Abstract : Les campagnes d’opportunité sont une pratique courante depuis des décennies, en particulier pour l’observation de l’océan. De nouveau acteurs privés tentent désormais de faire évoluer cette pratique en valorisant cette opportunité commercialement auprès de leurs clients, en particulier dans le cadre du tourisme polaire. Suite à une interpellation de Scientifiques en rébellion, le PDG du CNRS a saisi le Comité d’éthique du CNRS, qui a rendu un avis le 14 septembre sur ce sujet (https://comite-ethique.cnrs.fr/avis-du-comets-les-campagnes-dopportunite-des-partenariats-ethiques-pour-la-recherche-scientifique/).

J’en partagerai les principales conclusions et recommandations.
Lien zoom: https://ird-fr.zoom.us/j/98997616116?pwd=Yi93U2FLSVJZL0gvYmVGK1RUQlUvZz09
Contact at LOCEAN in charge of the seminar: Eric.Guilyardi@locean.ipsl.fr

Abstract : Water isotopic composition in ice core records is a favour proxy of past temperatures. This climatic signal is acquired across the hydrological cycle from evaporation to the formation of snowflakes in Polar Regions. In between, an array of processes affecting the water isotopes, which provide opportunities to study the atmospheric boundary layers and its exchange between the ice and the ocean.
Making use of new infrared spectroscopy developments to measure in situ water isotopes in the field, it is now possible to monitor the variations of isotopic composition in the atmospheric, in the precipitation and the surface snow, and to use water isotopes as a tracer of the water cycle. In this seminar, I will provide examples of on-going projects using water isotopes to study the hydrological cycle in the three poles (Antarctica, the Arctic, and the Himalayas) and to identify the signature of climate change in ice core records.
Lien zoom: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09
Contact at LOCEAN in charge of the seminar: mathieu.casado@lsce.ipsl.fr

Abstract: Ever since the United Arab Emirates took over the COP28 presidency, appointing a minister who is also CEO of the national oil company as COP President, controversy has been rife. This year, even more than in previous years, many NGOs have called for a boycott of this doomed COP. On the other hand, since the adoption of the Paris Agreement, we know that COP28 will be a crucial COP that is supposed to take stock of the commitments made by countries under the Paris Agreement, which only happens once every 5 years. It was therefore a closely watched COP, with high expectations on the part of civil society. The aim of this presentation will be to shed light on the course of COP28, the tensions that took place, the advances and failures, and more generally to discuss the usefulness of COPs.

Lien zoom:  https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09

Abstract:

The Northwest Tropical Atlantic (NWTA) is a region with complex surface ocean circulation. The most prominent feature is the North Brazil Current (NBC) and its retroflection at 8ºN that leads to the formation of numerous mesoscale eddies known as NBC rings. The NWTA also receives the outflow of the Amazon River, generating freshwater plumes that can extend up to 100,000 km2. These two processes affect the spatial variability of the region’s surface latent heat flux (LHF). First, the presence of surface freshwater modifies the vertical stratification of the ocean limiting the amount of heat that can be released to the atmosphere. Second, they create a highly heterogeneous mesoscale sea-surface temperature (SST) field that directly influences near-surface atmospheric circulation. These effects are illustrated by observations from the ElUcidating the RolE of Cloud-Circulation Coupling in ClimAte – Ocean Atmosphere (EUREC4A-OA) and Atlantic Tradewind Ocean-Atmosphere Interaction Campaign (ATOMIC) experiments, satellite and reanalysis data. We decompose the LHF budget into several terms controlled by different atmospheric and oceanic processes to identify the mechanisms leading to LHF changes. We find LHF variations of up to 160Wm2, of which 100Wm2 are associated with wind speed changes and 40Wm2 with SST variations. Surface currents or stratification-change associated heat release remain as second-order contributions with LHF variations of less than 10Wm2 each. The results highlight the importance of considering these three components to properly characterize LHF variability at different spatial scales.

Lien zoom: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09

Abstract: We use a coupled physical-biogeochemical model to investigate the drivers and mechanisms responsible for the spatiotemporal variability of the partial pressure of carbon dioxide in seawater (pCO2) and associated air-sea CO2 fluxes in the Northern Humboldt Current System (NHCS). The highly productive upwelling region, 300 km from the shore and between 5 and 17 °S, is shown to be a strong CO2 source with an averaged flux of 5.60 ± 2.94 mol C m −2 year−1, which represents an integrated carbon flux of 0.028 ± 0.015 Pg C year−1. Through a series of model experiments, we show that the high pCO2 is primarily the result of coastal upwelling, which is incompletely compensated by biology. Specifically, the supply of dissolved inorganic carbon (DIC)-rich waters to the surface pushes pCO2 up to levels around 1100 μatm. Even though biological production is high, it reduces pCO2 only by about 300 μatm. We show that this relatively low degree of biological compensation results from a spatio-temporal decoupling between the counteracting effects of biological production and the transport and mixing of DIC. The contribution of the outgassing and the processes affecting CO2 solubility, associated with the seasonal cycle of heating and cooling, are minor. We demonstrate that seawater pCO2 is more sensitive to changes in DIC and sea surface temperature, while alkalinity plays a minor role.
lien zoom: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09

Abstract : Le monde de la recherche française offre de nombreuses portes d’entrées, que l’on veuille y officier comme chercheur.e, ingénieur.e, technicien.ne, personnel administratif, etc… Le point commun de nombre de ces portes d’entrées est qu’elles consistent en un concours de la fonction publique. Pas forcément facile de se repérer dans la forêt d’acronymes et de pratiques qui permettent de se frayer un chemin jusqu’à un poste permanent dans le métier de vos rêves. Notre participation actuelle à des commissions de recrutement du CNRS (Claire pour la section 19) et de l’IRD (Jérôme pour la CSS1) nous permettra peut-être de vous éclairer, et idéalement de vous aider dans vos futures candidatures.

Section 19, CSS1, INSU, planète IRD, admissibilité, admission, pré-sélection, oraux n’auront plus de secret pour vous suite à ce séminaire qui laissera la part belle à vos questions et à un temps d’échange. Venez aussi à ce moment d’échange avec vos expériences de candidat ou jury à des postes d’enseignant-chercheur, d’ingénieur, etc…
Contact at LOCEAN in charge of the seminar: cartlod@locean-ipsl.upmc.fr
lien zoom: https://ird-fr.zoom.us/j/92240587693?pwd=Skk4ZGV0VGVKclhBYWs2b2hxN0RrQT09

Abstract : The melting of Arctic sea ice in spring is driven by the absorption of solar radiation and its conversion into heat within the sea ice. Despite the importance of this thermodynamic process, numerous uncertainties persist regarding the schemes used in Earth system models. These uncertainties persist because current measurement methods make it difficult to estimate the amount of solar energy absorbed within the sea ice.

The objective of my doctoral project is to quantify this heat absorption using spectral albedo measurements taken in the field. Spectral albedo is a commonly performed measurement during field campaigns on sea ice. By applying our method to these existing datasets, we hope to provide data on solar energy absorption for different regions and times of the year in the Arctic. These data will then be used to evaluate the schemes for solar radiation partitioning currently implemented in Earth system models.

