 and that of Zhemchug is 8,500 km 3; Zhemchug Canyon may well be the world's largest slope valley; most other large submarine canyons have volumes less than 500 km 3. Pribilof and Zhemchug canyons are further distinguished by the headward bifurcation of their slope axes to form elongated trough-shaped basins behind the regionally projected position of the shelf edge. These troughs are superimposed over structural depressions formed by down-faulted basement rocks of Mesozoic and older ages. Prior to canyon cutting these depressions were filled with as much as 2,600 m of shallow-water diatomaceous, tuffaceous, and detrital sediments largely of Tertiary age. Deposition of these sediments took place concurrently with general margin subsidence of at least 2,000 m. The data and conclusions presented in this paper stress that the location, trend, and shape of the enormous submarine canyons cutting the Bering margin are structurally determined. However, axial cutting and headward erosion within the relatively unconsolidated Tertiary strata and the older, lithified basement rock is thought to have been caused by basinward-sliding masses of sediment; these unstable sediment bodies accumulated on the upper continental slope and outer shelf, probably near the mouths of major Alaskan rivers. Bering Canyon was periodically cut and filled by axial sedimentation during Late Tertiary and Quaternary time. Pribilof and Zhemchug canyons, however, are thought to have been excavated entirely during the Pleistocene. It is presumed that, during one or more periods of glacially lowered sea level, the Kuskokwim and Yukon rivers emptied into or near the heads of Pribilof and Zhemchug canyons. The enormous size and unusual shape of Zhemchug Canyon resulted from the breaching of the seaward wall of an outer-shelf basement depression and the subsequent removal of nearly 4,500 km 3 of Tertiary deposits filling it.

The Gulf of Corinth floor

The Gulf of Corinth is a narrow, 65-mile-long, 470-fathom-deep trench. The canyons of the steep southern continental slope lead from major river mouths to coalescing sub-sea fans. A narrow abyssal plain underlain by turbidites occupies the deepest part of the gulf. Three telegraph cables were laid the length of the gulf and maintained for over fifty years. Two of the cables lay on the continental slope and one traversed the abyssal plain. The two cables on the continental slope were broken frequently by turbidity currents originating at the mouth of the major rivers. On the few occasions when cable repairs were made to the cable which crosses the abyssal plain, the cable was found buried.

Abyssal Basin Sedimentation: ABSTRACT

Clastic sands and silts transported and deposited by turbidity currents have created the vast abyssal plains of the ocean basins and have constructed the abyssal cones and natural levee systems of the continental rise. Clastic silts and lutites, largely transported by ocean currents, have created much of the continental rise and the outer ridges which parallel the continental margins. Biogenous sediment, resulting from near-surface productivity, more or less redistributed by currents, has created the rolling abyssal swales of productive mid-oceanic areas and has contributed to the continental rise and marginal trench sediments. Although turbidity currents are responsible for the leveling of the abyssal plains, turbidites constitute less than one-third of the sediments beneath the plains. Horizontal size grading in turbidites away from source areas is detectable but small. Apparently a much more important control on size is imposed by the lower courses of the major rivers. Turbidity currents originate near the mouths of several major rivers at the rate of 50 per century but in many other likely areas none have occurred for thousands of years. End_of_Article - Last_Page 344------------

THE PREVAILING DIRECTION AND MECHANICS OF BEACH DRIFT INFERRED FROM VARIATION SERIES OF BEACH SEDIMENTS ALONG THE SAGAMI BAY COAST, JAPAN

A petrographic study of beach sediments can be expected to contribute much to the understanding of their source, transportation and deposition. Therefore, we examined the gravel and mineral content of sediments samples taken along the shoreline in an effort to determine the prevailing direction of beach drift and to make clear the mechanics of littoral transport. Field work was done in the Sagami Bay area, on the Pacific coast of Japan. The shoreline along the coast of the Bay is marked by some 40 miles continuous beach which is exposed to the open sea. At the eastern end of beach, there lies Miura Peninsula and at the western end, Izu Peninsula. 38 sampling stations were selected at one mile intervals along this stretch of beach. Then, those samples collected were used as basic data for petrographic analyses. The major conclusions of this investigation are as below : 1) The lithological composition of beach deposits in the coast of major river mouths and their neigh borhood are similar to that of fluvial deposits of those rivers. This similarity led to the conclusion that beach deposits have a close relationship to river-transported materials. In addition, the beach sediments deposited in this coastal region are in a great quantity derived from the rivers of Sagami, Sahawa and Maya. 2) Based on the areal distribution and systematic variation series, it is believed that littoral brift in this Bay prevailingly moves eastwards by longshore currents. 3) There is decrease in grain size of the beach gravels with increase in distance away from the source areas. This decrease in size is probably due to the result of abrasion of gravels rather than the sorting action of waves which transports gravels selectively. Moreover, beach gravels seem to move intermittently along the shoreline and once these gravels deposit on the beach, they should be abraded and deformed to various shapes in accordance with the strength of local littoral force. 4) In some places of this stretch of beach, where are islands or reefs in the offshore, numerous wellrounded, extremly flat gravels are present. In addition, both the amount of heavy mineral contents and the ratio of quartz to feldspar increase materially. Those phenomena might be explained by the fact that the beach sediments once deposited remain for a long time under the effect of the refracted offshore waves caused by the hindrance of islands or reefs.