180 research outputs found
Vivaspin ultrafiltration: A new approach for high resolution measurements of colloidal and soluble iron species
No full textVivaspin6® ultrafiltration units with molecular weight “cut-off” membranes of 5, 10, 30, 50, and 100 kDa were used together to examine the size distribution of newly formed iron (Fe) colloids in natural seawater samples and in the presence of several different Fe chelators with varying Fe binding strength. Artificial Fe chelators, such as TAC, and 2 kDG, when added at equimolar levels to Fe, supported the formation of a continuum of Fe-ligand colloids between 5 and 100 kDa. More than 90% of the added 55Fe in these solutions occurred in Fe aggregates/particles larger than 100 kDa. The strong siderophore DFO held the majority of the added 55Fe in the “truly” soluble fraction ≤ 5 kDa, whereas 90% of 55Fe added to UV-irradiated seawater was converted into Fe colloids with a size between 50 to 100 kDa (5–6 nm). Membranes with ≥ 10 kDa showed similar “cut-off” properties on natural seawater samplescollected in the water column off the Peruvian coast. Fe solubility determined with these membranes was approximately six times greater than Fe solubility determined with the 5 kDa membrane and the 0.02 μm syringe filters. This suggests that a seamless size continuum of organic chelators (≤5 kDa–10 kDa) is present in these seawaters and that estimates of ligand production based on 0.02 μm Anotop solubility experiments underestimates the abundance of soluble/colloidal ligands. Regarding these results, we recommend the use of Vivaspin 5 kDa membranes to separate the “truly” soluble from the colloidal Fe fraction
Identifying the processes controlling the distribution of H2O2 in surface waters along a meridional transect in the eastern Atlantic
No full textHydrogen peroxide (H2O2) is an important oxidant for many bio?relevant trace metals and organic compounds and has potential as a tracer for mixing in near surface waters. In this study we combine H2O2 and bio?optical measurements with satellite data for a meridional transect from 46°N to 26°S in the eastern Atlantic in order to determine the key processes affecting its distribution. Surface H2O2 ranged from 21–123 nmol L?1, with maximum inventories (0–200 m) of 5.5–5.9 mmol m?2 found at 30°N and 25°S. Analyses showed a strong positive correlation of surface H2O2 with daily irradiances and recent precipitation, though poor correlations with CDOM suggest sunlight is the limiting reactant for H2O2 formation. Vertical distributions of H2O2 were controlled by a combination of mixing processes and phytoplankton activity. The present study highlights processes controlling global H2O2 distributions and points towards the development of parameterization schemes for prediction via satellite data
Rapid Determination of Picomolar Titanium in Seawater with Catalytic Cathodic Stripping Voltammetry
No full textTitanium (Ti) is present as a trace element in seawater at extremely low concentrations (5-350 pM, where 1 pM = 10(-12) mol L(-1)) throughout the water column. Presently, little is known about the marine biogeochemistry of Ti and there is a distinct lack of oceanic measurements of Ti, because of the combined difficulties of trace-metal clean sampling for an element at such low levels and the lack of a suitable shipboard method of analysis. Here, a new cathodic stripping voltammetry procedure is presented for the rapid determination of Ti at pM concentrations in seawater that is capable of being used directly at sea. This method utilizes the catalytic enhancement of the reduction of the complex formed between Cupferron (N-nitrosophenylhydroxylamine) and Ti(IV). While Cupferron itself acts as both a complexing agent and an oxidizing agent, it was found that the optimal sensitivity was with bromate as an auxiliary oxidant. An advantage of this method is that it is useable over the pH range of 5.5-8. Under the conditions employed in this work, detection limits ranged from 5 pM to 12 pM. This new catalytic method is significantly more sensitive than existing methods and has been extensively tested at sea in the Atlantic and Southern Oceans
Depth profile of Fe solubility from GO-Flo station M68/3_284
