bluuebunny/crossref_metadata_2025 huggingface dataset:
Bacterial chemotaxis and its potential role in marine dimethylsulfide production and biogeochemical sulfur cycling
Authors: Zimmer‐Faust Richard K. , de Souza Mark P. , Yoch Duane C.
Published: May 2010

Dimethylsulfide (DMS) gas constitutes 90% of biogenic sulfur emissions from oceans and is an important agent in climate regulation. DMS in seawater arises primarily via lyase degradation of dimethylsulfoniopropionate (DMSP), an osmolyte produced in high concentrations by some marine phytoplankton. After being induced to synthesize DMSP lyase, cells of a marine bacterium (Alcaligenes strain M3A) significantly reduce their rate of change in direction and tumbling frequency, and they are attracted to DMSP at levels similar to those occurring near senescing phytoplankton cells (10‒7–10‒6 M). In contrast, genetically identical bacteria without lyase induction are not attracted to DMSP. Combined with lyase activity, bacterial chemotaxis to DMSP could increase the rate of DMS production and therefore play a critical role in biogeochemical sulfur cycling between dissolved organic matter in seawater and the atmosphere.
Application of 222Rn and CH4 for assessment of groundwater discharge to the coastal ocean
Authors: Cable Jaye E. , Bugna Glynnis C. , Burnett William C. , Chanton Jeffrey P.
Published: May 2010

Groundwater discharge is a neglected source of freshwater and dissolved constituents to the ocean. It can occur via diffuse seepage and point source spring discharge. Two naturally occurring trace gases, 222Rn and CH4, are present in groundwater at concentrations that are elevated by several orders of magnitude relative to seawater, and they may be useful in tracing groundwater inputs to surface waters. Water samples collected near a submarine spring in the northeastern Gulf of Mexico displayed radon and methane concentrations inversely related to salinity and considerably greater than those found in surrounding waters. Coastal water 222Rn and CH4 inventories varied directly with groundwater seepage rates. The integrated quantities of 222Rn and CH4 in the nearshore waters overlying a seepage meter transect showed a significant positive relationship (95% C.L.) to direct measurements of seepage. Diffusive fluxes (178±56 dpm m‒2 d‒1), obtained by three different approaches at the same site, showed that these waters receive only a small contribution of 222Rn by diffusion. In contrast, benthic flux chamber measurements revealed a total advective‐diffusive contribution of 5,200±1,800 dpm m‒2 d‒1 (n = 14). Radon inventories in these shallow nearshore marine waters are consistent with the input of radon‐bearing groundwaters.
A preliminary study of the geochemical and microbiological characteristics of modern sedimentary concretions
Authors: Duan W. M. , Hedrick D. B. , Pye K. , Coleman hf. L. , White D. C.
Published: May 2010

Parallel mineralogical, geochemical, and lipid biomarker analyses of sedimentary siderite concretions and their host sediments were undertaken to give detailed information about the microbially mediated diagenetic processes involved. Concretions were collected from two contrasting environments at Warham, north Norfolk—typical brownish silty marsh sediment and black anaerobic mud from a creek bank—but no major differences in their mineralogy or geochemistry were found. Samples consisted of siderite, amorphous iron oxides, and iron sulfides with more carbonate present in the outer than in the inner parts. Subsamples from the concretions were found to be more similar to each other in their sulfide and organic carbon contents than to the host sediments. The microbiological characteristics revealed by lipid biomarker analysis showed considerable variation between concretions and host sediments, between individual concretions, and between inner and outer parts of the concretions. The predominant sulfate‐reducing bacteria were more numerous in the concretions than in host sediments, but varied greatly within the concretions. The biomarker i17 : 1ω7c for Desulfovibrio was enriched within the concretions, suggesting that these bacteria, which are capable of reducing iron directly, played an important role in concretion formation. The lipid biomarker data indicated that the bacterial community changed during concretion formation and that different conditions for preservation existed in the concretions compared with the host sediments.
Pulsed delivery of subthermocline water to Conch Reef (Florida Keys) by internal tidal bores
Authors: Leichter James J. , Wing Stephen R. , Miller Steven L. , Denny Mark W.
Published: May 2010

Internal tidal bores generated by breaking internal waves cause dramatic, high‐frequency variation in temperature, salinity, water velocities, and concentration of chlorophyll a on Conch Reef, Florida Keys. The arrival of bores on the reef slope is linked to a semidiurnal internal tide and is marked by temperature drops of up to 5.4°C and salinity increases of up to 0.6‰ in 1–20 min. These changes are accompanied by the sudden onset of upslope flow 1–15 m above the bottom with speeds of 10–30 cm s−1. Cool, high‐salinity water is transported from below the thermocline seaward of the reef and is resident on the reef slope for up to 4 h before it mixes with surface waters and recedes downslope. Compared with ambient surface water, this deep water can contain significantly elevated concentrations of dissolved nitrate. Physical variability produced by this mechanism increases significantly with depth on the reef slope. Analysis of 3‐yr temperature records indicates the arrival of internal bores is a consistent feature at this site from May through November, with peak activity in July–September. Pulsed delivery of subthermocline water appears to significantly affect the temperature, nutrient, and particle flux regimes on this coral reef.
Dynamic response of deep‐sea sediments to seasonal variations: A model
Authors: Soetaer Karline , Herman Peter M. J. , Middelburg Jack J.
Published: May 2010

We present a dynamic, numerical model of early diagenetic processes that can be used to examine the response of different organic carbon mineralization pathways, concentration vs. depth profiles, and the resultant fluxes to seasonally varying carbon deposition. We show that there can be substantial temporal variability in sediment‐water fluxes as well as in the relative contribution of different organic carbon mineralization pathways and oxygen consumption processes in deep‐sea sediments. The timing and amplitude of the sediment response are most sensitive to the reactivity of the organic matter. We show that the fluxes of dissolved substances can be approximated by assuming that these constituents are at steady state with the carbon profiles.

