bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen uptake kinetics in the benthic boundary layer
Authors: Hall Per O. J. , Anderson Leif G. , van der Loeff Michiel M. Rutgers , Sundby Bjørn , Westerlund Stig F. G.
Published: April 2010

A simple, one‐dimensional, transport‐reaction model of oxygen uptake by sediments during incubation experiments assumes zero‐order reaction kinetics for oxygen removal in the pore water of sediments and takes the apparent diffusive limitation posed by the benthic boundary layer into account. Model calculations are in excellent agreement with experimental data obtained during in situ benthic flux chamber experiments in Gullmarsfjorden, Sweden, during fall (water temp, 10°C) and winter (−1°C). The boundary layer “resistance,” represented by a mean diffusive sublayer thickness, was estimated with a series of radioactive tracers. The oxygen uptake curve was initially approximately linear but became exponential below ~100 µM oxygen. The half‐removal time of oxygen below 100 µM corresponds to a boundary layer resistance similar to that obtained with the radiotracers. The nearly constant rate of decrease of oxygen during the initial phase of the incubations suggests that incubation techniques can be used to obtain an approximate measure of the oxygen uptake rate of sediments as long as the concentration remains above the transition where the curve changes from approximately linear to exponential. This procedure, however, underestimates the oxygen uptake rate by 28–34% compared to model results. Model calculations also suggest that oxygen uptake rates can differ substantially between chamber and outside sediments, especially when hydrodynamic conditions influencing the apparent boundary layer resistance are different within and outside chambers.
Sulfate reduction and the formation of 35S‐labeled FeS, FeS2, and S0 in coastal marine sediments
Authors: Thode‐Andersen Søren , Jørgensen Bo Barker
Published: April 2010

A comparative survey was done of the formation of radiolabeled end‐products during 35SO42− reduction measurements in coastal sediments of Denmark. The distribution of reduced 35S in acid‐volatile sulfides (AVS), pyrite, and elemental sulfur in the upper 0–15 cm of sediment depended on the sulfur chemistry and on the overall sulfate reduction rates. In sediments with relatively low metabolic rates, undetectable H2S, and low FeS : FeS2 ratio : 20), only 32–55% of the reduced 35S was recovered in the AVS pool. In sediments with high metabolic rates, high H2S, and high FeS : FeS2 ratio (>1 : 10), the 35S recovery in AVS was 63–92%. The relative contribution of Fe35S2 formation showed little depth dependence, whereas the formation of 35S° was highest in the more oxidizing sediment layers near the surface. Inclusion of 35S‐labeled FeS2 and S° in the sulfate reduction measurement yields more accurate rate data than are obtained from AVS alone. Due to possible isotopic exchange reactions and unknown pathways of H2S transformation into AVS, S°, and FeS2, however, the radioactivities of the three pools cannot be used directly to calculate their differential rates of formation.
Gas transport from methane‐saturated, tidal freshwater and wetland sediments
Authors: Chanton Jeffrey P. , Martens Christopher S. , Kelley Cheryl A.
Published: April 2010

Variations in hydrostatic pressure controlled by diurnal tides triggered ebullition from subtidal freshwater sediments dominated by methanogenesis in the White Oak River estuary, North Carolina. Pulses of gas consisting of 50–80% methane were released when the tidal cycle reached its nadir. In August, site‐to‐site variations in these fluxes ranged from 60 to 650 ml (39–425 mg) CH4 m−2 d−1. At a single site, ebullition made up 50% of the total CH4 flux out of the sediments; the remainder was transported across the sediment‐water interface by molecular diffusion.

The sedimentary gas bubble reservoir varied seasonally between 2.6 and 14.8 liters m−3 at two White Oak sites. These quantities represented 10–30% of the total sedimentary CH4 inventory, the balance of which was dissolved in pore waters. Methane shifted between the two pools with seasonal changes in temperature as bubble methane partial pressure maintained equilibrium with dissolved CH4.

Factors controlling the composition of sedimentary gas bubbles were investigated by collecting samples from several environments. These bubbles consisted primarily of CH4, N2, and CO2. The ratio of CH4 to N2 was found to be a useful indicator of mechanisms transporting gases from sediments and was controlled by both the ebullition rate and the presence of rooted emergent macrophytes.
Florida diatom assemblages as indicators of trophic state and pH
Authors: Whitmore Thomas J.
Published: April 2010

Predictive models were developed that relate lake trophic state to diatom assemblages in surface sediments. These models can be used to assess quantitatively the historical impact of cultural activities on lake productivity. One set of models relates trophic state index (TSI) values to a new diatom index based on autecological nutrient categories. A second set uses nutrient categories in multiple regression equations to predict TSI. Both types of models explain ~80% of the variance in total phosphorus TSI and averaged TSI values. Diatom‐pH transfer functions were also developed to assess the influence of eutrophication on lake pH.

