bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential effects of phosphorus limitation on cellular metals in Chlorella and Microcystis
Authors: Ji Yongcheng , Sherrell Robert M.
Published: November 2010

We investigated the effect of phosphate bioavailability on cellular metal quotas in two species of freshwater phytoplankton (the eukaryote Chlorella sp. UTCC522 and the cyanobacterium Microcystis sp. LE3), grown in semicontinuous culture over four controlled levels of phosphate availability, encompassing phosphorus (P) deplete to P replete conditions. P limitation caused reduced growth rate, high C: P (up to 1800 mol mol‐1), and increased alkaline phosphatase (APase) activity. Low P availability led to enriched cobalt (Co), cadmium (Cd), and zinc (Zn) in Chlorella (up to 2.8‐fold, 1.7‐fold, and 1.8‐fold, respectively, normalized to cellular N, relative to P‐replete control) but resulted in enriched Co and nickel (Ni) in Microcystis (up to 4.4‐fold and 3.0‐fold). In contrast, cellular iron (Fe), manganese (Mn) and copper (Cu) were largely unchanged (±~20%) in both organisms. Cd and Co may substitute for Zn in the APase of Chlorella while in Microcystis the dominant phosphatase may be strictly Co‐requiring, as has been reported for other prokaryotes and is consistent with its evolutionary emergence before the oxygenation of the atmosphere, when Co was relatively abundant in natural waters. By extension, the absolute Co requirement of the important marine cyanobacteria Synechococus and Prochlorococcus may be related in part to widespread depletion of orthophosphate (PO43‐) in the oligotrophic surface ocean. The enrichment of Ni in Microcystis may indicate increased activity of Ni‐requiring superoxide dismutase under P limitation or, speculatively, a co‐uptake of Ni and Co by a shared transport system. These results shed light on the interaction between trace metals, macronutrient availability, and phytoplankton assemblage composition, and suggest intensified biological cycling of Zn, Cd, Co, and Ni in low‐P freshwater and marine systems.
Vitamin B12 and cobalt cycling among diatoms and bacteria in Antarctic sea ice microbial communities
Authors: Taylor Gordon T. , Sullivan Cornelius W.
Published: November 2010

Within McMurdo SoundÂs annual sea ice, assimilation and concentrations of vitamin B12 (cobalamin), microbial community productivity, and biomass were examined among three 100‐m2 quadrats where light penetration was manipulated by snow cover during austral summer. From late October through December, B12 concentrations (6−32 pmol L−1) and assimilation rates (17−780 pmol m−2 d−1) in congelation ice covaried with primary productivity (0.0001−250 mmol C m−2 d−1) and chlorophyll a (0.6−36 mg m−2). Within ice core samples, incorporation of 57Co‐B12 into the >1.0‐mm size fraction (mostly diatoms) was almost 100 times faster than into 0.2−1.0−mm particles (mostly heterotrophic bacteria) and was dependent on light and active transport across cell membranes. Microalgal B12:C cell quotas in field communities varied widely (2.6‐150,000 nmol B12 (mol C)−1; x̄x = 500) and generally exceeded those of cultured temperate diatoms (0.4‐55 nmol B12 (mol C)−1; x̄x = 4.1). Comparisons of dissolved B12 pools in the ice and their turnover (0.02‐0.6 d‐1) with underlying seawater suggest that this vitamin is produced in situ rather than delivered from waters below. Production and uptake of B12 and uptake of cobalt, required for B12 synthesis, were then examined among bacteria isolated from these communities. Only 23% of 78 bacterial isolates were incapable of B12 uptake, but these clones assimilated dissolved cobalt. Intracellular B12 production was evident in 9 of the 11 isolates screened and their cell quotas varied widely, 0.6‐6,800 nmol B12 (mol C)‐1. Mass balance analyses and published kinetics data independently suggest that microalgal growth in sea ice was not limited by vitamin B12 in most of our field observations and that in situ bacterial B12 production could potentially meet microalgal demands. Similar analyses, however, suggest that cobalt supply from underlying waters may have limited community growth and B12 production.
Role of hydrophobic extracellular polysaccharide of Aulacoseira granulata (Bacillariophyceae) on aggregate formation in a turbulent and hypereutrophic reservoir
Authors: Henriques Vieira, Armando Augusto , Coelho Ortolano Pedro Ivo , Giroldo Danilo , Dellamano Oliveira, Maria José , Bittar Thais Beraldo , Lombardi Ana Teresa , Sartori Antonio Luiz , Paulsen Berit Smestad
Published: November 2010

