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See detailA Multiplatform Experiment to Unravel Meso- and Submesoscale Processes in an Intense Front (AlborEx)
Pascual, Ananda; Ruiz, Simon; Olita, Antonio et al

in Frontiers in Marine Science (2017)

The challenges associated with meso- and submesoscale variability (between 1 and 100 km) require high-resolution observations and integrated approaches. Here we describe a major oceanographic experiment ... [more ▼]

The challenges associated with meso- and submesoscale variability (between 1 and 100 km) require high-resolution observations and integrated approaches. Here we describe a major oceanographic experiment designed to capture the intense but transient vertical motions in an area characterized by strong fronts. Finescale processes were studied in the eastern Alboran Sea (Western Mediterranean) about 400 km east of the Strait of Gibraltar, a relatively sparsely sampled area. In-situ systems were coordinated with satellite data and numerical simulations to provide a full description of the physical and biogeochemical variability. Hydrographic data confirmed the presence of an intense salinity front formed by the confluence of Atlantic Waters, entering from Gibraltar, with the local Mediterranean waters. The drifters coherently followed the northeastern limb of an anticyclonic gyre. Near real time data from acoustic current meter data profiler showed consistent patterns with currents of up to 1 m/s in the southern part of the sampled domain. High-resolution glider data revealed submesoscale structures with tongues of chlorophyll-a and oxygen associated with the frontal zone. Numerical results show large vertical excursions of tracers that could explain the subducted tongues and filaments captured by ocean gliders. A unique aspect of AlborEx is the combination of high-resolution synoptic measurements of vessel-based measurements, autonomous sampling, remote sensing and modeling, enabling the evaluation of the underlying mechanisms responsible for the observed distributions and biogeochemical patchiness. The main findings point to the importance of fine-scale processes enhancing the vertical exchanges between the upper ocean and the ocean interior. [less ▲]

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See detailPotential for Composite Analysis in the Black Sea
Capet, Arthur ULg; Mason, Evan; Troupin, Charles et al

Conference (2016, October)

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See detailOperational forecasting of the Black sea: merging model simulations and satellite products
Vandenbulcke, Luc ULg; Capet, Arthur ULg; Ivanov, Evgeny ULg et al

Scientific conference (2016, September 29)

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See detailDINEOF analyses of Sea Surface Temperature data in the Black Sea
Alvera Azcarate, Aida ULg; Vandenbulcke, Luc ULg; Barth, Alexander ULg et al

Scientific conference (2016, September 29)

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See detailImpact of vertical and horizontal advection on nutrient distribution in the southeast Pacific
Barceló-Llull, Barbara; Mason, Evan; Capet, Arthur ULg et al

in Ocean Science (2016), 12(4), 1003-1011

An innovative approach is used to analyze the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the redistribution and uptake of nitrate in the southeast Pacific (SEP). A ... [more ▼]

An innovative approach is used to analyze the impact of vertical velocities associated with quasi-geostrophic (QG) dynamics on the redistribution and uptake of nitrate in the southeast Pacific (SEP). A total of 12 years of vertical and horizontal currents are derived from an observation based estimate of the ocean state. Horizontal velocities are obtained through the application of thermal wind balance to weekly temperature and salinity fields. Vertical velocities are estimated by integration of the QG omega equation. Seasonal variability of the synthetic vertical velocity and kinetic energy associated with the horizontal currents is coincident, with peaks in austral summer (November–December) in accord with published observations. The impact of vertical velocity on SEP nitrate uptake rates is assessed by using two Lagrangian particle tracking experiments that differ according to vertical forcing (ω = ωQG vs. ω = 0). From identical initial distributions of nitrate-tagged particles, the Lagrangian results show that vertical motions induce local increases in nitrate uptake reaching up to 30 %. Such increases occur in low uptake regions with high mesoscale activity. Despite being weaker than horizontal currents by a factor of up to 10−4, vertical velocity associated with mesoscale activity is demonstrated to make an important contribution to nitrate uptake, hence productivity, in low uptake regions. [less ▲]