The model is used to reconcile a time series of community oxygen consumption rates, dissolved oxygen, nitrate, ammonia, and manganese profiles, and solid‐phase organic carbon profiles at a deep‐sea station in the Pacific. The organic carbon that is deposited is very reactive (7.2 yr‒1), which causes a fast response of the sediment community to seasonal pulses in carbon flux and significant temporal variation in oxygen and nutrient fluxes. The model predicts large seasonal variations in the relative importance of oxic (48–71%), denitrification (12–17%), and anoxic (16–37%) pathways. There is also substantial variation in the pore‐water profiles of oxygen, nitrate, ammonia, and other reduced substances over the seasonal cycle, indicating that seasonal variability should be taken into account when extrapolating from a single observation to yearly averaged values.
Effects of exposure to air and subsequent drying on the phosphate sorption characteristics of sediments from a eutrophic reservoir
Authors: Baldwin D. S.
Published: May 2010

The effects of exposure to air and subsequent drying on the phosphate adsorptive characteristics of sediments taken from Chaffey Dam—a small eutrophic water storage reservoir in New South Wales, Australia—were studied. Sediments were sampled along a transect that covered heavily desiccated, wet‐littoral, and submerged sediments, both from above and below the oxycline. Phosphate adsorption isotherms showed that there was a definite transition in P affinity along the transect, with sediments taken from the driest sites displaying the least adsorptive capacity for phosphate and samples taken from beneath the oxycline the highest. A similar transition was observed for the kinetics of phosphate uptake. The order of reaction with respect to phosphate loading decreased from approximately first order for anoxic sediments to fractional order for desiccated sediments. These effects are mostly the result of sediment oxidation and aging rather than desiccation, variation in elemental composition, or differences in the amount of native P adsorbed to the sediment.
Inorganic carbon pools in the bloom‐forming dinoflagellate Peridinium gatunense
Authors: Berman‐Frank Ilana , Erez Jonathan
Published: May 2010

Peridinum gatunense, the main bloom‐forming species in Lake Kinneret, acquires a carbon‐concentrating mechanism (CCM) during the progression of the annual winter–spring bloom. Previous indications for CCM activity in P. gatunense were based on decreased carbon isotope fractionation and higher activity of carbonic anhydrase (both external and internal). In the present study, CCM activity in low‐density, natural, and cultured P. gatunense populations was demonstrated by cells showing higher internal inorganic carbon (Ci) concentrations than those in the external medium. The presence, size, and dynamics of these Ci pools were measured using pulse‐chase experiments of 14C uptake into photosynthetic acid‐stable products under varying Ci, pH, CO2(aq), and light regimes. Internal Ci levels in P. gatunense were higher by a factor of ∼20–80 relative to the ambient Ci. The time required to reach isotopic equilibration of the pool ranged from 30 to 90 min, whereas the time required for the assimilation of the pool into cellular carbon ranged from 10 to 50 min. These long timescales are attributed to the larger vol: surface area ratio of this organism. Induction of the CCM was triggered by CO2(aq) rather than Ci and was evident at CO2(aq) concentrations <15 M. Preincubation in either the dark or with high CO2(aq) levels diminished the Ci pool. The data we report represent the steady‐state carbon metabolism of the species since the cells were not deprived of Ci prior to the measurements. The CCM in P. gatunense is an important adaptation mechanism contributing to the high primary production observed in the lake at the peak of the bloom under CO2‐limiting conditions [pH >9.5 and CO2(aq) <5 µM].
Separating biological and physical changes in dissolved oxygen concentration in a coral reef
Authors: Kraines Steven , Suzuki Yoshimi , Yamada Koichi , Komiyama Hiroshi
Published: May 2010

Measured changes in dissolved oxygen (DO) concentrations in a coral reef at Miyako Island are markedly different from the diurnal sinusoidal pattern expected if biological processes are dominant. We were able to resolve this paradox by constructing a simple model that combines the influences of organic production and air–sea exchange with water flow and mixing through the reef system. The model successfully replicates the observed DO behavior, suggesting that the simple flow system we propose adequately accounts for these water advection effects. Our optimized estimates of gross production and respiration on the reef flat are 13 m and 5.2 g C m‒2 d‒1, giving a P : R ratio of 2.5. We obtained best fits to the data in the lagoon with a production rate of 4.9 g C m‒2 d‒1 and a respiration rate of 5.2 g C m‒2 d‒1 for a P : R ratio of 0.9.
Movement response of Chaoborus to chemicals from a predator and prey
Authors: Berendonk Thomas U. , O'Brien W. John
Published: May 2010