Because trophic state and pH are positively correlated in Florida lakes, statistical confounding might result when predictive models for pH and trophic state are calibrated. Long‐term changes in pH might lead to errors when inferring historical TSI values, while changes in trophic state could similarly influence historical pH inferences. Partial correlations showed that two multiple regression models were statistically confounded by the nontarget variable, though predictive models based on diatom indices were free from such effects.
The Helix experiment: Differential localized dispersal and recruitment patterns in Great Barrier Reef corals
Authors: Sammarco Paul W. , Andrews John C.
Published: April 2010

In a large‐scale oceanographic study, we attempted to determine whether reefs of the central Great Barrier Reef are primarily self‐seeded with respect to corals. Twenty‐four moorings were deployed for 7 months around the small, relatively isolated Helix Reef (diam ≃ 800 m). Settling plates were placed on moorings 15–18 m below the surface. Moorings were placed 0, 0.3, 0.6, 1.2, 2.5, and 5.0 km from the reefs perimeter. Water movements were recorded concurrently via current meters and tide gauges. Most larvae settled on or within 300 m of the reef; settlement was generally lower in pocilloporids than acroporids. Most spat in the far field (acroporids) were derived from corals utilizing externally fertilized eggs with an obligate planktonic larval development period of 24–72 h, implying higher effective dispersal capabilities. Densities of settling pocilloporids (obligate brooders), however, were highest directly on the reef. Postsettlement mortality of recruits decreased significantly with distance from the reef. Coral spat were concentrated in two areas where water residence times were high and flushing rates were low. Highly localized circulation patterns appear to retain larvae near the reef. Effective larval dispersal in corals seems to be a small‐scale phenomenon, although measurable far‐field dispersal indicates sufficient gene flow between reefal populations to prevent allopatric speciation.
Chemical composition and phosphate uptake kinetics of limnetic bacterial communities cultured in chemostats under phosphorus limitation
Authors: Vadstein Olav , Olsen Yngvar
Published: April 2010

Natural bacterial communities were grown in chemostats diluted with filtered lake water manipulated to yield phosphorus limitation. The results suggested P limitation of the bacteria when the P : C and the surplus : C ratios were between 17–120 and 2.7–100 µg P(mg C)−1, respectively. These high values indicate that heterotrophic bacteria are net consumers of phosphate and that they sequester a considerably higher fraction of the particulate P in lakes than expected from their biomass in terms of carbon. Estimates of maximal uptake velocity and affinity for phosphate at low concentrations for the mixed bacterial communities were influenced by the degree of P limitation. A review of published data indicates that under P limitation bacteria are superior to phytoplankton in taking up phosphate at low concentrations, whereas their abilities are comparable at saturation.
High long‐term nitrate uptake by oyster‐pond microalgae in the presence of high ammonium concentrations
Authors: Collos Y. , Maestrini S. Y. , Robert J.‐M.
Published: April 2010

Natural assemblages and axenic cultures of oyster‐pond microalgae (dominated by pennate diatoms) were subjected to nutrient pulses in which the concentrations of ammonium and nitrate simulated the natural pulses to which these populations are regularly exposed. In natural populations, nitrate uptake (per unit of Chl a or particulate N) always presented a maximum at ammonium levels between 10 and 30 µg‐atoms N liter ‘. Such maxima coincided either with the maximal ammonium uptake rate or with the start of a decrease in ammonium uptake. Nitrate uptake then decreased and went through a secondary maximum at lower ammonium levels. Although species succession could not be ruled out as a possible cause for these patterns, 48–69% of the variability in nitrate uptake could be explained by variations in the concentration of nitrate relative to the sum of nitrate and ammonium, corrected for biomass increases. In axenic cultures of three species of diatoms isolated from these environments, this percentage varied between 78 and 99%.
Light‐limited growth on ammonium vs. nitrate: What is the advantage for marine phytoplankton?
Authors: Thompson Peter A. , Levasseur Maurice E. , Harrison Paul J.
Published: April 2010

Thalassiosira pseudonana (3H) was grown in semicontinuous culture on either NO3− or NH4+ at nine different photon flux densities (PFDs). At PFDs >29 µEinst m−2 s−1, growth rates (µ) were 8% lower for cells growing on NO3− compared to cells growing on NH4+. At high PFDs NO3−‐grown cells had 21% lower carbon quotas than NH4+‐grown cells. At high PFDs the possibility exists that competition for reductant may reduce µ and carbon quotas for NO3−‐grown cells.

At PFDs ≤29 µEinst m−2 s−1 NO3−‐grown cells had equal growth rates, nitrogen quotas, Chl a cell−1, and equal or greater carbon quotas compared to NH4+‐grown cells. At these light‐limited growth rates NO3−‐grown cells used more reductant overall and up to 51% more reductant per unit Chl a than NH4+‐grown cells to store carbon and nitrogen. These results suggest that use of NO3− rather than NH4+ is of little energetic importance in terms of growth rate at low PFDs.
Diel periodicity in ammonium uptake and regeneration in the oceanic subarctic Pacific: Implications for interactions in microbial food webs
Authors: Wheeler Patricia A. , Kirchman David L. , Landry Michael R. , Kokkinakis Steven A.
Published: April 2010

