| 1. |
- Bigg, E Keith, et al.
(author)
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Particulates of the surface microlayer of open water in the central Arctic Ocean in summer
- 2004
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In: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 91, s. 131-141
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Journal article (peer-reviewed)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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| 2. |
- Bigg, E. Keith, et al.
(author)
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The composition of fragments of bubbles bursting at the ocean surface
- 2008
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In: Journal of geophysical research: Atmospheres. ; 113:D11, s. D11209-
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Journal article (peer-reviewed)abstract
- Air bubbles bursting on artificial seawater in laboratory experiments have been found to inject numerous particles <200 nm diameter into the atmosphere, some experiments showing copious production of particles as small as 10 nm. Some observations of the real marine aerosol support the presence of a large proportion of sea salt <200 nm diameter, while others suggest that it is absent, or nearly so. It is argued here that the observations showing its presence may be misinterpretations. If this is so, modification of currently accepted theories of particle injection into the atmosphere by bursting bubbles would be required. Highly surface active exopolymers produced by bacteria and algae, the microgels formed by them, and large concentrations of submicrometer particulates are known to be present in the ocean. Their possible influence on bubble formation, bubble bursting and particle injection into the atmosphere are discussed. Electron microscopy of individual particles at a number of sites supports the proposal that the exopolymers are involved in these processes. Ultraviolet light and acidification cause structural and chemical changes to exopolymers and their gels exposed to the atmosphere so that marine aerosol will have properties that change with atmospheric residence time.
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| 3. |
- Leck, Caroline, et al.
(author)
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A modified aerosol-cloud-climate feedback hypothesis
- 2007
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In: Environmental Chemistry. - 1448-2517 .- 1449-8979. ; 4:6, s. 400-403
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Journal article (peer-reviewed)abstract
- Problems with the aerosol–cloud–climate feedback process known as the ‘CLAW’ hypothesis are discussed and a modified scheme that poses a stronger possible link between marine biology, cloud properties and climate than is provided by dimethyl sulfide alone is proposed.
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| 4. |
- Leck, Caroline, et al.
(author)
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Comparison of sources and nature of the tropical aerosol with the summer high Arctic aerosol
- 2008
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In: Tellus. Series B: Chemical and physical meteorology. ; 60:1, s. 118-126
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Journal article (peer-reviewed)abstract
- Marine aerosol was collected in September 1998 and July 2005 on the upwind coast of an island at latitude 15◦ S, about 15 km downwind from the outer edge of the Great Barrier Reef, Australia, and examined by electron microscopy.Exopolymer gels, aggregates of organic particles, marine micro-organisms and fragments of marine life formed a substantial part of the accumulation mode aerosol. Differences in transparency, firmness of outlines and shape of gels and the influence of organic vapours on them, suggested progressive physical and chemical changes with atmospheric residence time. The organic aggregate components had a size distribution remarkably close to that found in similar particles over the central Arctic Ocean peaking at diameters of 30–40 nm. Single components or small groups of these aggregates were found within at least 75% of particles resembling ammonium sulphate in appearance, indicating that aggregates fragmented in the atmosphere. Sea salt was not detected in particles <200 nm diameter unlike many observations showing it to be a major component, a result that was entirely consistent with the Arctic findings. The deduced sequence of changes to particles entering the atmosphere from the ocean is also very similar to that found in the Arctic, suggesting that it is a common pattern over the oceans. That conclusion would require modification of the parametrization of the marine aerosol used in climate models and of possible climate feedback effects.
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| 5. |
- Leck, Caroline, et al.
(author)
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New Particle Formation of Marine Biological Origin
- 2010
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In: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 44:7, s. 570-577
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Journal article (peer-reviewed)abstract
- Large increases in concentration of particles smaller than 20 nm diameter are relatively common over the central Arctic Ocean in summer and have occasionally been observed over lower latitude oceans. These events often do not readily fit theoretical models of homogeneous nucleation from known precursor gases. It is shown that aggregates and gels of marine biological origin are often common over remote oceans and have a partially granular structure. Previous work in the central Arctic Ocean in summer has shown evidence of release of particles of the order of 40 nm diameter in the presence of evaporating fogs. It is suggested here that under some circumstances disintegration of the primary particles may be more complete, releasing particles smaller than 5 nm that would then be mistaken for recently nucleated particles. Examination of particles present during an apparent nucleation event at Cape Grim, Tasmania supports this interpretation. Correlation coefficients of concentrations of particles of different sizes during the period before apparent nucleation events suggests a distinct difference between vigorous true nucleation events and those over the central Arctic Ocean in summer where little subsequent growth is observed.
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| 6. |
- Welti, André, et al.
(author)
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Ship-based measurements of ice nuclei concentrations over the Arctic, Atlantic, Pacific and Southern oceans
- 2020
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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:23, s. 15191-15206
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Journal article (peer-reviewed)abstract
- Ambient concentrations of ice-forming particles measured during ship expeditions are collected and summarised with the aim of determining the spatial distribution and variability in ice nuclei in oceanic regions. The presented data from literature and previously unpublished data from over 23 months of ship-based measurements stretch from the Arctic to the Southern Ocean and include a circumnavigation of Antarctica. In comparison to continental observations, ship-based measurements of ambient ice nuclei show 1 to 2 orders of magnitude lower mean concentrations. To quantify the geographical variability in oceanic areas, the concentration range of potential ice nuclei in different climate zones is analysed by meridionally dividing the expedition tracks into tropical, temperate and polar climate zones. We find that concentrations of ice nuclei in these meridional zones follow temperature spectra with similar slopes but vary in absolute concentration. Typically, the frequency with which specific concentrations of ice nuclei are observed at a certain temperature follows a log-normal distribution. A consequence of the log-normal distribution is that the mean concentration is higher than the most frequently measured concentration. Finally, the potential contribution of ship exhaust to the measured ice nuclei concentration on board research vessels is analysed as function of temperature. We find a sharp onset of the influence at approximately -36 degrees C but none at warmer temperatures that could bias ship-based measurements.
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