No full textDFG grant CR145/5-1 (contribution to German SOLAS). WOCE quality flags converted to internal format, see hdl:10013/epic.31518.d00
Solubility of iron in the Southern Ocean
No full textIron solubility (cFeS) ranged from 0.4 to 1.5 nmol L?1, decreasing from south to north in three different Southern Ocean zones (the Coastal Zone, the Antarctic Zone, and the Polar Frontal Zone plus the Subantarctic Zone). This decrease was at times correlated with an increase in temperature. Organic Fe solubility (cFeS,org), which was obtained by subtracting from total measured Fe solubility the solubility of inorganic species of iron (Fe) at the measurement temperature (20°C), ranged from 0.3 to 1.3 nmol L?1, representing an average of 32 ± 14% of the concentration of ligands in the dissolved size fraction as determined via competitive ligand exchange–absorptive cathodic stripping voltammetry (barring a handful of extremely high values from a transect run to the east of Prydz Bay). Values of cFeS were mainly lower than the predicted value for inorganic Fe solubility at the in situ temperature. Total in situ Fe solubility (cFeS,adj) was therefore estimated by adjusting for inorganic Fe solubility at in situ temperatures (between ?2°C and +18°C). Because in situ temperatures in the Antarctic Circumpolar Current were mostly lower than +3°C, such cFeS,adj values, ranging from 0.5 to 1.8 nmol L?1, were roughly twice as large as cFeS,org. The adjustment relies heavily on model calculations of inorganic Fe solubility but, if correct, indicates that the bulk of the solubility of Fe in the cold waters of the Southern Ocean is tied to the solubility of inorganic Fe rather than to Fe ligands in the soluble size fraction
Die Biogeochemie des Mangans in der euphotischen Zone
No full textThe trace metal manganese (Mn) plays a significant role in seawater as it is bio-essential for phytoplankton. Mn plays a critical role as a redox center in Photosystem II (PSII) during the conversion of water to oxygen in photosynthesis. It is also essential in other redox related enzymatic processes; in particular Mn is important as the active metal center in superoxide dismutase (SOD) which provides intracellular protection against oxidative stress due to photochemically produced superoxide (O2 ). Mn exists in seawater in three redox states: soluble and prevalent Mn(II), insoluble Mn(III) and Mn(IV)-oxides. In the euphotic zone the biogeochemical cycling of Mn is strongly influenced by reactive oxygen species (ROS). The highly reactive and short-lived superoxide (O2 ) and hydrogen peroxide (H2O2) can both act as oxidants and reductants, and they play a key role in the Mn processes in seawater. For example the dominant Mn sources to the open ocean are the Mn-oxides which are present in atmospheric dust which are reduced to soluble Mn(II) by photochemically produced H2O2. While these processes have been crudely identified, the dominant reactions and mechanisms of Mn and ROS in seawater are poorly understood. This lack of knowledge demands investigations into the in-situ dissolution processes of Mn from dust and into studying the exact reaction mechanisms between Mn and ROS in the euphotic zone.
This thesis comprises four manuscripts. Manuscripts 1 and 2 (Wuttig et al., subm., 2013a; Wuttig et al., subm., 2013b) focus on the cycling and reaction mechanisms of Mn and ROS. Manuscript 3 (Wuttig et al., in prep., 2013) addresses differences in the input and distribution of cadmium (Cd), iron (Fe) and Mn in the Eastern Tropical Atlantic Ocean off Cape Verde, and manuscript 4 (Wuttig et al., 2013) describes Mn cycling after dust additions in a trace metal clean mesocosm experiment in the Mediterranean Sea.
This study has conclusively shown that Mn and organic matter are the dominant sinks for O2 in the Eastern Tropical North Atlantic (manuscripts 1; Wuttig et al., subm., 2013a). Mn dominates this decay especially in the surface waters which are influenced by high atmospheric dust deposition and near the sediment/water interface due to Mn sediment resuspension. This contrasts with current knowledge based on findings from the Mn poor Southern Ocean where copper (Cu) was shown to be the major sink.
