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Showing papers on "Water column published in 2014"


Journal ArticleDOI
07 Aug 2014-Nature
TL;DR: In this paper, the authors present an estimate of the total amount and spatial distribution of anthropogenic mercury in the global ocean based on oceanographic measurements of mercury and related parameters from several expeditions including data from recent GEOTRACES cruises.
Abstract: GEOTRACES sampling of deep water from the Atlantic, Pacific and Southern oceans allows an estimate of the amount (tripled in surface waters) and distribution (two-thirds increase in water less than a thousand metres deep) of anthropogenic mercury accumulating in the global ocean. Large amounts of the toxic trace metal mercury have been released into the environment as a result of human activities such as mining and burning of fossil fuels. Estimates of the amount of mercury that have reached the ocean as a result of such anthropogenic activities remain uncertain and are largely based on model studies. This paper presents an estimate of the total amount and spatial distribution of anthropogenic mercury in the global ocean based on oceanographic measurements of mercury and related parameters from several expeditions including data from recent GEOTRACES cruises. The findings suggest that there has been a tripling of the surface water mercury content and a ∼150% increase in the amount of mercury in the underlying thermocline water layer. Mercury is a toxic, bioaccumulating trace metal whose emissions to the environment have increased significantly as a result of anthropogenic activities such as mining and fossil fuel combustion1,2. Several recent models have estimated that these emissions have increased the oceanic mercury inventory by 36–1,313 million moles since the 1500s2,3,4,5,6,7,8,9. Such predictions have remained largely untested owing to a lack of appropriate historical data and natural archives. Here we report oceanographic measurements of total dissolved mercury and related parameters from several recent expeditions to the Atlantic, Pacific, Southern and Arctic oceans. We find that deep North Atlantic waters and most intermediate waters are anomalously enriched in mercury relative to the deep waters of the South Atlantic, Southern and Pacific oceans, probably as a result of the incorporation of anthropogenic mercury. We estimate the total amount of anthropogenic mercury present in the global ocean to be 290 ± 80 million moles, with almost two-thirds residing in water shallower than a thousand metres. Our findings suggest that anthropogenic perturbations to the global mercury cycle have led to an approximately 150 per cent increase in the amount of mercury in thermocline waters and have tripled the mercury content of surface waters compared to pre-anthropogenic conditions. This information may aid our understanding of the processes and the depths at which inorganic mercury species are converted into toxic methyl mercury and subsequently bioaccumulated in marine food webs.

383 citations


Journal ArticleDOI
22 Aug 2014-Science
TL;DR: In this paper, the dominant fate of dissolved organic carbon (DOC) released from permafrost soils to inland waters is either complete oxidation to CO2 or partial oxidation and river export to oceans.
Abstract: Carbon in thawing permafrost soils may have global impacts on climate change; however, the factors that control its processing and fate are poorly understood. The dominant fate of dissolved organic carbon (DOC) released from soils to inland waters is either complete oxidation to CO2 or partial oxidation and river export to oceans. Although both processes are most often attributed to bacterial respiration, we found that photochemical oxidation exceeds rates of respiration and accounts for 70 to 95% of total DOC processed in the water column of arctic lakes and rivers. At the basin scale, photochemical processing of DOC is about one-third of the total CO2 released from surface waters and is thus an important component of the arctic carbon budget.

369 citations


17 Dec 2014
TL;DR: It is shown that light is the biggest culprit in the breakdown of carbon from thawing permafrost soils, and photochemical oxidation exceeds rates of respiration and accounts for 70 to 95% of total DOC processed in the water column of arctic lakes and rivers.
Abstract: Illuminating the pathway to destruction Arctic lakes are an important source of atmospheric CO2 and therefore play a role in climate change. It is thus vital to know how the rapid Arctic warming will affect them. Cory et al. now show that light is the biggest culprit in the breakdown of carbon from thawing permafrost soils (see the Perspective by Tranvik). This carbon then moves out into Arctic lakes and streams. Contrary to previous expectations, these photochemical processes cause much more destruction of the organic molecules in fresh water than bacterial respiration does. Science, this issue p. 925; see also p. 870 Photochemical reactions cause most of the breakdown of carbon released from permafrost into arctic inland waters. [Also see Perspective by Tranvik] Carbon in thawing permafrost soils may have global impacts on climate change; however, the factors that control its processing and fate are poorly understood. The dominant fate of dissolved organic carbon (DOC) released from soils to inland waters is either complete oxidation to CO2 or partial oxidation and river export to oceans. Although both processes are most often attributed to bacterial respiration, we found that photochemical oxidation exceeds rates of respiration and accounts for 70 to 95% of total DOC processed in the water column of arctic lakes and rivers. At the basin scale, photochemical processing of DOC is about one-third of the total CO2 released from surface waters and is thus an important component of the arctic carbon budget.

