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  • Open Access English
    Authors: 
    Alexis Khripounoff; Annick Vangriesheim; Philippe Crassous; Joel Etoubleau;
    Publisher: Elsevier
    Country: France

    This study aimed to analyze the role river floods play in triggering gravity flows and to investigate the role of submarine canyon systems as a conduit for terrigenous material to the deep sea. Two years of measurements in the Var canyon at depths ranging from 1200 m to 2350 m indicate that six floods of the Var River triggered hyperpycnal flows, an important mechanism for transporting particulate matter to the deep-sea floor. These sediment gravity flows were characterized by a sudden increase of current velocity that lasted 8 to 22 h and by downward particle fluxes that reached up to 600 g m(-2)d(-1) of particles and 3.1 g m(-2)d(-1) in terms of organic carbon. These large inputs of sediment and organic carbon may have a significant impact on deep-sea ecosystems and carbon storage in the Mediterranean Sea.

  • Publication . Article . Other literature type . 2020
    Open Access English
    Authors: 
    Alexandre Supply; Jacqueline Boutin; Jean-Luc Vergely; Nicolas Kolodziejczyk; Gilles Reverdin; Nicolas Reul; Anastasiia Tarasenko;
    Publisher: HAL CCSD
    Countries: Germany, France, France, France, France

    <p>Since 2010, the Soil Moisture and Ocean Salinity (SMOS) satellite mission monitors the earth emission at L-Band, providing the longest time series of Sea Surface Salinity (SSS) from space over the global ocean. However, retrieving SSS at high latitudes with a reasonable accuracy remains challenging, in particular due to the low sensitivity of L-Band radiometric measurements to SSS in cold waters and to the contamination of SMOS measurements by the vicinity of continents and sea ice as well as the presence of Radio Frequency Interferences. In this paper, we assess the quality of weekly SSS fields derived from swath-ordered instantaneous SMOS SSS (so called Level 2) distributed by the European Space Agency. These products are filtered according to new criteria. We use the pseudo-dielectric constant retrieved from SMOS brightness temperatures to filter SSS pixels polluted by sea ice. We identify that the dielectric constant model and the sea surface temperature auxiliary parameter used as prior information in the SMOS SSS retrieval are significant sources of uncertainty. We develop a novel correction methodology accordingly.</p><p>SSS Standard deviation of differences (STDD) between weekly SMOS SSS and in-situ near surface salinity significantly decrease after applying the SSS correction, from 1.46 pss to 1.26 pss. The correlation between new SMOS SSS and in-situ near surface salinity reaches 0.94. SMOS estimates better capture SSS variability in the Arctic Ocean in comparison to TOPAZ reanalysis (STDD = 1.86 pss), particularly in river plumes fresher by about 10 pss than surrounding waters. Furthermore, comparisons with in-situ measurements ranging from 1 to 11 m depths identify huge vertical stratification in fresh regions. This emphasizes the need to consider in-situ salinity as close as possible to the sea surface when validating L-band radiometric SSS which are representative of the first top centimeter.</p>

  • Open Access English
    Authors: 
    Tony Gardon; Céline M. O. Reisser; Claude Soyez; Virgile Quillien; Gilles Le Moullac;
    Publisher: Amer Chemical Soc
    Country: France

    Plastic pollution in the environment is increasing at global scale. Microplastics (MP) are derived from degradation of larger plastic items or directly produced in microparticles form (<5 mm). Plastics, widely used in structures and equipments of pearl farming, are a source of pollution to the detriment of the lagoon ecosystem. In order to evaluate the impact of MP on the physiology of Pinctada margaritifera, a species of ecological and commercial interests, adult oysters were exposed to polystyrene microbeads (micro-PS of 6 and 10 μm) for 2 months. Three concentrations were tested: 0.25, 2.5, 25 μg L-1 and a control. Ingestion and respiration rate and assimilation efficiency were monitored on a metabolic measurement system to determine the individual energy balance (Scope For Growth, SFG). Effects on reproduction were also assessed. The assimilation efficiency decreased significantly according to micro-PS concentration. The SFG was significantly impacted by a dose-dependent decrease from 0.25 μg L-1 (p < 0.0001). A negative SFG was measured in oysters exposed to 25 μg L-1. Gonads may have provided the missing energy to maintain animals’ metabolism through the production of metabolites derived from germ cells phagocytosis. This study shows that micro-PS significantly impact the assimilation efficiency and more broadly the energy balance of P. margaritifera, with negative repercussions on reproduction.

