Stable Salinity Research Articles

Cardiac responses to salinity variations in two differently zoned Mediterranean limpets

Cardiac activity of two Mediterranean limpets was tested at different salinities. Patella caerulea inhabits the lower midlittoral where it is exposed to variations in salinity, while P. aspera experiences more stable salinity conditions in the infralittoral fringe. When exposed to moderate hypo- and hypersalinity (23 g l−1 and 43 g l−1) for 24 min, P. caerulea showed no significant variation in heart rate with respect to the control salinity (33 g l−1), while P. aspera exhibited a significant increase in heart rate in both conditions. This suggests a rise in metabolic rate due to activation of behavioural responses or physiological regulation. When exposed to extremely low salinity (3 g l−1) for 24 min, heart contractions ceased in most specimens of P. caerulea. A smaller number of specimens also displayed cessation of heart beat when exposed to extremely high salinity (63 g l−1). The heart beat resumed quickly in all specimens when they were returned to control salinity conditions. In contrast, cardiac activity was not interrupted in any of the P. aspera specimens at the 3 g l−1 and 63 g l−1 salinity levels, but strong bradycardia was evident. Contractile activity of the heart ceased in all specimens of P. caerulea and P. aspera when they were exposed to prolonged hypo-osmotic stress (3 g l−1 for 24 h). This acardia was largely reversible in P. caerulea, but most specimens of P. aspera did not recover from the treatment.

Stratification, vertical mixing, and upward ammonium flux in hypersaline Mono Lake, California

The effects of freshwater inputs and wind on stratification, vertical mixing, and upward fluxes of ammonium were evaluated during 6-yr (1989-1994) of monomixis (one period of complete mixing a year) in hypersaline Mono Lake, California. Falling lake level (evaporation > freshwater inputs) during 5-yr led to unstable salinity (S) profiles (mixed-layer S > hypolimnetic S) over the period of strong thermal stratification (June-October). Profiles in October 1991 and 1994 indicate the occurrence of double diffusive salt fingering because of unstable salinity stratification. Stable salinity stratification persisted throughout the summer and delayed holomixis in 1993, the only year freshwater inputs were greater than evaporation. Biweekly to monthly eddy diffusivities (Kz) at the thermocline were estimated with the flux-gradient heat method corrected for solar heating. June-September K Z averages ranged from 9.5 x 10 -7 m 2 /s (SE = 4.8 x 10 -7 ) during wet 1993 (0.4 m lake level rise) to 4.2x10 -6 m 2 /s (SE = 1.9x10 -6 ) during the 1989 drought (0.6 m lake level decrease). The Lake Number, an index of seiche-induced mixing below the mixed-layer, explained 68 % of the variance in April-September metalimnetic diffusivities. Over the 6-yr 50-90 % of the seasonal (April-September) upward flux of ammonium was used or converted within the metalimnion likely from algal uptake and nitrification.

Upper Permian lacustrine organic facies evolution, Southern Junggar Basin, NW China

The Jingjingzigou, Lucaogou, and Hongyanchi Formations of the southern Junggar basin together comprise over 1000 m of organic-rich lacustrine facies. They record an overall evolution from relatively shallow, evaporative lakes to freshwater lakes associated with fluvial systems. The Jingjingzigou Formation is characterized by low TOC and HI, and biomarker features (such as abundant β-carotane) consistent with a specialized saline or hypersaline biota. Biomarker distributions in Jingjingzigou Formation extracts most closely resemble oils from the giant Karamay oilfield. The Lucaogou Formation represents one of the richest and thickest lacustrine source rock intervals in the world, yet it contradicts conventional lacustrine source rock models in at least two important aspects. First, deposition occurred at middle paleolatitudes (39–43°N) rather than in the tropics. Second, limited nutrient supply in a drainage basin dominated by intermediate volcanic rocks appears to have caused low to moderate primary productivities. Stable salinity stratification and low inorganic sedimentation rates in a deep lake nonetheless resulted in deposits with up to 20% TOC and HI near 800. The overlying Hongyanchi Formation has 1–5% TOC but low HI, and was deposited in freshwater oxic to sub-oxic lakes.

A mathematical model of an estuarine seagrass

A discrete simulation model for the dynamics of a submerged macrophyte, Zostera capensis Setchell, is presented. The model describes the vegetative spread of Zostera sp. which occurs through runners. The model can be used to analyse the response of Zostera sp. to various freshwater-related scenarios. The model shows how reduced freshwater inflow and associated stable salinities have contributed to the increased Zostera sp. population. The effect of floods and dry conditions are simulated. The dynamics of Zostera sp. was investigated for various mouth breaching scenarios.