By means of a silhouette videotaping system we studied the frequency of movements of Chaoborus americanus and Chaoborus punctipennis when exposed to water conditioned in different ways. Four treatments were investigated: unconditioned water was used as a control; predator‐conditioned water was water in which fish had been held; prey‐conditioned water was water in which cladocerans had been grown; and mixed water was a mixture of predator‐ and prey‐conditioned waters. The movement frequency of C. punctipennis significantly increased in prey water and decreased in predator water as compared to unconditioned water. The movement frequency of C. americanus significantly increased in prey‐conditioned water; however, when exposed to predator‐conditioned water the movement frequency was not significantly different from unconditioned water.
Simultaneous mooring‐based measurements of seawater CO2 and O2 off Cape Hatteras, North Carolina
Authors: DeGrandpre M. D. , Hammar T. R. , Wallace D. W. R. , Wirick C. D.
Published: May 2010

We deployed CO2 and O2 sensors on the U.S. continental shelf off Cape Hatteras, North Carolina, during late summer 1994. A continuous 32‐d gas record was obtained at 20 m in 25 m of water, below the thermocline for most of the period. Analysis of the correlation between CO2 and O2 indicates that biological and advective processes dominated the gas variability, with small or insignificant fluxes due to air–sea exchange, vertical eddy diffusion, and carbonate dissolution or formation. The observed O2 : CO2 correlation was 1.39, within the range predicted for the photosynthetic quotient. Photosynthesis and respiration appeared to be tightly coupled, resulting in no net community production in these waters during the late summer. It is evident from these results that the combination of mooring‐based CO2 and O2 measurements will be a powerful tool for studying the marine carbon cycle.
Ammonium uptake by coral reefs: Effects of water velocity and surface roughness on mass transfer
Authors: Thomas F. I. M. , Atkinson M. J.
Published: May 2010

To test the hypothesis that ammonium uptake by coral reefs is mass‐transfer limited and to determine the relative effects of water velocity and community roughness on uptake, we measured the rates of ammonium uptake by reefs at velocities ranging from 3.3 to 37.5 cm s‒1. Two assemblages of coral rubble (relatively rough and relatively smooth) and two assemblages of live coral (Porites compressa and Pocillopora damicornis) were used. Rate constants for uptake ranged from 16 to 144 × 10‒6 m ‒1, and were positively correlated to water velocity. We estimated roughness of each assemblage as mean height, relief, and by measuring the friction coefficient of each assemblage at water velocities ranging from 3.3 to 58.0 cm s‒1. Friction coefficients ranged from 0.033 to 0.264. Stanton numbers (a dimensionless ratio of uptake rate to advection past the uptake surface) calculated from experimental data were within 80% of those calculated from empirically derived engineering equations describing heat transfer to rough surfaces. Results support the hypothesis that ammonium uptake is mass‐transfer limited and are consistent with mass transfer relationships for nonbiotic surfaces.
Response of otolith microchemistry to environmental variations experienced by larval and juvenile Atlantic croaker (Micropogonias undulatus)
Authors: Thorrold Simon R. , Jones Cynthia M. , Campana Steven E.
Published: May 2010

Minor and trace elements incorporated into otoliths during growth may permanently record environmental conditions experienced by fishes. To determine the validity of this approach, we used laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS) to assay sectioned otoliths from juvenile Atlantic croaker (Micropogonias undulatus) collected from each of three sites in the Neuse River, North Carolina, and the Elizabeth River, Virginia. Elemental concentrations at the center of the otoliths did not differ between locations, although both Mg:Ca and Ba:Ca were significantly higher at the edge of otoliths from the Neuse River than from the Elizabeth River. Three of the elements (Mg:Ca, Sr:Ca, and Ba:Ca) showed significant variation across otoliths. Sr:Ca, and to a lesser extent Mg:Ca, showed progressive decreases as the fish moved from offshore spawning sites to estuarine nursery areas. The opposite pattern was shown by Ba: Ca. We hypothesize that: these patterns were related to the elemental concentrations within oceanic and estuarine water masses. Although both Sr: Ca and Ba: Ca seem to be useful tracers of offshore‐inshore migration of estuarine‐dependent species, the sensitivity of the technique to more subtle changes in water chemistry remains to be determined.
Comparing annual population growth estimates of the exotic invader Bythotrephes by using sediment and plankton records
Authors: Hall Roland I. , Yan Norman D.
Published: May 2010

The annual population growth of the exotic invader Bythotrephes cederstroemi was calculated from the spatial distribution and rate of accumulation of its diagnostic caudal processes in the sediments of Harp Lake, Ontario. To our knowledge, this is the first use of the sediment record to quantify the annual population growth of a zooplankton species on a whole‐lake scale with confidence estimates. In 1994, 553±254 (95% C.L.) animals m−2 were produced in Harp Lake, an estimate statistically indistinguishable from that developed independently from the plankton data and temperature‐dependent growth models (459 animals m−2). When annual population growth estimates will suffice, the sediment record offers several advantages. It requires less fieldwork than do plankton‐based approaches and requires the quantification of the means and variances of fewer parameters. It also can provide population growth estimates for the past. For example, the sediment record indicated that one‐third of all B. cederstroemi ever produced in Harp Lake predated the start of our plankton records in 1994. The sediment record may have other uses. The breakage of caudal processes may provide clues to the rates of fish predation on B. cederstroemi, suggesting, for example, that 40% of the Harp Lake B. cederstroemi were eaten by fish in 1994.
Trophic effects of sponge feeding within Lake Baikal's littoral zone. 1. Insitu pumping rates
Authors: Patterson Mark R. , Chernykh Valeri I. , Fialkov Vladimir A. , Savarese Michael
Published: May 2010