In manuscript 2 it is demonstrated that O2 decays by reaction with inorganic Mn(II) in seawater following a first order loss rate which appears to involve a catalytic reaction involving the Mn(II)/MnO2+ couple, in which MnO2+ is a manganous superoxide complex (Wuttig et al., subm., 2013a). Thus in sunlit and oxygenated waters Mn(III) is unlikely to be found in significant concentrations when strong Mn(III) binding ligands are not present. In other studies Mn(III) was found under anoxic conditions in the presence of unknown strong Mn(III) binding ligands. Therefore, in contrast to the Mn(II)/MnO2+ pair, Mn(III) cannot act as a SOD in the oxygenated surface ocean.
In the Eastern Tropical North Atlantic Ocean atmospheric dust is the main source of Mn to surface waters (manuscript 3; Wuttig et al., in prep., 2013). However this study provides clear evidence that equatorial upwelling and sediment resuspension are important Mn sources in this region. In contrast to findings from the Eastern Tropical Pacific, where unexpected high surface concentrations were observed, no secondary Mn(II) maximum was found in the Eastern Tropical North Atlantic Ocean. This could have been introduced by a combination of lateral transport of Mn rich waters from the coastal margins and reduction of Mn-oxides.
While Aeolian sources were predominantly influencing Mn and also Fe cycling in the Eastern Tropical Atlantic, Cd was not controlled by dust deposition (manuscript 3; Wuttig et al., in prep., 2013). These biologically relevant elements exhibited contrasting distribution patterns. For Fe and Mn, atmospheric depositions masked a classical nutrient type profile, while Cd was very depleted at the surface and concentrations steadily increased with depth. Cd was highly correlated to Phosphate (hereafter referred to as P). The Cd/P ratio was mainly controlled by P with elevated concentrations at depth resulting in strongly differing ratios in surface and subsurface layers of 16.6 pmol / µmol and 237 pmol / µmol, respectively.
The complex photochemical processes during the dissolution of Mn dust are also subject of manuscript 4. This paper describes a mesocosm project in the Mediterranean with two consecutive additions of evapocondensed dust conducted. The data also show that the dissolution and loss rates of Mn were comparable during both seedings. The calculated fractional solubilities for the first and the second dust addition were 41 ± 9 % and 27 ± 19 %, respectively.
The results presented in this thesis have significantly improved our understanding of Mn distribution and especially cycling in the euphotic zone. An insight into the mechanisms between Mn and ROS and into the dissolution processes from dust is given.Das Spurenelement Mangan (Mn) ist von zentraler Bedeutung im Meer, da es ein essenzieller Mikronährstoff für Phytoplankton ist. Es spielt eine wichtige Rolle im Photosystem II (PSII) bei der Sauerstoffbildung aus Wasser in der Photosynthese. Des Weiteren ist Mn wichtig für weitere enzymatische Redoxprozesse, insbesondere als aktives Metallzentrum in Superoxiddismutase (SOD), welche als intrazelluläre Schutzmechanismen vor oxidativem Stress durch photochemisch produziertes Superoxid (O2 ) fungieren. Im Meerwasser kommt Mn in drei Oxidationsstufen vor: in erster Linie als lösliches Mn(II), als unlösliches Mn(III) und als Mn(IV)-Oxide. Der biogeochemische Kreislauf von Mn im lichtdurchfluteten Ozean ist signifikant durch reaktive Sauerstoffspezies (ROS) beeinflusst. Hierbei können das stark reaktive und kurzlebige Superoxid (O2 ) und seine Tochterprodukt Wasserstoffperoxid (H2O2) gleichermaßen eine oxidierende als auch eine reduzierende Wirkung haben und spielen somit eine Schlüsselrolle für Mn Prozesse im Meerwasser. Im offenen Ozean beispielsweise ist atmosphärischer Staub die Haupteintragsquelle für Mn und das in oxidierter Form vorliegende Mn im Staub kann durch photochemisch gebildetes H2O2 reduziert und als Mn(II) im Wasser gelöst werden. Obwohl die groben Zusammenhänge dieser Prozesse bekannt sind, sind die Hauptreaktionen und Mechanismen des Zusammenspiels von Mn und ROS im Meerwasser kaum verstanden.
