 Weather is probably the most frequent topic of small talk people engage in. We split our year into seasons according to what type of weather dominates them. The climate in which we live affects how we build our homes, how we produce our food, even how we feel. Lately, climate change has become globally the most debated topic. And yet, most of us are not familiar with processes and factors driving the weather and climate we experience. One of the most important weather features is temperature. Temperature is a result of many interacting factors like altitude, wind circulation and, very importantly, the amount of sunlight that reaches the surface of the earth. How much sunlight we get depends primarily on the position of our planet towards the sun. Another important factor are clouds. During the day, they act like moving shields, reflecting heat from the sun or letting it through. At night, they act like a cover, preventing the heat from radiating back into space. Just that would make clouds a major factor influencing the heat balance of the earth. But additionally, they have the ability to carry around water and thereby impact rain patterns. Sunlight and fresh water availability directly determine which places we inhabit and which we don't. Although not always given the credit, clouds play an important role in how human population is distributed and organized. There is a whole array of different types of clouds with different properties, for example shape or opacity. The processes behind these variations are far from being fully understood. Recently, an exciting puzzle piece has been introduced into the picture. Despite their pure appearance, clouds are teeming with particles of various origin. The type of the particles determines how clouds form, how long they survive and how likely it is to rain from them. These particles dispersed in the air are called aerosols. They are small bits of organic or inorganic matter in the atmosphere. Inorganic aerosols are for example mineral dusts coming from deserts. While bio aerosols are fragments of plants, cells of microalgae, fungi and bacteria. New observations suggest that bio aerosols, a previously unnoticed factor, may play an important role in shaping weather and contributing to the occurrence of rain, snow or hail. One major source of bio aerosols are oceans. It is not surprising considering that they cover 71% of the Earth's surface. Bio aerosols derived from the ocean are the heroes of our story. The most quantitatively important types of ocean derived bio aerosols are bacteria, microalgae and organic compounds that they produce. Question to start off with will be how do they get from the ocean into the atmosphere? While aerosols from land surfaces get carried into the atmosphere directly by wind, the transport of aerosols from the ocean is more complicated. First, when produces waves. When they break, bubbles of air get introduced into the water. These bubbles move upwards through water and on the way they collect microorganisms and organic compounds. When the bubbles reach the surface, they burst and produce a small jet ejecting biological material out of the water. Once in the air, the material can be taken by wind and carried higher up into the atmosphere where it can stay for anywhere from minutes to weeks. These organic compounds produced by marine microorganisms have been found globally in the Southern Ocean, North Pacific Ocean and North Atlantic Ocean. They are concentrated in the top one millimeter of water from where bubbles can eject them into the atmosphere over the ocean. Several studies support the idea that marine microorganisms and organic compounds are present in the atmosphere and involved in weather shaping processes. Let's look into the connection between microbes and weather, specifically their effect on cloud formation. What is a recipe for a cloud and how do marine microorganisms fit in? The main ingredients are as follows. Water molecules dispersed in the atmosphere as vapor. Areosolized particles, in our case marine bio aerosols, and subzero temperatures. The starting point of a cloud development is a droplet. Droplets are formed by water molecules gathering around an aerosolized particle, the marine bio aerosol. Individual droplets are very light and will not fall down as rain. Instead, they will stay in the atmosphere suspended as a kind of mist. There are two ways by which droplets can increase their size and ultimately fall onto the ground as rain. They can either grow by collision with other droplets, or they can grow after having been converted into an ice crystal. Ice crystal conversion starts from an initial stage called an ice embryo. Once an ice embryo is formed, it grows throughout the droplet by adding more water molecules onto the initial frozen structure. So the droplet freezes in a sort of a chain reaction. Ice crystals grow bigger than cloud droplets by accumulating additional water molecules from the air. Ultimately, they grow too big and too heavy to float in the air and they start falling onto the ground. These crystals usually melt on the way down, which is why we experience liquid droplets of rain. In complete absence of any