Lagrangian pathways under the Filchner-Ronne ice shelf and in the Weddell Sea

Peer reviewe

Transport and Fate of 137Cs Released From Multiple Sources in the North Atlantic and Arctic Oceans

The North Atlantic and Arctic oceans, along with the North Pacific, are the main reservoirs of anthropogenic radionuclides introduced in the past 75 years. The POSEIDON-R compartment model was applied to the North Atlantic and Arctic oceans to reconstruct 137Cs contamination in 1945–2020 due to multiple sources: global fallout, exchange flows with other oceans, point-source inputs in the ocean from reprocessing plants and other nuclear facilities, the impact of the Chernobyl accident and secondary contamination resulting from river runoff and redissolution from bottom sediments. The model simulated the marine environment as a system of 3D compartments comprising the water column, bottom sediment, and biota. The dynamic model described the transfer of 137Cs through the pelagic and benthic food chains. The simulation results were validated using the marine database MARIS. The calculated concentrations of 137Cs in the seaweed and non-piscivorous and piscivorous pelagic fish mostly followed the concentration of 137Cs in water. The concentration in coastal predator fish lagged behind the concentration in water as a result of a diet that includes both pelagic and benthic organisms. The impact of each considered source on the total concentration of 137Cs in non-piscivorous fish in the regions of interest was analyzed. Whereas the contribution from global fallout dominated in 1960–1970, in 1970–1990, the contribution of 137Cs released from reprocessing plants exceeded the contributions from other sources in almost all considered regions. Secondary contamination due to river runoff was less than 4% of ocean influx. The maximum total inventory of 137Cs in the Arctic Ocean (31,122 TBq) was reached in 1988, whereas the corresponding inventory in the bottom sediment was approximately 6% of the total. The general agreement between simulated and observed 137Cs concentrations in water and bottom sediment was confirmed by the estimates of geometric mean and geometric standard deviation, which varied from 0.89 to 1.29 and from 1.22 to 1.87, respectively. The approach used is useful to synthesize measurement and simulation data in areas with observational gaps. For this purpose, 13 representative regions in the North Atlantic and Arctic oceans were selected for monitoring by using the “etalon” method for classification

A fully coupled 3D wave-current interaction model on unstructured grids

We present a new modeling system for wave-current interaction based on unstructured grids and thus suitable for very large-scale high-resolution multiscale studies. The coupling between the 3D current model (SELFE) and the 3rd generation spectral wave model (WWM-II) is done at the source code level and the two models share same sub-domains in the parallel MPI implementation in order to ensure parallel efficiency and avoid interpolation. We demonstrate the accuracy, efficiency, stability and robustness of the coupled SELFE-WWM-II model with a suite of progressively challenging benchmarks with analytical solution, laboratory data, and field data. The coupled model is shown to be able to capture important physics of the wave-current interaction under very different scales and environmental conditions with excellent convergence properties even in complicated test cases. The challenges in simulating the 3D wave-induced effects are highlighted as well, where more research is warranted

Fukushima Daiichi-derived radionuclides in the ocean: Transport, fate, and impacts

The events that followed the Tohoku earthquake and tsunami on March 11, 2011, included the loss of power and overheating at the Fukushima Daiichi nuclear power plants, which led to extensive releases of radioactive gases, volatiles, and liquids, particularly to the coastal ocean. The fate of these radionuclides depends in large part on their oceanic geochemistry, physical processes, and biological uptake. Whereas radioactivity on land can be resampled and its distribution mapped, releases to the marine environment are harder to characterize owing to variability in ocean currents and the general challenges of sampling at sea. Five years later, it is appropriate to review what happened in terms of the sources, transport, and fate of these radionuclides in the ocean. In addition to the oceanic behavior of these contaminants, this review considers the potential health effects and societal impacts

Modeling of transformation of surface wave packets interacting with abrupt bottom change

The paper presents results of numerical modelling on interaction of linear surface wavetrains with a bottom step. Small-amplitude wavetrains with different wavelengths are examined. Dependence of the transformation coefficients (transmission and reflection coefficients) of surface waves on the ratio of the depths before and after the step is obtained. Applicability of the hydrostatic approximation to simulation of wave transformation is discussed. It is shown that the hydrostatic model can be used for the modelling of wavetrains with sufficiently long career waves. Transformation coefficients obtained in this case are in a good agreement with analytical formulae. The results obtained on the basis of earlier developed numerical code are in agreement with results obtained by means of freely available package MITgcm

Experiences from a case study of multi-model application to assess the behaviour of pollutants in the Dnieper–Bug Estuary

The present paper describes the results of the application of four state-of-the-art models to predict the concentrations of pollutants in the abiotic components of the Dnieper–Bug Estu ary (Ukraine). The estuary was contaminated by the radioactive substances introduced in the environment following the Chernobyl accident. The scope, the methodological approaches and the theoretical foundations underpinning the examined models are presented and compared. The model performances were assessed by comparison with available empir ical data of water contamination. The main factors influencing the inherent uncertainty of the models were examined: incomplete knowledge, paucity of extensive data sets relevant to some environmental quantities, the vagueness and the ambiguity of certain information about environmental processes that can be hardly parameterised in quantitative way, etc. Model performances reflect the intrinsic uncertainty of knowledge concerning the quan titative behaviour of the involved environmental process, the ambiguity of interpretation and parameterisation of such processes, the inherent variability of environmental quanti ties, etc. The difficulties in selecting the “best performance” model and the benefits arising from a multi-model approach to afford complex environmental problems are presented and discussed. Multi-model approach helps to get an insight into complex problems of envi ronmental management, to promote co-operation among modellers and to profit by the different perspectives of the models.European Union (EU) FIGE-CT-2001-2012