354 citations


Journal ArticleDOI
TL;DR: Fluorescence spectroscopy was used to explore DOM quality from 560 lakes distributed across Sweden and encompassed a wide climatic gradient typical of the boreal ecozone, suggesting that DOM reactivity depends more heavily on the duration of time taken to pass through the landscape, rather than temperature.
Abstract: Inland waters transport large amounts of dissolved organic matter (DOM) from terrestrial environments to the oceans, but DOM also reacts en route, with substantial water column losses by mineralization and sedimentation. For DOM transformations along the aquatic continuum, lakes play an important role as they retain waters in the landscape allowing for more time to alter DOM. We know DOM losses are significant at the global scale, yet little is known about how the reactivity of DOM varies across landscapes and climates. DOM reactivity is inherently linked to its chemical composition. We used fluorescence spectroscopy to explore DOM quality from 560 lakes distributed across Sweden and encompassed a wide climatic gradient typical of the boreal ecozone. Six fluorescence components were identified using parallel factor analysis (PARAFAC). The intensity and relative abundance of these components were analyzed in relation to lake chemistry, catchment, and climate characteristics. Land cover, particularly the percentage of water in the catchment, was a primary factor explaining variability in PARAFAC components. Likewise, lake water retention time influenced DOM quality. These results suggest that processes occurring in upstream water bodies, in addition to the lake itself, have a dominant influence on DOM quality. PARAFAC components with longer emission wavelengths, or red-shifted components, were most reactive. In contrast, protein-like components were most persistent within lakes. Generalized characteristics of PARAFAC components based on emission wavelength could ease future interpretation of fluorescence spectra. An important secondary influence on DOM quality was mean annual temperature, which ranged between � 6.2 and +7.5 °C. These results suggest that DOM reactivity depends more heavily on the duration of time taken to pass through the landscape, rather than temperature. Projected increases in runoff in the boreal region may force lake DOM toward a higher overall amount and proportion of humic-like substances.

288 citations


Journal ArticleDOI
TL;DR: Recent technical developments have led to insights into the high biogeochemical and biological activity of these permeable sediments and their role in the global cycles of matter.
Abstract: The sandy sediments that blanket the inner shelf are situated in a zone where nutrient input from land and strong mixing produce maximum primary production and tight coupling between water column and sedimentary processes. The high permeability of the shelf sands renders them susceptible to pressure gradients generated by hydrodynamic and biological forces that modulate spatial and temporal patterns of water circulation through these sediments. The resulting dynamic three-dimensional patterns of particle and solute distribution generate a broad spectrum of biogeochemical reaction zones that facilitate effective decomposition of the pelagic and benthic primary production products. The intricate coupling between the water column and sediment makes it challenging to quantify the production and decomposition processes and the resultant fluxes in permeable shelf sands. Recent technical developments have led to insights into the high biogeochemical and biological activity of these permeable sediments and their role in the global cycles of matter.

263 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the effects of human activities on the development of hypoxia (lower oxygen concentration) in many areas of the world's coastal ocean, especially increased nutrient loads that set in motion a cascading chain of events related to eutrophication.
Abstract: Human activities, especially increased nutrient loads that set in motion a cascading chain of events related to eutrophication, accelerate development of hypoxia (lower oxygen concentration) in many areas of the world's coastal ocean. Climate changes and extreme weather events may modify hypoxia. Organismal and fisheries effects are at the heart of the coastal hypoxia issue, but more subtle regime shifts and trophic interactions are also cause for concern. The chemical milieu associated with declining dissolved oxygen concentrations affects the biogeochemical cycling of oxygen, carbon, nitrogen, phosphorus, silica, trace metals, and sulfide as observed in water column processes, shifts in sediment biogeochemistry, and increases in carbon, nitrogen, and sulfur, as well as shifts in their stable isotopes, in recently accumulated sediments.

