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M Latimier - One of the best experts on this subject based on the ideXlab platform.
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spatio temporal dynamics of biogeochemical processes and air sea co2 fluxes in the western english channel based on two years of ferrybox deployment
Journal of Marine Systems, 2014Co-Authors: P Marrec, M Latimier, Thierry Cariou, E Mace, Pascal Morin, Marc Vernet, Yann BozecAbstract:Abstract From January 2011 to January 2013, a FerryBox system was installed on a Voluntary Observing Ship (VOS), which crossed the Western English Channel (WEC) between Roscoff (France) and Plymouth (UK) up to 3 times a day. The FerryBox continuously measured sea surface temperature (SST), sea surface salinity (SSS), dissolved oxygen (DO), fluorescence and partial pressure of CO 2 (from April 2012) along the ferry track. Sensors were calibrated based on 714 bimonthly surface samplings with precisions of 0.016 for SSS, 3.3 μM for DO, 0.40 μg L − 1 for Chlorophyll- a (Chl- a ) (based on fluorescence measurements) and 5.2 μatm for pCO 2 . Over the 2 years of deployment (900 crossings), we reported 9% of data lost due to technical issues and quality checked data was obtained to allow investigation of the dynamics of biogeochemical processes related to air–sea CO 2 fluxes in the WEC. Based on this unprecedented high-frequency dataset, the physical structure of the WEC was assessed using SST anomalies and the presence of a thermal front was observed around the latitude 49.5°N, which divided the WEC in two main provinces: the seasonally stratified northern WEC (nWEC) and the all-year well-mixed southern WEC (sWEC). These hydrographical properties strongly influenced the spatial and inter-annual distributions of phytoplankton blooms, which were mainly limited by nutrients and light availability in the nWEC and the sWEC, respectively. Air–sea CO 2 fluxes were also highly related to hydrographical properties of the WEC between late April and early September 2012, with the sWEC a weak source of CO 2 to the atmosphere of 0.9 mmol m − 2 d − 1 , whereas the nWEC acted as a sink for atmospheric CO 2 of 6.9 mmol m − 2 d − 1 . The study of short time-scale dynamics of air–sea CO 2 fluxes revealed that an intense and short (less than 10 days) summer bloom in the nWEC contributed to 29% of the CO 2 sink during the productive period, highlighting the necessity for high frequency observations in coastal ecosystems. During the same period in the sWEC, the tidal cycle was the main driver of air–sea CO 2 fluxes with a mean difference in pCO 2 values between spring and neap tides of + 50 μatm. An extraction of day/night data at 49.90°N showed that the mean day–night differences accounted for 16% of the mean CO 2 sink during the 5 months of the study period implying that the diel biological cycle was also significant for air–sea CO 2 flux computations. The 2 years of deployment of our FerryBox allowed an excellent survey of the variability of biogeochemical parameters from inter-annual to diurnal time scales and provided new insights into the dynamics of air–sea CO 2 fluxes in the contrasted ecosystems of the WEC.
