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End date: 2020 × Start date: 2020 × Start date: 1990 × DDC: 550 × Subject: Arctic Ocean ×

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Now showing 1 - 4 of 4
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    Aerosol number size distributions from 3 to 500 nm diameter in the arctic marine boundary layer during summer and autumn
    (Copenhagen : Blackwell Munksgaard, 1996) Covert, D.S.; Wiedensohler, A.; Aalto, P.; Heintzenberg, J.; Mcmurry, P.H.; Leck, C.
    Aerosol physics measurements made onboard the Swedish icebreaker Oden in the late Summer and early Autumn of 1991 during the International Arctic Ocean Expedition (IAOE-91) have provided the first data on the size distribution of particles in the Arctic marine boundary layer (MBL) that cover both the number and mass modes of the size range from 3 to 500 nm diameter. These measurements were made in conjunction with atmospheric gas and condensed phase chemistry measurements in an effort to understand a part of the ocean-atmosphere sulfur cycle. Analysis of the particle physics data showed that there were three distinct number modes in the submicrometric aerosol in the Arctic MBL. These modes had geometric mean diameters of around 170 nm. 45 nm and 14 nm referred to as accumulation, Aitken and ultrafine modes, respectively. There were clear minima in number concentrations between the modes that appeared at 20 to 30 nm and at 80 to 100 nm. The total number concentration was most frequently between 30 and 60 particles cm-3 with a mean value of around 100 particles cm-3, but the hourly average concentration varied over two to three orders of magnitude during the 70 days of the expedition. On average, the highest concentration was in the accumulation mode that contained about 45% of the total number, while the Aitken mode contained about 40%. The greatest variability was in the ultrafine mode concentration which is indicative of active, earby sources (nucleation from the gas phase) and sinks; the Aitken and accumulation mode concentrations were much less variable. The ultrafine mode was observed about two thirds of the time and was dominant 10% of the time. A detailed description and statistical analysis of the modal aerosol parameters is presented here.
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    A hindcast simulation of Arctic and Antarctic sea ice variability, 1955-2001
    (Tromsø : Norwegian Polar Institute, 2003) Fichefet, T.; Goosse, H.; Morales Maqueda, M.A.
    A hindcast simulation of the Arctic and Antarctic sea ice variability during 1955-2001 has been performed with a global, coarse resolution ice-ocean model driven by the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis daily surface air temperatures and winds. Both the mean state and variability of the ice packs over the satellite observing period are reasonably well reproduced by the model. Over the 47-year period, the simulated ice area (defined as the total ice-covered oceanic area) in each hemisphere experiences large decadal variability together with a decreasing trend of ∼1% per decade. In the Southern Hemisphere, this trend is mostly caused by an abrupt retreat of the ice cover during the second half of the 1970s and the beginning of the 1980s. The modelled ice volume also exhibits pronounced decadal variability, especially in the Northern Hemisphere. Besides these fluctuations, we detected a downward trend in Arctic ice volume of 1.8% per decade and an upward trend in Antarctic ice volume of 1.5% per decade. However, caution must be exercised when interpreting these trends because of the shortness of the simulation and the strong decadal variations. Furthermore, sensitivity experiments have revealed that the trend in Antarctic ice volume is model-dependent.
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    Near-ubiquity of ice-edge blooms in the Arctic
    (Göttingen : Copernicus GmbH, 2011) Perrette, M.; Yool, A.; Quartly, G.D.; Popova, E.E.
    Ice-edge blooms are significant features of Arctic primary production, yet have received relatively little attention. Here we combine satellite ocean colour and sea-ice data in a pan-Arctic study. Ice-edge blooms occur in all seasonally ice-covered areas and from spring to late summer, being observed in 77-89% of locations for which adequate data exist, and usually peaking within 20 days of ice retreat. They sometimes form long belts along the ice-edge (greater than 100 km), although smaller structures were also found. The bloom peak is on average more than 1 mg m-3, with major blooms more than 10 mg m -3, and is usually located close to the ice-edge, though not always. Some propagate behind the receding ice-edge over hundreds of kilometres and over several months, while others remain stationary. The strong connection between ice retreat and productivity suggests that the ongoing changes in Arctic sea-ice may have a significant impact on higher trophic levels and local fish stocks.
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    Polynyas in a high-resolution dynamic-thermodynamic sea ice model and their parameterization using flux models
    (Abingdon : Taylor and Francis Ltd., 2001) Bjornsson, H.; Willmott, A.J.; Mysak, L.A.; Morales Maqueda, M.A.
    This paper presents an analysis of the solutions for a steady state latent heat polynya generated by an applied wind stress acting over a semi-enclosed channel using: (a) a dynamic-thermodynamic sea ice model, and (b) a steady state flux model. We examine what processes in the sea ice model are responsible for the maintenance of the polynya and how sensitive the results are to the choice of rheological parameters. We find that when the ice is driven onshore by an applied wind stress, a consolidated ice pack forms downwind of a zone of strong convergence in the ice velocities. The build-up of internal stresses within the consolidated ice pack becomes a crucial factor in the formation of this zone and results in a distinct polynya edge. Furthermore, within the ice pack the across-channel ice velocity varies with the across-channel distance. It is demonstrated that provided this velocity is well represented, the steady state polynya flux model solutions are in close agreement with those of the sea ice model. Experiments with the sea ice model also show that the polynya shape and area are insensitive to (a) the sea ice rheology; (b) the imposition of either free- slip or no-slip boundary conditions. These findings are used in the development of a simplified model of the consolidated ice pack dynamics, the output of which is then compared with the sea ice model results. Finally, we discuss the relevance of this study for the modelling of the North Water Polynya in northern Baffin Bay.