bluuebunny/crossref_metadata_2025_split huggingface dataset:
The disappearance of the long term meromictic stratification of the Dead Sea
Authors: Steinhorn Iiana 
Published: April 2010

Following a lowering of its surface level by 3.5–4 m, the water of the Dead Sea turned over in February 1979, ending a long period of stratification. The “classic” structure (a salinity gradient at a depth of 30–40 m separating the surface layers, through a transitional zone, from a “fossil” water spreading from 60 to 80 m to the bottom 320 m) was replaced by a reduction of the salinity difference between surface and deep waters from 25 g kg−1 in 1960 (50 g kg−1 in 1864) to 3 g kg−1 in 1975, and to <0.1 g kg−1 in 1978, and by a series of deepenings of the interface between the fossil waters and the upper, seasonally variable layers, from about 80‐m depth in 1975 to 180 m in 1978. The “eroded” deep waters maintained their original properties (mean salinity 275.8 g kg−1, mean potential temperature 21.34°C, mean density 1.2334 g cm−3, and tritium content 0.1 TU). In February 1979 the entire water column was essentially homogeneous and stable (Brunt‐Väisälä frequency 5.8 × 10−4 s−1), with temperature, salinity, and density somewhat higher than those of the former deep waters.The successive deepenings and the complete overturn were caused when the surface (10–25 m) layers cooled during autumn and winter from 37° to 18°C, and, following each dry year, reduced their excess salinity (3 g kg−1) by vertical mixing to a greater depth than in the previous winter. The meromixis of the Dead Sea is ectogenic, caused by freshwater inflow over hypersaline deep layers. The imbalance between the effects of salinity and temperature changes on the density of the water column, and variations (both natural and artificial) in amount and timing of the inflow rate, cause the seasonal changes of the water column to be nonrepetitive; the cumulative extreme development of this is an overturn.
Stream‐dwelling copepods: Their life history and ecological significance1
Authors: O'Doherty Erin Claire 
Published: April 2010

The stream‐dwelling harpacticoid copepod Bryocamptus zschokkei was reared in the laboratory at 3.5°, 10°, 15°, 18°, and 20°C with naturally conditioned leaf disks as a food source. Egg and naupliar development rates were fastest at 18°C.A complete life table experiment was conducted at 18°C. Females were longer‐lived than other copepods and produced eggs continuously until death. The intrinsic rate of natural increase (r) and the net reproductive rate (Ro) were found to be lower than those of most copepods. Reproduction is probably continuous throughout the year in the stream, since animals reproduced in the laboratory at the extreme temperatures experienced by the natural population. Since most copepods reproduce seasonally, the annual intrinsic rate of increase of B. zschokkei may be comparable to those of other copepods.
Selective predation by the carnivorous marine copepod Euchaeta elongata: Laboratory measurements of predation rates verified by field observations of temporal and spatial feeding patterns1,2
Authors: Yen J. 
Published: April 2010

The size of copepod prey strongly influenced dietary selectivity by Euchaeta elongata. Adult females (4.2‐mm prosome length) showed highest predation rates on adult copepod prey 650– 1,000 µm long and on intermediate sized copepodid stages of Calanus pacificus. Selective feeding curves of copepodid stages IV and V of E. elongata showed a slight shift toward smaller prey. The prosome length of the primary prey was 70% the length of the second basipodal segment of the maxilliped for CIV, CV, and adult females of E. elongata. In both single and multispecies experiments at two concentrations, predation rates of adult female E. elongata seemed to be invariably focused on prey 650–1,000 µm long. Because E. elongata can consume adults of small copepod prey and the young copepodid stages of large copepod prey, it causes mortality of the entire copepod assemblage. Apparent recognition of a preferred prey, Pseudocalanus spp., and the nonpreferred cyclopoids seems to depend partly on their activity patterns. Thus, although size is an important determinant of dietary selectivity, species‐specific behavioral differences can also influence feeding rates.Variations in predatory feeding activity on copepod prey were closely related to diel vertical migrations of E. elongata. The number of adult females with ingested prey began to increase soon after sunset, when the predatory copepod entered the surface layers containing prey of the preferred size, thus corroborating the selective feeding pattern observed in the laboratory. The timing of the migrations coincided well with sunset (ascent) and sunrise (descent) in winter, spring, and summer.
Flux comparisons between sediments and sediment traps in the eastern tropical Pacific: Implications for atmospheric C02 variations during the Pleistocene1
Authors: Dymond Jack , Lyle Mitchell 
Published: April 2010

