A new method for nanomolar determination of silicic acid in seawater

International audienc

Decadal phytoplankton biomass variability in two contrasted French coastal ecosystems in a climate change context

Coastal environments are highly impacted by the combined influence of anthropogenic climate change and the occurrence of persistent episodes of extreme meteorological events: warming of sea waters and changes in nutrient inputs due to the modification of precipitation patterns and consequently on river flows. Here, we study the impact of climate driven changes on phytoplankton biomass dynamics by analyzing high and low frequency of phytoplankton fluorescence and chlorophyll measurements in two French eutrophic ecosystems (Bay of Brest 2000-2019 and Bay of Vilaine 2011-2019). While the frequency and intensity of blooms in the Bay of Vilaine is driven by the supply of nutrients from rivers, no clear relationship is detected in the Bay of Brest where the residence time of water masses is short and the nutrient limitations infrequent. Long-term changes in phytoplankton biomass in these two contrasted ecosystems revealed a strong interannual variability in the timing, intensity and magnitude of blooms that occurred during the growing period (mid-March to mid-September). We observed that the first spring bloom is initiated in 2019 about 30 days earlier than 20 years ago in the Bay of Brest while it is delayed by 20 days in a decade in the Bay of Vilaine. These modifications in the timing of the phytoplankton bloom are related to a “shift” in sea surface temperature and changes in solar irradiance, as originating from the influence of large-scale hydro- climatological processes.  

SOMLIT-Brest / MAREL-Iroise : des séries d’observation physico-chimiques au service de la recherche scientifique

Les écosystèmes côtiers sont soumis à de multiples forçages physiques et chimiques qui agissent à des échelles de temps très différentes. Pour décrire et prédire l’impact de ces forçages sur les écosystèmes, il est impératif de mesurer à long terme les caractéristiques physiques, chimiques et biologiques des eaux côtières. Depuis plus de 15 ans, un partenariat réunit l’IUEM/UBO, l’IFREMER et l'INSU pour assurer le suivi régulier et à long terme de la physico-chimie des eaux côtières à l’interface de la rade de Brest et de la mer d’Iroise (site de Ste Anne du Portzic, 48°21’60 N, 4°33’04 W ). Ce suivi repose sur une stratégie combinée de mesures à basse fréquence (série SOMLIT-Brest - Service d’Observation en Milieu LITtoral) et de mesures à haute fréquence (série MAREL-Iroise - Mesure Automatisée en Réseau de l’Environnement Littoral)

Guide pour la qualification des données hautes fréquences côtières acquises dans le cadre de l'IR-ILICO et du SNO-COAST-HF.

French national observation "services" (SNO) are scientific research networks dedicated to the observation, collection and use of data. 9 of them are dedicated to the coastal ocean and are coordinated by the Coastal Research Infrastructure (IR-Ilico). Among them, there is the COAST-HF network (Coastal OceAn observing SysTem – High Frequency) which aims to bring together and coordinate a set of fixed high-frequency hydrological measurement platforms. The data acquired is used to monitor the evolution of coastal environments in the long term and detect the impact of extreme events (e.g. floods, storms, droughts, ecological crises). This data must be of optimal quality which must be controlled, evaluated and formalized.To contribute to this, 3 months of work was carried out from October to December 2022 (CDD) with the financial support of IR-ILICO. It aimed to implement the quality control tool Scoop 3 (System Of Control Oriented Oceanographic Parameters, Ifremer) in “routine” mode and apply it to standard SNO (Coast-HF-Iroise) datasets in order to test it and make it accessible to the entire network. Accessibility is ensured by this report which documents “step by step” the main stages of the validation process. This work aims to contribute to the definition and formalization of the network’s “Best Practices”.As a reminder, the data is collected by multi-parameter probes, and is sent and disseminated on various websites, including the coastal Coriolis portal. They are then checked and corrected if necessary, by expert validators, using other datasets available at the same measuring stations. This inter-comparison is essentially made with Somlit data (SNO-Service d’Observation en Milieu LITtoral), collected at low frequency, manually and analyzed in the laboratory.Specifically, three objectives were set (Fig. 1):(i) explore, test and document all websites with standard data (Iroise) in order to facilitate their use(ii) take charge of the SCOOP qualification tool and test it by qualifying the standard data (Iroise),(iii) correct the standard data (Iroise) using secondary data sets (Somlit, Météo France, etc.) and result in the establishment of the best available data for DOIsation.Les services nationaux d’observations (SNO) sont des réseaux de recherche scientifiques dédiés à l’observation, la collecte et la valorisation de données. 9 d’entre eux sont dédiés à l’océan côtiers et sont coordonnés par l’Infrastructure de Recherche Littorale et Côtière (IR-Ilico). Parmi eux, existe le réseau COAST-HF (Coastal OceAn observing SysTem – High Frequency) qui vise à fédérer et coordonner un ensemble de plateformes fixes de mesures hydrologiques hautes fréquences. Les données acquises sont utilisées pour suivre l’évolution des environnements littoraux à long terme et détecter l’impact des évènement extrêmes (e.g. crues, tempêtes, sécheresses, crises écologiques). Ces données se doivent de présenter une qualité optimale qu’il convient de maîtriser, d’évaluer et de formaliser. Pour y contribuer, un travail de 3 mois a été mené d’octobre à décembre 2022 (CDD) avec le soutien financier de l’IR-ILICO. Il visait à mettre en place l’outil de contrôle qualité Scoop 3 (Système Of Control Oriented Oceanographic Parameters, Ifremer) en mode « routine » et à l’appliquer sur des jeux de données-types du SNO (Coast-HF-Iroise) afin de l’éprouver et de le rendre accessible pour l’ensemble du réseau. L’accessibilité est assurée par le présent compte-rendu qui documente « pas à pas » les principales étapes du processus de validation. Ce travail a vocation à contribuer à la définition et la formalisation des « Bonnes pratiques » du réseau.Pour rappel, les données sont recueillies par des sondes multi paramètres, et sont envoyées et diffusées sur différents sites web, dont le portail Coriolis côtier. Elles sont ensuite vérifiées et corrigées si nécessaire, par des experts-valideurs, au moyen d’autres jeux de données disponibles sur les mêmes stations de mesure. Cette inter comparaison est faite essentiellement avec les données Somlit (SNO-Service d’Observation en Milieu LITtoral), collectées à basse fréquence, de façon manuelle et analysées en laboratoire.De façon précise, trois objectifs ont été fixés (Fig. 1) : (i)explorer, tester et documenter l’ensemble des sites web disposant des données-type ( Iroise) afin d’en faciliter l’exploitation par un public large, (ii)prendre en main l’outil de qualification SCOOP et l’éprouver en opérant la qualification des données-type (Iroise), (iii)corriger les données-type (Iroise) grâce aux jeux de données secondaires (Somlit, Météo France, etc.) et aboutir par la mise en base des données ajustées en vue de la DOIsation

Interannual variability of the initiation of the phytoplankton growing period in two French coastal ecosystems

International audienceAbstract. Decadal time series of chlorophyll a concentrations sampled at high and low frequencies are explored to study climate-induced impacts on the processes inducing interannual variations in the initiation of the phytoplankton growing period (IPGP) in early spring. We specifically detail the IPGP in two contrasting coastal temperate ecosystems under the influence of rivers highly rich in nutrients: the Bay of Brest and the Bay of Vilaine. In both coastal ecosystems, we observed a large interannual variation in the IPGP influenced by sea temperature, river inputs, light availability (modulated by solar radiation and water turbidity), and turbulent mixing generated by tidal currents, wind stress, and river runoff. We show that the IPGP is delayed by around 30 d in 2019 in comparison with 2010. In situ observations and a one-dimensional vertical model coupling hydrodynamics, biogeochemistry, and sediment dynamics show that the IPGP generally does not depend on one specific environmental factor but on the interaction between several environmental factors. In these two bays, we demonstrate that the IPGP is mainly caused by sea surface temperature and available light conditions, mostly controlled by the turbidity of the system before first blooms. While both bays are hydrodynamically contrasted, the processes that modulate the IPGP are similar. In both bays, the IPGP can be delayed by cold spells and flood events at the end of winter, provided that these extreme events last several days

Decadal Dynamics of the CO2 System and Associated Ocean Acidification in Coastal Ecosystems of the North East Atlantic Ocean

International audienceWeekly and bi-monthly carbonate system parameters and ancillary data were collected from 2008 to 2020 in three coastal ecosystems of the southern Western English Channel (sWEC) (SOMLIT-pier and SOMLIT-offshore) and Bay of Brest (SOMLIT-Brest) located in the North East Atlantic Ocean. The main drivers of seasonal and interannual partial pressure of CO2 (pCO2) and dissolved inorganic carbon (DIC) variabilities were the net ecosystem production (NEP) and thermodynamics. Differences were observed between stations, with a higher biological influence on pCO2 and DIC in the near-shore ecosystems, driven by both benthic and pelagic communities. The impact of riverine inputs on DIC dynamics was more pronounced at SOMLIT-Brest (7%) than at SOMLIT-pier (3%) and SOMLIT-offshore (<1%). These three ecosystems acted as a weak source of CO2 to the atmosphere of 0.18 ± 0.10, 0.11 ± 0.12, and 0.39 ± 0.08 mol m–2 year–1, respectively. Interannually, air-sea CO2 fluxes (FCO2) variability was low at SOMLIT-offshore and SOMLIT-pier, whereas SOMLIT-Brest occasionally switched to weak annual sinks of atmospheric CO2, driven by enhanced spring NEP compared to annual means. Over the 2008–2018 period, monthly total alkalinity (TA) and DIC anomalies were characterized by significant positive trends (p-values < 0.001), from 0.49 ± 0.20 to 2.21 ± 0.39 μmol kg−1 year−1 for TA, and from 1.93 ± 0.28 to 2.98 ± 0.39 μmol kg–1 year–1 for DIC. These trends were associated with significant increases of calculated seawater pCO2, ranging from +2.95 ± 1.04 to 3.52 ± 0.47 μatm year–1, and strong reductions of calculated pHin situ, with a mean pHin situ decrease of 0.0028 year–1. This ocean acidification (OA) was driven by atmospheric CO2 forcing (57–66%), Sea surface temperature (SST) increase (31–37%), and changes in salinity (2–5%). Additional pHin situ data extended these observed trends to the 2008–2020 period and indicated an acceleration of OA, reflected by a mean pHin situ decrease of 0.0046 year–1 in the sWEC for that period. Further observations over the 1998–2020 period revealed that the climatic indices North Atlantic Oscillation (NAO) and Atlantic Multidecadal Variability (AMV) were linked to trends of SST, with cooling during 1998–2010 and warming during 2010–2020, which might have impacted OA trends at our coastal stations. These results suggested large temporal variability of OA in coastal ecosystems of the sWEC and underlined the necessity to maintain high-resolution and long-term observations of carbonate parameters in coastal ecosystems.Introductio

Interannual variability of the initiation of the phytoplankton growing period in two French coastal ecosystems

Abstract. Decadal time series of chlorophyll-a concentrations sampled at high and low frequencies are explored to study climate-induced changes on the processes inducing interannual variations in the Initiation of the Phytoplankton Growing Period (IPGP) in early spring. In this study, we specifically detail the IPGP in two contrasting French coastal ecosystems: the Bay of Brest and the Bay of Vilaine. A large interannual variability in the IPGP is observed in both ecosystems in connection with variations of environmental drivers (solar radiation, sea temperature, wind direction and intensity, precipitation, river flow, sea level, currents and turbidity). We show that the IPGP is delayed by around 30 days in 2019 in comparison with 2010. The use of a one-dimensional vertical model coupling hydrodynamics, biogeochemistry and sediment dynamics shows that the IPGP is generally dependent on the interaction between several drivers. Interannual changes are therefore not associated with a unique driver (such as increasing sea surface temperature). Extreme events also impact the IPGP. In both bays, IPGP is sensitive to cold spells and flood events. The interannual variability of the IPGP is significant and strongly conditioned, at the local scale, by a combination of several environmental parameters, with a larger sensitivity to sea temperature and light conditions, linked to the turbidity of the system. While both bays are hydrodynamically contrasted, the processes that modulate IPGP are similar. Keywords Phytoplankton biomass, Long-term in situ observations, Coastal ecosystems, Extreme events, Climate change

Interannual variability of the initiation of the phytoplankton growing period in two French coastal ecosystems

International audienceAbstract. Decadal time series of chlorophyll a concentrations sampled at high and low frequencies are explored to study climate-induced impacts on the processes inducing interannual variations in the initiation of the phytoplankton growing period (IPGP) in early spring. We specifically detail the IPGP in two contrasting coastal temperate ecosystems under the influence of rivers highly rich in nutrients: the Bay of Brest and the Bay of Vilaine. In both coastal ecosystems, we observed a large interannual variation in the IPGP influenced by sea temperature, river inputs, light availability (modulated by solar radiation and water turbidity), and turbulent mixing generated by tidal currents, wind stress, and river runoff. We show that the IPGP is delayed by around 30 d in 2019 in comparison with 2010. In situ observations and a one-dimensional vertical model coupling hydrodynamics, biogeochemistry, and sediment dynamics show that the IPGP generally does not depend on one specific environmental factor but on the interaction between several environmental factors. In these two bays, we demonstrate that the IPGP is mainly caused by sea surface temperature and available light conditions, mostly controlled by the turbidity of the system before first blooms. While both bays are hydrodynamically contrasted, the processes that modulate the IPGP are similar. In both bays, the IPGP can be delayed by cold spells and flood events at the end of winter, provided that these extreme events last several days

Inter-laboratory comparison on a reference material for seawater spectrophotometric pH T measurements

International audienceReference materials, as well as inter-laboratory comparisons (ILCs), are two essential metrology principles allowing the validation and evaluation of a measurement method. This paper describes the use of a reference material for seawater pH(T) measurements in an inter-laboratory comparison carried out with the French coastal observation service SOMLIT, and laboratories within the project CocoriCO(2). The interpretation of the ILC results demonstrated the capability of the spectrophotometric measurement method to provide compatible results with the reference value. The ILC data also allowed the estimation of an uncertainty budget of the spectrophotometric pH(T) measurement method following the ISO standard 21748 guidelines. The estimated standard uncertainty of the method is of 0.0046 in terms of pH(T). This level of uncertainty doesn't meet the requirements of the "climate" quality objective of the Global Ocean Acidification Observing Network for the monitoring of ocean acidification. However, some recommendations that may allow reducing this uncertainty are proposed in the paper

Variabilité décennale de la biomasse phytoplanctonique dans deux écosystèmes côtiers français aux conditions contrastées

Les environnements côtiers sont fortement impactés par l'influence combinée du changement climatique d’origine naturelle et anthropique. Les impacts des épisodes d’évènements météorologiques extrêmes sur l’océan côtier restent à identifier et quantifier. Nous étudions ici l'impact du changement climatique sur la dynamique de la biomasse phytoplanctonique en analysant les mesures de fluorescence et de chlorophylle-a du phytoplancton à haute (détection des évènements extrêmes) et basse fréquence (détection des évolutions à plus long terme) dans deux écosystèmes eutrophes côtiers contrastés (rade de Brest 2000-2019 et baie de Vilaine 2011-2019). Alors que la fréquence et l'intensité des efflorescences phytoplanctoniques dans la baie de Vilaine sont sous influence directe des flux benthiques et des apports continentaux de nutriments, aucune relation n'est détectée dans la rade de Brest où le temps de résidence des masses d'eau est relativement court, et les limitations en nutriments peu fréquentes. Nos résultats mettent en évidence la forte variabilité interannuelle de la période productive des efflorescences algales - et de leur intensité - entre ces deux écosystèmes aux conditions écologiques contrastées. En se concentrant sur le début de la période productive, l'étude de ces années de floraison atypiques révèle une réponse différente entre ces deux sites d'étude face aux vagues de chaleur, aux crues extrêmes ou encore aux tempêtes. Après avoir relié l’occurrence des évènements de dessalures en rade de Brest à différents régimes de temps (AR and NAOp), les liens entre la réponse hydrodynamique de l’océan côtier, leur impact sur la biomasse phytoplanctonique et les processus à plus grande échelle  sont explorés.