Salinity Minimum Research Articles

Seasonal salinty variations in Cleveland Bay, northern Queensland

Weekly salinity measurements have been collected over 34 months at a 10 m deep station in Cleveland Bay. Minimum salinity during the summer wet season varied considerably from year to year and was mainly dependent on the discharge of small local rivers and the Burdekin River to the south-east. During the dry months, evaporative concentration generated a gradient of decreasing salinity from the shore across the continental shelf.

A simple maximum‐minimum salinity sampler

Bottles are described that collect water samples of maximum and minimum salinity when placed in a temporally varying estuary.

On the Hydrography of Shelf Waters off the Central Texas Gulf Coast

Abstract Temperature and salinity data from 1976 and 1977 are used to describe low-frequency hydrographic variations in Gulf of Mexico shelf waters off the central Texas coast. Data from 23 approximately monthly cruises define the annual cycle and suggest annually recurring seasonal events. Minimum salinities occur in late spring, when values decrease to as low as 18‰ over the inner shelf. Inner shelf salinities during the rest of the, year average 31–32‰. Surface salinities over the outer shelf may decrease to 32–33‰ in late spring, but deviate little from 36‰ at other times. Both the mean salinity and the standard deviation suggest that freshwater runoff effects are restricted largely to inner and mid-shelf waters, within 30 km of the coast. Highest annual surface temperatures are 28–29°C across the shelf in late summer. Lowest temperatures in February range from 12–13°C over the inner shelf to 20–21°C over the outer shelf; minima appear to be highly dependent on the severity of the winter season in a g...

Two phases of the phytoplankton community in the Baja California upwelling1

The method of principal component analysis has been applied to quantitative data on 60 species of phytoplankton from the cruises MESCAL I and MESCAL II. Dinoflagellatc dominance in the phytoplankton was associated with upwelling of water of relatively low salinity and lower nutrients from below the minimum salinity core of the California Current. Diatom dominance was related to upwelling of deeper saline and high nutrient water from the California Undercurrent.

Vertical distribution of polycystine radiolarians in the central North Pacific

Stratified opening/closing net tows in the upper 2000 m of the central North Pacific reveal the major features of the vertical zonation of polycystine radiolarians. Depth profiles of total radiolarian densities show high values at the surface, sharp decrease to a minimum at about 50 m, a maximum exceeding surface levels at about 100 m, and a decrease then to very low values at about 300 m which persist through the rest of the sampled water column. Individual species profiles indicate that the following zones can be identified: (1) A surface zone characterized by a sharp subsurface decrease from high densities at the surface. Densities are an order of magnitude lower by depths of 50–100 m. The rate of decrease resembles the temperature decrease in the thermocline. (2) An upper subsurface maximum zone characterized by species which are absent or very scarce at the surface and reach a pronounced maximum at about 50–100 m. Hydrographic features within the zone are the shallow salinity minimum and the oxygen maximum. A regional chlorophyll maximum occurs at about the same depth as the radiolarian maximum. (3) A lower subsurface maximum zone distinguished from the upper one by occurrence of the maximum about 100 m deeper. Species in this zone are generally scarce at the depth of the upper maximum while species in the upper maximum are scarce at the depth of this maximum. This zone is below the shallow salinity minimum and within the depth of the subjacent salinity maximum which characterizes the habitat of other (tripylean) radiolarians in this area. (4) A deep zone characterized by species which are never abundant but which are consistently absent from the upper few hundred meters. The North Pacific Intermediate Water, previously identified as a tripylean habitat, lies in the depth range of these species, though they may also extend deeper. Despite their lower densities, these species are conspicuous in deep-sea surface sediments.