Contact at LOCEAN in charge of the seminar: aplod@locean-ipsl.upmc.fr

lien zoom: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09

Abstract : The El Niño Southern Oscillation (ENSO) is the dominant mode of interanual climate variability on our planet. The recharge oscillator (RO) is a surprisingly simple conceptual model of ENSO, that can reproduce most of its essential properties. Those properties include ENSO amplitude, dominant periodicities, and asymmetries between the warm (El Niño) and cold (La Niña) phases. In this talk, I will present the outcomes of a review of the RO undertaken in the framework of the CLIVAR ENSO conceptual model working group. We will see that the simple mathematical form of the RO encapsulates a lot of the state-of-the-art knowledge about the essential physics of ENSO, and can be used to address questions such as predictability or ENSO biases in climate models. We will also discuss the limits of the current RO formulation, and pave the way for developments that will allow it to better address hot topics such as ENSO diversity, “super El Niño events, and the response of ENSO to climate change.
Lien zoom: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09
Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

Abstract : Over last decades, climate change has shifted from being primarily a scientific concern to emerging as one of the defining environmental challenges within our society. However, science alone cannot guide us on how to address this crisis. This challenge is also about how we envision living together, what we collectively value, and the level of risk we are prepared to assume. It fundamentally pertains to the kind of society we aspire to, making education a pivotal component. Inspired by the Paris Agreement, the time has arrived for Climate Change Education. It derives its momentum from the aspirations and mobilization of the youth, making it the most potent transformative action in response to climate change.

Climate Change Education comes with unique and exciting opportunities. Firstly, it offers a chance to learn about science in general and climate science specifically, drawing from authoritative sources like IPCC reports. Secondly, it provides an avenue to acquire life skills, humanities knowledge, and insights into global citizenship, imparting a holistic perspective to the young generation on a global scale. Lastly, it fosters critical thinking, hopeful hearts, and empathy in an ever-evolving educational landscape. However, Climate Change Education presents numerous challenges as it strives to balance the development of cognitive, emotional, and practical aspects within existing education systems. Educators need to be prepared for this unique combination of ‘head’, ‘heart’, and ‘hands’.

The mission of the Office for Climate Education (OCE), a center under the auspices of UNESCO, is precisely to empower educators in preparing young generations with a robust understanding of climate change and the skills needed to act as global citizens in a changing world. The OCE, driven by collaboration between climate science and educational communities, develops sets of pedagogical resources, offers teacher professional development opportunities, and facilitates networks of practice in more than 20 countries. As a pivotal co-coordinator of the newly established Greening Education Partnership of the UN, the OCE serves as a bridge between the global landscape of IPCC-based science and the specific needs of local primary and secondary education systems worldwide.

Zoom link: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09
Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

Abstract : Les variations de la précipitation sahélienne ont des conséquences importantes sur les populations locales (agriculture, sècheresses, inondations). Les changements futurs de la précipitation sahélienne sont cependant incertains avec les modèles de climat simulant baisse et hausse de la précipitation a la fin du 21ième siècle. J’aborde donc, dans cette présentation, la question de l’incertitude entre modèles à simuler l’évolution future de la précipitation Sahélienne. La source principale d’incertitude est la simulation de la circulation atmosphérique, et donc de la partie dynamique du changement de la précipitation. Je montre que ces incertitudes sont liées aux différences entre modèles à simuler la hausse des températures de l’hémisphère nord et propose plusieurs scenarios d’évolutions de la précipitation qui tiennent compte d’évolutions contrastées de la température de l’hémisphère nord (Atlantique nord et Mer Méditerranée).

lien zoom ici: https://ird-fr.zoom.us/j/97884343631?pwd=MkZMQlBsRnlDWURmTC9PR2VDTWU4dz09
Contact at LOCEAN in charge of the seminar: juliette.mignot@locean.ipsl.fr

Abstract : Le groupe info a mis en place un questionnaire dans le but de dresser un état des lieux au Locean sur l’utilisation des outils informatiques et d’orienter les choix d’investissement pour la définition future des services informatiques communs proposés par le laboratoire. Les résultats seront présentés et feront l’occasion d’échanges.
Contact at LOCEAN in charge of the seminar: frederic.boller@locean.ipsl.fr
lien zoom: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09

Camille nous rend visite jeudi et vendredi dans le cadre de sa candidature au poste MCF ouvert au LOCEAN. Vous pouvez la contacter à l’adresse camille.richon@univ-brest.fr

Abstract : Among all the anthropogenic contaminants found in the ocean, microplastics (MP) are particularly interesting because of their ubiquity and potential impacts in all oceanic regions and compartments. Over the past few years, most of my research has been dedicated to understanding the drivers of the global 3D distribution of MP in the global ocean and their potential impacts on ocean biogeochemical cycles. This seminar, in the context of my application for the MCF position at LOCEAN, will showcase my research on using numerical modeling to understand MP distribution and fate on a global scale. Then, I will present the main research questions I will explore in the next few years. The main question of my research project will be to characterise the global oceanic cycle of MP. To this end, I will mainly use numerical modelling, which is the only tool that allows the change of scale required to integrate all the current knowledge on MP, to 1) quantify the abiotic exchanges of MP at the oceanic boundaries in order to specify their mass balance and residence time in the ocean, 2) assess the influence of abiotic environmental factors on the distribution of MP, 3) understand the influence of interactions between MP and biotic factors on their fate in the water column. My project, based on strong interaction between disciplines and methodologies, will enable us to understand whether and how the factors influencing the oceanic cycle of MP observed on a small scale are significant on a global scale and will pave the way towards the study of the impact of MP on biogeochemical processes and marine ecosystems.

Zoom link: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09

Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

Abstract: Coccolithophores are a main marine calcifier critical to ocean carbon pumps (via organic matter ballast and the carbonate pump), ultimately controlling atmospheric CO2 and climate. However, their contribution to the global carbon cycle is still very uncertain, limiting our understanding of their impact and response to climate change. One major issue is that most coccolithophore studies rely solely on one outlier species (Emiliania huxleyi), which is relatively small and lightly calcified. Here, I present the development of two modelling approaches, deterministic and probabilistic, to explore the impact of coccolithophore diversity on the global ocean. The deterministic model represents processes and relies on trait-based approaches, where biodiversity is captured by functional diversity, which defines functional groups of similar traits (e.g., size, calcification) and trade-offs (costs and benefits of a particular trait). We review the costs and benefits of coccolithophore’s main trait of calcification and find that calcification has multiple benefits explaining their high diversity and broad ecological niches. We then apply novel machine-learning techniques to determine the global distribution of the top 52 species and the total calcite production of coccolithophores. These techniques build predictive models of coccolithophore carbon stocks and calcite production based on newly compiled datasets of coccolithophore abundance and calcification rates, which we combined with environmental data. Our species predictive model shows that a handful of species, including Emiliania huxleyi, are responsible for the global calcite standing stock, with subtropical species being a significant contributor. Our rate predictive model also supports this finding, showing large calcification rates in the subpolar and subtropical regions. This result revisits the traditional view that coccolithophore calcification primarily occurs in subpolar bloom-like events and that other species besides Emiliania huxleyi should be considered to resolve coccolithophore’s subtropical contribution. 