Seawater acclimation of tilapia, Oreochromis spilurus spilurus Gunter, fry and fingerlings

The effect of size and acclimation period to full-strength sea water was investigated using the mortality, growth, chloride cell proliferation and plasma Na concentration in four size groups (0.03-1.6 g mean initial weight) of mixed-parentage, sex-reversed, all-male fry and fingerlings of Oreochromis spilurus spilurus Günter obtained from University of Stirling. The fish were transferred from fresh water to sea water (36.6%0) through a continuous salinity increase during a 48, 72 or 120 h acclimation period. Survival was high in all groups, although the smallest fish (0.03 g) showed significantly higher mortality than the larger fish. The acclimation regime had no effect on growth rate, but 120 h acclimation gave highest final weight in the newly released group. Regardless of acclimation period, size and plasma Na concentration during the acclimation period, the plasma Na level stabilized within 12 h after full salinity in the two largest size groups. Ovoid voluminous chloride cells proliferated in all groups during the acclimation period, and numbers stabilized with stable salinity. It is concluded in this study that O. spilurus spilurus can successfully be acclimated to sea water with a gradual continuous acclimation period of 48 h, even as newly released fry (0.03 g). However, an acclimation period of 120 h gave the highest final weight for this size group.

Effects of freshwater canal discharge on fish assemblages in a subtropical bay:field and laboratory observations

A 14 mo trawl survey was conducted at 8 study sites in Biscayne Bay, Florida, USA, to compare the species composition and structure of juvenile fish assemblages found near the mouths of freshwater flood control canals with those in similar areas with relatively stable salinity regimes. Water temperature, salinity, dissolved oxygen and depth measurements were recorded during fish sampling and bottom vcgctation was also quantified. The survey yielded a total of 38 134 individuals from 95 taxa. Fish species composition was similar among sites, but more species were collected from stableversus variable-salinity areas Mean fish abundance dnd the mean abundances of Euc~nostonius gula. Lagodon rhornboides, Opsanus beta and Lutjanus grlseus shared a general pattern of increase from north to s o ~ . ~ t h , with highest values occurring at one or more of the canal-influenced sites In contrast, mean specles nchness and the mean abundances of Lucanlaparva, Haenlirlon sciurw, H. plurnleri, and H. parra were signif~cantly greater at stable-salinity sltes than at variable-salinity sites Freshwdter challenge experiments \yere then condu.ctcd on each of the fishes above, as well as on 2 relatively uncommon species, Cynoscion nebulosus and Cypnnodon vadegatus. The mortality of groups exposed to a single, rapid, freshwater pulse (i.e. salinity was changed from approximately 32 ppt to 0 to 32 ppt over 2 h ) was compared with that of controls. Of the 8 fishes that dominated the nearshore habitats of Biscaync Bay, 5 exhibited no mortality and L. rhornboldrs, L. parva, and H. plurnleri exhibited 12.5, 50 and loo'% mortality rates, respectively. Mortality was 10Oo0 for the relatively uncommon C. nebulos~ls and C. variegatus. Results suggest that the differential osmoregulatory abilities of the species tested may underlie some, but not all, of the structural differences observed between fish assemblages from stable-sa1i:nity habitats versus those ddjacent to freshwater canals.

DISTRIBUTION OF EPIPHYTIC DIATOM SPECIES COMPOSITION, DIVERSITY AND BIOMASS ON DIFFERENT MACROALGAL HOSTS ALONG SEASONAL AND SALINITY GRADIENTS IN THE BALTIC SEA

In spring 1990 and 1991, some weeks after ice-break, macroalgae and their epiphytes were sampled from 8 areas along the stable salinity gradient of the Baltic Sea from the southern Baltic Sea proper (8‰) to the northern Bothnian Sea (5‰). The macroalgal hosts included the brown alga Pilayella littoralis (L.) Kjellm., the red alga Ceramium gobii Waern, and the green alga Cladophora glomerata (L.) Kutz. In addition, seasonal succession was studied from monthly samples throughout one growing season (March-November 1991) at one of the sampling sites (5‰ salinity). Host preference was highest in spring when the diatoms were newly colonizing the rapidly growing macroalgae, and higher in the Baltic Sea proper (higher salinity) than in the Bothnian Sea (lower salinity). Biomass was generally highest on Pilayella and lowest on Cladophora, whereas community diversity was generally highest on Ceramiutn and lowest on Pilayella. The differences in epiphytic diatom community composition and biomass between the three mac...