Die Dissertation umfasst vier Manuskripte. Manuskripte 1 (Wuttig et al., subm., 2013a) und 2 (Wuttig et al., subm., 2013b) konzentrieren sich auf Kreisläufe und Reaktionsmechanismen von Mn und ROS. Manuskript 3 beschreibt die Unterschiede zwischen den Eintragsprozessen und der Verteilung von Cd, Fe und Mn im östlichen tropischen Atlantik nahe den Kapverdischen Inseln (Wuttig et al., in prep., 2013). Manuskript 4 (Wuttig et al., 2013) widmet sich der Untersuchung des Mn Kreislaufs in Folge der wiederholten Staubzugabe in das oligotrophe Oberflächenwasser von spurenmetall-sauberen Mesokosmen im Mittelmeer.
Im Gegensatz zu früheren Beobachtungen im Südpolarmeer, konnte in dieser Studie klar gezeigt werden, dass im östlichen tropischen Atlantik Mn und organische Substanzen als vorwiegende Senken für O2 darstellen (Manuskript 1; Wuttig et al., subm., 2013a). Mn dominiert diesen Zerfall besonders im Oberflächenwasser, welches stark durch atmosphärischen Staubfluss beeinflusst ist, und nahe dem Meeresboden durch die Resuspension aus dem Sediment.
Zudem konnte gezeigt werden, dass der Abbau von O2 durch Reaktion mit anorganischem Mn(II) in Seewasser einer Zerfallsrate erster Ordnung folgt (Manuskript 2, Wuttig et al., subm., 2013b). Diese scheint eine katalytische Reaktion des Mn(II)/MnO2+ Paars zu beinhalten, wobei MnO2+ der Superoxidkomplex ist. Des Weiteren ist es in der euphotischen und sauerstoffreichen Zone unwahrscheinlich, nennenswerte Mn(III) Konzentrationen aufzufinden, welche ohne starke Mn(III) bindende Liganden nur unter anoxischen Bedingungen erwartet werden. Somit kann Mn(III) im Gegensatz zum Mn(II)/MnO2+ Paar im sauerstoffreichen Oberflächenwasser nicht als SOD agieren.
Atmosphärischer Staub ist die Haupteintragsquelle von Mn im Oberflächenwasser des östlichen tropischen Atlantiks (Manuskript 3; Wuttig et al., in prep., 2013). Jedoch wurden in dieser Region zusätzlich auch Einträge von Mn durch äquatorialen Auftrieb und Resuspension aus dem Sediment beobachtet. Zusätzlich wurde hier kein sekundäres Mn(II) Maximum gefunden, welches bei gleichen Untersuchungen im östlichen tropischen Pazifik in 200 m Tiefe der Fall war und vermutlich durch eine Kombination aus Einträgen durch atmosphärischen Staub und laterale Transportprozesse verursacht wurde.
Während atmosphärische Quellen dominierend den Mn und Fe Kreislauf beeinflussen, sind Cd Konzentrationen im tropischen Atlantik nicht durch Staubeintrag kontrolliert (Manuskript 3; Wuttig et al., in prep., 2013). Generell zeigten diese Spurenelemente unterschiedliche Verteilungsmuster. Während die für biologisch relevante Elemente zu erwartenden typischen nährstoffähnlichen Tiefenprofiele durch den atmosphärischen Eintrag von Fe und Mn überlagert wurden, waren die Cd Konzentrationen im Oberflächenwasser sehr niedrig und nahmen mit der Tiefe zu. Das Cd/P Verhältnis wurde dabei in erster Linie durch die in der Tiefe erhöhten P Konzentrationen bestimmt und wies dort ein Cd/P Verhältnis von 237 pmol / µmol gegenüber 16.6 pmol / µmol im Oberflächenwasser aus.
