A simulation of the southern North Sea in comparison with measurements from the North Sea Project Part 2 Suspended Particulate Matter - a compilation of field data and comparison with laboratory studies (original) (raw)
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Continental Shelf Research, 1999
We simulate the distribution of suspended particulate matter in the southern North Sea using a three-dimensional baroclinic shelf-sea model. Process studies with individual coastal sources show the transport of material across the southern North Sea and out into the Norwegian trench is sensitive to speci"c wind conditions and settling velocities, so that material which settles during the summer can be transported faster than a passive tracer if its #ux is unidirectional. Results from model runs with a number of coastal sources and size classes are compared with CTD data from the North Sea Project, using multiple linear regression to estimate the source strengths. The agreement is best during the winter, with correlation coe$cients greater than 0.7; this falls below 0.4 in the summer. We estimate the input from Holderness and the Wash to be 5.6 M tonnes/year, and from the East Anglian coast to be 2.1 M tonnes/year. Due to the limited resolution of the model and the observations, we "nd we are unable to estimate the input from the English Channel or the Rhine with any degree of certainty.
Oceanologica Acta, 2000
Suspended Particulate Matter (SPM) concentrations at various levels within the water column, together with salinity and temperature, were measured using water samples collected from six stations across the Straits of Dover. The sampling programme covered a 16-month period, undertaken during 23 cruises. On the basis of the spatial variability in the concentrations, the water bodies are divided by several boundaries, controlled by tidal and wind conditions. Within the water column, SPM concentrations were higher near the sea bed than in the surface waters. Throughout the cross-section, maximum concentrations occurred adjacent to the coastlines. Temporal variability in the SPM concentration exists on daily and seasonal scales within the coastal waters (4.2 to 74.5 mg·L − 1 ): resuspension processes, in response to semi-diurnal tidal cycles (with a period of around 12.4 h) and spring-neap cycles (with a period of 15 days) make significant contributions. Distinctive seasonal/annual concentration changes have also been observed. In the offshore waters, such variability is much less significant (0.9 to 6.0 mg·L − 1 ). In the summer the English Coastal Zone is associated with relatively high SPM concentrations: the Central Zone has a low and stable SPM concentration between these zones, there is a Transitional Zone, where there is a rapid response of SPM concentration to wind forcing. Finally, the French Coastal Zone is characterized by variable (sometimes high) SPM concentrations. Because of the zonation, SPM fluxes within the Dover Strait are controlled by different transport mechanisms. Within the Central Zone, the flux can be represented by the product of mean water discharges and SPM concentrations. However, within the coastal zones fluctuations in SPM concentrations on various time-scales must be considered. In order to calculate the maximum and minimum SPM fluxes, 10 cells were divided in the strait. A simple modelling calculation has been proposed for this complex area. The effect of spring-neap tidal cycles and seasonal changes can contribute significantly to the overall flux, which is of the order of 20× 10 6 t·yr − 1 (through the Dover Strait, towards the North Sea). Such an estimate is higher than most obtained previously. © 2000 Ifremer/ CNRS/IRD/É ditions scientifiques et médicales Elsevier SAS suspended particulate matter / flux / transport mechanisms / straits / English Channel Résumé -Flux de matière particulaire en suspension dans le détroit du Pas-de-Calais : observations et modélisation. Les concentrations pondérales de matières en suspension (MES) ont été mesurées, conjointement à la salinité et la température, sur six stations dans le détroit du Pas-de-Calais, au cours de 23 campagnes en mer programmées sur une période de 16 mois. Les variabilités spatiales des concentrations de MES permettent d'identifier des masses d'eaux dont les limites sont contrôlées par les conditions de marée et de vent. Dans la colonne d'eau, les concentrations de MES sont plus fortes près du fond qu'en surface. Dans le détroit du Pas-de-Calais, les concentrations maximales sont observées le long des cô tes. Des variations temporelles des concentrations de MES sont observées à l'échelle journalière et saisonnière dans les eaux cô tières (de 4,2 à 74,5 mg·L -1 ), variations liées principalement à des phénomènes de remise en suspension au cours des cycles