The bottom boundary layer model approach of Beckmann and Doescher has been adopted for application in a coarse-resolution model of the North Atlantic Ocean. Both components of the approach (advective ...and conditional diffusive) are found to affect the deep water stratification and circulation. A significant deepening of the downward spreading North Atlantic Deep Water (NADW) is the major effect. This is associated with an enhanced spatial coverage of the NADW cell in the meridional circulation.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The authors use different versions of the model of the wind- and thermohaline-driven circulation in the North and Equatorial Atlantic developed under the WOCE Community Modeling Effort to investigate ...the mean flow pattern and deep-water formation in the subpolar region, and the corresponding structure of the basin-scale meridional overturning circulation transport. A suite of model experiments has been carried out in recent years, differing in horizontal resolution (1 degrees x 1.2 degrees , 1/3 degrees x 0.4 degrees , 1/6 degrees x 0.2 degrees ), thermohaline boundary conditions, and parameterization of small-scale mixing. The mass transport in the subpolar gyre and the production of North Atlantic Deep Water (NADW) appears to be essentially controlled by the outflow of dense water from the Greenland and Norwegian Seas, in the present model simulated by restoring conditions in a buffer zone adjacent to the boundary near the Greenland-Scotland Ridge. Deep winter convection homogenizes the water column in the center of the Labrador Sea to about 2000 m. The water mass properties (potential temperature about 3 degrees C, salinity about 34.9 psu) and the volume (1.1 x 10 super(5) km super(3) ) of the homogenized water are in fair agreement with observations. The convective mixing has only little effect on the net sinking of upper-layer water in the subpolar gyre. Sensitivity experiments show that the export of NADW from the subpolar North Atlantic is more strongly affected by changes in the overflow conditions than by changes in the surface buoyancy fluxes over the Labrador and Irminger Seas, even if these suppress the deep convection completely. The host of sensitivity experiments demonstrates that realistic meridional overturning and heat transport distributions for the North Atlantic (with a maximum of 1 PW) can be obtained with NADW production rates of 15-16 Sv, provided the spurious upwelling of deep water that characterizes many model solutions in the Gulf Stream regime is avoided by adequate horizontal resolution and mixing parameterization.
The heat and water cycles of the Baltic Sea are calculated utilizing multi-year model simulations. This is one of the major objectives of the BALTEX program. For the period 1988–1993, results of a 3D ...ice-ocean model forced with observed atmospheric surface fields are compared with results of a fully coupled atmosphere-ice-ocean model using re-analysis data at the lateral boundaries. The state-of-the-art coupled model system has been developed for climate study purposes in the Nordic countries. The model domain of the atmosphere model covers Scandinavia, Europe and parts of the North Atlantic whereas the ocean model is limited to the Baltic Sea. The annual and monthly mean heat budgets for the Baltic Sea are calculated from the dominating surface fluxes, i.e. sensible heat, latent heat, net longwave radiation and solar radiation to the open water or to the sea ice. The main part of the freshwater inflow to the Baltic is the river runoff. A smaller part of about 11% is added from net precipitation. The heat and water cycles are compared with the results of a long-term simulation (1980–1993) using the stand-alone Baltic Sea model forced with observed atmospheric surface fields. In general, both approaches, using the uncoupled or coupled Baltic Sea model, give realistic estimates of the heat and water cycles and are in good agreement with results of other studies. However, in the coupled model the parameterizations of the latent heat flux and the incoming longwave radiation need to be improved.
To avoid an explicit simulation of the overflows across the Greenland-Scotland ridge, many models of the large-scale ocean circulation seek to include the net effect of the inflowing dense water ...masses by restoring temperature and salinity near the ridge to observed conditions. In this paper the authors examine the effect of different datasets for the northern restoring condition in two versions, eddy resolving and non-eddy resolving, of the model of the North and equatorial Atlantic that has been developed in recent years as a Community Modeling Effort for WOCE. It is shown that the use of smoothed climatological fields of temperature and salinity south of the Denmark Strait leads to strong deficiencies in the simulation of the deep flow field in the basin. A switch to actual hydrographic data from the Denmark Strait ignites a rapid dynamic response throughout the North Atlantic, affecting transport and vertical structure of the deep western boundary current and, by virtue of the JEBAR effect, the transport of the horizontal gyres.
A high-resolution model of the wind-driven and thermohaline circulation in the North and equatorial Atlantic Ocean is used to study the structure and variability of the boundary current system at 26 ...degree N, including the Florida Current, the Antilles Current, and the Deep Western Boundary Current (DWBC). The model was developed by Bryan and Holland as a Community Modeling Effort of the World Ocean Circulation Experiment. Subsequent experiments have been performed at IfM Kiel, with different friction coefficients, and different climatologies of monthly mean wind stress: Hellerman-Rosenstein (HR) and Isemer-Hasse (IH). The southward volume transports in the upper 1000 m of the interior Atlantic, at 26 degree N, are 25.0 Sv (Sv identical with 10 super(6) m super(3)/s) for HR, and 34.9 Sv for IH forcing, in good agreement with the transport from the integrated Sverdrup balance at this latitude (23.9 Sv for HR, 35.6 Sv for IH). The return flow of this wind-driven transport, plus the southward transport of the DWBC (6-8 Sv), is partitioned between the Florida Current and Antilles Current.
The monthly mean wind stress climatology of Hellerman and Rosenstein (HR) is compared with the climatology of Isemer and Hasse (IH), which represents a version of the Bunker atlas (BU) for the North ...Atlantic based on revised parameterizations. The drag coefficients adopted by IH are 21% smaller than the values of BU and HR, and the calculation of wind speed from marine estimates of Beaufort force (Bft) is based on a revised Beaufort equivalent scale similar to the scientific scale recommended by WMO. The latter choice significantly increases wind speed below Bft 8, and effectively counteracts the reduction of the drag coefficients. An eddy-resolving model of the North Atlantic circulation is used to examine the effect of the different wind stresses on the seasonal cycle of the Florida Current. The transport predicted by the numerical model is in much better agreement with observations when the circulation is forced by IH than by HR, regarding both the annual mean (29.1 Sv vs 23.2 Sv) and the seasonal range (6.3 Sv vs 3.4 Sv).
In this study, we demonstrate how functional groups on the surface of mesoporous silica nanoparticles (MSNPs) can influence the encapsulation and release of the anticancer drug doxorubicin, as well ...as cancer cell response in the absence or presence of serum proteins. To this end, we synthesized four differently functionalized MSNPs with amine, sulfonate, polyethylene glycol, or polyethylene imine functional surface groups, as well as one type of antibody-conjugated MSNP for specific cellular targeting, and we characterized these MSNPs regarding their physicochemical properties, colloidal stability in physiological media, and uptake and release of doxorubicin in vitro. Then, the MSNPs were investigated for their cytotoxic potential on cancer cells. Cationic MSNPs could not be loaded with doxorubicin and did therefore not show any cytotoxic and antiproliferative potential on osteosarcoma cells, although they were efficiently taken up into the cells in the presence or absence of serum. In contrast, substantial amounts of doxorubicin were loaded into negatively charged and unfunctionalized MSNPs. Especially, sulfonate-functionalized doxorubicin-loaded MSNPs were efficiently taken up into the cells in the presence of serum and showed an accelerated toxic and antiproliferative potential compared to unfunctionalized MSNPs, antibody-conjugated MSNPs, and even free doxorubicin. These findings stress the high importance of the surface charge as well as of the protein corona for designing and applying nanoparticles for targeted drug delivery.
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