How effective and efficient are multiobjective evolutionary algorithms at hydrologic model calibration?

International audienceThis study provides a comprehensive assessment of state-of-the-art evolutionary multiobjective optimization (EMO) tools' relative effectiveness in calibrating hydrologic models. The relative computational efficiency, accuracy, and ease-of-use of the following EMO algorithms are tested: Epsilon Dominance Nondominated Sorted Genetic Algorithm-II (?-NSGAII), the Multiobjective Shuffled Complex Evolution Metropolis algorithm (MOSCEM-UA), and the Strength Pareto Evolutionary Algorithm 2 (SPEA2). This study uses three test cases to compare the algorithms' performances: (1) a standardized test function suite from the computer science literature, (2) a benchmark hydrologic calibration test case for the Leaf River near Collins, Mississippi, and (3) a computationally intensive integrated surface-subsurface model application in the Shale Hills watershed in Pennsylvania. One challenge and contribution of this work is the development of a methodology for comprehensively comparing EMO algorithms that have different search operators and randomization techniques. Overall, SPEA2 attained competitive to superior results for most of the problems tested in this study. The primary strengths of the SPEA2 algorithm lie in its search reliability and its diversity preservation operator. The biggest challenge in maximizing the performance of SPEA2 lies in specifying an effective archive size without a priori knowledge of the Pareto set. In practice, this would require significant trial-and-error analysis, which is problematic for more complex, computationally intensive calibration applications. ?-NSGAII appears to be superior to MOSCEM-UA and competitive with SPEA2 for hydrologic model calibration. ?-NSGAII's primary strength lies in its ease-of-use due to its dynamic population sizing and archiving which lead to rapid convergence to very high quality solutions with minimal user input. MOSCEM-UA is best suited for hydrologic model calibration applications that have small parameter sets and small model evaluation times. In general, it would be expected that MOSCEM-UA's performance would be met or exceeded by either SPEA2 or ?-NSGAII

Impacts of dust deposition on dissolved trace metal concentrations (Mn, Al and Fe) during a mesocosm experiment

The deposition of atmospheric dust is the primary process supplying trace elements abundant in crustal rocks (e.g. Al, Mn and Fe) to the surface ocean. Upon deposition, the residence time in surface waters for each of these elements differs according to their chemical speciation and biological utilization. Presently, however, the chemical and physical processes occurring after atmospheric deposition are poorly constrained, principally because of the difficulty in following natural dust events in situ. In the present work we examined the temporal changes in the biogeochemistry of crustal metals (in particular Al, Mn and Fe) after an artificial dust deposition event. The experiment was contained inside trace metal clean mesocosms (0–12.5 m depths) deployed in the surface waters of the northwestern Mediterranean, close to the coast of Corsica within the frame of the DUNE project (a DUst experiment in a low Nutrient, low chlorophyll Ecosystem). Two consecutive artificial dust deposition events, each mimicking a wet deposition of 10 g m−2 of dust, were performed during the course of this DUNE-2 experiment. The changes in dissolved manganese (Mn), iron (Fe) and aluminum (Al) concentrations were followed immediately after the seeding with dust and over the following week. The Mn, Fe and Al inventories and loss or dissolution rates were determined. The evolution of the inventories after the two consecutive additions of dust showed distinct behaviors for dissolved Mn, Al and Fe. Even though the mixing conditions differed from one seeding to the other, Mn and Al showed clear increases directly after both seedings due to dissolution processes. Three days after the dust additions, Al concentrations decreased as a consequence of scavenging on sinking particles. Al appeared to be highly affected by the concentrations of biogenic particles, with an order of magnitude difference in its loss rates related to the increase of biomass after the addition of dust. In the case of dissolved Fe, it appears that the first dust addition resulted in a decrease as it was scavenged by sinking dust particles, whereas the second seeding induced dissolution of Fe from the dust particles due to the excess Fe binding ligand concentrations present at that time. This difference, which might be related to a change in Fe binding ligand concentration in the mesocosms, highlights the complex processes that control the solubility of Fe. Based on the inventories at the mesocosm scale, the estimations of the fractional solubility of metals from dust particles in seawater were 1.44 ± 0.19% and 0.91 ± 0.83% for Al and 41 ± 9% and 27 ± 19% for Mn for the first and the second dust addition. These values are in good agreement with laboratory-based estimates. For Fe no fractional solubility was obtained after the first seeding, but 0.12 ± 0.03% was estimated after the second seeding. Overall, the trace metal dataset presented here makes a significant contribution to enhancing our knowledge on the processes influencing trace metal release from Saharan dust and the subsequent processes of bio-uptake and scavenging in a low nutrient, low chlorophyll are