The Shallow Salinity Minimum of the Eastern North Pacific in Winter

Abstract Extensive STD data at a 100 km station spacing from a recent winter cruise (March–April 1976) along 35°N between California and Japan are used to describe the large-scale (5000 km) shallow salinity minimum within the upper 500 m in the eastern half of the transect in relation to the salinity structure above and below it, and to the mesoscale (500 km) variations in salinity in the western Pacific. The shallow salinity minimum, which has a vertical scale of order 100 m, was found to be a continuous feature less than 200 m from the sea surface on more than 50 consecutive stations from about 125°W to about 175°W. The depth of the shallow salinity minimum has a large-scale maximum of about 160 m near 135°W and it decreases to about 60 m east and west of the maximum. The salinity, temperature and density at the shallow salinity minimum increase westward monotonically, and the salinity deficits between the salinity at the minimum and at the salinity maxima above and below the minimum decrease westward. ...

Influence of the Southern Atlantic Central Water on the distribution of salinity and oxygen in the northeast tropical Atlantic Ocean

Two main features of the Southern Atlantic Central Water allow its extention to be followed in the northern hemisphere: a salinity minimum located on σt = 26.8 and an oxygen minimum. The salinity minimum has been associated with the coastal upwelling undercurrent of the northwestern coast of Africa but it is not an exclusive feature of this undercurrent south of Cap Blanc. The lowest values of the oxygen minimum are observed in summer in the centre of the Guinea Dome.

Maintenance of Non-Breeding Populations of the Estuarine Prawn Callianassa Kraussi (Crustacea, Anomura, Thalassinidea)

Despite the occurrence of populations of the anomuran prawn Callianassa kraussi Stebbins in salinities as low as one part per thousand, investigation showed that a minimum salinity of 25-30 parts per thousand was required for successful development of the eggs and larval stages. Dispersal into areas of low salinity and maintenance of these non-breeding populations is accomplished by migration of the early post-larval stages from higher salinity areas.

A study of the subarctic boundary region in the Western North Pacific

During autumn 1968 an oceanographic investigation was conducted in the region of the Subarctic boundary between 155°E and 180°. The geostrophic flow of the upper 500 m was remarkably similar in direction; hence the salinity-minimum, Intermediate water must have the same path of flow as water at the surface. A water mass analysis revealed a decrease in the percentage of Subarctic water to the south and east, plus an increase in the homogeneity of water to the east, which supports Reid's conclusions that the salinity minimum results mainly from lateral mixing in the pycnocline in this region. Salinity at the minimum increases toward the south and east, and the density at this level also increases slightly from the western to the central Pacific, perhaps as a result of unequal vertical mixing above and below the minimum.

Oceanographic Features, Currents, and Transport in Cabot Strait

Seventy oceanographic sections across Cabot Strait, taken at various times of the year between 1950 and 1974, were utilized to describe the average oceanographic featues, currents, and volume transport patterns as well as their variations with depth and time. The water mass structure in Cabot Strait is a two-layered structure; the water in the upper 50–100 m is typically moving seaward, while below that depth it is commonly found to be moving into the Gulf. The character of the upper layer which is normally not of uniform thickness across the Strait, but is distinctly wedge-shaped, is subject to considerable seasonal variation, whereas that of the lower is quite uniform the year round. Seasonal and long-term variations of the physical properties in Cabot Strait are described.Outflow through Cabot Strait is shown to be concentrated in the upper layer off Cape Breton and is balanced by inflow at intermediate depths on the Newfoundland side and in the deep portions of the section. The maximum and minimum transports, both inflow and outflow, occur in August and June, respectively. The net outward volume transport through the Strait increases from 9 × 103m3/s in April to 25 × 103m3/s in August and decreases to about 0.1 × 103m3/s in February. The weighted mean value, 13 × 103m3/s agrees well with the value obtained from an estimate of net freshwater input rate (run-off plus precipitation minus evaporation) above the section. The maximum transport occurs at times of surface minimum salinity. Horizontal advective transport of salt is found to be more important than horizontal diffusive transport. Recommendations for future transport studies in Cabot Strait are presented.

Relation of radiolarian distributions to subsurface hydrography in the North Pacific

Based on opening-closing net plankton collections, the vertical and horizontal distributions of some triplyean radiolarian species have been plotted for the eastern North Pacific. In a mid-ocean profile of the upper 400 m, there emerge: (1) a zone including subarctic near-surface waters and extending southward at greater depths, (2) a narrow zone to the south concentrated above the first zone, and (3) a zone yet farther south ranging from the surface to a lower boundary that shoals northward. These zones correspond generally to the following respective hydrographic features: (1) the Subarctic Water Mass and the Intermediate Water, centered on a salinity minimum, (2) an unnamed mid-latitude zone characterized by a salinity maximum above the salinity minimum and (3) the warm, high salinity, Central Water Mass. Toward the North American continent, distributions of species from the two more northern (and deeper) zones overlap as the respective water masses become mixed in the California Current. The southernmost (and shallowest) zone retains hydrographic and biologic continuity as a surface layer at the outer edge of the California Current. Semi-closed circulation systems in the hydrographic zones provide physical and biological continuity within the zones with minor interchange among them. The horizontal distributions of these radiolarians in the upper 150 m are comparable to those of other kinds of plankton in the same area, and they are generally consistent, hydrographically, with previously reported distributions of the same species in other oceans.

The plankton of Lake Eyre

On the occasion of only its second filling this century, Lake Eyre was sampled seven times between July 1974 (when the minimum salinity value of 7%, was obtained) and April 1975 (salinity 40%,). The dominant zooplanktonic forms recorded were Moina mongolica (first Australian record), Apocyclops dengizicus, Diacypris, Hexarthra fennica and Brachionus plicatilis. It is thought that Daphniopsis pusilla was prevented from obtaining significant numbers because its relatively large size made it vulnerable to fish predation. The most significant phytoplanktonic genera recorded were Nodularia, Anabaenopsis and Glaucocystopsis.

Salinity Distribution in the Tay Estuary.

SynopsisSalinity distribution in the Tay estuary measured during the years 1969–70 is influenced by freshwater flow and tidal range. Between Pool and Flisk, tidal-depth-mean salinity is a strong function of river flow but is much less influenced by tidal range. The relationship between salinity range (difference between maximum and minimum depth-mean salinities) and tidal range can be approximated by a linear function. The observed vertical salinity distribution varies with tidal state. The net non-tidal circulation has been estimated at Pool, Broughty Ferry, Newport, Balmerino and Flisk, and found to be dependent on river flow and position.

Surface waters in the north of the Coral Sea

North of New Guinea, the eastward flow is not fast enough to bring the diluted water from the westernmost Pacific to the Coral Sea where, in the north, from February to June, the surface salinity is less than 34.5‰. This low salinity is always associated with a west wind component bringing rainfall. The surface salinity chart in January-February 1971 shows a salinity minimum isolated from its once supposed western origin by saltier water in the north of New Guinea. These features suggest local formation of this low salinity.

Calcium in the South Pacific, and its correlation with carbonate alkalinity

Calcium concentrations in profiles from the western boundary region of the South Pacific were measured by a modified method of J.B. Pate and R.J. Robinson. The calcium content increases with depth from salinity minimum to benthic front, and then decreases slightly to the Antarctic Bottom Water. The calcium content was found to be closely related to carbonate alkalinity. The relation is expressed by the equation:(Ca) = 9.1497 + 0.5260 × (C.A.) where (C.A.) is carbonate alkalinity in meq/kg, and (Ca) is calcium content in mmole/kg. The slope, 0.5260, is consistent with the theoretical value predicted by the dissolution of calcium carbonate within the experimental error.

Development of Young Bluefish (Pomatomus saltatrix) and Distribution of Eggs and Young in Virginian Coastal Waters

Cruises were made off Chesapeake Bight from December 1959 through April 1963 to determine species composition and distribution of fishes spawned on the Continental Shelf. Illustrations of young fish, herein provided, now complete figures from newly hatched larvae to juveniles. Verbal descriptions provide prominent features of young bluefish to aid in identification and osteological development and to compare similar appearing larvae. Bluefish larvae can be distinguished from similar appearing species (Peprilus triacanthus and Urophycis chuss) with which they were taken in Chesapeake Bight by myomere numbers and pigment patterns. Bluefish larvae closely resemble the larval scombrids, Scomber scombrus and S. japonicus, and larval carangids. They may be separated by myomere numbers or relative lengths of the preopercular spine. Continental Shelf waters off the Virginia-North Carolina coast are major spawning grounds of bluefish. Major spawning sites in the Chesapeake Bight were located over the outer half of the shelf between 55 km (30 nautical mi) and 148 km (80 nautical mi) offshore and where water temperatures were 22 C or greater and surface salinities were 31‰ or greater. Minimum temperature at the onset of spawning was 18 C and minimum salinity was 26.6%. Our data show that bluefish spawning commences in June, peaks in July, and continues into August. Peak spawning activity occurred in early evening near sundown (1900-2100 hr). Eggs are thought to be transported south and offshore by prevailing surface currents. Larval bluefish inhabit surface waters and greatest numbers were found near the edge of the Continental Shelf. Juvenile bluefish move inshore during their first growing season. Despite intensive sampling, none were captured in offshore waters. We speculate that with growth young bluefish move to depths above the thermocline. We suspect that the most important single factor in determining the fate of every year class is the circulation of Continental Shelf waters.

A COMPONENT OF LABRADOR SEA WATER IN THE BAY OF BISCAY

The salinity minimum at about 1,900 m in the Bay of Biscay, which lies along a well‐defined line on a θ,S graph, is used to test the idea of large‐scale mixing along a neutral surface. Contours of temperature and salinity values along a neutral surface indicate that the source region responsible for the salinity minimum lies off the slopes of Newfoundland. This description gains support from the continuity of both the salinity minimum on a T,S curve across the mid‐Atlantic Ridge and the distribution of the oxygen saturation contours on the mid‐Atlantic Ridge.

The physical and chemical oceanography of the Rockall channel

Between August, 1963, and February, 1968, a hydrographic section was worked between Rockall Bank and Malin Head on twelve occasions. In addition to the vertical distributions of temperature, salinity and their variabilities, the data allow the annual cycles of temperature and density to be described to the depth of seasonal mixing (500–600 m). Results from repeated chemical sampling at two stations indicate the scale of annual charges in dissolved oxygen, phosphate and silicate and their general distribution through the water column. A 23-year series of surface observations in the area provides data about year-to-year changes. The T-S characteristics of the upper waters represent a mixed water formed in the vicinity of the Biscay-Porcupine Bank continental shelf, and not North Atlantic Central Water, during the years of our surveys. (Earlier work shows that this is not always so.) Low oxygen content clearly indicated the presence of Gulf of Gibraltar Water between depths of 800–1200 m, and below this a salinity minimum characterized Labrador Sea Water. At the lowest levels a water-mass having a Norwegian Sea Deep Water component was observed and limited evidence points to a source in the northern Rockall Channel. The largest northeast-going transport was normally found over the western half of the section, but a smaller northeast-going flow occured at the Irish continental slope. A net southwesterly flow above 1800 m was found once (July, 1964), but net northeasterly transport was the general rule. The mean 0–500 m volume transport relative to 1800 m was 2·70 x 10 6 m 3 sec −1. At 500–1200 m a mean transport of 0·99 x 10 6 m 3sec −1 must have left the Channel by the northwestern gaps. Correlations significant at the 0·1% level were found between net transport in the upper layers and 5-day mean east-southeast wind components. Estimates made from these suggest that the mean annual northeast-going 0–500 m transport in the years 1964 and 1965 was about 3 x 10 6 m 3sec −1.

