Center Ird Of Bretagne

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Center Ird Of Bretagne

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Ibanhez J.S.P.,Institute Of Recherche Pour Le Developpement | Ibanhez J.S.P.,Federal University of Pernambuco | Diverres D.,Center Ird Of Bretagne | Araujo M.,Federal University of Pernambuco | And 2 more authors.
Global Biogeochemical Cycles | Year: 2015

CO2 fugacities obtained from a merchant ship sailing from France to French Guyana were used to explore the seasonal and interannual variability of the sea-air CO2 exchange in the western tropical North Atlantic (TNA; 5-14-N, 41-52-W). Two distinct oceanic water masses were identified in the area associated to the main surface currents, i.e., the North Brazil Current (NBC) and the North Equatorial Current (NEC). The NBC was characterized by permanent CO2 oversaturation throughout the studied period, contrasting with the seasonal pattern identified in the NEC. The NBC retroflection was the main contributor to the North Equatorial Counter Current (NECC), thus spreading into the central TNA, the Amazon River plume, and the CO2-rich waters probably originated from the equatorial upwelling. Strong CO2 undersaturation was associated to the Amazon River plume. Total inorganic carbon drawdown due to biological activity was estimated to be 154 μmol kg-1 within the river plume. As a consequence, the studied area acted as a net sink of atmospheric CO2 (from -72.2 ± 10.2 mmol m-2 month-1 in February to 14.3 ± 4.5 mmol m-2 month-1 in May). This contrasted with the net CO2 efflux estimated by the main global sea-air CO2 flux climatologies. Interannual sea surface temperature changes in the TNA caused by large-scale climatic events could determine the direction and intensity of the sea-air CO2 fluxes in the NEC. Positive temperature anomalies observed in the TNA led to an almost permanent CO2 outgassing in the NEC in 2010. ©2015. American Geophysical Union. All Rights Reserved.

Lefevre N.,University Pierre and Marie Curie | Diverres D.,Center Ird Of Bretagne | Gallois F.,IRD Noumea
Tellus, Series B: Chemical and Physical Meteorology | Year: 2010

Underway fCO2 has been measured from two merchant ships sailing from France to French Guyana and France to Brazil, and during two zonal cruises from Africa to French Guyana. In the western Tropical Atlantic, the strongest undersaturation is associated with the Amazon discharge near 55°W. In the 5°S-10°N, 65-35°W region, the carbon system is strongly correlated to salinity and robust empirical relationships could be determined. This region is a sink of CO2 in May-June during the high-flow period of the Amazon river. The eastward propagation of Amazon waters is observed when the retroflection of the North Brazil Current takes place. In August 2008, freshwater is observed as far as 40°W when the North Equatorial Counter Current is quite strong. The Amazon plume, defined as salinities less than 34.9, is a sink of CO2 of 0.96 mmol m-2-d-1. Further east, near 27°W, CO2 undersaturation is recorded thoughout the year between 5°N and 8°N. This is caused by the high precipitation associated with the presence of the intertropical convergence zone (ITCZ). Removing the temperature effect leads to low (high) fCO2 associated with low (high) salinities in boreal summer (winter), which is consistent with the seasonal migration of the ITCZ. © 2010 The Authors Tellus B © 2010 International Meteorological Institute in Stockholm.

Tagliabue A.,CEA Saclay Nuclear Research Center | Tagliabue A.,University Pierre and Marie Curie | Bopp L.,CEA Saclay Nuclear Research Center | Dutay J.-C.,CEA Saclay Nuclear Research Center | And 10 more authors.
Nature Geoscience | Year: 2010

