Local Hydrography Research Articles

Displacement of diverse ichthyoplankton assemblages by a coastal upwelling event on the Sydney shelf

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 176:49-62 (1999) - doi:10.3354/meps176049 Displacement of diverse ichthyoplankton assemblages by a coastal upwelling event on the Sydney shelf Kimberley A. Smith*, Iain M. Suthers School of Biological Science, University of New South Wales, Sydney, New South Wales 2052, Australia *E-mail: marsci@unsw.edu.au ABSTRACT: The influences of upwelling-favourable winds and thermocline displacement on the distribution of temperate/tropical ichthyoplankton assemblages were determined from vertically stratified plankton hauls across the Sydney shelf, southeastern Australia. Five stations were sampled along a shore-normal transect off Sydney, Australia, on 3 or 4 consecutive nights during January and April 1994. High taxonomic diversity (111 ichthyoplankton families) was attributed to the convergence of temperate and tropical waters in this region. Total larval abundance was higher in January than in April, reflecting the spawning times of many coastal taxa. In both months, highest larval density and taxonomic diversity were associated with the interface between the mixed layer and the thermocline. In April, a period of upwelling-favourable winds resulted in the offshore displacement of the nearshore mixed layer, as well as numerous shelf-spawned larvae (e.g. Centroberyx affinis, Chromis hypsilepsis, Arripis trutta) from the nearshore region, and coincided with the injection of deeply distributed mesopelagic larvae into the nearshore zone (e.g. Scopelosaurus sp., Melamphaes sp.). Shelf-spawned larvae were displaced to the outer shelf, where they were still associated with the mixed layer/thermocline interface. Dynamic ichthyoplankton distributions are interpretable, at least at a scale of weeks, by considering larvae as tracers of the local hydrography. KEY WORDS: Ichthyoplankton assemblages · Hydrography · Upwelling · Thermocline Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 176. Publication date: January 18, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Spatial distribution of planktivorous fish schools in relation to krill abundance and local hydrography off Otago, New Zealand

Side-scan sonar allows mapping of near-surface schools of fish, but it has seldom been used for this purpose. Data were collected off the coast of Otago, New Zealand for 21 days during 1994 to 1996 using a 130 kHz Klein 595 digital side-scan sonar. A total of 2198 schools were detected. Of these, 348 schools of barracouta ( Thyrsites atun), 67 schools of jack mackerel ( Trachurus murphyi), and 17 schools of slender tuna ( Allothunnus fallai) were identified. Barracouta schools were significantly smaller than schools of jack mackerel or slender tuna, but the size of schools was not related to state of tide, location, water depth, salinity, temperature, or density of krill. Fish schools were detected throughout daylight hours, but dispersed at night. Analysis of stomach contents revealed barracouta, jack mackerel and slender tuna were feeding on krill, Nyctiphanes australis, and fish schools occurred in areas with high densities of N. australis. Variability in the abundance of N. australis was related to salinity; catches were highest in a band of low-salinity water which was present in the study area following periods of high river runoff.

Intertidal clam harvesting: benthic community change and recovery

Mechanical harvesting of intertidal bivalve molluscs inevitably leads to the physical disturbance of the substratum and its associated fauna. Hence, it is necessary to consider the consequences of such activities for the requirements of other species (e.g. fish and birds) which utilize these areas. The present study reports a long-term experiment that studied the effects of Manila clam, Tapes philippinarum Adams & Reeve, cultivation on an estuarine benthic habitat and its fauna. The study began with the initial seeding of the clams, and continued through ongrowing, and finally, harvesting 30 months later. Earlier observations revealed that plots covered with netting elevated sedimentation rate, and hence, encouraged the proliferation of certain deposit-feeding worm species which persisted throughout the cultivation cycle until harvesting took place. The immediate effects of harvesting by suction dredging caused a reduction of infaunal species and their abundance by ∼80%. Recovery of the sediment structure and the invertebrate infaunal communities, judged by similarity to the control plots on both the harvested and unharvested but originally netted plots, had occurred 12 months after harvesting. Comparisons with other similar studies demonstrate that, in general, suction harvesting causes large short-term changes to the intertidal habitat. The rate at which recolonization occurs and sediment structure is restored varies according to local hydrography, exposure to natural physical disturbance and sediment stability. The management of clam farming procedures and other forms of mechanical harvesting should incorporate a consideration of site selection, rotational seeding, cultivation and harvesting to create fallow areas, and seasonal harvesting to ameliorate the recovery of sites.