Demosponges dominate the littoral zone of Lake Baikal, Russia. During August 1993, we measured the in situ pumping activity of a globose sponge, Baikalospongia bacillifera, common at depths of 8–50 m. Excurrent flow speed, surface area, and oscular diameter were measured with fluorescein dye release, underwater video, and image processing for nine individual sponges; diel deployments of a heated thermistor flowmeter were made on another three individuals. Mean pumping rates for oscula ranged from 0.2 to 3.3 cm s−1, with instantaneous measurements as high as 25 cm s−1. Although between‐sponge variability is large, oscula from an individual maintain speeds within 1 cm s−1 of each other. Volume fluxes for oscula measured from all individuals range from 0.01 to 0.60 cm3 s−1. Fluxes for individuals indicate that a sponge processes its volume in 17–24 s, comparable to values obtained for marine species. Oscula are not continuously active and often reduce pumping for several hours at irregular intervals. Two of three individuals monitored over a diel cycle exhibited negative correlations between the ambient current and oscular excurrent flow. Boundary layer measurements and diffusivity calculations demonstrate that sponges are capable of depleting picoplankton near the bottom.
Assessing the short‐term stability of spatial patterns of macrobenthos in a dynamic estuarine system
Authors: Hewitt J. E. , Pridmore R. D. , Thrush S.F. , Cummings V. J.
Published: May 2010

Recent studies of macrofauna on sandflats have emphasized postsettlement dispersal, particularly associated with sediment bedload transport. This study investigated the short‐term (3 weeks) stability in spatial patterns of eight common, potentially mobile, near‐surface macrofaunal species inhabiting a 4,000‐m2 area of intertidal sandflat. Over this period, wind conditions reworked the sediment to a depth of 3 cm, thus generating sediment and animal transport. Movement and changes in spatial arrangement of juvenile Macomona liliana and Paphies australis demonstrated the need to consider postsettlement dispersal in survivorship and experimental studies and to conduct such studies at a relevant scale. However, the majority of the species exhibited stability of spatial pattern, even when undergoing movement and changes in mean density. This finding suggests that biological interactions and organism‐habitat relationships are important processes even in habitats where the sediment and organisms are mobile.
Pigment specific growth and grazing rates of phytoplankton in the central equatorial Pacific
Authors: Latasa Mikel , Landry Michael R. , Louise SchlÜter , Bidigare Robert R.
Published: May 2010

Dilution experiments were performed during two transects across the central equatorial Pacific (3°N–3°S, 140°W) to estimate growth and mortality rates of select phytoplankton groups distinguished by their characteristic pigments. The first transect was conducted in February–March 1992 during a moderate El Niño event; the second transect took place in August–September 1992, under normal upwelling conditions. Experiments with and without added nutrients (N, P, Fe, and Mn) indicated that growth rates were nutrient limited during El Niño conditions. Nevertheless, the enhanced growth rates with added nutrients during El Niño were less than rates without added nutrients during the normal upwelling period; therefore, nutrients alone did not account for all of the differences between cruises. Growth rates were different for the various algal groups. In August–September, diatoms grew at 1.7 d−1, and prochlorophytes and prymnesiophytes at −0.5 d−1. Grazing by microzooplankton balanced growth for algal groups exhibiting the lowest growth rates (i.e. prymnesiophytes and prochlorophytes). Although microzooplankton grazing on diatoms and pelagophytes was also significant, a substantial fraction of their growth escaped consumption, accounting for most of the net chlorophyll production of the phytoplankton community.
Altered cell wall morphology in nutrient‐deficient phytoplankton and its impact on grazers
Authors: Donk E. Van , LÜrling M. , Hessen D. O. , Lokhorst G. M.
Published: May 2010

Grazing experiments were performed with the zooplankters Daphnia pulex and Daphnia magna feeding on nitrogen‐ and phosphorus‐limited cells of two green algae (Chtamydomonas reinhardtii and Selenastrum capricornutum). To analyze the role of the cell wall structure in digestibility of the algae by Daphnia, the same experiments were carried out with both wild‐type C. reinhardtii and a cell wall‐deficient mutant.

The nonlimited algae were efficiently assimilated, whereas P‐ and N‐limited algal cells were not. Especially P‐limited cells passed mostly intact and viable through the gut and were thus spared from heavy grazing pressure. In life‐history experiments, D. pulex grazing on nonlimited algae reached the largest body size, whereas animals fed N‐ or P‐limited algae exhibited reduced growth. Cells of the wall‐deficient mutant of Chlamydomonas, grown under both nutrient‐limited and nonlimited conditions, were efficiently ingested and digested by Daphnia. Morphological changes in the cell wall of nutrient‐limited cells most probably reduced their digestibility. This phenomenon might be considered a defense mechanism by the algae to reduce grazing pressure when their growth rates are low.
Copepod grazing in the equatorial Pacific
Authors: Roman Michael R. , Gauzens Anne L.
Published: May 2010

