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Atmosphere-ocean interactions are known to dominate seasonal to decadal sea level variability in the southeastern North Sea. In this study an atmospheric proxy for the observed sea level variability in the German Bight is introduced. Monthly mean sea level (MSL) time series from 13 tide gauges located in the German Bight and one virtual station record are evaluated in comparison to sea level pressure fields over the North Atlantic and Europe. A quasi-linear relationship between MSL in the German Bight and sea level pressure over Scandinavia and the Iberian Peninsula is found. This relationship is used (1) to evaluate the atmospheric contribution to MSL variability in hindcast experiments over the period from 1871-2008 with data from the twentieth century reanalysis v2 (20CRv2), (2) to isolate the high frequency meteorological variability of MSL from longer-term changes, (3) to derive ensemble projections of the atmospheric contribution to MSL until 2100 with eight different coupled global atmosphere-ocean models (AOGCM's) under the A1B emission scenario and (4) two additional projections for one AOGCM (ECHAM5/MPI-OM) under the B1 and A2 emission scenarios. The hindcast produces a reasonable good reconstruction explaining approximately 80 % of the observed MSL variability over the period from 1871 to 2008. Observational features such as the divergent seasonal trend development in the second half of the twentieth century, i.e. larger trends from January to March compared to the rest of the year, and regional variations along the German North Sea coastline in trends and variability are well described. For the period from 1961 to 1990 the Kolmogorov-Smirnow test is used to evaluate the ability of the eight AOGCMs to reproduce the observed statistical properties of MSL variations. All models are able to reproduce the statistical distribution of atmospheric MSL. For the target year 2100 the models point to a slight increase in the atmospheric component of MSL with generally larger changes during winter months (October-March). Largest MSL changes in the order of ~5-6 cm are found for the high emission scenario A2, whereas the moderate B1 and intermediate A1B scenarios lead to moderate changes in the order of ~3 cm. All models point to an increasing atmospheric contribution to MSL in the German Bight, but the uncertainties are considerable, i.e. model and scenario uncertainties are in the same order of magnitude. [ABSTRACT FROM AUTHOR]

Abstract: The spatial and temporal evolution of the beta-emitting, anthropogenic radionuclide Technetium-99 (99Tc) in the North and Norwegian Seas have been simulated with a regional isopycnic Ocean General Circulation Model (OGCM), forced with realistic, daily averaged atmospheric forcing fields for the period 1975 to 2003. The main source of this soluble radionuclide is the reprocessing plants at Sellafield in the Irish Sea and La Hague on the French coast in the English Channel. The radioactive contaminants follow the general ocean circulation in the area, and are eventually transported northwards along the Norwegian coast heading towards the Arctic Ocean. Comparison with observational time series from two stations along the coast of Norway shows that the model fairly realistically captures both the amplitude and the temporal trend of 99Tc from Sellafield and La Hague. To isolate the effect of changes in the ocean circulation and mixing on the released tracers, idealized tracers with a clock attribution are included for both sources. These idealized tracers measure the age along the pathways of the tracers from the two sources. The age from the Sellafield-derived tracer at the island Hillesøy on the northern coast of Norway is found to be in the range 5–8 years, which is slightly older than previous estimates of the related concept of transit time. A complex pattern of variability is identified, with local and regional atmospheric forcing influencing both the northward tracer flux and the time elapsed since the tracer left the source. [Copyright &y& Elsevier]

Abstract Oceanic inflow is estimated to contribute more than 90% of the nutrient input into the North Sea. Variability in the volume, chemical properties, biological content and source of the inflowing water is thus likely to have a considerable effect on North Sea ecosystems. Changes seen in the plankton, and in particular Calanus finmarchicus and Calanus helgolandicus , over the last 40 years as measured by the Continuous Plankton Recorder survey, allow clear periods to be identified that appear to be associated with variability in inflow. Monthly estimates of inflow and outflow across a section between Orkney and Utsira in Norway as well as netflow (sum of Baltic outflow, runoff and Channel inflow), have been derived from runs of the NORWECOM model for two integrated depth intervals: surface to 150 m and >150 m. A comparison is made between the physical model output and plankton results for the period 1958–99. Distinct plankton periods that appear to reflect changing inflow events are discussed in relation to hydrometeorological and earlier plankton studies over approximately the last 100 years. [ABSTRACT FROM AUTHOR]