37 research outputs found

    Thermally driven interaction of the littoral and limnetic zones by autumnal cooling processes

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    In autumn, during the transition period, shores influence the interior dynamics of large temperate lakes by the formation of horizontal water-temperature gradients between the shallow and deep areas, whilst vertical temperature gradients are smoothed by convection due to surface cooling. A simple heat budget model, based on the heat balance of the water column without horizontal advection and turbulent mixing, allows deduction of the time-dependent difference between the mean temperature within the littoral area and the temperature in the upper mixed layer. The model corroborates that littoral areas cool faster than regions distant from shores, and provides a basis for an estimation of structure of flows from the beginning of cooling process till the formation of the thermal bar. It predicts the moment in the cooling process, when the corresponding density difference between the littoral and limnetic parts reaches a maximum. For a linear initial vertical temperature profile, the time-dependent "target depth" is explicitly calculated; this is the depth in the pelagic area with a temperature, characteristic of the littoral zone. This depth is estimated as 4/3 of the (concurrent) thickness of the upper mixed layer. It is shown that, for a linear initial vertical temperature profile, the horizontal temperature profile between the shore and the lake has a self-similar behavior, and the temperature difference between the littoral waters and the upper mixed off-shore layer, divided by the depth of the upper mixed layer, is an invariant of the studied process. The results are in conformity with field data

    The physical oceanography of the transport of floating marine debris

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    Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales

    Toward the integrated marine debris observing system

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    Plastics and other artificial materials pose new risks to the health of the ocean. Anthropogenic debris travels across large distances and is ubiquitous in the water and on shorelines, yet, observations of its sources, composition, pathways, and distributions in the ocean are very sparse and inaccurate. Total amounts of plastics and other man-made debris in the ocean and on the shore, temporal trends in these amounts under exponentially increasing production, as well as degradation processes, vertical fluxes, and time scales are largely unknown. Present ocean circulation models are not able to accurately simulate drift of debris because of its complex hydrodynamics. In this paper we discuss the structure of the future integrated marine debris observing system (IMDOS) that is required to provide long-term monitoring of the state of this anthropogenic pollution and support operational activities to mitigate impacts on the ecosystem and on the safety of maritime activity. The proposed observing system integrates remote sensing and in situ observations. Also, models are used to optimize the design of the system and, in turn, they will be gradually improved using the products of the system. Remote sensing technologies will provide spatially coherent coverage and consistent surveying time series at local to global scale. Optical sensors, including high-resolution imaging, multi- and hyperspectral, fluorescence, and Raman technologies, as well as SAR will be used to measure different types of debris. They will be implemented in a variety of platforms, from hand-held tools to ship-, buoy-, aircraft-, and satellite-based sensors. A network of in situ observations, including reports from volunteers, citizen scientists and ships of opportunity, will be developed to provide data for calibration/validation of remote sensors and to monitor the spread of plastic pollution and other marine debris. IMDOS will interact with other observing systems monitoring physical, chemical, and biological processes in the ocean and on shorelines as well as the state of the ecosystem, maritime activities and safety, drift of sea ice, etc. The synthesized data will support innovative multi-disciplinary research and serve a diverse community of users

    Marine Litter Stormy Wash-Outs: Developing the Neural Network to Predict Them

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    Observations show that after stormy events, anthropogenic litter is washed ashore for short periods of time, providing the opportunity to collect and remove it from the environment. However, water dynamics in sea coastal zones during and after storms are very complicated, and the transport properties of litter items are very diverse; thus, predicting litter wash-outs using classical numerical models is challenging. We analyze meteorological and hydrophysical conditions in the Baltic Sea coastal zone to further use the obtained data as a training sequence for an artificial neural network (ANN). Analysis of the physical processes behind large litter wash-outs links open-source meteorological (wind speed and direction) and hydrodynamic reanalysis (surface wave parameters) data to the time and location of these wash-outs. A detailed analysis of 25 cases of wash-outs observed at the shore of the Sambian Peninsula was performed. The importance of the duration of the storm and its subsiding phase was revealed. An ANN structure is proposed for forecasting marine debris wash-outs as the first step in the creation of a neural network-based tool for managers and beach cleaners, helping to plan effective measures to remove plastics and other anthropogenic contaminants from the marine environment

    Autumn physical limnological experimental campaign in the Island Mainau littoral zone of Lake Constance

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    From October 12th to November 19th 2001 a hydrophysical field measurement campaign was carried out in the littoral zone of Lake Überlingen and the Upper Lake Constance around the Island Mainau and in the adjacent aquatic area. Measurements involved (i) deployment of current-meters, thermistors and thermistor–chains at fixed positions, (ii) CTD-towing with the boat in the subsurface layer, (iii) CTD profiling at selected positions and deployment of drifters at selected depths and positions around the Island Mainau. The measurements that were conducted are described and illustrated by typical plots. The data as well as closer description of the campaign are public domain and can be downloaded for use through Internet

    Barotropic wind-driven circulation patterns in a closed rectangular basin of variable depth influenced by a peninsula or an island

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    We study how a coastal obstruction (peninsula or coastal island) affects the three-dimensional barotropic currents in an oblong rectangular basin with variable bathymetry across the basin width. The transverse depth profiele is asymmetric and the peninsula or island lies in the middle of the long side of the rectangle. A semi-spectral model for the Boussinesq-approximated shallow water equations, developed in Haidvogel et al. and altered for semi-implicit numerical integration in time in Wang and Hutter, is used to find the steady barotropic state circulation pattern to external winds. The structural (qualitative) rearrangements and quantitative features of the current pattern are studied under four principal wind is inclination relative to the shore. The essentially non-linear relationships of the water flux between the two sub-basins (formed by the obstructing penisula) and the corresponding crosssectional area left open are found and analysed. It is further analysed whather the depth- integrated model, usually adopted by others, is meaningful when applied to the water exchange problems. The flow through the challel narrowing is quantitatively estimmated and compared with the three- dimensional results. The dynamics of the vortex structure and the indentification of the up-welling/down-welling zones around the obsrruction are discussed in detail. The influence of the transformation of the penisula into a coastal islang on the gloabal basin circulation is considered as are the currents in the channel. The geometric and physical reasons for the anisotropy of the current structure which prevail through all obtained solutions are also discussed

    Wind-driven current simulations around the Island Mainau (Lake Constance)

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    Using three-dimensional numerical modelling for the shallow water equations on the rotating Earth in the Boussinesq approximation, we study the steady barotropic motion around the Island Mainau in Lake ĂŒberlingen, forced by uniformly distributed winds of different directions. The method of substructuring is used to resolve the flow pattern near the Island Mainau with greater accuracy and thus to identify the peculiarities that are induced by the island as an obstruction to the current field within the lake basin. The barotropic response is analysed in detail for 16 different wind directions. It is shown to what extent these winds determine the distribution of the horizontal current and the up- and down-welling zones in the vicinity of the island. Current peculiarities, such as diverging and converging elements, locations of maximum current speeds and, in particular, the flow through the Mainau channel are identified. They provide hints to an optimal design of a flow measuring campaign under homogeneous conditions. It is further demonstrated that the island acts as an obstructing entity that effectively influences the flow within Lake Überlingen. For wind blowing along Lake Überlingen the baroclinic motion was also studied. The flow in the upper-layer and the lower-layer-return flow are modified over the lake

    Introduction

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