The vertical distribution of copepod (>64 µm) grazing was measured on the equator at 140°W during March/April (19 d) and October 1992 (21 d). El Niño conditions prevailed during the March/April time series. Hydrographic variables were similar to the climatological mean during the October time series. We found higher weight‐specific copepod filtration rates in October when mixed‐layer temperatures were generally 3°C cooler; there were more phytoplankton >2.0 µm and more calanoid copepods than in March/April. The grazing impact of the copepod community (biomass × weight‐specific filtration rate) was similar for the 64–200‐µm copepod fraction during both time series (0.023 and 0.028 d−1 for March/April and October) but was higher in October (0.114 d−1) as compared to March/April (0.040 d−1) for >200‐µm copepods. Within‐cruise variability was highest in October when a tropical instability wave advected colder water with higher nitrate and chlorophyll through the study area. We observed over six‐fold increases in copepod biomass, weight‐specific filtration rates, and copepod grazing rates during this advective event. Grazing rates calculated by assuming that copepods capture only >2‐µm phytoplankton (0.25 d−1 in March/April; 0.88 d−1 in October) suggest that copepod grazing could limit the production of >2‐µm phytoplankton, primarily diatoms, in October but not during the El Niño conditions of March/April when there was less copepod biomass as well as a greater dominance of cyclopoid copepods. Estimates of fecal pellet production compared with export flux measurements suggest that most copepod fecal pellets produced in the euphotic zone decompose or are ingested by other zooplankton. Our estimates of copepod grazing rates on phytoplankton and protozoa are in agreement with previous calculations, which suggest that most of the carbon consumed by copepods in the equatorial Pacific is from protozoa.
Seasonal variation of CDOM and DOC in the Middle Atlantic Bight: Terrestrial inputs and photooxidation
Authors: Vodacek Anthony , Blough Neil V. , DeGrandpre Michael D. , DeGrandpre Michael D. , Nelson Robert K.
Published: May 2010

Extensive surveys of the fluorescence and absorption of chromophore‐containing dissolved organic matter (CDOM), dissolved organic C (DOC) concentration, chlorophyll fluorescence, and salinity were performed during August and November 1993 and March and April 1994 along a cruise line extending from the mouth of Delaware Bay southeast to the Sargasso Sea. With shallow stratification in August, photobleaching dramatically altered the optical properties of the surface waters, with ∼70% of the CDOM absorption and fluorescence lost through photooxidation in the waters at the outer shelf. S, the slope of the log‐linearized absorption spectrum of CDOM, increased offshore and seemed to increase with photodegradation. The increase in S combined with the seasonal variation in the relationship between Chl and CDOM underscores the difficulty in developing algorithms to predict Chl concentrations in turbid coastal waters with ocean color data. Despite the photooxidation of CDOM, the seasonal variation in the CDOM fluorescence‐absorption relationship and fluorescence quantum yields was <15%. When using appropriate methods, the airborne lidar approach for remote determination of CDOM absorption coefficients seems to be a very robust technique. The photooxidation of CDOM in August also affected the relationship between CDOM and DOC concentration in the surface waters, although for the rest of the year the relationship was reasonably linear. The results of a simple model suggest ∼10% of the DOC in the mixed layer was directly converted photochemically to dissolved inorganic C (DIC).
Acetate cycling in the water column and surface sediment of Long Island Sound following a bloom
Authors: Wu Hanguo , Green Mark , Scranton Mary I.
Published: May 2010

A number of workers have suggested that rates of acetate cycling in sediments may approximate the rates of anaerobic decomposition of organic matter. However, few studies have examined whether this relationship holds over very short time scales, such as those encountered during the deposition of the spring bloom into coastal sediments. In this study, we measured acetate concentrations and uptake rate constants in surface and bottom waters and in the top few centimeters of sediment in Long Island Sound. Samples were collected every 2–3 weeks from early spring to early summer of 1993. Acetate concentrations varied from 85 to 530 nM in the water column and from <2 to µMsed in pore water. Acetate concentrations in pore water showed a strong depth variation, with a concentration maximum in the surface few millimeters, as well as a strong temporal variation. The concentration of acetate averaged over the top 4 cm varied from about 5 µMsed in the early spring to 14.3 µMsed following the addition of spring bloom‐derived organic carbon. Acetate uptake rate constants in the water column varied from 0.0012 to 0.037 h−1 (turnover time 33.4 to 1.13 d). The average uptake rate constants in the sediment over the top 4 cm varied from 0.07 to 0.59 h−1 (turnover time 0.59 to 0.07 d) and tended to increase over the course of the experiment in both the sediment and the water column. In the water column, acetate uptake rates (calculated as rate constant times concentration) varied from less than one nanomole per liter per hour in the early spring to tens of nanomoles per liter per hour in the early summer. In the sediment over the same period, acetate uptake rates averaged over the top 4 cm varied from 0.13 to 5.25 µMsed−1 h−1. Rates of acetate metabolism to CO2 agreed within a factor of two to estimates of the ∑CO2 flux from the sediments, and both increased sharply following the deposition of the spring bloom. However, because temperatures were also increasing during this period, we are unable to separate unambiguously the effects of supply of labile carbon and of temperature on the acetate uptake rate.
Use of elemental composition to predict bioavailability of dissolved organic matter in a Georgia river
Authors: Sun L. , Perdue E. M. , Meyer J. L. , Weis J.
Published: May 2010

