Showing papers on "Shore published in 1990"

Significance of time‐averaging for palaeocommunity analysis

Abstract: Fursich, F. T. & Aberhan, M. 1990 04 15: Significance of time-averaging for palaeo community analysis. Lethaia, Vol. 23, pp. 143–152. Oslo. ISSN 0024–1164. Time-averaging caused by sedimentological, biological, or digenetic factors is widespread in marine environments. It can be recognized using stratigraphic, ecological, taphonomic, or sedimcntologic criteria. Community parameters such as diversity, relative abundance of species, taxonomic and, to a lesser extent, trophic and life habit composition may seriously differ between thanatocoenosis (death assemblage) and time-averaged taphocoenosis, depending on the degree of community stability. Time-averaged community relics have a quality different from that of Recent communities and any comparison between the two has to take this into account. Whereas allochthonous time-averaging, which is strongly related to the energy level, is particularly common in very shallow environments, the importance of autochthonous time-averaging, related in addition to the rate of net sedimentation, increases with distance from the shore and with depth. Short-term time-averaging (in the order of up to several thousand years) prevails in near shore shallow environments, whilst long-term time-averaging (in the order of 104 to 105 years) becomes more important towards lower shelf and deep sea environments.

Numerical Study of the Influence of Environmental Conditions on Lake-Effect Snowstorms over Lake Michigan

Abstract: Numerical simulations are used to examine the influence of environmental parameters on the morphology of lake effect snowstorms over Lake Michigan. A series of model sensitivity studies are performed using the Colorado State University mesoscale model to examine the effects of lake–land temperature difference, surface roughness, atmospheric boundary layer stability, humidity, and wind speed and direction on the morphology of simulated storms. Four morphological types of lake effect snowstorms have been identified: (i) Broad area coverage, which may become organized into wind parallel bands or cellular convection; (ii) shoreline bands with a line of convection roughly parallel to the lee shore and a well developed land breeze on the lee shore; (iii) midlake band with low-level convergence centered over the lake; and (iv) mesoscale vortices with a well-developed cyclonic flow pattern in the boundary layer. The model is able to reproduce all four morphological types. Simulations varying environmenta...

Spatial population-dynamics of a marine organism with a complex life-cycle

Abstract: This paper presents a modeling framework within which mesoscale features in ocean currents can be integrated with coastal habitat structure to predict the distribution and abundance of a marine organism with a coastal adult phase and a pelagic larval phase. The processes in the model that influence larvae away from shore are advection, diffusion, and mortality; the processes influencing larvae adjacent to the coast are settlement and reproduction by adults. The adults on the coast are influenced by recruitment, mortality, and the availability of suitable habitat. Larvae are passive particles in the ocean whose movement is modeled with a transport equation. The water column is represented by a two—dimensional plane and the coast by a straight line. Age—integrated biological parameters for the barnacle Balanus glandula are used in numerical examples. A one—dimensional model illustrates the interaction of eddy—diffusion and larval mortality in determining larval wastage that, in turn, affects whether a species can persist. In a two—dimensional model (solved using finite difference techniques) the persistence of a population also depends on the length of suitable habitat, the strength and structure of the along—shore flow field, and biological parameters of the species concerned. Initial conditions may have a large influence on the growth and spread of the population, especially in the presence of along—shore flow.

Interannual variability in particle flux in the southwestern Black Sea

Abstract: Vertical particle flux was measured at two sites in the southwestern Black Sea using automated time-series sediment traps over a period of 4.5 years. The particle flux between both sites varied considerably. (1) At site BSC (80 km from shore) the dominant fraction of the annual flux was deposited during short blooms; at site BS (40 km from shore, but still beyond the shelf break), the particle flux was less dominated by short-term blooms. (2) At site BSC, plankton blooms were the dominant cause for removal of suspended lithogenic matter; at site BS, vertical transport of lithogenic matter was linked also to the occurrence of storms and to high discharge periods of local rivers. Upwelling in the southwestern Black Sea may play an important role in triggering plankton blooms.

