 Hello, my name is Sylvie Tesson, I am an IAS Co-Found Fellow at Orus University in Denmark, and today I will present an overview of my IAS project which aims at investigating the dispersal and ice nucleation activity in airborne microalgae, and in particular the impact on atmospheric processes. Our blue planet is covered by 71% of water, which is an essential element to life. Water is visible under the form of ice, oceans, rivers, lakes, precipitation such as rain and snow, but also under more subtle forms such as groundwater, water vapor, permafrost, and in the biota. In the water, in a bit of mysterious and fascinating diversity of invisible microorganisms, they play a crucial role in biogeochemical processes at different scales. And if we consider, for example, one milliliter of sea water, which contains about 20 droplets of water, or a quarter of a teaspoon in volume, and we place a pinhead for scaling the organisms, then in this volume we will have about 10 million of viruses, 1 million of bacteria, 1,000 of protists, and few metasolones. Among the protists are the microalgae. Microalgae are unicellular prokaryotic or eukaryotic organisms able to perform photosynthesis so they can provide oxygen and food source for local communities. Microalgae are present in many habitats in the aquatic and terrestrial ecosystems. They are, for example, present in ice, sea, stream, lake, pond, but also in the soil, sand, on the bark of the trees, or even on human-made surfaces. And in the atmosphere, there have been several records of microalgae. Locally, microalgae can live in interconnected habitats. For example, in the Arctic, which is a fragile ecosystem, microalgae are present in the sea, but also at the interface sea ice, at the bottom of the ice cover, or into the brine pockets within the ice cover, and sometimes in small holes called cryonite located at the surface of the ice cover. Together, there's a sustained local food web. There's cold adaptive microalgae, can also form a source of potential active by your aerosol once emitted into the atmosphere. Some microalgae can also have a negative impact and be the cause of environmental and sanitary issues, such as, for example, the deterioration of building surfaces. They can also be a source of allergens and a source of toxic evans. Some microalgae can also play a role in climatic water and carbon cycles. Here, I will take the example of seawater microalgae dispersal. Aquatic microalgae can be emitted from sea surface into the atmosphere, mediated wind erosion of the interface sea air. This will generate little droplets of water at times containing microorganisms, among which the microorganisms, among which the microalgae. Once in the atmosphere, they will start to diffuse and then progressively be transported over geographical scales prior to be deposited by, for example, precipitation into new environments where they can proliferate. During the airborne experience, certain microorganisms have the capacity to attract water molecules or to transform surrounding water molecules into ice molecules. This biological reaction occurs at subzero temperatures close to the zero Celsius degrees. The nucleation of ice particles can lead to the formation of mixed-face clouds and, in return, affect the reverberation of the sun, which is called albedo, bioprecipitation pattern, as well as a dispersal capacity of airborne microorganisms. In this project, I am interested in the causes and consequences of microalgae dispersal through the investigation of the organism's survival capacities and their dynamic interaction with the atmosphere. The take-home message is that microalgae from different sources can disperse mediated air transportation and they can contribute either positively or negatively to the ecosystem equilibrium. Certain microalgae are able to actively nucleate ice under cold atmospheric conditions at temperature just below zero degrees Celsius, thus entering in competition with potent known biogenic aerosols. Also, local ice nucleation event can affect atmospheric and aquatic processes. The aims of the project are to investigate microalgae as a source of biogenic aerosols using eco-physiological and genetic tools, with the goals of refining the mechanistic understanding of their ice nucleation capacity and deciphering the impact of atmospheric factors on airborne microalgies. Results will provide a better understanding of the microalgae ecology and will bring novel knowledge in aeroecology. Results will also generate new parameters that will be used to refine model descriptors to improve atmospheric prediction, but also to foresee these personal changes. The project is based at IS and at the Department of Biology, Section Microbiology at Uruz University and is performing collaboration with international and interdisciplinary experts. I would like to thank ISCOFON program for the support and for providing me with the opportunity to develop further my research and I would like to thank you for your attention.