Regeneration rates of labile elements and biogenic components were measured at two sites in the Guatemala Basin by comparing fluxes of material caught in sediment traps to fluxes of that preserved in the sediments. From 95 to 99% of the N, P, organic C, CaCO3, opal, and Br reaching the sea floor are regenerated at the two sites. For elements bound largely in refractory phases (e.g. Al, Sc, Ti, and Fe), the particle‐associated flux to the bottom is within 20% of the accumulation rate in the sediment.The two MANOP sites, about 800 km apart, have similar fluxes of organically associated N, P, and C, reflecting similar and relatively high primary productivity. There is a marked contrast in the opal/carbonate fluxes which leads to differences in CO2 cycling at the two locations. At least 95% of the total particulate organic carbon and >97% of the total particulate phosphate are regenerated at <1,500‐m depth in the oceans. In contrast, much of the CaCO3 is destroyed at the sea floor. By a simple three‐box ocean model we show that the recycling and storage depths of organic C, CaCO3, and P can be important factors in the control of the CO2 content of the atmosphere. We suggest that Pleistocene CO2 variations were due in part to global increases in upwelling during glacial periods with synchronous increases in total oceanic productivity and differences in diatom vs. carbonate productivity.
The diurnal mixed layer1
Authors: Imberger J. 
Published: April 2010

Fine‐scale measurements and temperature gradient microstructure data are used to describe the diurnal energetics of the mixed layer in the Wellington Reservoir in Western Australia. The data covered a morning period of solar heating, a period of severe wind mixing induced by an afternoon sea breeze, and a period of pure penetrative convection extending through most of the night. The Wedderburn number (W) ranged from a value of 0.02 at the start of the heating phase to a value of about 10 at the end of the convective period. During the intermediate strong wind period the value of W remained about 0.1; the surface wind stress induced a strong tilt of the isotherms at the base of the mixed layer. The other main parameter, the ratio of the Monin‐Obukhov length to the depth of the mixed layer, ranged from about 5.0 during the morning down to 0.005 at the end of the convective period. The full range of mixed‐layer deepening processes could thus be analyzed.A simple one‐dimensional integral mixed‐layer model was applied to assess the importance of the temporal terms in diurnal simulations and to verify the values of the energy conversion efficiencies used in such models. Overall, the model performed extremely well; however, the results showed the need to develop parameterizations for the energetics of billowing induced by large shears across the base of the mixed layer and for the mixing accompanying upwelling.
Anaerobic methane oxidation rates at the sulfate‐methane transition in marine sediments from Kattegat and Skagerrak (Denmark)1
Authors: Iversen Niels , Jorgensen Bo Barker 
Published: April 2010

Concomitant radiotracer measurements were made of in situ rates of sulfate reduction and anaerobic methane oxidation in 2–3‐m‐long sediment cores. Methane accumulated to high concentrations (>1 mM CH4) only below the sulfate zone, at 1 m or deeper in the sediment. Sulfate reduction showed a broad maximum below the sediment surface and a smaller, narrow maximum at the sulfate‐methane transition. Methane oxidation was low (0.002–0.1 nmol CH4 cm−3 d−1) throughout the sulfate zone and showed a sharp maximum at the sulfate‐methane transition, coinciding with the sulfate reduction maximum. Total anaerobic methane oxidation at two stations was 0.83 and 1.16 mmol CH4 m−2 d−1, of which 96% was confined to the sulfate‐methane transition. All the methane that was calculated to diffuse up into the sulfate‐methane transition was oxidized in this zone. The methane oxidation was equivalent to 10% of the electron donor requirement for the total measured sulfate reduction. A third station showed high sulfate concentrations at all depths sampled and the total methane oxidation was only 0.013 mmol m−2 d−1.From direct measurements of rates, concentration gradients, and diffusion coefficients, simple calculations were made of sulfate and methane fluxes and of methane production rates.
Seawater filtration: Particle flow and impaction considerations
Authors: Johnson B. D. , Wangersky P. J. 
Published: April 2010