  • Open Access English
    Authors: 
    Kao, S. J.; Dai, M. H.; Wei, K. Y.; Blair, N. E.; Lyons, W. B.;
    Publisher: Amer Geophysical Union
    Country: France

    Significantly older C-14 ages by 2500-7900 years are found for sedimentary total organic carbon (TOC) when compared to ages of codeposited surface-dwelling foraminifera in the southern Okinawa Trough. This age discrepancy increases with rising sea level since the Last Glacial Maximum. A progressive shift in TOC delta C-13 toward more negative values with rising sea level reflects an increasing fractional contribution of terrestrial organics (soil organics, plant debris, and/or fossil organics) to the buried organic pool. Organic matter previously stored on the East China Sea shelf during sea level lowstand and riverine material from Taiwan may be the sources that cause the delta C-13(TOC) to shift to more terrestrial values. During the Holocene when sea level is above -40 m, delta C-13(TOC) values stabilize within a narrow range (-22.3 to -22.8 parts per thousand) while age discrepancies continue to increase and less chemically weathered sediments are deposited. The increase in age discrepancy between TOC and foraminifera in the Holocene may be due to a wetter climate that drove higher rates of physical weathering on Taiwan and greater transport rates of fossil organic C-bearing lithogenic sediment to the ocean. The climate impact on the relative delivery of fossil and nonfossil TOC in depositional settings influenced by fluvial sources should be considered in interpretations of sedimentary C isotope records.

  • Publication . Conference object . Other literature type . 2021
    Open Access English
    Authors: 
    Hocdé, Régis; Fiat, Sylvie; Varillon, David; Aucan, Jérôme;
    Publisher: HAL CCSD
    Country: France

    International audience; ReefTEMPS is a sensor network which is part of the French national federative Research Infrastructure for coastal ocean and seashore observations ILICO.

  • Publication . Other literature type . Article . 2010
    Open Access English
    Authors: 
    Laurent Brodeau; Bernard Barnier; Anne-Marie Tréguier; Thierry Penduff; Sergei K. Gulev;
    Publisher: Elsevier Sci Ltd
    Country: France

    We develop, calibrate and test a dataset intended to drive global ocean hindcasts simulations of the last five decades. This dataset provides surface meteorological variables needed to estimate air-sea fluxes and is built from 6-hourly surface atmospheric state variables of ERA40. We first compare the raw fields of ERA40 to the CORE.v1 clataset of Large and Yeager (2004). used here as a reference, and discuss our choice to use daily radiative fluxes and monthly precipitation products extracted from satellite data rather than their ERA40 counterparts. Both datasets lead to excessively high global imbalances of heat and freshwater fluxes when tested with a prescribed climatological sea surface temperature. After identifying unrealistic time discontinuities (induced by changes in the nature of assimilated observations) and obvious global and regional biases in ERA40 fields (by comparison to high quality observations), we propose a set of corrections. Tropical surface air humidity is decreased from 1979 onward, representation of Arctic surface air temperature is improved using recent observations and the wind is globally increased. These corrections lead to a significant decrease of the excessive positive global imbalance of heat. Radiation and precipitation fields are then submitted to a small adjustment (in zonal mean) that yields a near-zero global imbalance of heat and freshwater. A set of 47-year-long simulations is carried out with the coarse-resolution (2 degrees x 2 degrees) version of the NEMO OGCM to assess the sensitivity of the model to the proposed corrections. Model results show that each of the proposed correction contributes to improve the representation of central features of the global ocean circulation. (c) 2009 Elsevier Ltd. All rights reserved.

