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Showing papers on "Water column published in 2013"


Journal ArticleDOI
TL;DR: It is shown for the first time ever, that microplastics have indeed reached the most remote of marine environments: the deep sea, and microplastic pollution has spread throughout the world's seas and oceans.

1,117 citations


Journal ArticleDOI
TL;DR: There are notable differences between taxa and regions that inform the understanding of ocean metal biogeochemistry, and differences in the quotas estimated by the various techniques also provide information on metal behavior.
Abstract: Trace metals are required for numerous processes in phytoplankton and can influence the growth and structure of natural phytoplankton communities. The metal contents of phytoplankton reflect biochemical demands as well as environmental availability and influence the distribution of metals in the ocean. Metal quotas of natural populations can be assessed from analyses of individual cells or bulk particle assemblages or inferred from ratios of dissolved metals and macronutrients in the water column. Here, we review the available data from these approaches for temperate, equatorial, and Antarctic waters in the Pacific and Atlantic Oceans. The data show a generalized metal abundance ranking of Fe≈Zn>Mn≈Ni≈Cu≫Co≈Cd; however, there are notable differences between taxa and regions that inform our understanding of ocean metal biogeochemistry. Differences in the quotas estimated by the various techniques also provide information on metal behavior. Therefore, valuable information is lost when a single metal stoichi...

391 citations


Journal ArticleDOI
TL;DR: This result shows that eutrophication in relatively small, isolated, stratifying lakes can be restored by targeting both water column and sediment P using a combination of flocculent and solid phase P-sorbent.

229 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the redox dynamics of manganese (Mn) in the sediment of Lake Zurich using precise sediment core age models, monthly long-term oxygen (O 2 ) monitoring data of the water column (1936-2010) and high-resolution XRF core scanning.

210 citations


Book ChapterDOI
17 Mar 2013
TL;DR: The largest zone of oxygen-depleted coastal waters in the United States, and the entire western Atlantic Ocean, is found in the northern Gulf of Mexico on the Louisiana/Texas continental shelf influenced by the freshwater discharge and nutrient load of the Mississippi River system as mentioned in this paper.
Abstract: Nutrient over-enrichment in many areas around the world is having pervasive ecological effects on coastal ecosystems. These effects include reduced dissolved oxygen in aquatic systems and subsequent impacts on living resources. The largest zone of oxygen-depleted coastal waters in the United States, and the entire western Atlantic Ocean, is found in the northern Gulf of Mexico on the Louisiana/Texas continental shelf influenced by the freshwater discharge and nutrient load of the Mississippi River system. The mid-summer bottom areal extent of hypoxic waters (< 2 mg l -1 O2) in 1985-1992 averaged 8,000 to 9,000 km 2 but increased to up to 16,000 to 20,000 km 2 in 1993-2000. Hypoxic waters are most prevalent from late spring through late summer, and hypoxia is more widespread and persistent in some years than in others. Hypoxic waters are distributed from shallow depths near shore (4 to 5 m) to as deep as 60 m water depth but more typically between 5 and 30 m. Hypoxia occurs mostly in the lower water column but encompasses as much as the lower half to two -thirds of the water column. The Mississippi River system is the dominant source of fresh water and nutrients to the northern Gulf of Mexico. Mississippi River nutrient concentrations and loading to the adjacent continental shelf have changed in the last half of the 20 th century. The average annual nitrate concentration doubled, and the mean silicate concentration was reduced by 50%. There is no doubt that the average concentration and flux of nitrogen (per unit volume discharge) increased from the 1950s to 1980s, especially in the spring. There is considerable evidence that nutrient enhanced primary production in the northern Gulf of Mexico is causally related to the oxygen depletion in the lower water column. Evidence from long-term data sets and the sedimentary record demonstrate that historic increases in riverine dissolved inorganic nitrogen concentration and loads over the last 50 years are highly correlated with indicators of increased productivity in the overlying water column, i.e., eutrophication of the continental shelf waters, and subsequent worsening of oxygen stress in the bottom waters. Evidence associates increased coastal ocean productivity and worsening oxygen depletion with changes in landscape use and nutrient management that resulted in nutrient enrichment of receiving waters. Thus, nutrient flux to coastal systems has increased over time due to anthropogenic activities and has led to broad -scale degradation of the marine environment.

