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Nutrient dynamics and phytoplankton development along an estuary-coastal zone continuum: A model study.
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This study presents a first attempt to quantify the biogeochemical transformations and fluxes of carbon and nutrients along the entire mixing zone of the shallow, tidally-dominated estuary–coastal zone continuum of the Scheldt (Belgium/The Netherlands). A fully transient, two-dimensional, nested-grid hydrodynamic model of the continuum is coupled to the biogeochemical MIRO model for the coastal zone and the CONTRASTE model for the estuary. Transient model simulations are performed with a high spatial (80–750 m) and temporal (30 min) resolution over a period of one year (January–December 1995). The high temporal resolution allows including the short-term variability triggered by the tides, the freshwater discharge and the wind stress. System scale simulations provide time series of nutrient transformations and fluxes along the entire estuary–coastal zone continuum, as well as highly resolved nutrient inventories for the estuarine and the coastal zone sub-domains. Simulation results reveal that the balance between highly variable estuarine nutrient inputs and physical constrains set by the unsteady residual transport field exert an important control on the magnitude and succession of phytoplankton blooms and the ecosystem structure in the coastal zone. In addition, they suggest that the poorly surveyed estuarine–coastal zone interface plays a central role in the continuum. In this dynamic area, marked spatial concentration gradients develop and episodically lead to a reversal of material fluxes from the coast into the estuary. During distinct episodes of the productive period, euryhaline coastal diatoms intrude far upstream into the saline estuary. This intrusion reduces the estuarine nutrient concentrations and export fluxes, thereby reinforcing the nutrient limitation in the coastal area. As a consequence, the estuarine filter does not operate independently from the processes in the coastal zone. The dynamic interplay between the two ecosystems and the intense process rates operating at their transition, therefore, strongly supports our continuum approach.
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Seasonal and inter-annual variability of air-sea CO2 fluxes and seawater carbonate chemistry in the Southern Bight of the North Sea.
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A 3D coupled biogeochemical–hydrodynamic model (MIRO-CO2&CO) is implemented in the English Channel (ECH) and the Southern Bight of the North Sea (SBNS) to estimate the present-day spatio-temporal distribution of air–sea CO2 fluxes, surface water partial pressure of CO2 (pCO2) and other components of the carbonate system (pH, saturation state of calcite (Xca) and of aragonite (Xar)), and the main drivers of their variability. Over the 1994–2004 period, air–sea CO2 fluxes show significant interannual variability, with oscillations between net annual CO2 sinks and sources. The inter annual variability of air–sea CO2 fluxes simulated in the SBNS is controlled primarily by river loads and changes of biological activities (net autotrophy in spring and early summer, and net heterotrophy in winter and autumn), while in areas less influenced by river inputs such as the ECH, the inter annual variations of air–sea CO2 fluxes are mainly due to changes in sea surface temperature and in near-surface wind strength and direction. In the ECH, the decrease of pH, of Xca and of Xar follows the one expected from the increase of atmospheric CO2 (ocean acidification), but the decrease of these quantities in the SBNS during the considered time period is faster than the one expected from ocean acidification alone. This seems to be related to a general pattern of decreasing nutrient river loads and net ecosystem production (NEP) in the SBNS. Annually, the combined effect of carbon and nutrient loads leads to an increase of the sink of CO2 in the ECH and the SBNS, but the impact of the river loads varies spatially and is stronger in river plumes and nearshore waters than in offshore waters. The impact of organic and inorganic carbon (C) inputs is mainly confined to the coast and generates a source of CO2 to the atmosphere and low pH, of Xca and of Xar values in estuarine plumes, while the impact of nutrient loads, highest than the effect of C inputs in coastal nearshore waters, also propagates offshore and, by stimulating primary production, drives a sink of atmospheric CO2 and higher values of pH, of Xca and of Xar.
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Modelling diatom and Phaeocystis blooms and nutrient cycles in the Southern Bight of the North Sea: the MIRO model.