Calculating Long-Term Shoreline Recession Rates Using Aerial Photographic and Beach Profiling Techniques

Abstract: Quantifying measurement error and precision may be the most difficult step of shoreline recession rate calculations. Calculation of long-term shoreline recession rates based on aerial photograph analysis reflect only the shoreline positions at the time of photography. Conventional methods of long-term recession rate calculation were combined with beach profiling techniques in order to quantify potential errors that can be produced by short -term variations in shoreline position. Monthly beach profiling of a typical northeastern/mid -Atlantic microtidal and wave dominated shoreline demonstrated short-term shoreline position changes of up to 20m over a one year period. Average long-term shoreline recession rates in this area were 1.2 m/yr ± 1.0 m/yr. Short-term shore line position changes were the largest source of error in the long-term recession rate measurements. This emphasizes that photographed shorelines do not necessarily represent the seasonal mean shore line position, particularly in locations where shorelines characteristically exhibit relatively large short-term variations in shoreline position.

Metabolic activity of size-fractionated microbial plankton in estuarine, near-shore, and continental shelf waters of Georgia

Abstract: Estimates of bacterial production and activity, and of planktonic community respiration, were made at a series of stations starting in an estuary, passing through the coastal front, and across the continental shelf to a distance of 120 km offshore in the Georgia Bight. Measurements were made on unfiltercd and on 1.0 pm (pore-size) filtered water samples to examine the small free-living bacterial size fraction relative to the larger plankton. In waters landward of the coastal front, ca 50 to 80'70 of bacterial and community activity was associated with the larger size fraction, indicating the importance of larger and particle-associated heterotrophs in the nearshore, hghly turbid water. Seaward of the front, 80 to 99 U/o of activity was in the C 1.0 pm fraction. Thus, the < 1.0 pm size fraction is responsible for most of the respiration in shelf-waters. Bacterial production and activity decreased markedly with distance from shore; community respiration also decreased across the shelf, but not as much as the bactclrial production decreased. Bacterial growth efficiency was low in estuarine waters (11 %), and decreased in nearshore (6 40) and shelf (2 %) waters.

A Study of Internal Wave Propagation in the Strait of Gibraltar Using Shore-Based Marine Radar Images

Abstract: An X-band marine radar on Windmill Hill, Gibraltar, was used to monitor the propagation of internal waves in the Strait of Gibraltar during March, April, and June 1986. Surface roughness features of the waves were observed out to a range of ∼15 km. From photographic images of the radar screen, the positions of image features were measured manually using a digitizing table, and these data were then computer processed to give wave arrival times and phase speeds. During most tidal cycles, an internal undular bore generated at Camarinal Sill was observed to pass eastward (A-waves). These occurred throughout the experiments although less frequently near neap tides. The time of travel to Gibraltar varied significantly, so that the bore arrived between four and nine hours after high water. Arrival times were found to be closely related to the amplitude of the upper layer tidal current. This current had a strong diurnal component, which was manifested as an inequality between the arrival times of success...

Modelling shore response to sea-level rise on sedimentary coasts

Abstract: Most sandy shorelines worldwide have retreated during the past century (Bird, 1985). Progradation has been restricted to coastal areas where locally excess sediment is supplied by river sources or where the land is being elevated due to tectonic uplift or isostatic glacial rebound. Human interference cannot be considered a primary cause of erosion worldwide since it is also occurring on sparsely populated and little developed sandy coasts. Such recession could result from an increase in storminess, but this trend would have to be almost worldwide

Enhancement of habitat heterogeneity and species richness on rocky shores inundated by sand.

Abstract: Many rocky shores are subject to periodic inundation by sand, which is often thought to reduce species richness by eliminating organisms intolerant of sand scour or sand smothering. However, regular disturbance (e.g. inundation) should promote richness by preventing the development of low diversity climax communities. A study of faunal richness on 10 regularly inundated shores showed that inundation does promote richness, but by increasing habitat heterogeneity. Some species are excluded from parts of the shore by sand, but because of the patchiness of sand deposits they are rarely excluded from the entire shore. Other species are found only on rocks associated with sand, while typically sandy shore animals occur in the sand deposits themselves. Total richness (281 species) was greater than for local noninundated shores and sandy beaches combined.