240 citations


Journal ArticleDOI
TL;DR: The incidence of severe pteropod shell dissolution owing to anthropogenic OA has doubled in near shore habitats since pre-industrial conditions across this region and is on track to triple by 2050 and the observed impacts represent a baseline for future observations towards understanding broader scale OA effects.
Abstract: Few studies to date have demonstrated widespread biological impacts of ocean acidification (OA) under conditions currently found in the natural environment. From a combined survey of physical and chemical water properties and biological sampling along the Washington–Oregon–California coast in August 2011, we show that large portions of the shelf waters are corrosive to pteropods in the natural environment. We show a strong positive correlation between the proportion of pteropod individuals with severe shell dissolution damage and the percentage of undersaturated water in the top 100 m with respect to aragonite. We found 53% of onshore individuals and 24% of offshore individuals on average to have severe dissolution damage. Relative to pre-industrial CO2 concentrations, the extent of undersaturated waters in the top 100 m of the water column has increased over sixfold along the California Current Ecosystem (CCE). We estimate that the incidence of severe pteropod shell dissolution owing to anthropogenic OA has doubled in near shore habitats since pre-industrial conditions across this region and is on track to triple by 2050. These results demonstrate that habitat suitability for pteropods in the coastal CCE is declining. The observed impacts represent a baseline for future observations towards understanding broader scale OA effects.

218 citations


Journal ArticleDOI
TL;DR: It is shown that oxic water methanogenesis is a significant component of the overall CH4 budget in a small, shallow lake, and evidence is provided that this pathway may be the main CH4 source in large, deep lakes and open oceans.
Abstract: Aquatic methane originates in anoxic sediments and bottom waters, but some studies suggest it may also come from the oxic water column. Here, the authors experimentally confirm this hypothesis, and explore the rates, controls and biochemical pathways of oxic water methanogenesis.

211 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the seasonal turnover and marine and terrestrial sources of DOM in an intertidal creek bank of the southern North Sea down to 3m depth and link the biogeochemical processes to FT-ICR-MS data and the analyses of inorganic porewater chemistry, δ 13 C of solid-phase extracted dissolved organic carbon (SPE-DOC), dissolved black carbon (DBC), and dissolved carbohydrates (DCHO).

199 citations


Journal ArticleDOI
TL;DR: The sea ice ecosystem provides food for a host of animals, with crustaceans being the most conspicuous, and ice algae likely contribute a shrinking fraction of the total amount of organic matter produced in polar waters.
Abstract: Polar sea ice is one of the largest ecosystems on Earth. The liquid brine fraction of the ice matrix is home to a diverse array of organisms, ranging from tiny archaea to larger fish and invertebrates. These organisms can tolerate high brine salinity and low temperature but do best when conditions are milder. Thriving ice algal communities, generally dominated by diatoms, live at the ice/water interface and in recently flooded surface and interior layers, especially during spring, when temperatures begin to rise. Although protists dominate the sea ice biomass, heterotrophic bacteria are also abundant. The sea ice ecosystem provides food for a host of animals, with crustaceans being the most conspicuous. Uneaten organic matter from the ice sinks through the water column and feeds benthic ecosystems. As sea ice extent declines, ice algae likely contribute a shrinking fraction of the total amount of organic matter produced in polar waters.

190 citations


Journal ArticleDOI
TL;DR: In this article, the applicability of Fe-based redox proxies in carbonates through three approaches is explored: modern marine sediments, with an average Fe/Al ratio of 0.55 ± 0.11, with some higher values potentially being attributable to steady-state early diagenetic remobilization of Fe towards the sediment-water interface.

Journal ArticleDOI
TL;DR: The results provide quantitative knowledge of nutrient release and recycling processes under various environmental conditions in support of decision support tools underlying the Baltic Sea Action Plan.
Abstract: Hypoxia has occurred intermittently over the Holocene in the Baltic Sea, but the recent expansion from less than 10 000 km 2 before 1950 to (60 000 km 2 since 2000 is mainly caused by enhanced nutrient inputs from land and atmosphere. With worsening hypoxia, the role of sediments changes from nitrogen removal to nitrogen release as ammonium. At present, denitrification in the water column and sediments is equally important. Phos- phorus is currently buried in sediments mainly in organic form, with an additional contribution of reduced Fe-phos- phate minerals in the deep anoxic basins. Upon the tran- sition to oxic conditions, a significant proportion of the organic phosphorus will be remineralized, with the phos- phorus then being bound to iron oxides. This iron-oxide bound phosphorus is readily released to the water column upon the onset of hypoxia again. Important ecosystems services carried out by the benthic fauna, including bio- geochemical feedback-loops and biomass production, are also lost with hypoxia. The results provide quantitative knowledge of nutrient release and recycling processes under various environmental conditions in support of decision support tools underlying the Baltic Sea Action Plan.

