bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal dynamics of new production from Trichodesmium N2 fixation and nitrate uptake in the upstream Kuroshio and South China Sea basin
Authors: Lee Chen Yuh-ling , Chen Houng-Yung , Tuo Sing-how , Ohki Kaori
Published: November 2010

The seasonal dynamics of primary production in the upstream Kuroshio was studied to understand why pelagic fish are relatively populous in this oligotrophic tropical ocean region. The relative importance of new production from nitrate uptake vs. Trichodesmium N2 fixation was compared to differentiate the seasonal production dynamics in the upstream Kuroshio from that in the neighboring and interacting northern South China Sea (SCS). Unlike the SCS, which was most productive in the winter, seasonal fluctuation of primary production (0.51‐0.53 g C m−2 d−1) was not apparent in the upstream Kuroshio. The seasonality in new production in the Kuroshio, in contrast, was pronounced. Its nitrate‐uptake‐based new production was high in the winter (0.27 g C m−2 d−1) and low in the summer (0.16 g C m−2 d−1); conversely, Trichodesmium N2‐fixation‐based new production was low in the winter (2.4 µmol N m−2 d−1) and high in the summer (168.1 µmol N m−2 d−1). In the summer when nitrate‐uptake‐based new production was low due to nitrate depletion, the Kuroshio remained productive because of enhanced Trichodesmium N2 fixation from strong stratification and a deepened nitracline. The standing crop of Trichodesmium was consistently much higher in the Kuroshio (34.61 × 106 and 0.49 × 106 trichomes m−2 in the summer and winter, respectively) than in the SCS (4.87 × 106 and 0.15 × 106 trichomes m−2, respectively). In both regions, surface water temperature correlated significantly with increased Trichodesmium stocks. At a given temperature, higher Trichodesmium standing crop in the Kuroshio than the SCS was related to the deeper nitracline and ensuing decrease in nitrate availability in the Kuroshio.
The onset and evolution of a spring bloom on the Scotian Shelf
Authors: Greenan B. J. W. , Petrie B. D. , Harrison W. G. , Strain P. M.
Published: November 2010

The spring bloom on the Scotian Shelf is examined using a mooring array deployed from 18 March 2002 to 18 April 2002 to provide physical, chemical, and biological measurements with high temporal and vertical resolution. These measurements are complemented by the Atlantic Zone Monitoring Program (AZMP) biweekly occupations of a station near the mooring site (HL2). Results from AZMP sampling and Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) ocean color imagery in early March show that coastal upwelling played an important role in the initiation of the spring bloom near the coast. This was a period of very strong horizontal gradients in surface chlorophyll. The main bloom at HL2 was sustained for most of the mooring period with peak chlorophyll levels reaching 6 mg m‐3. Following the drawdown of nutrients in the upper 20 m, the bloom continued for 9 d and then disappeared at the surface but remained at the depth of the nutricline (30‐50 m). The onset and evolution of the spring bloom on the inner Scotian Shelf is a complex process in which nutrient inventory, vertical mixing, and coastal upwelling play roles of varying importance throughout its lifetime. Mesozooplankton biomass does not change significantly until the very end of the mooring period indicating the grazing by this component of the zooplankton did not have as important a role in the termination of the bloom as the exhaustion of near‐surface nutrients.
Climate‐induced effects on the meroplankton and the benthic‐pelagic ecology of the North Sea
Authors: Kirby Richard R. , Beaugrand Gregory , Lindley John A.
Published: November 2010

Analyses of long‐term time series of North Sea plankton and sea surface temperature (SST) data reveal that the annual planktonic larval abundance of three benthic phyla, Echinodermata, Arthropoda, and Mollusca, responds positively and immediately to SST. Long‐term outcomes for the planktonic abundance of these three phyla are different, however. The planktonic larvae of echinoderms and decapod crustaceans have increased in abundance from 1958 to 2005, and especially since the mid‐1980s, as North Sea SST has increased. In contrast, the abundance of bivalve mollusc larvae has declined, despite the positive year‐to‐year relationship between temperature and bivalve larval abundance continuing to hold. We argue that the changes in meroplankton abundance, coincident with increased phytoplankton and declining holoplankton, reflect the synchronous effect of rising SST and related changes in the pelagic community on the reproduction and recruitment of many benthic marine invertebrates. Under this scenario, the long‐term decline in bivalve mollusc larvae will reflect increased predation on the settled larvae and adults by benthic decapods. These alterations in the zooplankton may therefore describe an ecosystem‐wide restructuring of North Sea trophic interactions.
Thin layers of Pseudo‐nitzschia spp. and the fate of Dinophysis acuminata during an upwelling‐downwelling cycle in a Galician RÃa
Authors: Suárez L. Velo , Gil S. González , Gentien P. , Lunven M. , Bechemin C. , Fernand L. , Raine R. , Reguera B.
Published: November 2010