Features, boundaries and connecting mechanisms of the Mauritanian Province exemplified by oceanic fish larvae

The Mauritanian Province, which comprises the area from the NW-African shelf to about 20°W and from Cape Timiris to Cape Verde, is redefined on the basis of fish larvae distribution patterns, direct and indirect current measurements, CTD-O2 hydrography and SST-remote sensing. Its northern and western boundaries coincide with, the permanent, although not stationary, Cape-Verde-Frontal-Zone separating North- and South-Atlantic-Central-Water masses. Its southern boundary is characterized by tropical temperatures throughout the year. The oceanic Mauritanian Province is a myctophid dominated system that lacks genuine endemic species. Many deep-mesopelagic species of Myctophidae as well as other families are absent or rare in its centre, whilst some northern oceanic Myctophidae acquire a pseudoceanic character and prosper. On the other hand, tropical species of both oceanic and neritic origin co-occur alongside such cold-temperate Myctophidae. Distribution patterns of fish larvae were partly directly dependent on currents intruding into the province and partly indirectly on the impact of the circulation system on the local hydrography. Local hydrography could affect the survival capability of either larvae or adults. While an oxygen deficit southeast of the frontal zone is a limiting factor for subsurface-epipelagic and mesopelagic species, southwestward Ekman-drift and the related temperature deficit hampers the intrusion or survival of tropical fish larvae with neustonic or shallow vertical distribution. Southern, deep living or eurybathic species with lower temperature preferences are transported into or even beyond the province by northward currents. A transport model describing the input/output mechanisms of the province and defining its limiting features is presented and discussed in respect to recent literature.

Phytopigments and fatty acids as molecular markers for the quality of near-bottom particulate organic matter in the North Sea

In February, May and August 1994, four stations in the North Sea (viz. at the Broad Fourteens, Frisian Front, German Bight and Skagerrak) were visited to sample near-bottom particulate organic matter. Samples, taken by means of a pump, a sediment trap and a sediment recorder, were analysed on organic carbon, total nitrogen, phytopigments and fatty acids. These molecular markers were used to describe the nature and quality of the organic particles in the near-bottom water. Principal component analysis showed chlorophyll a, phaeopigments and fatty acids to be useful markers for the quality of organic matter and yield complementary information. The quality of the near-bottom particles appeared to be related to the local hydrography and depositional circumstances. The Broad Fourteens station, a non-depositional sandy site along the Dutch coast, showed organic particles to be relatively fresh, little influenced by resuspended sedimentary material. Near-bottom organic particles on this site contained relatively high shares of chlorophyll a and polyunsaturated fatty acids, characteristic of algal matter. On the other hand the particulate organic material on the two depositional locations, the Frisian Front and the German Bight stations, was influenced by resuspension of sedimentary organic particles poor in pigments and fatty acids. Amounts of carbon trapped in the near-bottom environment at the Skagerrak station were lower than expected from the literature.

Benthic foraminiferal responses to estuarine pollution; a review

Other| July 01, 1995 Benthic foraminiferal responses to estuarine pollution; a review E. Alve E. Alve University of Oslo, Department of Geology, Oslo, Norway Search for other works by this author on: GSW Google Scholar Author and Article Information E. Alve University of Oslo, Department of Geology, Oslo, Norway Publisher: Cushman Foundation for Foraminiferal Research First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 GeoRef, Copyright 2004, American Geological Institute. Journal of Foraminiferal Research (1995) 25 (3): 190–203. https://doi.org/10.2113/gsjfr.25.3.190 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation E. Alve; Benthic foraminiferal responses to estuarine pollution; a review. Journal of Foraminiferal Research 1995;; 25 (3): 190–203. doi: https://doi.org/10.2113/gsjfr.25.3.190 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 SocietyJournal of Foraminiferal Research Search Advanced Search 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.