Diel periodicity in NH4+ uptake and regeneration in the nutrient‐rich environment of the oceanic subarctic Pacific was examined. Surface water was incubated in large shipboard microcosms that allowed repeated sampling of the planktonic community for NH4+ cycling rates, bacterial production rates, and population densities of the dominant autotrophs and heterotrophs. Changes in NH4+ concentrations and isotopic enrichments indicated that regeneration took place exclusively at night. Nitrogen uptake rates and bacterial production were maximal during the day. Abundance of <2‐µm autotrophic flagellates reached a maximum at the end of day or beginning of night, whereas abundance of zooflagellates in the <2‐µm and 1–10‐µm size classes showed a twofold variation with maximal abundances occurring at the beginning of day. These contrasting diel patterns suggest short‐term, cyclic disequilibrium in production and grazing within the microbial food web. Hence, analysis of relationships among the various components of microbial populations in this type of environment will require sampling on much shorter time scales than has been attempted in past studies.
Zooplanktivorous fish and variable diel vertical migration in the marine planktonic copepod Calanus pacificus
Authors: Bollens Stephen M. , Frost Bruce W.
Published: April 2010

As a field test of the hypothesis that variable diel vertical migration in zooplankton is a response to variations in the abundance of visually orienting predators, we sampled juvenile and adult planktivorous fish inhabiting a temperate fjord (Dabob Bay, Washington) concurrently with the vertical distributions of a population of adult female Calanus pacificus (Copepoda: Calanoida) known to exhibit seasonally variable diel vertical migration. Results of nighttime trawling on seven dates between April 1985 and October 1986 and subsequent stomach content analyses showed that eight species of fish, comprising 45 different size classes, fed on adult female C. pacificus; all species of fish showed marked seasonal and interannual variations in their abundances. The extent to which the population of C. pacificus exhibited diel vertical migration was determined for each cruise date by calculating the proportion of the population crossing 75‐m depth on a diel cycle. A statistically significant regression was obtained between strength of diel vertical migration in C. pacificus and abundance of fish actively preying on the copepod. We propose that the timing and magnitude of changes in the migration behavior of C. pacificus in Dabob Bay are directly linked to the year‐class strengths of the dominant species of planktivorous fish.
An experimentally determined carbon : volume ratio for marine “oligotrichous” ciliates from estuarine and coastal waters
Authors: Putt Mary , Stoecker Diane K.
Published: April 2010

The biomass of marine “oligotri chous” ciliates has often been estimated by measuring the cell volume of preserved samples and converting to units of carbon based on theoretical carbon: volume (C: vol) ratios of 0.07–0.11 pg µm−3. Using laboratory cultures of several strains of Laboea strobila, Strombidium spp., and Strobilidium spiralis, we experimentally derived a C: vol conversion factor of 0.19 pg µm−3 for cells preserved with 2% vol : vol Lugol’s iodine. Cell volume estimates of Lugol’s‐preserved cells averaged 76% of cell volume estimates of Formalin‐preserved cells. Hence a C : vol ratio of 0.14 pg µm−3 applies to Formalin‐preserved cells. Our study indicates that the biomass of oligotrichous ciliates in marine systems has been significantly underestimated by the use of inappropriate C: vol ratios.
Maximal growth rates of Antarctic phytoplankton: Only weak dependence on cell size
Authors: Sommer Ulrich
Published: April 2010

Maximal growth rates of 15 Antarctic phytoplankton species at 0°C ranged from 0.32 to 0.72 d−1, showing only a weak dependence on cell size. Comparisons were made with two models for size dependence of temperature‐corrected rates of maximal growth. Schlesinger's general phytoplankton model predicts a strong size dependence of growth rates and grossly underestimates the maximal growth rates of the larger species, but gives reasonable estimates for the smallest ones. Banse's marine diatom model assumes a weak size dependence of growth rates and gives generally better predictions.
Distinguishing between extra‐ and intracellular iron in marine phytoplankton.
Authors: Hudson Robert J. M. , Morel Francois M. M.
Published: April 2010

Iron associated with marine phytoplankton occurs adsorbed to and precipitated on cell surfaces in addition to being in metabolically active or stored intracellular forms. We demonstrate the utility of the inorganic reductant titanium(III) complexed by citrate and EDTA as a reagent for rapidly dissolving extracellular iron at pH 8 without causing cell breakage or toxicity. The method allows an experimental distinction to be made between extra‐ and intracellular iron, even in the presence of large quantities of precipitated iron hydroxides. Our results confirm previous work showing that such a distinction is essential for the study of transplasmalemma iron transport by these and other aquatic organisms.
An experimental test of the egg‐ratio method with instantaneous birth rate as an independent variable
Authors: Bennett William N. , Boraas Martin E.
Published: April 2010

The accuracy of three mathematical models that have been used to calculate instantaneous birth rate (b) from the ratio of eggs to females (E) in a population was determined with steady state populations of the rotifer Brachionus calycifllorus. Typically, b is calculated from E with these models. We were able to choose b as an independent variable, with the physical characteristics of our culture device (a two‐stage steady state chemostat), which also satisfied the major assumptions of the models. We then measured E and calculated b from E with the three models. The model of Paloheimo gave the best fit to these steady state data when the calculated b and observed b were compared.
Diffusion methods for the determination ofreduced inorganic sulfur species in sediments
Authors: Hsieh Y. P. , Yang C. H.
Published: April 2010