The relationship between the bioavailability of dissolved organic matter (DOM) and its bulk chemical composition was examined on three dates at 10 sites on the Ogeechee River, a blackwater river in Georgia. Samples of riverine DOM were concentrated from filtered river water using reverse osmosis. In addition, particulate organic matter (POM), in the form of leaf litter, algae, and macrophytes, was leached with synthetic rainwater to obtain fresh DOM. Elemental composition, carboxylic acid content, and bacterial growth were measured on all samples. The results of this study indicate that fresh DOM in POM leachates is generally more bioavailable than riverine DOM. The bioavailability of riverine DOM appears to be greater under low discharge conditions and decreases with distance downstream. The bioavailability of all DOM samples is very well predicted (r2 = 0.93, n = 20) by an empirical equation of the form: bioavailability = a0 + a1(H:C) + a2(O:C) + a3(N:C). When compositional data are plotted on a van Krevelen diagram, it is evident that POM leachates and, to a lesser degree, DOM from headwater sites have compositions that differ little from simple mixtures of major components of biomass (lipids, sugars, proteins, and lignins). Father downstream, major diagenetic alteration of organic matter is evident from the compositions of DOM samples, whose H: C and O: C ratios are lower and higher, respectively, than for any possible mixture of biomass components. Bioavailability of DOM is closely related to the percentage of aliphatic carbon in a sample, and downstream decreases in bioavailability are mainly attributable to selective degradation of aliphatic carbon in riverine DOM.
Hydromechanical mechanisms of colony organization and cost of hefense in an encrusting bryozoan, Membranipora membranacea
Authors: Grünbaum Daniel
Published: May 2010

In bryozoans, hydrodynamic interactions among colony members can substantially affect filtering rates and access to food‐rich water for zooids within a colony and for the colony as a whole. Hydrodynamic theory suggests that highly integrated (area‐filling) colony architectures lead to strong interference between neighboring zooids, whereas less integrated architectures do not. The highly integrated bryozoan Membranipora membranacea displays two morphological specializations that modify hydrodynamic interactions: internal excurrent zones (chimneys) and inducible defensive spines. In this study, possible hydrodynamic mechanisms underlying the cost of inducible defense and chimney organization were tested experimentally by culturing spined and unspined colonies under controlled flow conditions.

Spines reduced colony growth rate when growth was limited by clearance rates, but not when transport of particles from upstream limited growth. This supports the hypothesis that the cost of inducible defense is primarily a reduction in clearance rate (i.e. spines cause hydrodynamic interference with feeding currents) rather than metabolic investment in spine construction. Chimneys were more closely spaced in spined than unspined colonies, consistent with a mechanism for organizing chimney formation based on responses by zooids to local hydromechanical cues rather than a rigid, colony‐level control of zooid growth form (astogeny). Direct manipulation of hydrodynamic cues resulted in substantial changes in chimney morphology, again supporting the hydromechanical organization mechanism. More generally, these experimental results support the theoretical assessment that the highly integrated architecture is hydrodynamically unfavorable. The success of Membranipora in some habitats suggests that its architecture confers compensating advantages, such as improved ability to compete for space. This tradeoff in growth habit may explain shifts in relative prevalence of bryozoan architectures with depth and across other environmental gradients.
Morphological changes in Scenedesmus induced by infochemicals released in situ from zooplankton grazers
Authors: Lürling Miquel , Van Donk Ellen
Published: May 2010

Biochemical substances released from Daphnia galeata induced colony formation in the green alga Scenedesmus acutus. Normally this strain consisted mainly of single cells in cultures. However, if exposed for 48 h to either water with live Daphnia or to 0.1‐µm filtered water from a culture with Daphnia present, these unicellular “Chodatella” stages were induced to form colonies (coenobia). Colony induction was not unique to Daphnia; other zooplankters (rotifers and copepods) were able to induce colonies in S. acutus as well. This morphological response could also be evoked when Scenedesmus was exposed to 0.1‐µm filtered lake water during high zooplankton abundances. Especially during early spring, a clear relationship was found between rotifer abundance and colony formation in our test alga in the laboratory. Filtered lake water, incubated nonaxenically for at least 2 d at 20°C, did not induce colony formation, possibly due to microbial degradation. The morphological changes in Scenedesmus could promote grazing resistance in small zooplankters and can be interpreted as an adaptive antipredator strategy.
History of atmospheric SF6 from 1973 to 2008
Authors: Rigby M. , Mühle J. , Miller B. R. , Prinn R. G. , Krummel P. B. , Steele L. P. , Fraser P. J. , Salameh P. K. , Harth C. M. , Weiss R. F. , Greally B. R. , O'Doherty S. , Simmonds P. G. , Vollmer M. K. , Reimann S. , Kim J. , Kim K. R. , Wang H. J. , Dlugokencky E. J. , Dutton G. S. , Hall B. D. , Elkins J. W.
Published: May 2010

Abstract. We present atmospheric sulfur hexafluoride (SF6) mole fractions and emissions estimates from the 1970s to 2008. Measurements were made of archived air samples starting from 1973 in the Northern Hemisphere and from 1978 in the Southern Hemisphere, using the Advanced Global Atmospheric Gases Experiment (AGAGE) gas chromatographic–mass spectrometric (GC-MS) systems. These measurements were combined with modern high-frequency GC-MS and GC-electron capture detection (ECD) data from AGAGE monitoring sites, to produce a unique air history of this potent greenhouse gas. Atmospheric mole fractions were found to have increased by more than an order of magnitude between 1973 and 2008. The 2008 growth rate was found to be the highest recorded, at 0.29 ± 0.02 pmol mol−1 yr−1. A three-dimensional chemical transport model and a minimum variance Bayesian inverse method was used to estimate annual emission rates using the measurements. Consistent with the mole fraction growth rate maximum, global emissions during 2008 were also found to be highest in the 1973–2008 period, reaching 7.5 ± 0.4 Ggyr−1 and surpassing the previous maximum in 1995. The 2008 values follow an increase in emissions of 50 ± 25% since 2000. A second global inversion which also incorporated National Oceanic and Atmospheric Administration (NOAA) flask measurements and in situ monitoring site data was found to agree well with the emissions derived using AGAGE measurements alone. By estimating continent-scale emissions using all available AGAGE and NOAA surface measurements covering the period 2004–2008, we find that it is likely that much of the global emissions rise during this five-year period originated primarily from Asian countries that do not report emissions to the United Nations Framework Convention on Climate Change (UNFCCC). We also find it likely that SF6 emissions reported to the UNFCCC were underestimated between at least 2004 and 2007.
Continuous-flow isotope ratio mass spectrometry method for carbon and hydrogen isotope measurements on atmospheric methane
Authors: Brass M. , Röckmann T.
Published: May 2010

Abstract. We describe a continuous-flow isotope ratio mass spectrometry (CF-IRMS) technique for high-precision δD and δ13C measurements of atmospheric methane on 40 mL air samples. CH4 is separated from other air components by utilizing purely physical processes based on temperature, time and mechanical valve switching. Chemical agents are avoided. Trace amounts of interfering compounds can be separated by gas chromatography after pre-concentration of the CH4 sample. The fully purified sample is then either combusted to CO2 or pyrolyzed to H2 for stable isotope measurement. Apart from connecting samples and refilling liquid nitrogen as coolant the system is fully automated and allows an unobserved, continuous analysis of samples. The analytical system has been used for analysis of air samples with CH4 mixing ratios between ~100 and ~10000 ppb, for higher mixing ratios samples usually have to be diluted.
Seasonal distribution of dissolved inorganic carbon and net community production on the Bering Sea shelf
Authors: Mathis J. T. , Cross J. N. , Bates N. R. , Bradley Moran S. , Lomas M. W. , Mordy C. W. , Stabeno P. J.
Published: May 2010

Abstract. In order to assess the current state of net community production (NCP) in the southeastern Bering Sea, we measured the spatio-temporal distribution and controls on dissolved inorganic carbon (DIC) concentrations in spring and summer of 2008 across six shelf domains defined by differing biogeochemical characteristics. DIC concentrations were tightly coupled to salinity in spring and ranged from ~1900 μmoles kg−1 over the inner shelf to ~2400 μmoles kg−1 in the deeper waters of the Bering Sea. In summer, DIC concentrations were lower due to dilution from sea ice melt, terrestrial inputs, and primary production. Concentrations were found to be as low ~1800 μmoles kg−1 over the inner shelf. We found that DIC concentrations were drawn down 30–150 μmoles kg−1 in the upper 30 m of the water column due to primary production and calcium carbonate formation between the spring and summer occupations. Using the seasonal drawdown of DIC, estimated rates of NCP on the inner, middle, and outer shelf averaged 28 ± 9 mmoles C m−2 d−1. However, higher rates of NCP (40–47 mmoles C m−2 d−1) were observed in the "Green Belt" where the greatest confluence of nutrient-rich basin water and iron-rich shelf water occurs. We estimated that in 2008, total NCP across the shelf was on the order of ~96 Tg C yr−1. Due to the paucity of consistent, comparable productivity data, it is impossible at this time to quantify whether the system is becoming more or less productive. However, as changing climate continues to modify the character of the Bering Sea, we have shown that NCP can be an important indicator of how the ecosystem is functioning.
CO2-induced seawater acidification affects physiological performance of the marine diatom Phaeodactylum tricornutum
Authors: Wu Y. , Gao K. , Riebesell U.
Published: May 2010

Abstract. CO2/pH perturbation experiments were carried out under two different pCO2 levels (39.3 and 101.3 Pa) to evaluate effects of CO2-induced ocean acidification on the marine diatom Phaeodactylum tricornutum. After acclimation (>20 generations) to ambient and elevated CO2 conditions (with corresponding pH values of 8.15 and 7.80, respectively), growth and photosynthetic carbon fixation rates of high CO2 grown cells were enhanced by 5% and 12%, respectively, and dark respiration stimulated by 34% compared to cells grown at ambient CO2. The K1/2 (dissolved inorganic carbon, DIC) for carbon fixation increased by 20% under the low pH and high CO2 condition, reflecting a decreased photosynthetic affinity for HCO3− or/and CO2 and down-regulated carbon concentrating mechanism (CCM). In the high CO2 grown cells, the electron transport rate from photosystem II (PSII) was photoinhibited to a greater extent at high levels of photosynthetically active radiation, while non-photochemical quenching was reduced compared to low CO2 grown cells. This was probably due to the down-regulation of CCM, which serves as a sink for excessive energy. Increasing seawater pCO2 and decreasing pH associated with atmospheric CO2 rise may enhance diatom growth, down-regulate their CCM, and enhanced their photo-inhibition and dark respiration. The balance between these positive and negative effects on diatom productivity will be a key factor in determining the net effect of rising atmospheric CO2 on ocean primary production.
Sediment core fossils in ancient Lake Ohrid: testing for faunal change in molluscs since the Last Interglacial period
Authors: Albrecht C. , Vogel H. , Hauffe T. , Wilke T.
Published: May 2010