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The link between anthropogenic nutrient loads and the magnitude and extent of diatom and Phaeocystis colony blooms in the Southern Bight of the North Sea was explored with the complex ecosystem model MIRO. The model was adapted for resolving the changing nutrient loads, the complex biology of the bloom species and the tight coupling between the benthic and pelagic compartments that characterise this shallow coastal shelf sea ecosystem. State variables included the main inorganic nutrients (nitrate [NO3], ammonium [NH4], phosphate [PO4] and dissolved silica [DSi]), 3 groups of phytoplankton with different trophic fates (diatoms, nanophytoflagellates and Phaeocystis colonies), 2 zooplankton groups (copepods and microzooplankton), bacteria, and 5 classes of detrital organic matter with different biodegradability. The capability of the MIRO model to properly simulate the observed SW–NE gradient in nutrient enrichment and the seasonal cycle of inorganic and organic C and nutrients, phytoplankton, bacteria and zooplankton in the eastern English Channel and Southern Bight of the North Sea is demonstrated by running the model for the period from 1989 to 1999. The MIRO code was implemented in a simplified multi-box representation of the hydrodynamic regime. These model runs give the first general view of the seasonal dynamics of Phaeocystis colony blooms and nutrient cycling within the domain. C, N and P budget calculations show that (1) the coastal ecosystem has a low nutrient retention and elimination capacity, (2) trophic efficiency of the planktonic system is low, and (3) both are modulated by meteorological forcing.
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Modelling the impact of the Scheldt and Rhine/Meuse plumes on the salinity distribution in Belgian waters (Southern North Sea).
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A 3D hydrodynamical model has been set up to describe the distribution and variability of the salinity in Belgian coastal waters. Particular attention was paid to determining the relative impact of the Scheldt and Rhine/Meuse freshwater plumes and testing the hypothesis that the salinity of Belgian waters is primarily a mix between salty offshore water and freshwater from the Scheldt Estuary. Attention was also paid to determining whether the Seine has significant impact on the Belgian zone. The 3D hydrodynamical model, based on COHERENS, has been applied to the Channel and the Southern Bight of the North Sea using a 5′ (longitude) by 2.5′ (latitude) grid. The model has been run for the years 1991–2002. Real river runoffs have been taken into account for the main rivers within the domain: the Scheldt, the Rhine/Meuse, the Seine and the Thames. Model tracers were used to characterise the signature of water masses in terms of Atlantic and riverine waters. Results indicate that the salinity of Belgian waters is dominated by inflow of the Channel water mass which mixes with freshwater originating mainly from the Rhine/Meuse with a much smaller contribution from the Scheldt Estuary. This conclusion is further supported by simulation results obtained when each river discharge is separately set to zero. Thus, the ‘generally accepted’ hypothesis of a ‘continental coastal river’ with fresher coastal water flowing north-eastward up the French-Belgian-Dutch coast and picking up freshwater from successive outflows seems inappropriate for Belgian waters where horizontal dispersion of Rhine/Meuse water in the opposite direction is significant.
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Traumatism in the wild animals kept and offered at predynastic Hierakonpolis, Upper Egypt
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A description is given of the violence related pathologies that are observed in a number of wild mammals that were buried in the predynastic cemetery HK6 at Hierakonpolis, Upper Egypt. Unlike other predynastic graveyards, where only domestic cattle, sheep, goat and dogs are interred, the elite cemetery HK6 yielded also a wide variety of wild species that were buried as part of extensive mortuary complexes surrounding the graves of the highest local elite. The animals were interred, singly or in groups, often in graves of their own, but some also accompany human burials. Pathologies were found on the skeletons of 20 of the 38 wild animals discovered thus far, namely in 15 anubis baboons (Papio anubis), one leopard (Panthera pardus), one jungle cat (Felis chaus), one hartebeest (Alcelaphus buselaphus), one aurochs (Bos primigenius) and one hippo (Hippopotamus amphibius). Most of the pathologies are healed fractures resulting from violent blows, and a smaller proportion seems to be related to tethering. These conditions indicate that the animals were held in captivity for a prolonged period of time after their capture. The type and frequency of the encountered deformations differ from those seen in wild animals from other, more recent Egyptian cemeteries (Abydos, Tuna el-Gebel, Gabanet el-Giroud, Saqqara) where mainly metabolic disorders are observed that have been attributed to chronic malnutrition and to vitamin D deficiency as a result of inadequate housing in a dark environment. Keywords: archaeozoology - palaeopathology - bone fracture - hartebeest - aurochs - baboon - leopard - jungle cat.
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The Halomonhystera disjuncta population is homogeneous across the Håkon Mosby mud volcano (Barents Sea) but is genetically differentiated from its shallow-water relatives
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A critique of Rossberg et al.: noise obscures the genetic signal of meiobiotal ecospecies in ecogenomic datasets
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Benthos distribution modelling and its relevance for marine ecosystem management
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The Mousny massive quartz occurrence – the vestige of a late-orogenic dilational jog in the High-Ardenne slate belt (Belgium)
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The Coccodus lindstroemi species complex (Pycnodontiformes, Gladiopycnodontidae) from the marine Late Cretaceous of Lebanon, with the description of two new genera
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