Zoom link: https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09 (Meeting ID: 986 8549 8044 / Passcode: 627318)
Contact at LOCEAN in charge of the seminar: sakina-dorothee.ayata@locean.ipsl.fr

Cosme Mosneron-Dupin: Reconstructing the 2003-2022 Sea Level Anomalies field in ice-covered regions of the Southern Ocean.

Abstract : Despite its pivotal role in the climate system, subpolar circulation in the Southern Ocean remains poorly observed, primarily owing to the physical limitations of conventional satellite altimetry in ice-covered regions. However, recent progress in processing methods now enables precise SLA (Sea Level Anomalies) estimations within sea-ice fractures and leads. Thanks to these advances, previous studies were able to construct altimetry maps with a complete Southern Ocean coverage over the period 2011-2019. It allowed for the quantification of its full SLA seasonal cycle. Here, we introduce a novel SLA product that encompasses both open and ice-covered oceanic domains, and covers a larger temporal expanse amounting to two decades (2003-2022). Employing an optimal interpolation approach, multiple satellite missions, namely Envisat, Cryosat, SARAL/AltiKa, and Sentinel-3, are combined together, improving spatial resolution and increasing temporal range. A newly developed algorithm ensures the seamless continuity of observations, bridging the observational disconnect between open-ocean and leads data points. The robustness of the derived SLA product is corroborated against in-situ data from moorings and bottom pressure recorders. The observed seasonal cycle aligns consistently with the existing literature. Overall, the temporal extent of this dataset provides, for the first time, the opportunity to investigate the interannual variability of the whole Southern Ocean circulation through observational data.

Linus Vogt: Increased future ocean heat uptake constrained by Antarctic sea ice extent

Abstract: The ocean moderates global warming by absorbing most of the excess heat resulting from anthropogenic climate change. However, this ocean heat uptake also causes sea level rise, more frequent extreme events, ocean deoxygenation, and multiple impacts on marine ecosystems. Despite their importance for informing climate mitigation and adaptation measures, ocean heat uptake projections still strongly differ between climate models. Here, we provide improved global ocean heat uptake projections by identifying a relationship between present-day Antarctic sea ice extent and future ocean heat uptake across an ensemble of 28 state-of-the-art climate models. Models with a higher present-day sea ice extent also simulate greater sea ice loss over the 21st century, a stronger global cloud feedback and atmospheric warming, and hence increased ocean heat uptake. By combining this relationship with satellite observations of Antarctic sea ice, we reduce the uncertainty of ocean heat uptake projections under realistic future emissions scenarios by 12-33%, and show that models underestimate present-day sea ice extent and consequently future ocean heat uptake by 5-7%. Our findings indicate that accounting for biases in the Southern Ocean mean state in the latest generation of climate models implies larger future climate warming.

Stephane Doleac: Toward more robust NPP projections in the North Atlantic Ocean

Abstract : Phytoplankton plays a crucial role in various oceanic environmental services but is currently under mounting pressure due to climate change, which jeopardizes the oceans’ ability to uphold these services. However, the impact of climate change on the net primary production (NPP) of phytoplankton in the North Atlantic Ocean remains uncertain. The traditional method of model inter-comparison fails at providing robust projections, because the processes controlling them strongly differ from one model to another, thus causing model divergence. The identification of these processes enables an assessment of CMIP6 models’ reliability to project NPP in the region, and thus lay the ground for an informed selection of models to obtain more robust and precise projections. Such an approach was conducted over the North Atlantic Ocean with eight CMIP6 models exhibiting substantial divergence in NPP projections. The North Atlantic basin was divided into three bioregions tailored to each model’s characteristics using a novel method based on a clustering procedure. Each region was then studied successively and new estimates of NPP projections in the subpolar and subtropical regions were obtained. These revised NPP projections provide new insights into the future evolution of carbon export and phytoplankton biomass in the subtropical region, indicating larger decreases than previously anticipated.

Léonard Barthélemy: Future Atmospheric Rivers in Antarctica using CMIP6-IPSL model : intensity and impacts

Abstract: Atmospheric Rivers (AR) are extreme hydrological events that have strong impacts on the different components of the Antarctic ice sheet surface mass balance (SMB), through both snow accumulation and surface melt due to heating and rain. Their evolving characteristics are therefore important to understand for an accurate prediction of future SMB changes. We use here an ensemble of simulations of the mid-21st century climate using the IPSL-CM6 model. The future Antarctic ARs are identified using a detection algorithm adapted to the region, and taking into account in the detection threshold (based on moisture fluxes) the rising background moisture in a warmer climate. While a constant detection threshold leads to a continuous increase of the number of ARs detected, the use of this adaptative threshold leads instead to a relatively stable frequency of occurence, but with a larger penetration over Antarctica (+5% occurence over the continent). In addition, a wave number 3 component appears in the future change in frequency, as well as in AR-related snowfall. While the number of ARs does not change much, their intensity, as measured by the associated water vapor transport, increases in line with the Clausius-Clapeyron relation. Their different impacts on the SMB also become larger, with both increasing snowfall, and surface melt and rainfall in the coastal regions. The direct effect on the SMB is however dominated by the increase in snow accumulation.

Zoom link: https://ird-fr.zoom.us/j/98688494717?pwd=SG5zRDNOc0pQZC84dHg0VklMMzJqUT09 (Meeting ID: 986 8849 4717 / Passcode: 189793)
Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

Abstract : title: Une vocation du Sud: an enduring 20-year Franco-Australian bio-physics research collaboration in the Southern Ocean (Pr Mark Hindell)

short abstract: The year 2004 saw the first deployments of ocean sensing satellite tags on southern elephant seals at Iles Kerguelen, marking the beginning of an extraordinary international collaboration which now spans two decades. This is one of longest continuous running telemetry studies in world and has to date produced invaluable data observing and integrating essential physical and biological variables and properties of the Southern Ocean to provide a remarkable body of information allowing us to link changes in the ocean with animal behaviour at a time that has seen major shifts in the global climate and the World’s oceans that store vast amounts of anthropogenically generated heat and carbon dioxide. Here we describe this unique 20-year time series conducted collaboratively by CEBC, IMOS, L’Ocean and IMAS focusing on three areas: (1) Seals now provide more CTD profiles from south of 65o than any other method which play an important role in characterising the physical oceanography, including discovering areas of Antarctic Dense Water production that are central to global current formation and strength, on the Southern Indian Ocean and how it is changing and improving Antarctic bathymetry. (2) New insights into how seals use the marine environment, and in particular how they respond to spatial and temporal variability in that environment and (3) How the tracking data can assist with spatial management of marine resources by testing for the likelihood of competition with fishers and, when combined with information from multiple other species, can identify areas of particular ecological importance. Finally, we will look to the future of the collaboration and the important roll it will play in ongoing programs seeking to understand and protect the Southern Ocean and its ecosystems.

title: Southern Ocean pinnipeds provide bathymetry across the Antarctic continental shelf (Dr Clive McMahon)