Iron limits phytoplankton growth and hence the biological carbon pump in the Southern Ocean. Models assessing the impacts of iron on the global carbon cycle generally rely on dust input and sediment resuspension as the predominant sources. Although it was previously thought that most iron from deep-ocean hydrothermal activity was inaccessible to phytoplankton because of the formation of particulates, it has been suggested that iron from hydrothermal activity may be an important source of oceanic dissolved iron. Here we use a global ocean model to assess the impacts of an annual dissolved iron flux of approximately 9×108 mol, as estimated from regional observations of hydrothermal activity, on the dissolved iron inventory of the worlds oceans. We find the response to the input of hydrothermal dissolved iron is greatest in the Southern Hemisphere oceans. In particular, observations of the distribution of dissolved iron in the Southern Ocean (Chever etal., manuscript in preparation; Bowie etal., manuscript in preparation) can be replicated in our simulations only when our estimated iron flux from hydrothermal sources is included. As the hydrothermal flux of iron is relatively constant over millennial timescales, we propose that hydrothermal activity can buffer the oceanic dissolved iron inventory against shorter-term fluctuations in dust deposition. © 2010 Macmillan Publishers Limited. All rights reserved.

Tagliabue A.,University of Liverpool | Aumont O.,Center Ird Of Bretagne | Bopp L.,CEA Saclay Nuclear Research Center
Geophysical Research Letters | Year: 2014

Variable supply of iron to the ocean is often invoked to explain part of past changes in atmospheric CO2 (CO2atm). Using model simulations, we find that CO2atm is sensitive on the order of 15, 2, and 1 ppm to sedimentary, dust, and hydrothermal iron input. CO2atm is insensitive to dust because it is not the major iron input to the Southern Ocean. Modifications to the relative export of Si(OH)4 to low latitudes are opposite to those predicted previously. Although hydrothermalism is the major control on the iron inventory in ∼25% of the ocean, it remains restricted to the deep ocean, with minor effects on CO2atm. Nevertheless, uncertainties regarding the iron-binding ligand pool can have significant impacts on CO2atm. Ongoing expansion of iron observations as part of GEOTRACES will be invaluable in refining these results. Key Points Atmospheric CO2 is relatively insensitive to changes to dust supply of iron Hydrothermal Fe is key to the iron inventory, but has a small effect on CO2 There are unexpected changes to Si cycling due to changes in Fe input ©2014. American Geophysical Union. All Rights Reserved.

Gorgues T.,Center Ird Of Bretagne | Menkes C.,LOCEAN IRD Noumea | Slemons L.,University of Washington | Aumont O.,Center Ird Of Bretagne | And 4 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2010

A biogeochemical model of the tropical Pacific has been used to assess the impact of interannual variability in a western Pacific iron source on the iron-limited ecosystem of the central and eastern Pacific during the 1997-1998 El Niño. A reference simulation and two simulations with an iron source in the western Pacific have been performed. The two "source" simulations differed only in the temporal variability of the iron source. In the variable source simulation, the iron concentration in the source region was proportional to the velocity of the New Guinea Coastal Undercurrent (NGCUC). In the constant source simulation, the same time-averaged concentration of iron was imposed with no temporal variability. The variable source was designed to mimic variations of iron flux from the northeast slope of New Guinea to the NGCUC due to modulation of sedimentary iron resuspension as previously hypothesized. Through the comparison of these simulations, it appeared that: (i) an iron source in the NGCUC, regardless of its source variability, increases biomass in the eastern equatorial Pacific because of the greater eastward iron flux by the Equatorial Undercurrent and (ii) a variable NGCUC iron source does not change the temporal variability of eastern Pacific chlorophyll, and in particular the timing and intensity of the June 1998 bloom. To explain eastern Pacific biological variability, local rather than remote processes are needed, such as wind-driven upwelling, the local depth of the thermocline, tropical instability waves and biological processes such as high grazing pressure. Therefore, while the western Pacific sources of dissolved iron are important in our model to sustain annually integrated equatorial Pacific production, they are unlikely to strongly constrain the timing of blooms in the central and eastern Pacific such as during the 1998 La Niña. © 2010 Elsevier Ltd. All rights reserved.