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seasonal and latitudinal variability of the co2 system in the western english channel based on voluntary Observing Ship vos measurements
Marine Chemistry, 2013Co-Authors: P Marrec, T Cariou, E Collin, A Durand, M LatimierAbstract:We investigated the dynamics of the CO2 system across the Western English Channel (WEC) between Roscoff (France) and Plymouth (UK) using a Voluntary Observing Ship (VOS). From December 2010 to December 2011, 20 return crossings were carried out to collect a comprehensive dataset of CO2 system parameters and ancillary data. The hydrographical structure of the water column across the latitudinal transect was investigated at 3 fixed stations: ASTAN (southern WEC, offshore Roscoff), El and L4 (northern WEC, offshore Plymouth). Based on these profiles, we defined two provinces, the stratified northern WEC (>49.5 degrees N) and the well-mixed southern WEC (<49.5 degrees N), which were periodically separated by a thermal front. These contrasted hydrographical properties strongly influenced the ecosystem dynamics. Biological production/respiration processes were the main driver of pCO(2) variability during the year except for winter cooling in the northern WEC. The seasonally stratified northern WEC showed enhanced biological activities characterized by an extensive autotrophic phase, which maintained the pCO(2) below the atmospheric equilibrium until early fall and acted as a sink for atmospheric CO2 at a rate of 1.1 mol C m(-2) y(-1). The permanently well mixed southern WEC was characterized by a shorter autotrophic phase due to a delayed spring phytoplankton growth and an early start of the fall heterotrophic phase, resulting in an annual air-sea CO2 flux close to equilibrium at a rate of -0.4 mol C m(-2) y(-1). On annual scale, calculation of Net Ecosystem Production (NEP) revealed that surface waters at El and ASTAN were both autotrophic at rates of 1.5 mol C m(-2) y(-1) and 1.0 mol C m(-2) y(-1), respectively. Our latitudinal approach resolved the discrepancy between the directions of the fluxes in the WEC observed in previous studies by differentiating between the hydrological regions. The combined approach of using data from VOS tracks and fixed coastal observatories stations provided new insights into the control of air-sea CO2 fluxes in the different provinces of the WEC. This combined approach could be applied in other continental shelf systems where data on the CO2 system are sparse. (C) 2013 Elsevier B.V. All rights reserved.
P Marrec - One of the best experts on this subject based on the ideXlab platform.
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spatio temporal dynamics of biogeochemical processes and air sea co2 fluxes in the western english channel based on two years of ferrybox deployment
Journal of Marine Systems, 2014Co-Authors: P Marrec, M Latimier, Thierry Cariou, E Mace, Pascal Morin, Marc Vernet, Yann BozecAbstract:Abstract From January 2011 to January 2013, a FerryBox system was installed on a Voluntary Observing Ship (VOS), which crossed the Western English Channel (WEC) between Roscoff (France) and Plymouth (UK) up to 3 times a day. The FerryBox continuously measured sea surface temperature (SST), sea surface salinity (SSS), dissolved oxygen (DO), fluorescence and partial pressure of CO 2 (from April 2012) along the ferry track. Sensors were calibrated based on 714 bimonthly surface samplings with precisions of 0.016 for SSS, 3.3 μM for DO, 0.40 μg L − 1 for Chlorophyll- a (Chl- a ) (based on fluorescence measurements) and 5.2 μatm for pCO 2 . Over the 2 years of deployment (900 crossings), we reported 9% of data lost due to technical issues and quality checked data was obtained to allow investigation of the dynamics of biogeochemical processes related to air–sea CO 2 fluxes in the WEC. Based on this unprecedented high-frequency dataset, the physical structure of the WEC was assessed using SST anomalies and the presence of a thermal front was observed around the latitude 49.5°N, which divided the WEC in two main provinces: the seasonally stratified northern WEC (nWEC) and the all-year well-mixed southern WEC (sWEC). These hydrographical properties strongly influenced the spatial and inter-annual distributions of phytoplankton blooms, which were mainly limited by nutrients and light availability in the nWEC and the sWEC, respectively. Air–sea CO 2 fluxes were also highly related to hydrographical properties of the WEC between late April and early September 2012, with the sWEC a weak source of CO 2 to the atmosphere of 0.9 mmol m − 2 d − 1 , whereas the nWEC acted as a sink for atmospheric CO 2 of 6.9 mmol m − 2 d − 1 . The study of short time-scale dynamics of air–sea CO 2 fluxes revealed that an intense and short (less than 10 days) summer bloom in the nWEC contributed to 29% of the CO 2 sink during the productive period, highlighting the necessity for high frequency observations in coastal ecosystems. During the same period in the sWEC, the tidal cycle was the main driver of air–sea CO 2 fluxes with a mean difference in pCO 2 values between spring and neap tides of + 50 μatm. An extraction of day/night data at 49.90°N showed that the mean day–night differences accounted for 16% of the mean CO 2 sink during the 5 months of the study period implying that the diel biological cycle was also significant for air–sea CO 2 flux computations. The 2 years of deployment of our FerryBox allowed an excellent survey of the variability of biogeochemical parameters from inter-annual to diurnal time scales and provided new insights into the dynamics of air–sea CO 2 fluxes in the contrasted ecosystems of the WEC.