The poor coverage of bathymetric data for the Antarctic continental shelf is an impediment to understanding oceanographic processes affecting Antarctica’s role in global climate. The shape of the bed on the continental shelf influences how warm water infiltrates onto the shelf, making it an important factor promoting ice shelf melting and influencing the flow of ice shelves into the ocean. These issues have global implications for sea-level rise and deep ocean circulation. Building on previous work using seal dives to redefine bathymetry, our decades-long study of ocean physics and animal behaviour provided new ocean depth information from over 500,000 individual dives from 265 seals on the East Antarctica continental shelf. The seal tags have a post-processed position uncertainty of 2-3 km, and provide transmitted depth data with a resolution of 10-25 m. About 25% of these seal dives were, on average, 220 m (sometimes over 1000 m) deeper than the interpolated seafloor in the International Bathymetric Chart of the Southern Ocean Version 2. Focusing on four well-sampled regions, we show that the bathymetry of between 22% and 60% of the sampled area was improved by incorporating seal dive data. This revealed new bathymetric features, including troughs off the Shackleton Ice Shelf and Underwood Glacier and a deep canyon near the Vanderford Glacier. Further acquisitions of seal data will improve our understanding and modelling of Antarctic coastal ocean processes and ice sheet dynamics. A new circumpolar initiative; the Southern Ocean Animal Borne Bathymetry Atlas (SO-ABBA), will use seal dive depths to map the Antarctic Shelf and identify key areas for targeted and detailed hydrographic analyses which will help better model hydrodynamic process and heat exchange along the Antarctic Coast.

zoom: https://ird-fr.zoom.us/j/97911060256?pwd=VWdFT1dESUdYSVpjdVFFOFFYbzB1QT09
id: 979 1106 0256
password: 186823

Contact at LOCEAN in charge of the seminar: jbclod@locean.ipsl.fr

Abstract : The expansion of autonomous observation platforms offers vast opportunities for analyzing ocean ecosystems and their role in carbon export. As part of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaigns, we autonomously measured the productivity regimes in two contrasting endmember sites. The first campaign occurred in a high nutrient, low chlorophyll site in the subpolar North Pacific (NPac) near Ocean Station Papa, characterized by iron limitation and a highly regenerative regime, while the second captured a springtime bloom in the North Atlantic (NAtl), which typically drives efficient export of productivity. Using a combination of floats and gliders equipped with biogeochemical sensors, gross primary productivity (GPP), net community production (NCP), and an organic carbon flux (fCorg) were quantified and compared to ship-based measurements. The NAtl site demonstrated higher cruise-period productivity, with roughly 5x the GPP and 14x the euphotic zone NCP seen in the NPac. Greater export efficiency in the NAtl was reflected in numerous indices, such as the ratio of new production to NPP (ef-ratio; NPac: 0.23; NAtl: 0.74), the ratio of sinking particulate organic carbon (POC) to NPP (ez-ratio; NPac: 0.35; NAtl: 0.70), and total cruise-integrated 100m fCorg (NPac: 87; NAtl: 514 mmol C m-2). Together with POC flux derived from thorium-234 measurements, we infer that observed low NCP was almost entirely routed to sinking POC in the NPac, while the much higher NCP in the NAtl resulted in near equal proportions routed to dissolved organic carbon production and sinking POC flux.
https://ird-fr.zoom.us/j/92668042850?pwd=UUZrRHVSRTVwWHZyN2FBck9ZMGljUT09
ID reunion: 926 6804 2850
Mot de passe: 829690

Contact at LOCEAN in charge of the seminar: cartlod@locean-ipsl.upmc.fr

Abstract : Ce séminaire est organisé sur invitation de l’Académie de Marine, il sera donc EN FRANCAIS.

Les océans perdent de l’oxygène en raison du changement climatique. Nos décideurs politiques sont conscients du phénomène et communiquent sur son importance. Par exemple, Emanuel Macron a déclaré sur Twitter : L’oxygène que nous respirons ? L’océan en produit plus de la moitié. L’océan est notre poumon, un poumon qui menace aujourd’hui de s’étouffer. Le protéger est un impératif au moins aussi grand que celui de la préservation de l’Amazonie, notre autre poumon. Malgré la réelle nécessité de protéger nos océans, ces messages sont entachés d’incompréhension. L’océan a produit 6/7 du stock d’oxygène atmosphérique au cours des temps géologiques. Aujourd’hui, la moitié de la photosynthèse terrestre a lieu dans les océans et cette production d’oxygène permet aux écosystèmes marins de respirer. La désoxygénation des océans menace donc directement le stock d’oxygène océanique et les écosystèmes marins.

Pour comprendre la distribution de l’oxygène terrestre et son cycle moderne, je vais retracer l’histoire de l’oxygène et les mécanismes qui ont conduit à sa lente accumulation dans l’atmosphère. Dans l’océan, l’oxygène se trouve sous forme dissoute, de sorte que la circulation océanique crée une distribution spatiale de l’oxygène très hétérogène. Les zones de minimum d’oxygène (OMZ), où les niveaux d’oxygène sont inférieurs aux niveaux d’hypoxie, sont des régions critiques pour les écosystèmes marins et dont les niveaux d’oxygène ont une grande variabilité naturelle. Ces zones sont affectées par la désoxygénation de l’océan. Nous avons utilisé le modèle couplé IPSL-CM6A-LR pour déterminer quand le signal anthropique fera sortir ces zones vulnérables de leur variabilité naturelle, rendant des zones inhabitable pour les écosystèmes marins.

Le processus de communication et de partage d’informations claires, précises et complètes entre les scientifiques et les décideurs politiques semble avoir échoué en ce qui concerne la désoxygénation des océans. Pour comprendre comment ces informations sont communiquées, nous avons examiné les discussions sur la désoxygénation des océans dans les six cycles du GIEC et dans le rapport spécial sur l’océan et la cryosphère (SROCC). Je présenterai l’attention accordée et les choix de communication sur la désoxygénation des océans au sein des rapports du GIEC.

https://cnrs.zoom.us/j/98698085788?pwd=V0gxdHJxTDl0dlAvQ0kyRHBvOTEvUT09

ID de réunion: 986 9808 5788

Code secret: zgZYs6

Contact at LOCEAN in charge of the seminar: mathieu.delteil@locean.ipsl.fr

Abstracts:

– Valentin Deteix 

title: Assessing the activity and structure of the phytoplankton community in the South Indian Ocean

short abstract: The biological carbon pump (BCP), i.e. the transfer of organic carbon biologically fixed by primary production (PP) from the euphotic zone to the deep ocean, constitutes one of the major processes for removing CO2 from the atmosphere and sequestering it for long periods of time. One of the main factors controlling the BCP is the intensity of the PP and the structure of the phytoplankton community, which in turn depend on the chemicophysical conditions of the ocean. In this seminar, I will present results from the SOCARB cruise (South Indian Ocean CARBon fluxes from the surface to the mesopelagic twilight zone) conducted during the late austral summer of 2023. This includes: (i) PP from 13C tracer method and on-deck incubations, (ii) pigments from high performance liquid chromatography and (iii) phytoplankton abundance from onboard cytometry flux analyses. PP and pigment samples were size-fractionated ( 20 µm) to quantify the impact of these different size groups on CO2 uptake and to assess the structure of the phytoplankton community. I will discuss the intensity level of PP and the variability of the phytoplankton community in the South Indian Ocean, and conclude with perspectives for future work (e.g. coupling with carbon export data, metagenomics). 