  • Open Access English
    Authors: 
    Berthou, Patrick; GUYADER OLIVIER; Emilie Leblond; Demaneche, Sebastien; Daures, Fabienne; Merrien, Claude; Lespagnol, Patrick;
    Publisher: ICES 2008 Annual Science Conference, 22-26 september 2008, HALIFAX, CANADA
    Country: France

    The development on the ecosystem-based approach to fisheries implies to improve integrated analysis of fisheries by considering the biological as well as the socio-economic dimensions of the exploitation and thus, an improvement in the knowledge of fleets structure, evolution and activity. Since 2000, Ifremer has been implemented a Fisheries Information System (FIS), a multidisciplinary monitoring network allowing an integrated and comprehensive view of fishery systems including biological, technical, environmental and economical components. The FIS covers all the French fisheries, including the so-often neglected small-scale fisheries. One of the originalities of the FIS lies in the fleet monitoring procedure: a comprehensive collection of annual activity calendars aiming at characterizing the inactivity or activity of the vessels each month of the year and, in the latter case, the métiers practised (use of a gear to target one or several species) and the main fishing areas. This survey covers all the French fishing fleets and provides minimum but exhaustive information on the vessels. It is particularly instructive for the small-scale fisheries, where catches and effort data are often incomplete. Furthermore, this exhaustive data allows stratifying the fleet in fleets (typologies) and thus provides the basis (i) for the implementation of sampling schemes to estimate catches, landings, discards or economic performance of the different fleets and (ii) for the development of a fleet-métier matrix giving the possibility of identifying at the time, the structure of the whole fleet in fleets, the métier polyvalence of the vessels and the allocation of fishing effort on the different exploited fishing resources.

  • Open Access English
    Authors: 
    Pautot, Guy; Auzende, Jean-marie; Olivet, Jean-louis; Mauffret, Alain;
    Publisher: U.S. Government
    Country: France

    The alignment of the Balearic Islands, stretching from the Spanish mainland towards the Corsican-Sardinian block, has long intrigued many geologists. Since Suess (1886), we know that the Balearic block (Ibiza, Formentera, and Majorca) is part of the Alpine system. Many authors (Kober, 1914; Staub, 1928; Kober, 1931) have subsequently attempted to comprehensively integrate the history of the Balearic block within the history of the Alpine chain. In this paper, we will use data from marine geology and geophysics to define the location of the Balearic Islands during the diverse phases of distension, shearing, and compression between the European and African plates, which created the present western Mediterranean and the Alpine chain. In particular, we will try to explain the way in which the Balearic Islands have reacted to these diverse drift phenomena, and discuss the manifestations of these phenornena in this area. [NOT CONTROLLED OCR]

  • Open Access English
    Authors: 
    Stefano Ciavatta; Susan Kay; S. Saux-Picart; Momme Butenschön; Julian Icarus Allen;
    Publisher: Amer Geophysical Union
    Country: France

    This paper presents the first decadal reanalysis simulation of the biogeochemistry of the North West European shelf, along with a full evaluation of its skill, confidence, and value. An error-characterized satellite product for chlorophyll was assimilated into a physical-biogeochemical model of the North East Atlantic, applying a localized Ensemble Kalman filter. The results showed that the reanalysis improved the model simulation of assimilated chlorophyll in 60% of the study region. Model validation metrics showed that the reanalysis had skill in matching a large data set of in situ observations for 10 ecosystem variables. Spearman rank correlations were significant and higher than 0.7 for physical-chemical variables (temperature, salinity, and oxygen), similar to 0.6 for chlorophyll and nutrients (phosphate, nitrate, and silicate), and significant, though lower in value, for partial pressure of dissolved carbon dioxide (similar to 0.4). The reanalysis captured the magnitude of pH and ammonia observations, but not their variability. The value of the reanalysis for assessing environmental status and variability has been exemplified in two case studies. The first shows that between 325,000 and 365,000 km(2) of shelf bottom waters were vulnerable to oxygen deficiency potentially threatening bottom fishes and benthos. The second application confirmed that the shelf is a net sink of atmospheric carbon dioxide, but the total amount of uptake varies between 36 and 46 Tg C yr(-1) at a 90% confidence level. These results indicate that the reanalysis output data set can inform the management of the North West European shelf ecosystem, in relation to eutrophication, fishery, and variability of the carbon cycle.

  • Open Access English
    Authors: 
    Enlou Zhang; Yongbo Wang; Weiwei Sun; Ji Shen;
    Publisher: Copernicus Gesellschaft Mbh
    Country: France

    Abstract. We present the results of pollen analyses from a 1105-cm-long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed strengthening of the ISM in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño Southern Oscillation strength in the tropical Pacific.

