Showing papers on "Water column published in 1982"

After the deluge: Mediterranean stagnation and sapropel formation

Abstract: In an East Mediterranean marine core, the upper sapropel begins soon after the start of a global event—a very heavy precipitation which occurred in the equatorial latitudes during the late Glacial–early Holocene. This heavy precipitation in Africa, channelled by the Nile River across 35° of latitude, produced a low-salinity surface layer in the East Mediterranean. In this confined basin, with high bottom salinity, the steep salinity gradient stratified the water column. The stagnant bottom waters triggered the sapropel formation. Cretaceous sapropels in the tropical oceans may result from the same chain of events in warm, humid climates, with contrasting wet-and-dry seasonal rhythm.

Relative Contributions of Ice Algae, Phytoplankton, and Benthic Microalgae to Primary Production in Nearshore Regions of the Beaufort Sea

Abstract: Phytoplankton, ice algae, and benthic microalgae are the three sources of primary production in the western Beaufort Sea in winter and spring. Phytoplankton levels in winter are low with chlorophyll a levels near the limit of detection. Microflagellates are the most abundant organisms present in the water column along with a few diatoms. Low chlorophyll a, standing stock, and primary productivity continue into June when the ice breaks up. Cells are present in sea ice from the time it forms in the fall and are generally scattered throughout the ice thickness. Microflagellates are the most abundant organisms, but some diatoms, mostly pennate species, are also present. Cells concentrate in the bottom few cm of ice during March-April in response to increasing light levels. Growth continues until late May-early June when maximum production and standing stock occur. Benthic microalgal production was barely detectable in spring although chlorophyll a levels were high, perhaps left from the previous production season. Light is apparently the major factor controlling production in the spring, with the ice algae being able to take advantage of increasing light levels early in spring. This community shades both the water column and benthos so that production in those habitats does not increase until after the ice algae disappear in early June, but the ice community may be inhibited by layers of sediment in the ice. During this study, the ice algae provided about two-thirds and the phytoplankton one-third of the spring primary production; the benthic community contribution was negligible. Key words: western Beaufort Sea, phytoplankton, ice algae, benthic microalgae, primary productivity, chlorophyll a , standing stock, species present, environmental factors

Nutrient exchange across the sediment-water interface in the Potomac River estuary

Abstract: The flux of ammonia, phosphate, silica and radon-222 from Potomac tidal river and estuary sediments is controlled by processes occurring at the sediment-water interface and within surficial sediment. Calculated diffusive fluxes range between 0·6 and 6·5 mmol m−2 day−1 for ammonia, 0·020 and 0·30 mmol m−2 day−1 for phosphate, and 1·3 and 3·8 mmol m−2 day−1 for silica. Measured in situ fluxes range between 1 and 21 mmol m−2 day−1 for ammonia, 0·1 and 2·0 mmol m−2 day−1 for phosphate, and 2 and 19 mmol m−2 day−1 for silica. The ratio of in situ fluxes to diffusive fluxes (flux enhancement) varied between 1·6 and 5·2 in the tidal river, between 2·0 and 20 in the transition zone, and from 1·3 to 5·1 in the lower estuary. The large flux enhancements from transition zone sediments are attributed to macrofaunal irrigation. Nutrient flux enhancements are correlated with radon flux enhancements, suggesting that fluxes may originate from a common region and that nutrients are regenerated within the upper 10–20 cm of the sediment column. The low fluxes of phosphate from tidal viver sediments reflect the control benthic sediment exerts on phosphorus through sorption by sedimentary iron oxyhydroxides. In the tidal river, benthic fluxes of ammonia and phosphate equal one-half and one-third of the nutrient input of the Blue Plains sewage treatment plant. In the tidal Potomac River, benthic sediment regeneration supplies a significant fraction of the nutrients utilized by primary producers in the water column during the summer months.

Sediment nutrient regeneration in three North Carolina estuaries

Abstract: Sediment-water column exchanges of oxygen, ammonium, nitrate and phosphase were measured in three North Carolina estuaries by means of diverinstalled chambers placed in the sediments. Significant fluxes were observed in two of the estuaries characterized as organic-rich, depositional environments. The third was a highly flushed system dominated by sandy to shelly muds, and no measurable fluxes were found. In the former two estuaries, fluxes were weakly influenced by temperature, and ammonium and phosphate fluxes were highly correlated. Nitrate fluxes were very small, and phosphate sorption was frequently observed at temperatures less than 15°C. Data from this research and the literature show a general correlation of sediment inorganic N and P fluxes and the computed water column N and P uptake, demonstrating that sediments supply, as an annual average, 28–35% of the N and P required for the primary production of shallow marine systems.

