nM In Surface Waters Research Articles

Nitrous oxide distribution in the north-eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula)

The distribution of nitrous oxide (N 2O) was investigated in the coastal waters of the north-eastern shelf of the Gulf of Cádiz during four campaigns that took place in June 2006, November 2006, February 2007 and May 2007. N 2O distributions showed strong temporal fluctuations in both concentration and saturation values, which were significantly higher in June and November 2006 compared to February and May 2007. Measured concentrations ranged from 8.2 to 23.2 nM in surface waters and from 8.9 to 28.5 nM in bottom waters, corresponding to saturations that varied between 105–335% and 100–340%, respectively. Tidal exchange with rivers, creeks and the surrounding salt marshes, together with enhanced drainage during rainy periods, were important factors controlling N 2O distribution. The region behaved as a net source of N 2O to the atmosphere throughout the year, with mean air–sea fluxes for each survey that varied between 1.0–15.3 µmol N 2O m − 2 d − 1 and 2.2–25.4 µmol N 2O m − 2 d − 1 , depending on the parameterization used to calculate gas transfer velocities.

Spatial variability in the coupling of organic carbon, nutrients, and phytoplankton pigments in surface waters and sediments of the Mississippi River plume

River-dominated coastal areas are typically sites of active biogeochemical cycling, with productivity enhanced by terrestrial inputs of nutrients and organic matter. To examine the spatial variability and relationship between river discharge, phytoplankton, and organic carbon distributions, we analyzed surface water and sediment from the Louisiana shelf adjacent to the Mississippi River. Samples were collected during April and October 2000 to capture high and low river discharge, and were analyzed for dissolved and particulate organic carbon (DOC and POC), nutrients, and phytoplankton pigments. Pigments, determined by high performance liquid chromatography (HPLC), were also analyzed from sediment to evaluate marine carbon inputs to the seafloor. DOC in surface waters was generally within 200–300 μM, ranging up to 399 μM. Chlorophyll a ranged from below the limits of detection (BLD) up to 31 nM in surface waters, with higher values located further from the river mouth during high flow. Although community diversity increased during low discharge, diatoms dominated the phytoplankton population (50–80% of the community throughout the study) and consequently made more important contributions than other species to both the DOC and POC pools. Chlorophyll and degradation products (indicative of zooplankton grazing) observed in surface sediment indicated a transfer of autochthonous carbon from the highly productive photic zone to the sediment, coupling phytoplankton-derived POC in surface waters with organic carbon deposition in surface sediment. Cross-shelf changes in chlorophyll indicated a westward transport of phytoplankton that was directly and indirectly linked with river discharge and pigment decay dynamics.

Physicochemical speciation of bioactive trace metals (Cd, Cu, Fe, Ni) in the oligotrophic South China Sea

Bioactive trace elements Cd, Cu, Fe, and Ni in the oligotrophic South China Sea (SCS) waters exhibit distinct chemical affinities and physical size distributions when using cross flow ultrafiltration and ion exchange techniques, even though they display similar nutrient-type distributions. Dissolved Cu (≤ 0.4 μm) concentrations increased from 0.9 nM in surface waters to 3 nM at depths below 500 m, while those of dissolved Ni increased from 2 to 9 nM; those of dissolved Cd, from 0.01 to 0.9 nM; and those of dissolved Fe, from 0.1 to 0.7 nM. The majority of the dissolved Cd (∼ 100%) and Ni (> 80%) concentrations were found in the ≤ 1 kDa size fraction and as cationic labile forms. More than 50% of the total dissolved Cu in surface waters was in the ≤ 1 kDa cationic labile form, while the non-exchangeable fraction that cannot be adsorbed by either cation or anion exchange resins increased from 28% at the surface to 50% below 500 m depth. Similarly, about 60% of total dissolved Fe in surface waters was in the ≤ 1 kDa fraction; the colloidal (1 kDa–0.4 μm) form of Fe was relatively constant throughout the water column, and amounted to 40% at the surface and 20% in deeper waters. Some fractions of the total dissolved Cu and Fe could be adsorbed by both cation and anion exchange resins, suggesting binding to “zwitterionic” molecules with both anionic and cationic binding sites. The cationic labile form of Fe tightly correlates with phosphate and nitrate, total dissolved Ni significantly correlates with silicate, and total dissolved Cd with phosphate, with different slopes in the upper 100 m than below. These correlations suggest a tight coupling of the cycling of these trace metals with those of individual nutrient elements. Biogeochemical and biophysical interactions between metals and organisms are not only through surface complexation to organic molecules of different molecular weights but they are also tightly coupled to colloidal aggregation due to their surfactant activity, properties that should be considered in future studies of oceanic elemental cycles.

