311 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
Controls on seawater Fe(III) solubility in the Mauritanian upwelling zone
No full textIron solubility measurements in the Mauritanian upwelling and the adjacent Open Ocean of the Tropical Atlantic show for all stations lower values in the surface mixed layer than at depth below the pycnocline. We attribute this distribution to a combination of loss terms, chiefly photo-oxidation of organic ligands in the surface, and supply terms, predominantly from the release of ligands from the decomposition of organic matter. Significant correlations with pH, oxygen and phosphate for all samples below the surface mixed layer indicate that biogenic remineralisation of organic matter results in the release of iron binding ligands into the dissolved phase. The comparison of the cFe(S)/PO(4)(3-) ratio with other published data from intermediate and deep waters in the Pacific suggests an enhanced release of iron chelators in the more productive Mauritanian upwelling zone. Citation: Schlosser, C., and P.L. Croot (2009), Controls on seawater Fe(III) solubility in the Mauritanian upwelling zon
Copper speciation and distribution in the Atlantic sector of the Southern Ocean
No full textThe distribution and speciation of dissolved copper (Cu) was investigated in the Atlantic sector of the Southern Ocean in austral autumn of 2008 as part of the IPY GEOTRACES expedition ZERO & DRAKE. Distribution measurements focused on two transects across the major frontal systems along the Zero Meridian and across the Drake Passage whereas speciation work was investigated in the Drake Passage and the ice covered Weddell Sea. Along the two transects the dissolved Cu concentration exhibited a gradient in the surface with Cu values increasing poleward. Vertical profiles of Cu showed in general monotonic increases with depth, which correlated slightly with silicate but poorly with phosphate. Benthic sources of Cu were observed along the Zero Meridian transect and close to the Antarctic Peninsula for the Drake Passage. Dissolved Cu (DCu) appears to be removed from surface waters through adsorption/complexation by particulate matter. Speciation measurements on DCu indicated a relatively uniform distribution of 25-50nM of L2 (log K ~11.8) class ligands. No L1 class ligands (log K >13) were detected in any of the samples examined. Estimates of free Cu (pCu=13.5 to 12.5) showed only small variations in the upper water column and was generally uniform in deep waters. These findings indicate that there is insufficient free copper to account for the rapid reactivity of superoxide (O2 -) with Cu in these waters (Heller and Croot, 2010c) suggesting that the organic Cu complexes present in seawater can undergo rapid redox reactions
Application of flow cytometry and membrane inlet mass spectrometry as tools to assess dimethyl sulfide produced in emiliania huxleyi (CHC108) cultures
No full textDimethyl sulphide (DMS) is a key component in the global sulphur cycle with emphasized significance in areas away from anthropogenic sources. Phytoplankton produce DMS when under stress as a defence mechanism from abiotic and biotic influences such as high wind stress and grazing. E. huxleyi was used as the phytoplankton of choice because of the cosmopolitan nature of the species along with the more robust nature of the coccolith. DMS has a high diffusion rate in the atmosphere so immediately monitoring the levels in the water column has proven difficult especially when looking at continuous input flux. In this study, membrane inlet mass spectrometry was used to monitor DMS flux over varying periods of time along with a possible variation of DMS under Mass 47 which excludes one of the methyl groups under different stressors. This continuous observation allowed for the observation in minute changes over longer periods of time rather than using the snapshot method which looks at chemical concentrations at singular points in time. This novel technique can give insights to the response times of the phytoplankton to the changing environment in real time. The added stressors to the water column did result in an increase of DMS but the lag time to the addition and the visible increase in DMS did not follow the expected trend. Of the parameters tested here, the most likely to initiate DMS production is heavy metal loading and water column acidification
Space based observations of marine phytoplankton in NE Atlantic waters
No full textThe main aims of this PhD thesis were To develop a suite of satellite derived tools for the Irish monitoring programme for Harmful Algal Blooms (HABs) To highlight the importance of in situ data for validating satellite derived data and developing regional algorithms and address the gap in the availability of such data in the North East Atlantic. In situ data is essential for the calibration, validation and bio-optical algorithm development of ocean colour remote sensing. Chapter 2 describes in detail the difficulties associated with ocean colour measurements in Irish waters due to the persistent issue with cloud cover. This chapter introduces how invaluable the optical data collected is for ocean colour research, especially in areas that are difficult to sample frequently. The main aims of this thesis were achieved by the successful installation and development of an operational hyperspectral radiometer system on board the RV Celtic Explorer, which collects valuable data for satellite validation, algorithm development, and water quality monitoring. Additionally, in chapters 4 and 5, I present a successful validation of the Red Band Difference (RBD) algorithm to monitor HABs in Irish coastal waters, and a preliminary feasibility study of the HABscope, an artificial intelligence technology for detecting Karenia spp. via their swimming pattern. The primary goal of this thesis was accomplished by introducing the three products to the Irish monitoring programme. The developed tools, including the hyperspectral radiometry system, the RBD algorithm, and the HABscope, are valuable for monitoring marine phytoplankton and associated optically active constituents and can be utilised by the Marine Institute, Researchers, and the global ocean colour community for effective HAB monitoring and mitigation efforts
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
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
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