Bio-optical classification and model of natural waters. 21

Abstract: A bio-optical tcchniquc is presented which allows both the classification and optical modeling of natural waters. The spectral diffllse attenuation coefficient for irradiance (300-700 nm) has been related to two biological quantities: the total concentration of chlorophyll-like pigments and the dissolved organic material (DOM). Th c model is a component model which nllgmcnts our previous work in that it includes new data in the analysis, utilizes an improved analytic fit, extends into the UV region of the spectrum, and adds a DOM component. Our model, which permits quantitative calculation of spectral irradiance at any point in the water column in a variety of nontcrrigcnous water types, facilitates prcdictivc modcling. The term bio-optical state was coined (Smith and Baker 1978u) to represent a measure of the total effect of biological material on the optical properties of natural waters. WC then introduced (Smith and Baker 1978b) a general technique for optically classifying and predictively modeling natural waters in terms of the total chlorophyll-like pigment concentration in these waters, hereafter referred to as SBl. The method was built upon two concepts: the pioneering insight of Jcrlov (1951, 1976) that ocean waters could be optically classified; and the idea that the diffuse attenuation coefficient for irradiance could be partitioned (Riley 1956; Steele and Menzel 1962; Yentsch 1963) into the components responsible for the total attenuation (e.g. water, phytoplankton, and other attenuating substances). Our first classification (SBl) was based on spectral irradiance data from a wide range of ocean waters varying in chlorophyll concentrations from 0.01 to 10 mg Chl LL * mP3 (Tyler and Smith 1967, 1970; Smith and Tyler 1968; Smith 1973; Smith and Baker 1978u,b) whose dissolved and suspended materials are primarily of bio

Upwelling as a source of nutrients for the Great Barrier Reef ecosystems: a solution to Darwin's question?

Abstract: The Great Barrier Reef shelf ecosystem is examined for nutrient enrichment from within the seasonal thermocline of the adjacent Coral Sea using moored current and temperature recorders and chemical data from a year of hydrology cruises at 3 to 5 wk intervals. The East Australian Current is found to pulsate in strength over the continental slope with a period near 90 d and to pump cold, saline, nutrient rich water u p the slope to the shelf break. The nutrients are then pumped inshore in a bottom Ekman layer forced by periodic reversals in the longshore wind component. The period of this cycle is 12 to 25 d in summer (30 d year round average) and the bottom surges have an alternating onshoreoffshore speed up to 10 cm S-'. Upwelling intrusions tend to be confined near the bottom and phytoplankton development quickly takes place inshore of the shelf break. There are return surface flows which preserve the mass budget and carry silicate rich Lagoon water offshore while nitrogen rich shelf break water is carried onshore. Upwelling intrusions penetrate across the entire zone of reefs, but rarely into the Lagoon. Nutrition is del~vered out of the shelf thermocline to the living coral of reefs by localised upwelling induced by the reefs. Bottom chlorophyll concentrations average 0.4 mg m-3 a t the inner reefs and 0.8 mg m-3 near the shelf break while surface concentrations average 0.3 mg m-3; annual top and bottom variances are respectively 0.5 and 1.9 mg m-3 and there is no apparent seasonal cycle. The estimated onshore nitrogen flux in a 10 m thick bottom layer gives an annual nitrogen input of 20 yg at 1-' throughout the water column in a 50 km zone of reefs, an enormous value for tropical waters.

Environmental distribution of Recent benthic foraminifera on the northeast United States continental slope

Abstract: Several bathymetrically consistent Recent benthic foraminiferal biofacies have been recognized from the continental slope south-east of Cape Cod. Faunal assemblages are dominated by Globobulimina / Bulimina (upper slope; less than 1,000 m) and Uvigerina peregrina (lower slope-uppermost rise; water depths between 1,000 and 2,500 m). The Globobulimina / Bulimina assemblage coincides with the oxygen minimum zone; this agrees with the occurrence of Globobulimina in Mediterranean sapropels, organic-rich sediments deposited under anoxic conditions. Previous studies have noted the association of U. peregrina with bathyal water depths, deep-water temperatures of 3 to 4 ° C, and water of low oxygen content. However, correlations between abundance of U. peregrina and water depth or temperature are not the same everywhere, and no correlation with dissolved oxygen in the water column is seen on the United States continental slope and rise. The highest abundances of U. peregrina coincide with maxima of organic carbon and silt within the slope sediments. This suggests that the distribution of U. peregrina in this region may be influenced more by low oxygen in the sediments, rather than by low oxygen content of the overlying water.