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See detailDecline of the Black Sea oxygen inventory
Capet, Arthur ULg; Stanev, Emil; Beckers, Jean-Marie ULg et al

in Biogeosciences (2016), 13

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See detailIntegrating sediment biogeochemistry into 3D oceanic models: A study of benthic-pelagic coupling in the Black Sea
Capet, Arthur ULg; Meysman, Filip; Akoumianaki, Ioanna et al

in Ocean Modelling (2016), 101

Three-dimensional (3D) ecosystem models of shelf environments should properly account for the biogeochemical cycling within the sea floor. However, a full and explicit representation of sediment ... [more ▼]

Three-dimensional (3D) ecosystem models of shelf environments should properly account for the biogeochemical cycling within the sea floor. However, a full and explicit representation of sediment biogeochemistry into 3D ocean models is computationally demanding. Here, we describe a simplified approach to include benthic processes in 3D ocean models, which includes a parameterization of the different pathways for organic matter mineralization and allows for organic matter remobilization by bottom currents and waves. This efficient approach enables decadal simulations that resolve the inertial contribution of the sea floor to the biogeochemical cycling in shelf environments. The model was implemented to analyze the benthic-pelagic coupling in the northwestern shelf of the Black Sea. Three distinct biogeochemical provinces were identified on the basis of fluxes and rates associated with benthic-pelagic coupling. Our model simulations suitably capture the seasonal variability of in situ flux data as well as their regional variation, which stresses the importance of incorporating temporally varying sediment biogeochemistry and resuspension/redeposition cycles in shelf ecosystem models. [less ▲]

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See detailImplications of Refined Altimetry on Estimates of Mesoscale Activity and Eddy-Driven Offshore Transport in the Eastern Boundary Upwelling Systems
Capet, Arthur ULg; Mason, Evan; Rossi, Vincent et al

in Geophysical Research Letters (2014), 41

We investigate the extent to which the recently upgraded version of the Ssalto/Duacs sea level anomaly product affects the description of mesoscale activity in the Eastern Boundary Upwelling Systems (EBUS ... [more ▼]

We investigate the extent to which the recently upgraded version of the Ssalto/Duacs sea level anomaly product affects the description of mesoscale activity in the Eastern Boundary Upwelling Systems (EBUS). Drifter observations confirm that the new data set released by Archiving, Validation and Interpretation of Satellite Oceanographic data (AVISO) in April 2014 (DT14) offers an enhanced description of mesoscale activity for the four EBUS. DT14 returns significantly higher eddy kinetic energy levels (+80%) within a 300 km coastal band, where mesoscale structures are known to induce important lateral physical and biogeochemical fluxes. When applied to DT14, an automatic eddy detection algorithm detects more eddies in the EBUS (+37%), and lower eddy radius estimates, in comparison with results using the former altimetry product (DT10). We show that despite higher eddy densities, the smaller eddy radii result in westward eddy transport estimates that are smaller than those obtained from DT10 ( −12%). [less ▲]

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See detailStudy of the multi-decadal evolution of the Black Sea hydrodynamics and biogeochemistry using mathematical modelling
Capet, Arthur ULg

Doctoral thesis (2014)

This thesis addresses the biogeochemical cycles in the Black Sea (BS) during the shifting environmental context that affected the BS during the last decades of the 20th century. The study is based on ... [more ▼]