semi-diurnes de marée (période moyenne de 12,4 h) et au cours de cycles vives-eaux / mortes-eaux (période de 15 j). Des modifications de concentrations de MES à l'échelle saisonnière ou annuelle ont été également observées. Dans les eaux du large, ces variations sont nettement moins significatives (de 0,9 à 6,0 mg·L -1 ). Pendant la période estivale, la zone cô tière anglaise est caractérisée par des concentrations relativement fortes de MES, la zone centrale du Pas-de-Calais conservant de faibles valeurs de concentrations. Entre ces deux zones, se trouve une zone de transition, où l'élévation des concentrations de MES peut être rapide, en raison de la houle. Enfin, la zone cô tière française est caractérisée par des concentrations de MES variables dans le temps. Les flux de MES dans le détroit du Pas-de-Calais sont contrôlés par des mécanismes de transport différents selon la zone considérée. Dans les eaux centrales, le flux peut être représenté par le produit des flux moyens d'eau par les concentrations de MES. Dans les eaux cô tières, les variations des concentrations de MES doivent être appréhendées à plusieurs échelles de temps. Pour calculer les flux particulaires minimum et maximum, le détroit a été subdivisé en dix cellules. Un calcul simple de modélisation est proposé pour cette zone très complexe. Les cycles vives-eaux / mortes-eaux et les variations saisonnières peuvent modifier significativement le flux total, qui est de l'ordre de 20 × 10 6 t par an à travers le Pas-de-Calais, de la Manche vers la Mer du Nord. Cette estimation est plus élevée que celles obtenues antérieurement. © 2000 Ifremer/CNRS/IRD/É ditions scientifiques et médicales Elsevier SAS matières en suspension / flux / mécanismes de transport / détroit / Manche
Continental Shelf Research, 2015
The objective of the study described in this paper is to localize the transport path of suspended particulate matter (SPM) in the Dutch coastal zone in the southern North Sea. It is known that a large mass of SPM is transported northward from the Strait of Dover, which is however mostly hidden from satellite and other surface measurements. The study area is located at 80 km north of the Rhine-Meuse estuary mouth in the far-field plume of the region of freshwater influence (ROFI). We investigate the occurrence and persistence of a turbidity maximum zone (TMZ) in an area closer to the coast than studied in previous observational programs. Shipboard measurements of vertical profiles of SPM concentrations, density and current velocities with a high cross-shore spatial resolution are presented. A turbidity maximum zone is found at a distance between 0.5 and 3 km from the coast along 30 km of the coastline. Observed concentrations are shown to vary strongly within a tidal cycle, and also between contrasting meteorological conditions in terms of the spring-neap tidal cycle, the significant wave height and the wind force. Temporary stratification is observed during spring tides, and occurs on the ebb phase of the tidal cycle. Cross-shore transports at a transect perpendicular to the coast show an accumulation of SPM in the TMZ within one tidal cycle. Possible mechanisms for this accumulation close to the coast are discussed.
Estuarine, Coastal and Shelf Science, 2008
An algorithm is presented for estimating near-surface SPM concentrations in the turbid Case 2 waters of the southern North Sea. The single band algorithm, named POWERS, was derived by parameterising Gordon's approximation of the radiative transfer model with measurements of Belgian and Dutch inherent optical properties. The algorithm was used to calculate near-surface SPM concentration from 491 SeaWiFS datasets for 2001. It was shown to be a robust algorithm for estimating SPM in the southern North Sea. Regression of annual geometric mean SPM concentration derived from remote sensing (SPM rs ), against in situ (SPM is ) data from 19 Dutch monitoring stations was highly significant with an r 2 of 0.87. Further comparison and statistical testing against independent datasets for 2000 confirmed the consistency of this relationship. Moreover, time series of SPM rs concentrations derived from the POWERS algorithm, were shown to follow the same temporal trends as individual SPM is data recorded during 2001. Composites of annual, winter and summer SPM rs for 2001 highlight the three dominant water masses in the southern North Sea, as well as their winter-fall and spring-summer variability. The results indicate that wind induced wave action and mixing cause high surface SPM signals in winter in regions where the water column becomes well mixed, whereas in summer stratification leads to a lower SPM surface signal. The presented algorithm gives accurate near-surface SPM concentrations and could easily be adapted for other water masses and seas.