Diffusion procedures for the separation of acid‐volatile sulfide (AVS), CR(II)‐reducible sulfur (CRS), and elemental sulfur (ES) were developed to replace the conventional active distillation procedures. In these new procedures, reduced inorganic sulfur species are converted to hydrogen sulfide in a closed container at ambient temperature, and the hydrogen sulfide is allowed to diffuse into an alkaline zinc trap which subsequently can be retrieved and analyzed. The advantages of the diffusion methods are suitability for a large number of samples, specificity of the CRS diffusion procedure to pyrite‐S after AVS removal, and capability to determine elemental sulfur without prior extraction. Percent recovery of the added ferrous monosulfide, pyrite, and elemental sulfur by the diffusion methods is comparable to those of active distillation. The diffusion methods were tested on the sediments of a Juncus roemerianus tidal marsh in Florida.
Metalimnetic cyanobacteria in hard‐water lakes: Buoyancy regulation and physiological state
Authors: Konopka Allan
Published: April 2010

During summer stratification, Crooked and Little Crooked Lakes, Indiana, contained phytoplankton dominated by populations of Aphanizomenonflos‐aquae that stratified in the metalimnion where photon irradiance was 6% of that at the surface. The gas vacuolate Aphanizomenon filaments from Little Crooked Lake lost buoyancy when exposed to irradiances >100 µmol photons m−2 s−1. If 2 µM KH2PO4 was added to the water samples, however, exposure to irradiances >200 µmol photons m−2 s−1 was necessary to obtain buoyancy losses. Phosphate also affected the recovery of buoyancy by sinking filaments. Filaments that had lost buoyancy due to incubation in the light recovered it when incubated for 5 h in the dark. Addition of phosphate increased the rate of buoyancy recovery by 50%.

The metalimnetic populations had stratified in a zone of relatively low irradiance and inorganic nutrient concentration. The physiological state of the populations was evaluated by determining the kinetic characteristics for phosphate, nitrate, and ammonia uptake and the cellular contents of surplus phosphate and chlorophyll a. On the basis of the premise that cells limited by a particular element will express a high uptake potential for that element, the metalimnetic populations showed characteristics of organisms not limited by the availability of light, phosphorus, or nitrogen.
The geochemical evolution of halite structures in hypersaline lakes: The Dead Sea, Israel
Authors: Ganor Jiwchar , Katz Amitai
Published: April 2010

Depressions in the floor of the southern basin of the Dead Sea contain dense (1.26–1.29 g cm−3) brines which formed by evaporation at the lake’s surface. Absorbance of solar radiation heats these brines by about 2.4°C d−1, as long as the density gradient of the lake prevents overturn. As a result, bottom halite is dissolved in the warmer brines at about 0.4 g NaCl liter−1 °C−1. Continuous heating of the brine of these holes and cooling of the overlying liquids at night causes frequent overturns of the brine column, followed by mixing and cooling of the NaCl‐rich brine. The extra load of halite is precipitated near the holes in the form of halite cones and mushroomlike structures. Whereas the initial NaCl supply to the growing halite structures comes from the floor of the lake, the later growth stage is supported by NaCl supplied from the upper (evaporating) brine layer.

Crude mass and heat balances show that the proposed model may well explain the occurrence and distribution of halite islands in the Dead Sea. The model may be applicable to any shallow enough (a few meters) hypersaline lake that is saturated with respect to halite.
Rates and patterns of estuarine sediment accumulation
Authors: Brush Grace S.
Published: April 2010

Estuarine sedimentation rates are estimated for vertical increments of sediment cores by adjusting average rates between dated horizons with the ratio of pollen concentration to concentration of sediment. The method assumes independent influxes of pollen and sediment into the estuary, similar patterns of transport and deposition for both pollen and fine sediment, a uniform influx of pollen over the time interval between dated horizons, and preservation of the majority of pollen entering the estuary.

Comparisons of detailed, pollen‐derived sedimentation rates with historical records of climatic and anthropogenic events in upper Chesapeake Bay show that highest rates of sediment accumulation occur in upper and middle stretches of tidal tributaries and coincide with major storms and periods of intensive land clearance when > 20% of total land area in a given watershed is deforested and under cultivation.
Phototaxis in Daphnia: Interaction of hunger and genotype
Authors: De Meester Luc , Dumont Henri J.
Published: April 2010

The effect of hunger on the phototactic behavior of Daphnia magna was tested experimentally. Four different clones were used, selected for their different phototactic responses when well fed. A two‐way ANOVA revealed significant effects of both genotype and satiation.
Vitamin C in marine copepods
Authors: Poulet S. A. , Hapette A. M. , Cole R. B. , Tabet J. C.
Published: April 2010

The occurrence and variation of l(+)‐ascorbic acid (vitamin C) have been investigated in marine copepods with a new anion‐exchange, high‐performance liquid chromatographic method. The occurrence of this compound in Calanus helgolandicus was verified with mass spectrometry. The observed contents ranged from traces in carnivorous species to >500 µg g−1 wet weight in herbivorous‐omnivorous species. This is the first report of the presence of vitamin C in zooplankton. The variations of vitamin C observed in copepods may reflect the ecological importance of this nutrient in the marine food chain.
Anomalous, short‐term influx of water into seepage meters
Authors: Shaw R. D. , Prepas E. E.
Published: April 2010