Perrin J.L.,UMR HydroSciences Montpellier | Rais N.,University Sidi Mohammed Ben Abdellah | Chahinian N.,UMR HydroSciences Montpellier | Moulin P.,Center Ird Of Bretagne | Ijjaali M.,University Sidi Mohammed Ben Abdellah
Journal of Hydrology | Year: 2014

Oued Fez (one of the Sebou River tributaries - Morocco) allowed us to study and quantify the effect of the lack of wastewater treatment on surface water quality in semi-arid hydrological context. The analysis is based on field data collected from June 2009 to December 2011. Concentration and load patterns of nitrogen, phosphorus and chromium (used in the processing of leather) are compared in stable hydrological conditions during low flow and high flow periods in an eight-location sampling network.The Oued Fez and the Sebou River are characterised by severe pollution downstream from the city of Fez, particularly TN (mainly NH4 and Norg), TP (mainly Ppart) and TCr. The most polluted sites are those directly under the influence of domestic and industrial waste water inputs, particularly tannery effluents. Obviously, the concentrations measured at these locations are above all environmental quality standards. Pollutant loads are very heavy in the Sebou River and can contaminate the river course for kilometres. Moreover, as the water of the Sebou River is used for the irrigation of vegetables, serious problems of public health could arise.A better understanding of contaminant dynamics and self-purifying processes in these rivers will help implement actions and steps aimed at improving water quality in the Sebou River, which is the primary water supply source in Morocco and is used for agricultural and industrials purposes as well as for drinking water. © 2013 Elsevier B.V.

Arrizabalaga H.,Tecnalia | Dufour F.,NALDEO | Kell L.,ICCAT Secretariat | Merino G.,Tecnalia | And 14 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2015

In spite of its pivotal role in future implementations of the Ecosystem Approach to Fisheries Management, current knowledge about tuna habitat preferences remains fragmented and heterogeneous, because it relies mainly on regional or local studies that have used a variety of approaches making them difficult to combine. Therefore in this study we analyse data from six tuna species in the Pacific, Atlantic and Indian Oceans in order to provide a global, comparative perspective of habitat preferences. These data are longline catch per unit effort from 1958 to 2007 for albacore, Atlantic bluefin, southern bluefin, bigeye, yellowfin and skipjack tunas. Both quotient analysis and Generalised Additive Models were used to determine habitat preference with respect to eight biotic and abiotic variables. Results confirmed that, compared to temperate tunas, tropical tunas prefer warm, anoxic, stratified waters. Atlantic and southern bluefin tuna prefer higher concentrations of chlorophyll than the rest. The two species also tolerate most extreme sea surface height anomalies and highest mixed layer depths. In general, Atlantic bluefin tuna tolerates the widest range of environmental conditions. An assessment of the most important variables determining fish habitat is also provided. © 2014 Elsevier Ltd.

Louzao M.,Helmholtz Center for Environmental Research | Louzao M.,Spanish Institute of Oceanography | Aumont O.,Center Ird Of Bretagne | Hothorn T.,Ludwig Maximilians University of Munich | And 2 more authors.
Ecography | Year: 2013

Spatial modelling studies stress the importance of predicting future species distribution in changing environments, but it is also important to establish historical distribution ranges of species to provide baseline conditions for understanding distribution shifts. We focused on pelagic ecosystems, the largest ecosystem on Earth. Based on boosting algorithms, we reconstructed the foraging patterns of an oceanic predator, wandering albatross Diomedea exulans, in the highly dynamic Southern Ocean over the last half century. To access the unobserved past oceanographic conditions, we used simulations of the OPA-PISCES oceanic model for the 1958-2001 period. Firstly, we validated the simulated oceanographic variables (sea surface temperature and height, wind speed and chlorophyll a) for the 1998-2001 period with remotely sensed oceanographic data, which were highly correlated, except chlorophyll a. Secondly, we developed two habitat models (based on simulated and observed oceanographic variables) describing the foraging probability of albatrosses. We detected no statistically significant differences between the two models and predictions of both models matched the observed distribution patterns reasonably. Finally, we projected the most likely historical key pelagic habitats of albatross for the 1958 to 2001 period and characterised recurrent, occasional and unfavourable foraging areas in a decadal basis based on average predictions and their standard deviations. Our findings 1) provided a historical baseline (1958-1968) of recurrent, occasional and unfavourable foraging habitats, 2) evidenced a progressive habitat shift the following decades driven by a propagation of sea surface height from SE South Africa towards Antarctica from 1958 to 2001 and 3) measured habitat change rates of wandering albatross over the last half century. To our knowledge, our study provides the first quantitative long-term assessment of the spatial response of a marine top predator to changing pelagic habitats of the Southern Ocean and highlighted the oceanographic mechanisms involved, offering new insights on future effects of climate change on the pelagic realm. © 2012 The Authors. Ecography © 2012 Nordic Society Oikos.

