Sabrina Speich | École Normale Supérieure (original) (raw)

Papers by Sabrina Speich

Boletín - Organización Meteorológica Mundial, 2021

EGU General Assembly Conference Abstracts, Apr 1, 2012

ABSTRACT Precise estimations of global ocean indicators (GOIs) such as global ocean heat content ... more ABSTRACT Precise estimations of global ocean indicators (GOIs) such as global ocean heat content (GOHC) and global steric sea level (GSSL) are necessary to observe the ocean's role in the Earth's climate system. To improve accuracy of these estimations, our knowledge of deep ocean and regional contributions to GOIs needs to be quantified. Data from the global Argo array are used here to analyze these contributionsduring the period 2005 to 2010. GOHC/GMSH rise increases by 25% /35% for the upper 2000m depth compared to the upper ocean 700m depth. A comparison of Argo steric sea level to total sea level from satellite altimetry (AVISO) and ocean mass (GRACE) is performed during this period. We could close the global and regional sea level budgets for 2005 to 2010 in terms of 6-year trends. Results show that largest correlation of global GSSL, ocean mass and global total sea level can be observed in the global tropical basin. Differences of the 6-year trend between global mean total sea level and GSSL in this basin are mostly explained by Argo sampling issues, especially in the - by Argo under sampled - Indonesian Archipelago. The differences of the 6-year trend in the Southern Ocean can be attributed to mass changes and deep ocean steric changes, whereas in the Northern Ocean mass changes clearly dominate decadal and longer-term variability. The results are only valid under the assumption that no systematic errors remain in either one of the global observing systems, although the comparison of all three observing systems indicates that these errors appear to be small during the years 2005 to 2010.

bioRxiv (Cold Spring Harbor Laboratory), May 8, 2015

The Tara Oceans expedition (2009-2013) sampled contrasting ecosystems of the world oceans, collec... more The Tara Oceans expedition (2009-2013) sampled contrasting ecosystems of the world oceans, collecting environmental data and plankton, from viruses to metazoans, for later analysis using modern sequencing and state-of-the-art imaging technologies. It surveyed 210 ecosystems in biogeographic provinces, collecting over 35000 samples of seawater and plankton. The interpretation of such an extensive collection of samples in their ecological context requires means to explore, assess and access raw and validated data sets. To address this challenge, the Tara Oceans Consortium offers open science resources, including the use of open access archives for nucleotides (ENA) and for environmental, biogeochemical, taxonomic and morphological data (PANGAEA), and the development of on line discovery tools and collaborative annotation tools for sequences and images. Here, we present an overview of Tara Oceans Data, and we provide detailed registries (data sets) of all campaigns (from port-to-port), stations and sampling events. .

Eos, Transactions American Geophysical Union, Jun 28, 2018

AGU Fall Meeting Abstracts, Dec 1, 2020

Trabajo presentado en la AGU Fall Meeting (2020), celebrada online del 1 al 17 de diciembre de 20... more Trabajo presentado en la AGU Fall Meeting (2020), celebrada online del 1 al 17 de diciembre de 2020.Funded by the European Commission, the H2020 EuroSea project has the objective to improve the European ocean observing system as an integrated entity within a global context, delivering ocean observations and forecasts to advance scientific knowledge about ocean climate, marine ecosystems, and their vulnerability to human impacts and to demonstrate the importance of the ocean to an economically viable and healthy society. In the framework of this project, our goal is to improve the design of multi-platform in situ experiments for validation of high-resolution SWOT observations with the aim of optimizing the utility of these observing platforms. To achieve this goal, a set of Observing System Simulation Experiments (OSSEs) will be developed to evaluate different sampling strategies and their impact on the reconstruction of fine-scale sea surface height fields and currents. Observations from CTD, ADCP, gliders, and altimetry will be simulated from three nature run models to study the sensitivity of the results to the model used. Different sampling strategies will be evaluated to analyze the impact of the spatial and temporal resolution of the observations, the depth of the measurements, the season of the multi-platform experiment, and the impact of changing rosette CTD casts for a continuous underway CTD, and adding gliders. After generating the simulated observations in different scenarios, three methods of reconstruction will be tested: multivariate reconstruction analysis, machine-learning techniques, and modelling data assimilation. To assess the best sampling strategies to validate SWOT observations during the fast-sampling phase, the reconstructed fields will be compared to (i) the ocean “truth” from the nature run models, (ii) simulated SWOT observations, and (iii) simulated observations of drifters, Argo buoys and moorings. The regions of study are the western Mediterranean Sea and the northwestern Atlantic Ocean

AGU Fall Meeting Abstracts, Dec 1, 2020

Journal Of Geophysical Research: Oceans, May 1, 2016

An enhanced Altimetry Gravest Empirical Mode (AGEM), including both adiabatic and diabatic trends... more An enhanced Altimetry Gravest Empirical Mode (AGEM), including both adiabatic and diabatic trends, is developed for the Antarctic Circumpolar Current (ACC) south of Africa using updated hydrographic CTD sections, Argo data, and satellite altimetry. This AGEM has improved accuracy compared to traditional climatologies and other proxy methods. The AGEM for the Atlantic Southern Ocean offers an ideal technique to investigate the thermohaline variability over the past two decades in a key region for water mass exchanges and transformation. In order to assess and attribute changes in the hydrography of the region, we separate the changes into adiabatic and diabatic components. Integrated over the upper 2000 dbar of the ACC south of Africa, results show mean adiabatic changes of 0.16 6 0.118C decade 21 and 0.006 6 0.014 decade 21 , and diabatic differences of 20.044 6 0.138C decade 21 and 20.01 6 0.017 decade 21 for temperature and salinity, respectively. The trends of the resultant AGEM, that include both adiabatic and diabatic variability (termed AD-AGEM), show a significant increase in the heat content of the upper 2000 dbar of the ACC with a mean warming of 0.12 6 0.0878C decade 21. This study focuses on the Antarctic Intermediate Water (AAIW) mass where negative diabatic trends dominate positive adiabatic differences in the Subantarctic Zone (SAZ), with results indicating a cooling (20.178C decade 21) and freshening (20.032 decade 21) of AAIW in this area, whereas south of the SAZ positive adiabatic and diabatic trends together create a cumulative warming (0.318C decade 21) and salinification (0.014 decade 21) of AAIW.

Earth System Science Data, Apr 12, 2021

Ocean mesoscale eddies are ubiquituos in the global ocean. They are responsible of about 80% of t... more Ocean mesoscale eddies are ubiquituos in the global ocean. They are responsible of about 80% of the total eddy kinetic energy and are suggested to exert a significant impact on air-sea interactions, ocean large-scale circulation, weather and marine ecosystems. They have been qualified as "coherent" structures as they can leave for months if not years propagating in the ocean interior. As ocean observations are very sparse, they have been essentially characterized from satellite altimetry fields, which provides access to a limited number of surface characteristics of only those eddies having an imprint on sea surface height. Observations of mesoscale eddies 3D structure, or even 2D vertical sections are rare. On the other hand, accurate description of ocean eddies from high-resolution ocean numerical simuation are also limited. In general, they have been accoubted for via statistics, instead of individual descriptions as the latter is difficult as they move away from fixed positions. In this work we present a detailed study of ocean eddies (surface and subsurface intensified) sampled during 10 oceanographic cruises which have a sufficient horizontal spatial resolution of the vertical eddy sampling - 9 in the Atlantic Ocean (during experiments EUREC4A-OA, M124, MSM60, MSM74, M160, HM2016611, KB2017606, KB 2017618), and one in the Indian (during the Physindien 2011 experiment). Our study characterizes the eddy core and boundary in a generic way using diagnostics based on active (PV, oxygen) and passive (temperature, salinity) tracers. Despite the different resolutions of the eddy sampling in the 9 studied regions, we show that the 3D boundary of an eddy behaves like a frontal zone characterized by the Ertel PV where the water mass trapped in the eddy joins with the surrounding waters. Whatever the origin and size of the eddy are, the core is homogeneous in properties with the anomaly maximum located at depth, which makes its altimetric characterization difficult. Moreover, these analyses provide a new metrix for defining the coherence of an ocean eddy, a concept that has been always ill-defined because of the elusive character and undersampling of these structures.

<p>EUREC<sup>4</sup>A-OA is a large international proje... more <p>EUREC<sup>4</sup>A-OA is a large international project, connecting experts of ocean and atmosphere observations and modelling to enhance the understanding of key ocean and air-sea processes at the and to improve the skill of forecasts and future projections.</p> <p>The core of EUREC<sup>4</sup>A-OA has been a one-month (Jan/Feb 2020) field study in the western tropical North Atlantic Ocean where high-resolution, synchronized observational data have been collected using cutting-edge technology on ships, airplanes and autonomous vehicles. EUREC<sup>4</sup>A-OA investigates heat, momentum, water and CO<sub>2</sub> transport within the ocean and exchanges across the air/sea interface using innovative high-resolution ocean observations and a hierarchy of numerical simulations. EUREC<sup>4</sup>A-OA focuses on ocean dynamics at the small-scale (0.1–100 km) and related atmospheric boundary layer processes. EUREC<sup>4</sup>A-OA is centered on the tropics where the primary external time scale affecting air-sea exchange is the diurnal cycle. However, the internal ocean and atmosphere dynamics convolute the diurnal, synoptic, seasonal and longer time scales to climate variability.</p> <p>The talk will present some of the results we obtained so far from the observations collected during the field experiment and from numerical simulations. The analyses carried out revealed with unprecedented detail the particular characteristics of the ocean small-scale dynamics, enlightening that such scales are also very active in the tropical regions and not only over the mid and higher latitudes ocean.  Observations and models also unveil that the ocean small scales is important in contributing to the exchanges of heat, freshwater and CO2 between the ocean and the atmosphere. Moreover, the evaluation of the intensity of the coupling between the ocean and the atmosphere assessed from data and high-resolution simulations show that they are very important and intimately linked with the 3D structure of the small-scale ocean dynamics. The project has also provided preliminary results in terms of parametrization of different processes influencing the ocean and atmosphere exchanges that have been uncovered by the EUREC<sup>4</sup>A-OA field experiment. Notably a better representation of the small-scale freshwater patches due to precipitation has been introduced in the French Earth-System model that improves the overall simulations of air-sea interactions and clouds. A similar parametrization is now been introduced to take into account these physical processes in air-sea fluxes of CO2.</p>

Remote Sensing, Mar 31, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Authorea (Authorea), Mar 13, 2023

This a preprint and has not been peer reviewed. Data may be preliminary.

Journal of Geophysical Research, Sep 5, 2008

Data from five CTD and 18 XBT sections are used to estimate the baroclinic transport (referenced ... more Data from five CTD and 18 XBT sections are used to estimate the baroclinic transport (referenced to 2500 dbar) of the ACC south of Africa. Surface dynamic height is derived from XBT data by establishing an empirical relationship between vertically integrated temperature and surface dynamic height calculated from CTD data. This temperature-derived dynamic height data compare closely with dynamic heights calculated from CTD data (average RMS difference = 0.05 dyn m). A second empirical relationship between surface dynamic height and cumulative baroclinic transport is defined, allowing us to study a more extensive time series of baroclinic transport derived from upper ocean temperature sections. From 18 XBT transects of the ACC, the average baroclinic transport, relative to 2500 dbar, is estimated at 90 ± 2.4 Sv. This estimate is comparable to baroclinic transport values calculated from CTD data. We then extend the baroclinic transport time-series by applying an empirical relationship between dynamic height and cumulative baroclinic transport to weekly maps of absolute dynamic topography derived from satellite altimetry, between 14 October 1992 and 23 May 2007. The estimated mean baroclinic transport of the ACC, obtained this way, is 84.7 ± 3.0 Sv. These transports agree well with simultaneous in-situ estimates (RMS difference in net transport = 5.2 Sv). This suggests that sea level anomalies largely reflect baroclinic transport changes above 2500 dbar.

Boletín - Organización Meteorológica Mundial, 2021

EGU General Assembly Conference Abstracts, Apr 1, 2012

ABSTRACT Precise estimations of global ocean indicators (GOIs) such as global ocean heat content ... more ABSTRACT Precise estimations of global ocean indicators (GOIs) such as global ocean heat content (GOHC) and global steric sea level (GSSL) are necessary to observe the ocean's role in the Earth's climate system. To improve accuracy of these estimations, our knowledge of deep ocean and regional contributions to GOIs needs to be quantified. Data from the global Argo array are used here to analyze these contributionsduring the period 2005 to 2010. GOHC/GMSH rise increases by 25% /35% for the upper 2000m depth compared to the upper ocean 700m depth. A comparison of Argo steric sea level to total sea level from satellite altimetry (AVISO) and ocean mass (GRACE) is performed during this period. We could close the global and regional sea level budgets for 2005 to 2010 in terms of 6-year trends. Results show that largest correlation of global GSSL, ocean mass and global total sea level can be observed in the global tropical basin. Differences of the 6-year trend between global mean total sea level and GSSL in this basin are mostly explained by Argo sampling issues, especially in the - by Argo under sampled - Indonesian Archipelago. The differences of the 6-year trend in the Southern Ocean can be attributed to mass changes and deep ocean steric changes, whereas in the Northern Ocean mass changes clearly dominate decadal and longer-term variability. The results are only valid under the assumption that no systematic errors remain in either one of the global observing systems, although the comparison of all three observing systems indicates that these errors appear to be small during the years 2005 to 2010.

bioRxiv (Cold Spring Harbor Laboratory), May 8, 2015

The Tara Oceans expedition (2009-2013) sampled contrasting ecosystems of the world oceans, collec... more The Tara Oceans expedition (2009-2013) sampled contrasting ecosystems of the world oceans, collecting environmental data and plankton, from viruses to metazoans, for later analysis using modern sequencing and state-of-the-art imaging technologies. It surveyed 210 ecosystems in biogeographic provinces, collecting over 35000 samples of seawater and plankton. The interpretation of such an extensive collection of samples in their ecological context requires means to explore, assess and access raw and validated data sets. To address this challenge, the Tara Oceans Consortium offers open science resources, including the use of open access archives for nucleotides (ENA) and for environmental, biogeochemical, taxonomic and morphological data (PANGAEA), and the development of on line discovery tools and collaborative annotation tools for sequences and images. Here, we present an overview of Tara Oceans Data, and we provide detailed registries (data sets) of all campaigns (from port-to-port), stations and sampling events. .

Eos, Transactions American Geophysical Union, Jun 28, 2018

AGU Fall Meeting Abstracts, Dec 1, 2020

Trabajo presentado en la AGU Fall Meeting (2020), celebrada online del 1 al 17 de diciembre de 20... more Trabajo presentado en la AGU Fall Meeting (2020), celebrada online del 1 al 17 de diciembre de 2020.Funded by the European Commission, the H2020 EuroSea project has the objective to improve the European ocean observing system as an integrated entity within a global context, delivering ocean observations and forecasts to advance scientific knowledge about ocean climate, marine ecosystems, and their vulnerability to human impacts and to demonstrate the importance of the ocean to an economically viable and healthy society. In the framework of this project, our goal is to improve the design of multi-platform in situ experiments for validation of high-resolution SWOT observations with the aim of optimizing the utility of these observing platforms. To achieve this goal, a set of Observing System Simulation Experiments (OSSEs) will be developed to evaluate different sampling strategies and their impact on the reconstruction of fine-scale sea surface height fields and currents. Observations from CTD, ADCP, gliders, and altimetry will be simulated from three nature run models to study the sensitivity of the results to the model used. Different sampling strategies will be evaluated to analyze the impact of the spatial and temporal resolution of the observations, the depth of the measurements, the season of the multi-platform experiment, and the impact of changing rosette CTD casts for a continuous underway CTD, and adding gliders. After generating the simulated observations in different scenarios, three methods of reconstruction will be tested: multivariate reconstruction analysis, machine-learning techniques, and modelling data assimilation. To assess the best sampling strategies to validate SWOT observations during the fast-sampling phase, the reconstructed fields will be compared to (i) the ocean “truth” from the nature run models, (ii) simulated SWOT observations, and (iii) simulated observations of drifters, Argo buoys and moorings. The regions of study are the western Mediterranean Sea and the northwestern Atlantic Ocean

AGU Fall Meeting Abstracts, Dec 1, 2020

Journal Of Geophysical Research: Oceans, May 1, 2016

An enhanced Altimetry Gravest Empirical Mode (AGEM), including both adiabatic and diabatic trends... more An enhanced Altimetry Gravest Empirical Mode (AGEM), including both adiabatic and diabatic trends, is developed for the Antarctic Circumpolar Current (ACC) south of Africa using updated hydrographic CTD sections, Argo data, and satellite altimetry. This AGEM has improved accuracy compared to traditional climatologies and other proxy methods. The AGEM for the Atlantic Southern Ocean offers an ideal technique to investigate the thermohaline variability over the past two decades in a key region for water mass exchanges and transformation. In order to assess and attribute changes in the hydrography of the region, we separate the changes into adiabatic and diabatic components. Integrated over the upper 2000 dbar of the ACC south of Africa, results show mean adiabatic changes of 0.16 6 0.118C decade 21 and 0.006 6 0.014 decade 21 , and diabatic differences of 20.044 6 0.138C decade 21 and 20.01 6 0.017 decade 21 for temperature and salinity, respectively. The trends of the resultant AGEM, that include both adiabatic and diabatic variability (termed AD-AGEM), show a significant increase in the heat content of the upper 2000 dbar of the ACC with a mean warming of 0.12 6 0.0878C decade 21. This study focuses on the Antarctic Intermediate Water (AAIW) mass where negative diabatic trends dominate positive adiabatic differences in the Subantarctic Zone (SAZ), with results indicating a cooling (20.178C decade 21) and freshening (20.032 decade 21) of AAIW in this area, whereas south of the SAZ positive adiabatic and diabatic trends together create a cumulative warming (0.318C decade 21) and salinification (0.014 decade 21) of AAIW.

Earth System Science Data, Apr 12, 2021

Ocean mesoscale eddies are ubiquituos in the global ocean. They are responsible of about 80% of t... more Ocean mesoscale eddies are ubiquituos in the global ocean. They are responsible of about 80% of the total eddy kinetic energy and are suggested to exert a significant impact on air-sea interactions, ocean large-scale circulation, weather and marine ecosystems. They have been qualified as "coherent" structures as they can leave for months if not years propagating in the ocean interior. As ocean observations are very sparse, they have been essentially characterized from satellite altimetry fields, which provides access to a limited number of surface characteristics of only those eddies having an imprint on sea surface height. Observations of mesoscale eddies 3D structure, or even 2D vertical sections are rare. On the other hand, accurate description of ocean eddies from high-resolution ocean numerical simuation are also limited. In general, they have been accoubted for via statistics, instead of individual descriptions as the latter is difficult as they move away from fixed positions. In this work we present a detailed study of ocean eddies (surface and subsurface intensified) sampled during 10 oceanographic cruises which have a sufficient horizontal spatial resolution of the vertical eddy sampling - 9 in the Atlantic Ocean (during experiments EUREC4A-OA, M124, MSM60, MSM74, M160, HM2016611, KB2017606, KB 2017618), and one in the Indian (during the Physindien 2011 experiment). Our study characterizes the eddy core and boundary in a generic way using diagnostics based on active (PV, oxygen) and passive (temperature, salinity) tracers. Despite the different resolutions of the eddy sampling in the 9 studied regions, we show that the 3D boundary of an eddy behaves like a frontal zone characterized by the Ertel PV where the water mass trapped in the eddy joins with the surrounding waters. Whatever the origin and size of the eddy are, the core is homogeneous in properties with the anomaly maximum located at depth, which makes its altimetric characterization difficult. Moreover, these analyses provide a new metrix for defining the coherence of an ocean eddy, a concept that has been always ill-defined because of the elusive character and undersampling of these structures.