In filtration of seawater, adsorption of substances dispersed at sizes smaller than the filter pore dimension can result in major error. This error may be particularly severe for pore sizes approaching the 0.45‐µm delineation between dissolved and particulate.A model based on diffusion in forced convection and interception predicts that, under typical conditions for filtration of seawater, a large portion of materials dispersed at sizes smaller than the filter pore dimension will interact with the filter pore wall. However, the fraction of these interacting materials that adsorb must be a function of many variables, both physical and surface chemical.
Production of heterotrophic bacteria inhabiting macroscopic organic aggregates (marine snow) from surface waters1
Authors: Alldredge Alice L. , Cole Jonathan J. , Caron David A. 
Published: April 2010

Macroscopic detrital aggregates, known as marine snow, are a ubiquitous and abundant component of the marine pelagic zone. Descriptions of microbial communities occurring at densities 2–5 orders of magnitude higher on these particles than in the surrounding seawater have led to the suggestion that marine snow may be a site of intense heterotrophic activity. We tested this hypothesis using incorporation of [3H]thymidine into macromolecules as a measure of bacterial growth occurring on marine snow from oceanic waters in the North Atlantic and from neritic waters off southern California.Abundances of marine snow ranged from 0.1 to 4.3 aggregates liter−1. However, only 0.1–4% of the bacteria in the water occurred in association with marine snow. Mean thymidine incorporation per cell on aggregates was generally equal to or lower than that of bacteria found free‐living in the surrounding seawater, indicating that attached bacteria were not growing more rapidly than free‐living bacteria. Bacteria inhabiting aggregates were up to 25 times larger than free‐living forms. Thus, the contribution of these attached bacteria to total bacterial production in surface waters was low but occasionally significant, ranging from 3 to 26% and averaging 8 ± 7%
Nitrogen metabolism of the eutrophic Delaware River ecosystem1
Authors: Lipschultz Fredric , Wofsy Steven C. , Fox Lewis E. 
Published: April 2010

A comprehensive investigation of the nitrogen cycle in the Delaware River was carried out using 15N tracers to measure rates for important transformations of nitrogen. Daily, depth‐averaged 15N rates for the principal inorganic nitrogen species were consistent with rates derived from longitudinal profiles of concentration in the river.The data indicated that nitrification was a rapid, irreversible sink for NH4+, with export of the product NO3− from the study area. Utilization of NO3− by primary producers was negligible, owing to low irradiance levels and to high NH4+ concentrations.The oxygen sag near Philadelphia was found to result from oxygen demand in the water column, with only minor benthic influence. Reaeration provided the major oxygen input. Nitrification accounted for about 1% of the net oxygen demand near Philadelphia but as much as 25% farther downstream.
Dissolved humic substances of the Amazon River system1
Authors: Ertel John R. , Hedges John I. , Devol Allan H. , Richey Jeffrey E. , Ribeiro Maria de Nazaré Góes 
Published: April 2010

Aquatic humic and fulvic acids from nine mainstem and seven major tributary sites in the Amazon River Basin are characterized by their elemental and lignin phenol compositions. Combined humic substances represent 60% of the riverine dissolved organic carbon (DOC), with fulvic to humic acid (FA : HA) ratios in the mainstem averaging 4.7±1.0. All dissolved humic and fulvic acids have clearly recognizable lignin components at levels (8 and 3% of the carbon) suggesting a predominantly allochthonous source. Lignin compositional characteristics are dominated by diagenetic transformations, which include preferential loss of methoxylated structural units and oxidative degradation of lignin side chains. Fulvic acids have consistently lower lignin levels, lower lignin phenol methoxylation, higher acid : aldehyde ratios, and higher C: N ratios than coexisting humic acids, all indicative of greater aerobic degradation of the fulvic acid fraction. An extreme example of lignin degradation is seen in the Rio Negro humic and fulvic acids, which differ significantly in lignin and elemental compositions from other blackwater tributary and mainstem samples.Over most of the mainstem humic and fulvic acids behave conservatively. However, downstream of the Rio Negro confluence, humic acids appear to be selectively adsorbed onto fine suspended particles. Approximately 25 and 40% of the total fluxes of lignin and of carbon are represented in the dissolved humic substances. The annual flux of dissolved, chemically recognizable lignin in the Amazon River at Obidos is calculated to be 1.2 × 1011 g yr−1.
The measurement of bacterial chlorophyll and algal chlorophyll a in natural waters
Authors: Caraco N. , Puccoon A. H. 
Published: April 2010