– Margaux Perhirin 

title: Could faecal pellets be identified from in situ images in the Arctic? 

short abstract: Mesozooplankton play a crucial role in pelagic ecosystems by linking primary producers to higher trophic levels and by controlling the biological carbon pump (BCP) through the production of sinking particles, including sloppy feeding, faecal pellets, moults, and carcasses. However, the quantification of their impacts on the carbon cycle remains difficult. Usually, faecal pellets’ contribution is assessed using data from sediment traps or from laboratory studies followed by extrapolations. Here, using a morphological approach we identified 50,771 faecal pellet-like particles distributed in three morphological clusters among 987,236 in situ images of non-living particles collected from the Underwater Vision Profiler (UVP) in the Baffin Bay. By comparing their morphology with faecal pellets produced by copepods in laboratory, and their size with faecal pellets from copepod incubations, sediment traps sampling and literature review, we tried to determine which organisms produced them. We then emphasise the importance to develop imaging tools with a higher size resolution and/or capable of imaging large crustaceans zooplankton. This study paves the way for a better comprehension of faecal pellets’ dynamics which could help to gain a more detailed knowledge of their role in carbon export and potentially improve their representation in biogeochemical models. 

Contact at LOCEAN in charge of the seminar: margaux.perhirin@locean.ipsl.fr

Résumé: L’activité de recherche au LOCEAN dépend largement de grandes infrastructures nationales et européennes organisées d’une part autour de la capacité à observer systématiquement l’océan et pour des ‘campagnes recherche’, et d’autre part à le modéliser numériquement. Si nous sommes pour la plupart familiers au LOCEAN du deuxième domaine – bientôt 40 ans pour l’ancêtre de NEMO qui est largement utilisé en Europe – paradoxalement pour un laboratoire d’océanographie, nous le sommes moins du premier, au moins en ce qui concerne les données in-situ, les produits spatiaux faisant désormais largement partie du quotidien. Il sera question dans ce séminaire de l’observation in-situ de l’océan, de son organisation, en pleine transformation actuellement, et du rôle des infrastructures de recherche.

Le GOOS, créé il y a 30 ans à la suite de la 2ème Conférence Mondiale sur le Climat de 1990, s’est particulièrement appuyé sur les initiatives des grandes institutions américaines soutenues par la NOAA, mais aussi Européennes, pour créér les programmes GO-SHIP, ARGO, OceanSITES, OceanGliders, … qui structurent actuellement l’observation de l’océan à l’échelle globale. Les infrastructures de recherche européennes établies à partir de 2010 environ à l’initiative de l’ESFRI et de la CE (Euro-Argo, EMSO, ICOS OTC) et les projets (EuroGO-SHIP, GROOM RI, JERICO RI, …) reflètent en grande partie l’organisation globale et structurent à leur tour largement l’activité des grands organismes en Europe, comme l’INSU/CNRS et l’Ifremer pour la France. Et pour la plupart, les pays organisent aujourd’hui leurs propres infrastructures de recherche en cohérence avec ces niveaux européen et global (par ex. Euro-Argo France, EMSO France, ICOS-France, ILICO, …).

A l’instar du séminaire de Francesco D’Ovidio sur SWOT il y a quelques mois, après une présentation de ces infrastructures, des transformations qui s’y opèrent, du défi du ‘net zero observation’ auquel elles font face, nous pourrons répondre à vos questions, analyser ensemble la position du LOCEAN vis-à-vis de ces infrastructures et sa capacité (qui est à renouveler si on considère la pyramide des âges dans le laboratoire) à y contribuer et de quelle façon.

https://ird-fr.zoom.us/j/91997113145?pwd=Wm96MWN3cmdPK25sZU9NdXJucldwdz09
Meeting ID: 919 9711 3145
Passcode: 304201

Contact at LOCEAN in charge of the seminar: aplod@locean-ipsl.upmc.fr

abstract: As well as having an impact on the background state of the climate, global warming due to human activities could affect its natural oscillations and internal variability. In this study, we use four initial-condition ensembles from the CMIP6 framework to investigate the potential evolution of internal climate variability under different warming pathways for the 21^st century. Our results suggest significant changes in natural climate variability, and point to two distinct regimes driving these changes. First, a decrease of internal variability of surface air temperature at high latitudes and all frequencies, associated with a poleward shift and the gradual disappearance of sea-ice edges, which we show to be an important component of internal variability. Second, an intensification of the interannual variability of surface air temperature and precipitation at low latitudes, which appears to be associated with the El Niño–Southern Oscillation (ENSO). This second regime is particularly alarming because it may contribute to making the climate more unstable and less predictable, with a significant impact on human societies and ecosystems.

https://ird-fr.zoom.us/j/98685498044?pwd=bC9HUDJMemkwVUx2bWthWFIxQkNOdz09

Meeting ID: 986 8549 8044

Passcode: 627318

Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

Abstract: Understanding the consequences of global warming on marine ecosystems and ultimately on foraging behavior of marine predators is key. To address this challenge, a set of new sensors, and associated algorithms, have been developed and implemented on female elephant seals from the Kerguelen Islands. The high-resolution used to assess the biological landscapes associated with intermediate trophic levels, i.e. zooplankton and micronekton, include the measurement of light associated with the bioluminescence flash, passive acoustics, echo-sounding and the assessment of the number of prey capture attempts (PrCA) from acceleration measurements. Miniature echo sounders are used to characterize the composition in terms of size, abundance and acoustic intensity of the particles present in the water column and the presence or absence of nycthemeral migratory behavior over a 24-hour recording period. Simultaneously, the in-situ oceanographic context was established from measurements of temperature, salinity and chlorophyll a. In-situ measurements were supplemented by satellite ocean color data to evaluate the presence of contrasted different phytoplankton communities. Twelve elephant seal females were equipped with these tags for their 3-month post-breeding foraging trips. Data show significant variations in biological landscapes, particularly bioluminescence, and to a lesser extent diffusive acoustic landscapes, in relation to the oceanographic context. With the exception of the passive acoustic landscape, PrCA varied according to all parameters investigated. Seal fishing performance was the highest when females encountered phytoplankton communities dominated by the presence of diatoms. In addition, the number of PrCA performed at the bottom of the dives are strongly correlated with the amount of bioluminescence detected during the transit phases (descent and ascent) of dives. This result suggests that the bioluminescent landscape is directly related to the biological quality of the area and seal prey density. Current biologging technical development focusses on the in-situ characterization of mid-trophic level organisms.