Laboratory and field tests revealed that there was an anomalous, short‐term influx of water into plastic bags after they were attached to seepage meters. Plastic bags (3.5‐liter capacity) were submerged in an 830‐liter tank of stagnant water; within 45 min, the volume of water in bags that initially were empty increased to 297 ml, bags prefilled with 1,000 and 2,000 ml of water increased by 160 ml, and bags prefilled with 3,000 ml decreased in volume. At Narrow Lake, Alberta, the anomalous, short‐term (30 min) influx of water averaged 237 ml to bags that were initially empty, but the anomaly was effectively eliminated when bags were prefilled with 1,000 ml of water before they were attached to seepage meters. The impact of the anomaly on calculated seepage rates was greatest when seepage rates were low, e.g. 0.3 ml m−2 min−1. The anomaly may be due to mechanical properties of the bag, and it may be alleviated by partially filling bags before they are attached to seepage meters.
The upwelling light stream in natural waters
Authors: Kirk J. T. O.
Published: April 2010

The upwelling light field in natural waters is of great importance for the appearance of the water bodies, for visibility of objects seen through the water, and for remote sensing of water properties. As a contribution to the understanding of this radiant flux, a study has been carried out by the Monte Carlo simulation technique of the behavior of photons scattered upward from the downwelling light stream within water bodies. Immediately after scattering the angular distribution of these photons is biased very much toward small angles to the horizontal. As a consequence, the rate of attenuation of this photon population as it travels upward is initially very high. With increasing distance upward the rate of attenuation progressively diminishes as the more horizontally traveling photons are selectively extinguished.

The upwelling flux at any depth originates in upward scattering events at lower depths, mostly within quite small optical distances below the reference depth. A new parameter, κ(z), is defined which is the average upward vertical attenuation coefficient exhibited by all the upwelling photons received at depth z meters as they travel upward from their point of origin by upward scattering to depth z : κ is always Kd (vertical attenuation coefficient for downward irradiance in that water) and, to a reasonable approximation, κ ∼ 2.5Kd in the middle of the euphotic zone.

The diffuse backscattering coefficient for the downwelling light stream is shown to be approximately equal to the irradiance reflectance for the downwelling light stream multiplied by (Kd + κ). This relationship is used to describe a new method for estimating the scattering coefficients of water bodies from irradiance data.
Shape factors, two‐flow models, and the problem of irradiance inversion in estimating optical parameters
Authors: Stavn Robert H. , Weidemann Alan D.
Published: April 2010

The problem of the inversion of irradiance measurements for the inherent optical properties of a hydrosol such as the world ocean has been examined with the NOARL optical model. This model is a Monte Carlo simulation of the radiative transfer equation that, given the optical properties of a hydrosol, generates the zonal radiances and the commonly measured irradiances of that hydrosol. This information allows us to test the optical inversion capability of any irradiance model. We have demonstrated that the two‐flow model, used often in atmospheric optics, cannot be inverted to yield the inherent backscatter coefficient of natural hydrosols due to the extreme asymmetry of the hydrosol volume scattering function. The asymmetry of the volume scattering function interacting with the radiance distribution introduces parameters called shape factors into the models for irradiance inversion. The presence of shape factors in an irradiance model renders it unsolvable; thus, simplifying assumptions are required for an inverse solution. We inquire into the possibilities for irradiance inversion given the existence of shape factors.
Photosynthetically available radiation at high latitudes
Authors: Campbell Janet W. , Aarup Thorkild
Published: April 2010

Low solar elevations at high latitudes result in two phenomena that affect the quantity and quality of light entering the sea. High surface reflectances significantly reduce the direct solar irradiance and, to a lesser extent, the global irradiance. Furthermore, there is an apparent spectral shift such that proportionately more blue (diffuse) light is transmitted and more red (direct) light is reflected by the sea surface. A model of photosynthetically available radiation (PAR) has been used to quantify these effects. The model was developed to predict daily broadband (400–700 nm) photon flux as a function of latitude and time of year for varying cloud‐free atmospheric conditions. Seasonal and spectral variability of the surface albedo is described at latitudes between 40° and 70°N. Ranges are established for surface albedo which encompass variability due to atmospheric turbidity and wind‐induced surface waves.
A model of the spring bloom in the North Atlantic and its impact on ocean optics
Authors: Wroblewski J. S.
Published: April 2010

A model of the development of the spring phytoplankton bloom in the North Atlantic and its effect on light attenuation in the water column is presented. The model uses as input data on the climatological mixed‐layer depth, solar irradiance at the sea surface, and basin‐scale distribution of nitrate at standard depths. The simulated phytoplankton bloom progresses from mid‐ to high latitudes following the shallowing of the mixed layer during March through June. The bloom occurs first in coastal waters where the mixed layer is shallow and later in the open ocean. Local peak concentrations of phytoplankton last 1–2 weeks. As phytoplankton are the major absorbers and scatterers of light in the open ocean, the relationship between chlorophyll concentration and light attenuation can be used to predict time‐varying fields of light extinction. The basin‐scale variability in the attenuation coefficient for downwelling irradiance at 490 nm (K490) in May is computed as an example.
Polarized‐light scattering studies of marine Chlorella
Authors: Quinby‐Hunt M. S. , Hunt A. J. , Lofftus K. , Shapiro D.
Published: April 2010