Holocene evolution of an estuarine coast and tidal wetlands

Abstract: Modern facies-distribution patterns, extensive core data, and chronostratigraphic cross sections provide a detailed history of Holocene inundation within the Delaware Bay estuary and sedimentation in adjacent coastal environments. Flooding of the estuary occurred with rising sea level as the shoreline retreated northwest along a path determined by the pre-transgression topography. Simultaneous migration of an estuarine turbidity maximum depocenter provided the bulk of fine sediments which form the coastal Holocene section of the estuary. Prior to 10 Ka, the ancestral bay was predominantly a tidal river, and the turbidity maximum depocenter was located southeast of the modern bay mouth. By 10 Ka, lowlands adjacent to the ancestral channel of the Delaware River were flooded, forming localized tidal wetlands, and the depocenter had initiated high rates of fine-grained sedimentation near the present bay mouth. At that time, coastal Holocene strata began to onlap the interfluve highlands. By 8 Ka, the fine-grained depocenter had migrated northwest along the main channel of the Delaware River, although the widened mouths of tributary valleys continued to be active sites of sediment accumulation. Following the passage of the fine-grained depocenter, coarse-grained sediments accumulated along the coast in response to increased wind-wave activity. During the middle Holocene, portions of the estuarine coast began to resemble modern geomorphology, and washover barrier sands and headland beach sandy gravels accumulated along the southwest shore. The late Holocene was characterized by erosional truncation and submergence of aggraded coastal lithofacies and by planation of remnant highland areas. Knowledge of the eroded Holocene section is fragmentary. At present, continued sea-level rise is accompanied by deposition of tidally transported muds in coastal environments and deposition of sandy sediments in some offshore regions. An unconformity marks the base of the developing open estuarine sequence of coarse clastic lithofacies and denotes the end of coastal accumulations. Modeling of coastal-lithofacies transitions identifies specific lithofacies complexes in the Holocene stratigraphic section which were influential in the evolution of the coast. Development of the Holocene section of the estuary coast involved both constructive, or aggradational, and destructive, or erosional, phases.

An Analysis of Replenished Beach Design Parameters on U.S. East Coast Barrier Islands

Abstract: Forty-three beach replenishment projects on the United States Atlantic Coast are divided into 3 categories based on time of fill retention: (1) less-than-1-year beaches (26%), (2) l-to-5 year beaches (62%), and (3) greater-than-five-year beaches (12%). Filled or replenished beaches north of Florida generalIy have lifetimes of fewer than 5 years. Storm history is the most important factor In determining beach durability so important that the effects of the other parameters, which may also play a role in artificial beach behavior, are overshadowed. Beach length, grain size, shoreface slope, shelf width and method of fill emplacement show no correlation to regional replenished beach lifetime. Inlet proximity and a combination of shoreline orientation and dominant angle of wave approach may exert minor influence on beach behavior. Initial density of fill (volume per unit length) exerts significant influence on the percentage of fill remaining after one year, but the effect becomes less well defined beyond the first year.

Groundwater seepage along a Barrier Island

Abstract: Resistivity and water level measurements were made on a barrier island on the south shore of Long Island, New York to examine the distribution of fresh groundwater and the potential for recirculation of saline groundwater. The depth to the base of the freshwater lens was overpredicted by calculations of the static-equilibrium depth to a sharp interface apparently because of the sensitivity of the calculation to the low water-table elevations which are in turn sensitive to variations in sea level because of the existence of a transition zone between fresh and saline groundwater. Mixing and recirculation of saline groundwater at the base of the lens produced a transition zone up to 9.65 m thick. Measurements also support model forecasts of a mean bay level several centimeters above sea level, augmented by atmospheric forcing and wave setup. A time lag of about 8 hours between the response of the ocean level to longshore winds and the corresponding response of the bay level can result in a difference in elevation between the bay and the ocean that is up to four times that produced by other agents such as Stokes transport and density differences. In the presence of differential hydraulic head, bay and ocean water may be exchanged via groundwater flow between the base of the freshwater lens under the barrier beach and a deeper clay layer.