Abstract. Ancient Lake Ohrid is probably of early Pleistocene or Pliocene origin and amongst the few lakes in the world harboring an outstanding degree of endemic biodiversity. Although there is a long history of evolutionary research in Lake Ohrid, particularly on molluscs, a mollusc fossil record has been missing up to date. For the first time, gastropod and bivalve fossils are reported from the basal, calcareous part of a 2.6 m long sediment succession (core Co1200) from the north-eastern part of Lake Ohrid. Electron spin resonance (ESR) dating of mollusc shells from the same stratigraphic level yielded an age of 130±28 ka. Lithofacies III sediments, i.e. a subdivision of the stratigraphic unit comprising the basal succession of core Co1200 between 181.5–263 cm appeared solid, grayish-white, and consisted almost entirely of silt-sized endogenic calcite (CaCO3>70%) and intact and broken mollusc shells. Here we compare the faunal composition of the thanatocoenosis with recent mollusc associations in Lake Ohrid. A total of 13 mollusc species (9 gastropod and 4 bivalve species) could be identified within Lithofacies III sediments. The value of sediment core fossils for reconstructing palaeoenvironmental settings was evaluated. The agreement between sediment and palaeontological proxies was tested. The combined findings of the ecological study and the sediment characteristics suggest deposition in a shallow water environment during the Last Interglacial period. We tested for major faunal changes since the Last Interglacial period and searched for signs of extinction events. The fossil fauna exclusively included species also found in the present fauna, i.e. no extinction events are evident for this site since the Last Interglacial. The thanatocoenosis showed the highest similarity with recent Intermediate Layer (5–25 m) mollusc assemblages. The demonstrated existence of a mollusc fossil record in Lake Ohrid sediment cores also has great significance for future deep drilling projects. It can be hoped that a more far reaching mollusc fossil record will then be obtained, enabling insight into the early evolutionary history of Lake Ohrid.
Exchange across the shelf break at high southern latitudes
Authors: Klinck J. M. , Dinniman M. S.
Published: May 2010

Abstract. Exchange of water across the Antarctic shelf break has considerable scientific and societal importance due to its effects on circulation and biology of the region, conversion of water masses as part of the global overturning circulation and basal melt of glacial ice and the consequent effect on sea level rise. The focus in this paper is the onshore transport of warm, oceanic Circumpolar Deep Water (CDW); export of dense water from these shelves is equally important, but has been the focus of other recent papers and will not be considered here. A variety of physical mechanisms are described which could play a role in this onshore flux. The relative importance of some processes are evaluated by simple calculations. A numerical model for the Ross Sea continental shelf is used as an example of a more comprehensive evaluation of the details of cross-shelf break exchange. In order for an ocean circulation model to simulate these processes at high southern latitudes, it needs to have high spatial resolution, realistic geometry and bathymetry. Grid spacing smaller than the first baroclinic radius of deformation (a few km) is required to adequately represent the circulation. Because of flow-topography interactions, bathymetry needs to be represented at these same small scales. Atmospheric conditions used to force these circulation models also need to be known at a similar small spatial resolution (a few km) in order to represent orographically controlled winds (coastal jets) and katabatic winds. Significantly, time variability of surface winds strongly influences the structure of the mixed layer. Daily, if not more frequent, surface fluxes must be imposed for a realistic surface mixed layer. Sea ice and ice shelves are important components of the coastal circulation. Ice isolates the ocean from exchange with the atmosphere, especially in the winter. Melting and freezing of both sea ice and glacial ice influence salinity and thereby the character of shelf water. These water mass conversions are known to have an important effect on export of dense water from many Antarctic coastal areas. An artificial dye, as well as temperature, is used to diagnose the flux of CDW onto the shelf. Model results for the Ross Sea show a vigorous onshore flux of oceanic water across the shelf break both at depth and at the surface as well as creation of dense water (High Salinity Shelf Water) created by coastal polynyas in the western Ross Sea.
Brief Communication: Ikaite (CaCO3·6H2O) discovered in Arctic sea ice
Authors: Dieckmann G. S. , Nehrke G. , Uhlig C. , Göttlicher J. , Gerland S. , Granskog M. A. , Thomas D. N.
Published: May 2010

Abstract. We report for the first time on the discovery of calcium carbonate crystals as ikaite (CaCO3·6H2O) in sea ice from the Arctic (Kongsfjorden, Svalbard) as confirmed by morphology and indirectly by X-ray diffraction as well as XANES spectroscopy of its amorophous decomposition product. This finding demonstrates that the precipitation of calcium carbonate during the freezing of sea ice is not restricted to the Antarctic, where it was observed for the first time in 2008. This observation is an important step in the quest to quantify its impact on the sea ice driven carbon cycle.