This thesis addresses the biogeochemical cycles in the Black Sea (BS) during the shifting environmental context that affected the BS during the last decades of the 20th century. The study is based on sophisticated data analysis tools and on the development and implementation of a coupled 3D biogeochemical model on the BS domain. The long term variability of the BS hydrodynamical structure was first examined on the basis of in-situ profiles (1950-2012), satellite imagery (1985-2000) and 3D modelling (1960-2000). Profiles of temperature and salinity were used to derive vertical characteristics of the BS structure: the mixed layer depth and the cold content of the Cold Intermediate Layer. To untangle the spatial and temporal trends from this heterogeneous dataset, a general methodology was proposed and embedded in the data analysis software DIVA. The detrended climatologies and long-term time series provided by this approach were used to assess statistical relationships with local atmospheric conditions. Satellite data (sea surface temperature and altimetry) and model results were then analyzed to relate observable surface dynamics to internal hydrodynamic properties. The main multivariate modes of variability of the BS hydrodynamic structure were highlighted on the basis of Empirical Orthogonal Function analysis. Their temporal evolution was explained by the occurrences of specific atmospheric patterns, identified on the basis of neural algorithm analysis and related to the phases of well known teleconnection systems (i.e. the North Atlantic and East Asia/West Russia oscillations). To study the dynamics of eutrophication in the shallow Black Sea NorthWestern Shelf (BS-NWS), a benthic model component was developed that considers the environmental control on diagenetic processes and the bottom shear stress restriction on organic matter deposition. The model accurately reproduced the seasonal and spatial variability depicted by in-situ estimates of benthic nutrients and oxygen fluxes in the BS-NWS. Outputs were used to review the role of the benthic component in BS biogeochemical cycles. The multi-decadal simulations, enabled by the low computational requirements of the benthic-pelagic coupling approach, revealed an inertial component in the dynamics of eutrophication resulting from the accumulation of organic matter during the years of important nutrient loads. This refined resolution of the BS-NWS biogeochemistry allowed us to study the phenomenon of seasonal hypoxia, which is believed to have played a part in the sudden collapse of the fisheries stocks in the late 80s. An index H, combining the spatial and temporal extension of the seasonal hypoxic event, was proposed to quantify the annual intensity of hypoxia as a pressure on benthic communities. We have shown that hypoxia was first triggered in the late 70s by high nitrogen loads, and sustained by sedimentary organic matter accumulation after a rapid reduction of these loads in the 90s. After 2000, warmer summers again led to a increase of the H-index, by entraining hypoxic events of smaller spatial extension but increased duration. A practical relationship distinguishing the impacts of eutrophication and climatic drivers was proposed to assess the effect of their projected values on the future intensity of hypoxia. [less ▲]

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See detailUntangling spatial and temporal trends in the variability of the Black Sea Cold Intermediate Layer and mixed Layer Depth using the DIVA detrending procedure
Capet, Arthur ULg; Troupin, Charles ULg; Cartensen, Jacob et al

in Ocean Dynamics (2014), 64(3), 315-324

Current spatial interpolation products may be biased by uneven distribution of measurements in time. This manuscript presents a detrending method that recognizes and eliminates this bias. The method ... [more ▼]

Current spatial interpolation products may be biased by uneven distribution of measurements in time. This manuscript presents a detrending method that recognizes and eliminates this bias. The method estimates temporal trend components in addition to the spatial structure and has been implemented within the Data Interpolating Variational Analysis (DIVA) analysis tool. The assets of this new detrending method are illustrated by producing monthly and annual climatologies of two vertical properties of the Black Sea while recognizing their seasonal and interannual variabilities : the mixed layer depth, and the cold content of its Cold Intermediate Layer (CIL). The temporal trends, given as by-products of the method, are used to analyze the seasonal and interannual variability of these variables over the past decades (1955-2011). In particular, the CIL interannual variability is related to the cumulated winter air temperature anomalies, explaining 88\% of its variation. [less ▲]

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See detailHypoxia in the Black Sea northwestern shelf: From eutrophication to climatic stressors.
Capet, Arthur ULg; Beckers, Jean-Marie ULg; Grégoire, Marilaure ULg

in 40th CIESM congress proceedings (2013, October)

Abstract The dynamics of seasonal hypoxia, which affects the Black Sea north-western shelf since the mid 1970's until present days, is investigated by means of a 3D biogeochemical model. Comparison of the ... [more ▼]

Abstract The dynamics of seasonal hypoxia, which affects the Black Sea north-western shelf since the mid 1970's until present days, is investigated by means of a 3D biogeochemical model. Comparison of the model results with in -situ data reveals that the phenomenon may have been underestimated after the mid 1990's due to the distribution of observations. We investigate the mechanism of hypoxia at seasonal scale, and identify the main drivers of its interannual variability. While high nutrients discharge caused severe hypoxia in the 1980's, it was sustained in the 1990's by the pool of organic matter accumulated during the previous years in the sediments layer. With an increasing intensity, climatic stressors intensifies the response of hypoxia to nutrient discharge, and affect the seasonal dynamics of hypoxia by extending its temporal scale. [less ▲]