Influence of wind on breaking waves

Abstract: The influence of local wind on nearshore breaking waves was investigated in a laboratory wave‐wind flume. The breaker location, geometry, and type were found to depend strongly upon the wind direction. Onshore winds cause waves to break earlier, to break in deeper water farther from shore, and to spill; offshore winds cause waves to break later, to break in shallower water closer to shore, and to plunge. For onshore winds, it was observed that breaking of the wind‐generated ripples can initiate spilling breaking of the primary underlying wave by providing a perturbation on the crest of the underlying wave as it shoals. The implications of these results are that surf zone width, currents, and sediment transport can be affected by local winds. Thus, engineering estimates of these quantities could be improved by consideration of local wind. Surf zone dynamics models that ignore wind or include wind only as a surface shear may be missing a very important effect of the wind—its effect on the initiation and mec...

A coupled one-dimensional sea ice–ocean model applied to a semi-enclosed basin

Abstract: The objectives of the present study are to formulate and explore a coupled sea ice–ocean model for semi-enclosed basins. Both thermodynamic and dynamic processes are included. Variations in the on–off shore directions are considered, and the model is applied to the Bothnian Bay, where ridging due to southerly winds is a common feature. The importance of the different ice processes and their simulation are discussed. It is concluded that a one-dimensional model approach to the winter sea ice season can be used, giving realistic information about ice formation, growth and decay. Horizontal gradients in the sea and in the ice, however, imply that a two- or three-dimensional model is in general needed, particularly for the initial advance of the ice edge and for the ice deformation calculation. DOI: 10.1034/j.1600-0870.1990.t01-3-00007.x

Sessile Animals of the Sea Shore

Abstract: Sessile animals on the seashore - the shore community, features of the sessile lifestyle the sea shore environment - movement of the sea, exposure to the atmosphere the biotic environment - seaweed and micro-organisms, plankton and other animals requirements for life on the shore - attachment to the substratum, protection of the body, physiological adjustments for emersion acorn barnacles (Crustacea - Cirripedia) - structure of acorn barnacles, representative intertidal barnacles, structural adaptations for shore life, growth of barnacles, movements of barnacles, reproductive specializations for shore life, physiological adjustments of barnacles mussels and oysters (Mollusca: Bivalvia) - representative intertidal species, general organization, the shell, attachment to the substratum, nutrition, reproduction, metabolic adaptations to shore life tube-dwelling worms (Annelida - Polychaeta) - representative species from rocky shores, structures related to a tubicolous lifestyle, tube secretion in the serpulidae sea squirts (Tunicata - Ascidiacea) - representative sea squirts from the shore, the integument of tunicates, blood and circulation, generation of feeding current, sexual reproduction, advantages of asexual reproduction to shore life Bryozoans (Polyzoa - Ectopracta) - some common Bryozoans of the Littoral Zone, protection and attachment, the Lophophore and feeding, reproductive strategies sea anemones and related animals - (Cnidaria - Anthozoa) - general structure of sea anemones, representative sea anemones, anthozoan Cnidae, movements of sea anemones, behaviour of sea anemones and its control, physiological adaptations of sea anemomes to shore life hydroids (Cnidaria - Hydrozoa) - structural organization and examples of intertidal hydroids, importance of the Perisarc to hydroids, movements and behaviour of hydroids, hydroplasmic flow, growth of Thecate hydroids, functions of the stolon sponges (Porifera) structure of some Littoral sponges, the skeletal system of sponges, feeding currents and digestion, growth and reproduction of sponges colonization of the sea shore - reproductive strategies, larval mortality, dispersal and settlement community structure and interations - interaction between different species, interaction between members of the same species, predators, distribution of animals on the shore, the dynamic nature of shore communities. Appendix - systematic classification of sessile animals.

Acoustic Behavior in a Local Population of Bottlenose Dolphins

Abstract: Groups of bottlenose dolphins are a common sight in the Sado estuary, near Lisbon, Portugal. They make up a small resident population of about 40 animals, usually divided in groups of about 15, that move in and out of the estuary. They exploit the faunal riches upstream and also engage in frequent excursions to sea, covering distances yet unknown but following, as far as we can tell, routes close to shore.