186 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigate the ability of the models contributing to the fifth Coupled Models Intercomparison Project (CMIP5) to represent the Southern Ocean hydrological properties and its overturning in a water mass framework.
Abstract: [1] The ability of the models contributing to the fifth Coupled Models Intercomparison Project (CMIP5) to represent the Southern Ocean hydrological properties and its overturning is investigated in a water mass framework. Models have a consistent warm and light bias spread over the entire water column. The greatest bias occurs in the ventilated layers, which are volumetrically dominated by mode and intermediate layers. The ventilated layers have been observed to have a strong fingerprint of climate change and to impact climate by sequestrating a significant amount of heat and carbon dioxide. The mode water layer is poorly represented in the models and both mode and intermediate water have a significant fresh bias. Under increased radiative forcing, models simulate a warming and lightening of the entire water column, which is again greatest in the ventilated layers, highlighting the importance of these layers for propagating the climate signal into the deep ocean. While the intensity of the water mass overturning is relatively consistent between models, when compared to observation-based reconstructions, they exhibit a slightly larger rate of overturning at shallow to intermediate depths, and a slower rate of overturning deeper in the water column. Under increased radiative forcing, atmospheric fluxes increase the rate of simulated upper cell overturning, but this increase is counterbalanced by diapycnal fluxes, including mixed-layer horizontal mixing, and mostly vanishes.

175 citations


Journal ArticleDOI
Abstract: We report results collected year-round since 1998 in northern Marguerite Bay, just inside the Antarctic Circle. The magnitude of the spring phytoplankton bloom is much reduced following winters with reduced sea-ice cover. In years with little winter sea-ice the exposed sea surface leads to deep mixed layers in winter, and reduced water-column stratification the following spring. Summer mixed-layer depths are similar, however, so the change is not in overall light availability but toward a less stable water column with greater vertical mixing and increased variability in the light conditions experienced by phytoplankton. Macronutrient concentrations are replete at all times, but the increased vertical mixing likely reduces iron availability. The timing of bloom initiation is similar between heavy and light ice years, occurring soon after light returns in early spring, at a mixed-layer averaged light level of < 1 mol photon m−2 d−1. Ongoing regional climate change in the WAP area, and notably the ongoing loss of winter sea-ice, is likely to drive a downward trend in the magnitude of phytoplankton blooms in this region of the Antarctic Peninsula.

149 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compare and contrast the ecosystems of the Barents and Chukchi Seas and find that the difference in fish abundance is driven by differences in the heat and plankton advected into them, and the amount of primary production consumed in the upper water column.

138 citations


Journal ArticleDOI
TL;DR: A metagenome perspective on ecosystem-scale metabolism in an upwelling-influenced river-dominated coastal margin is provided, indicating possible formation of anoxic microniches within particles.
Abstract: The Columbia River (CR) is a powerful economic and environmental driver in the US Pacific Northwest. Microbial communities in the water column were analyzed from four diverse habitats: 1) an estuarine turbidity maximum (ETM); 2) a chlorophyll maximum of the river plume; 3) an upwelling-associated hypoxic zone; and 4) the deep ocean bottom. Three size fractions, 0.1-0.8, 0.8-3 and 3-200 μm were collected for each habitat in August 2007, and used for DNA isolation and 454 sequencing, resulting in 12 metagenomes of >5 million reads (>1.6 Gbp). To characterize the dominant microorganisms and metabolisms contributing to coastal biogeochemistry, we used predicted peptide and rRNA data. The 3- and 0.8-μm metagenomes, representing particulate fractions, were taxonomically diverse across habitats. The 3-μm size fractions contained a high abundance of eukaryota with diatoms dominating the hypoxic water and plume, while cryptophytes were more abundant in the ETM. The 0.1-μm metagenomes represented mainly free-living bacteria and archaea. The most abundant archaeal hits were observed in the deep ocean and hypoxic water (19% of prokaryotic peptides in the 0.1-μm metagenomes), and were homologous to Nitrosopumilus maritimus (ammonia-oxidizing Thaumarchaeota). Bacteria dominated metagenomes of all samples. In the euphotic zone (estuary, plume and hypoxic ocean), the most abundant bacterial taxa (≥40 % of prokaryotic peptides) represented aerobic photoheterotrophs. In contrast, the low-oxygen, deep water metagenome was enriched with sequences for strict and facultative anaerobes. Interestingly, many of the same anaerobic bacterial families were enriched in the 3-μm size fraction of the ETM (2-10X more abundant relative to the 0.1-μm metagenome), indicating possible formation of anoxic microniches within particles. Results from this study provide a metagenome perspective on ecosystem-scale metabolism in an upwelling-influenced river-dominated coastal margin.