Multiyear Fast Ice along the Taymyr Peninsula, Siberia

A 20 km wide zone of fast ice, reaching offshore to the 20 m isobath and sealing off coastal embayments along the Taymyr Peninsula, survived until at least 23 November 1993, becoming multiyear land-fast sea ice (MLSI). Barrier islands show characteristic recurved spits indicating dominant southeastward direction of longshore transport in intermittent years. At the time of observation, the fast ice was undisturbed, only heaving vertically with tides, protecting the coastal zone from wave reworking. The 1 to 2 m thick ice cover affects light and oxygen, creating profound effects on marine life in the zone. A herd of walrus, in other summers reported to haul out on local beaches, was displaced by the fast ice. We saw no evidence for sediment loading of the ice by rivers or eolian deposition on ice. MLSI is considered an incipient ice shelf, which could grow in thickness and strength in successive winters. Salinity and delta 18O profiles in ice cores from some smaller areas of MLSI provide a record of environmental conditions during the first year of ice growth, such as local hydrography and contribution of congealed snow to the solid fast ice. On ice charts we found no record of waxing and waning MLSI in the area, and do not know whether the observed ice survived the next summer. Since arctic ice shelves have developed from MLSI in the past, the observed phenomenon permits a view of how transitions from interglacial to full glacial conditions can begin.Key words: multiyear land-fast sea ice, incipient ice shelves, sediment entrainment, interglacial/glacial transition, Siberia, Laptev Sea

Buoyancy and wind forcing of a coastal current

Local winds and lateral buoyancy fluxes from estuaries constitute two major forcing mechanisms on the inner continental shelf of the Mid Atlantic Bight on the eastern seaboard of the U.S.A. We report observations of the resulting coastal current that suggest a linear superposition of the wind and buoyancy forced motions. This current, which we term the Delaware Coastal Current, has a mean flow of about 10 cm/s in the direction of Kelvin wave phase propagation. It opposes the generally upwelling favorable local winds there. The same winds, however, force important across-shelf flows that agree qualitatively with Ekman dynamics with Ekman numbers that are 0( 1). Velocity fluctuations at current meter mooring are consistent with the above dynamics, and explain the local hydrography well. Trajectories from drifters and derived velocity fields, too, reveal consistent flow patterns. We further find that Lagrangian and Eulerian integral time scales are similar, implying a linear flow field. We estimate dispersion coefficients for this buoyancy driven coastal current to be about 2000 and 200 mz/s in the along- and across-shelf direction, respectively. Our results disagree both qualitatively and quantitatively with those of a recent numerical model of the study area.

Diurnal variation in surface pCO2 and O2 at 60°N, 20°W in the North Atlantic

Abstract A method for rapid determination of the partial pressure of carbon dioxide at the sea-surface is described. The method was employed along with a pulsed oxygen electrode to monitor daily changes in surface pCO 2 and O 2 close to a drifting buoy deployed at approximately 59°N, 20°W. During a 4 day period a gradual rise in oxygen saturation and corresponding fall in pCO 2 was observed in the surface layer. Corrections are made for gas exchange of O 2 using wind speed data, the correction being an important fraction of the supersaturation observed in the water. Estimates of net community production and photosynthetic quotients are derived, giving a range of PQs from 0.9 to 1.5. Though variations in the local hydrography reduce the accuracy of these estimates, the potential of this approach to estimate productivity appears promising.

Tropidc ecology of carnivorous zooplankton in the Benguela

Carnivorous zooplankton in the Benguela system have tended to be ignored by all but early taxonomists and a handful of recent researchers. An attempt is made here to address the importance of carnivores in this system but, because the database is poor, it was necessary to apply material from outside the region. The taxa covered include ctenophores, cnidarians (Scyphozoa and Hydrozoa, including Siphonophora), chaetognaths and hyperiid amphipods as well as such minor groups as pelagic gastropods and decapods. Most groups of carnivores within the Benguela are represented by only one or two common species. These tend to be epiplanktonic and generally concentrated inshore of the shelf-break, where their distributions are influenced by changes in local hydrography. Their densities frequently exceed those of herbivores. The dominant carnivores share a number of attributes: wide-ranging diets, high assimilation and growth efficiencies and mostly a Type I functional response to food concentration. They fall into...