Fine‐resolution measurements of phytoplankton and physical parameters were made from 31 May to 14 June 2005 in the Ría de Pontevedra (Spain), which is subject to seasonal upwelling. The main objective of this work was to elucidate physical‐biological interactions leading to subsurface aggregations of toxin‐producing microalgae (Pseudo‐nitzschia spp. and Dinophysis spp.). A sequence of upwelling‐relaxation‐upwelling‐downwelling events was recorded with a moored Acoustic Doppler Current Profiler (ADCP). Thin layers (TLs) of Pseudo‐nitzschia spp. and other diatoms (up to 30 µg chlorophyll a L−1) developed and persisted in the pycnocline above cooler (12.5ºC) upwelled water but were vertically displaced and even dispersed during downwelling. The establishment of steep pycnoclines after upwelling pulses and the formation of TLs of Pseudo‐nitzschia spp. and other diatoms suggest that pycnoclines may act as retention areas for these populations. Their vertical displacement during downwelling would explain different patterns observed in the contamination of benthic resources and raft‐mussels. A decimeter‐scale segregation of Pseudo‐nitzschia micans and Dinophysis acuminata populations was observed. The population of D. acuminata, present since March 2005 in Ría de Pontevedra, was never found within the pycnocline, did not perform any significant vertical migration, and was not dispersed during upwelling. Instead, it formed patches (up to 8 × 103 cell L−1) in the warmer (15‐18ºC) surface (0‐4 m) waters associated with a diurnal thermocline, and it spread throughout the ría into a near‐surface layer during relaxation and downwelling. These results demonstrate the importance of considering species‐specific behavior to predict the location of cell maxima.
A model of photosynthesis and photo‐protection based on reaction center damage and repair
Authors: Ross Oliver N. , Moore C. Mark , Suggett Dave J. , MacIntyre Hugh L. , Geider Richard J.
Published: November 2010

Phytoplankton photosynthesis under the rapidly fluctuating irradiance which results from turbulent mixing through the vertical light gradient is poorly understood. Ship‐based measurements often apply the fast repetition rate fluorescence (FRRF) technique in situ or in vivo to gauge the physiological state of the phytoplankton community and infer some of the physical properties of the water column (such as mixing time scales). We describe the development and validation of a model of photosynthetic electron turnover at photosystemII with consideration of downstream limitation, based on the redox state of photosystem II. We also include empirical formulations for slower processes such as photo‐protection (from nonphotochemical quenching) and photo‐inhibition. By confronting the simple model with laboratory data for Dunaliella tertiolecta, we were able to refine the model so that it faithfully produced rates of photosynthetic electron transfer determined by FRR fluorescence. Further, we were able to validate the model estimates of linear photosynthetic electron transfer rates against completely independent measurements obtained using 14C‐bicarbonate assimilation in photosynthesis‐light curves.
Ballast, sinking velocity, and apparent diffusivity within marine snow and zooplankton fecal pellets: Implications for substrate turnover by attached bacteria
Authors: Ploug Helle , Iversen Morten Hvitfeldt , Fischer Gerhard
Published: November 2010

We analyzed size‐specific dry mass, sinking velocity, and apparent diffusivity in field‐sampled marine snow, laboratory‐made aggregates formed by diatoms or coccolithophorids, and small and large zooplankton fecal pellets with naturally varying content of ballast materials. Apparent diffusivity was measured directly inside aggregates and large (millimeter‐long) fecal pellets using microsensors. Large fecal pellets, collected in the coastal upwelling off Cape Blanc, Mauritania, showed the highest volume‐specific dry mass and sinking velocities because of a high content of opal, carbonate, and lithogenic material (mostly Saharan dust), which together comprised ~80% of the dry mass. The average solid matter density within these large fecal pellets was 1.7 g cm‐3, whereas their excess density was 0.25 ± 0.07 g cm‐3. Volume‐specific dry mass of all sources of aggregates and fecal pellets ranged from 3.8 to 960 µg mm‐3, and average sinking velocities varied between 51 and 732 m d‐1. Porosity was >0.43 and >0.96 within fecal pellets and phytoplankton‐derived aggregates, respectively. Averaged values of apparent diffusivity of gases within large fecal pellets and aggregates were 0.74 and 0.95 times that of the free diffusion coefficient in sea water, respectively. Ballast increases sinking velocity and, thus, also potential O2 fluxes to sedimenting aggregates and fecal pellets. Hence, ballast minerals limit the residence time of aggregates in the water column by increasing sinking velocity, but apparent diffusivity and potential oxygen supply within aggregates are high, whereby a large fraction of labile organic carbon can be respired during sedimentation.
Supply of gastropod larvae to hydrothermal vents reflects transport from local larval sources
Authors: K. Adams Diane , S. Mullineaux Lauren
Published: November 2010

Variation in larval supply to disjunct marine populations can provide insight into larval transport and delivery mechanisms, especially when compared with observations of physical transport. Daily variability in larval supply at two mussel‐dominated hydrothermal vents, East Wall and Choo Choo, near 9º50’N, East Pacific Rise, was quantified concurrently with hydrodynamic observations to investigate local dispersal processes. The magnitude and temporal variation in supply differed between the two vent sites despite their close proximity, 1.6 km. Larval supply was relatively high and uninterrupted at East Wall compared to low and episodic at Choo Choo. Observed variation in larval supply was compared to predictions based on advective transport from larval sources at neighboring vents. Variation in larval supply at Choo Choo correlated with along‐axis southward currents, consistent with larval transport from a northern larval source. Larval supply to East Wall appeared to be independent of current velocities, suggesting that larvae came from multiple sources north of and south of and possibly including East Wall. Transport of larvae from discrete local sources can explain differences in larval supply to vent communities, even on spatial scales of kilometers.
Settling larvae of a small coral‐reef fish discriminate reef features at large, but not small, spatial scales
Authors: Forrester Graham E. , Steele Mark A. , Samhouri Jameal F. , Vance Richard R.
Published: November 2010

Larval settlement of a small coral‐reef fish, the bridled goby (Coryphopterus glaucofraenum), to five entire reefs over 4 yr decreased with increasing cover of hard substrate (rock and coral). Experimentally increasing rock cover on these large reefs caused a reduction in settlement that lasted 3 yr, confirming that settling coral‐reef fish discriminate among sites at the mesoscale (hundreds of meters to tens of kilometers). Counterintuitively, a small‐scale manipulation of rock cover and an observational study both suggest that settlers show no response to rock cover at the microscale (few to tens of meters). Habitat selection at settlement can, thus, set initial benthic population size at much larger spatial scales than previously recognized, a finding consistent with the good swimming and sensory capabilities of late‐stage larvae.
Effects of the zebra mussel, an exotic freshwater species, on seston stoichiometry
Authors: Naddafi Rahmat , Pettersson Kurt , Eklöv Peter
Published: November 2010

We examined the effect of the zebra mussel, Dreissena polymorpha, an exotic species, on seston stoichiometry by conducting laboratory experiments in which we varied nutrient composition of seston and mussels over time. Zebra mussels altered the stoichiometry of seston through removal of particulate organic nutrients and changed the stoichiometry of the dissolved nutrient pool through nutrient excretion. Grazers had stronger effects on carbon : phosphorus (C : P) and nitrogen (N) : P ratios than on the C:N ratio of seston. Elemental residence time in tissue and high mass‐specific nutrient excretion by small mussels caused small mussels to be more efficient nutrient recyclers than larger mussels. Zebra mussels reduced P availability through enhancing C: P and N: P molar ratios of seston during the period extending from June to August, when P was limited in the lake, and increased the C:N molar ratio of seston in June, when N was at the minimum level in the lake. C: P and N: P molar ratios for zebra mussel tissue were higher in August and somewhat in September than in all other months. N was retained more efficiently than P in Dreissena tissue. Nutrient mass‐specific uptake rate was higher than excretion rate by zebra mussels.
Optical closure in lakes with contrasting extremes of reflectance
Authors: Gallegos C. L. , Davies-Colley R. J. , Gall M.
Published: November 2010

We measured inherent and apparent optical properties and computed ‘optical closure’ in four lakes on the South Island of New Zealand, ranging very widely in reflectance. Optical properties were measured by modern instruments deployed from boats, with supporting laboratory measurements on water samples. The radiative transfer model, Hydrolight, was used with measured inherent optical properties to predict characteristics of the light field for comparison with field measurements. Two glacier‐fed lakes were strongly light‐scattering and weakly light‐absorbing, with optical properties dominated by glacial flour. In marked contrast, two humic‐stained wetland lakes were strongly light‐absorbing and weakly light‐scattering, with optical properties dominated by colored dissolved organic matter. Very good optical “closure” (i.e., agreement of modeled with measured characteristics of the light field) was obtained for all apparent optical properties examined in all but the most strongly light‐scattering lake. Closure was achieved when systematic spectral bias in absorption in this lake, possibly caused by multiple scattering in the field absorption meter, was corrected using laboratory absorption measurements. The highest and lowest measured and modeled water‐leaving radiances exceeded the previous range for such studies by a factor of 5. The good optical closure observed over a very wide (200‐fold) range of reflectance increases confidence in our ability to specify inputs for radiative transfer modeling while highlighting the enduring challenge of accurately measuring absorption in highly scattering waters and backscattering in highly absorbing waters.
Introduction to the Limnology and Oceanography Special Issue on Autonomous and Lagrangian Platforms and Sensors (ALPS)
Authors: Dickey T. D. , Itsweire E. C. , Moline M. A. , Perry M. J.
Published: November 2010

This issue is devoted to recent developments of autonomous and Lagrangian platforms and sensors (ALPS) and their uses for solving a broad range of interdisciplinary aquatic problems. The collective papers treat a variety of problems that generally require measurements spanning a continuum of temporal and spatial scales. ALPS platforms in this issue include surface drifters, profiling and other types of subsurface floats, gliders, unmanned boats, autonomous underwater vehicles, and instrumented animals. ALPS platforms can provide access in difficult environments (e.g., under ice and in high‐sea states). They are also important for emerging networked ocean and lake observing systems that require continuous measurements and near‐real‐time data. This introductory paper provides historical perspectives, background, motivation for the issue, and a tabular summary of papers in the present collection.
Assessing plankton and other particles in situ with the SOLOPC
Authors: Checkley D. M. , Davis R. E. , Herman A. W. , Jackson G. A. , Beanlands B. , Regier L. A.
Published: November 2010

We combined a Sounding Oceanographic Lagrangian Observer float with a Laser Optical Plankton Counter (LOPC) and a fluorometer to make an autonomous biological profiler, the SOLOPC. The instrument senses plankton and other particles over a size range of 100 µm to 1 cm in profiles to 300 m in depth and sends data ashore via satellite. Objects sensed by the LOPC include aggregates and zooplankton, the larger of which can be distinguished from one another by their transparency. We hypothesized that the diel production of particles and their loss by sinking and grazing are reflected in the change of the particle distribution. We present data from four deployments of the SOLOPC off California. Particle volume was maximal at the base of the surface mixed layer and correlated with chlorophyll a fluorescence. In a 3‐d deployment in 2005, particle volume was greatest in the early evening and smallest in the morning, and average particle size increased with depth. Eigenvector analysis of the particle volume distribution as a function of diameter for each of the deployments yielded size peaks characteristic of planktonic crustaceans. Ship‐based measurements showed that the abundance of opaque particles of 1.1‐1.7 mm equivalent spherical diameter was positively correlated with copepods of this size and simultaneously collected in nets. This relationship was used with SOLOPC data to estimate the distribution of large copepods, which were most abundant beneath the depth of maximal particle flux, estimated from particle size and published sinking rates. Our data are consistent with a model with diel production of particles and their loss by sinking and grazing.
A diapycnal mixing budget on the Oregon shelf
Authors: D'Asaro Eric A.
Published: November 2010