Implementation and assessment of a model including mixotrophs and the carbonate cycle (Eco3M_MIX-CarbOx v1.0) in a highly dynamic Mediterranean coastal environment (Bay of Marseille, France) – Part 1: Evolution of ecosystem composition under limited light and nutrient conditions

Many current biogeochemical models rely on an autotrophic versus heterotrophic food web representation. However, in recent years, an increasing number of studies have begun to challenge this approach. Several authors have highlighted the importance of protists capable of combining photoautotrophic and heterotrophic nutrition in a single cell. These mixotrophic protists are known to play an important role in the carbon cycle. Here, we present a new biogeochemical model that represents the food web using variable stoichiometry. It contains the classic compartments such as zooplankton, phytoplankton, and heterotrophic bacteria and a newly added compartment to represent two types of mixotrophic protists: non-constitutive mixotrophs (NCMs) and constitutive mixotrophs (CMs). We demonstrate that the model correctly reproduces the characteristics of NCMs and CMs and proceed to study the impact of light and nutrient limitation on planktonic ecosystem structure in a highly dynamic Mediterranean coastal area, namely the Bay of Marseille (BoM, France), paying special attention to the dynamics of mixotrophic protists in these limiting conditions. In addition, we investigate the carbon, nitrogen, and phosphorus fluxes associated with mixotrophic protists and showed the following: (i) the portion of the ecosystem in terms of the percentage of carbon biomass occupied by NCMs decreases when resources (nutrient and prey concentrations) decrease, although their mixotrophy allows them to maintain a carbon biomass almost as significant as the copepod one (129.8 and 148.7 mmol C m−3, respectively), as photosynthesis increases as a food source, and (ii) the portion of the ecosystem in terms of the percentage of carbon biomass occupied by CM increases when nutrient concentrations decrease due to their capability to ingest prey to supplement their N and P needs. In addition to providing new insights regarding the conditions that lead to the emergence of mixotrophs in the BoM, this work provides a new tool to perform long-term studies and predictions of mixotroph dynamics in coastal environments under different environmental forcings.</p

Circulation and Oxygen Distribution in the Tropical Atlantic Cruise No. 80, Leg 1; October 26 to November 23, 2009 Mindelo (Cape Verde) to Mindelo (Cape Verde)

METEOR cruise 80/1 was a contribution to the SFB 754 “Climate-Biogeochemistry Interactions in the Tropical Ocean”. Shipboard, glider and moored observations are used to study the temporal and spatial variability of physical and biogeochemical parameters within the oxygen minimum zone (OMZ) of the tropical North Atlantic. As part of the BMBF “Nordatlantik” project, it further focuses on the equatorial current system including the Equatorial Undercurrent (EUC) and intermediate currents below. During the cruise, hydrographic station observations were performed using a CTD/O2 rosette, including water sampling for salinity, oxygen, nutrients and other biogeochemical tracers. Underway current measurements were successfully carried out with the 75 kHz ADCP borrowed from R/V POSEIDON during the first part of the cruise, and R/V METEOR’s 38 kHz ADCP during the second part. During M80/1, an intensive mooring program was carried out with 8 mooring recoveries and 8 mooring deployments. Right at the beginning of the cruise, a multidisciplinary mooring near the Cape Verde Islands was recovered and redeployed. Within the framework of SFB 754, two moorings with CTD/O2 profilers were recovered and redeployed with other instrumentation in the center and at the southern rim of the OMZ of the tropical North Atlantic. The equatorial mooring array as part of BMBF “North Atlantic” project consists of 5 current meter moorings along 23°W between 2°S and 2°N. It is aimed at quantifying the variability of the thermocline water supply toward the equatorial cold tongue which develops east of 10°W during boreal summer. Several glider missions were performed during the cruise. One glider was recovered that was deployed two months earlier. Another glider was deployed for two short term missions, near the equator for about 8 days and near 8°N for one day. This glider was equipped with a new microstructure probe in addition to standard sensors, i.e. CTD/O2, chlorophyll and turbidity

Assessing seasonal and interannual changes in carbonate chemistry across two time-series sites in the North Western Mediterranean Sea

Sustained time-series measurements are crucial to understand changes in oceanic carbonate chemistry. In the North Western Mediterranean Sea, the temporal evolution of the carbonate system is here investigated based on two 10-year time-series (between January 2010 and December 2019) of monthly carbonate parameters measurements at two sampling sites in the Ligurian Sea (ANTARES and DYFAMED). At seasonal timescale, the seawater partial pressure of CO2 (pCO2) within the mixed layer is mostly driven by temperature at both sites, and biological processes as stated by the observed relationships between total inorganic carbon (CT), nitrate and temperature. This study suggests also that mixing and water masses advection could play a role in modulating the CT content. At decadal timescale, significant changes in ocean chemistry are observed with increasing trends in CT (+3.2 ± 0.9 µmol.kg−1.a−1 – ANTARES; +1.6 ± 0.8 µmol.kg−1.a−1 – DYFAMED), associated with increasing pCO2 trends and decreasing trends in pH. The magnitude of the increasing trend in CT at DYFAMED is consistent with the increase in atmospheric pCO2 and the anthropogenic carbon transport of water originating from the Atlantic Ocean, while the higher trends observed at the ANTARES site could be related to the hydrological variability induced by the variability of the Northern Current

Surface water dissolved aluminum and titanium: Tracers for specific time scales of dust deposition to the Atlantic?