The highest density of aggregates (1.4 × 103 L‐1) in the hypereutrophic Barra Bonita Reservoir (mean depth of 10.2 m) coincided with the peak population density of the diatom Aulacoseira granulata (2.3 × 106 chains L‐1), which was present in 94% of the aggregates for 22 consecutive months. To investigate why this diatom, which produces very small amounts of free extracellular polysaccharide (EPS) and transparent exopolymer particles (TEP), occurs so frequently in natural aggregates, we carried out aggregation experiments with cultures of A. granulata with and without its free EPS and TEP. Stickiness (ά) was higher in exponential than stationary growth, either with or without EPS, but the highest value was obtained in cultures without EPS (0.37). During the stationary growth phase, ά decreased, both with and without EPS. Replacement of natural polymer carbohydrates by A. granulata free EPS (>14 kiloDalton [kD] < 0.4 µm), or adding cultured diatom to reservoir water, produced aggregates larger than the natural ones. The role of EPS in these aggregation characteristics was investigated by analyzing its monosaccharide composition. The proportion of terminal monosaccharides significant in the aggregation was 74.5%, 56.1% of them consisting of hydrophobic deoxy‐sugars fucose and rhamnose which increase the stickiness. Early in the growth, only hydrophobic‐adhering films are responsible for fast aggregation by chain‐to‐chain collision. With aging cells, aggregation was mainly by the trapping effect of free EPS and TEP, both formed by released adherent films. We hypothesize that aggregates have an important role in seeding A. granulata in environments with significant advective transport, such as reservoirs.
Saltmarshes as a source of chromophoric dissolved organic matter (CDOM) to Southern California coastal waters
Authors: Clark Catherine D. , Litz Liannea P. , Grant Stanley B.
Published: November 2010

To determine chromophoric dissolved organic matter (CDOM) sources in Southern California coastal waters, optical properties of a river outlet and adjacent tidally flushed salt marshes were monitored (dry season; June‐July 2001). Average absorption coefficients doubled at ebb vs. flood tides (4.8 ± 1.5 vs. 2.1 ± 0.9 m‐1; 300 nm), suggesting significant salt marsh CDOM inputs into coastal waters. Average spectral slopes were not statistically different for any sites or tides (0.010 ± 0.002 nm−1), consistent with salt marsh CDOM dominating coastal waters. Three‐dimensional fluorescence excitation‐emission matrices (EEMs) at ebb tide showed contributions from terrestrial, protein, and marine humic‐like peaks, suggesting production and output of these materials from the marsh. A marine humic signal at the river outlet during an offshore upwelling event indicated an additional sporadic nonmarsh marine humic‐like source. EEMs of six common salt marsh plant leachates showed protein, terrestrial, and marine humic‐like peaks. To estimate CDOM photodegradation in the marsh, fluorescence intensity decays from photobleaching experiments were fit to first‐order kinetics. Most humic peaks degraded with a half‐life of t1/2 = 10‐20 h, which overlaps the estimated residence time of water in the marshes (∼12 h). Most protein peaks were resistant to photodegradation, suggesting that the low levels of protein vs. humic‐like material measured in natural waters was due to rapid bioutilization of proteinaceous material. The rapid photodegradation of plant leachate humic material and the low spectral slopes for the field sites suggest that marsh sediments would be an important source of CDOM.
Short‐lived radionuclides (7Be and 210Pb) as tracers of particle dynamics in a river system in southeast Michigan
Authors: Jweda Jason , Baskaran Mark , van Hees Ed , Schweitzer Linda
Published: November 2010

Riverine water samples (dissolved and particulate), surficial bottom sediments, and trapped sediments were collected mostly monthly from three stations along the Clinton River, in southeastern Michigan, over a period of ~1 yr and analyzed for 7Be and 210Pb to elucidate the types and rates of processes affecting particle dynamics in a riverine system. Using a simple irreversible scavenging box model approach, sources and sinks for dissolved and particulate 7Be and 210Pb were quantified to estimate their residence times in the dissolved and particulate phases. Resuspension rates of surficial bottom sediments calculated from the mass balance of particulate 7Be varied from 0.50 to 1.34 (geometric mean: 0.83 ± 0.34) g cm−2 yr−1, while corresponding values varied from 0.16 to 1.48 (GM: 0.38 ± 0.38) g cm−2 yr−1 using particulate 210Pb. Based on the 210Pb mass balance, it appears that only ∼2% of 210Pb was derived from direct atmospheric deposition, while ∼98% was derived from resuspension of bottom sediments. Additionally, there was a large discrepancy between mass flux collected in the trap (GM: 8.9 g cm−2 yr−1) compared to net sediment accumulation rates (GM: 0.88 ± 0.38 g cm−2 yr−1), which was attributed to sediment resuspension; this may provide insight into the frequency of particle‐recycling events. Furthermore, desorption of particle‐reactive species during resuspension events could result in the mobility of contaminants to farther distances from the contaminated site. Therefore, this study has direct relevance to the uptake of particle‐reactive species in a riverine system and thereby the water quality of rivers.
Identification of octocoral recruits using microsatellite primers: Relationships between recruitment and adult distribution of Pseudopterogorgia spp.
Authors: Jamison Jennifer L. , Lasker Howard R.
Published: November 2010

Octocorals are commonly identified from the structure of their calcium carbonate sclerites. However, small recruits cannot always be identified in this manner. Primers for microsatellite loci developed for the Caribbean branching octocoral Pseudopterogorgia elisabethae were used to identify six common Pseudopterogorgia spp. on the Little Bahama Bank. The primers consistently generated polymerase chain reaction products of different molecular weights for each species, and a combination of up to three primers enabled identification of recruits whose identity was otherwise indeterminate. Recruits were collected and adult density was surveyed at three depths at Cross Harbour, Great Abaco, Bahamas, during May and November 2005. More recruits were collected during May than November, suggesting that most of the Pseudopterogorgia species reproduced between November and May. There were differences in both recruitment and adult density between the three sites among the surface‐brooding species. Covariation between adult and recruit abundance in P. bipinnata is consistent with the hypothesis that brooding species exhibit limited larval dispersal. Among the known broadcast‐spawning species, there was a significant difference in adult distribution between the sites but no significant difference in recruitment between sites, suggesting that larvae of broadcast‐spawning species are more widely dispersed.
Fish decomposition in boreal lakes and biogeochemical implications
Authors: Chidami Saad , Amyot Marc
Published: November 2010

A field study in a boreal lake using a remotely operated vehicle equipped with a camera established that falling fish carcasses did not tend to be buried in sediments after deposition. Decomposition rates of fish carcasses in three boreal lakes were experimentally assessed at different depths. In shallow waters (between 0 and 4 m), decomposition was fast (half lives, τ, ranging from 40 to 230 h) and controlled by vertebrates. In deep waters (below the thermocline), decomposition was slow (τ between 770 and 1,733 h) and was controlled by bacterial processes. Water temperature was a promising predictor of decomposition half‐lives in freshwater. Using a novel underwater infrared camera system, we identified the daily and seasonal patterns of scavenging activity by littoral fish. Only three species displayed scavenging behavior, with creek chubs being the most active. Fast fish‐mediated littoral recycling of fish carcass may explain the lack of direct observations of carcasses in lakes. Estimates of phosphorus fluxes in one of the studied lakes indicate that falling carcasses can represent a significant water‐to‐sediment flux of nutrient.
Intermittent oxygen flux from the interior into the bottom boundary of lakes as observed by eddy correlation
Authors: Brand Andreas , McGinnis Daniel F. , Wehrli Bernhard , Wüest Alfred
Published: November 2010

Turbulent oxygen transport from the overlying stratified water column into the bottom boundary layer (BBL) on the slope of a medium‐sized lake was investigated using the eddy correlation (EC) technique. The seicheinduced oscillatory flow of the BBL, with a period of ~1 d, was identified as the mechanism driving turbulent oxygen transport. Sporadic short‐term EC vertical oxygen fluxes exceeded the sedimentary oxygen uptake of 13 ± 2 mmol m‐2 d‐1 calculated from sediment oxygen profiles by more than a factor of three. The average EC flux over half of a seiching period was 9.2 mmol m‐2 d‐1 similar in range to the flux into the sediment; however, these two fluxes do not have to coincide spatially and temporally. The EC oxygen flux was only significant when the deep basin‐scale currents exceeded a velocity of 2 cm s‐1 and the corresponding bottom shear was sufficient to produce active turbulence. Below this threshold, decaying turbulence resulted in oxygen fluxes lower than 3.5 mmol m‐2 d‐1, with an even lower average flux of 0.8 mmol m‐2 d‐1 observed during reversals of the seiching. At low velocities, the weak turbulence is insufficient to transport dissolved oxygen through the stratified top of the BBL (stability N2 ~ 2.4 × 10‐4 s‐2), even though turbulence was found in the inertial subrange and periodical bottom convective mixing was still present. The EC technique provided valuable data on the temporal variability of oxygen transport related to the BBL hydrodynamics and flux pathways.
Are jellyfish increasing in response to ocean acidification?
Authors: Richardson Anthony J. , Gibbons Mark J.
Published: November 2010

Ocean acidification may negatively affect calcifying plankton, opening ecological space for noncalcifying species. Recently, a study of climate‐forcing of jellyfish reported the first analysis suggesting that there were more jellyfish (generally considered a noncalcifying group) when conditions were more acidic (lower pH) from one area within the North Sea. We examine this suggestion for a number of areas in the North Sea and beyond in the Northeast Atlantic using coelenterate records from the Continuous Plankton Recorder and pH data from the International Council for the Exploration of the Sea for the period 1946‐2003. We could find no significant relationships between jellyfish abundance and acidic conditions in any of the regions investigated. We conclude that the role of pH in structuring zooplankton communities in the North Sea and further afield at present is tenuous.
Ocean metabolism observed with oxygen sensors on profiling floats in the South Pacific
Authors: Martz Todd R. , Johnson Kenneth S. , Riser Stephen C.
Published: November 2010

We estimated rates of production and export in the South Pacific (80°W to 180°W in a zonal band between 35°S and 50°S) using 1.5 yr of oxygen measurements from profiling floats. Export production, calculated from oxygen utilization rates below the compensation depth from December to April, was 10.7 ± 2 mmol C m−2 d−1 (n = 36, 95% CI). The corresponding satellite net primary production was 46 ± 4 mmol C m−2 d−1, yielding a regional e‐ratio of 0.23 ± 0.05. Averaging oxygen utilization rates resulted in a net cancellation of most water mass changes related to advection and float migration. The composite vertical profile of remineralization rates, obtained by binning 36 rate profiles, agreed with published measurements based on oxygen utilization rates in hydrographic surveys and fits the classic form of a particulate organic carbon (POC) attenuation function. However, the disagreement between oxygen‐based remineralization rates and those obtained by sediment traps suggests fundamental differences between these two methods. Using float data to constrain a one‐dimensional mixed‐layer model, the annual net community production at 45°S, 144°W was ~2.5 mol C m−2 d−1. Spatial trends in export production coinciding with the New Zealand shelf and Subtropical Front are identified.
Observations of pigment and particle distributions in the western North Atlantic from an autonomous float and ocean color satellite
Authors: Boss E. , Swift D. , Taylor L. , Brickley P. , Zaneveld R. , Riser S. , Perry M. J. , Strutton P. G.
Published: November 2010

Profiling floats with optical sensors can provide important complementary data to satellite ocean color determinations by providing information about the vertical structure of ocean waters, as well as surface waters obscured by clouds. Here we demonstrate this ability by pairing satellite ocean color data with records from a profiling float that obtained continuous, high‐quality optical data for 3 yr in the North Atlantic Ocean. Good agreement was found between satellite and float data, and the relationship between satellite chlorophyll and floatderived particulate backscattering was consistent with previously published data. Upper ocean biogeochemical dynamics were evidenced in float measurements, which displayed strong seasonal patterns associated with phytoplankton blooms, and depth and seasonal patterns associated with an increase in pigmentation per particle at low light. Surface optical variables had shorter decorrelation timescales than did physical variables (unlike at low latitudes), suggesting that biogeochemical rather than physical processes controlled much of the observed variability. After 2.25 yr in the subpolar North Atlantic between Newfoundland and Greenland, the float crossed the North Atlantic Current to warmer waters, where it sampled an unusual eddy for 3 months. This anticyclonic feature contained elevated particulate material from surface to 1000‐m depth and was the only such event in the float's record. This eddy was associated with weakly elevated surface pigment and backscattering, but depthintegrated backscattering was similar to that previously observed during spring blooms. Such seldom‐observed eddies, if frequent, are likely to make an important contribution to the delivery of particles to depth.
Glider observations of sediment resuspension in a Middle Atlantic Bight fall transition storm
Authors: Glenn Scott , Jones Clayton , Twardowski Michael , Bowers Louis , Kerfoot John , Kohut Josh , Webb Doug , Schofield Oscar
Published: November 2010

In October of 2003 a fleet of autonomous underwater gliders began a time series of transects across the New Jersey shelf. The gliders are equipped with a conductivity‐temperature‐depth sensor, and some carry optical ECO‐sensor pucks. The physical‐optical data are used to examine storm‐induced sediment resuspension. There are two types of storm response found. In summer, the seasonal stratification limits midshelf sediment resuspension to below the pycnocline even during hurricanes. In contrast, winter storms suspend sediment throughout the full water column. The transition between summer and winter seasons starts with surface cooling that preconditions the shelf for rapid mixing during fall storms. The mixing storm of October 2003 was a classic northeaster. Early in the storm when waves were high, sediment resuspension was limited to below the pycnocline. After the pycnocline eroded through growth of the bottom boundary layer, particles immediately filled the full water column. The spectral ratio of backscatter indicated that the particles were likely similar materials both before and after the stratification was eroded. The backscatter profiles in the bottom boundary layer decay with distance from the bed at rates consistent with theory but with variable slopes. The reduced slope of the backscatter profiles increased after stratification was lost, which is consistent with an increase in vertical transport or turbulent mixing. Wave bottom orbital velocities during this time were decreasing, and the glider vertical velocities showed no enhancement consistent with Langmuir cells. Enhanced mixing was related to the interaction of the surface and bottom boundary layers while the stratification was eroded, and the observed variability in the resuspension during the event was also due to the tide.
Diel periodicity in both sei whale vocalization rates and the vertical migration of their copepod prey observed from ocean gliders
Authors: Baumgartner Mark F. , Fratantoni David M.
Published: November 2010

The daily activity cycles of marine predators may be dictated in large part by the timing of prey availability. For example, recent studies have observed diel periodicity in baleen whale vocalization rates that are thought to be governed by the diel vertical migration of their zooplanktonic prey. We addressed this hypothesis by studying associations between sei whale (Balaenoptera borealis) vocalization rates, oceanographic conditions, and the vertical distribution of the whales' prey, the calanoid copepod Calanus finmarchicus, during May 2005 in the southwestern Gulf of Maine using an array of autonomous ocean gliders. Each of the four gliders was equipped with sensors to measure temperature, salinity, and chlorophyll fluorescence. Three of the four gliders carried a digital acoustic recorder and the fourth carried a 1‐MHz acoustic Doppler current profiler. We observed strong diel periodicity in the acoustic backscatter measured by the current profiler that we attribute (based on a corroborating shipboard study) to the diel vertical migration of C. finmarchicus. Sei whale vocalization rates also exhibited diel periodicity, with more calls detected during the daytime when C. finmarchicus was observed at depth. We found no evidence to suggest that the observed patterns in sei whale calling rates were attributable to diel periodicity in background noise or acoustic propagation conditions. Sei whales are adept at foraging on nearsurface aggregations of C. finmarchicus; therefore we expect that the whales were feeding at night. We hypothesize that calling rates are reduced at night while the whales are feeding, but increase with social activity during the day when copepods are either more difficult or less efficient to capture at depth. The gliders' persistence during adverse weather conditions experienced during the study allowed continuous collocated observations of whale vocalization behavior and oceanographic conditions that have not been previously possible with traditional shipboard techniques.
Submesoscale physical‐biogeochemical coupling across the Ligurian current (northwestern Mediterranean) using a bio‐optical glider
Authors: Niewiadomska Katarzyna , Claustre HervÉ , Prieur Louis , d'Ortenzio Fabrizio
Published: November 2010

A bio‐optical autonomous underwater gliding vehicle, equipped with a conductivity, temperature, depth (CTD) sensor, an oxygen sensor, backscatter meters, chromophoric dissolved organic matter (CDOM) and chlorophyll fluorometers, and upwelling and downwelling radiometers was developed to characterize the biogeochemical response to physical forcing at the submesoscale (1‐10 km). Winter data obtained in the northwestern Mediterranean basin in a 50‐km transect that crossed the permanent, along‐coast Ligurian Current show tight physical‐biogeochemical coupling across the Ligurian Current, not observed using other sampling strategies. At the scale of the transect, the various biogeochemical parameters displayed independent behaviors, while at the submesoscale, there was a coherent covariance of these variables, especially in the frontal zone. Near‐isopycnal tongues of elevated fluorescence and oxygen concentration were recorded down to a depth of 180 m and are the likely signature of a converging horizontal and downwelled water flow. Local anomalies in a horizontal section well below the mixed‐layer depth are likely representative of downwelled waters from the euphotic layer. Intrusions of elevated CDOM concentrations together with signatures of smaller particles are the likely features of a local divergence and upwelled waters from subjacent aphotic layers. These are particularly apparent in the form of local anomalies in a horizontal section within the mixed layer. Similar tongues were observed in data from subsequent glider deployments. Such biogeochemical signatures enable the identification of upward and downward physical motions not observed by other technologies, reinforcing the need for coupled high‐resolution physical‐biogeochemical studies, not only for investigating biogeochemical processes themselves but also for resolving physical processes at these scales.
Mapping the spatial variability of plankton metabolism using nitrate and oxygen sensors on an autonomous underwater vehicle
Authors: Johnson Kenneth S. , Needoba Joseph A.
Published: November 2010

It is now possible to make highly resolved vertical (<1 m) and horizontal (3 m at constant depth and ~400 m when undulating from surface to 100 m) measurements of nitrate concentration in the upper ocean using sensors deployed on propeller‐driven autonomous underwater vehicles (AUVs). The ability to make such highly resolved measurements opens the possibility of detecting small‐scale anomalies in nutrient fields that are created by locally high rates of primary production. We employed an in situ ultraviolet spectrophotometer optical nitrate sensor and Sea‐Bird oxygen sensor mounted on the Monterey Bay Aquarium Research Institute Dorado AUV to investigate the spatial variability of nitrate and oxygen in Monterey Bay, California. The Dorado conducts missions up to 100 km in length. A very simplified diffusion and reaction model for nitrate, ignoring horizontal processes and advection and assuming steady state, would require that consumption rate = KZ × δ2NO3−/δZ2 (KZ = vertical eddy diffusion coefficient). Water column regions exhibiting elevated nitrate uptake rates are identified from anomalies in the second derivatives of the vertical concentration profiles relative to the second derivative of conservative properties. The relationship between chlorophyll a fluorescence and the inferred productivity rates exhibits coherent spatial variability across the bay.
Synergistic applications of autonomous underwater vehicles and the regional ocean modeling system in coastal ocean forecasting
Authors: Chao Yi , Li Zhijin , Farrara John D. , Moline Mark A. , Schofield Oscar M. E. , Majumdar Sharanya J.
Published: November 2010

The potential for using synergistic combinations of measurements from autonomous underwater vehicles (AUVs) and output from three‐dimensional numerical models for studying the central California coastal region is demonstrated. Two case studies are used to illustrate the approach. In the first, propeller‐driven AUV observations revealed a subsurface salinity minimum in northern Monterey Bay. A Regional Ocean Modeling System (ROMS) reanalysis of the three‐dimensional flow in the region suggested an offshore source for this water and particular propagation pathways from the south and west into the bay. In the second case study, the effectiveness of assimilating observations in improving the ROMS reanalysis fields is investigated. A significant improvement, especially in the salinity fields, is demonstrated through a single glider deployed outside the intensive observational domain. These results suggest that investigation of more sophisticated techniques for using data and models together is warranted. Such techniques include increasing model resolution in areas of interest identified by observing platforms and using model‐based “targeted observing” techniques to identify areas of uncertainty in the flow to guide placement of observational assets.
High‐latitude oceanography using the Autosub autonomous underwater vehicle
Authors: Nicholls Keith W. , Abrahamsen E. Povl , Heywood Karen J. , Stansfield Kate , østerhus Svein
Published: November 2010