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See detailBenthic-Pelagic coupling in the Black Sea - A model Study
Capet, Arthur ULg; meysman, Filip; Soetaert, Karline

Conference (2013, May 15)

While benthic and sediment processes are now recognized as major components of the shelf iogeochemical budget, their representation in 3D biogeochemical model has for long been oversimplified [Soetaert et ... [more ▼]

While benthic and sediment processes are now recognized as major components of the shelf iogeochemical budget, their representation in 3D biogeochemical model has for long been oversimplified [Soetaert et al., 2000]. These oversimplified formulations of the bottom boundary onditions prevent to account for the response of diagenetic processes to the environment. The onsequent absence of spatial and temporal variability of benthic/pelagic fluxes may lead to mis- valuation of important terms in the biogeochemical budgets (e.g. Oxygen, Nitrogen, Carbon, hosphate). More importantly, feedbacks mechanisms within the ecosystem response to utrophication may be overlooked, such as, for instance, the sensitivity of benthic denitrification o the oxygen content in the bottom waters. The GHER-ECO 3D biogeochemical model is xtended ith a refined benthic component explicitly accounting for the effect of organic matter transport, eposition and resuspension and for the influence of the environmental conditions on the iagenetic pathways. A semi-empirical approach allows to reproduce the variability and feedbacks riven by benthic diagenesis without the computational burden of a vertically resolved sediment ayer. This simplification allows to use the coupled model for the long term runs (several ecades) required to appreciate the slow dynamics introduced by the accumulation of organic atter in the sediment layer during the years of high riverine discharge. The extended model has een implemented for the Black Sea North western shelf [Capet et al., 2012]. After a presentation f the main assumptions used to construct the benthic module, results are analyzed with a focus n (1) spatial and seasonal variability of benthic diagenesis and consequent benthic/pelagic xchanges, (2) comparison to in-situ estimates of benthic/pelagic dissolved fluxes, (3) implication n biogeochemical budgets and eutrophication issue. Inherent limitations of the semi-empirical pproach are discussed in the perspective of the current challenges addressed to biogeochemical odels. [less ▲]

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See detailIntroducing dynamic benthic fluxes in 3D biogeochemical model : an application on the Black Sea North-Western shelf
Capet, Arthur ULg; Meysman, Filip; Soetaert, Karline et al

Conference (2013, April 15)

While benthic and sediment processes are now recognized as major components of the shelf iogeochemical budget, their representation in 3D biogeochemical model has for long been oversimplified [Soetaert et ... [more ▼]

While benthic and sediment processes are now recognized as major components of the shelf iogeochemical budget, their representation in 3D biogeochemical model has for long been oversimplified [Soetaert et al., 2000]. These oversimplified formulations of the bottom boundary onditions prevent to account for the response of diagenetic processes to the environment. The onsequent absence of spatial and temporal variability of benthic/pelagic fluxes may lead to mis- valuation of important terms in the biogeochemical budgets (e.g. Oxygen, Nitrogen, Carbon, hosphate). More importantly, feedbacks mechanisms within the ecosystem response to utrophication may be overlooked, such as, for instance, the sensitivity of benthic denitrification o the oxygen content in the bottom waters. The GHER-ECO 3D biogeochemical model is xtended ith a refined benthic component explicitly accounting for the effect of organic matter transport, eposition and resuspension and for the influence of the environmental conditions on the iagenetic pathways. A semi-empirical approach allows to reproduce the variability and feedbacks riven by benthic diagenesis without the computational burden of a vertically resolved sediment ayer. This simplification allows to use the coupled model for the long term runs (several ecades) required to appreciate the slow dynamics introduced by the accumulation of organic atter in the sediment layer during the years of high riverine discharge. The extended model has een implemented for the Black Sea North western shelf [Capet et al., 2012]. After a presentation f the main assumptions used to construct the benthic module, re- sults are analyzed with a focus n (1) spatial and seasonal variability of benthic diagenesis and con- sequent benthic/pelagic xchanges, (2) comparison to in-situ estimates of benthic/pelagic dissolved fluxes, (3) implication n biogeochemical budgets and eutrophication issue. Inherent limitations of the semi-empirical pproach are discussed in the perspective of the current challenges addressed to biogeochemical odels. [less ▲]