136 citations


Journal ArticleDOI
TL;DR: In this article, the effects of water residence time and other drivers on the dynamics of harmful cyanobacteria and microcystin concentrations (MCYST) were studied in a shallow Mediterranean lake.
Abstract: SUMMARY 1. Climate change affects aquatic ecosystems differently depending on local conditions. In the Mediterranean region, predicted drier seasons could especially affect lake water residence time and in consequence cyanobacteria and cyanotoxin dynamics. 2. We carried out a 3-year study of a shallow, Mediterranean lake (Lake Albufera, Spain), to study the effects of water residence time and other drivers on the dynamics of harmful cyanobacteria and microcystin concentrations (MCYST). 3. Longer water residence time in dry years and dry seasons increased total cyanobacteria biomass, Microcystis aeruginosa populations and MCYST concentrations in the lake water and seston. Droughts increased water retention time by about 45%, and M. aeruginosa populations and MCYST were 1–2 orders of magnitude higher. 4. All samples analysed contained MCYST, and among them 70% had values above the recommended guidelines. Flows lower than 10 m 3 s )1 raised toxicological risk from low to moderate-high according to international standards. Mean MCYST concentrations bound in the cells were one order of magnitude higher than in the water (11 ± 2.9 and 1.2 ± 0.3 l gL )1 , respectively). 5. The microcystin content per unit biovolume of M. aeruginosa was generally higher at the start of population growth (April–May) than at the population maximum (July–October). This was related to increase in water residence time, total phosphorus concentration and mean colony size within the edible range (<50 lm). The maximum MCYST content corresponded with average populations of 10 3 colonies L )1 and 2 mm 3 L )1 , which could additionally be used to evaluate toxicological risks in the lake. 6. Microcystis aeruginosa colonies were larger with increasing water residence time and more closely related to the lake hydrology and water column stagnation than to MCYST colony content. 7. Feasible measures for restoration and conservation of shallow Mediterranean lakes in a future climate scenario are discussed.

135 citations


Journal ArticleDOI
TL;DR: It was found that in the Columbia River coastal margin, freshwater-influenced environments were consistent and predictable, whereas coastal ocean community variability was difficult to interpret due to complex physical conditions.
Abstract: Bacterioplankton communities are deeply diverse and highly variable across space and time, but several recent studies demonstrate repeatable and predictable patterns in this diversity. We expanded on previous studies by determining patterns of variability in both individual taxa and bacterial communities across coastal environmental gradients. We surveyed bacterioplankton diversity across the Columbia River coastal margin, USA, using amplicon pyrosequencing of 16S rRNA genes from 596 water samples collected from 2007 to 2010. Our results showed seasonal shifts and annual reassembly of bacterioplankton communities in the freshwater-influenced Columbia River, estuary, and plume, and identified indicator taxa, including species from freshwater SAR11, Oceanospirillales, and Flavobacteria groups, that characterize the changing seasonal conditions in these environments. In the river and estuary, Actinobacteria and Betaproteobacteria indicator taxa correlated strongly with seasonal fluctuations in particulate organic carbon (ρ=−0.664) and residence time (ρ=0.512), respectively. In contrast, seasonal change in communities was not detected in the coastal ocean and varied more with the spatial variability of environmental factors including temperature and dissolved oxygen. Indicator taxa of coastal ocean environments included SAR406 and SUP05 taxa from the deep ocean, and Prochlorococcus and SAR11 taxa from the upper water column. We found that in the Columbia River coastal margin, freshwater-influenced environments were consistent and predictable, whereas coastal ocean community variability was difficult to interpret due to complex physical conditions. This study moves beyond beta-diversity patterns to focus on the occurrence of specific taxa and lends insight into the potential ecological roles these taxa have in coastal ocean environments.

Journal ArticleDOI
Abstract: Based on four cruises covering a seasonal cycle in 2009-2011, we examined the impact of the Kuroshio intrusion, featured by extremely oligotrophic waters, on the nutrient inventory in the central northern South China Sea (NSCS). The nutrient inventory in the upper 100m of the water column in the study area ranged from similar to 200 to similar to 290 mmol m(-2) for N+N (nitrate plus nitrite), from similar to 13 to similar to 24 mmol m(-2) for soluble reactive phosphate and from similar to 210 to similar to 430 mmol m(-2) for silicic acid. The nutrient inventory showed a clear seasonal pattern with the highest value appearing in summer, while the N+N inventory in spring and winter had a reduction of similar to 13 and similar to 30 %, respectively, relative to that in summer. To quantify the extent of the Kuroshio intrusion, an isopycnal mixing model was adopted to derive the proportional contribution of water masses from the SCS proper and the Kuroshio along individual isopycnal surfaces. The derived mixing ratio along the isopycnal plane was then employed to predict the genuine gradients of nutrients under the assumption of no biogeochemical alteration. These predicted nutrient concentrations, denoted as N-m, are solely determined by water mass mixing. Results showed that the nutrient inventory in the upper 100m of the NSCS was overall negatively correlated to the Kuroshio water fraction, suggesting that the Kuroshio intrusion significantly influenced the nutrient distribution in the SCS and its seasonal variation. The difference between the observed nutrient concentrations and their corresponding Nm allowed us to further quantify the nutrient removal/addition associated with the biogeochemical processes on top of the water mass mixing. We revealed that the nutrients in the upper 100m of the water column had a net consumption in both winter and spring but a net addition in fall.

Journal ArticleDOI
TL;DR: In this paper, a preservation model within the lower oil shale layer and a productivity model was established for oil shale deposition in the Songliao Basin, and it was shown that excellent preservation is the major controlling factor for OM enrichment in the lower and upper oil shale layers.

Journal ArticleDOI
TL;DR: In this paper, an upwelling of high CO2 water and subsequent removal of CO2 by phytoplankton imparts a dynamic range to ΩAr from ~1.0 to ~4.0 between spring and autumn.
Abstract: [1] Coastal upwelling zones may be at enhanced risk from ocean acidification as upwelling brings low aragonite saturation state (ΩAr) waters to the surface that are further suppressed by anthropogenic CO2. ΩAr was calculated with pH, pCO2, and salinity-derived alkalinity time series data from autonomous pH and pCO2 instruments moored on the Oregon shelf and shelf break during different seasons from 2007 to 2011. Surface ΩAr values ranged between 0.66 ± 0.04 and 3.9 ± 0.04 compared to an estimated pre-industrial range of 1.0 ± 0.1 to 4.7 ± 0.1. Upwelling of high-CO2 water and subsequent removal of CO2 by phytoplankton imparts a dynamic range to ΩAr from ~1.0 to ~4.0 between spring and autumn. Freshwater input also suppresses saturation states during the spring. Winter ΩAr is less variable than during other seasons and is controlled primarily by mixing of the water column.

Journal ArticleDOI
TL;DR: In this paper, the authors used the size controlled δ18O calcite trajectories to infer depth habitats and calculate species-specific calcification temperatures, which are then used to constrain species specific calcification depths along the modern vertical temperature profile in the western tropical Indian Ocean.

Journal ArticleDOI
09 Jan 2013-PLOS ONE
TL;DR: The results show that changes in reef-water carbonate chemistry depend primarily on the ratio of benthic metabolism to the square root of the onshore wave energy flux as well as on the length and depth of the reef flat; however, they are only weakly dependent on channel geometry and the total frictional resistance of the coral-reef lagoon system.
Abstract: We present a three-dimensional hydrodynamic-biogeochemical model of a wave-driven coral-reef lagoon system using the circulation model ROMS (Regional Ocean Modeling System) coupled with the wave transformation model SWAN (Simulating WAves Nearshore). Simulations were used to explore the sensitivity of water column carbonate chemistry across the reef system to variations in benthic reef metabolism, wave forcing, sea level, and system geomorphology. Our results show that changes in reef-water carbonate chemistry depend primarily on the ratio of benthic metabolism to the square root of the onshore wave energy flux as well as on the length and depth of the reef flat; however, they are only weakly dependent on channel geometry and the total frictional resistance of the reef system. Diurnal variations in pCO2, pH, and aragonite saturation state (Ωar) are primarily dependent on changes in net production and are relatively insensitive to changes in net calcification; however, net changes in pCO2, pH, and Ωar are more strongly influenced by net calcification when averaged over 24 hours. We also demonstrate that a relatively simple one-dimensional analytical model can provide a good description of the functional dependence of reef-water carbonate chemistry on benthic metabolism, wave forcing, sea level, reef flat morphology, and total system frictional resistance. Importantly, our results indicate that any long-term (weeks to months) net offsets in reef-water pCO2 relative to offshore values should be modest for reef systems with narrow and/or deep lagoons. Thus, the long-term evolution of water column pCO2 in many reef environments remains intimately connected to the regional-scale oceanography of offshore waters and hence directly influenced by rapid anthropogenically driven increases in pCO2.

Journal ArticleDOI
TL;DR: It is suggested that Nitrospina have a quantitatively important role in NO2− oxidation and N cycling in the ETNP, and provide new insight into their ecology and interactions with other N-cycling processes in this biogeochemically important region of the ocean.
Abstract: Nitrogen (N) is an essential nutrient in the sea and its distribution is controlled by microorganisms. Within the N cycle, nitrite (NO2−) has a central role because its intermediate redox state allows both oxidation and reduction, and so it may be used by several coupled and/or competing microbial processes. In the upper water column and oxygen minimum zone (OMZ) of the eastern tropical North Pacific Ocean (ETNP), we investigated aerobic NO2− oxidation, and its relationship to ammonia (NH3) oxidation, using rate measurements, quantification of NO2−-oxidizing bacteria via quantitative PCR (QPCR), and pyrosequencing. 15NO2− oxidation rates typically exhibited two subsurface maxima at six stations sampled: one located below the euphotic zone and beneath NH3 oxidation rate maxima, and another within the OMZ. 15NO2− oxidation rates were highest where dissolved oxygen concentrations were <5 μM, where NO2− accumulated, and when nitrate (NO3−) reductase genes were expressed; they are likely sustained by NO3− reduction at these depths. QPCR and pyrosequencing data were strongly correlated (r2=0.79), and indicated that Nitrospina bacteria numbered up to 9.25% of bacterial communities. Different Nitrospina groups were distributed across different depth ranges, suggesting significant ecological diversity within Nitrospina as a whole. Across the data set, 15NO2− oxidation rates were decoupled from 15NH4+ oxidation rates, but correlated with Nitrospina (r2=0.246, P<0.05) and NO2− concentrations (r2=0.276, P<0.05). Our findings suggest that Nitrospina have a quantitatively important role in NO2− oxidation and N cycling in the ETNP, and provide new insight into their ecology and interactions with other N-cycling processes in this biogeochemically important region of the ocean.