Littoral Cell Response to Interannual Climatic Forcing 1983-1987 on the Central Oregon Coast, USA

Abstract: Longshore distributions of beach sand (1983- 1987) in a 17.2 km long subcell (Seal Rocks Yachats Point) of the central Oregon coast have been studied to document interannual variability of longshore transport resulting from and following the anomalous 1982-83 north Pacific climatic event. Some 4-8 x 10 6 m 3 of beach sand was displaced northward from the 7.4 km long southern end of the headland bounded subcell during the 1982-83 winter. The 1982 -83 volume of interannual longshore displacement (5-11 x 10 2 m 3 per meter of shore line distance) from the southern 7.4 km of the cell exceeds a reported annual seasonal exchange (across -shore) from an adjacent cell by at least a factor of 5. The northward displacement of beach sand in 1982-83 resulted from (1) a southward 10° -15° latitude (1,000 -1,500 km) shift of the winter (Dec-Feb.) geostrophic wind guide (1014-1016 mb), i.e. a proxy for the seasonal storm tracks relative to a 16 year mean of 50-55° N, and (2) an above average (but not exceptional) energy of winter wave climate, based on weekly and daily mean significant wave heights (H 1/3 ). An EI Nino -Southern Oscillation (ENSO) related elevation of mean sea level (some 30 cm above a 16 year mean) might have facilitated offshore transport of the beach sand during the winter period, but it is not considered to have been important in the longshore redistributions of beach sand. A two year delay in the southward return of the northward displaced sand corresponds to winter geostrophic wind guides of very high latitude (55-65° N). Historical records of erosion and accretion of beaches and the Alsea Bay spit within the subcell indicate that the 1983-87 cycle of sand redistribution in central Oregon was the most extensive in the last 24 years (period of available records).

An incident of Southern Occean oil pollution: Effects of a spillage of diesel Fuel on the rocky shore of Macquarie Island (Sub-Antarctic)

Abstract: On 3 December 1987, the Australian resupply ship Nella Dan ran aground at Macquarie Island, releasing approximately 270 000 L of oil, mostly light marine diesel, into the sea. This represented one of the few spills to have occurred in southern hemisphere cold waters. Following the spill, thousands of marine invertebrates were washed up dead on beaches along 2 km of the shore. Twelve months after the spill, a study was conducted to examine the shore community in 5 zones at 2 oil- affected and 2 control locations. Three sites were examined within each of these locations. Densities of marine invertebrates appeared to have been markedly reduced in the lower littoral and sublittoral zones in the vicinity of the wreck. In the upper littoral zones, algal cover and invertebrate abundance were similar at oil-affected and control locations. The significance of the spill and its long-term effects are discussed.

Drift disseminules on cays of the Swain Reefs, Great Barrier Reef, Australia

Abstract: Drift disseminules were collected on cays of the beaches facing prevailing wind and current directions, but Swain Reefs (Great Barrier Reef, Australia) during twelve none survived for 1 year. Disseminules were also tested for expeditions over 7 years. At least thirty-four species not viability using tetrazolium, and glasshouse germination belonging to the small established cay floras are repre- tests. Altogether, seeds of seventeen 'exotic' species were sented in the collections. Assemblages varied between shown to drift to Swain Reefs cays in viable condition. visits and between cays, in both relative proportions of Comparisons are made with the drift disseminule floras species and in total number of disseminules. Most dis- of shores in New South Wales and in Japan. The bio- seminules probably derive from the New Caledonia- geographical significance of the findings is discussed. Vanuatu-Fiji region to the northeast and some are proba-

Observations of wave-induced set-up on a natural beach

Abstract: A new technique has been used to make field measurements of wave-induced set-up. The technique is reliable and accurate, and the results presented show the variation of mean set-up at the shoreline with incident wave height. The amount of set-up is well predicted by a linear function of incident wave height and is found to be in good agreement with theoretical predictions based on the observed decay of wave height across the surf zone. The maximum set-up observed was about 40 cm.