Identifying the mechanisms that contribute to the variability of suspended particulate matter concentrations in coastal areas is important but difficult, especially due to the complexity of physical and biogeochemical interactions involved. Our study addresses this complexity and investigates changes in the horizontal spread and composition of particles, focusing on cross-coastal gradients in the southern North Sea and the English Channel. A semi-empirical model is applied on in situ data of SPM and its organic fraction to resolve the relationship between organic and inorganic suspended particles. The derived equations are applied onto remote sensing products of SPM concentration, which provide monthly synoptic maps of particulate organic matter concentrations (here, particulate organic nitrogen) at the surface together with their labile and less reactive fractions. Comparing these fractions of particulate organic matter reveals their characteristic features along the coastal-offshore gradient, with an area of increased settling rate for particles generally observed between 5 and 30 km from the coast. We identify this area as the transition zone between coastal and offshore waters with respect to particle dynamics. Presumably, in that area, the turbulence range and particle composition favor particle settling, while hydrodynamic processes tend to transport particles of the seabed back towards the coast. Bathymetry plays an important role in controlling the range of turbulent dissipation energy values in the water column, and we observe that the transition zone in the southern North Sea is generally confined to water depths below 20 m. Seasonal variations in suspended particle dynamics are linked to biological processes enhancing particle flocculation, which do not affect the location of the transition zone. We identify the criteria that allow a transition zone and discuss the cases where it is not observed in the domain. The impact of these particle dynamics on coastal carbon storage and export is discussed.
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RBINS Staff Publications 2024 OA
The large-scale excavation at the prehistoric site of Tell el-Iswid made it possible to undertake a systematic archaeobotanical study of different structures covering the Predynastic and Early Dynastic period (Lower Egyptian Cultures (Buto II) to Naqada III Culture. Here we present the results of the analysis of carpological remains preserved mostly in charred state and coming from 62 samples processed by manual flotation, with total volume of 615 litres and containing a total of 9672 identifiable and quantifiable items. Further ca. 650 wood fragments (or woody vegetative remains) were subject to anthracological analysis. Besides the aim of overall characterising and exploring the plant economy of the site, the macrobotanical assemblages were also considered in relation to the structures from which they were uncovered. The study revealed that the agricultural economy of both studied periods relied on emmer, barley, lentils, and pea, but from the Early Dynastic times onwards also flax and condiments (like Anethum graveolens and cf. Origanum sp.) played a certain role. Together with the cultivated fields also the surrounding wetlands were an important part of the plant resources utilized at site. The stems of Phragmites are also the most common among the anthracological remains, together with a small proportion of Tamarix and Acacia charcoal fragments. The overall composition of the plant assemblages (charred and mineralised chaff, small weed or wild growing seeds capable to pass the herbivore digestion, dung fragments, awns) suggest that the major source of the retrieved plant remains was dung fuel.
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RBINS Staff Publications 2023 OA