This paper compares results of rigorous calculations of light scattering by a distribution of coated spheres with the measured light scattering of marine Chlorella. The elastic scattering properties of any organism are described completely by the 16‐element scattering matrix that gives all the intensity and polarization information as a function of angle. Fitting the angular dependence of several matrix elements affords a much more stringent test of scattering calculations than does fitting only one, such as the phase function or linear polarization. The added requirements of this test significantly narrow the range of acceptable optical models and thereby permit better characterization of the scattering medium. Measurements of several elements of the scattering matrix of laboratory cultures of Chlorella were obtained with a scanning polarization‐modulation nephelometer. The results for these elements were best fit by calculations based on a model of a Gaussian distribution of spheres with a relative complex refractive index of 1.08(±0.005)−0.05i(±0.005) and a 60‐nm coating of index1.13(±0.005)−0.04i(±0.005) to approximate the cell membrane. Good agreement was obtained for only a very narrow range of particle parameters. Experimental results were broken into spherical and nonspherical contributions to evaluate the effects of nonsphericity.
The response of beam attenuation to heterotrophic growth in a natural population of plankton
Authors: Spinrad R. W. , Yentsch C. M. , Brown J. , Dortch Q. , Haugen E. , Revelante N. , Shapiro L.
Published: April 2010

The results presented show a change in monochromatic light transmission of a natural ocean water sample corresponding to an increase of ∼30% in the particulate beam attenuation coefficient over 3 d. This optical change was a very sensitive indicator, measurable in real time, of complex changes in the microbial community. These results show that the beam attenuation coefficient is a sensitive indicator of change within a complex population. The virtue of such a measurement lies in the capability to make such assessments rapidly, in situ, in real time, and without the need to perform extensive laboratory analysis of sampled water volumes or even manipulate the sample.
Laboratory measurements of optical beams in young sea ice
Authors: Schoonmaker J. S. , Voss K. J. , Gilbert G. D.
Published: April 2010

The optical properties of young sea ice (<20 cm thick) have been measured in the Naval Ocean Systems Center Ice Optics Lab. Measurements of the upwelling irradiance from the ice surface as a function of distance from the center of the beam spot (r in cm) were performed. The irradiance distributions were transformed to find the modulation transfer function (MTF) and beam spread function (BSF) as a function of ice thickness. The BSF could be approximated by BSF(r, z) = exp(−kBz) exp(−r2/2 〈r2〉), with kB = 0.404 cm−1 and 〈r2〉½ = 0.105 z1.41 cm, where z is ice thickness (in cm). Angular radiance above the ice surface, resulting from a laser beam entering the ice from below, was measured as a function of ice thickness for a specific growth condition. The angular field followed a function of L(θ, z) = L(0, z)cosn(θ), with n = 8.1 z0.71, while the peak value followed a Beer’s law decay of the form L(0, z) = L(0, 0)exp(−0.514z).
Use of the radiance distribution to measure the optical absorption coefficient in the ocean
Authors: Voss K. J.
Published: April 2010

Recent advances in instrumentation have enabled the accurate measurement of radiance distribution profiles. These measurements with the electro‐optic radiance distribution camera system (RADS) can be used to explore theoretical treatments relating the radiance distribution to inherent properties such as absorption. I use a radiance distribution cast to obtain a profile of the optical absorption coefficient. Because this measurement of absorption is not direct, but rather is derived from the radiance distribution data, analysis of the possible sources of error is detailed, along with the advantages and disadvantages of the method.
Effects of algae on the Secchi transparency of the southeastern Mediterranean Sea
Authors: Megard Robert O. , Berman Tom
Published: April 2010

The mean transparency (37.5 m) measured by Secchi disk at “blue‐water” pelagic sampling stations in the southeastern Mediterranean Sea during 3 yr was greater than in most other seawater. Our measurements in the Mediterranean and those by others in the English Channel, Atlantic Ocean, and Pacific Ocean obey the Lambert‐Bouguer law if it is specified that transparency depends on the vertical attenuation coefficient for downward irradiance in the waveband of underwater sunlight that has lowest attenuance. Mean downward irradiance (±95% C.L.) at the depth where a Secchi disk disappears, calculated from 187 paired estimates of transparency and attenuation coefficients from these oceanic regions, is 22±1% of surface irradiance in this waveband. This value is significantly larger than the value (18%) that has been used widely since an early study by Poole and Atkins, who calculated attenuation coefficients incorrectly.

As predicted by the Lambert‐Bouguer law, reciprocal transparency was proportional to the attenuation coefficient for the most‐penetrating waveband. Attenuance of this waveband and reciprocal transparency both increase linearly with increasing concentration of phytoplankton chlorophyll in pelagic water. Chlorophyll concentrations in pelagic Mediterranean water were very low (0.02–0.14 mg m−3), but attenuance by units of phytoplankton chlorophyll was about 10 times larger than in more productive seawater, probably because blue light was predominant and many of the phytoplankton were very small coccolithophorids (cell diameters <10 µm) with optically dispersive cell surfaces.

Measurements of transparency by Secchi disk are as accurate and precise as estimates of attenuation coefficients calculated from irradiances measured at sea with photoelectric sensors. The Poole‐Atkins equation for transparency in terms of the waveband with lowest attenuance describes the variation of transparency as well as the Duntley‐Preisendorfer equation does. Much of the information needed for interpreting satellite ocean‐color imagery could be obtained very efficiently with closely spaced measurements of transparency from surface vessels during synoptic cruises.
Spectral reflectance and water quality of Adirondack mountain region lakes
Authors: Vertucci Frank A. , Likens Gene E.
Published: April 2010

The reflectance properties of lakes in the Adirondack mountain region are described. Five distinct types of reflectance spectra are identified and related to differences in water quality. No relationship was found between reflectance and acidification status.