Lefevre N.,University Pierre and Marie Curie | Lefevre N.,Institute Ciencias Do Mar | Urbano D.F.,National Institute for Space Research | Gallois F.,CIRAD - Agricultural Research for Development | Diverres D.,Center Ird Of Bretagne
Journal of Geophysical Research: Oceans | Year: 2014

The fugacity of CO2 (fCO2) has been measured underway during three quasi-synoptic cruises in the western tropical Atlantic in March/April 2009 and July/August 2010 in the region 6°S-15°N, 52°W-24°W. The distribution of fCO2 is related to the main features of the ocean circulation. Temperature exerts a dominant control on the distribution of fCO2 in March/April whereas salinity plays an important role in July/August due to the more developed North Equatorial Countercurrent (NECC) carrying Amazon water and to the high precipitation associated with the presence of the Intertropical Convergence Zone (ITCZ). The main surface currents are characterized by different fCO2. Overall, the NECC carries less saline waters with lower fCO2 compared to the South Equatorial Current (SEC). The North Equatorial Current (NEC) is usually characterized by CO2 undersaturation in winter and supersaturation in summer. Using empirical fCO2-SST-SSS relationships, two seasonal maps of fCO2 are constructed for March 2009 and July 2010. The region is a sink of CO2 of 0.40 mmol m-2d-1 in March, explained by the winter cooling in the northern hemisphere, whereas it is a source of CO2 of 1.32 mmol m-2d-1 in July. The equatorial region is a source of CO2 throughout the year due to the upwelling supplying CO2-rich waters to the surface. However, the evolution of fCO2 over time, determined from all the available cruises in a small area, 1°S-1°N, 32°W-28°W, suggests that the source of CO2 has decreased in February-March from 1983 to 2011 or has remained constant in October-November from 1991 to 2010. Key Points Seasonal CO2 maps from synoptic cruises are produced Surface fCO2 is mainly driven by temperature and salinity The equatorial source of CO 2 is decreasing or constant over time ©2014. American Geophysical Union. All Rights Reserved.

Duteil O.,Leibniz Institute of Marine Science | Koeve W.,Leibniz Institute of Marine Science | Oschlies A.,Leibniz Institute of Marine Science | Aumont O.,Center Ird Of Bretagne | And 7 more authors.
Biogeosciences | Year: 2012

Phosphate distributions simulated by seven state-of-the-art biogeochemical ocean circulation models are evaluated against observations of global ocean nutrient distributions. The biogeochemical models exhibit different structural complexities, ranging from simple nutrient-restoring to multi-nutrient NPZD type models. We evaluate the simulations using the observed volume distribution of phosphate. The errors in these simulated volume class distributions are significantly larger when preformed phosphate (or regenerated phosphate) rather than total phosphate is considered. Our analysis reveals that models can achieve similarly good fits to observed total phosphate distributions for a∼very different partitioning into preformed and regenerated nutrient components. This has implications for the strength and potential climate sensitivity of the simulated biological carbon pump. We suggest complementing the use of total nutrient distributions for assessing model skill by an evaluation of the respective preformed and regenerated nutrient components. © 2012 Author(s).

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