Vertical separation of light and available nutrients as a factor causing replacement of green algae by blue-green algae in the plankton of a stratified lake

Abstract: (1) A change from the green alga, Dictyosphaerium pulchellum to the blue-green algae Microcystis aeruginosa and Anabaena spiroides occurred in the plankton of Mt Bold reservoir, South Australia, during November and December 1978. (2) The reservoir was 30-34 m deep, thermally stratified with water mixed to 6-7 m, and a euphotic zone of less than 2.7 m. Measurements of photosynthesis and light penetration showed that photosynthesis was restricted probably to the upper 2.5 m. (3) Growth experiments with eight cultured species, and the natural phytoplankton assemblage, showed that during this change there was a decline of the potential of the water for algal growth to undetectable levels at a depth of 8 m. This could be restored by the combined addition of nitrogen, phosphorus and Fe-EDTA. (4) Continuous measurement of concentration of chlorophyll a in the water column demonstrated that the blue-green algal community was able to migrate to a depth of 12 m despite substantial density barriers. (5) In situ growth experiments, using dialysis bags, showed that populations which were artificially circulated between 0.2 and 10 m, were able to grow, whereas those maintained at a single depth (0-2 m or 10 m) were not. (6) The ability of blue-green algae to overcome successfully this spatial separation between light and nutrients was proposed as the probable cause of the change from green to blue-green algae.

Euryhaline zooplankton of the Sundays estuary and notes on trophic relationships

Abstract: The euryhaline component of the Zooplankton in the Sundays River estuary was sampled monthly at 10 stations from August 1979 to April 1981. In deeper regions surface and near-bottom samples were taken (Stations 1-7) using WP2 nets. Shallow (< 2,0 m) stations were sampled in surface waters only. Water temperature ranged between 14-27 °C. A full salinity gradient was present and salinity stratification was well developed. Acartia longipatella was most abundant during winter and spring (maximum 73 300 m-3) in the lower estuary. The interaction of temperature and salinity as factors regulating temporal and spatial distribution was evident, these factors also interacting in the water column owing to stratification. The pioneer copepod species, seudodiaptomus hessei, attained high abundance following floods or increased river inflow. Three species of mysid shrimps were common in the plankton in summer, each species showing clear zones of maximum distribution. Zooplankton standing stock (dry mass) ranged from < ...

Ammonium regeneration and assimilation in eelgrass zostera marina beds

Abstract: Regeneration and assimilation of ammonium in the water column and in sediments of eelgrass (Zostera marina L.) beds of Izembek Lagoon and Crane Cove, Alaska, USA and Mangoku-Ura, northeastern Japan, were investigated by using a 15N isotope dilution technique. In the water column of Mangoku-Ura, ammonium was regenerated at a rate of 12 nmol l-1 h-1 and assimilated at a rate of 74 nmol l-1 h-1. The ammonium regeneration rate in sediments ranged from 2 to 150 nmol g-1 h-1, and with one exception, exceeded ammonium assimilation in sediments (0.3 to 77 nmol g-1 h-1). The ammonium regeneration in the water column was of little significance for the nitrogen supply to the eelgrass bed ecosystem. Net ammonium production (regeneration minus assimilation) in the sediment of Izembek Laggon met nitrogen demand for eelgrass growth, suggesting that ammonium regeneration in the sediments was very important for the nitrogen cycle in the eelgrass bed ecosystem.

Factors Controlling Phytoplankton Production in Lake Vanda (77°S)

Abstract: At least three floristically distinct communities of algae were distributed down the permanently ice-capped water column of Lake Vanda. Phytoplankton at each depth were highly specialized towards specific conditions of light and temperature. Maximum photosynthesis and algal biomass was at the bottom of the euphotic zone (55–57.5 m) immediately above a region of nutrient-rich anoxic water. This Phormidium-dominated community was adapted towards warm temperatures (18–20 °C) but a dim light regime. Dissolved inorganic N to P ratios in this region were extreme (> 5000:1) and the plankton demonstrated strong cellular P deficiency. A much smaller photosynthetic maximum was recorded in the middle of a large thermohaline convection cell at 25–30 m where P deficiency was less severe, but detectable. A microflagellate community immediately under the ice demonstrated the least response to phosphorus enrichment, but photosynthetic characteristics appeared to be more attuned to the low irradiances which prevail early ...

In situ Measurements of Nutrient and Oxygen Fluxes in a Coastal Marine Benthic Community

Abstract: Benthic nutrient and oxygen fluxes were measured during summer in the nearshore zone of the Georgia Bight, USA. Ammonium, nitrite, nitrate and phosphate were released by the sediments to the overlying water, while dissolved organic nitrogen was taken up by sediments. Oxygen uptake was equivalent to 1.1 g Cm-* d-'. Based on other data available for this area the benthos accounted for the remineralization of approximately 55 % of net primary production and 25 % of total community (benthic and pelagic) metabolism. To balance a simple carbon budget for the nearshore region during summer an outside source of organic matter, most likely originating in adjacent estuaries, is required. The benthos supplied 16 % of the N and 53 % of the P required by phytoplankton. Pore water nutrient concentrations suggested substantial denitrification (estimated at 4.9 mg Nm-2 d by mass balance) in sediments which may have caused the low N : P benthic release ratios we observed. The results support the hypothesis that benthic processes in shallow marine areas control the availability of N and P for water column production.

Phytoplankton production and water motion in surface mixed layers

Abstract: An analog, incubator technique is described to simulate the effect of vertical motions, either organized or turbulent, on the photosynthesis of phytoplankton. Experiments using this method on natural assemblages of phytoplankton in the eastern Canadian Arctic support the view that, for these stations, vertical mixing has little quantitative effect on water column primary production.

Zooplankton of a bathyal benthic boundary layer: In situ rates of oxygen consumption and ammonium excretion1

Abstract: Oxygen consumption and ammonium excretion rates of bathyal macro- and mcgazooplankton from a benthic boundary layer were measured in situ. Collections of plankton were made using a four-chambcrcd slurp gun rcspiromctcr manipulated by the submcrsiblc Alvin in the Santa Catalina Basin off southern California at lcvcls 1, 5, 10, and 50 m above bottom in a 1,300-m water column. Abundance, biomass, oxygen consumption, and ammonium cxcrction of the mixed macrozooplankton dccrcased with incrcascd clcvation above the bottom. Two specimens of the scyphomedusa Poralia rufescens, a ‘dominant mcgazooplankton spcties, were individually collected at l- and 5-m elevations. Oxygen consumption rates of P. rufescens are similar to those of shallow-water gelatinous zooplankton. However, excretion rates for P. rufescens are significantly lower. Intcgratcd mixed macrozooplankton oxygen consumption for the 50-m benthic boundary layer is 1,575.5 p1.m “*d l, with the contribution from P. rufescens being only 91.6 ~1’ m-” * d ‘. This combined zooplankton respiration is only 3% of that mcasurcd for the sedimcnt community in the Santa Catalina Basin.

Dissolved hydrogen, carbon monoxide, and methane at the CEPEX site

Abstract: Concentrations of three trace gases—H2, CO, and CH4—were measured in the upper waters and in the near-surface atmosphere at the Controlled Ecosystem Population Experiment (CEPEX) site in Saanich Inlet, B.C., Canada. The upper 20 m of water contained these reduced gases at concentrations significantly higher than atmospheric equilibrium values in the presence of high levels of dissolved oxygen. Because vertical mixing was quite weak within the CEPEX container, distributions of CO, CH4, and H2 were most strongly influenced by in situ production and consumption. Concentrations of hydrogen and carbon monoxide were generally highest at or near the surface in all containers. Daily cycles of CO concentrations in the CEPEX enclosures and in the water outside the enclosures were observed. A similar, but less pronounced, H2 cycle was seen only inside the enclosure. In the CEPEX container that received no nutrient additions, a methane maximum was commonly found at depths between 8 and 12m. Methane concentrations and distributions in this container showed little change over a period of several weeks. Methane distribution did undergo significant change in the nutrient enriched containers. In Saanich Inlet, the CH4 maxima occurred deeper in the water column. No excess of H2 or CO was found in this methane-rich deeper water. Within the containers, changing hydrogen concentrations seem related to phytoplankton abundance, but the hydrogen distribution suggests zooplankton play a role. Carbon monoxide abundance varies with the amount of illumination received by the waters. Probably a variety of factors influence the distribution of each of the gases. Seawater samples collected at the site and incubated in dark containers, at in situ temperature, showed rapid decreases of CO and H2 levels to below air equilibrium. Carbon monoxide in these incubated samples reached subequilibrium levels within 12 hours. Shallow and deep water samples that had been briefly exposed to sunlight during sample handling subsequently showed higher levels of dissolved CO than did samples that were carefully shielded from outside light. Care is needed to avoid such artifacts when studying diurnal variations in dissolved CO.

Turbulence and vertical stability in the california current

Abstract: Summaries of historical surface marine wind observations and subsurface temperature data are used to examine the seasonal and spatial characteristics of wind-generated turbulent energy production and of stability of the upper water column over the California Current region. A recent hypothesis suggests that survival of first-feeding larval anchovies, Engruulis mordux, depends on the aggregation of properly sized food organisms in a stable water column in the absence of strong wind-induced turbulence. A comparison of wind mixing and stability indices for regions encompassing the principal spawning grounds of the three subpopulations of northern anchovy demonstrates that peak spawning occurs during seasons and in locations associated with stable stratification, relatively low rates of turbulent energy production, and weak offshore transport (upwelling). The average intensity of wind-generated turbulent energy production is similar during peak spawning periods in all three regions. This suggests optimum levels of turbulence and stability in the upper water column-levels that favor survival of first-feeding larvae. Although examination of mean conditions is useful in a comparative study, the average intensity of turbulent wind mixing over a spawning season is not likely to be well correlated with interannual variability in recruitment. Rather, the existence of sufficient time-space windows within which turbulence does not exceed critical values may be the relevant factor. To investigate this possibility, time series of windgenerated turbulent energy production are presented for recent periods associated with large variations in year-class strength.

Marine snow: major site of primary production in coastal waters

Abstract: Fragile aggregate particles, or ‘marine snow’, were collected by SCUBA from coastal surface waters using trace metal-free techniques, and their primary production (rates of photosynthesis by associated phytoplankton) was determined relative to corresponding water column production. Primary production associated with these particles was found to range from 11 to 58% of total production, indicating that large particles can have an important role as major sites of primary production in the marine environment. Our results suggest that the use of water bottles to collect samples for productivity measurements may not sample large particles adequately in certain conditions, and thus may lead to underestimates of primary production.

Production and vertical flux of attached bacteria in the hudson river plume of the new york bight as studied with floating sediment traps.

Abstract: We investigated the growth and vertical flux of attached bacteria with floating sediment traps in the Hudson River Plume of the New York Bight during the spring diatom blooms. Traps were floated at the base of the mixed layer (ca. 10 m) for 1-day periods. After recovery, we measured bacterial abundance and rates of [methyl-3H]thymidine incorporation in the trap samples. The vertical flux of attached bacteria was estimated with a model formulated to distinguish between bacterial accumulation in traps due to in situ growth and that due to vertical flux. Attached bacterial flux ranged from 0.6 × 1011 to 2.0 × 1011 cells m−2 day−1, and attached bacterial settling rates of 0.1 to 1.0 m day−1 were observed during periods of vertical particulate organic carbon flux ranging from 254 to 1,267 mg of C m−2 day−1. In situ growth of bacteria in sediment traps was unimportant as a source of bacterial increase when compared with vertical flux during our study. The vertical flux of attached bacteria removed 3 to 67% of the total daily bacterial production from the water column. Particulate organic carbon is not significantly mineralized by attached bacteria during its descent to the sea floor in the plume area during this period, when water temperature and grazing rates are at their annual minima.

Radionuclides in mono lake, california.

Abstract: Several radioisotopes of the naturally occurring uranium and thorium decay series, in addition to fallout plutonium, have unusually high concentrations in the water column of Mono Lake, a natural alkaline, saline lake. Complexing by carbonate ions appears to be responsible for the enhanced solubility of actinide elements with oxidation states of IV to VI. In contrast, fallout strontium-90 has been largely removed from the water, probably as a result of coprecipitation with calcium carbonate. The daughter/parent activity ratios of thorium, radium, and uranium isotopes suggest that thorium is removed from the water column to the sediments on time scales substantially longer than a month and that the desorption of thorium from the sediments to the water column requires less than a few years.