Early Use by Fish of a Mitigation Salt Marsh, Humboldt Bay, California

Fish numbers and biomass in a mitigation salt marsh, Humboldt Bay, California, were examined from July 1981 to October 1982 and were compared with a nearby established marsh to determine whether the restored marsh provided adequate mitigation for habitat lost due to construction of a nearby marina. The use by fish of channels adjacent to the two marshes and the channel at the Woodley Island Marina construction site, for which mitigation was required, were also compared. The mitigation marsh, adjacent to Freshwater Slough channel, was 5.2 km from the marina site. Fishes were sampled by otter trawl, ichthyoplankton net, fixed channel nets, drop traps, and beach seines. Thirty-one fish species and two crab species were collected. Wide ranges in seasonal salinities and water temperatures, and differences in marsh elevation influenced fish use of the mitigation marsh area. The intertidal area of the mitigation marsh, dominated by euryhaline sticklebacks and topsmelts, did not replace intertidal and subtidal habitat lost by marina construction, which had more stable salinities and water temperatures and was used extensively by juvenile English sole.

The role of buoyant thermals in salt gradient solar ponds and in convection more generally

A salt gradient solar pond is a large thermo-haline double-diffusive system of depth up to 3 m, having a lower convecting or storage zone with about 20% salt by weight, and a non-convecting uniformgradient zone above providing insulation. Heating by solar radiation is partly within the liquid and partly at the base. The principal fluid mechanics problems are growth of the lower convecting zone, emergence and growth of an upper convecting zone and the possible breakdown of the gradient zone into a number of convecting zones simultaneously. It is shown that the well accepted model of double-diffusive convection for ‘strong’ heating from below a stable salinity gradient does not apply at the very modest level of solar radiation, more especially when part (or even all) of the heat is generated within the fluid. New models are developed in which buoyant thermals play causal roles (as, indeed, they do in the case of ‘strong’ heating). Thermals from all three kinds of boundaries are investigated, and it is found that although there is a limited quantity of fluid in a thermal, connection is retained with the source during its lifetime. Thermals from the solid base are of the well known axisymmetric kind. Those from the boundary with air, and from liquid of a different density, the so-called ‘free’ boundaries, are shown to be two-dimensional and Gaussian in profile. Thermal ranges are found to be well defined and increase according to environmental (water) temperature, with a common form of range equation. The equation is calibrated experimentally for each type of thermal. For a given environmental temperature, axisymmetric thermals have by far the longest range whilst Gaussian thermals from a boundary with air have the shortest. If thermals do not reach the opposite boundary there is local heating or cooling ; if they do, there is boundary erosion and zone growth, that is, penetrative convection. Each convecting zone has two sets of thermals, upwards and downwards, which are the principal means of heat transfer. This is illustrated for the particular case of a solar pond. Finally, it is shown that the onset of ‘turbulence’ at Rayleigh numbers in the region of 5 × 10 4 to 10 5 marks the transition from laminar Bénard-Rayleigh heat flow to quantised flow by thermals.

The Influence of River Impoundment on the Estuarine Seagrass Zostera capensis Setchell

Photogrammatic methods spanning a 47-year period were used in conjunction with field studies to document the influence of altered catchment hydrology on the dynamics of Zostera capensis Setchell in the Kromme estuary, South Africa. Reduced freshwater inflow and associated lack of sedimentary disturbances, stable salinities and reducted turbidities are considered to have contributed to the increased Z. capensis population. Over the last nine years there has been a fourfold increase in the total standing biomass of Z. capensis (...)