Journal ArticleDOI
TL;DR: Evidence is provided for the coexistence of anammox bacteria and sulfide-dependent denitrifiers in the stratified water column of a lacustrine environment and maximum potential rates of anamsox and chemolithotrophic denitrification were comparatively low but consistent with nutrient fluxes calculated from concentration gradients.
Abstract: In addition to organotrophic denitrification, alternative pathways, such as anaerobic ammonium oxidation (anammox) or sulfide-dependent denitrification may be important modes for the removal of fixed nitrogen (N) from lakes. We used Lake Lugano as a model system with which to assess possible controls on the concurrence of multiple suboxic N2 production pathways in a lacustrine water column. In the northern basin of Lake Lugano, concentration gradients of dissolved inorganic N toward the hypolimnetic redox transition zone (RTZ) indicate ammonium oxidation and nitrate reduction occurring in close vicinity. Ammonium reaches undetectable levels 15 m below the depth of oxygen disappearance, indicating its anaerobic consumption. The presence of anammox bacteria was confirmed by 16S ribosomal ribonucleic acid gene sequencing. Quantitative polymerase chain reaction revealed a maximum in anammox bacterial abundance at the same water depth where ammonium becomes exhausted. 15N-labeling experiments indicate that anammox activity within the Lake Lugano RTZ can contribute up to , 30% of total N2 production. Incubation experiments with various potential electron donors— glucose, acetate, Mn(II), Fe(II), and H2S—revealed that N2 formation was sulfide-dependent and that organotrophic denitrification is only of minor importance for the elimination of fixed N from the Lake Lugano north basin. Maximum potential rates of anammox and chemolithotrophic denitrification were comparatively low but consistent with nutrient fluxes calculated from concentration gradients. This study provides evidence for the coexistence of anammox bacteria and sulfide-dependent denitrifiers in the stratified water column of a lacustrine environment.

Journal ArticleDOI
TL;DR: Data show that Eckernforde Bay represents a complex ecosystem where numerous environmental variables combine to influence benthic microbial activities involving N and sulfur cycling, and the presence of nifH sequences related to two known N2-fixing SRB is demonstrated, supporting the hypothesis that some of the nitrogenase activity detected may be attributed to SRB.
Abstract: Despite the worldwide occurrence of marine hypoxic regions, benthic nitrogen (N) cycling within these areas is poorly understood and it is generally assumed that these areas represent zones of intense fixed N loss from the marine system. Sulfate reduction can be an important process for organic matter degradation in sediments beneath hypoxic waters and many sulfate-reducing bacteria (SRB) have the genetic potential to fix molecular N (N2). Therefore, SRB may supply fixed N to these systems, countering some of the N lost via microbial processes such as denitrification and anaerobic ammonium oxidation. The objective of this study was to evaluate if N2-fixation, possibly by SRB, plays a role in N cycling within the seasonally hypoxic sediments from Eckernforde Bay, Baltic Sea. Monthly samplings were performed over the course of one year to measure N2-fixation and sulfate reduction rates, to determine the seasonal variations in bioturbation (bioirrigation) activity and important benthic geochemical profiles, such as sulfur and N compounds, and to monitor changes in water column temperature and oxygen concentrations. Additionally, at several time points, rates of benthic denitrification were also measured and the active N-fixing community was examined via molecular tools. Integrated rates of N2-fixation and sulfate reduction showed a similar seasonality pattern, with highest rates occurring in August (approx. 22 and 880 nmol cm−3 d−1 of N and SO42−, respectively) and October (approx. 22 and 1300 nmol cm−3 d−1 of N and SO42−, respectively), and lowest rates occurring in February (approx. 8 and 32 nmol cm−3 d−1 of N and SO42−, respectively). These rate changes were positively correlated with bottom water temperatures and previous reported plankton bloom activities, and negatively correlated with bottom water oxygen concentrations. Other variables that also appeared to play a role in rate determination were bioturbation, bubble irrigation and winter storm events. Molecular analysis demonstrated the presence of nifH sequences related to two known N2-fixing SRB, namely Desulfovibrio vulgaris and Desulfonema limicola, supporting the hypothesis that some of the nitrogenase activity detected may be attributed to SRB. Denitrification appeared to follow a similar trend as the other microbial processes and the ratio of denitrification to N2-fixation ranged from 6.8 in August to 1.1 in February, indicating that in February, the two processes are close to being in balance in terms of N loss and N gain. Overall, our data show that Eckernforde Bay represents a complex ecosystem where numerous environmental variables combine to influence benthic microbial activities involving N and sulfur cycling.

Journal ArticleDOI
Sha-sha Zheng1, Peifang Wang1, Chao Wang1, Jun Hou1, Jin Qian1 
TL;DR: In this article, surface sediment from Zhushan Bay in Taihu Lake was subjected to resuspension under 6 different wind forces using a pneumatic annular flume.

Journal ArticleDOI
TL;DR: It could be deduced that the dynamics of phytoplankton in the Daning River were mainly influenced by hydrologic regime.

Journal ArticleDOI
TL;DR: In this paper, the authors examine the local stratification control of productivity on interannual timescales over the global subtropical and tropical ocean by directly comparing in situ measures of stratification (from hydrographic profile data) with contemporaneous values of ocean chlorophyll (from satellite data).
Abstract: [1] Strengthened stratification of the upper ocean, associated with anthropogenic or climate-driven warming, is generally expected to inhibit marine primary productivity in light-replete, nutrient-limited environments, essentially, in the low and middle latitude ocean, based on the supposition that increased water column stability will inhibit vertical mixing and consequently the upward entrainment of deep nutrients into the euphotic zone. Herein, we examine the local stratification control of productivity on interannual timescales over the global subtropical and tropical ocean by directly comparing in situ measures of stratification (from hydrographic profile data) with contemporaneous values of ocean chlorophyll (from satellite data). In the subtropical ocean, we find no evidence of a strong local correlative relationship between these properties over the observational record, a result that challenges the widely held view that stratification variability is a primary driver of interannual variability in nutrient supply and productivity in these waters. A strong negative relationship is observed, however, in the tropical Pacific, suggesting that previously reported correlations between globally averaged stratification and productivity variability are driven by strong associations in this region. An examination of the long-term changes in our profile data also reveals trends of decreasing stratification scattered across the low-latitude and mid-latitude ocean, driven by faster rates of warming in the subsurface relative to the surface. This observation seemingly undercuts a fundamental assumption of the paradigm of local stratification control, namely that increases in upper ocean heat content necessarily produce strengthened stratification.

Journal ArticleDOI
01 Oct 2013-Ecology
TL;DR: A more holistic perspective regarding the role of animals in nutrient cycling is urged, with a focus on quantifying the rates at which animals consume, store, release, and transport nutrients under various conditions.
Abstract: Animals can be important in nutrient cycling through a variety of direct and indirect pathways. A high biomass of animals often represents a large pool of nutrients, leading some ecologists to argue that animal assemblages can represent nutrient sinks within ecosystems. The role of animals as sources vs. sinks of nutrients has been debated particularly extensively for freshwater fishes. We argue that a large pool size does not equate to a nutrient sink; rather, animals can be nutrient sinks when their biomass increases, when emigration rates are high, and/or when nutrients in animal carcasses are not remineralized. To further explore these ideas, we use a simple model to evaluate the conditions under which fish are phosphorus (P) sources or sinks at the ecosystem (lake) level, and at the habitat level (benthic and water column habitats). Our simulations suggest that, under most conditions, fish are sinks for benthic P but are net P sources to the water column. However, P source and sink strengths depend on fish feeding habits (proportion of P consumed from the benthos and water column), migration patterns, and especially the fate of carcass P. Of particular importance is the rate at which carcasses are mineralized and the relative importance of benthic vs. pelagic primary producers in taking up mineralized P (and excreted P). Higher proportional uptake of P by benthic primary producers increases the likelihood that fish are sinks for water column P. Carcass bones and scales are relatively recalcitrant and can represent a P sink even if fish biomass does not change over time. Thus, there is a need for better documentation of the fraction of carcass P that is remineralized, and the fate of this P, under natural conditions. We urge a more holistic perspective regarding the role of animals in nutrient cycling, with a focus on quantifying the rates at which animals consume, store, release, and transport nutrients under various conditions.