Transpacific hydrographic sections at Lats. 43°S and 28°S: the SCORPIO expedition—III. Upper water and a note on southward flow at mid-depth

The characteristics of the upper 2000 m on the SCORPIO plates are dominated by the subtropical anticyclonic gyre which brings shallower waters from higher latitudes equatorward along the eastern boundary. These incoming waters are cold, of low salinity, and high in oxygen and nutrient concentrations. Within the gyre they are warmed, made more saline, and the oxygen and nutrient concentrations modified. Exchange with the inter-tropical waters also modifies the characteristics, and the waters that return poleward near the western boundary are substantially different from those that entered in the east. Along the SCORPIO sections, temperature decreases monotonically downward to great depths, but the other water characteristics have various maxima and minima, the consequence of the different layers that make up the entering water and of the several sorts of modifications and exchanges that take place within the gyre.The principal salinity feature is the immense body of fresher water that enters from the south in the east, flowing at various depths according to the density field. A major subsurface salinity minimum, the Intermediate Water, is obvious on the greater part of both plates, and a shallower but similar minimum lies above it in the east, separated by a more saline layer extending poleward from low latitudes, as part of the eastern-boundary poleward countercurrent.The higher salinities from the great central south Pacific evaporation cell, centered north of the SCORPIO sections, also occur as weak subsurface maxima returning poleward near New Zealand.The oxygen distribution has a slight maximum near 50m to 100m depth, a relic in these (mostly) summer data of the higher concentrations of the winter mixed layer. Beneath this maximum is the decrease in oxygen that is usual in the upper part of the pycnocline. In these sections this decrease creates a shallow (150m to 400m) minimum because the underlying Intermediate Water, which dominates most of the 500-m to 1500-m depth range, is higher in oxygen concentration and accounts for the oxygen maximum immediately above the deepest oxygen minimum. The pycnocline oxygen minimum is intensified in the east by the poleward subsurface flow of water from lower latitudes where the oxygen concentration is very low.The deepest oxygen minimum has its extreme concentrations in two separate cells, in the eastern area and the central area, separated by a slightly greater minimum in the water overlying the East Pacific Rise.The nutrient distributions reflect principally the major oxygen features in the upper layers. The pycnocline oxygen minimum in the east is also a nutrient maximum, so great that the underlying Intermediate Water, even at high concentrations, exists as a nutrient minimum in the eastern parts. Farther west the nutrient concentrations increase monotonically downward through the Intermediate Water oxygen maximum: phosphate and nitrate reach maximum concentrations corresponding closely to the two cells of the deepest oxygen minimum. Silicate, however, has a deep maximum only in the central Pacific Ocean, somewhat deeper than the maximum in the other nutrients. In the east it increases monotonically from the level of the Intermediate Water all the way to the bottom.A comparison of the SCORPIO sections with earlier observations in both the South and North Pacific leads to the suggestion that the separate vertical minimum in oxygen and the associated maximum in phosphate east of the Kermadec Ridge on the SCORPIO sections are a consequence of southward flow at these depths from the North Pacific. There is evidence of an anticyclonic circulation that extends to more than 2000 m depth in these latitudes, confined at depths below 1500 m to the central ocean by the Tonga and Kermadec ridges. The southward-flowing western limb of this anticyclone extends from the intertropical zone to the Antarctic Circumpolar Current. At these depths it may carry water that has entered the North Pacific as dense abyssal water, moderate in oxygen and phosphate, has become nutrient-rich and oxygen-poor as it rises in the North Pacific and mixes with the less dense water, and returns at mid-depth.

Pampano, Trachinotus ovatus L. (Pisces, Carangidae) and its adaptability to various saline conditions

Laboratory experiments were conducted to determine the adaptability of Trachinotus ovatus to various salt concentrations. It was found that the minimum salinity tolerated by juvenile T. ovatus (pampano) on direct transfer is 20% sea water (S=8.7‰). Through gradual adaptation the fish can withstand salinity up to 1.5‰.