The evolution of diffusive thermohaline staircases

Diffusive thermohaline staircases have been observed over wide regions of the Northwestern Weddell Sea in the March 1986 AMERIEZ experiments.1 The spatial distribution and temporal evolution of these staircases suggests that these layers may migrate upwards and also may bifurcate into multiple layers. These observations provided the motivation for a laboratory study of the evolution of thermohaline staircases. In the present study, a thermohaline staircase was generated by heating a stable salinity gradient from below. The thicknesses of the convecting layers, heat and salt transports across the interfaces, and migration of the interfaces due to interfacial turbulent mixing were measured. During the experiments, the interfaces and convecting layers evolve with time, ultimately assuming steady positions and thicknesses h. The experimental measurements of h, away from the bottom boundary, were found to be in good agreement with a theoretical prediction based on the assumption that a balance between the kinetic and potential energies of the turbulent eddies within the convecting layers sets the thicknesses of the convecting layers. Further, the laboratory data showed an excellent agreement with the oceanic data gathered by the previous investigators. Because of buoyancy transport across the interfaces, the stratification in the system weakens and the buoyancy jump Δb across the interfaces reduces. When the interfacial Richardson number Ri=Δbδ/w*2, where δ is the thickness of the interface and w* is the convection velocity in the layers, drops below a critical value Ric, which is about 1.5, the interfaces showed rapid migration to new quasiequilibrium levels, at which they remain stationary until Ri drops below Ric again. Flow visualization studies show that these rapid migrations are caused by engulfment of the interfacial layer fluid by the eddies of the lower, strongly convecting, layers. The experiments also show that, under certain conditions involving low heat fluxes and high density stratifications, heating of a stable salinity gradient does not lead to the formation of a thermohaline staircase structure; a criterion is developed to predict the conditions favorable for their formation. In addition, when the stratification is small and heat flux is high, the convectively mixed layer propagates upward as in a nonstratified fluid and the stratification tends to be destroyed without forming layers. The laboratory results successfully explain some of the field observations, while providing insight into the physics of thermohaline convection.

Propagation of plane surface waves over an underwater obstacle and a submerged plate

15. V. S. Belyaev and Yu. D. Chashechkin, "Free thermoconcentration convection regimes over a localized heat source," Izv. Akad. Nauk SSSR, Mekh. Zhidk. Gaza, No. 2 (1989). B. R. Morton, "Buoyant plumes in a moist atmosphere," J. Fluid Mech., ~, Part 2 (1957). A. B. Tsinober, Y. Yahalom, and D. J. Shlien, "A point source of heat in a stable salinity gradient," J. Fluid Mech., 135, 199 (1983). D. E. Mowbray, "The use of schlieren and shadowgraph techniques in the study of flow patterns in density stratified liquids," J. Fluid Mech., 27, Part 2 (1967). S. N. Netreba, "Reaction of stratified rotating media to local thermal effects," Prikl. Mat. Mekh., 50, No. 5 (1986). A. S. Kabanov and S. N. Netreba; "Free convection from a point heat source in a stably stratified medium," Prikl. Mat. Mekh., 46, No. i (1982). Oceanology, Physics of the Ocean, Vol. 2: Ocean Hydrodynamics [in Russian], Nauka, Moscow (1978). : G. K. Batchelor, An Introduction to Fluid Dynamics, Cambridge Univ. Press (1973). F. Olver, Introduction to Asymptotics and Special Functions, Academic Press, New York (1974). L. N. Sretenskii, Theory of Fluid Wave Motions [in Russian], Nauka, Moscow (1977).

Physiology of Two Species of Deep-Water Crabs, Chaceon Fenneri and C. Quinquedens: Gill Morphology, and Hemolymph Ionic and Nitrogen Concentrations

The general physiology of two species of deep-water crabs, Chaceonfenneri and C. quinquedens, found in thermally stable environments at moderate depths, was investigated. Structurefunction relationships of the gills indicate animals that are typical of environments characterized by high and stable salinity. The gill lamellae are composed entirely of respiratory epithelium; no ion-transporting chloride cells were observed. Carbonic anhydrase, a marker enzyme for ion transport in the gill, was present in very low levels of activity, and blood osmotic and ionic concentrations were not different from ambient at salinities of either 35 or 20 ppt. Animals failed to survive in salinities lower than 20 ppt. Oxygen uptake values were typical of coldwater, benthic species, regardless of habitat depth. Chaceon quinquedens appears to have both a higher rate of oxidative metabolism and a higher rate of protein metabolism than C. fenneri, which may be indicative of a higher rate of growth. Both species, however, appear to be

The formation of a layered structure when a stable salinity gradient is heated from below

It is well known that heating a stable salinity gradient from below leads to the formation of a series of turbulently convecting layers separated by stable diffusive interfaces. It is argued theoretically and demonstrated experimentally that the first mixed layer grows to a critical height δc, which is determined by a balance between the vertical kinetic and potential energies of the turbulent eddies, before a growing second layer separated from the first layer by a quasi-stationary stable density interface can be formed. Although the thermal boundary layer that develops over the propagating turbulent front can become unstable and form a second mixed region before the first layer grows to δc, the density interface formed between these two layers is not sufficiently stable to resist quick entrainment of the second layer into the lower layer. Some aspects of the growth of the first turbulent layer and possible application of the results to oceanic situations are also discussed.

Super-Critical States of Double-Diffusive Convection under Time-Periodic Heating

Super-critical states of a horizontal double-diffusive fluid layer under time-periodic heating is investigated by truncation models. It is found that if there is no salinity stratification, the fluid layer immediately attains a periodic motion tuned with the oscillation of external temperature field. If there is a stable salinity stratification, not only a periodic motion but a nonperiodic or chaotic motion appears in the supercritical states.

Variable marine productivity and high eolian input recorded by rhythmic black shales in Mid‐Cretaceous pelagic deposits from central Italy

Rhythmic interbedding of dark gray to black, laminated, calcareous shale (black shale) with lighter colored limestone, marlstone, or mudstone is a prominent feature of the Aptian‐Albian Scisti a Fucoidi in the Italian Apennines. Organic carbon contents of most black shales in the Scisti are less than 1.5%. Sedimentary structures and levels of bioturbation indicate that periods of poorly oxygenated benthic conditions alternated with more extended periods of well‐oxygenated benthic conditions during deposition of the Scisti. Geoochemical, isotopic, and visual studies of organic matter indicate variable marine productivity (generally low) and relatively high input of eolian dust during deposition of the Scisti black shales. One organic‐rich black shale near the middle of the formation may represent a brief period of stimulated marine fertility and high productivity coincident with benthic stagnation. Production of warm saline brines in evaporitic coastal settings, sinking of these brines into deepwater basinal settings, and development of stable salinity stratification is suggested as a causal linkage between arid climate, strong winds, and poorly oxygenated bottom waters in the Alpine‐Mediterranean Tethys during mid‐Cretaceous time.

The Effect of Time-Periodic Heating on the Stability of a Horizontal Double-Diffusive Fluid Layer

The effect of the time-periodic temperature oscillation upon the stability of a horizontal fluid layer in the presence of a stable salinity gradient is studied theoretically using the Galerkin method. The results of numerical calculation show that the critical Rayleigh number R a c becomes minimum at a certain positive value of the saline Rayleigh number R s . The destabilizing effect of the salinity stratification is found to be due to the coupling of the oscillating basic temperature field with the salinity disturbance.

A point source of heat in a stable salinity gradient

When a salinity gradient is heated at a single point, a hot plume is formed with a series of layers around and above it in a ‘Christmas-tree’ flow pattern. Qualitative visual observations of the development of this system are reported. Three kinds of layers are observed: the first kind is formed above the basic plume from a hierarchy of secondary plumes on top of the basic one, the second develops around the upper part of the basic plume, and is driven by the same mechanism as the layers in sidewall-heating experiments, and the third, forming around the lower part of the basic plume, is of the same nature as the second type but also has something in common with double-diffusive intrusions. A characteristic feature for all the three kinds of layers is the existence of systematic shearing motions and vortices. Quantitative estimates for the plume height and the thickness of the layers are obtained.

The benthos of South Lake, St Lucia following a period of stable salinities

The invertebrate benthos of South Lake, St Lucia was monitored monthly from August 1981 to July 1982 following a period of stable salinities of approximately 35°/oo. The overall mean biomass for th...

Interferometric study of stable salinity gradients heated from below or cooled from above

Mixing-layer development is investigated in laboratory experiments of salt-stratified solutions which are cooled from above or heated from below through the imposition of isothermal boundaries. A Mach-Zehnder interferometer is used to infer salt and density distributions within stable regions of the solution and to determine the extent of mixing-layer development. In both heating from below and cooling from above, this development differs significantly from that which has been observed for constant heating from below. Although the formation of a secondary mixed layer is observed, it does not lead to the development of additional mixed layers. Instead, the secondary layer eventually recedes, and the existence of a single mixed layer is restored. This behaviour is due to the isothermal boundary and the effect which it has no decreasing the heat transfer to or from the solution with increasing time. Once the condition of a single mixed layer is restored, extremely large (stable) density gradients develop in the boundary layer separating the mixed and stable regions, and subsequent growth of the mixed layer is slow. In cooling from above, mixing-layer development depends strongly on whether the isothermal boundary is in direct contact with the solution or separated by an air space.