Zinc speciation in Lakes Manapouri and Hayes, New Zealand

A study of zinc complexation in Lakes Manapouri and Hayes revealed that zinc speciation in both lakes is dominated by its complexation to natural organic ligands. In Lake Manapouri, dissolved zinc concentrations increased from 0.9 nM in surface waters to ~1.4 nM at depth. Ligand concentrations for this lake were relatively uniform with depth, with values ranging between 2.9 and 4.2 nM. A similar ligand concentration was measured for Lake Hayes, which had a surface zinc concentration of 0.46 nM. Conditional stability constants (log K) for the complexation of zinc to these ligands were high,with values ranging between 10.0 and 11.1. Calculated free Zn 2+ concentrations for both lakes were in the low picomolar range (5—48 pM). Such low free Zn 2+ levels may limit the growth of some phytoplankton in both lakes.

Distribution and turnover of dissolved DMSP and its relationship with bacterial production and dimethylsulfide in the Gulf of Mexico

We measured the distribution of particulate and dissolved pools of the phytoplankton osmolyte dimethylsulfoniopropionate (DMSP) in the euphotic zone at a series of shelf (<40 m total water depth) and oceanic (>500 m depth) stations in the northern Gulf of Mexico. We also measured turnover rates of the dissolved DMSP pools (DMSPd) with tracer additions of 35S‐DMSPd and short‐term (<1 h) incubations, with the aim of examining the relationship between DMSPd turnover and bacterial production. Particulate DMSP concentrations were relatively low (<25 nM) throughout the study area with about twofold higher mean concentration at the shelf sites (15 nM) compared with the oligotrophic oceanic sites (7 nM). DMSPd concentrations averaged 3.0 nM in shelf waters and 1.3 nM in oceanic waters. Concentrations of dimethylsulfide (DMS), a degradation product of DMSP, also were low throughout the Gulf, averaging 2.0 nM for all depths sampled and 2.5 nM in surface waters. Microbial assem‐blages metabolized 35S‐DMSPd with the sulfur being incorporated into biomass, volatile compounds (DMS and methanethiol), and other dissolved products. DMSPd turnover was relatively slow (mean of 3.8 nM d−1) in oligotrophic oceanic waters and averaged 10‐fold higher (39 nM d−1) in mesotrophic shelf waters. DMS concentrations ranged from 0.2 to 5.1 nM in oceanic waters and appeared to be weakly related to DMSP turnover. In contrast, DMS concentrations in shelf waters fell within a narrow range (0.8–2.8 nM) and showed no relationship at all with DMSPd turnover. DMSPd turnover rates were high enough to sustain the measured concentrations and estimated turnover of DMS, even if the conversion efficiency of DMSPd into DMS was only 10%. DMSPd turnover was significantly correlated with bacterial production (as measured by 3H‐thymidine incorporation) and we estimate that DMSPd turnover contributed a mean of 3.4% of the carbon and ~100% of the sulfur required for bacterial growth in Gulf of Mexico surface waters. In addition to its role as a precursor of DMS, DMSP deserves attention as an important substrate for bacterioplankton in the euphotic zone.