<p>EUREC<sup>4</sup>A-OA is a large international proje... more <p>EUREC<sup>4</sup>A-OA is a large international project, connecting experts of ocean and atmosphere observations and modelling to enhance the understanding of key ocean and air-sea processes at the and to improve the skill of forecasts and future projections.</p> <p>The core of EUREC<sup>4</sup>A-OA has been a one-month (Jan/Feb 2020) field study in the western tropical North Atlantic Ocean where high-resolution, synchronized observational data have been collected using cutting-edge technology on ships, airplanes and autonomous vehicles. EUREC<sup>4</sup>A-OA investigates heat, momentum, water and CO<sub>2</sub> transport within the ocean and exchanges across the air/sea interface using innovative high-resolution ocean observations and a hierarchy of numerical simulations. EUREC<sup>4</sup>A-OA focuses on ocean dynamics at the small-scale (0.1–100 km) and related atmospheric boundary layer processes. EUREC<sup>4</sup>A-OA is centered on the tropics where the primary external time scale affecting air-sea exchange is the diurnal cycle. However, the internal ocean and atmosphere dynamics convolute the diurnal, synoptic, seasonal and longer time scales to climate variability.</p> <p>The talk will present some of the results we obtained so far from the observations collected during the field experiment and from numerical simulations. The analyses carried out revealed with unprecedented detail the particular characteristics of the ocean small-scale dynamics, enlightening that such scales are also very active in the tropical regions and not only over the mid and higher latitudes ocean.  Observations and models also unveil that the ocean small scales is important in contributing to the exchanges of heat, freshwater and CO2 between the ocean and the atmosphere. Moreover, the evaluation of the intensity of the coupling between the ocean and the atmosphere assessed from data and high-resolution simulations show that they are very important and intimately linked with the 3D structure of the small-scale ocean dynamics. The project has also provided preliminary results in terms of parametrization of different processes influencing the ocean and atmosphere exchanges that have been uncovered by the EUREC<sup>4</sup>A-OA field experiment. Notably a better representation of the small-scale freshwater patches due to precipitation has been introduced in the French Earth-System model that improves the overall simulations of air-sea interactions and clouds. A similar parametrization is now been introduced to take into account these physical processes in air-sea fluxes of CO2.</p>

Remote Sensing, Mar 31, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Authorea (Authorea), Mar 13, 2023

This a preprint and has not been peer reviewed. Data may be preliminary.

Journal of Geophysical Research, Sep 5, 2008

Data from five CTD and 18 XBT sections are used to estimate the baroclinic transport (referenced ... more Data from five CTD and 18 XBT sections are used to estimate the baroclinic transport (referenced to 2500 dbar) of the ACC south of Africa. Surface dynamic height is derived from XBT data by establishing an empirical relationship between vertically integrated temperature and surface dynamic height calculated from CTD data. This temperature-derived dynamic height data compare closely with dynamic heights calculated from CTD data (average RMS difference = 0.05 dyn m). A second empirical relationship between surface dynamic height and cumulative baroclinic transport is defined, allowing us to study a more extensive time series of baroclinic transport derived from upper ocean temperature sections. From 18 XBT transects of the ACC, the average baroclinic transport, relative to 2500 dbar, is estimated at 90 ± 2.4 Sv. This estimate is comparable to baroclinic transport values calculated from CTD data. We then extend the baroclinic transport time-series by applying an empirical relationship between dynamic height and cumulative baroclinic transport to weekly maps of absolute dynamic topography derived from satellite altimetry, between 14 October 1992 and 23 May 2007. The estimated mean baroclinic transport of the ACC, obtained this way, is 84.7 ± 3.0 Sv. These transports agree well with simultaneous in-situ estimates (RMS difference in net transport = 5.2 Sv). This suggests that sea level anomalies largely reflect baroclinic transport changes above 2500 dbar.