A combination of measurements from Autosub, an autonomous underwater vehicle, and ship‐based instruments are used to describe the oceanographic conditions beneath Fimbul Ice Shelf, Antarctica. The data show an intricate oceanographic regime that is suggestive of variability at seasonal or longer time scales. Results from a numerical model of the flow beneath the ice shelf lend support to a strong seasonal variability, and data from instruments moored beneath the ice shelf show substantial temporal variations. The Autosub data indicate temperatures within the cavity somewhat lower than our model results would suggest; thus, our modeled melt rates (average of 0.85 m yr−1) might be overestimates, although they are substantially lower than from previously published model studies (4.9 and 1.9 m yr−1). The contribution of ice shelf melt in the freshwater balance of the waters upstream of the climatically important Filchner‐Ronne Ice Shelf needs to be reassessed.
Living in transparent lakes: Low food P:C ratio decreases antioxidant response to ultraviolet radiation in Daphnia
Authors: Balseiro Esteban , Souza María Sol , Modenutti Beatriz , Reissig Mariana
Published: November 2010

We experimentally tested the effect of food quality (phosphorus [P] : carbon [C] ratio) on the response of antioxidant enzymes to ultraviolet radiation (UVR) in Daphnia commutata fed with Chlamydomonas reinhardtii. Algal cultures were grown at different concentrations of phosphorus and light intensities, resulting in significant differences in the P :C ratios (mmol P[µmol C]−1; 6.05, 1.70, and 0.83). After 12 d of D. commutata growth under these three food quality treatments, we observed significant differences in individual biomass and protein content of Daphnia. Subsequently, we carried out an ultraviolet exposure experiment to determine if stoichiometric constraints imposed would limit enzymatic defenses against UVR oxidative stress. The UVR‐exposure experiment consisted of a factorial design with three levels of food P :C (low, medium, and high) and two levels of UVR (exposed and protected). The activities of glutathione S‐transferases (GST) and catalase (CAT), enzymes involved in protection and repair of damage caused by UVR, were determined. Enzyme activities in the animals exposed to or protected from UVR showed a direct relationship with food P :C ratio that fit exponential models. Although GST and CAT differed slightly in their response to UVR, both enzymes were significantly affected by food quality: In low P :C treatments, there was significantly lower enzyme activity in response to UVR for both enzymes. Low food quality (less P for biosynthesis) may also impose a weaker antioxidant response on the organisms, a response of considerable ecological relevance in transparent Andean lakes which combine high UVR intensities with low seston P :C ratios.
Seasonal changes in planktonic bacterivory rates under the ice‐covered coastal Arctic Ocean
Authors: Vaqué Dolors , Guadayol Òscar , Peters Francesc , Felipe Jordi , Angel-Ripoll Laia , Terrado Ramon , Lovejoy Connie , Pedrós-Alioó Carlos
Published: November 2010

Bacterivory was determined in surface waters of Franklin Bay, western Arctic, over a seasonal ice‐covered period (winter‐spring, 2003‐2004). The objectives were to obtain information on the functioning of the microbial food web under the ice, during winter (from 21 December 2003 to 21 March 2004) and during spring (from 22 March 2004 to 29 May 2004), and to test whether bacterial losses would increase after the increase in bacterial production following the spring phytoplankton bloom. Chl a concentrations ranged from 0.04 to 0.36 µg L−1, increasing in March and reaching a peak in April. Bacterial biomass showed no consistent trend for the whole period, and protist biomass followed a pattern similar to that of Chl a. Bacterial production increased 1 week after Chl a concentrations started to increase, while bacterivory rates increased very slightly. Average bacterivory rates in winter (0.16 ± 0.07 µg C L−1 d−1) were not significantly different from those in spring (0.29 ± 0.24 µg C L−1 d−1). Average bacterial production, on the other hand, was similar to bacterivory rates in winter (0.19 ± 0.38 µg C L−1 d−1), but higher than bacterivory in spring (0.93 ± 0.28 µg C L−1 d−1). Therefore, bacterial production was controlled by grazers during winter and by substrate concentration in spring.
The cyanate utilization capacity of marine unicellular Cyanobacteria
Authors: Kamennaya Nina A. , Chernihovsky Mark , Post Anton F.
Published: November 2010

Cyanate, a by‐product of urea decomposition, is a potential nitrogen (N) source in marine environments, but to date it has received scant attention. Cyanobacteria presumably acquire this compound via a substrate‐specific ABC‐type transporter (cynABD), and they convert it to ammonium and carbon dioxide by cyanase (cynS) activity. Participation of cyanate utilization genes in N‐stress responses in cyanobacteria has been implied previously, but its ecological context has not been studied. We employed polymerase chain reaction protocols for cynA amplification to examine the potential for cyanate recruitment in the Gulf of Aqaba, northern Red Sea. We also monitored growth of cyanobacterial strains with different cynABDS complements on cyanate‐containing media. We showed that cyanate is utilized as the sole N source by strains with the full gene complement, and residual growth, fed by natural decay of cyanate to ammonium, was observed in strains lacking any of these genes. Natural abundance of cynA products in the oligotrophic Gulf of Aqaba indicates that cyanate constitutes an essential N source for Prochlorococcus, but not for Synechococcus populations. Noncyanobacterial cynA sequences indicate cyanate utilization by a variety of other phototrophic microorganisms. We hypothesize that in stratified water bodies, cyanate utilization is confined to the N‐deplete upper photic zone, where it plays a role in "regenerated" primary production.
Assessment of relative phosphorus limitation of Trichodesmium spp. in the North Pacific, North Atlantic, and the north coast of Australia
Authors: Sohm Jill A. , Mahaffey Claire , Capone Douglas G.
Published: November 2010

