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Seasonality of floc strength in the southern North Sea
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The suspended particulate matter (SPM) concentration in the high turbidity zones of the south- ern North Sea is inversely correlated with chlorophyll (Chl) concentration. During winter, SPM concentration is high and Chl concentration is low and vice versa during summer. This seasonality has often been associated with the seasonal pattern in wind forcing. However, the decrease in SPM concentration corresponds well with the spring algal bloom. Does the decrease of SPM concentration caused by changing wind conditions cause the start of algae bloom, or does the algae bloom decrease SPM concentrations through enhanced floccula- tion and deposition? To answer the question, measurements from 2011 of particle size distribution (PSD), SPM, and Chl concentrations from the southern North Sea have been analyzed. The results indicate that the frequency of occurrence of macroflocs has a seasonal signal, while seasonality has little impact upon floc size. The data from a highly turbid coastal zone suggest that the maximum size of the macroflocs is controlled by turbulence and the available flocculation time during a tidal cycle, but the strength of the macroflocs is con- trolled by the availability of sticky organic substances associated with enhanced primary production during spring and summer. The results highlight the shift from mainly microflocs and flocculi in winter toward more muddy marine snow with larger amounts of macroflocs in spring and summer. The macroflocs will reduce the SPM concentrations in the turbidity maximum area as they settle faster. Consequently, the SPM concen- tration decreases and the light condition increases in the surface layer enhancing algae growth further.
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RBINS Staff Publications
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Seasonality only works in certain parts of the year: The reconstruction of fishing seasons through otolith analysis
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Seasonality estimations using incremental data usually suffer from small sample sizes and from the lack of comparison with sufficiently large modern samples. The present contribution reports on incremental studies carried out on large assemblages of plaice (Pleuronectes platessa) and haddock (Melanogrammus aeglefinus) from a late medieval fishing village (Raversijde, Belgium) on the North Sea coast. In an attempt to refine previous seasonality estimates made for this site, and to expand conclusions concerning general methodology, extensive monthly samples of modern otoliths of these species, caught within the North Sea, have also been investigated. The modern material shows that the timing of the seasonal changes in the edge type (hyaline or opaque) of the otoliths is extremely variable and that it is dependent on the fishing ground, the year considered, and the age of the fish. It also appears that the increase of the marginal increment thickness is highly variable, to such an extent that the thickness of the last increment of a single otolith is mostly useless for seasonality estimation. Where large archaeological otolith assemblages can be studied, preferably from single depositional events, seasonality determination becomes possible on the condition, however, that the archaeological assemblage corresponds to fish that were captured during their period of fast growth. The growth ring study on the otoliths from Raversijde shows that plaice fishing took place in spring and that it was preceded by a haddock fishing season, probably in late winter/early spring.
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RBINS Staff Publications
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Second Record and DNA Barcode of the Ant Tyrannomyrmex rex Fernández (Hymenoptera: Formicidae: Myrmicinae)
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RBINS Staff Publications
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Secrets of de Selys Longchamps archives: one watercolour and two records of nineteenth century observations of the grasshopper species Psophus stridulus (Linnaeus, 1758) and Locusta migratoria (Linnaeus, 1758) in Belgium (Orthoptera: Acrididae)
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Next to voucher specimens in entomological collections, also historical archives and historical illustrations can contain valuable taxonomical as well as ecological and faunistic data. We report here faunistic data for two currently extinct Belgian grasshopper species from the year 1862, deduced from a letter accompanied by a watercolour. The letter and watercolour are stored in the archives of Edmond de Selys Longchamps at the Royal Belgian Institute for Natural Sciences (RBINS). Both the watercolour and the letter are discussed, focusing on the observations of Psophus stridulus (Linnaeus, 1758) and Locusta migratoria (Linnaeus, 1758) (Orthoptera) at Lanaken in 1862. Two voucher specimens of these observations and their original labels, that are stored in the RBINS collections, were studied. We can conclude that Egide Fologne was the first to observe P. stridulus in Belgium. He reported this in a letter to Edmond de Selys Longchamps and supplied the watercolour depicting the specimen he collected and donated to Selys for his collection.
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RBINS Staff Publications 2017
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Sediment oxygen distribution in ancient lakes
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RBINS Staff Publications
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Sediment variability in intermittently extracted sandbanks in the Belgian part of the North Sea
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RBINS Staff Publications 2023
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Sedimentary evidence of the Late Holocene tsunami in the Shetland Islands (UK) at Loch Flugarth, northern Mainland
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Tsunami deposits around the North Sea basin are needed to assess the long-term hazard of tsunamis. Here, we present sedimentary evidence of the youngest tsunami on the Shetland Islands from Loch Flugarth, a coastal lake on northern Mainland. Three gravity cores show organic-rich background sedimentation with many sub-centimetre-scale sand layers, reflecting recurring storm overwash and a sediment source limited to the active beach and uppermost subtidal zone. A basal 13-cm-thick sand layer, dated to 426–787 cal. a CE based on 14C, 137Cs and Bayesian age–depth modelling, was found in all cores. High-resolution grain-size analysis identified four normally graded or massive sublayers with inversely graded traction carpets at the base of two sublayers. A thin organic-rich ‘mud’ drape and a ‘mud’ cap cover the two uppermost sublayers, which also contain small rip-up clasts. Grain-size distributions show a difference between the basal sand layer and the coarser and better sorted storm layers above. Multivariate statistical analysis of X-ray fluorescence core scanning data also distinguishes both sand units: Zr, Fe and Ti dominate the thick basal sand, while the thin storm layers are high in K and Si. Enriched Zr and Ti in the basal sand layer, in combination with increased magnetic susceptibility, may be related to higher heavy mineral content reflecting an additional marine sediment source below the storm-wave base that is activated by a tsunami. Based on reinterpretation of chronological data from two different published sites and the chronostratigraphy of the present study, the tsunami seems to date to c. 1400 cal. a BP. Although the source of the tsunami remains unclear, the lack of evidence for this event outside of the Shetland Islands suggests that it had a local source and was smaller than the older Storegga tsunami (8.15 cal. ka BP), which affected most of the North Sea basin.
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RBINS Staff Publications 2023
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Sedimentary evolution of the Bruniquel cave, France. in press
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RBINS Staff Publications 2021
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Sedimentary evolution of the Sagara coastal area in Japan and its potential to preserve extreme wave deposits
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RBINS Staff Publications 2018
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Sedimentary imprints of tsunami and storm deposits on the Shizuoka coastline, south central Japan.
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RBINS Staff Publications 2016