Zinc speciation in the Northeastern Atlantic Ocean

Measurements of zinc and zinc complexation by natural organic ligands in the northeastern part of the Atlantic Ocean were made using cathodic stripping voltammetry with ligand competition. Total zinc concentrations ranged from 0.3 nM in surface waters to 2 nM at 2000 m for open-ocean waters, whilst nearer the English coast, zinc concentrations reached 1.5 nM in the upper water column. In open-ocean waters zinc speciation was dominated by complexation to a natural organic ligand with conditional stability constant (log KZnL′) ranging between 10.0 and 10.5 and with ligand concentrations ranging between 0.4 and 2.5 nM. The ligand was found to be uniformly distributed throughout the water column even though zinc concentrations increased with depth. Organic ligand concentrations measured in this study are similar to those published for the North Pacific. However the log KZnL′ values for the North Atlantic are almost and order of magnitude lower than those reported by Bruland [Bruland, K.W., 1989. Complexation of zinc by natural organic-ligands in the central North Pacific. Limnol. Oceanogr., 34, 269–285.] using anodic stripping voltammetry for the North Pacific. Free zinc ion concentrations were low in open-ocean waters (6–20 pM) but are not low enough to limit growth of a typical oceanic species of phytoplankton.

Mercury and Arsenic at the Redoxcline of the Black Sea

The Black Sea is a very suitable site to investigate the marine geochemical cycling of trace elements at redoxcline. This oxic-anoxic interface is permanent around between 100 and 200 m depth. We present here detailed profiles (10-1400 m) for dissolved (0.4 gm) mercury and arsenic from one station located in the Northwestern Black sea (44~ 32~ which has been occupied in summer 1995 during a cruise of the EROS-2000 project (Environment RTD Programme of the European Union). Mercury concentrations varied from 0.12 pM in surface waters to 6.15 pM at the redoxcline; the concentrations were lower than 3.75 pM in the anoxic zone. Arsenic concentration varied from 18.3 nM in surface waters to 44.7 nM at the redoxcline; concentrations in the anoxic were relatively stable around 40 pM. Both mercury and arsenic profiles exhibited a maximum coincidental with the dissolved iron peak. A seconda~ peak was observed for both elements at the basis of the manganese gradient. The concentration gradients at the redoxcline are interpreted in terms of scavenging, partial regeneration and diffusion. In the oxic layer, the arsenic distribution suggests removal and mixing. In the case of mercury, a subsurface bulge in the profile suggests elemental mercury formation. The redoxcline would supply the dissolved Hg(II) necessary for this reaction, the atmosphere being a sink for Hg8.

Iron stress in the Pacific region of the Southern Ocean:evidence from enrichment bioassays

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 166:27-41 (1998) - doi:10.3354/meps166027 Iron stress in the Pacific region of the Southern Ocean: evidence from enrichment bioassays K. R. Timmermans1,*, M. A. van Leeuwe1,**, J. T. M. de Jong1, R. M. L. McKay3, R. F. Nolting1, H. J. Witte2, J. van Ooyen1, M. J. W. Swagerman1, H. Kloosterhuis1, H. J. W. de Baar1 1Department of Marine Chemistry and Geology and 2Department of Biological Oceanography, Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands 3Brookhaven National Laboratory, Department of Applied Science, Oceanographic and Atmospheric Sciences Division, Building 318, Upton, New York 11973, USA *E-mail: klaas@nioz.nl **Present address: University of Groningen, Dept of Marine Biology, PO Box 14, 9750 AA Haren, The Netherlands The effect of iron on phytoplankton physiology in a scarcely investigated part of the Pacific region of the Southern Ocean was studied during an expedition aboard RV 'Polarstern'. Physiological effects of iron enrichments were studied during short-term bottle experiments (72 h) in high-nutrient, low-chlorophyll (HNLC) water samples. Throughout the expedition (March to May 1995), surface water nitrate concentrations were high (21 to 27 µM) and surface water silicate concentrations varied considerably north (<3.5 µM) and south (>13 µM) of the Polar Front, whereas low chlorophyll a concentrations (<0.2 µg l-1) were measured in the research area. Small-sized cells (<5 µm) dominated the phytoplankton community; diatoms were observed only occasionally north of the Polar Front. Total phytoplankton numbers, as determined by flow cytometry, ranged from 1500 to 8000 cells ml-1. Ambient dissolved iron concentrations in the experimental area were low and ranged from 0.1 to 0.4 nM in surface waters. In the experimental series, indications of iron stress in the indigenous phytoplankton assemblage were found. Whereas the species composition remained virtually unaltered upon addition of 2 nM iron, significant increases in nitrate uptake and enhanced nitrate reductase activities were observed within 32 h after the start of the experiments. Ammonium uptake, which prevailed over nitrate uptake, remained unaltered by the iron additions. In addition to the physiological effects, a molecular marker of iron stress, flavodoxin, was detected in phytoplankton protein extracts collected after 72 h of incubation. Irrespective of iron deficiency, silicate concentrations in the northern part of the research area were likely below half-saturation values for growth for diatoms and thereby likely prevented diatom blooms. The results of this study indicate that the nano-phytoplankton in the Pacific region of the Southern Ocean are iron stressed; upon iron enrichment, a physiological stimulation is observed. Our results support a lack of iron as one of the causes of HNLC conditions in this region. Iron stress · Nitrogen assimilation · Phytoplankton · Flavodoxin Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 166. Publication date: May 28, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Iodine speciation: a potential indicator to evaluate new production versus regenerated production