Surface water distributions of dissolved Al (dAl) and dissolved Ti (dTi) were investigated along a meridional Atlantic transect and related to dust deposition estimates. In the zone of Saharan dust deposition, highest dAl concentrations occurred in the tropical salinity minimum and suggest increasing Al dissolution from Saharan aerosols with wet deposition. By contrast, the dTi distribution is not related to precipitation but agrees with the pattern of annual dust deposition. In the zone of Patagonian dust deposition, elevated dTi concentrations contrasted with decreased dAl concentrations, indicating excess dAl scavenging onto biogenic particles in surface waters. Estimated residence times range from months to years for dAl and are ∼10 times higher for dTi. This suggests that dAl reflects seasonal changes in dust deposition, while dTi is related to longer temporal scales. However, spatial variations in input and removal processes complicate the quantification of dust deposition from surface water concentrations

Biogeochemical iron budgets of the Southern Ocean south of Australia : decoupling of iron and nutrient cycles in the subantarctic zone by the summertime supply

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 23 (2009): GB4034, doi:10.1029/2009GB003500.Climate change is projected to significantly alter the delivery (stratification, boundary currents, aridification of landmasses, glacial melt) of iron to the Southern Ocean. We report the most comprehensive suite of biogeochemical iron budgets to date for three contrasting sites in subantarctic and polar frontal waters south of Australia. Distinct regional environments were responsible for differences in the mode and strength of iron supply mechanisms, with higher iron stocks and fluxes observed in surface northern subantarctic waters, where atmospheric iron fluxes were greater. Subsurface waters southeast of Tasmania were also enriched with particulate iron, manganese and aluminum, indicative of a strong advective source from shelf sediments. Subantarctic phytoplankton blooms are thus driven by both seasonal iron supply from southward advection of subtropical waters and by wind-blown dust deposition, resulting in a strong decoupling of iron and nutrient cycles. We discuss the broader global significance our iron budgets for other ocean regions sensitive to climate-driven changes in iron supply.T.W. was supported by a BDI grant from CNRS and Région PACA, by CNRS PICS project 3604, and by the “Soutien à la mer” CSOA CNRS-INSU. P.W.B. was supported by the New Zealand FRST Coasts and Oceans OBI. This research was supported by the Australian Government Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems CRC (ACE CRC) and Australian Antarctic Science project 2720

Le fer à l'interface océan-atmosphère : Flux et processus de dissolution dans l'eau de mer.

Studying the fluxes and the fate of atmospheric iron in seawater is crucial to estimate its contribution to ocean iron stock and biogeochemical cycles. For large oceanic areas in the southern hemisphere so far unexplored regarding aerosols, this work shows that iron atmospheric inputs are associated to extremely low concentrations of lithogenic particles which have been transported over very long distances. Atmospheric inputs of iron to these oceanic regions, determined in this work, are well below (up to two orders of magnitude) recent estimations from global dust models which are commonly used in biogeochemical models. Regarding the fate of atmospheric iron in seawater, this work suggests that iron dissolution results from the combination of a fast process (i.e. instantaneous) and a slow process (scale of several days). The “instantaneous” process is controlled by physicochemical parameters depending both on the nature (source) and on the history (atmospheric transport) of aerosols at the atmosphere-ocean interface. The “slow” process depends on the amount of free ligands in seawater and it is proportional to dissolved organic matter concentration. The dissolution of atmospheric iron is thus related not only to the source and transport of the particles but also to the characteristics of the seawater where they are deposited, illustrating the unfeasibility of considering a unique value of atmospheric iron dissolution at the global scale. A parametrization integrating all these controlling factors is proposed. This work, by estimating both the fluxes and the dissolution of atmospheric iron, shows that, for certain oceanic regions, the incertitude on iron fluxes is as much critical as the incertitude on dissolution.L'étude des flux et du devenir du fer atmosphérique dans l'eau de mer est essentielle pour estimer sa contribution au stock de fer dans l'océan de surface et donc sa contribution dans les cycles biogéochimiques. Pour de larges zones océaniques de l'hémisphère Sud, inexplorées en ce qui concerne les aérosols, ce travail montre que les apports de fer atmosphérique sont liés à de très faibles concentrations de particules d'origine lithogénique ayant voyagé sur de très longues distances. Les flux de fer vers l'océan, déterminés au cours de ce travail, sont largement inférieurs (de 1 à 2 ordres de grandeur) aux estimations récentes par des modèles globaux de poussières minérales, qui sont largement utilisés dans les modèles biogéochimiques. En ce qui concerne le devenir du fer atmosphérique dans l'eau de mer, ce travail propose de considérer le processus de dissolution comme la combinaison d'un processus rapide (considéré instantané) et d'un processus lent (à l'échelle de plusieurs jours). Le processus instantané est contrôlé par des paramètres physico-chimiques des particules qui dépendent à la fois de la nature (source) et de l'histoire (transport dans l'atmosphère des particules) des aérosols à l'interface océan-atmosphère. Le processus « lent » dépend de la quantité de ligands libres dans l'eau de mer et est proportionnel à la quantité de matière organique dissoute. La dissolution du fer transporté par les particules atmosphériques est donc liée à la fois aux sources, au transport et à la nature de l'eau de mer où elles se déposent, illustrant l'impossibilité de considérer une valeur unique de dissolution du fer atmosphérique à l'échelle globale. Une paramétrisation intégrant ces différents forçages est proposée. Ce travail, en estimant à la fois les flux et la dissolution, montre que pour certaines zones océaniques, la connaissance des flux présente une incertitude au moins aussi importante que celle de la dissolution