Several groups of chlorophyll‐bearing photosynthetic organisms often coexist in anoxic waters. Because of the close similarity between the absorbance spectra of chlorophyll a (in cyanobacteria and algae) and the chlorophylls of green sulfur bacteria (Chl‐GSB) it is difficult to distinguish these two groups of organisms where they co‐occur.We have developed a simple method to measure both chlorophyll a and Chl‐GSB and used it in a meromictic coastal pond. In anoxic bottom waters Chl‐GSB was the major pigment present (averaging 20 mg m−3), but chlorophyll a accounted for from 5 to > 50% of the total pigment present throughout the year. Without our method large errors in calculated Chl‐GSB and chlorophyll a concentrations would have resulted.
Competition in zooplankton communities: Suppression of small species by Daphnia pulex1
Authors: Vanni Michael J. 
Published: April 2010

The hypothesis that a large zooplankton herbivore, Daphnia pulex, can competitively reduce the abundance of resident zooplankton when colonizing a community of small species was tested in two lakes. When introduced to enclosures in eutrophic Larimore Pond, D. pulex decreased phytoplankton abundance by an order of magnitude, resulting in drastically reduced densities of Tropocyclops prasinus and Mesocyclops edax, the two dominant crustaceans in the pond. Daphnia pulex was also added to enclosures in oligo‐mesotrophic Dynamite Lake, along with nutrients, in a factorial design. Three Dynamite Lake zooplankters were reduced in density by D. pulex under both enriched and unenriched conditions: Bosmina longirostris, Trichocerca multicrinis, and copepod nauplii. Nutrient additions allowed these taxa to overcome some effects of competition with D. pulex. Daphnia pulex reduced the densities of copepods and rotifers common to both lakes more in eutrophic Larimore Pond than in unenriched Dynamite Lake enclosures.These results show that a large herbivore can reduce the density of some small zooplankton species and therefore contribute to the scarcity of small species in lakes dominated by large herbivores. Furthermore, the results suggest that the competitive effects of a large herbivore on rotifers and copepods may be more pronounced in eutrophic systems because the large species can attain a higher population density, and subsequently alter the resource base to a greater extent, in eutrophic systems.
The effect of food concentration on fecal pellet size in marine copepods1
Authors: Dagg Michael J. , Walser W. Edward 
Published: April 2010

Three species of copepods, Temora turbinata, Eucalanus pileatus, and Neocalanus plumchrus, were fed cultures of the diatom, Thalassiosira weissflogii, at concentrations ranging from 0.3 to 14.5 µg Chl liter−1 to determine whether fecal pellet size was related to food concentration. In all three copepods, pellet size increased with food concentration up to about 3 µg Chl liter−1. At higher concentrations pellet size was constant. Pellets were less compact and appeared to be more fragile at low food concentrations.The level of gut contents in these copepods was also related to food concentration up to about 3 µg Chl liter−1. Below this concentration, ingestion and defecation were balanced in such a way that the gut did not fill, and therefore pellet size was smaller. Food concentrations sufficient to allow a copepod to fill its gut result in the production of fecal pellets of maximum size.It is concluded that fecal pellets produced by large copepods under conditions of low food availability are less likely to sink out of the euphotic zone than pellets produced by the same copepods under conditions of higher food availability.
Littoral slope as a predictor of the maximum biomass of submerged macrophyte communities1,1
Authors: Duarte Carlos M. , Kalff Jacob 
Published: April 2010

The hypothesis that the morphometric characteristics of the littoral zone of lakes are a major determinant of submerged macrophyte biomass was tested in Lake Memphremagog (Québec‐Vermont) by studying the relationship between maximum biomass of submerged macrophytes and physical and sediment characteristics of the littoral zone. The slope of the littoral zone accounted for 72% of the observed variability in maximum submerged macrophyte biomass (MSMB). By also incorporating sediment organic matter the variance explained was raised to 88% (P < 0.0001). A model based on only slope as predictor of MSMB was improved by considering slopes ≷5.33%:

urn:x-wiley:00243590:media:lno19863151072:lno19863151072-math-0001
The power of these two equations to predict the MSMB in a variety of temperate lakes was high (r = 0.90, P < 0.0001). However, the temperate zone model overestimates the MSMB in highly turbid lakes where irradiance rather than slope is pre‐eminent and underestimates the biomass in semitropical and tropical lakes.
Tests of an extension to internal seiches of Defant's procedure for determination of surface seiche characteristics in real lakes1
Authors: Lemmin U. , Mortimer C. H. 
Published: April 2010

The success of A. Defant's method of calculating surface seiche periods and structures in real lakes is well known. To test whether it can be adapted and applied with similar success in studies of internal seiches in stratified lakes, in which density structure is simulated by two homogeneous layers, we compare the predictions of a computerized version of Mortimer's modified Defant procedure against observations of internal seiche motion in eight lake basins and (in three examples) against the results of more elaborate models. The acceptably close agreement inspires confidence that the modified method is useful for practical predictions which, although approximate, described the principal characteristics of the often large water mass displacements and oscillations. Through their influence on mixing and dispersal, those motions profoundly affect the chemical and biological economies of many lakes. To aid in microcomputer and even pocket calculator applications, we set out steps in the calculation in tabular flow‐chart form. A comparable table for surface seiche calculation is added.The procedure is not applicable to large lakes in which effects of the earth's rotation are dominant; but for the two largest basins tested here (Léman and Ness) a modification is introduced to take approximate account of rotation.
Ingestion, gut passage, and egestion by the copepod Neocalanus plumchrus in the laboratory and in the subarctic Pacific Ocean12
Authors: Dagg Michael J. , Walser W. Edward 
Published: April 2010

The relationships between ingestion rate, gut content, gut passage time, and egestion rate in the copepod Neocalanus plumchrus were determined in laboratory experiments over a wide range of food concentrations. Ingestion, gut content, and egestion were related to food concentration in a rectilinear manner; increases were linear up to about 4.0 µg Chl liter−1 of Thalassiosira weissflogii and constant at higher concentrations. Gut passage time was constant at food concentrations >4.0 µg Chl liter−1, but passage slowed dramatically at lower concentrations.Levels of gut pigments in N. plumchrus collected from the central subarctic Pacific Ocean during June 1983 and May 1984 were very low. There was no diel periodicity in gut contents, and no vertical spatial patterns in gut fullness were observed in copepods collected from the upper 80 m. The gut pigment levels were converted to in situ ingestion rates using a gut passage time derived from laboratory and field experiments. Resultant ingestion rates, although extremely low, were approximately what laboratory experiments predicted for the low food concentrations available in this oceanic region. Budgetary considerations suggest that N. plumchrus in the subarctic Pacific Ocean must be supplementing its ingestion of phytoplankton with microzooplankton or that metabolic expenditures must be less than reported for the same species in the Bering Sea.
Specific in vivo absorption coefficient of chlorophyll a at 675 nm1
Authors: Haardt Hauke , Maske Helmut 
Published: April 2010

Spectral absorption of phytoplankton from cultures and natural samples was measured by means of an integrating‐sphere photometer. Measurements on suspension yielded specific absorption coefficients for healthy phytoplankton cultures in collimated light at 675 nm between 0.007 and 0.013 m2 (mg Chl a)−1. These values were independent of cell density and cell wall material.Natural samples of Kiel harbor water yielded specific absorption coefficients at 675 nm of 0.009 and 0.017 m2 (mg Chl a)−1. The specific absorption coefficients in suspension were dependent on the optical properties of the individual cells (packaging effect), decreasing (ca. 1/r) with increasing cell size (r radius) and increasing chlorophyll a content per cell as predicted by theory, but are significantly lower than theoretically expected. Comparison with published values shows that specific absorption coefficients of cell suspensions are often overestimated, presumably because of methodological problems.