Trichodesmium spp. is a colonial diazotrophic cyanobacterium that occurs in the oligotrophic tropics and subtropics. Because of its ability to fix atmospheric N2, it is likely to be growth limited by P or Fe, and it has been hypothesized that limitation differs among different ocean basins. Two assays used as indices of P limitation or stress in Trichodesmium spp. are uptake of 33PO43‐ to determine maximal P uptake (Vmax) and hydrolysis of P from methylumbelliferone phosphate to estimate alkaline phosphatase activity (APA). The kinetics of PO43‐ uptake were determined for Trichodesmium spp. colonies in the North Pacific, North Atlantic, and in waters north of Australia, whereas APA was determined in the North Pacific and North Atlantic. Trichodesmium spp. Vmax was significantly greater (~fourfold or more) in the North Atlantic compared with the North Pacific and waters north of Australia when normalized to both chlorophyll a content and number of trichomes per colony. APA in the North Atlantic was also greater than in the North Pacific. The half‐saturation constant for PO43‐ uptake (Ks) was not significantly different among the three locations. These data indicate that Trichodesmium spp. is more strongly P limited in the North Atlantic compared with the North Pacific or waters along the north coast of Australia. We suggest that the Trichodesmium spp. communities in the North Pacific and waters north of Australia are primarily Fe rather than P stressed and that these differences reflect differing relative inputs and availability of two major controlling variables for diazotrophy, P and Fe, in these geographically divergent areas.
An assessment of nitrogen removal from headwater streams in an agricultural watershed, northeast Ohio, U.S.A
Authors: Herrman Kyle S. , Bouchard Virginie , Moore Richard H.
Published: November 2010

The objective of this project was to assess in‐stream nitrogen removal capacity in a fragmented agricultural landscape and to compare removal capacities in streams with agricultural or residential (hereafter referred to as agricultural streams) and forested riparian land use. We also identified what stream characteristics control nitrogen removal in these systems. We examined paired reaches (one agricultural and one forested reach) along five headwater streams in an agricultural watershed (Upper Sugar Creek Watershed) in northeast Ohio. Although denitrification rates were high (<0.1‐17.2 mg N m−2 h−1), annual nitrogen removal was most likely low because during spring and fall, when in‐stream nitrogen loads were high, removal was low, and during summer when instream nitrogen loads were low, removal was high. Between the agricultural and forested reaches removal rates were similar in terms of loss rate and uptake velocity. Removal capacities were similar despite forested reaches having higher hydraulic residence times. Using a redundancy analysis we identified temperature, in‐stream nitrate concentration, and relative transient storage as stream characteristics that affect nitrogen removal. Further analysis suggests that nitrogen removal via denitrification in these headwater streams was not limited by the availability of nitrate. In this fragmented agricultural watershed in‐stream nitrogen removal was low and riparian land use had no effect on this process, most likely because of nitrate saturation.
Exploring riverine zooplankton in three habitats of the Illinois River ecosystem: Where do they come from?
Authors: Wahl David H. , Goodrich Jodi , Nannini Michael A. , Dettmers John M. , Soluk Daniel A.
Published: November 2010

We sampled three habitats (main channel, side channels, and backwater lakes) during 2 yr along 32 km of the Illinois River to compare zooplankton distribution and dynamics, as well as evaluate the possible effects of hydrology on taxonomic abundance and distribution. Zooplankton assemblages displayed both spatial and temporal variation. Whereas the riverine zooplankton assemblage was dominated by rotifers, the backwater lake assemblage was dominated by copepods. Zooplankton densities in the main channel peaked earlier in the season in both years than the backwater lake habitats. To determine if these patterns were caused by fluvial exchanges occurring between habitats during flooding, we sampled the connections between the backwater lake and main channel habitats and found that large numbers of zooplankton entered the main channel via these connections. Further, calculations of main channel population growth, birth, and death rates showed that population growth rates most commonly exceeded birth rates during the flooding period. Seasonal inoculums from off‐channel habitats could play an important role in riverine zooplankton dynamics. However, for the main channel to achieve the measured zooplankton densities, ~400,000 backwater lakes would be required and zooplankton would need to travel an unrealistic number of days and distance based on estimated growth rates. Thus, other mechanisms (hatching of resting eggs or in situ reproduction) are likely responsible for zooplankton abundances.
Sex‐related differential mortality of a marine copepod exposed to a toxic dinoflagellate
Authors: Avery David E. , Altland KristaJoy K. , Dam Hans G.
Published: November 2010

In this study we hypothesized that the sexes of the copepod Acartia hudsonica experience different mortalities when exposed to the toxic dinoflagellate Alexandrium fundyense. In laboratory experiments, we manipulated toxin dose and measured sex‐specific mortality. We also used a split‐family design to determine whether there were genetic influences on sex determination, and therefore on sex ratio. When the dose of the toxic alga was high (25% of diet by carbon content), population mortality was high, and the fraction of males surviving to adulthood was low (20‐30% of the adult population). No such effect was observed when A. fundyense comprised only 10% of the diet. Adult male copepods were also more susceptible to the toxic alga, though prior selection for resistance to toxins also had an effect on mortality. No genetic variation for sex ratio was detected in the split‐family experiment. Males of A. hudsonica are more sensitive to the toxins of A. fundyense than are females. Resistance may be sex‐linked, and copepod populations exposed to a bloom of toxic Alexandrium sp. may experience shifts in sex ratios away from males and toward females. Differential mortality and skewed sex ratios are feedback mechanisms potentially affecting both the population dynamics of grazers and the development of toxic algal blooms.
Bypassing the abyssal benthic food web: Macrourid diet in the eastern North Pacific inferred from stomach content and stable isotopes analyses
Authors: Drazen Jeffrey C. , Popp Brian N. , Choy C. Anela , Clemente Tara , Forest Lisa De , Smith Kenneth L.
Published: November 2010