Le fer à l'interface océan-atmosphère (Flux et processus de dissolution dans l'eau de mer)

L'étude des flux et du devenir du fer atmosphérique dans l'eau de mer est essentielle pour estimer sa contribution au stock de fer dans l'océan de surface et donc sa contribution dans les cycles biogéochimiques. Pour de larges zones océaniques de l'hémisphère Sud, inexplorées en ce qui concerne les aérosols, ce travail montre que les apports de fer atmosphérique sont liés à de très faibles concentrations de particules d'origine lithogénique ayant voyagé sur de très longues distances. Les flux de fer vers l'océan, déterminés au cours de ce travail, sont largement inférieurs (de 1 à 2 ordres de grandeur) aux estimations récentes par des modèles globaux de poussières minérales, qui sont largement utilisés dans les modèles biogéochimiques. En ce qui concerne le devenir du fer atmosphérique dans l'eau de mer, ce travail propose de considérer le processus de dissolution comme la combinaison d'un processus rapide (considéré instantané) et d'un processus lent (à l'échelle de plusieurs jours). Le processus instantané est contrôlé par des paramètres physico-chimiques des particules qui dépendent à la fois de la nature (source) et de l'histoire (transport dans l'atmosphère des particules) des aérosols à l'interface océan-atmosphère. Le processus lent dépend de la quantité de ligands libres dans l'eau de mer et est proportionnel à la quantité de matière organique dissoute. La dissolution du fer transporté par les particules atmosphériques est donc liée à la fois aux sources, au transport et à la nature de l'eau de mer où elles se déposent, illustrant l'impossibilité de considérer une valeur unique de dissolution du fer atmosphérique à l'échelle globale. Une paramétrisation intégrant ces différents forçages est proposée. Ce travail, en estimant à la fois les flux et la dissolution, montre que pour certaines zones océaniques, la connaissance des flux présente une incertitude au moins aussi importante que celle de la dissolutionStudying the fluxes and the fate of atmospheric iron in seawater is crucial to estimate its contribution to ocean iron stock and biogeochemical cycles. For large oceanic areas in the southern hemisphere so far unexplored regarding aerosols, this work shows that iron atmospheric inputs are associated to extremely low concentrations of lithogenic particles which have been transported over very long distances. Atmospheric inputs of iron to these oceanic regions, determined in this work, are well below (up to two orders of magnitude) recent estimations from global dust models which are commonly used in biogeochemical models. Regarding the fate of atmospheric iron in seawater, this work suggests that iron dissolution results from the combination of a fast process (i.e. instantaneous) and a slow process (scale of several days). The instantaneous process is controlled by physicochemical parameters depending both on the nature (source) and on the history (atmospheric transport) of aerosols at the atmosphere-ocean interface. The slow process depends on the amount of free ligands in seawater and it is proportional to dissolved organic matter concentration. The dissolution of atmospheric iron is thus related not only to the source and transport of the particles but also to the characteristics of the seawater where they are deposited, illustrating the unfeasibility of considering a unique value of atmospheric iron dissolution at the global scale. A parametrization integrating all these controlling factors is proposed. This work, by estimating both the fluxes and the dissolution of atmospheric iron, shows that, for certain oceanic regions, the incertitude on iron fluxes is as much critical as the incertitude on dissolution.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF