The Copernicus Marine Environment Monitoring Service Ocean State Report

The Copernicus Marine Environment Monitoring Service (CMEMS) Ocean State Report (OSR) provides an annual report of the state of the global ocean and European regional seas for policy and decision-makers with the additional aim of increasing general public awareness about the status of, and changes in, the marine environment. The CMEMS OSR draws on expert analysis and provides a 3-D view (through reanalysis systems), a view from above (through remote-sensing data) and a direct view of the interior (through in situ measurements) of the global ocean and the European regional seas. The report is based on the unique CMEMS monitoring capabilities of the blue (hydrography, currents), white (sea ice) and green (e.g. Chlorophyll) marine environment. This first issue of the CMEMS OSR provides guidance on Essential Variables, large-scale changes and specific events related to the physical ocean state over the period 1993–2015. Principal findings of this first CMEMS OSR show a significant increase in global and regional sea levels, thermosteric expansion, ocean heat content, sea surface temperature and Antarctic sea ice extent and conversely a decrease in Arctic sea ice extent during the 1993–2015 period. During the year 2015 exceptionally strong large-scale changes were monitored such as, for example, a strong El Niño Southern Oscillation, a high frequency of extreme storms and sea level events in specific regions in addition to areas of high sea level and harmful algae blooms. At the same time, some areas in the Arctic Ocean experienced exceptionally low sea ice extent and temperatures below average were observed in the North Atlantic Ocean

Influence de la dynamique mésoéchelle et submésoéchelle sur la compétition au sein d'un écosystème planctonique

The ocean is characterized by a high degree of turbulence with energetic eddies interacting together. In surface layers, observations and modeling studies reveal that mesoscale and submesoscale dynamics associated with the mixed layer dynamics strongly constrain the distribution of phytoplankton species. The aim of this PhD thesis is to carry out a numerical process study in order to rationalize the effect of mesoscale and submesoscale turbulence firstly, and of vertical mixing secondly, on phytoplankton diversity. The analytical study of the intrinsic dynamics of a simple ecosystem model with two phytoplankton species allowed us to determine the non-linear equilibria and their stability in the parameter space thanks to the dynamical system theory. Then, we showed that turbulent vertical diffusion is able to drive the coexistence between phytoplankton species. A sensitivity analysis to the depth of the mixed layer, to the mixing intensity and to the number of species was performed. Finally, we showed that surface quasi-geostrophic dynamics also allow the coexistence of two phytoplankton species on one single limiting resource at statistical steady state. Moreover phytoplankton species distribution depends on the turbulent structure considered: filaments are better adapted to the large phytoplankton whereas eddies are found out to be ecological niches for the small phytoplankton. Whatever the turbulent structure, this study reveals that vertical nutrient injections are a key mechanism inducing these features concerning the distribution of phytoplankton species.L'océan est un milieu fortement turbulent caractérisé notamment par de nombreuses structures tourbillonnaires très énergétiques interagissant entre elles. Dans les couches de surface, les observations ainsi que les modèles montrent que cette dynamique mésoéchelle et submésoéchelle combinée à la dynamique de la couche mélangée, contraint fortement la distribution des espèces phytoplanctoniques. L'objet de cette thèse est de réaliser une étude de processus en modélisation numérique afin de rationaliser l'effet de la turbulence méso- et subméso-échelle d'une part et du mélange vertical d'autre part, sur la diversité phytoplanctonique. L'étude analytique de la dynamique intrinsèque d'un modèle d'écosystème simple avec deux espèces de phytoplancton à l'aide de la théorie des systèmes dynamiques a tout d'abord permis de déterminer les équilibres non-linéaires ainsi que leur stabilité en fonction des paramètres. Nous avons montré ensuite que la diffusion verticale turbulente est un moteur de la coexistence des espèces phytoplanctoniques. La sensibilité de ces résultats a été testée à la fois vis à vis de la profondeur de la couche mélangée, de l'intensité du mélange et du nombre d'espèces phytoplanctoniques. Enfin, nous avons montré que la turbulence quasi-géostrophique de surface permet également la coexistence de deux espèces phytoplanctoniques sur une ressource limitante à l'équilibre statistique. De plus, ce type de turbulence organise différemment les espèces selon les structures : les structures filamentaires sont favorables au grand phytoplancton alors que les tourbillons apparaissent comme des niches écologiques pour le petit phytoplancton. Cette étude révèle que dans tous les cas, les injections verticales de nutriments sont un facteur important induisant cette différence de distribution entre les espèces

Influence de la dynamique mésoéchelle et submésoéchelle sur la compétition au sein d'un écosystème planctonique

L océan est un milieu fortement turbulent caractérisé par des structures tourbillonnaires très énergétiques interagissant entre elles. Dans les couches de surface, les observations et les modèles montrent que cette dynamique méso- et subméso-échelle combinée à la dynamique de la couche mélangée, contraint fortement la distribution des espèces phytoplanctoniques. L objet de cette thèse est de réaliser une étude de processus en modélisation numérique afin de rationaliser l effet de la turbulence méso- et subméso-échelle d une part et du me lange vertical d autre part, sur la diversité phytoplanctonique. L étude de la dynamique intrinsèque d un modèle d écosystème avec deux phytoplanctons à l aide de la théorie des systèmes dynamiques a tout d abord permis de déterminer les équilibres non-linéaires ainsi que leur stabilité en fonction des paramètres. Nous avons montré ensuite que la diffusion verticale turbulente est un moteur de la coexistence phytoplanctonique. La sensibilité de ces résultats a étè testée à la fois vis à vis de la profondeur de la couche mélangée, de l intensité du mélange et du nombre d espèces. Enfin, nous avons montré que la turbulence quasi-géostrophique de surface permet la coexistence de deux phytoplanctons sur une ressource limitante à l équilibre statistique. Ce type de turbulence organise différemment les espèces selon les structures les structures filamentaires sont favorables au grand phytoplancton alors que les tourbillons apparaissent comme des niches écologiques pour le petit phytoplancton. Cette étude révèle que les injections verticales de nutriments sont un facteur important induisant cette différence de distribution entre les espèces.The ocean is characterized by a high degree of turbulence with energetic eddies interacting together. In surface layers, observations and modeling studies reveal that mesoscale and submesoscale dynamics associated with the mixed layer dynamics strongly constrain the distribution of phytoplankton species. The aim of this PhD thesis is to carry out a numerical process study in order to rationalize the effect of mesoscale and submesoscale turbulence firstly, and of vertical mixing secondly, on phytoplankton diversity. The analytical study of the intrinsic dynamics of a simple ecosystem model with two phytoplankton species allowed us to determine the non-linear equilibria and their stability in the parameter space thanks to the dynamical system theory. Then, we showed that turbulent vertical diffusion s able to drive the coexistence between phytoplankton species. A sensitivity analysis to the depth of the mixed layer, to the mixing intensity and to the number of species was performed. Finally, we showed that surface quasi-geostrophic dynamics also allow the coexistence of two phytoplankton species on one single limiting resource at statistical steady state. Moreover phytoplankton species distribution depends on the turbulent structure considered filaments are better adapted to the large phytoplankton whereas eddies are found out to be ecological niches for the small phytoplankton. Whatever the turbulent structure, this study reveals that vertical nutrient injections are a key mechanism inducing these features concerning the distribution of phytoplankton species.BREST-BU Droit-Sciences-Sports (290192103) / SudocPLOUZANE-Bibl.La Pérouse (290195209) / SudocSudocFranceF

Phytoplankton competition and coexistence: Intrinsic ecosystem dynamics and impact of vertical mixing

International audienceThis paper aims at studying analytically the functioning of a very simple ecosystem model with two phytoplankton species. First, using the dynamical system theory, we determine its nonlinear equilibria, their stability and characteristic timescales with a focus on phytoplankton competition. Particular attention is paid to the model sensitivity to parameter change. Then, the influence of vertical mixing and sinking of detritus on the vertically-distributed ecosystem model is investigated. The analytical results reveal a high diversity of ecosystem structures with fixed points and limit cycles that are mainly sensitive to variations of light intensity and total amount of nitrogen matter. The sensitivity to other parameters such as re-mineralisation, growth and grazing rates is also specified. Besides, the equilibrium analysis shows a complete segregation of the two phytoplankton species in the whole parameter space. The embedding of our ecosystem model into a one-dimensional numerical model with diffusion turns out to allow coexistence between phytoplankton species, providing a possible solution to the ‘paradox of plankton' in the sense that it prevents the competitive exclusion of one phytoplankton species. These results improve our knowledge of the factors that control the structure and functioning of plankton communities

Effects of surface quasi-geostrophic turbulence on phytoplankton competition and coexistence

International audienceThis paper aims at studying numerically the competition between two mutually exclusive phytoplankton species in a fully-turbulent field consisting of interacting mesoscale and submesoscale structures. A simple NPPZD ecosystem model is embedded in a Surface Quasi-Geostrophic model which is able to reproduce frontogenesis and the associated nutrient vertical pump. The two simulated phytoplankton species differ by their size and their affinity for nutrients. In this study, we rationalize the role played by eddies and filaments in the distribution of the two phytoplankton species. We show that the SQG dynamics are responsible for the coexistence of the two phytoplankton species on a single limiting resource at statistical steady state. In addition, we show that as a result of strong vertical injections, filaments contain 64% of the phytoplankton biomass. The two phytoplankton species coexist in filaments but the large phytoplankton is predominant. By contrast, this latter is completely excluded from eddy cores where only the small phytoplankton develops. Since eddies are coherent structures (unlike filaments) and since their edges are almost impermeable to horizontal transport, the large phytoplankton can barely enter eddies. Therefore, eddies are ecological niches which shelter the small phytoplankton. Finally we show that interactions between eddies such as eddy merger can favor the survival of phytoplankton species within eddies on long time scales in the ocean

Amazon River propagation evidenced by a CO2 decrease at 8°N, 38°W in September 2013

The surface fugacity of CO2 (fCO2) has been measured hourly at a mooring at 8°N, 38°W, using a spectrophotometric CO2 sensor, from June to October 2013. In September 2013, the fCO2 and the sea surface salinity (SSS) decrease significantly. The high precipitation due to the presence of the Intertropical Convergence Zone (ITCZ) and the propagation of low salinity waters from the Amazon River plume explain the decrease of SSS. Indeed, in fall, the retroflection of the North Brazil Current (NBC) feeds the North Equatorial Counter Current (NECC) and transports Amazon waters to the eastern part of the tropical Atlantic. Simulations from a three dimensional physical and biogeochemical model and observations at the mooring show that the Amazon plume reached the mooring in September 2013. The decrease of fCO2 is associated with a moderate peak of chlorophyll. Over the period of the CO2 observations, the site is a source of CO2 to the atmosphere of 0.65 ± 0.47 mmol m−2 day−1. Although the wind speed is at its lowest intensity in September 2013, the flux over the whole period would be about 14% higher without this month. Every month of September from 2006 to 2017, the model simulates a decrease of dissolved inorganic carbon corresponding to the SSS minimum

The Ocean's Meridional Oxygen Transport

Quantification of oxygen uptake at the ocean surface and its surface‐to‐interior pathways is crucial for understanding oxygen concentration change in a warming ocean. We investigate the mean meridional global oxygen transport between 1950 and 2009 using coupled physical‐biogeochemical model output. We introduce a streamfunction in latitude‐oxygen coordinates to reduce complexity in the description of the mean meridional oxygen pathways. The meridional oxygen transport occurs in two main cells: (a) the Northern Cell, dominated by the Atlantic Meridional Overturning Circulation, is nearly adiabatic in the Northern Hemisphere, and transports well oxygenated waters equatorward; (b) The Southern Cell, strongly diabatic, is shaped by the circulation in the Indo‐Pacific basin, and combines the subtropical and abyssal meridional circulation cells when represented in depth‐latitude coordinates. Analysis of isopycnal meridional oxygen transport shows that the northward flow from the Southern Ocean transports well oxygenated waters within intermediate and bottom layers, while oxygen‐rich waters reach the Southern Ocean within deep layers (27.6 < σ0 < 27.9 kg m−3), carried by the North Atlantic Deep Water (NADW). This oxygenated NADW loses around 25% of its oxygen concentration along its meridional journey from the North Atlantic (at 55°N) to the Southern Ocean. These insights into the oxygen dynamics as driven by the meridional overturning circulation provide a new framework for future studies on ocean deoxygenation

Basin‐Scale Estimate of the Sea‐Air CO₂ Flux During the 2010 Warm Event in the Tropical North Atlantic

Following the anomalous warming event occurring in the tropical North Atlantic in 2010, higher than usual surface fugacity of CO2 (fCO2) was observed. To evaluate the spatial extent of these anomalies and their drivers, and to quantify the sea-air CO2 flux at basin scale, the Mercator-Ocean model is used from 2006 to 2014 within the region 0-30°N, 70-15°W. Model outputs are generally in accordance with underway sea surface temperature, sea surface salinity, and surface fCO2 recorded by two merchant ships. The anomalous warming of 2010 is well reproduced by the model and is the main driver of fCO2 anomalies. The first coupled Empirical Orthogonal Function mode, between sea surface temperature and fCO2 , captures more than 70% of the total variance and is characterized by a basin-scale warming associated to positive fCO2 anomalies. The corresponding principal components are correlated to the Tropical North Atlantic Index and identify 2010 as the year with the highest positive anomaly over 2006-2014. Exceptions to this general pattern are located near the African coast, where the weakening of the coastal upwelling causes negative inorganic carbon anomalies, and close to the Amazon River plume, where fCO2 anomalies are primarily associated with sea surface salinity anomalies. Although the fCO2 anomalies of 2010 appear mostly in spring, they affect the annual CO2 budget and lead to an increased CO2 outgassing twice as large (46.2 Tg C per year) as the mean annual flux over the 2006-2014 period (23.3 Tg C per year)

Excessive productivity and heat content in tropical Pacific analyses: Disentangling the effects of in situ and altimetry assimilation

International audienceMonitoring and predicting global ocean biogeochemistry and marine ecosystems is one of the biggest challenges for the coming decade. In operational systems, biogeochemical (BGC) models are forced - or coupled - with physical ocean models fields that are generally constrained by data assimilation of temperature, salinity and sea level anomalies. Yet, while physical data assimilation substantially improves simulated physical fields, BGC models forced by such analyses are commonly degraded, and more especially in equatorial regions. Here impacts of physical data assimilation on surface chlorophyll and nitrate concentrations are investigated in the tropical Pacific, based on three ocean reanalysis runs using the same physical-BGC model configuration but differing in their level of physical data assimilation. It is shown that, in the Mercator Ocean operational system, the assimilation of satellite altimetry and sea surface temperature in addition to temperature and salinity in situ profiles leads to spurious vertical velocities in the western equatorial Pacific. Our analysis suggests that these unrealistic vertical velocities are explained by the use of an inaccurate mean dynamic topography for the assimilation of altimetry that modifies the pressure-driven horizontal circulation in the upper ocean layer. Moreover, the biases found in this key region modify the subtle dynamical and BGC balances in the whole tropical Pacific and result in unrealistic trends of ocean heat content and nitrate concentration. This study demonstrates that looking into details of the physics is indispensable to improve physical data assimilation systems and to ensure that they make the best use of observations. This is also a key point to refine the strategy of the BGC models forcing and further improve ocean predictions