19 Aug 2014
TL;DR: Results indicate that effective eDNA sampling methods should be informed by fish distribution, as eDNA concentration was shown to vary dramatically between samples taken less than 100 m apart.
Abstract: Although environmental DNA (eDNA) has been used to infer the presence of rare aquatic species, many facets of this technique remain unresolved. In particular, the relationship between eDNA and fish distribution is not known. We examined the relationship between the distribution of fish and their eDNA (detection rate and concentration) in a lake. A quantitative PCR (qPCR) assay for a region within the cytochrome b gene of the common carp (Cyprinus carpio or ‘carp’), an ubiquitous invasive fish, was developed and used to measure eDNA in Lake Staring (MN, USA), in which both the density of carp and their distribution have been closely monitored for several years. Surface water, sub-surface water, and sediment were sampled from 22 locations in the lake, including areas frequently used by carp. In water, areas of high carp use had a higher rate of detection and concentration of eDNA, but there was no effect of fish use on sediment eDNA. The detection rate and concentration of eDNA in surface and sub-surface water were not significantly different (p$0.5), indicating that eDNA did not accumulate in surface water. The detection rate followed the trend: high-use water . low-use water . sediment. The concentration of eDNA in sediment samples that were above the limit of detection were several orders of magnitude greater than water on a per mass basis, but a poor limit of detection led to low detection rates. The patchy distribution of eDNA in the water of our study lake suggests that the mechanisms that remove eDNA from the water column, such as decay and sedimentation, are rapid. Taken together, these results indicate that effective eDNA sampling methods should be informed by fish distribution, as eDNA concentration was shown to vary dramatically between samples taken less than 100 m apart.

Journal ArticleDOI
TL;DR: In this paper, the authors focused on U isotopes in recent sediments from the two largest modern anoxic ocean basins, the Black Sea and the Cariaco Basin, with the aim of advancing the understanding of the U isotope systematics in reducing marine environments.

Journal ArticleDOI
10 Nov 2014-PLOS ONE
TL;DR: The relationship between the distribution of fish and their eDNA (detection rate and concentration) in a lake was examined in this article, showing that areas of high carp use had a higher rate of detection and concentration of eDNA, but there was no effect of fish use on sediment eDNA.
Abstract: Although environmental DNA (eDNA) has been used to infer the presence of rare aquatic species, many facets of this technique remain unresolved. In particular, the relationship between eDNA and fish distribution is not known. We examined the relationship between the distribution of fish and their eDNA (detection rate and concentration) in a lake. A quantitative PCR (qPCR) assay for a region within the cytochrome b gene of the common carp (Cyprinus carpio or ‘carp’), an ubiquitous invasive fish, was developed and used to measure eDNA in Lake Staring (MN, USA), in which both the density of carp and their distribution have been closely monitored for several years. Surface water, sub-surface water, and sediment were sampled from 22 locations in the lake, including areas frequently used by carp. In water, areas of high carp use had a higher rate of detection and concentration of eDNA, but there was no effect of fish use on sediment eDNA. The detection rate and concentration of eDNA in surface and sub-surface water were not significantly different (p≥0.5), indicating that eDNA did not accumulate in surface water. The detection rate followed the trend: high-use water > low-use water > sediment. The concentration of eDNA in sediment samples that were above the limit of detection were several orders of magnitude greater than water on a per mass basis, but a poor limit of detection led to low detection rates. The patchy distribution of eDNA in the water of our study lake suggests that the mechanisms that remove eDNA from the water column, such as decay and sedimentation, are rapid. Taken together, these results indicate that effective eDNA sampling methods should be informed by fish distribution, as eDNA concentration was shown to vary dramatically between samples taken less than 100 m apart.

Journal ArticleDOI
TL;DR: Zn concentration and isotope data for seawater samples from the Atlantic sector of the Southern Ocean, collected during the IPY/GEOTRACES ANT-XXIV/III cruise along the Greenwich Zero Meridian Data are reported for the full depth range of the water column at three stations, as well as a transect of surface samples, using a new analytical approach as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, a detailed study of anoxic and ferruginous Lac Pavin (France) sedimentary cores was conducted, and it was shown that most of the Fe isotope variability observed in sedimentary pyrites can be tied to water column cycling and the oxidation of dissolved ferrous iron.

Journal ArticleDOI
TL;DR: It is suggested that water column oxygen depletion has a substantial impact on Cd biogeochemical cycling, impacting the global relationship between Cd and major nutrients and suggesting that Cd may be a previously unidentified tracer for water columnoxy deficiency on geological timescales.
Abstract: Cadmium (Cd) is a micronutrient and a tracer of biological productivity and circulation in the ocean. The correlation between dissolved Cd and the major algal nutrients in seawater has led to the use of Cd preserved in microfossils to constrain past ocean nutrient distributions. However, linking Cd to marine biological processes requires constraints on marine sources and sinks of Cd. Here, we show a decoupling between Cd and major nutrients within oxygen-deficient zones (ODZs) in both the Northeast Pacific and North Atlantic Oceans, which we attribute to Cd sulfide (CdS) precipitation in euxinic microenvironments around sinking biological particles. We find that dissolved Cd correlates well with dissolved phosphate in oxygenated waters, but is depleted compared with phosphate in ODZs. Additionally, suspended particles from the North Atlantic show high Cd content and light Cd stable isotope ratios within the ODZ, indicative of CdS precipitation. Globally, we calculate that CdS precipitation in ODZs is an important, and to our knowledge a previously undocumented marine sink of Cd. Our results suggest that water column oxygen depletion has a substantial impact on Cd biogeochemical cycling, impacting the global relationship between Cd and major nutrients and suggesting that Cd may be a previously unidentified tracer for water column oxygen deficiency on geological timescales. Similar depletions of copper and zinc in the Northeast Pacific indicate that sulfide precipitation in ODZs may also have an influence on the global distribution of other trace metals.

Journal ArticleDOI
23 Dec 2014-PLOS ONE
TL;DR: This research supports the existence of a causal link between positive thermal anomalies and observed invertebrate mass mortalities in the Mediterranean Sea, invoking focused mitigation initiatives in sensitive areas.
Abstract: Satellite data show a steady increase, in the last decades, of the surface temperature (upper few millimetres of the water surface) of the Mediterranean Sea. Reports of mass mortalities of benthic marine invertebrates increased in the same period. Some local studies interpreted the two phenomena in a cause-effect fashion. However, a basin-wide picture of temperature changes combined with a systematic assessment on invertebrate mass mortalities was still lacking. Both the thermal structure of the water column in the Mediterranean Sea over the period 1945–2011 and all documented invertebrate mass mortality events in the basin are analysed to ascertain if: 1- documented mass mortalities occurred under conditions of positive temperature trends at basin scale, and 2- atypical thermal conditions were registered at the smaller spatial and temporal scale of mass mortality events. The thermal structure of the shallow water column over the last 67 years was reconstructed using data from three public sources: MEDAR-MEDATLAS, World Ocean Database, MFS-VOS programme. A review of the mass mortality events of benthic invertebrates at Mediterranean scale was also carried out. The analysis of in situ temperature profiles shows that the Mediterranean Sea changed in a non-homogeneous fashion. The frequency of mass mortalities is increasing. The areas subjected to these events correspond to positive thermal anomalies. Statistically significant temperature trends in the upper layers of the Mediterranean Sea show an increase of up to 0.07°C/yr for a large fraction of the basin. Mass mortalities are consistent with both the temperature increase at basin scale and the thermal changes at local scale, up to 5.2°C. Our research supports the existence of a causal link between positive thermal anomalies and observed invertebrate mass mortalities in the Mediterranean Sea, invoking focused mitigation initiatives in sensitive areas.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the effects of regional warming and water quality on phytoplankton community succession, focussing on the bloom-forming cyanobacterial genus Microcystis in subtropical Lake Taihu, China.
Abstract: SUMMARY 1. We examined the effects of regional warming and water quality on phytoplankton community succession, focussing on the bloom-forming cyanobacterial genus Microcystis in subtropical Lake Taihu, China. Daily air temperatures from 1991 to 2010 indicated that onset of the Microcystis growing season has advanced by approximately 20 days over the last two decades, and accumulated air temperature (from 1 March to 31 May) has increased significantly. 2. Since 2005, Microcystis blooms have begun in May more frequently than in June. An increase in degree days for growth indicated that the early warming trend in spring would have benefitted Microcystis populations that overwintered on the sediment surface, by allowing them to grow, gain buoyancy and float into water column earlier in the year. 3. Results of canonical correspondence analysis showed that both water quality (i.e. nutrient loading) and water temperature have affected phytoplankton community succession in spring over the past two decades. When nutrient concentrations are adequate to support Microcystis blooms, rising temperature promotes their earlier onset and proliferation, a phenomenon previously documented for temperate regions, and now demonstrated for this subtropical lake.

Journal ArticleDOI
TL;DR: In this paper, the depth variations of Fe and P speciation in Lake Pavin (Massif Central, France), a deep (bottom depth 92 m) and permanently stratified lake with anoxic and ferruginous conditions in the water column below 60 m depth.

Journal ArticleDOI
TL;DR: A global dataset consisting of 100,605 total measurements of particulate organic carbon, nitrogen, or phosphorus analyzed as part of 70 cruises or time-series is presented to assist in a wide range of future studies of ocean elemental ratios.
Abstract: Knowledge of concentrations and elemental ratios of suspended particles are important for understanding many biogeochemical processes in the ocean. These include patterns of phytoplankton nutrient limitation as well as linkages between the cycles of carbon and nitrogen or phosphorus. To further enable studies of ocean biogeochemistry, we here present a global dataset consisting of 100,605 total measurements of particulate organic carbon, nitrogen, or phosphorus analyzed as part of 70 cruises or time-series. The data are globally distributed and represent all major ocean regions as well as different depths in the water column. The global median C:P, N:P, and C:N ratios are 163, 22, and 6.6, respectively, but the data also includes extensive variation between samples from different regions. Thus, this compilation will hopefully assist in a wide range of future studies of ocean elemental ratios.

Journal ArticleDOI
TL;DR: In this paper, the effect of temperature on rates of sediment methanogenesis and water column Mox in two shallow Arctic Alaskan lakes were evaluated in 2010, and the results suggest that Mox will likely offset increased MG in response to elevated temperature regimes as a function of ongoing climate change.
Abstract: Large uncertainties exist regarding the influence of ongoing climate change to microbially mediated methane cycling in arctic lakes. Specifically, the coupled response of methanogenesis (MG) and methane oxidation (Mox) to increased temperature is poorly understood. Therefore, the effect of temperature on rates of sediment MG and water column Mox in two shallow Arctic Alaskan lakes were evaluated in 2010. To understand the capacity of Mox to offset potential increases in dissolved methane concentrations, kinetics of water column Mox were also determined. Rates of MG responded positively to increased temperature with a greater influence exerted at higher incubation temperatures. Substrate-saturated Mox significantly increased with temperature and was controlled by substrate and temperature interactions. In contrast, substrate-limited Mox was not influenced by temperature and was controlled by substrate supply. Analysis of Mox kinetics pointed to a community of water column dwelling methane oxidizing bacteria that are capable of oxidizing dissolved methane concentrations far in excess of observed levels. Assuming no diffusion limitation, our results suggest that Mox will likely offset increased MG in response to elevated temperature regimes as a function of ongoing climate change.

Journal ArticleDOI
TL;DR: In this paper, a wealth of studies using water column multibeam data to address questions in fisheries, marine mammal and zooplankton research as well as seeps and hydrothermal vents.
Abstract: Multibeam echosounder systems (MBES) have long provided bathymetric data with high temporal and spatial resolution. In the last couple of decades, MBES observations of scattering in the water column have been finding increasing use in oceanographic studies. Here we review the wealth of studies using water column multibeam data to address questions in fisheries, marine mammal and zooplankton research as well as seeps and hydrothermal vents. We also summarize some of the tantalizing new oceanographic applications of water column MBES, such as kelp ecosystems, near surface bubbles, suspended sediment, mixing and internal waves, as well as the proper determination of the extent of shipwreck above the sea floor. We highlight the many advantages of using water column MBES and discuss the challenges.