Zoom link: https://cnrs.zoom.us/j/94023435816?pwd=bStJHOdEss0cs1Rek7JbUtGCVyCYvG.1

– Lisa Di Matteo

titre : Trait-based modeling of marine mesozooplankton feeding strategies at global-scale

abstract : Marine planktonic organisms represent an essential component of global biodiversity and play critical roles in ecosystem functioning. This is particularly true for mesozooplankton, heterotrophic planktonic organisms ranging in size from 200 to 2000 μm. Although they have traditionally been studied via their taxonomy, functional trait approaches present real opportunities to better characterize the links between biodiversity and marine ecosystem functioning. Functional traits are the individual characteristics of an organism (e.g., size, reproductive strategy, thermal niches, etc.) that control its fitness as well as its impacts on
ecosystem functioning.
In ocean biogeochemical models, zooplankton are generally represented as a single size or two size classe(s). However, studies have shown the key role that functional diversity can play in ecosystem dynamics and marine biogeochemistry. This argues for the need to develop a more precise representation of zooplankton diversity through functional traits such as feeding strategy, reproductive strategy, thermal niches and behavior. While a better representation of zooplankton size diversity has gained attention, feeding strategy, a trait with implications for functions such as energy intake, predation risk, energetic losses and mate finding, has been less studied.
In this study, we implemented several feeding strategies of mesozooplankton in the ocean biogeochemical model PISCES. The predation mode is an essential trait of zooplankton, resulting from a trade-off between food acquisition, metabolic cost and predation risk. Simulations have been performed using NEMO-PISCES at global scale. Our results highlight the fact that these functional groups have distinct global, regional and vertical distributions as well as different contributions to biogeochemical fluxes. Thus, our findings emphasize the necessity for a better integration of mesozooplankton trophic strategies within global biogeochemical models.

– Robin Rolland

titre : Near-inertial wave trapping by anticyclonic eddy during the BioSWOT-Med 2023 cruise: characterization and energy fluxes estimated from in-situ data

abstract : Near-inertial wave-anticyclonic eddy interactions are a source of energy injection at depth, contributing then to the mixing of the deep ocean. In the Mediterranean Sea, they are only few evidences of this process in large anticyclonic eddy. However, SWOT reveals that small and intense mesoscale structures are widely found in the Mediterranean Sea, rising questions about the importance of NIW trapping for the mixing at depth in this quiescent sea.
The BioSWOT-Med cruise (https://doi.org/10.17600/18002392) took place in the Western Mediterranean Sea northeast of Minorca, during the fast-sampling phase of the SWOT mission from 20 April 2023 to 15 May 2023 on board of the R/V L’Atalante. The aim of this cruise was to studied the bio-physical coupling in a moderately energetic finescale front (in opposition with strong energetic fronts found for example in the Gulf Stream and the Kuroshio).
During the cruise, we targeted an intense ($Ro \sim 0.4$) anticyclonic eddy of $\sim 30$ km of diameter, a typical Mediterranean mesoscale structure elusive to nadir altimetry but well captured by SWOT. Two consecutive strong wind events generated strong inertial oscillations and particularly near-inertial waves into the anticyclonic eddy.
The sampling strategy enabled to sample the eddy before the first, between the two, and after the second wind event, allowing to characterize the evolution of the NIW activity as well as the induced turbulence. These conditions provided an ideal case study for near-inertial wave–anticyclonic eddy interactions in the Mediterranean Sea.
We first characterize the eddy sampled and the forcing of inertial motions. We then describe the evolution of the turbulence and wave activities before and after the two wind events. We characterize the NIWs trapped into the anticyclonic eddy and estimate the NIW-induced energy flux at depth from in-situ data. Finally, we discuss the significance of this process in the Mediterranean Sea taking advantage of the 21-day SWOT data.

lien zoom: https://ird-fr.zoom.us/j/95265301719?pwd=eZ8BMpCpibWokNZ24jXJaaoRh3bTkv.1

Matt Pinkerton
National Institute of Water and Atmospheric Research (NIWA), 301 Evans Bay Parade, Wellington 6021, New Zealand

Bioregions of change: mapping patterns and consequences of environmental change in the Southern Ocean

Environmental conditions are changing as a result of increasing atmospheric carbon dioxide and this is having an effect on ecosystems across the world. This talk will focus on the effects of climate change on the ecosystems of the Southern Ocean: (1) How can we detect changes to the Antarctic marine environment and its ecosystems? (2) To what extent can we anticipate future trajectories of change? (3) What are the opportunities for international management to promote ecosystem resilience, noting that commercial fishing and tourism in the Southern Ocean can act as co-stressors with climate change. 

Dr Matt Pinkerton is a Principal Scientist at the New Zealand National Institute of Water and Atmospheric Research (NIWA), based in Wellington. His research brings together satellite remote sensing of the ocean and ecosystem modelling, with an interest in how environmental variability affects the structure and function of marine food-webs with special focus on the role of middle trophic-level species including zooplankton and mesopelagic fishes. He has worked on the ecology and management of the Ross Sea region for nearly 20 years, including at CCAMLR meetings and Southern Ocean bioregionalisation workshops. He was programme leader of the New Zealand Ross Sea Monitoring and Research Programme, a 5-year project to monitor and evaluate the conservation value of the Ross Sea region Marine Protected Area.

zoom: https://ird-fr.zoom.us/j/92305390405?pwd=gY8L9JsthatQeSEpIemsbfB2cF6F95.1

Abstract : lien zoom: https://ird-fr.zoom.us/j/92096894324?pwd=JjtqDCTI5P6Dhfy6ml4EoOnrFngV3a.1
Contact at LOCEAN in charge of the seminar: jbclod@locean.ipsl.fr

Abstract : How fast Antarctica will lose ice and contribute to sea-level rise has become one of today’s most urgent scientific questions. Antarctic ice-sheet mass loss is primarily triggered by the ocean, but relatively little is understood about the drivers of ocean warming where it matters – at the ice sheet margin – nor about the impact of ice-shelf melting on the ocean. I (a) conduct oceanographic observations, (b) improve ocean simulations achieving high model-data agreement, and (c) develop ice-ocean coupled simulations to better understand the past, present, and future state of the Southern Ocean and identify the causes of ocean warming and Antarctic ice loss on various time scales. In this presentation, I will review the literature, including work from my group, that shows how ocean heat intrudes towards the West Antarctic ice shelves, the most rapidly melting region in Antarctica, and controls ice shelf melting. I will also discuss ongoing projects – using both data acquisition and modeling – aimed at a deeper understanding of the processes that control the future of the Antarctic ice sheet.
Contact at LOCEAN in charge of the seminar: katherine.hutchinson@locean.ipsl.fr

https://ird-fr.zoom.us/j/92533318933?pwd=E9XKPA5J319gwAOVtN1jt0403rSjas.1
Meeting ID: 925 3331 8933
Passcode: 927826

Abstract : The Arctic experiences climate changes that are among the fastest in the world and affect all Earth system components. Despite expected increase in terrigenous inputs to the Arctic Ocean, their impacts on biogeochemical cycles are currently largely neglected in IPCC-like models. We used a state-of-the-art high-resolution ocean biogeochemistry model, that includes carbon and nutrient inputs from rivers and coastal erosion, to produce twenty-first-century pan-Arctic projections. Surprisingly, even with an anticipated rise in primary production across a wide range of emission scenarios, our findings indicate that climate change leads to a counterintuitive 40% reduction in the efficiency of the Arctic’s biological carbon pump by 2100, to which terrigenous inputs contribute 10%. Terrigenous inputs will also drive intense coastal CO2 outgassing, reducing the Arctic Ocean’s carbon sink by at least 10% (33 TgC yr-1). These unexpected positive feedbacks, mostly due to accelerated remineralization rates, lower the Arctic Ocean’s capacity for sequestering carbon.

https://ird-fr.zoom.us/j/92533318933?pwd=E9XKPA5J319gwAOVtN1jt0403rSjas.1
Meeting ID: 925 3331 8933
Passcode: 927826
Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

Abstract: The ocean, and in particular the Southern Ocean, critically mitigated global surface warming by taking up a large portion of the additional carbon released to the climate system by human activities. The strength of this carbon sink depends on ocean dynamics and its interaction with the natural carbon cycle, both of which are critically altered by the ongoing climatic changes, making detailed global monitoring essential. However, the vastness and variability of the ocean make collecting enough long-term CO2 observations challenging.
In this talk, I will present studies on the primary drivers of oceanic CO2, from the vast Southern Ocean to the North Atlantic with a stopover in the tropics. I will focus on how changing ocean dynamics are altering the exchange of CO2 with the atmosphere. Using circumpolar hydrographic observations, I will present how the observed freshening of the Southern Ocean since the 1980s has prevented the weakening of the Southern Ocean carbon sink. Understanding these processes and their changes requires the collection of extensive data across time and space. Finally, I will highlight how using platforms such as sailboats to collect CO2 data offers new insights into the future of the ocean carbon sink and its role in the global carbon cycle.

https://ird-fr.zoom.us/j/92244839036?pwd=hs6XjNq7EgtNMHpZ55HJvG9OXrHRpu.1
Meeting ID: 922 4483 9036
Passcode: 432033Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

speaker: Adélie Antoine & Matthias Noël
abstracts:
– Adélie Antoine –
The sea ice zone constitutes the annual breeding and foraging habitat for vast populations of species, underlining its ecological importance. Given the sensitivity of this zone to global warming, there is an urgent need to determine how predators use their environment, in order to predict their response to climate change in the different regions of Antarctica. To do this, we need to understand how they use their physical and biological environment, an objective that can be achieved thanks to biologging technologies. Since 2006, CTD tags (temperature, salinity, diving behaviour) have been deployed on Weddell seals in Terre Adélie, to study their diving behaviour and record in situ oceanographic conditions. This 18-year time series of behavioural and oceanographic data allows for a better understanding of the feeding behaviour of these predators over several years. Here we examine the feeding areas preferred by Weddell seals, and monitor the evolution of their behaviour over the period 2006-2023. This study lays the foundations for analysing the influence of variability in oceanographic conditions on their foraging ecology, by distinguishing patterns of feeding behaviour and outlining trends in their diving behaviour.
– Matthias Noël –
Coastal polynyas are ice-free regions that form within areas normally covered by sea ice during winter. In Antarctica, these polynyas develop due to strong katabatic winds that push sea ice offshore. This exposure facilitates the release of heat from the ocean to the atmosphere, driving intense sea ice production and the formation of dense water masses.
Despite the critical role of Antarctic coastal polynyas in forming Antarctic Bottom Water (AABW), which constitutes 30-40% of the global ocean volume, the atmospheric and physical processes governing their dynamics remain poorly understood.This study examines the atmospheric response of Antarctic coastal polynyas using high-resolution (~3 km) simulations from the WRF regional atmospheric model, focusing on the Prydz Bay region in East Antarctica and containing 2 coastal polynyas: Cape Darnley and Mackenzie Bay polynyas. Through sensitivity experiments involving artificially open and closed polynyas, I show that an open polynya induces significant heat release (up to 1000 W-m-²), increases surrounding air temperatures by more than 14°C, creates intense convection (increasing the atmospheric boundary layer by +550 m), forms clouds and accelerates surface winds by more than 6 m-s-¹. Above the polynya, two recirculation anomaly cells form upstream and downstream of the polynya. An analysis of the meridional wind trend terms is proposed, showing that the structure of the wind anomalies results from a balance between the terms associated with advection, vertical diffusion and pressure gradient. The advection term is particularly important in areas of atmospheric boundary layer height gradient.These results suggest that the presence of polynyas significantly modulates the local atmospheric conditions, indicating a potential feedback mechanism that influences polynya dynamics and, consequently, the formation of AABW.

https://cnrs.zoom.us/j/99536466522?pwd=kFvRkOYH2ztkISKk0iLgsOUbZAjUUg.1
contact email at LOCEAN: margaux.perhirin@locean.ipsl.fr

Présentation de l’intranet du LOCEAN

https://ird-fr.zoom.us/j/92533318933?pwd=E9XKPA5J319gwAOVtN1jt0403rSjas.1

Meeting ID: 925 3331 8933
Passcode: 927826

Abstract : Le Centre de Modélisation du Climat de l’IPSL (ICMC, ou, plus court, CMC) a pour vocation de rassembler les forces vives de l’IPSL souhaitant construire le modèle couplé système Terre de l’IPSL et en analyser les résultats. Il comprend des ingénieurs et chercheurs de la fédération IPSL et des laboratoires constituant l’IPSL. Lors de ce séminaire, nous vous présenterons ce centre et son fonctionnement, élaborés depuis la prise de fonction de sa direction collégiale.
Un des projets fédérateurs pour CMC est, régulièrement depuis sa création, la participation à de grands exercices d’intercomparaison des modèles de climat. Nous abordons cette année la mise en place de la 7e phase du projet exercice CMIP (Coupled Model Intercomparison Project), dont les résultats partagés au niveau international sont analysés par de nombreux groupes de recherches. Les simulations CMIP sont aussi des références pour d’autres projets, tels que ceux portant sur les paléoclimats (PMIP), sur les forçages radiatifs et les nuages (CFMIP), sur les forçages radiatifs (RFMIP), sur les aérosols et la chimie atmosphériques (AerChemMIP), sur l’impact des couplages climat-carbone (C4MIP). La 7e phase de CMIP est prévue en deux étapes: le FastTrack, phase resserrée dont les résultats contribueront au 7e rapport du GIEC, et CMIP7, qui complètera l’ensemble compact du FastTrack. Nous présenterons l’organisation de CMIP7 et discuterons avec l’auditoire de possiblités de nouvelles participations à ce travail de développement et d’analyse sur ces futures simulations.

https://ird-fr.zoom.us/j/92533318933?pwd=E9XKPA5J319gwAOVtN1jt0403rSjas.1
Meeting ID: 925 3331 8933
Passcode: 927826
Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