Journal ArticleDOI
TL;DR: In this article, a combination of radio-tracer-based incubation assays, stable C-CH4 isotope measurements, and molecular tools (16S rRNA gene Denaturing Gradient Gel Electrophoresis (DGGE) fingerprinting, pmoA- and mxaF gene analyses) were used to investigate the bacterially mediated aerobic methane oxidation (MOx) in the Arctic fjord Storfjorden (Svalbard).
Abstract: . The bacterially mediated aerobic methane oxidation (MOx) is a key mechanism in controlling methane (CH4) emissions from the world's oceans to the atmosphere. In this study, we investigated MOx in the Arctic fjord Storfjorden (Svalbard) by applying a combination of radio-tracer-based incubation assays (3H-CH4 and 14C-CH4), stable C-CH4 isotope measurements, and molecular tools (16S rRNA gene Denaturing Gradient Gel Electrophoresis (DGGE) fingerprinting, pmoA- and mxaF gene analyses). Storfjorden is stratified in the summertime with melt water (MW) in the upper 60 m of the water column, Arctic water (ArW) between 60 and 100 m, and brine-enriched shelf water (BSW) down to 140 m. CH4 concentrations were supersaturated with respect to the atmospheric equilibrium (about 3–4 nM) throughout the water column, increasing from ∼20 nM at the surface to a maximum of 72 nM at 60 m and decreasing below. MOx rate measurements at near in situ CH4 concentrations (here measured with 3H-CH4 raising the ambient CH4 pool by

Journal ArticleDOI
TL;DR: In this paper, a field study conducted in the western part of the central basin of Lake Erie in 2008 and 2009 was conducted to investigate the dynamics of the oxygen depletion and create a vertical oxygen budget.
Abstract: depletion (e.g., � 0.7 to þ0.3 mg L � 1 d � 1 ) were examined in a field study conducted in the western part of the central basin of Lake Erie in 2008 and 2009. Data were obtained from a spatial array of moorings as well as sampling cruises that examined the physical and biological conditions needed to investigate the dynamics of the oxygen depletion and create a vertical oxygen budget. The flux of oxygen through the thermocline to the hypolimnion was a significant source of oxygen equivalent to � 18% of the total oxygen depletion in the hypolimnion over the stratified period. The total oxygen depletion in the hypolimnion was due to equivalent amounts of hypolimnetic oxygen demand due to respiration in the water column and flux of oxygen to the bottom due to sediment oxygen demand. This latter finding was strongly dependent on hypolimnion thickness in Lake Erie, which also appeared to be an important parameter driving the rate of oxygen depletion by controlling the vertical volumetric fluxes and hence the competition between vertical flux and community respiration in the hypolimnion of shallow lakes.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the geochemical behavior of nutrients associated with early diagenesis of organic matter (OM), and to study the accumulation and transformation processes of nutrients at the sediment-water interface (SWI), as well as to discuss the impact of riverine inputs on nutrients in the Pearl River estuary and adjacent offshore areas.
Abstract: Spatio-temporal distribution of pore water nutrients and the fluxes at the sediment-water interface (SWI) were investigated to probe into the geochemical behavior of nutrients associated with early diagenesis of organic matter (OM), and to study the accumulation and transformation processes of nutrients at the SWI, as well as to discuss the impact of riverine inputs on nutrients in the Pearl River estuary (PRE) and adjacent offshore areas. Nutrient concentrations decreased from the upper to the lower reaches of the estuary, suggesting that there was a high input of anthropogenic nutrients and the estuary was acting as a nutrient sink. Dissolved inorganic nitrogen (DIN: the sum of NH4-N, NO3-N and NO2-N) concentrations in the water column and the pore water were higher in the estuary than at offshore areas due to the riverine discharge and the high accumulation rate in the estuary. NO3-N concentration was the highest of the three forms of DIN in the overlying water and showed a sharp decrease from the surficial sediment with increasing sediment depth, indicating that there was strong denitrification at the SWI. NH4-N, mainly deriving from the anaerobic degradation of OM, was the main form of DIN in the pore water and increased with depth. Negative NO3-N fluxes (into the sediment) and positive NH4-N fluxes (from the sediment) were commonly observed from incubation experiments, indicating the denitrification occurred at the SWI. DIN flux suggested that the sediment was a sink of DIN in spring, however, the sediment was the source of DIN in summer and winter. Nutrients dominantly diffused out of the sediment, suggesting that the sediment was the source of nutrients in spring at adjacent offshore areas. The fluxes directed that PO4-P mainly diffused into the sediment while SiO4-Si mainly diffused out of the sediment. (C) 2013 Elsevier Ltd. All rights reserved.

Journal ArticleDOI
TL;DR: In this article, the results of a lake model intercomparison study conducted within the framework of Lake Model Intercomparisons Project are presented, and the conclusion is drawn that underestimation of real fluxes by the eddy covariance technique is the most probable reason.
Abstract: . Results of a lake model intercomparison study conducted within the framework of Lake Model Intercomparison Project are presented. The investigated lake was Groser Kossenblatter See (Germany) as a representative of shallow, (2 m mean depth) turbid midlatitude lakes. Meteorological measurements, including turbulent fluxes and water temperature, were carried out by the Lindenberg Meteorological Observatory of the German Meteorological Service (Deutscher Wetterdienst, DWD). Eight lake models of different complexity were run, forced by identical meteorological variables and model parameters unified as far as possible given different formulations of processes. All models generally captured diurnal and seasonal variability of lake surface temperature reasonably well. However, some models were incapable of realistically reproducing temperature stratification in summer. Total heat turbulent fluxes, computed by the surface flux schemes of the compared lake models, deviated on average from those measured by eddy covariance by 17–28 W m−2. There are a number of possible reasons for these deviations, and the conclusion is drawn that underestimation of real fluxes by the eddy covariance technique is the most probable reason. It is supported by the fact that the eddy covariance fluxes do not allow to close the heat balance of the water column, the residual for the whole period considered being ≈–28 W m−2. The effect of heat flux to bottom sediments can become significant for bottom temperatures. It also has profound influence on the surface temperatures in autumn due to convective mixing but not in summer when the lake stratification is stable. Thus, neglecting sediments shifts the summer–autumn temperature difference in models lacking explicit treatment of sediments considerably. As a practical recommendation based on results of the present study, we also infer that in order to realistically represent lakes in numerical weather prediction and climate models, it is advisable to use depth-resolving turbulence models (or equivalent) in favor of models with a completely mixed temperature profile.

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TL;DR: The spatial and temporal distribution of radionuclidean activity in seawater samples collected off the coast of Miyagi, Fukushima, and Ibaraki Prefectures were measured as part of a monitoring program initiated by the Japanese Ministry of Education, Sports, Science and Technology immediately after the Fukushima Dai-ichi Nuclear Power Plant accident.
Abstract: The activities of artificial radionuclides in seawater samples collected off the coast of Miyagi, Fukushima, and Ibaraki Prefectures were measured as part of a monitoring program initiated by the Japanese Ministry of Education, Sports, Science and Technology immediately after the Fukushima Dai-ichi Nuclear Power Plant accident. The spatial and temporal distributions of those activities are summarized herein. The activities of strontium-90, iodine-131, cesium-134 and -137 (i.e. 90 Sr, 131 I, 134 Cs, and 137 Cs) derived from the accident were detected in seawater samples taken from areas of the coastal ocean adjacent to the power plant. No 131 I was detected in surface waters (≤ 5 m depth) or in intermediate and bottom waters after 30 April 2011. Strontium-90 was found in surface waters collected from a few sampling stations in mid-August 2011 to mid-December 2011. Temporal changes of 90 Sr activity in surface waters were evident, although the 90 Sr activity at a given time varied widely between sampling stations. The activity of 90 Sr in surface waters decreased slowly over time, and by the end of December 2011 had reached background levels recorded before the accident. Radiocesium, 134 Cs and 137 Cs, was found in seawater samples immediately after the accident. There was a remarkable change in radiocesium activities in surface waters during the first 7 months (March through September 2011) after the accident; the activity reached a maximum in the middle of April and thereafter decreased exponentially with time. Qualitatively, the distribution patterns in surface waters suggested that in early May radiocesium-polluted water was advected northward; some of the water then detached and was transported to the south. Two water cores with high 137 Cs activity persisted at least until July 2011. In subsurface waters radiocesium activity was first detected in the beginning of April 2011, and the water masses were characterized by σ t (an indicator of density) values of 25.5–26.5. From 9–14 May to 5–16 December 2011, the depths of the water masses increased with time, an indication that deepening of the isopycnal surfaces with time can be an important mechanism for the transport of radiocesium downward in coastal waters. During 4–21 February 2012, the water column became vertically homogeneous, probably because of convective mixing during the winter; the result was nearly constant values of radiocesium activity throughout the water column from the surface to the bottom (~200 m depth) at each station.

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TL;DR: In this paper, the early diagenesis of the major carrier phases (Fe and Mn minerals), trace elements (As, Co, Cr, Hg, MeHg, Ni) and nutrients (RNO 3, NH þ 4, RPO 4) and their exchange at the sediment water/interface were studied in the Berre Lagoon, a Mediterranean lagoon in France, at one site under two contrasting oxygen-ation conditions (strictly anoxic and slightly oxic) and at an adjacent site with perennially welloxygen-ated water.

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TL;DR: Contrary evidence from a synergy of modern observations and palaeo-records suggest that diatom production and associated export of organic carbon may actually increase with greater ocean stratification, and potentially act as a negative feedback to global warming.