Journal ArticleDOI
TL;DR: In this article, a 3-year time series of approximately monthly samples of settling particles, supplemented with a depth profile of suspended particulate matter (SPM) and sets of profundal surface-sediment and catchment soil samples, were analysed for both the intact polar lipids (IPLs) and fossil core lipids of GDGTs.

Journal ArticleDOI
01 Jan 2014
TL;DR: In this article, a detailed study of a subregion of this area, which covers an active gas ebullition area of 175 km2 characterized by 10 gas flares reaching from the seafloor at ~245 m up to 50 m water depth, was conducted to identify the fate of the released gas due to dissolution of methane from gas bubbles and subsequent mixing, transport and microbial oxidation.
Abstract: In the Arctic Seas, the West Spitsbergen continental margin represents a prominent methane seep area. In this area, free gas formation and gas ebullition as a consequence of hydrate dissociation due to global warming are currently under debate. Recent studies revealed shallow gas accumulation and ebullition of methane into the water column at more than 250 sites in an area of 665 km2. We conducted a detailed study of a subregion of this area, which covers an active gas ebullition area of 175 km2 characterized by 10 gas flares reaching from the seafloor at~245 m up to 50 m water depth to identify the fate of the released gas due to dissolution of methane from gas bubbles and subsequent mixing, transport and microbial oxidation. The oceanographic data indicated a salinity-controlled pycnocline situated ~20 m above the seafloor. A high resolution sampling program at the pycnocline at the active gas ebullition flare area revealed that the methane concentration gradient is strongly controlled by the pycnocline. While high methane concentrations of up to 524 nmol L−1 were measured below the pycnocline, low methane concentrations of less than 20 nmol L−1 were observed in the water column above. Variations in the δ13CCH4 values point to a 13C depleted methane source (~−60‰ VPDB) being mainly mixed with a background values of the ambient water (~−37.5‰ VPDB). A gas bubble dissolution model indicates that ~80% of the methane released from gas bubbles into the ambient water takes place below the pycnocline. This dissolved methane will be laterally transported with the current northwards and most likely microbially oxidized in between 50 and 100 days, since microbial CH4 oxidation rates of 0.78 nmol d−1 were measured. Above the pycnocline, methane concentrations decrease to local background concentration of ~10 nmol L−1. Our results suggest that the methane dissolved from gas bubbles is efficiently trapped below the pycnocline and thus limits the methane concentration in surface water and the air–sea exchange during summer stratification. During winter the lateral stratification breaks down and fractions of the bottom water enriched in methane may be vertically mixed and thus be potentially an additional source for atmospheric methane.

Journal ArticleDOI
TL;DR: It is shown that excess NH4+ delivery from the benthic system during the A. marina and M. viridis expansion period enriched the overlying water in DIN and stimulated phytoplankton concentration, in support of the second hypothesis that changes in species functional traits affect biogeochemical cycling with cascading effects on ecological functioning.
Abstract: We identify how ecosystem functioning in shallow estuaries is affected by shifts in benthic fauna communities. We use the shallow estuary, Odense Fjord, Denmark, as a case study to test our hypotheses that (1) shifts in benthic fauna composition and species functional traits affect biogeochemical cycling with cascading effects on ecological functioning, which may (2) modulate pelagic primary productivity with feedbacks to the benthic system. Odense Fjord is suitable because it experienced dramatic shifts in benthic fauna community structure from 1998 to 2008. We focused on infaunal species with emphasis on three dominating burrow-dwelling polychaetes: the native Nereis (Hediste) diversicolor and Arenicola marina, and the invasive Marenzelleria viridis. The impact of functional traits in the form of particle reworking and ventilation on biogeochemical cycles, i.e. sediment metabolism and nutrient dynamics, was determined from literature data. Historical records of summer nutrient levels in the water column of the inner Odense Fjord show elevated concentrations of NH4+ and NO3- (DIN) during the years 2004-2006, exactly when the N. diversicolor population declined and A. marina and M. viridis populations expanded dramatically. In support of our first hypothesis, we show that excess NH4+ delivery from the benthic system during the A. marina and M. viridis expansion period enriched the overlying water in DIN and stimulated phytoplankton concentration. The altered benthic-pelagic coupling and stimulated pelagic production may, in support of our second hypothesis, have feedback to the benthic system by changing the deposition of organic material. We therefore advice to identify the exact functional traits of the species involved in a community shift before studying its impact on ecosystem functioning. We also suggest studying benthic community shifts in shallow environments to obtain knowledge about the drivers and controls before exploring deep-water environments.

Journal ArticleDOI
05 Feb 2014-Tellus A
TL;DR: In this paper, for the first time, a set of one-dimensional lake models are evaluated for Lake Kivu (2.28°S; 28.98°E), East Africa.
Abstract: The African great lakes are of utmost importance for the local economy (fishing), as well as being essential to the survival of the local people. During the past decades, these lakes experienced fast changes in ecosystem structure and functioning, and their future evolution is a major concern. In this study, for the first time a set of one-dimensional lake models are evaluated for Lake Kivu (2.28°S; 28.98°E), East Africa. The unique limnology of this meromictic lake, with the importance of salinity and subsurface springs in a tropical high-altitude climate, presents a worthy challenge to the seven models involved in the Lake Model Intercomparison Project (LakeMIP). Meteorological observations from two automatic weather stations are used to drive the models, whereas a unique dataset, containing over 150 temperature profiles recorded since 2002, is used to assess the model’s performance. Simulations are performed over the freshwater layer only (60 m) and over the average lake depth (240 m), since salinity increases with depth below 60 m in Lake Kivu and some lake models do not account for the influence of salinity upon lake stratification. All models are able to reproduce the mixing seasonality in Lake Kivu, as well as the magnitude and seasonal cycle of the lake enthalpy change. Differences between the models can be ascribed to variations in the treatment of the radiative forcing and the computation of the turbulent heat fluxes. Fluctuations in wind velocity and solar radiation explain inter-annual variability of observed water column temperatures. The good agreement between the deep simulations and the observed meromictic stratification also shows that a subset of models is able to account for the salinity- and geothermal-induced effects upon deep-water stratification. Finally, based on the strengths and weaknesses discerned in this study, an informed choice of a one-dimensional lake model for a given research purpose becomes possible. Keywords: lake modelling, model intercomparison, surface–atmosphere interactions, tropical lakes, Lake Kivu (Published: 5 February 2014) Citation: Tellus A 2014, 66 , 21390, http://dx.doi.org/10.3402/tellusa.v66.21390 This publication is part of a Thematic Cluster entitled "Parameterization of lakes in numerical weather prediction and climate models". Read the other papers from this thematic cluster here

Journal ArticleDOI
TL;DR: The results clearly suggest that the resuspension of sedimentary particles into the overlying water significantly increased the dissolved electrolabile Pb and Zn contents.

Journal ArticleDOI
TL;DR: In this paper, the authors used the natural gradients in physicochemical and biological properties that upwelling establishes in surface waters to study their roles in nitrification, and how their activity varies in response to environmental fluctuations.
Abstract: The occurrence of nitrification in the oceanic water column has implications extending from local effects on the structure and activity of phytoplankton communities to broader impacts on the speciation of nitrogenous nutrients and production of nitrous oxide. The ammonia-oxidizing archaea, responsible for carrying out the majority of nitrification in the sea, are present in the marine water column as two taxonomically distinct groups. Water column group A (WCA) organisms are detected at all depths, whereas Water column group B (WCB) are present primarily below the photic zone. An open question in marine biogeochemistry is whether the taxonomic definition of WCA and WCB organisms and their observed distributions correspond to distinct ecological and biogeochemical niches. We used the natural gradients in physicochemical and biological properties that upwelling establishes in surface waters to study their roles in nitrification, and how their activity—ascertained from quantification of ecotype-specific ammonia monooxygenase (amoA) genes and transcripts—varies in response to environmental fluctuations. Our results indicate a role for both ecotypes in nitrification in Monterey Bay surface waters. However, their respective contributions vary, due to their different sensitivities to surface water conditions. WCA organisms exhibited a remarkably consistent level of activity and their contribution to nitrification appears to be related to community size. WCB activity was less consistent and primarily constrained to colder, high nutrient and low chlorophyll waters. Overall, the results of our characterization yielded a strong, potentially predictive, relationship between archaeal amoA gene abundance and the rate of nitrification.