Plume Dispersion of Dilute Suspensions: A Model of Barge Overflow Adapted for Use in a Personal Computer

A practical method was developed to estimate the areal extent of the plume associated with the overflow of dredged material during barge filling operations in shallow waters. The predictive model is based on the Okubo-Pritchard relationship for horizontal diffusion; it solves the transport equation which governs the distribution of total suspended solids or dissolved species. The model runs in a Personal Computer and provides the spatial distribution of particulate concentrations in the plume from minimum information on local hydrography, the intensity of advective and dispersive processes and the characteristics and discharge rate of the dredged material. The extent of the plume is defined as the isoline of acceptable concentration of a specified material. The rate of decay of the plume once the overflow terminates is also computed.

Influence of Sediment Disturbance and Water Flow on the Growth of the Soft-Shell Clam,Mya arenariaL.

The importance of sediment disturbance and water flow to the production of the soft-shell clam, Mya arenaria, was assessed in laboratory flumes by measuring growth rates of clams exposed to a gradation of bed shear stress, free-stream velocity, and frequency and depth of sediment disturbance over a 10-m period. In the absence of sediment disturbance, growth of soft-tissue was directly proportional to both free-stream (U) and shear (U*) velocity (r2 = 0.64 and 0.72, respectively). It was suggested that increased organic seston flux linked higher water flow to higher growth. In all treatments, maximum growth rates were observed with daily disturbance of the top centimeter of sediment. No level of disturbance resulted in growth rates lower than those of undisturbed clams in low flow (U = 0.4 cm∙s−1, U* = 0.1 cm∙s−1). The stimulation of growth under maximum sediment disturbance was removed when U exceeded ~3 cm∙s−1(U* = 0.7 cm∙s−1). An energy budget for M. arenaria indicated that the amount of organic material suspended during sediment disturbance was insufficient to account for the increased growth in clams subjected to high levels of disturbance. It was suggested that the sediment disturbance associated with intense clam harvesting, and changes in local hydrography resulting from coastal development, may be responsible for some of the unexplained growth variation in commercial clam stocks.

Stratigraphy and depositional history of the Pliocene Bianco section, Calabria, southern Italy

An integrated micropaleontological and geochemical study was carried out on the Pliocene-age Bianco section located in Calabria, southern Italy. This section is somewhat unique for the Pliocene of the Mediterranean region in that it contains abundant calcareous and siliceous microfossils. Based on the biostratigraphic findings, it ranges in age from approximately 3.7-3.0 Ma. The Bianco section is composed of marly mudstones intercalated with diatomites, with the diatomites being particularly common in the upper 50 m of the section (above 3.1 Ma). The diatomites contain an abundant benthic foraminiferal assemblage and have a low organic carbon content indicating that bottom waters were fairly well-oxygenated during their deposition. Faunal and floral indicators suggest a cooling of surface waters in this region at 3.1 Ma. The diatom assemblages within the Bianco diatomites are very similar to those living in the Gulf of California, suggesting an upwelling origin for these silica-rich units. A model is proposed which attributes diatomite formation to upwelling induced by climatically controlled changes in local hydrography.

Transport of mud on continental shelves: Evidence from the Texas Shelf

Transmissivity and suspended-sediment data from three cruises on the East Texas continental shelf confirm that a bottom nepheloid layer (BNL) exists across the shelf; this layer is most turbid in the nearshore and outer shelf regions. In addition, surface nepheloid layers exist close to shore due to river and bay outflows, and on the outer shelf intermediate nepheloid layers are present as a result of quasi-horizontal advection from the BNL. The character of the BNL is not directly linked to local hydrography or substrate, being instead a function of the shelf dynamics. In the nearshore regime high-energy coastal processes and high sediment input from bays and rivers maintain the BNL. At the shelf edge, the BNL is formed by near-inertial internal waves and shelf waves which resuspend and transport fine sediment. Present-day sediment deposition on the East Texas Shelf can be directly related to the above processes. Mud is accumulating in the nearshore environment, due to river input, and on the inner and midshelf regions as a result of deposition from BNLs and SNLs. On the outer shelf, BNLs and INLs transport fine sediment further offshore, so that in effect suspended sediment bypasses the outer shelf.