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seasonal and latitudinal variability of the co2 system in the western english channel based on voluntary Observing Ship vos measurements
Marine Chemistry, 2013Co-Authors: P Marrec, T Cariou, E Collin, A Durand, M LatimierAbstract:We investigated the dynamics of the CO2 system across the Western English Channel (WEC) between Roscoff (France) and Plymouth (UK) using a Voluntary Observing Ship (VOS). From December 2010 to December 2011, 20 return crossings were carried out to collect a comprehensive dataset of CO2 system parameters and ancillary data. The hydrographical structure of the water column across the latitudinal transect was investigated at 3 fixed stations: ASTAN (southern WEC, offshore Roscoff), El and L4 (northern WEC, offshore Plymouth). Based on these profiles, we defined two provinces, the stratified northern WEC (>49.5 degrees N) and the well-mixed southern WEC (<49.5 degrees N), which were periodically separated by a thermal front. These contrasted hydrographical properties strongly influenced the ecosystem dynamics. Biological production/respiration processes were the main driver of pCO(2) variability during the year except for winter cooling in the northern WEC. The seasonally stratified northern WEC showed enhanced biological activities characterized by an extensive autotrophic phase, which maintained the pCO(2) below the atmospheric equilibrium until early fall and acted as a sink for atmospheric CO2 at a rate of 1.1 mol C m(-2) y(-1). The permanently well mixed southern WEC was characterized by a shorter autotrophic phase due to a delayed spring phytoplankton growth and an early start of the fall heterotrophic phase, resulting in an annual air-sea CO2 flux close to equilibrium at a rate of -0.4 mol C m(-2) y(-1). On annual scale, calculation of Net Ecosystem Production (NEP) revealed that surface waters at El and ASTAN were both autotrophic at rates of 1.5 mol C m(-2) y(-1) and 1.0 mol C m(-2) y(-1), respectively. Our latitudinal approach resolved the discrepancy between the directions of the fluxes in the WEC observed in previous studies by differentiating between the hydrological regions. The combined approach of using data from VOS tracks and fixed coastal observatories stations provided new insights into the control of air-sea CO2 fluxes in the different provinces of the WEC. This combined approach could be applied in other continental shelf systems where data on the CO2 system are sparse. (C) 2013 Elsevier B.V. All rights reserved.
Eberhard Ruprecht - One of the best experts on this subject based on the ideXlab platform.
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estimation of the impact of sampling errors in the vos observations on air sea fluxes part ii impact on trends and interannual variability
Journal of Climate, 2007Co-Authors: Sergey K Gulev, Thomas Jung, Eberhard RuprechtAbstract:Abstract Using the same approach as in Part I, here it is shown how sampling problems in voluntary Observing Ship (VOS) data affect conclusions about interannual variations and secular changes of surface heat fluxes. The largest uncertainties in linear trend estimates are found in relatively poorly sampled regions like the high-latitude North Atlantic and North Pacific as well as the Southern Ocean, where trends can locally show opposite signs when computed from the regularly sampled and undersampled data. Spatial patterns of shorter-period interannual variability, quantified through the EOF analysis, also show remarkable differences between the regularly sampled and undersampled flux datasets in the Labrador Sea and northwest Pacific. In particular, it is shown that in the Labrador Sea region, in contrast to regularly sampled NCEP–NCAR reanalysis fluxes, VOS-like sampled NCEP–NCAR reanalysis fluxes neither show significant interannual variability nor significant trends. These regions, although quite loca...
