Montreal, Canada

Time filter

Source Type

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.


Holt J.,National Oceanography Center | Schrum C.,Institute of Coastal Research | Schrum C.,University of Bergen | Cannaby H.,Middle East Technical University | And 13 more authors.
Progress in Oceanography | Year: 2016

Regional seas are potentially highly vulnerable to climate change, yet are the most directly societally important regions of the marine environment. The combination of widely varying conditions of mixing, forcing, geography (coastline and bathymetry) and exposure to the open-ocean makes these seas subject to a wide range of physical processes that mediates how large scale climate change impacts on these seas' ecosystems. In this paper we explore the response of five regional sea areas to potential future climate change, acting via atmospheric, oceanic and terrestrial vectors. These include the Barents Sea, Black Sea, Baltic Sea, North Sea, Celtic Seas, and are contrasted with a region of the Northeast Atlantic. Our aim is to elucidate the controlling dynamical processes and how these vary between and within these seas. We focus on primary production and consider the potential climatic impacts on: long term changes in elemental budgets, seasonal and mesoscale processes that control phytoplankton's exposure to light and nutrients, and briefly direct temperature response. We draw examples from the MEECE FP7 project and five regional model systems each using a common global Earth System Model as forcing. We consider a common analysis approach, and additional sensitivity experiments.Comparing projections for the end of the 21st century with mean present day conditions, these simulations generally show an increase in seasonal and permanent stratification (where present). However, the first order (low- and mid-latitude) effect in the open ocean projections of increased permanent stratification leading to reduced nutrient levels, and so to reduced primary production, is largely absent, except in the NE Atlantic. Even in the two highly stratified, deep water seas we consider (Black and Baltic Seas) the increase in stratification is not seen as a first order control on primary production. Instead, results show a highly heterogeneous picture of positive and negative change arising from complex combinations of multiple physical drivers, including changes in mixing, circulation and temperature, which act both locally and non-locally through advection. © 2015 The Authors.


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.


Daewel U.,Sensing Dynamics | Daewel U.,University of Bergen | Schrum C.,Sensing Dynamics | Schrum C.,University of Bergen | Gupta A.K.,University of Bergen
Marine Ecology Progress Series | Year: 2015

Using a spatially explicit individual-based model (IBM), we examined the potential larval survival (PLS) and growth of early life stages of Atlantic cod Gadus morhua in the North Sea ecosystem in response to changes in physical and biological forcing. We employed a 3-dimensional coupled model system that includes a hydrodynamic model, a physiologically based IBM and the lower trophic level ecosystem model ECOSMO, to provide related prey fields. The statistical analysis of a long-term (1949 to 2008) hindcast integration and the comparison to a set of 30-yr-long scenario experiments revealed a strong impact of atmospheric forcing on changes in PLS, where variations in transport processes and in the prey field are equally as important as temperature-dependent processes. Furthermore, the scenario experiments show that the different impacting environmental factors interact non-linearly and are non-homogeneous in time and space. A correlation analysis between estimated PLS and observed Atlantic cod recruitment in the North Sea indicated that time periods of high correlation alternate with periods of low or negative correlation. In the 1960s and from the end of the 1980s onwards, we identified high correlations between estimated PLS and recruitment and concluded that the model exhibits a significant predictive potential for cod recruitment during these periods. However, we also identified contrasting periods, e.g. during the 1970s and 1980s, for which we conclude that recruitment variability during these periods was significantly influenced by alternative processes, such as top-down or bottom-up controls during post-larval life stages. © Inter-Research 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.


Davy R.,Sensing Dynamics | Esau I.,Sensing Dynamics
Atmospheric Science Letters | Year: 2014

New results from the Coupled Model Intercomparison Project phase 5 (CMIP5) and multiple global reanalysis datasets are used to investigate the relationship between the mean and standard deviation (SD) in the surface air temperature (SAT) at intra- and inter-annual timescales. A combination of a land-sea mask and orographic filter was used to investigate the geographic region with the strongest correlation and in all cases this was found to be for low-lying over-land locations. This result is consistent with the expectation that differences in the effective heat capacity of the atmosphere are an important factor in determining the SAT response to forcing. © 2013 Royal Meteorological Society.


Loading Sensing Dynamics collaborators
Loading Sensing Dynamics collaborators