Advanced search in
Research products
arrow_drop_down
Searching FieldsTerms
Any field
arrow_drop_down
includes
arrow_drop_down
Include:
13,391 Research products, page 1 of 1,340
  • Open Access English
    Authors: 
    Alexis Khripounoff; Annick Vangriesheim; Philippe Crassous; Joel Etoubleau;
    Publisher: Elsevier
    Country: France

    This study aimed to analyze the role river floods play in triggering gravity flows and to investigate the role of submarine canyon systems as a conduit for terrigenous material to the deep sea. Two years of measurements in the Var canyon at depths ranging from 1200 m to 2350 m indicate that six floods of the Var River triggered hyperpycnal flows, an important mechanism for transporting particulate matter to the deep-sea floor. These sediment gravity flows were characterized by a sudden increase of current velocity that lasted 8 to 22 h and by downward particle fluxes that reached up to 600 g m(-2)d(-1) of particles and 3.1 g m(-2)d(-1) in terms of organic carbon. These large inputs of sediment and organic carbon may have a significant impact on deep-sea ecosystems and carbon storage in the Mediterranean Sea.

  • Publication . Article . Other literature type . 2020
    Open Access English
    Authors: 
    Alexandre Supply; Jacqueline Boutin; Jean-Luc Vergely; Nicolas Kolodziejczyk; Gilles Reverdin; Nicolas Reul; Anastasiia Tarasenko;
    Publisher: HAL CCSD
    Countries: Germany, France, France, France, France

    &lt;p&gt;Since 2010, the Soil Moisture and Ocean Salinity (SMOS) satellite mission monitors the earth emission at L-Band, providing the longest time series of Sea Surface Salinity (SSS) from space over the global ocean. However, retrieving SSS at high latitudes with a reasonable accuracy remains challenging, in particular due to the low sensitivity of L-Band radiometric measurements to SSS in cold waters and to the contamination of SMOS measurements by the vicinity of continents and sea ice as well as the presence of Radio Frequency Interferences.&amp;#160;In this paper, we assess the quality of weekly SSS fields derived from swath-ordered instantaneous SMOS SSS (so called Level 2) distributed by the European Space Agency. These products are filtered according to new criteria. We use&amp;#160;the pseudo-dielectric constant retrieved from SMOS brightness temperatures to filter SSS pixels polluted by sea ice. We identify that the dielectric constant model and the sea surface temperature auxiliary parameter&amp;#160;used as prior information in the SMOS SSS retrieval&amp;#160;are significant sources of uncertainty. We develop a novel correction methodology accordingly.&lt;/p&gt;&lt;p&gt;SSS Standard deviation of differences (STDD) between weekly SMOS SSS and in-situ near surface salinity significantly decrease after applying the SSS correction, from 1.46 pss to 1.26 pss. The correlation between new SMOS SSS and in-situ near surface salinity reaches 0.94. SMOS estimates better capture SSS variability in the Arctic Ocean in comparison to TOPAZ reanalysis (STDD = 1.86&amp;#160;pss), particularly in river plumes fresher by about 10&amp;#160;pss than surrounding waters. Furthermore, comparisons with in-situ measurements ranging from 1 to 11 m depths identify huge vertical stratification in fresh regions. This emphasizes the need to consider in-situ salinity as close as possible to the sea surface when validating L-band radiometric SSS which are representative of the first top centimeter.&lt;/p&gt;

  • Open Access English
    Authors: 
    Tony Gardon; Céline M. O. Reisser; Claude Soyez; Virgile Quillien; Gilles Le Moullac;
    Publisher: Amer Chemical Soc
    Country: France

    Plastic pollution in the environment is increasing at global scale. Microplastics (MP) are derived from degradation of larger plastic items or directly produced in microparticles form (<5 mm). Plastics, widely used in structures and equipments of pearl farming, are a source of pollution to the detriment of the lagoon ecosystem. In order to evaluate the impact of MP on the physiology of Pinctada margaritifera, a species of ecological and commercial interests, adult oysters were exposed to polystyrene microbeads (micro-PS of 6 and 10 μm) for 2 months. Three concentrations were tested: 0.25, 2.5, 25 μg L-1 and a control. Ingestion and respiration rate and assimilation efficiency were monitored on a metabolic measurement system to determine the individual energy balance (Scope For Growth, SFG). Effects on reproduction were also assessed. The assimilation efficiency decreased significantly according to micro-PS concentration. The SFG was significantly impacted by a dose-dependent decrease from 0.25 μg L-1 (p < 0.0001). A negative SFG was measured in oysters exposed to 25 μg L-1. Gonads may have provided the missing energy to maintain animals’ metabolism through the production of metabolites derived from germ cells phagocytosis. This study shows that micro-PS significantly impact the assimilation efficiency and more broadly the energy balance of P. margaritifera, with negative repercussions on reproduction.