Auch im Manuskript 4 (Wuttig et al., 2013), welches sich mit der Löslichkeit und dem Kreislauf von Mn nach zwei Zugaben prozessierten Staubs während eines Mesokosmen Projektes im Mittelmeer beschäftigt, spielen die komplexen photochemischen Experimente eine zentrale Rolle. Hinzukommend zeigen die Daten, dass die Mn Löslichkeits- und Verlustraten nach den beiden Staubzugaben vergleichbar sind. Die anteilige Löslichkeit von Mn aus dem Staubmaterial betrug 41 ± 9 % für die erste Staubzugabe und 27 ± 19 % für die zweite Staubzugabe
Measurements of organic complexation of iron during the CARUSO-EISENEX experiment
No full textThe speciation of strongly chelated iron during the 22-day course of an iron enrichment experiment in the Atlantic sector of the Southern Ocean deviates strongly from ambient natural waters. Three iron additions (ferrous sulfate solution) were conducted, resulting in elevated dissolved iron concentrations (Nishioka, J., Takeda, S., de Baar, H.J.W., Croot, P.L., Boye, M., Laan, P., Timmermans, K.R., 2005, Changes in the concentration of iron in different size fractions during an iron enrichment experiment in the open Southern Ocean. Marine Chemistry, doi:10.1016/j.marchem.2004.06.040) and significant Fe(II) levels (Croot, P.L., Laan, P., Nishioka, J., Strass, V., Cisewski, B., Boye, M., Timmermans, K.R., Bellerby, R.G., Goldson, L., Nightingale, P., de Baar, H.J.W., 2005, Spatial and Temporal distribution of Fe(II) and H2O2 during EisenEx, an open ocean mescoscale iron enrichment. Marine Chemistry, doi:10.1016/j.marchem.2004.06.041). Repeated vertical profiles for dissolved (filtrate 200 kDa-< 0.2 µm), as opposed to the soluble fraction (< 200 kDa) which dominated prior to the iron infusions. Yet these colloidal ligands would exist in a more transient nature than soluble ligands which may have a longer residence time. The production of dissolved Fe-chelators was generally smaller than the overall increase in dissolved iron in the surface infused mixed layer, leaving a fraction (about 13-40%) of dissolved Fe not bound by these dissolved Fe-chelators. It is suggested that this fraction would be inorganic colloids. The unexpected persistence of such high inorganic colloids concentrations above inorganic Fe-solubility limits illustrates the peculiar features of the chemical iron cycling in these waters. Obviously, the artificial about hundred-fold increase of overall Fe levels by addition of dissolved inorganic Fe(II) ions yields a major disruption of the natural physical-chemical abundances and reactivity of Fe in seawater. Hence the ensuing responses of the plankton ecosystem, while in itself significant, are not necessarily representative for a natural enrichment, for example by dry or wet deposition of aeolian dust.