Vertical profiles of iodide, iodate and total free iodine were determined monthly for one year (from July 1993 to June 1994) at the DYFAMED permanent station located in the northwestern Mediterranean Sea. Dissolved iodate and iodide were directly determined by differential pulse polarography and cathodic stripping square wave voltammetry, respectively. Iodate is the predominant species, ranging from 390 nM in surface waters to 485 nM in deep waters. Iodide is present in significant concentrations up to 80 nM in surface waters and from undetectable levels to several nanomolar (< 10 nM) in deep waters. Concentrations of total free iodine are slightly lower in surface waters (467–478 nM with an average of 472 nM) than in deep waters (475–486 nM with an average of 481 nM). Considerable variations in iodine speciation were observed. Iodide concentrations in surface waters were relatively low and stable from February to April (about 20 nM), increased up to 80 nM from May until November, and then decreased from December to February. Comparison between iodide abundance and primary production demonstrates that the transformation from iodate to iodide in surface waters is linked to the regenerated production. The stability of regenerated iodide in surface seawater makes iodide a potential indicator to evaluate new production vs regenerated production.

Determination of a strong organic ligand dissolved in seawater: Thorium-complexing capacity of oceanic dissolved organic matter

A new method has been developed to measure a strong ligand in oceanic dissolved organic matter (DOM) by Th complexation in acidic media and the adsorption of the Th complex onto XAD-2 resin. Th reacts quantitatively with organic binding site of DOM in strong acid media (around 0.1M H+ solution), which is equilibrated within 24 hours. According to mass action analysis, Th forms a 1∶1 complex with the binding site in DOM, whose conditional stability constant is 106.7M−1. The conditional stability constant of the Th complex in DOM is in good agreement with that determined for oceanic Particulate Matter (PM) under similar experimental conditions. This finding suggests that the chemical properties of the strong ligand in DOM are similar to these in biogenic PM. The Th-complexing capacity in DOM, which corresponds to the total concentration of the strong organic ligand, can be determined (2–3 nM in surface waters) in a small volume (about 200 ml). The method has a detection limit of approximately 0.05 nM for the thorium-complexing capacity of DOM by using230Th.

Iodine speciation in the northwestern Mediterranean Sea, method and vertical profile

Abstract Iodine speciation analysis was carried out upon seawater samples collected in July 1993 at the Dyfamed station (43 °25′N, 7 °52′E) located in the northwestern Mediterranean Sea. Dissolved iodate and iodide were directly determined by differential pulse polarography and cathodic stripping square wave voltammetry, respectively, and organically bound iodine was estimated by wet-chemical oxidation with sodium hypochlorite. Iodate is the predominant species ranging from 416 nM in surface waters to 480 nM in bottom waters. Iodide is present in significant concentrations up to 60 nM in surface waters, undetectable between 500 and 1000 m depth and present in very low but measurable concentrations (about 6 nM) in deep waters. The vertical profile of total free iodine demonstrates observable removal from surface waters, slight enrichment at about 200 m depth and constant there below. Up to 40 nM of organically bound iodine has been estimated between 20 to 30 m. Factorial analysis of different iodine species with biologically relevant parameters provided strong evidence for iodine biophilic features.

Factors controlling the stability of submicron colloids in natural waters

Particles are ubiquitous in all natural systems and play an important role in the control and fate of nutrients and pollutants. Submicron particles are especially important because they have large specific surface areas and high surface free energies which facilitate sorption of significant quantities of substances. Currently, only limited information is available on particle number and size distributions of natural submicron particles, owing to the significant problems involved in their experimental determination. In the present paper, existing data are discussed and compared with theoretical predictions based on a classical coagulation/sedimentation model where the kinetics of coagulation is described by Smoluchowski's equations and sedimentation is characterized by Stokes' law. Model predictions agree well with reported particle behaviour for particles larger than 100 nm. While classical theory does not explain the presence of colloids smaller than 100 nm in surface waters, the existence of such small colloids, embedded in large organic matrices, has been observed recently by high resolution transmission electron microscopy. Improvements in the measurement techniques available as well as development of the necessary theory to describe these organic/inorganic associations would be most welcome.

Complexation of zinc by natural organic ligands in the central North Pacific

The complexation of zinc by natural organic ligands in the upper 600 m of the central North Pacific was determined with differential pulse anodic stripping voltammetry at a thin mercury film, rotating glassy‐carbon disk electrode. Of the dissolved zinc in surface waters &gt;98% was bound in strong complexes (log K′cond, Zn2+ = 11.0) by relatively zinc‐specific organic ligands existing at low concentrations (1.2 nM). Although the vertical distribution of this ligand class is relatively uniform, total dissolved zinc varies from concentrations close to 0.1 nM in surface waters of the central North Pacific to 3 nM at 500 m. Complexation of dissolved zinc by this class of organic ligands causes the concentration of inorganic zinc to vary from 2 pM in surface waters to 2 nM at 500 m, a 1,000‐fold variation. The free zinc ion activity, expressed as pZn, is calculated to be of the order of 12.7 in the surface waters of the central North Pacific. This low free zinc ion activity may influence distributions of oceanic and neritic phytoplankton species.

Copper complexation profiles in the Atlantic Ocean: A comparative study using electrochemical and ion exchange techniques

The dissolved copper concentrations in several profiles of the water column in the Atlantic Ocean were between 1 and 6 nM, and indicate copper removal from the surface layer and mixing of water masses at greater depth. The ligand concentrations ( C L) decreased from a maximum of 1800 nM in surface waters to 6–20 nM in deeper waters, with values for log K′ CuL (conditional stability constants) between 9.4 and 11, as indicated by the MnO 2 technique. Ligand concentrations obtained with the DPASV (differential pulse anodic stripping voltammetry) technique showed more variability and were generally higher, whereas the log K′ CuL values were smaller at 7.5–10.3. Such differences in results obtained with different techniques may be due to certain operational parameters of each technique, which to some extent govern the detection window. Speciation calculations showed that the organic copper fraction at all depths amounts to 89–99.8% using data from the MnO 2 method, and 98.8–99.4% using data from the DPCSV (differential pulse cathodic stripping voltammetry) method. Comparison of the techniques used showed that the stronger ligands, or sites, detected by the DPCSV, and to a smaller extent MnO 2 procedures were of most relevance to the study of metal speciation, since these ligands form much more stable copper complexes than those detected by DPASV. The strong complexing ligands are not detected by DPASV due to lack of sensitivity. For reasons of convenience and sensitivity DPCSV is to be preferred over the MnO 2 method.