| 1. |
- Gustafsson, Örjan, et al.
(författare)
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Colloid dynamics and transport of major elements through a boreal river - brackish bay mixing zone
- 2000
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Ingår i: Marine Chemistry. - 0304-4203 .- 1872-7581. ; 71:1-2, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- A range of biogeochemical methodologies were applied to investigate how aggregation processes affected the phase distribution and mixing of Fe, Si, and organic carbon between the Kalix River and the Bothnic Bay, northernmost Baltic Sea (salinity≤3; the low-salinity zone (LSZ) was stretching over 60 km in the spring). During the dynamic springflood conditions studied, small 238U-234Th disequilibria, low sediment trap fluxes, laboratory mixing experiments, as well as results from an independent two-box, two-dimensional mixing model combine to suggest that no significant removal of Fe, Si, or organic C was occurring in the highly-resolved LSZ. While no conclusions may be drawn based solely on property-salinity plots over narrow salinity ranges, apparently linear graphs for Fe and Si over 3 separate years also suggest minimal removal in this regime. At the same time, size distributions both of elements -from cross-flow ultrafiltration - and of bulk suspended solids - from light scattering (photon correlation spectroscopy [PCS]) - indicated that significant aggregation was taking place.The aggregation-without-significant-settling scenario in this low-salinity mixing regime, with a geochemistry similar to that of neighboring Russian Arctic rivers, is hypothesized to result from a comparatively high organic-to-detrital matter characteristic of the aggregates. While first principles would indeed suggest that decreasing electrostatic repulsion during mixing lead to aggregation, a low specific density of mineral-poor amorphous organic aggregates may lead to transport of these authigenic particles further away from the river mouth. The role of detrital "sinkers" on vertical removal of suspended organic matter is discussed in the wider context of scavenging mechanisms in the ocean.
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| 2. |
- Bigg, E Keith, et al.
(författare)
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Particulates of the surface microlayer of open water in the central Arctic Ocean in summer
- 2004
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 91, s. 131-141
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Tidskriftsartikel (refereegranskat)abstract
- The particulate content of samples of the surface microlayer water collected from the open water between ice floes at latitudes 88° to 89°N in August 2001 was examined by transmission electron microscopy. Concentrations varied from 2×107 ml−1 to more than 1014 ml−1 although bacterial counts made in the same samples varied by only about 50%. Size distributions of the particles were also very variable with modal diameter sizes of 10 nm in some samples and 50 nm in others, the 50-nm particles appearing to be clusters of the 10 nm ones. A mucus-like material held the particles together in rafts, strings or in balls. The largest particles were compact electron-opaque aggregates of smaller particles. The particles appeared to have very similar characteristics to the “microcolloids” observed in bulk seawater in lower latitude oceans. X-ray analyses of the elements with atomic numbers >16 showed all signals to be weak, suggesting a mainly organic composition. The elements that were most commonly greater than background levels were all those associated with marine biological activity. Rapid aggregation of polymers to form colloids has been noted and is likely to be an important cause of the observed variability of particulate concentrations in the surface microlayer. The possibility of an equally rapid dispersal under the influence of ultraviolet light is raised.
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| 3. |
- Ingri, Johan, et al.
(författare)
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Size distribution of colloidal trace metals and organic carbon during a coastal bloom in the Baltic Sea
- 2004
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203 .- 1872-7581. ; 91:1-4, s. 117-130
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Tidskriftsartikel (refereegranskat)abstract
- The physico-chemical speciation of organic carbon and selected metals was measured during a coastal bloom in Ekhagen Bay, Baltic Sea, using ultrafiltration.One important objective with the study was to see if any depletion of trace metals could be measured in the directly bioavailable fraction (<1000 Da, the soluble low molecular weight fraction, LMW) during a plankton bloom. Filters with five different cut-offs were used (1 kD (1000 Da), 5 kD, 10 kD, 100 kD and 0.22 μm) in order to delineate the size distribution of colloidal organic carbon (COC) and trace metals. During the bloom in May, LMW Al, Co, Cu, Mn and Ni concentrations decreased although the colloidal and particulate concentrations were relatively high. Data show that desorption of colloidal and particulate bound trace metals to the LMW fraction was slower than the process depleting the LMW fraction. Estimates of the maximum active uptake of Cu, Ni and Mn by the phytoplankton, and the loss of non-bioactive Al from the LMW fraction, indicate that processes other than active uptake by phytoplankton must contribute to the observed depletion of trace metals in the LMW fraction. Hence, in order to estimate the bioavailable pool of trace metals for plankton during bloom conditions, these other processes must be understood and quantified. Transparent Exopolymeric Particles (TEP, reflecting sugar-rich phytoplankton exudates) increased around eight times during the plankton bloom. We hypothesize that the formation of TEP is a process that might be important for the transfer of trace metals from the LMW to the particulate fraction during the phytoplankton bloom, but the significance of TEP for this depletion in Baltic Sea surface water remains to be shown.
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