  • Open Access English
    Authors: 
    Kao, S. J.; Dai, M. H.; Wei, K. Y.; Blair, N. E.; Lyons, W. B.;
    Publisher: Amer Geophysical Union
    Country: France

    Significantly older C-14 ages by 2500-7900 years are found for sedimentary total organic carbon (TOC) when compared to ages of codeposited surface-dwelling foraminifera in the southern Okinawa Trough. This age discrepancy increases with rising sea level since the Last Glacial Maximum. A progressive shift in TOC delta C-13 toward more negative values with rising sea level reflects an increasing fractional contribution of terrestrial organics (soil organics, plant debris, and/or fossil organics) to the buried organic pool. Organic matter previously stored on the East China Sea shelf during sea level lowstand and riverine material from Taiwan may be the sources that cause the delta C-13(TOC) to shift to more terrestrial values. During the Holocene when sea level is above -40 m, delta C-13(TOC) values stabilize within a narrow range (-22.3 to -22.8 parts per thousand) while age discrepancies continue to increase and less chemically weathered sediments are deposited. The increase in age discrepancy between TOC and foraminifera in the Holocene may be due to a wetter climate that drove higher rates of physical weathering on Taiwan and greater transport rates of fossil organic C-bearing lithogenic sediment to the ocean. The climate impact on the relative delivery of fossil and nonfossil TOC in depositional settings influenced by fluvial sources should be considered in interpretations of sedimentary C isotope records.

  • Publication . Conference object . Other literature type . 2021
    Open Access English
    Authors: 
    Hocdé, Régis; Fiat, Sylvie; Varillon, David; Aucan, Jérôme;
    Publisher: HAL CCSD
    Country: France

    International audience; ReefTEMPS is a sensor network which is part of the French national federative Research Infrastructure for coastal ocean and seashore observations ILICO.

  • Publication . Other literature type . Article . 2010
    Open Access English
    Authors: 
    Laurent Brodeau; Bernard Barnier; Anne-Marie Tréguier; Thierry Penduff; Sergei K. Gulev;
    Publisher: Elsevier Sci Ltd
    Country: France

    We develop, calibrate and test a dataset intended to drive global ocean hindcasts simulations of the last five decades. This dataset provides surface meteorological variables needed to estimate air-sea fluxes and is built from 6-hourly surface atmospheric state variables of ERA40. We first compare the raw fields of ERA40 to the CORE.v1 clataset of Large and Yeager (2004). used here as a reference, and discuss our choice to use daily radiative fluxes and monthly precipitation products extracted from satellite data rather than their ERA40 counterparts. Both datasets lead to excessively high global imbalances of heat and freshwater fluxes when tested with a prescribed climatological sea surface temperature. After identifying unrealistic time discontinuities (induced by changes in the nature of assimilated observations) and obvious global and regional biases in ERA40 fields (by comparison to high quality observations), we propose a set of corrections. Tropical surface air humidity is decreased from 1979 onward, representation of Arctic surface air temperature is improved using recent observations and the wind is globally increased. These corrections lead to a significant decrease of the excessive positive global imbalance of heat. Radiation and precipitation fields are then submitted to a small adjustment (in zonal mean) that yields a near-zero global imbalance of heat and freshwater. A set of 47-year-long simulations is carried out with the coarse-resolution (2 degrees x 2 degrees) version of the NEMO OGCM to assess the sensitivity of the model to the proposed corrections. Model results show that each of the proposed correction contributes to improve the representation of central features of the global ocean circulation. (c) 2009 Elsevier Ltd. All rights reserved.

