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Most applications of laser induced fluorescence (LIF) for dissolved oxygen (DO) imaging in flowing water are based on luminescence intensity measurements of a dissolved indicator. A major limitation for applying the technique in the bottom boundary layer (BBL) is the sorption of the luminescent dye to organic surfaces at the sediment. Many sediment and soil studies have used planar optodes on transparent foils as an imaging technique for observing concentration distributions across the sediment-water interface. The presence of the foil, however, is restricting the free flow and therewith the DO concentration above the sediment surface. In this study, we applied the phosphorescence lifetime LIF (τLIF) technique in combination with nanoparticles coated with platinum complexes as DO indicators. By using a planar laser light sheet for fluorescence excitation, the three-dimensional flow field around the sampling area is not restricted. In contrast to the intensity-based LIF technique, this method extracts the lifetime of the luminescence by evaluating the exponential decrease of the phosphorescence intensity after a short excitation light pulse. The method is therefore independent of dye concentration and is not affected by spatial inhomogeneities of the excitation light intensity. We applied the technique to visualize the burrow-ventilation activity of the tube-dwelling Chironomus plumosus larvae. Sequences of the two-dimensional DO concentration distributions showed the intermittent outburst of highly-depleted plumes from the outlet of the burrows, which mixed rapidly with the ambient oxygen-rich water. [ABSTRACT FROM AUTHOR]

ABSTRACT Annual air-sea exchange of CO2 in Young Sound, NE Greenland was estimated using pCO2 surface-water measurements during summer (2006-2009) and during an ice-covered winter 2008. All surface pCO2 values were below atmospheric levels indicating an uptake of atmospheric CO2. During sea ice formation, dissolved inorganic carbon (DIC) content is reduced causing sea ice to be under saturated in CO2. Approximately 1% of the DIC forced out of growing sea ice was released into the atmosphere while the remaining 99% was exported to the underlying water column. Sea ice covered the fjord 9 months a year and thereby efficiently blocked air-sea CO2 exchange. During sea ice melt, dissolution of CaCO3 combined with primary production and strong stratification of the water column acted to lower surface-water pCO2 levels in the fjord. Also, a large input of glacial melt water containing geochemically reactive carbonate minerals may contribute to the low surface-water pCO2 levels. The average annual uptake of atmospheric CO2 was estimated at 2.7 mol CO2 m−2 yr−1 or 32 g C m−2 yr−1 for the study area, which is lower than estimates from the Greenland Sea. Variability in duration of sea ice cover caused significant year-to-year variation in annual gas exchange. [ABSTRACT FROM AUTHOR]

Studies the flow-induced flushing of relict tube structures in the central Skagerrak, Norway. Benthic solute exchange rates; Flushing of Spiochaetopterus bergensis tube structures; Implications of tube flushing.