Deep‐sea fishes prey on benthic fauna and scavenge on the carcasses of surface‐living animals. Few studies have addressed the relative importance of each trophic pathway. Recent documentation of inter‐decadal fluctuations in macrourid densities in the abyssal Pacific, related to changing food supplies, hastens the need for information. We conducted stomach content and stable isotope analyses of two abyssal macrourids, carrion sources, and benthic prey, collected concurrently at 4100 m off California. Squid and fishes were the most frequent prey for Coryphaenoides armatus, with small crustaceans numerous in the diet of small specimens. The diet of Coryphaenoides yaquinae included more benthic prey such as crustaceans, polychaetes, and the holothuroid Protankyra brychia. Carrion was present in both species and it was 69% of the mass of food of large C. armatus. Carrion δ15N values were comparable to those in abyssal deposit feeders, but carrion was relatively enriched in 13C, giving it a unique isotopic signature compared to benthic prey sources. The highest δ13C and δ15N values were observed in benthic shrimps and large polychaetes. The two macrourids had intermediate values, with C. armatus having slightly but significantly lower δ15N relative to C. yaquinae. Results of isotope mass balance suggest that carrion was the most important prey resource for both species but to a lesser extent in C. yaquinae. These two species bypass the conventional phytodetritus‐based abyssal food web for much of their nutrition. Their population dynamics may be tied more closely to fluctuations in epipelagic nekton populations through fishing effects and direct climatic forcing on top trophic levels.
Tracing abyssal food supply back to upper‐ocean processes over a 17‐year time series in the northeast Pacific
Authors: Smith K. L. , Ruhl H. A. , Kaufmann R. S. , Kahru M.
Published: November 2010

Detrital aggregates episodically deposited on the seafloor represent an underestimated food source to deep‐sea communities. A 17‐yr time‐series study was conducted from 1990 to 2006 in the abyssal northeast Pacific (Sta. M, 4100 m in depth) to evaluate the importance of this food source and its temporal relationship to water column and surface ocean processes. Detrital aggregates appeared on the seafloor from June through December, with the highest peaks in 1990, 1994, 2001, and 2002 reaching a maximum density of 23 m−2 in fall 2001. A total of 15,816 aggregates were measured, most less than 20 cm2 in area and with a mode of 9 cm2. Density of detrital aggregates was highly correlated with particulate organic carbon (POC) flux at 600 and 50 m above the bottom (p < 0.001) with no time lag. Export flux of organic carbon from the euphotic zone was significantly correlated with aggregate density, lagged earlier by 1‐4 months (p ≤ 0.001). Zooplankton displacement volume was significantly correlated with POC flux (p = 0.023) and with detrital aggregate density (p = 0.028) on the seafloor when lagged earlier by ≤1 month. The Bakun upwelling index computed for the region around Sta. M was significantly correlated with detrital aggregate density when lagged earlier by 2‐5 months (p < 0.001). A strong correlation exists between surface ocean processes and abyssal food supply, including POC flux and detrital aggregates. This direct coupling through the entire water column must be considered in resolving the marine carbon cycle.
Episodic circulation and exchange in a wave‐driven coral reef and lagoon system
Authors: Hench James L. , Leichter James J. , Monismith Stephen G.
Published: November 2010

We examined the role of wave‐driven circulation relative to wind and buoyancy forcing in a coral reef‐lagoon system. Circulation measurements in Paopao Bay, Moorea, French Polynesia, during austral summer show the importance of waves in driving flows over the reef crest, through the lagoon, and out the reef pass. Tides were comparatively weak, due to proximity to amphidromic points, and exhibited an unusual spring‐neap cycle where the major lunar tide modulated the major solar tide, and the overall tidal phase stayed approximately constant. Wind had only a secondary effect compared to surface waves. A simple fluid mass balance indicated rapid flushing of the shallow back reef and export through the reef pass, and a reef capture zone width of ~2.3 km. The reef pass circulation dynamics exhibited two‐layer baroclinic exchange flow when waves were small, which was suppressed during large wave events. The unusually weak tidal forcing provided an opportunity to more closely investigate wave‐driven circulation dynamics. As expected theoretically, there was a wave‐driven setup of the free surface across the shallow lagoon, which drove a highly frictional flow, evident by a large drag coefficient CP ~ 0.1. Diverging from extant theory, the observed setup varied strongly with significant wave height and period. Overall, the circulation and exchange between this coral reef system and the adjacent open ocean were largely determined by episodic remote‐forcing events and differed significantly from periodic tidal‐exchange mechanisms.