A reflectance model based on literature absorbance and scattering cross‐sections of water, plant pigments, dissolved organic carbon (DOC), and suspended inorganic matter is used to generate reflectance spectra of each reflectance type. Use of a variable Q factor during the conversion of remotely sensed reflectance to irradiance reflectance improves the correspondence between measured and modeled irradiance reflectance spectra. Comparison of measured reflectance with model reflectance also demonstrates the importance of small concentration changes as well as the interactive influence of plant pigments, DOC, and suspended material on lake color.

Correlograms depict the wavelength‐dependent relationships between reflectance and water quality. Plant pigments, DOC, and suspended material are negatively correlated with reflectance from 400 to 600 nm and positively correlated from 600 to 750 nm; parameters associated with lake acidification, pH, alkalinity, and aluminum concentrations are poorly correlated with reflectance. Adirondack lakes exhibit a high degree of covariance between pigment, DOC, and suspended matter concentrations.

Regression models predicting total pigments and DOC are developed which suggest that these parameters can be estimated remotely in these lakes, but remote estimation of pH, alkalinity, and aluminum is not possible with reflectance measures. A regression model estimating total pigments from the reflectance ratio of 525 : 554 nm is similar in slope and accuracy to one derived for the Coastal Zone Color Scanner (CZCS) for coastal marine waters. However, neither of the “recommended” CZCS pigment algorithms perform best with the Adirondack lake reflectance and pigment data.
A bridge between ocean optics and microbial ecology
Authors: Yentsch Charles S. , Phinney David A.
Published: April 2010

Phytoplankton cell size is believed to be closely regulated by the nutrient regime of water masses in the western North Atlantic Ocean. Since particle size affects attenuation of light in ocean water, we argue that a bridge between classical ocean optics and microbial ecology has formed whereby the physics of ocean color must include consideration of ecological factors important to the diversity of phytoplankton species.

Observations of the specific absorption coefficient, a*, have been made during 10 oceanographic cruises in the western North Atlantic. The range in Chl a concentration for ocean samples from the various water masses in this region was 0.1–8.0 µg liter−1. Diffuse attenuation spectra of particles measured by a glass‐fiber filter technique show strong correlations between extracted chlorophyll and blue (440 nm) or red (670 nm) absorption. Of the two, a*440 is the most variable. Average specific absorption coefficients are calculated to be 0.049 m2 mg−1 at 440 nm and 0.028 at 670 nm, but both relationships are seen to be nonlinear. The nonlinearity observed is attributed to differences in cell size “packaging” within natural phytoplankton populations. Variation in cell size and a* are primarily related to the availability of nitrate‐N. In addition, other factors contribute to the variability in a*440, such as detritus and short wavelength UV‐absorbing pigments.
Determination of the cross‐section absorption coeffcient of individual phytoplankton cells by analytical flow cytometry
Authors: Perry Mary Jane , Porter Steven M.
Published: April 2010

An empirical relationship between the cellular cross‐section absorption coefficient (σ) and the Chl a fluorescence of individual plankton cells was established. Chl a fluorescence of single cells was measured in a flow cytometer with 488‐nm argon‐ion laser excitation. Absorption by dilute suspensions of cells was measured spectrophotometrically and normalized to cell number for computation of σ(488) (m2 cell−1). At the high excitation irradiances characteristic of lasers, a constant proportion of photons absorbed by photosynthetic pigments was re‐emitted as Chl a fluorescence; a strong correlation was observed between absorption at 488 nm and Chl a fluorescence (r2 = 0.93; P ≪ 0.001). The regression predicted the total phytoplankton absorption coefficient [aphyt(488) (m−1)] at 488 nm for mixtures of five monospecific cultures with <9% error. For field samples, discrepancies between the flow cytometric method and the filter pad spectrophotometric method for estimating aphyt(488) were greater.

Relatively large, rare phytoplankton cells accounted for a disproportionate percentage of total aphyt(488). The coherence between absorption at 488 nm and at other wavelengths was high and provides a basis for extrapolating from σ(488) to single‐cell absorption coefficients at all visible wavelengths. The single‐cell spectral absorption coefficients can be used to compute total in situ photon absorption for modeling light‐limited photosynthetic rates of individual phytoplankton cells in the ocean.
Bio‐optical inferences from chlorophyll a fluorescence: What kind of fluorescence is measured in flow cytometry?
Authors: Neale Patrick J. , Cullen John J. , Yentsch Clarice M.
Published: April 2010