Annual variations in suspended particulate matter within the Dover Strait
During a survey at six stations in the Dover Strait, from Ju1y 1990 to November 1991 , water samples were collected to measure : suspended sediment load and its organic content; particle characteristics; photosynthesis pigments; and heavy metals. In this contribution, particle measurements are interpreted in terms of hydrodynamical effects and seasonal evolution. Mu1ti-modal grain size spectra are indicative of depth and cross-sectional variations, from the coastline to the central waters. Tidal variations, biological productivity and wind effects can be identified. Suspended particulate matter (SPM) components (determined using SEM, when combined with size spectra) illustrate hydrodynamical, geomorphological and biological effects on the composition of the suspended matter. Living and non-living diatom valves, used as particulate tracers, provide information on the sources and hydrodynamic behaviour of the suspended particles. Although the Seine input is high, riverine SPM input is not detected within the Dover Strait. SPM fluxes from the Eastern Channel into the southern North Sea, across the Dover Strait, originate mainly from: Atlantic waters; coastal and sea bed erosion; biological activity; and resuspension from the intertidal zone. SPM studies in the Eastern Channel could provide information on the complex behaviour of river pollutants over the region.
Ocean Science Journal, 2011
The integration of remote sensing data of suspended particulate matter (SPM) into numerical models is useful to improve the understanding of the temporal and spatial behaviour of SPM in dynamic shelf seas. In this paper a generic method based on the Ensemble Kalman Filtering (EnKF) for assimilating remote sensing SPM data into a transport model is presented. The EnKF technique is used to assimilate SPM data of the North Sea retrieved from the MERIS sensor, into the computational water quality and sediment transport model, Delft3D-WAQ. The satellite data were processed with the HYDROPT algorithm that provides SPM concentrations and error information per pixel, which enables their use in data assimilation. The uncertainty of the transport model, expressed in the system noise covariance matrix, was quantified by means of a Monte Carlo approach. From a case study covering the first half of 2003, it is demonstrated that the MERIS observations and transport model application are sufficiently robust for a successful generic assimilation. The assimilation results provide a consistent description of the spatial-temporal variability of SPM in the southern North Sea and show a clear decrease of the model bias with respect to independent in-situ observations. This study also identifies some shortcomings in the assimilated results, such as over prediction of surface SPM concentrations in regions experiencing periods of rapid stratification/de-stratification. Overall this feasibility study leads to a range of suggestions for improving and enhancing the model, the observations and the assimilation scheme.
Suspended sediment modelling in a shelf sea (North Sea
Coastal Engineering, 2000
Ž . This paper extends the modelling of suspended particulate matter SPM on the local coastal Ž . scale described in preceding papers to SPM modelling on the scale of the North Sea, focusing on representing SPM patterns and their seasonal distribution. The modelling includes a sensitivity study, in which model results are assessed using surface SPM concentration patterns extracted from NOAA reflectance imagery, as well as North Sea Project in situ data.
Impact of Density Gradients on Net Sediment Transport into the Wadden Sea
Journal of Physical Oceanography, 2008
This study tests the hypothesis that horizontal density gradients have the potential to significantly contribute to the accumulation of suspended particulate matter (SPM) in the Wadden Sea. It is shown by means of long-term observations at various positions in the Wadden Sea of the German Bight that the water in the inner regions of the Wadden Sea is typically about 0.5–1.0 kg m−3 less dense than the North Sea water. During winter this occurs mostly because of freshwater runoff and net precipitation; during summer it occurs mostly because of differential heating. It is demonstrated with idealized one-dimensional water column model simulations that the interaction of such small horizontal density gradients with tidal currents generates net onshore SPM fluxes. Major mechanisms for this are tidal straining, estuarine circulation, and tidal mixing asymmetries. Three-dimensional model simulations in a semienclosed Wadden Sea embayment with periodic tidal forcing show that SPM with suffic...