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See detailSeasonal hypoxia in the Black Sea north-western shelf. Is there any recovery after eutrophication ?
Capet, Arthur ULg; Beckers, Jean-Marie ULg; Grégoire, Marilaure ULg

in 9th EGU General Assembly (2013, April 11)

The Black Sea North-western shelf (NWS) is a shallow eutrophic area in which seasonal tratification of the water column isolates bottom waters from the atmosphere and prevents entilation to compensate for ... [more ▼]

The Black Sea North-western shelf (NWS) is a shallow eutrophic area in which seasonal tratification of the water column isolates bottom waters from the atmosphere and prevents entilation to compensate for the large consumption of oxygen, due to respiration in the bottom aters and in the sediments. A 3D coupled physical biogeochemical model is used to investigate he dynamics of bottom hypoxia in the Black Sea NWS at different temporal scales from seasonal o interannual (1981-2009) and to differentiate the driving factors (climatic versus eutrophication) f hypoxic conditions in bottom waters. Model skills are evaluated by comparison with 14500 in- itu oxygen measurements available in the NOAA World Ocean Database and the Black Sea ommission data. The choice of skill metrics and data subselections orientate the validation rocedure towards specific aspects of the oxygen dynamics, and prove the model’s ability to esolve the seasonal cycle and interannual variability of oxygen concentration as well as the patial location of the oxygen depleted waters and the specific threshold of hypoxia. During the eriod 1981-2009, each year exhibits seasonal bottom hypoxia at the end of summer. This henomenon essentially covers the northern part of the NWS, receiving large inputs of nutrients rom the Danube, Dniestr and Dniepr rivers, and extends, during the years of severe hypoxia, owards the Romanian Bay of Constanta. In order to explain the interannual variability of bottom ypoxia and to disentangle its drivers, a statistical model (multiple linear regression) is proposed sing the long time series of model results as input variables. This statis- tical model gives a eneral relationships that links the intensity of hypoxia to eutrophication and climate related variables. The use of four predictors allows to reproduce 78% of hypoxia interannual variability: he annual nitrate discharge (N ), the sea surface temperature in the month preceding tratification (T ), the amount of semi-labile organic matter in the sediments (C) and the duration f the stratification (D). Eutrophication (N ,C) and climate (T ,D) predictors explain a similar mount of variability (∼ 35%) when considered separately. A typical timescale of 9.3 years is found to describe the inertia of sediments in the recovering process after eutrophication. From his analysis, we find that under standard conditions (i.e. average atmospheric conditions, ediments in equi- librium with river discharges), the intensity of hypoxia can be linked to the evel of nitrate discharge through a non-linear equation (power law). Bottom hypoxia does not ffect the whole Black Sea NWS but rather exhibits an important spatial variability. This heterogeneous distribution, in addition to the seasonal fluctuations, complicates the monitoring f ottom hypoxia leading to contradictory conclusions when the interpretation is done from different ets of data. We find that it was the case after 1995 when the recovery process was verestimated due to the use of observations concentrated in areas and months not typically ffected by hypoxia. This stresses out the urging need of a dedicated monitoring effort in the WS f the Black Sea focused on the areas and the period of the year concerned by recurrent hypoxic events. [less ▲]

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See detailWP4: Developing integrated tools for environmental assessment, Region : Black Sea
Capet, Arthur ULg; daskalov, georgi; Grégoire, Marilaure ULg et al

Conference (2013, January 22)

Status of the PERSEUS Work Package 4 in the Black Sea

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