Although isopycnal mixing is undoubtedly important at global and gyre scales, the relative importance of isopycnal and diapycnal mixing on much smaller scales is uncertain. This issue is investigated using 35 d of data from a Lagrangian float deployed on a mid‐depth isopycnal on the Oregon shelf. Measurements of temperature, salinity, and pressure maintain the float on the isopycnal; its high‐frequency diapycnal deviations are used to estimate the diapycnal diffusivity using an inertial subrange method; lower‐frequency deviations, including intentional profiles to the surface, are used to estimate diapycnal derivatives near the target isopycnal. Downward irradiance at 490 nm is used to calibrate chlorophyll fluorescence measurements and compute solar heating rates. Corrections for the diapycnal deviations provide a nearly continuous isopycnal time series of spice (a temperature and salinity combination nearly orthogonal to potential density) and chlorophyll. A new formulation of the diffusion equation in isopycnal coordinates is derived and used to test the accuracy of purely diapycnal mixing balances for spice and chlorophyll. On vertical scales of about 10 m and timescales of about 2 d, isopycnal spice variations are mostly controlled by diapycnal mixing, although other processes, presumably isopycnal mixing, are sometimes important. Processes other than diapycnal mixing control isopycnal chlorophyll variations on these scales. Likely candidates include isopycnal mixing with a nearby bloom, planktonic sinking out of this bloom, or possibly local phytoplankton growth. Thus both isopycnal and diapycnal mixing can be important at these small scales.
Glider surveillance of physics and biology in the southern California Current System
Authors: Davis Russ E. , Ohman Mark D. , Rudnick Daniel L. , Sherman Jeff T.
Published: November 2010

Since 2005, Spray underwater gliders have been used to sample sections across the southern California Current System (CCS). Properties measured are depth‐averaged velocity and profiles of temperature, salinity, Acoustic Doppler Profiler shear, chlorophyll a fluorescence, and 750‐kHz acoustic backscatter. Although slow and carrying a relatively small sensor suite, gliders observed multiple 350‐700‐km sections that reveal details of known elements of the CCS circulation like the California Current and Undercurrent as well as a previously undescribed undercurrent 100‐200 km offshore. The long time series with high spatial resolution disclose the close link between fronts in physical and biological variables, both the main pycnocline front and secondary weaker but sharp fronts farther offshore. These fronts appear to organize chlorophyll and acoustic backscatter fields, particularly during spring. Much of the patchiness of chlorophyll is associated with vertical displacements of fields that are much smoother within potential density surfaces. The horizontal structure of both chlorophyll and spice (the dynamically passive variable formed from temperature and salinity) appear to be formed by mesoscale stirring.
Mapping bathymetric and hydrographic features of Glover's Reef, Belize, with a REMUS autonomous underwater vehicle
Authors: Shcherbina Andrey Y. , Gawarkiewicz Glen G. , Linder Christopher A. , Thorrold Simon R.
Published: November 2010

We used an autonomous underwater vehicle (AUV) to survey bathymetry and water mass properties at Glover's Reef atoll in Belize as part of a multidisciplinary study of population connectivity of Nassau grouper (Epinephelus striatus). Nassau grouper populations are declining dramatically throughout its range in the Caribbean because of overfishing. In response, Marine Protected Areas have been established at several spawning aggregation (SPAG) sites. However, effectiveness of these measures is presently unclear, as the regional patterns of transport and recruitment of grouper larvae have not been measured in extensive field studies. As part of a pilot study to relate oceanographic processes with transport and recruitment of Nassau grouper larvae, we used a Remote Environmental Monitoring Unit(S) (REMUS) AUV to measure the bathymetry, stratification, current velocity, and chlorophyll a fluorescence around Glover's Reef. The portability of the REMUS system enabled comprehensive oceanographic data collection in a remote location with minimal infrastructure. Using REMUS, we were able to effectively map the bathymetry of the reef and the shelfbreak. These data were merged with historical bathymetric data to develop a new chart of the atoll margin. A distinct contrast in the width of the shelves on the eastern and western sides of the atoll was demonstrated, with the widest shelf coinciding with the SPAG site. Water mass structure in the vicinity of SPAG site was also markedly different from other locations on the reef, suggesting an offshore advective influence on eggs and early‐stage larvae released there.
Ice‐ocean turbulent exchange in the Arctic summer measured by an autonomous underwater vehicle
Authors: Hayes Daniel R. , Morison James
Published: November 2010

The first‐ever observed horizontal profiles of summertime ice‐ocean boundary layer fluxes were obtained using vertical water velocity, temperature, and salinity collected by an Autonomous Underwater Vehicle during the Surface Heat Balance of the Arctic Ocean (SHEBA) experiment of 1998. Scalars and their vertical fluxes, as well as vertical stability, varied in the horizontal direction with correspondence to changes in the overlying surface. In early summer, fresh meltwater was trapped at the upper ice surface and only entered the ocean through leads. A highly stable fresh layer was formed in the SHEBA lead, which eventually grew to depths greater than the mean draft of the local first‐year ice. Near the end of July, a storm removed this layer via shear‐generated turbulence, supercritical hydraulic flow speeds, and ice divergence. The mixed layer freshened and deepened at this time. Particularly strong fluxes were observed under and downstream of rough, ridged ice, and properties changed rapidly with distance downstream of leads. The location and signs of the fluxes are suggestive of a mechanism of instability in which fresh surface water is forced under salty water downstream of leads and/or ridges. Simulations from a two‐dimensional unsteady model suggest that both mechanical forcing from ice topography and a dynamic instability near downstream lead edges may enhance vertical mixing, particularly when ice velocity is large. The horizontal variability in interfacial fluxes observed at SHEBA may explain the difference between the observed melt rates and those calculated using a bulk relationship because this relationship may not adequately parameterize the large lateral heat fluxes at lead edges and basal heat fluxes under ridge keels.
Convectively driven transport in temperate lakes
Authors: Forrest Alexander L. , Laval Bernard E. , Pieters Roger , Lim Darlene S. S.
Published: November 2010

Penetrative convection in the surface layer of a midsize temperate lake (5 km2) was investigated in both summer and winter using a conductivity‐temperature‐depth (CTD) logger mounted on an autonomous underwater vehicle (AUV) flown repeatedly along horizontal transects at selected depths. In summer, the epilimnion cooled differentially during a calm evening (240 and 297 W m−2 on the east and west sides of the lake, respectively). These cooling rates agree well with the average net heat flux of 270 W ths. In summer, the epilimnion cooled differentially during a calm evening (240 and 297 W estimated from meteorological data. Density currents were driven by this differential cooling. In winter, CTD profiles during a sunny day showed four distinct thermal layers beneath the ice (~50 cm thick), consistent with radiative penetrative convection: a stratified diffusive layer just beneath the ice (top 1.6 m); a well‐mixed convective layer (that deepens at 1.14 m d−1 and warms at 0.015°C d−1 during the observation period); an entrainment layer (1.5 m thick); and a weakly stratified quiescent layer (to bottom). AUV transects, flown at constant depths in each layer, revealed a 150‐m wide region displaying evidence of penetrative convection, surrounded by regions with negligible heat changes. These high‐resolution, horizontal CTD measurements provided insight into previously unresolved physical dynamics of the well‐mixed layer of a temperate lake in quasi‐shear‐free conditions that would have been difficult to quantify during summer months and impossible under winter ice cover without the use of an AUV platform.
Macro‐ to fine‐scale spatial and temporal distributions and dynamics of phytoplankton and their environmental driving forces in a small montane lake in southern California, USA
Authors: Caron David A. , Stauffer Beth , Moorthi Stefanie , Singh Amarjeet , Batalin Maxim , Graham Eric A. , Hansen Mark , Kaiser William J. , Das Jnaneshwar , Pereira Arvind , Dhariwal Amit , Zhang Bin , Oberg Carl , Sukhatme Gaurav S.
Published: November 2010

A wireless network of buoys, two autonomous robotic boats, and an autonomous tethered vertical profiling system were used to characterize phytoplankton dynamics and spatiotemporal changes in chemical and physical forcing factors in a small montane lake (Lake Fulmor, Idyllwild, California). Three deployments each year were conducted in 2005 and 2006 to examine seasonal changes in the structure of the lake and phytoplankton assemblage, as well as fine‐scale temporal and spatial variations. The buoys yielded fine‐scale temporal patterns of in situ fluorescence and temperature, while the vertical profiling system yielded two‐dimensional, cross‐sectional profiles of several parameters. The autonomous vehicles provided information on fluorescence and corresponding temperature patterns across the surface of the lake. Average, lake‐wide chlorophyll concentrations increased 10‐ fold seasonally, and strong anoxia developed in the hypolimnion during the summer. The latter process dramatically affected vertical chemical gradients in the 5 m water column of the lake. Small‐scale spatial (<1 m) and temporal (minutes) heterogeneity in fluorescence were surprisingly large. These variations were due predominantly to vertical mixing of the phytoplankton assemblage and to phytoplankton vertical migratory behavior. Large peaks in fluorescence at 0.5‐m occurred at very short time intervals (minutes) during all deployments, and appeared to be due to upward mixing of deeper dwelling eukaryotic phytoplankton during early‐mid‐summer, or downward mixing of surface‐associated cyanobacteria during late summer.
Monitoring Drake Passage with elephant seals: Frontal structures and snapshots of transport
Authors: Boehme L. , Thorpe S. E. , Biuw M. , Fedak M. , Meredith M. P.
Published: November 2010

Conductivity‐temperature‐pressure satellite relay data loggers (CTD‐SRDLs) were attached to southern elephant seals (Mirounga leonina) on the island of South Georgia. During the animals' migration the CTDSRDLs recorded and transmitted hydrographic profiles at a rate of approximately two profiles per day to an average depth of about 547 m, representing transect‐type sections with a spatial resolution of 16‐47 km along the migratory routes of the seals. Two sections are used to clearly identify the locations of the Antarctic Circumpolar Current fronts across Drake Passage, providing in situ data complementary to satellite and other techniques. An empirical relationship between upper ocean temperature and baroclinic mass transport is used to determine the transport through Drake Passage at the times of the sections, and these transports are compared with estimates derived by other techniques. An absolute geostrophic velocity section across Drake Passage is calculated using CTD‐SRDL data and data of absolute geostrophic surface velocities from altimetry. The mean total baroclinic transports in June 2004 and April 2005 are estimated to be 124 × 106 ± 14 × 106 m3 s−1 and 112 × 106 ± 14 × 106 m3 s−1 respectively.
Vertical distribution of zooplankton in subalpine and alpine lakes: Ultraviolet radiation, fish predation, and the transparency‐gradient hypothesis
Authors: Kessler Kirsten , Lockwood Ryan S. , Williamson Craig E. , Saros Jasmine E.
Published: November 2010

The transparency‐gradient hypothesis argues that ultraviolet radiation (UV) is a primary determinant of the vertical distribution of zooplankton in transparent lakes with fewer fish, while fish predation is the primary driver in less transparent lakes where fish are more abundant. We measured vertical profiles of UV, photosynthetically active radiation (PAR, essentially visible light used as a proxy for fish predation), temperature, pH, conductivity, chlorophyll a (Chl a), and zooplankton in seven subalpine and alpine lakes and examined the distribution and abundance of the major zooplankton groups relative to environmental variables using a canonical correspondence analysis (CCA) and multiple regression. Pigment concentrations and UV tolerance of representative species were examined experimentally. The CCA revealed that conductivity, PAR, and UV were most related to zooplankton distribution and abundance. The cladoceran Daphnia was associated with high PAR, while cyclopoids and nauplii were associated with low PAR. In contrast, the vertical distribution of calanoids was positively related to UV, while Holopedium was negatively associated with UV. The regressions revealed that UV consistently explained more of the variance in zooplankton vertical distribution than did either PAR or chlorophyll. Calanoids had high concentrations of photoprotective compounds and a relatively high UV tolerance compared to Daphnia. The positive association of Daphnia with visible light (PAR) and the importance of UV in overall zooplankton vertical distribution support the transparency‐gradient hypothesis, indicating that UV is more important than fish predation in controlling the vertical distribution of zooplankton in more transparent lakes.
The effects of Cu and Fe availability on the growth and Cu:C ratios of marine diatoms
Authors: Annett Amber L. , Lapi Suzanne , Ruth Thomas J. , Maldonado Maria T.
Published: November 2010

We investigated the effects of copper (Cu) and iron (Fe) availability on the growth rates, cellular Cu content, and steady‐state Cu uptake rates of eight species of centric diatoms (coastal and oceanic strains). Whereas Fe and Cu availability had a significant effect on the growth rates of both costal and oceanic diatoms, an interaction between Fe and Cu availability and growth rates was only observed for the oceanic diatoms. Determination of cellular Cu : carbon (C) quotas using the radiotracers 67Cu and 14C revealed that under Cu‐sufficient conditions oceanic diatoms had elevated Cu :C ratios relative to coastal strains, regardless of Fe availability. Two species (one oceanic and one coastal) significantly increased their Cu demands in response to Fe limitation, indicating upregulation of the Cu‐dependent high‐affinity Fe uptake system in these organisms. The changes in cellular Cu :C ratios were accompanied by variations in steady‐state Cu uptake rates. Thus, in some cases Cu uptake rates appear to be regulated by the cell in response to Fe availability. Rates of Cu acquisition also responded significantly to Cu variability. The variation in Cu uptake was more closely correlated with changes in total Cu concentration in the medium than in inorganic, free Cu concentrations, implying that organic Cu complexes may be bioavailable to diatoms. These findings indicate a greater biological role for Cu than was previously thought in open ocean regions.
Interactions between changing pCO2, N2 fixation, and Fe limitation in the marine unicellular cyanobacterium Crocosphaera
Authors: Fu Fei-Xue , Mulholland Margaret R. , Garcia Nathan S. , Beck Aaron , Bernhardt Peter W. , Warner Mark E. , Sañudo-Wilhelmy Sergio A. , Hutchins David A.
Published: November 2010

We examined the physiological responses of steady‐state iron (Fe)‐replete and Fe‐limited cultures of the biogeochemically critical marine unicellular diazotrophic cyanobacterium Crocosphaera at glacial (19 Pa; 190 ppm), current (39 Pa; 380 ppm), and projected year 2100 (76 Pa; 750 ppm) CO2 levels. Rates of N2 and CO2 fixation and growth increased in step with increasing partial pressure of CO2 (pCO2), but only under Fe‐replete conditions. N2 and carbon fixation rates at 75 Pa CO2 were 1.4‐1.8‐fold and 1.2‐2.0‐fold higher, respectively, relative to those at present day and glacial pCO2 levels. In Fe‐replete cultures, cellular Fe and molybdenum quotas varied threefold and were linearly related to N2 fixation rates and to external pCO2. However, N2 fixation and trace metal quotas were decoupled from pCO2 in Fe‐limited Crocosphaera. Higher CO2 and Fe concentrations both resulted in increased cellular pigment contents and affected photosynthesis vs. irradiance parameters. If these results also apply to natural Crocosphaera populations, anthropogenic CO2 enrichment could substantially increase global oceanic N2 and CO2 fixation, but this effect may be tempered by Fe availability. Possible biogeochemical consequences may include elevated inputs of new nitrogen to the ocean and increased potential for Fe and/or phosphorus limitation in the future high‐CO2 ocean, and feedbacks to atmospheric pCO2 in both the near future and over glacial to interglacial timescales.
Factors influencing the initiation of blooms of the raphidophyte Heterosigma akashiwo and the diatom Skeletonema costatum in a port in Japan
Authors: Shikata Tomoyuki , Nagasoe Sou , Matsubara Tadashi , Yoshikawa Souta , Yamasaki Yasuhiro , Shimasaki Yohei , Oshima Yuji , Jenkinson Ian R. , Honjo Tsuneo
Published: November 2010

We investigated how environmental factors initiate Heterosigma akashiwo and Skeletonema costatum blooms from resting stages in bottom sediments in a shallow port over 2 yr. Using field‐collected sediments, we also conducted laboratory experiments on how light intensity affects germination of resting stages and growth of the germinated cells. Both phytoplankton species bloomed only in summer, when water temperature and solar radiation were high enough for growth. All three blooms of H. akashiwo and the earliest bloom of S. costatum in a year occurred right after transmission of strong light (>200 [mol quanta m−2 s−1) to the bottom layer and a peak occurred in dissolved inorganic phosphorus (DIP). In the laboratory, resting stages of H. akashiwo and S. costatum germinated even in dim light (20 and 65 [mol quanta m−2 s−1, respectively), but germinated cells required stronger light of >130 and 280 [mol quanta m−2 s−1, respectively, for rapid growth. This value is much higher than the threshold for survival, and is higher than the half‐saturating light intensity for growth of vegetative cells. Abundance of the resting stages of both species in the sediments rapidly increased during blooms and logarithmically decreased during nonbloom periods, suggesting that resting stages are continuously consumed. For both species, our results suggest that blooms initiate when transmission of sufficient light permits: first, germination of cells from the sediment; second, rapid growth of these germinated cells. Temperature and DIP must also exceed a facilitating threshold.
Effects of inorganic nitrogen on taxa‐specific cyanobacterial growth and nifH expression in a subtropical estuary
Authors: Moisander Pia H. , Paerl Hans W. , Zehr Jonathan P.
Published: November 2010

The potentially toxic, diazotrophic filamentous cyanobacterium Cylindrospermopsis raciborskii has recently become a common component in the summer phytoplankton in the St. Johns River (SJR) estuary, Florida, where Anabaena spp. historically dominated. Using a microcosm nutrient enrichment experiment, we investigated the ability of C. raciborskii and Anabaena spp. to compete under a range of available NO3− and NH4+ concentrations, to test the hypothesis that C. raciborskii benefits from increased dissolved inorganic nitrogen (DIN) availability. TaqMan quantitative polymerase chain reaction (PCR) probes were designed, tested, and applied to target the nifH gene in one C. raciborskii and two Anabaena spp. strains from the SJR. N limitation prevailed, as shown by increased N2‐fixation rates if no N was added, increased chlorophyll a concentrations when DIN was added, and depletion of added DIN. Anabaena spp. and C. raciborskii showed rapid growth with no DIN additions and were the main taxa responsible for N2 fixation. Abundances of C. raciborskii increased if NH4+ was added, but nifH was expressed at low levels, suggesting growth was relying on NH4+. Anabaena spp. and C. raciborskii expressed nifH genes when NO3− or NH4+ were present, but expression was higher with NO3−. The narB gene sequence was amplified from Anabaena spp. and C. raciborskii from the SJR, suggesting these taxa are capable of assimilating NO3−. However, even small NO3− additions blocked the growth of Anabaena spp. in the mixed phytoplankton community but not that of C. raciborskii. The results suggest that C. raciborskii in the SJR is a stronger competitor than Anabaena spp. when DIN is present.
Nitrification in Mono Lake, California: Activity and community composition during contrasting hydrological regimes
Authors: Carini Stephen A. , Joye Samantha B.
Published: November 2010

Rates of nitrification, geochemical variables, and the associated ammonia oxidizer microbial community were investigated in the water column of Mono Lake, California, between August 2002 and August 2003. Ammonia oxidation rates were measured using a 15N isotope tracer technique. 16S ribosomal deoxyribonucleic acid, functional gene, and fluorescence in situ hybridization (FISH) analyses were used to characterize the ammonia oxidizer population. Peak ammonia oxidation activity occurred consistently between 12 and 14 m; the maximum integrated rate was observed in November 2002. The ammonia‐oxidizing bacterial (AOB) community exhibited sequences most closely related to halo and/or alkaline tolerant Nitrosomonas‐like sequences. The observed phylogeny represented a significant shift from previously documented AOB community composition and was coincident with Mono Lake's transition from monomixis to meromixis. Samples were also analyzed for ammoniaoxidizing archaea (AOA). FISH analysis revealed a substantial population of Crenarchaeota, the phylum encompassing all known AOA; however, no archaeal ammonia monooxygenase (amoA) sequences were detected. Unrealistic AOB cell‐specific nitrification rates strongly indicate the possibility of a missing nitrification source, and correlations between nitrification rates, geochemical variables, and crenarchaeal and AOB abundance also indicate a significant AOA contribution to nitrification. However, the lack of verifiable archaeal amoA genes leaves open the question of whether AOA contribute to nitrification in Mono Lake.
Assimilatory uptake rather than nitrification and denitrification determines nitrogen removal patterns in streams of varying land use
Authors: Arango C. P. , Tank J. L. , Johnson L. T. , Hamilton S. K.
Published: November 2010

Agricultural and urban land use increase nitrogen (N) concentrations in streams, which can saturate biotic demand by plants, algae, and bacteria via assimilative uptake, and by nitrification and denitrification. We studied six streams per year in each of three land‐use categories (agricultural, urban, and forested) for 3 yr (n = 18 streams), and we compared whole‐stream N uptake and microbial N transformation rates during spring, summer, and autumn. We measured whole‐stream removal of added ammonium (NH4+) and nitrate (NO3−) in the field and quantified sediment nitrification and denitrification rates in laboratory assays. Relative demand for NNH4+ (as uptake velocity, Vf) was highest in spring and in streams with open canopies, implying a link with aquatic autotrophy. In agricultural and urban streams, whole‐stream removal (as areal uptake, U) of NH4+ and NO3−, nitrification, and denitrification rates approached saturation at higher inorganic N concentrations. Nitrification and denitrification rates measured in redox‐optimized laboratory assays were roughly equivalent, suggesting that in situ redox conditions will determine whether stream sediments are a net source or sink of NO3−. Though nitrification and denitrification rates were measured under ideal redox conditions, they were always more than an order of magnitude lower than whole‐stream NO{3 uptake, demonstrating their limited influence on wholestream NO3− dynamics. Assimilatory processes, which temporarily store N removed from the water column, dominated whole‐stream N demand and controlled downstream N flux. The ultimate fate of assimilated N remains unknown; in‐channel storage cannot account for it, and thus a key question is what fraction may eventually be stored in downstream depositional zones or denitrified upon remineralization.
A comparative study of carbon dioxide degassing in river‐ and marine‐dominated estuaries
Authors: Jiang Li-Qing , Cai Wei-Jun , Wang Yongchen
Published: November 2010

The partial pressure of carbon dioxide (pCO2), concentration of total dissolved inorganic carbon, and total alkalinity were measured at both high tide and low tide in the surface water of three Georgia estuaries from September 2002 to May 2004. Of the three estuaries, Sapelo and Doboy Sounds are marine‐dominated estuaries, while Altamaha Sound is a river‐dominated estuary. During all sampling months, the three estuaries were supersaturated in CO2 with respect to the atmosphere (39.5–342.5 Pa, or 390–3380 [atm) because of CO2 inputs from within the estuarine zone (mainly intertidal marshes) and the river. Overall, pCO2 in the river‐dominated estuary is much higher than that in the marine‐dominated estuaries. The calculated annual air‐water CO2 flux in Altamaha Sound (69.3 mmol m−2 d−1) is 2.4 times those of Sapelo and Doboy Sounds (28.7–29.4 mmol m−2 d−1). The higher CO2 degassing in the river‐dominated estuary is fueled largely by CO2 loading from the river. Because of the substantial differences between river‐ and marine‐dominated estuaries, current estimates of air‐water CO2 fluxes in global estuaries (which are based almost entirely on river‐dominated estuaries) could be overestimated.
Settling blooms of filamentous cyanobacteria as food for meiofauna assemblages
Authors: Nascimento Francisco J. A. , Karlson Agnes M. L. , Elmgren Ragnar
Published: November 2010

Summer blooms of filamentous nitrogen‐fixing cyanobacteria in the Baltic Sea are normally dominated by Aphanizomenon sp. and the toxin‐producing Nodularia spumigena. In a 2‐week laboratory experiment, we followed the uptake by representative benthic meiofauna species of 14C‐labeled organic carbon from blooms, each dominated by one of these cyanobacteria. Natural bloom material was collected and labeled by incubation with NaH14CO3. Uptake of cyanobacterial carbon was recorded for the major meiofauna taxa living in the first‐centimeter layer, namely ostracods, harpacticoids, and nematodes. The uptake rates were within the range found for diatoms in other studies, indicating that cyanobacteria may be an important food resource for the meiobenthos. The uptake of cyanobacterial carbon varied significantly among species, even within the same class. The ostracod Candona neglecta showed the highest uptake values, whereas two other ostracod species took up very little of the label. There was no significant difference in utilization of carbon from Aphanizomenon sp. and N. spumigena and no reduction in the abundance of the meiofaunal taxa analyzed compared to unexposed controls, indicating that Baltic meiofaunal assemblages in general experience no mortality when exposed to settled cyanobacteria, even the hepatotoxic N. spumigena.
Evidence for the inherent unsteadiness of a river plume: Satellite observations of the Niagara River discharge
Authors: Horner-Devine Alexander R. , Fong Derek A. , Monismith Stephen G.
Published: November 2010

We present satellite data from the Niagara River plume showing that a large eddy, or bulge, forms and grows in the plume near the mouth of the river. The plume consists of a semicircular bulge region immediately offshore of the mouth and a narrow current that propagates east along the shoreline. During the low‐wind period from 27 to 29 May 1999, the width of the bulge more than doubled and the current width increased only slightly. Approximately one‐third of the Niagara River water accumulated in the bulge near the mouth during this period, implying that the transport rate in the shore‐parallel current was reduced to two‐thirds of the river discharge rate. The effective radius and the growth rate of the bulge computed from the satellite images was in good agreement with previous laboratory results and a numerical model of the Niagara River plume. This is the first field evidence of the unsteadiness of the bulge.