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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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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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Cloud filling of ocean color and sea surface temperature remote sensing products over the Southern North Sea by the Data Interpolating Empirical Orthogonal Functions methodology.
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Optical remote sensing data is now being used systematically for marine ecosystem applications, such as the forcing of biological models and the operational detection of harmful algae blooms. However, applications are hampered by the incompleteness of imagery and by some quality problems. The Data Interpolating Empirical Orthogonal Functions methodology (DINEOF) allows calculation of missing data in geophysical datasets without requiring a priori knowledge about statistics of the full data set and has previously been applied to SST reconstructions. This study demonstrates the reconstruction of complete space-time information for 4 years of surface chlorophyll a (CHL), total suspended matter (TSM) and sea surface temperature (SST) over the Southern North Sea (SNS) and English Channel (EC). Optimal reconstructions were obtained when synthesising the original signal into 8 modes for MERIS CHL and into 18 modes for MERIS TSM. Despite the very high proportion of missing data (70%), the variability of original signals explained by the EOF synthesis reached 93.5 % for CHL and 97.2 % for TSM. For the MODIS TSM dataset, 97.5 % of the original variability of the signal was synthesised into 14 modes. The MODIS SST dataset could be synthesised into 13 modes explaining 98 % of the input signal variability. Validation of the method is achieved for 3 dates below 2 artificial clouds, by comparing reconstructed data with excluded input information. Complete weekly and monthly averaged climatologies, suitable for use with ecosystem models, were derived from regular daily reconstructions. Error maps associated with every reconstruction were produced according to Beckers et al. (2006) [6]. Embedded in this error calculation scheme, a methodology was implemented to produce maps of outliers, allowing identification of unusual or suspicious data points compared to the global dynamics of the dataset. Various algorithms artefacts were associated with high values in the outlier maps (undetected cloud edges, haze areas, contrails, cloud shadows). With the production of outlier maps, the data reconstruction technique becomes also a very efficient tool for quality control of optical remote sensing data and for change detection within large databases.
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Regional environmental pressure influences population differentiation in turbot (Scophthalmus maximus).
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Unravelling the factors shaping the genetic structure of mobile marine species is challenging due to the high potential for gene flow. However, genetic inference can be greatly enhanced by increasing the genomic, geographical or environmental resolution of population genetic studies. Here, we investigated the population structure of turbot (Scophthalmus maximus) by screening 17 random and gene-linked markers in 999 individuals at 290 geographical locations throughout the northeast Atlantic Ocean. A seascape genetics approach with the inclusion of high-resolution oceanographical data was used to quantify the association of genetic variation with spatial, temporal and environmental parameters. Neutral loci identified three subgroups: an Atlantic group, a Baltic Sea group and one on the Irish Shelf. The inclusion of loci putatively under selection suggested an additional break in the North Sea, subdividing southern from northern Atlantic individuals. Environmental and spatial seascape variables correlated marginally with neutral genetic variation, but explained significant proportions (respectively, 8.7% and 10.3%) of adaptive genetic variation. Environmental variables associated with outlier allele frequencies included salinity, temperature, bottom shear stress, dissolved oxygen concentration and depth of the pycnocline. Furthermore, levels of explained adaptive genetic variation differed markedly between basins (3% vs. 12% in the North and Baltic Sea, respectively). We suggest that stable environmental selection pressure contributes to relatively strong local adaptation in the Baltic Sea. Our seascape genetic approach using a large number of sampling locations and associated oceanographical data proved useful for the identification of population units as the basis of management decisions.
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Modelling dispersal dynamics of the early life stages of a marine flatfish (Solea solea L.).
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Connectivity throughout the life cycle of flatfish remains an open question, especially during the early life stages. Their effective management requires understanding of how spawning grounds and nurseries are connected and what processes influence larval retention and dispersal. The case of sole (Solea solea L.) is of particular interest because it is one of the most valuable commercial species in the North Sea, although stocks are chronically overexploited and variability in interannual recruitment is high. The transport of sole larvae from the spawning grounds to the nurseries is driven by hydrodynamic processes, but the final dispersal pattern and larval survival/abundance might be influenced by both behavioral and environmental factors. Therefore it is important to understand the relative impact of hydrodynamics, environment, behavior and ecophysiology on sole larval dispersal. Here we use a particle-tracking transport model coupled to a 3D hydro-dynamic model of the North Sea to investigate interannual variability of the transport of sole larvae over a 12-year period (1995–2006). A sensitivity analysis is performed to assess the relative impact of hydrodynamics, temperature and behavior on the recruitment dynamics to the nurseries. Four scenarios have been tested: (i) constant forcing of sea surface temperature during all years but varying meteorological forcing and river runoff, (ii) constant meteorological forcing during the whole period but varying sea surface temperature and river runoff, (iii) no vertical migration and (iv) an extended drift period (max. 30 days) before settlement if the larvae are not close to a suitable sediment type. Results suggest that year-to-year variability of larval supply to the nurseries is high, both in terms of abundance and larval source (balance between retention and dispersal). Sensitivity analysis shows that larval abundance at the end of the larval stage increases considerably if a settling delay is included. The impact of vertical migration on larval transport and the variations in larval retention at the nurseries due to varying meteorological conditions and sea surface temperature forcing are not spatially consistent.
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Annotated Checklist of the Terrestrial Gastropods of Nepal
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Species-area relationships are modulated by trophic rank, habitat affinity, and dispersal ability
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Context-dependent specialization in colony defence in the red wood ant Formica rufa
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New Hamacantha from Peru and resurrection of Zygherpe as subgenus (Demospongiae, Poecilosclerida, Hamacanthidae)
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A new archaic homodont toothed whale (Mammalia, Cetacea, Odontoceti) from the early Miocene of Peru
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