Morphology and Sedimentology of a Central Brazos River Point Bar, Boxley Bend, Brazos County, Texas: ABSTRACT

A reconnaissance of Brazos River point bars reveals great variety in their morphology and sedimentology, owing to the complex interaction of climate, local hydrography, and local sediment sources. This paper presents the first in a series of studies of point bars of the Brazos River and concentrates on the Boxley Bend point bar near Snook, Texas. The summer morphology of the point bar is complex, consisting of an upper and lower tier separated by a scarp but connected by a central ramp. The surfaces of the lower tier and ramp display numerous large gravel bars and shallow scour pools as well as low-amplitude sand waves, ripples, and current lineations. In cross section, the lower tier and ramp are characterized by (1) trough cross-bedded, medium to fine sand produced by megaripple migration during floods; (2) massive gravel beds, the product of formation and migration of gravel bars during floods; and (3) fine rippled sand and clay drapes formed during falling flood. The surface of the upper tier displays ripple-laminated eolian sand and deflation deposits of mud clasts. In cross section, the upper tier is characterized by thick beds of horizontally stratified fine sand. During the winter, the entire surface of themore » point bar is covered by large (2 m high) transverse bars separated by deep scour troughs. Transverse bars migrate into the troughs to produce a sequence of fine sand with backflow ripple cross-stratification overlain by thick beds of tabular cross-bedded medium sand. The transverse bars appear to be transitory features with little net effect on sedimentation, because they are removed from the surface of the point bar by summertime.« less

Effects of El Niño on local hydrography and growth of the giant kelp, Macrocystis pyrifera, at Santa Catalina Island, California1

Deepened isotherms associated with El Niño resulted in severe nutrient limitation and very low kelp productivity during the last half of 1983. Frond growth rates were so low that terminal blades formed before reaching the surface, eliminating the canopy. Frond initiation rates were also extremely low, resulting in significant reductions in mean plant size. Plants growing above 10 m were more severely affected than plants at 20 m. These results suggest that nutrient pulses associated with internal waves are critical for survival of Macrocystis pyrifera in nutritionally marginal habitats in southern California.

Oceanic winds measured from the seafloor

Acoustic ambient noise in the ocean at frequencies of 4.3, 8.0, and 14.5 kHz has been shown to be highly correlated with surface wind speed. Measurement of noise at the sea floor yields estimates of wind speed to within ±1 m/s (r2≥0.845) when compared with coincident surface observations. The frequency dependence of the wind speed‐noise relation reported by others (17 dB/decade) has been confirmed, except that separate calibrations are required above and below the speed characterizing whitecap formation. There is also some evidence of local hydrography influencing the absolute calibration.

Rapid and Widespread Generation of Recent Oolitic Hardgrounds on a High Energy Bahamian Platform, Eleuthera Bank, Bahamas

ABSTRACT Contemporary intergranular submarine cementation occurs in close association with strongly agitated oolitic sands in the Schooner Cays tidal bar belt, resulting in widespread generation of surficial oolitic hardgrounds. Hardground formation takes place from near the shelf margin bankward up to 15-17 kilometers, within the zone of active oolitic sand, in water depths ranging from 1-II meters. Two forms of lithified oolitic sediment (hardgrounds) are recognized: in situ surficial crusts and unattached clasts (erosional crust fragments). Isopachous fibrous aragonite constitutes the major physicochemical cement; other cement forms of aragonite and high magnesium calcite are widespread but subordinate. Previously undocumented, probable chasmolithic/endolithic algae also effectively bind and cement surficial unconsolidated oolitic sediment by filament calcification. Characteristic decrease in cementation downward from crust surfaces substantiates their formation at or near the sediment-water interface. Patterns of hardground formation apparently result from the interaction of tidal bar surface topography, local hydrography and stabilization by algal scum mats. Radiocarbon dating, field relationships and crust petrography document the rapid and contemporaneous formation of oolitic hardgrounds. Initial crust formation can occur within a few months or less. Hand probing of tidal bars and radiocarbon dating of erosional oolitic clasts suggest that similar patterns of hardground formation occurred during earlier growth stages of the tidal bars.