A comparison is made of the in vivo Chl a fluorescence per cell measured by the flow cytometer (Fcyt) and dark‐adapted bulk fluorescence measured in a standard field fluorometer for the marine cryptomonad Chroomonas sp. (clone Chang 2). The bulk fluorescence protocol estimated the levels of the minimum (F0) and maximum (Fmax) fluorescence yields that are exhibited depending on the redox state of the photosystem II reaction center. Both F0 and Fmax are known to be functions of cell irradiance history. During the illumination of control samples at growth irradiance (40 µmol quanta m−2 s−1), F0, Fmax, and Fcyt (EPICS V) all increased by about the same proportion. After exposure to photoinhibiting irradiance (1,700 µmol quanta m−2 s−1), Fmax decreased and F0 increased. Parameters of the photosynthesis‐irradiance curve verified that photoinhibition had occurred, indicating less activity at all irradiances. In contrast to bulk fluorescence measurements, relative changes in Fcyt in response to strong‐irradiance treatment were much smaller than changes in F0, and Fmax. We conclude that this is because Fcyt is intermediate between F0 and Fmax. Multiple regression analyses suggest that, under the flow cytometry conditions used, Fcyt exhibits ∼20% enhancement above F0, i.e. an average of 20% of the increase from F0 to Fmax. Time scales of photosystem II primary photochemistry are consistent with this amount of fluorescence enhancement occurring over the residence time of the cell in the laser beam. These results suggest caution in using oversimplified interpretations of Fcyt. The enhancement effect should also be considered in other instances where fluorescence is excited by a brief saturating flash, for example, some types of in situ fluorometers.
Periodic bacterivore activity balances bacterial growth in the marine environment
Authors: Johan Wikner , Rassoulzadegan Fereidoun , Hagström Åke
Published: April 2010

The grazing rate of pelagic bacteria was repeatedly determined during 36‐h time‐course experiments with the minicell recapture technique. Diel variation in the rate of grazing occurred in all water masses investigated. Maximal rates reached 2 × 105 cells ml−1 h−1, whereas minimal values were 20 times lower. Highest grazing rates were found during the day in most cases, but grazing could also dominate at night as found in one study. Diel periodicity was mainly due to variation in the per‐cell feeding rate of bacterivorous flagellates. Accumulation of the bacterial biomass into the 1–3‐µm size fraction was positively correlated with changes in bacterial grazing. The transfer efficiency to organisms >10 µm was low. On average, the daily grazing rate equaled 60% of the bacterial standing stock, exceeding bacterial growth by a factor of 2.6, as estimated from [3H]thymidine incorporation.
Variations in sedimentary carbon remineralization rates in the White Oak River estuary, North Carolina
Authors: Kelley Cheryl A. , Martens Christopher S. , Chanton Jefrey P.
Published: April 2010

Rates of microbially mediated sedimentary organic carbon remineralization vary along the salinity gradient of the White Oak River estuary, N.C. A direct comparison of two sites, one upriver dominated by methanogenesis and one downriver dominated by sulfate reduction, indicates a more rapid rate of remineralization upriver. Measurements of diffusive ∑CO2 flux plus CH4 diffusive (56%) and bubble (44%) fluxes at the upriver, freshwater site from June 1986 to March 1988 yield an average yearly flux of 1.35 ± 0.35 mmol m−2 h−1. At the downriver midestuarine site, the dominant ∑CO2 flux for the same period is 0.46±0.02 mmol m−2 h−1. The uncertainties in these yearly fluxes are calculated from observed ranges in duplicate flux measurements. About 43% of the incoming organic C is remineralized at both sites. The greater remineralization upriver, of which 47% can be attributed to methanogenesis, appears to be supported by rapid decomposition of detritus derived from freshwater, emergent and submersed macrophytes, including Pontederia, Ceratophyllum, and Najas in surficial sediments. The high organic C content of these upriver sediments may, however, result from the long‐term storage of slower degrading plants, such as Typha and Taxodium.
Carbon, nitrogen, and phosphorus budgets for the mixotrophic phytoflagellate Poterioochromonas malhamensis (Chrysophyceae) during bacterial ingestion
Authors: Caron David A. , Porter Karen G. , Sanders Robert W.
Published: April 2010

Growth, grazing, C and nutrient in corporation by the mixotrophic phytoflagellate Poterioochromonas malhamensis were examined under various nutrient and light regimes in the presence of heat‐killed bacteria. Poterioochromonas malhamensis readily ingested bacteria in all culture treatments containing heat‐killed bacteria, and growth rates of the protist were much greater for heterotrophic (bacterivorous) growth than for phototrophic growth. C incorporation efficiencies by the phytoflagellate were virtually identical to P incorporation efficiencies during heterotrophic growth, but N incorporation efficiencies were somewhat lower in nearly all of the treatments. Algal growth in cultures with heat‐killed bacteria was similar in continuous darkness and in continuous light. Bacterial organic C was the primary source of protist cellular C for P. malhamensis during heterotrophic growth. Based on our observations, we conclude that P. malhamensis is primarily heterotrophic and phagotrophic and that it is highly competent in this mode of nutrition.
Episodic changes in lateral transport and phytoplankton distribution in South San Francisco Bay
Authors: Huzzey Linda M. , Cioern James E. , Powell Thomas M.
Published: April 2010

Observations in South San Francisco Bay during 1982 showed that substantial cross‐channel, nontidal flows accompanied episodic increases in the longitudinal, nontidal flows. Along the channel the nontidal circulation was enhanced during the monthly minima in tidal energy or as a result of wind forcing, producing upestuary flows 2–3 times greater than normal. These longitudinal pulses modified the horizontal and vertical salinity distributions and generated cross‐channel flows of up to 0.07 m s−1 that persisted for several days. The increased lateral flows were directed to the west and may explain the large fluctuations in phytoplankton biomass observed over the broad eastern shoal during spring.