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Samuelsen A.,Sensing Dynamics | Hansen C.,Norwegian Institute of Marine Research | Wehde H.,Norwegian Institute of Marine Research
Geoscientific Model Development | Year: 2015

The HYCOM-NORWECOM (HYbrid Coordinate Ocean Model-NORWegian ECOlogical Model) modeling system is used both for basic research and as a part of the forecasting system for the Arctic Marine Forecasting Centre through the MyOcean project. Here we present a revised version of this model. The present model, as well as the sensitivity simulations leading up to this version, have been compared to a data set of in situ measurements of nutrient and chlorophyll from the Norwegian Sea and the Atlantic sector of the Arctic Ocean. The model revisions having the most impact included adding diatoms to the diet of microzooplankton, increasing microzooplankton grazing rate and decreasing the silicate-to-nitrate ratio in diatoms. Model runs are performed both with a coarse- (∼ 50 km) and higher-resolution (∼ 15 km) model configuration, both covering the North Atlantic and Arctic oceans. While the new model formulation improves the results in both the coarse- and high-resolution model, the nutrient bias is smaller in the high-resolution model, probably as a result of the better resolution of the main processes and improved circulation. The final revised version delivers satisfactory results for all three nutrients as well as improved results for chlorophyll in terms of the annual cycle amplitude. However, for chlorophyll the correlation with in situ data remains relatively low. Besides the large uncertainties associated with observational data this is possibly caused by the fact that constant C:N- and Chl:N ratios are implemented in the model. © Author(s) 2015.

Kural C.,Harvard University | Kural C.,Ohio State University | Tacheva-Grigorova S.K.,Harvard University | Boulant S.,Harvard University | And 7 more authors.
Cell Reports | Year: 2012

Clathrin/AP1- and clathrin/AP3-coated vesicular carriers originate from endosomes and the trans-Golgi network. Here, we report the real-time visualization of these structures in living cells reliably tracked by rapid, three-dimensional imaging with the use of a spinning-disk confocal microscope. We imaged relatively sparse, diffraction-limited, fluorescent objects containing chimeric fluorescent protein (clathrin light chain, σ adaptor subunits, or dynamin2) with a spatial precision of up to ∼30 nm and a temporal resolution of ∼1 s. The dynamic characteristics of the intracellular clathrin/AP1 and clathrin/AP3 carriers are similar to those of endocytic clathrin/AP2 pits and vesicles; the clathrin/AP1 coats are, on average, slightly shorter-lived than their AP2 and AP3 counterparts. We confirmed that although dynamin2 is recruited as a burst to clathrin/AP2 pits immediately before their budding from the plasma membrane, we found no evidence supporting a similar association of dynamin2 with clathrin/AP1 or clathrin/AP3 carriers at any stage during their lifetime. We found no effects of chemical inhibitors of dynamin function or the K44A dominant-negative mutant of dynamin on AP1 and AP3 dynamics. This observation suggests that an alternative budding mechanism, yet to be discovered, is responsible for the scission step of clathrin/AP1 and clathrin/AP3 carriers.

Tack A.,Finnish Meteorological Institute | Koskinen J.,Finnish Geodetic Institute | Hellsten A.,Finnish Meteorological Institute | Sievinen P.,Aalto University | And 4 more authors.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing | Year: 2012

This paper presents a morphological database, aimed to be applied as boundary data for atmospheric modeling. The database has been created from freely available sources and 13 ASAR images that were provided by European Space Agency (ESA) through Announcement of Opportunity (AO). Urban themes were extracted from optical data and digital maps by supervised spectral minimum distance to means classification. Urban topography was modeled using multibaseline Interferometric Synthetic Aperture Radar (InSAR) with phase unwrapping based on Maximum Likelihood (ML) estimation. In combining obtained InSAR height data with urban classification from optical images, additional features that are beyond the SAR resolution were added to the urban topography layer. The methods of retrieval of morphological data are discussed as well as the generation of the height model. The results are compared to the existing Shuttle Radar Topography Mission (SRTM) elevation model and the BDTopo Parisian database. We also address an example application of the database, a Large Eddy Simulation (LES) of urban canopy flow over the Paris area. © 2008-2012 IEEE.

Kedra M.,Polish Academy of Sciences | Kedra M.,University of Maryland Center for Environmental science | Moritz C.,Institute des Sciences de la Mer de Rimouski | Moritz C.,EPHE Paris | And 12 more authors.
Polar Research | Year: 2015

Ongoing climate warming is causing a dramatic loss of sea ice in the Arctic Ocean, and it is projected that the Arctic Ocean will become seasonally ice-free by 2040. Many studies of local Arctic food webs now exist, and with this review paper we aim to synthesize these into a large-scale assessment of the current status of knowledge on the structure of various Arctic marine food webs and their response to climate change, and to sea-ice retreat in particular. Key drivers of ecosystem change and potential consequences for ecosystem functioning and Arctic marine food webs are identified along the sea-ice gradient, with special emphasis on the following regions: seasonally ice-free Barents and Chukchi seas, loose ice pack zone of the Polar Front and Marginal Ice Zone, and permanently sea-ice covered High Arctic. Finally, we identify knowledge gaps in different Arctic marine food webs and provide recommendations for future studies. © 2015 M. Kȩdra et al.

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