Ultimately, the temporal changes of the Fe(III)-binding ligand and iron concentrations were dominated by the mixing events that occurred during EISENEX, with storms leading to more than an order of magnitude dilution of the dissolved ligands and iron concentrations. This had strongest impact on the colloidal size class (> 200 kDa-< 0.2 µm) where a dramatic decrease of both the colloidal ligand and the colloidal iron levels (Nishioka, J., Takeda, S., de Baar, H.J.W., Croot, P.L., Boye, M., Laan, P., Timmermans, K.R., 2005, Changes in the concentration of iron in different size fractions during an iron enrichment experiment in the open Southern Ocean. Marine Chemistry, doi:10.1016/j.marchem.2004.06.040) was observed
Major deviations of iron complexation during 22 days of a mesoscale iron enrichment in the open Southern Ocean
No full textThe speciation of strongly chelated iron during the 22-day course of an iron enrichment experiment in the Atlantic sector of the Southern Ocean deviates strongly from ambient natural waters. Three iron additions (ferrous sulfate solution) were conducted, resulting in elevated dissolved iron concentrations (Nishioka, J., Takeda, S., de Baar, H.J.W., Croot, P.L., Boye, M., Laan, P., Timmermans, K.R., in press. Changes in the concentration of iron in different size fractions during an iron enrichment experiment in the open Southern Ocean. Marine Chemistry.) and significant Fe(II) levels (Croot, P.L., Laan, P., Nishioka, J., Strass, V., Cisewski, B., Boye, M., Timmermans, K.R., Bellerby, R.G., Goldson, L., Nightingale, P., de Baar, H.J.W., in press. Spatial and Temporal distribution of Fe(II) and H2O2 during EisenEx, an open ocean mescoscale iron enrichment. Marine Chemistry.). Repeated vertical profiles for dissolved (filtrate 200 kDa–< 0.2 μm), as opposed to the soluble fraction (< 200 kDa) which dominated prior to the iron infusions. Yet these colloidal ligands would exist in a more transient nature than soluble ligands which may have a longer residence time. The production of dissolved Fe-chelators was generally smaller than the overall increase in dissolved iron in the surface infused mixed layer, leaving a fraction (about 13–40%) of dissolved Fe not bound by these dissolved Fe-chelators. It is suggested that this fraction would be inorganic colloids. The unexpected persistence of such high inorganic colloids concentrations above inorganic Fe-solubility limits illustrates the peculiar features of the chemical iron cycling in these waters. Obviously, the artificial about hundred-fold increase of overall Fe levels by addition of dissolved inorganic Fe(II) ions yields a major disruption of the natural physical–chemical abundances and reactivity of Fe in seawater. Hence the ensuing responses of the plankton ecosystem, while in itself significant, are not necessarily representative for a natural enrichment, for example by dry or wet deposition of aeolian dust.
Ultimately, the temporal changes of the Fe(III)-binding ligand and iron concentrations were dominated by the mixing events that occurred during EISENEX, with storms leading to more than an order of magnitude dilution of the dissolved ligands and iron concentrations. This had strongest impact on the colloidal size class (> 200 kDa–< 0.2 μm) where a dramatic decrease of both the colloidal ligand and the colloidal iron levels (Nishioka, J., Takeda, S., de Baar, H.J.W., Croot, P.L., Boye, M., Laan, P., Timmermans, K.R., in press. Changes in the concentration of iron in different size fractions during an iron enrichment experiment in the open Southern Ocean. Marine Chemistry.) was observed
Seasonal cycle of copper speciation in Gullmar Fjord, Sweden
No full textThe chemical speciation of dissolved Cu was investigated by voltammetric methods in Gullmar Fjord, Sweden, over the course of a year from September 1996 until August 1997. Sampling was carried out on a roughly monthly basis, with an intensive survey carried out in May 1997. Surface water temperatures ranged from 21 to 22°C, whereas bottom waters in the fjord were approximately 6°C throughout. Macronutrient concentrations in the fjord during the period of the survey were investigated independently by the Göteborgs och Bohus läns Vattenvårdsförbund (Water Quality Association of Göteborg and Bohus). Surface phosphate concentrations were highest in early spring with low levels ( 12.5) were not detected during the winter or early spring and could be related to the temperature-related seasonal appearance of the cyanobacterium Synechoccocus in these waters. The appearance of the strong Cu ligands led to a decrease in the concentration of free copper, resulting in a seasonal cycle for free copper in the fjord. This is the first study to examine Cu speciation over an annual cycle in a coastal environmen
- …