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estimation of the impact of sampling errors in the vos observations on air sea fluxes part i uncertainties in climate means
Journal of Climate, 2007Co-Authors: Sergey K Gulev, Thomas Jung, Eberhard RuprechtAbstract:Sampling uncertainties in the voluntary Observing Ship (VOS)-based global ocean–atmosphere flux fields were estimated using the NCEP–NCAR reanalysis and ECMWF 40-yr Re-Analysis (ERA-40) as well as seasonal forecasts without data assimilation. Air–sea fluxes were computed from 6-hourly reanalyzed individual variables using state-of-the-art bulk formulas. Individual variables and computed fluxes were subsampled to simulate VOS-like sampling density. Random simulation of the number of VOS observations and simulation of the number of observations with contemporaneous sampling allowed for estimation of random and total sampling uncertainties respectively. Although reanalyses are dependent on VOS, constituting an important part of data assimilation input, it is assumed that the reanalysis fields adequately reproduce synoptic variability at the sea surface. Sampling errors were quantified by comparison of the regularly sampled (i.e., 6 hourly) and subsampled monthly fields of surface variables and fluxes. In poorly sampled regions random sampling errors amount to 2.5°–3°C for air temperature, 3 m s−1 for the wind speed, 2–2.5 g kg−1 for specific humidity, and 15%–20% of the total cloud cover. The highest random sampling errors in surface fluxes were found for the sensible and latent heat flux and range from 30 to 80 W m−2. Total sampling errors in poorly sampled areas may be higher than random ones by 60%. In poorly sampled subpolar latitudes of the Northern Hemisphere and throughout much of the Southern Ocean the total sampling uncertainty in the net heat flux can amount to 80–100 W m−2. The highest values of the uncertainties associated with the interpolation/extrapolation into unsampled grid boxes are found in subpolar latitudes of both hemispheres for the turbulent fluxes, where they can be comparable with the sampling errors. Simple dependencies of the sampling errors on the number of samples and the magnitude of synoptic variability were derived. Sampling errors estimated from different reanalyses and from seasonal forecasts yield qualitatively comparable spatial patterns, in which the actual values of uncertainties are controlled by the magnitudes of synoptic variability. Finally, estimates of sampling uncertainties are compared with the other errors in air–sea fluxes and the reliability of the estimates obtained is discussed.
Sergey K Gulev - One of the best experts on this subject based on the ideXlab platform.
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estimation of the impact of sampling errors in the vos observations on air sea fluxes part ii impact on trends and interannual variability
Journal of Climate, 2007Co-Authors: Sergey K Gulev, Thomas Jung, Eberhard RuprechtAbstract:Abstract Using the same approach as in Part I, here it is shown how sampling problems in voluntary Observing Ship (VOS) data affect conclusions about interannual variations and secular changes of surface heat fluxes. The largest uncertainties in linear trend estimates are found in relatively poorly sampled regions like the high-latitude North Atlantic and North Pacific as well as the Southern Ocean, where trends can locally show opposite signs when computed from the regularly sampled and undersampled data. Spatial patterns of shorter-period interannual variability, quantified through the EOF analysis, also show remarkable differences between the regularly sampled and undersampled flux datasets in the Labrador Sea and northwest Pacific. In particular, it is shown that in the Labrador Sea region, in contrast to regularly sampled NCEP–NCAR reanalysis fluxes, VOS-like sampled NCEP–NCAR reanalysis fluxes neither show significant interannual variability nor significant trends. These regions, although quite loca...
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estimation of the impact of sampling errors in the vos observations on air sea fluxes part i uncertainties in climate means
Journal of Climate, 2007Co-Authors: Sergey K Gulev, Thomas Jung, Eberhard RuprechtAbstract:Sampling uncertainties in the voluntary Observing Ship (VOS)-based global ocean–atmosphere flux fields were estimated using the NCEP–NCAR reanalysis and ECMWF 40-yr Re-Analysis (ERA-40) as well as seasonal forecasts without data assimilation. Air–sea fluxes were computed from 6-hourly reanalyzed individual variables using state-of-the-art bulk formulas. Individual variables and computed fluxes were subsampled to simulate VOS-like sampling density. Random simulation of the number of VOS observations and simulation of the number of observations with contemporaneous sampling allowed for estimation of random and total sampling uncertainties respectively. Although reanalyses are dependent on VOS, constituting an important part of data assimilation input, it is assumed that the reanalysis fields adequately reproduce synoptic variability at the sea surface. Sampling errors were quantified by comparison of the regularly sampled (i.e., 6 hourly) and subsampled monthly fields of surface variables and fluxes. In poorly sampled regions random sampling errors amount to 2.5°–3°C for air temperature, 3 m s−1 for the wind speed, 2–2.5 g kg−1 for specific humidity, and 15%–20% of the total cloud cover. The highest random sampling errors in surface fluxes were found for the sensible and latent heat flux and range from 30 to 80 W m−2. Total sampling errors in poorly sampled areas may be higher than random ones by 60%. In poorly sampled subpolar latitudes of the Northern Hemisphere and throughout much of the Southern Ocean the total sampling uncertainty in the net heat flux can amount to 80–100 W m−2. The highest values of the uncertainties associated with the interpolation/extrapolation into unsampled grid boxes are found in subpolar latitudes of both hemispheres for the turbulent fluxes, where they can be comparable with the sampling errors. Simple dependencies of the sampling errors on the number of samples and the magnitude of synoptic variability were derived. Sampling errors estimated from different reanalyses and from seasonal forecasts yield qualitatively comparable spatial patterns, in which the actual values of uncertainties are controlled by the magnitudes of synoptic variability. Finally, estimates of sampling uncertainties are compared with the other errors in air–sea fluxes and the reliability of the estimates obtained is discussed.
A Durand - One of the best experts on this subject based on the ideXlab platform.
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seasonal and latitudinal variability of the co2 system in the western english channel based on voluntary Observing Ship vos measurements
Marine Chemistry, 2013Co-Authors: P Marrec, T Cariou, E Collin, A Durand, M LatimierAbstract:We investigated the dynamics of the CO2 system across the Western English Channel (WEC) between Roscoff (France) and Plymouth (UK) using a Voluntary Observing Ship (VOS). From December 2010 to December 2011, 20 return crossings were carried out to collect a comprehensive dataset of CO2 system parameters and ancillary data. The hydrographical structure of the water column across the latitudinal transect was investigated at 3 fixed stations: ASTAN (southern WEC, offshore Roscoff), El and L4 (northern WEC, offshore Plymouth). Based on these profiles, we defined two provinces, the stratified northern WEC (>49.5 degrees N) and the well-mixed southern WEC (<49.5 degrees N), which were periodically separated by a thermal front. These contrasted hydrographical properties strongly influenced the ecosystem dynamics. Biological production/respiration processes were the main driver of pCO(2) variability during the year except for winter cooling in the northern WEC. The seasonally stratified northern WEC showed enhanced biological activities characterized by an extensive autotrophic phase, which maintained the pCO(2) below the atmospheric equilibrium until early fall and acted as a sink for atmospheric CO2 at a rate of 1.1 mol C m(-2) y(-1). The permanently well mixed southern WEC was characterized by a shorter autotrophic phase due to a delayed spring phytoplankton growth and an early start of the fall heterotrophic phase, resulting in an annual air-sea CO2 flux close to equilibrium at a rate of -0.4 mol C m(-2) y(-1). On annual scale, calculation of Net Ecosystem Production (NEP) revealed that surface waters at El and ASTAN were both autotrophic at rates of 1.5 mol C m(-2) y(-1) and 1.0 mol C m(-2) y(-1), respectively. Our latitudinal approach resolved the discrepancy between the directions of the fluxes in the WEC observed in previous studies by differentiating between the hydrological regions. The combined approach of using data from VOS tracks and fixed coastal observatories stations provided new insights into the control of air-sea CO2 fluxes in the different provinces of the WEC. This combined approach could be applied in other continental shelf systems where data on the CO2 system are sparse. (C) 2013 Elsevier B.V. All rights reserved.