Abstract : The overarching theme of my research has been understanding how human perturbations to the Earth system, particularly greenhouse gas emissions, affect elemental cycles in the ocean, the associated climate feedbacks, and the impact of these interactions on marine ecosystems. I am interested in research questions that encompass particularly broad spatiotemporal scales within the Anthropocene, from global centennial-scale trends to diel impacts on coastal ecosystems. I have used numerical tools such ocean biogeochemistry models and Earth system models, as well as observations and oceanographic experiments performed in the field to explore research questions. A dominant thread running through my research is that of reducing uncertainties associated with projections of ocean-climate interactions and marine ecosystem sensitivities. This has often been aligned with multi-model projections performed as part of international exercises such as the Coupled Model Intercomparison Projects (CMIPs). In some instances, these multi-model projections can be highly divergent and techniques that use emergent model ensemble properties, alongside relevant observations, may be used to reduce projection uncertainties. In other instances, an entire ESM ensemble may fail to represent an ocean biogeochemical processes (often for good reason) and therefore have systematic biases. Here targeted simulations with a carefully curated ocean biogeochemical model may be used to assess the magnitude of such biases and provide recommendations for future ESM development.

https://cnrs.zoom.us/j/92207921380?pwd=Ma4masKh7AbFBArN6BcT897a1Ca9aq.1
Contact at LOCEAN in charge of the seminar: lester.morgan-kwiatkowski@locean.ipsl.fr

Abstract : Sea ice dynamics are highly complex and generally poorly resolved by sea ice models. This is problematic, as they modulate the amount of momentum exchanged between the atmosphere and the ocean in polar regions, as well as play a key role in heat and light fluxes through the opening/closing of sea ice leads. A solution to improve simulated sea ice dynamics is to use a brittle rheology to represent the mechanical behaviour of sea ice. Such rheology is included in the sea ice model neXtSIM, and we demonstrated its ability to capture the observed characteristics and complexity of fine-scale sea ice deformations. Here, we present two cases where we coupled this sea ice model to better understand the role of ice dynamics in ice-ocean interactions.
In the first case, we set up a 12km resolution ocean–sea-ice coupled model, using OPA, the ocean component of NEMO. We investigate the sea ice mass balance of the model for the period 2000-2018. After evaluating the modelled sea ice against available observations (extent, drift, volume, deformations, etc.), we estimate the contribution of leads and polynyas to winter ice production. We find this contribution to add up from 25% to 35% of the total ice growth in pack ice in winter, showing a significant increase over the 18 years covered by the model simulation.
In the second case, we focus on the marginal ice zone (MIZ) and couple neXtSIM with the wave model WAVEWATCH III. We use this configuration to investigate how wave-induced breakup impacts sea ice dynamics in the MIZ. We show how, using the “damage” quantity that is at the core of the brittle rheology framework, we can represent the loss of ice strength associated with wave-induced breakup, and how breakup can increase the mobility of the thickest ice in the MIZ after storms.

https://ird-fr.zoom.us/j/92533318933?pwd=E9XKPA5J319gwAOVtN1jt0403rSjas.1

Meeting ID: 925 3331 8933
Passcode: 927826
Contact at LOCEAN in charge of the seminar: alice.pietri@locean.ipsl.fr

abstract: Mass balance of the Arctic Sea ice depends on thermodynamical and dynamical factors. Thermodynamical and mechanical sea ice state variables are strongly coupled, but the strength of coupling varies in daily, seasonal and climate time scales. When the ice pack is thick, solid and compact, this coupling is strong and large areas of the ice pack are mechanically connected.   In these circumstances, internal stress of pack ice is accumulating and reducing differences in ice motion. In these conditions drift speed of Arctic Sea decreases, age of ice increases and total mass of ice pack increases. On a contrary, thinner ice pack which includes cracks, leads or larger open water areas is in turn mechanically weakly connected, exhibits larger variations in motions in shorter time and length scales, drifts with higher speed and exhibits shorter residence time in the Arctic. In this talk, the importance of ice dynamics on sea ice mass balance is reviewed and new findings based the MOSAiC campaign are discussed.

https://cnrs.zoom.us/j/94468479292?pwd=udR0Rt6prioUwsRarAMjvKbmsnv3NX.1

Contact at LOCEAN in charge of the seminar: martin.vancoppenolle@locean.ipsl.fr

short abstract:

– Kirtana Naeck –
The physical and biogeochemical processes governing the air-sea CO2 flux in the Southern Ocean are still widely debated. The Southern Ocean Carbon and Heat Impact on Climate cruise in summer 2022 aimed at studying these processes in the Weddell Sea and in its vicinity. A CARbon Interface OCean Atmosphere (CARIOCA) drifting buoy was deployed in January 2022 in the subpolar Southern Ocean, providing hourly surface ocean observations of fCO2 (fugacity of CO2), dissolved oxygen, salinity, temperature and chlorophyll-a fluorescence for 17 months. An underwater glider was piloted with the buoy for the first 6 weeks of the deployment to provide vertical ocean profiles of hydrography and biogeochemistry. These datasets reveal an anomalously strong ocean carbon sink for over 2 months occuring in the region of Bouvet Island and associated with large plumes of chlorophyll-a (Chl-a). Based on Lagrangian backward trajectories reconstructed using various surface currents fields, we identified that the water mass reaching the Bouvet Island region originated from the south-west, from the vicinity of sea ice edge in spring 2021. We suggest that a strong phytoplankton bloom developed there in November 2021 through dissolved iron supplied by early sea ice melt in 2021 in the Weddell Sea. These waters, depleted in carbon, then travelled to the position of the CARIOCA buoy. The very low values of ocean fCO2, measured by the buoy (down to 310 μatm), are consistent with net community production previously observed during blooms occurring near the sea ice edge, partly compensated by air-sea CO2 flux along the water mass trajectory. Early sea ice retreat might therefore have caused a large CO2 sink farther north than usual in summer 2022, in the Atlantic sector of the subpolar Southern Ocean. Such events might become more frequent in the future as a result of climate change.

– Nicolas Michalezyk –
Climate models often show important winter near-surface temperature biases over Arctic sea ice, increasing uncertainties in future sea ice and Arctic climate projections. Such biases reflect difficulties in representing air-sea-ice interactions, and limited observations in the Arctic. Mitigating them in future model versions requires proper evaluation and understanding of their origin. To progress on these matters, we compare historical simulations using atmosphere-only and coupled configurations of the IPSL-CM6A-LR climate model regarding near-surface air temperature and find substantial differences. To establish a reliable baseline for evaluating simulations, we identified a linear relationship between ERA5 near-surface air temperature values and their bias relative to in situ observations from Soviet North Pole drift stations. This relationship is then used to correct the bias in ERA5 data. We find the winter near- surface temperature bias in the atmosphere-only IPSL-CM6A-LR configuration turns from cold to warm once ERA5 is linearly corrected, reaching +2.2°C over Arctic multiyear ice. The bias increases to +4.8°C in the fully-coupled configuration. A pan-Arctic energy budget evaluation indicates that excess poleward atmospheric heat transport is the most likely cause of the warm bias. In the coupled configuration, presumably due to interactive sea ice and ocean components, we find compensation effects between high atmospheric heat transport, low poleward oceanic heat transport and surface energy budget. This translates to a weaker-than-expected heat release from the ocean to the atmosphere. The methods developed here could be used in multi-model evaluations to further progress in understanding and reducing biases in climate models.

https://cnrs.zoom.us/j/94037205697?pwd=xOjU7LtGTNVxzagGecrlEbX0IhaZsb.1

Contact at LOCEAN in charge of the seminar: margaux.perhirin@locean.ipsl.fr