  • Open Access English
    Authors: 
    Berthou, Patrick; GUYADER OLIVIER; Emilie Leblond; Demaneche, Sebastien; Daures, Fabienne; Merrien, Claude; Lespagnol, Patrick;
    Publisher: ICES 2008 Annual Science Conference, 22-26 september 2008, HALIFAX, CANADA
    Country: France

    The development on the ecosystem-based approach to fisheries implies to improve integrated analysis of fisheries by considering the biological as well as the socio-economic dimensions of the exploitation and thus, an improvement in the knowledge of fleets structure, evolution and activity. Since 2000, Ifremer has been implemented a Fisheries Information System (FIS), a multidisciplinary monitoring network allowing an integrated and comprehensive view of fishery systems including biological, technical, environmental and economical components. The FIS covers all the French fisheries, including the so-often neglected small-scale fisheries. One of the originalities of the FIS lies in the fleet monitoring procedure: a comprehensive collection of annual activity calendars aiming at characterizing the inactivity or activity of the vessels each month of the year and, in the latter case, the métiers practised (use of a gear to target one or several species) and the main fishing areas. This survey covers all the French fishing fleets and provides minimum but exhaustive information on the vessels. It is particularly instructive for the small-scale fisheries, where catches and effort data are often incomplete. Furthermore, this exhaustive data allows stratifying the fleet in fleets (typologies) and thus provides the basis (i) for the implementation of sampling schemes to estimate catches, landings, discards or economic performance of the different fleets and (ii) for the development of a fleet-métier matrix giving the possibility of identifying at the time, the structure of the whole fleet in fleets, the métier polyvalence of the vessels and the allocation of fishing effort on the different exploited fishing resources.

  • Open Access English
    Authors: 
    Pautot, Guy; Auzende, Jean-marie; Olivet, Jean-louis; Mauffret, Alain;
    Publisher: U.S. Government
    Country: France

    The alignment of the Balearic Islands, stretching from the Spanish mainland towards the Corsican-Sardinian block, has long intrigued many geologists. Since Suess (1886), we know that the Balearic block (Ibiza, Formentera, and Majorca) is part of the Alpine system. Many authors (Kober, 1914; Staub, 1928; Kober, 1931) have subsequently attempted to comprehensively integrate the history of the Balearic block within the history of the Alpine chain. In this paper, we will use data from marine geology and geophysics to define the location of the Balearic Islands during the diverse phases of distension, shearing, and compression between the European and African plates, which created the present western Mediterranean and the Alpine chain. In particular, we will try to explain the way in which the Balearic Islands have reacted to these diverse drift phenomena, and discuss the manifestations of these phenornena in this area. [NOT CONTROLLED OCR]

  • Open Access English
    Authors: 
    Stefano Ciavatta; Susan Kay; S. Saux-Picart; Momme Butenschön; Julian Icarus Allen;
    Publisher: Amer Geophysical Union
    Country: France

    This paper presents the first decadal reanalysis simulation of the biogeochemistry of the North West European shelf, along with a full evaluation of its skill, confidence, and value. An error-characterized satellite product for chlorophyll was assimilated into a physical-biogeochemical model of the North East Atlantic, applying a localized Ensemble Kalman filter. The results showed that the reanalysis improved the model simulation of assimilated chlorophyll in 60% of the study region. Model validation metrics showed that the reanalysis had skill in matching a large data set of in situ observations for 10 ecosystem variables. Spearman rank correlations were significant and higher than 0.7 for physical-chemical variables (temperature, salinity, and oxygen), similar to 0.6 for chlorophyll and nutrients (phosphate, nitrate, and silicate), and significant, though lower in value, for partial pressure of dissolved carbon dioxide (similar to 0.4). The reanalysis captured the magnitude of pH and ammonia observations, but not their variability. The value of the reanalysis for assessing environmental status and variability has been exemplified in two case studies. The first shows that between 325,000 and 365,000 km(2) of shelf bottom waters were vulnerable to oxygen deficiency potentially threatening bottom fishes and benthos. The second application confirmed that the shelf is a net sink of atmospheric carbon dioxide, but the total amount of uptake varies between 36 and 46 Tg C yr(-1) at a 90% confidence level. These results indicate that the reanalysis output data set can inform the management of the North West European shelf ecosystem, in relation to eutrophication, fishery, and variability of the carbon cycle.

  • Open Access English
    Authors: 
    Enlou Zhang; Yongbo Wang; Weiwei Sun; Ji Shen;
    Publisher: Copernicus Gesellschaft Mbh
    Country: France

    Abstract. We present the results of pollen analyses from a 1105-cm-long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed strengthening of the ISM in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño Southern Oscillation strength in the tropical Pacific.

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