particles, water droplets will only freeze at minus 38 degrees Celsius. That is the freezing point of pure water. Inorganic particles like dusts can catalyze the freezing process at temperatures up to minus 15 degrees Celsius. But biological particles can make water freeze at temperatures as high as minus 2 degrees Celsius. These are called biological ice nucleating particles and they are abundant in the oceans. The research linking microbes and weather could potentially contribute to a more complete understanding of weather systems useful for example to study climate change. Moreover, we know that a large number of microorganisms is captured in the sea ice of the Arctic and the Antarctic. As the ice melts, these microbes are released into the ocean from where they can enter the atmosphere and impact cloud formation. We still cannot reliably predict the consequences of this. But potentially it could be changes in global rain patterns, influence in climate change and access to fresh water. A group of scientists from the Arctic Research Center at Aarhus University in Denmark has been looking into these processes. Led by Tina Shantel-Temkev, they launched an expedition to the high Arctic following up on previous studies. Equipped without theoretical knowledge of marine influence on cloud formation, we proceed by following the researchers on their journey from Greenlands capital Nuuk to a far north town Kanak. In multiple locations they have sampled the air and water and examined them for presence of microorganisms. Here is how some of the samples were collected. Tina is collecting samples of previously mentioned sea surface micro-layer water. That is the top one millimeter boundary between the ocean and the atmosphere. This layer has a high concentration of marine microorganisms and compounds they produce. The plate and the scraper are made of inert and non-adhesive materials to minimize any alternation of the sample by the instruments. Tina is submerging the plate and the water, waiting for the subsurface water to run off, and then the PhD student, Malin Elsvet, is scraping the surface micro-layer water into a sterile bottle. The subsurface water runs off faster because of its lower surface tension. The surface micro-layer water drips into the bottle visibly slower. That is due to its organic content. Here Tina is collecting bulk water. That is the water underneath the one millimeter surface micro-layer. The concentration of microorganisms in bulk water is lower than in the micro-layer. In order to keep the bulk water from mixing with the micro-layer water, the sampling bottle needs to be submerged all the way on the level of bulk water while being closed, then be opened, filled and sealed again using a pole. Here we can see the process of collecting microorganisms from the atmosphere above the sea surface. Tina is attaching a sampling device that collects microorganisms on a filter to a vacuum pump that creates suction. As the air passes through the filter, the microorganisms stick to it. Depending on a section intensity and sampling time, the researchers are able to collect different volumes of air, typically between 20 and 150 cubic meters. In this clip you can also see a member of the Danish Royal Navy. The Danish Royal Navy supports scientific projects with logistic help. In this case, the scientists have been provided a stay-on-board of the vessel that the Navy uses to patrol Danish waters around Greenland. The Navy personnel also helps with various tasks during the expedition. In this clip we can see another sampling method which is using a vortex chamber. This chamber collects microorganisms from the air at a rate of 3100 liters per minute and deposits them into liquid that contains RNA preservation solution. This solution stops any metabolic activities of the organisms and preserves them in exactly the state in which they were collected. With this system, several hundred cubic meters of air can be collected in just a few hours. Here Tina is inserting a vortex inset into a high flow rate impinger with a built-in pump. Interestingly, the pump used for this task is a commercial vacuum cleaner for asthmatics, which is both inexpensive and highly efficient at collecting microorganisms. At the moment, the group continues their research on the other side of the globe in Antarctica. This project is conducted in collaboration with the Institute of Marine Sciences in Barcelona, funded by the Spanish Ministry of Economy and Finance. When finalized, their data will contribute to a more complete picture of global distribution of microorganisms capable of affecting cloud formation and thereby weather. The polar regions are more affected by climate change than any other regions on Earth. Analyzing the poles can give us the ability to better understand and predict events associated with climate change everywhere else. Additionally, bioprecipitation research contributes to a more complete understanding of local and global rain patterns. Water scarcity in densely populated regions is predicted to be an issue associated with progress in climate change. Understanding rain patterns more completely can help navigate water management, agriculture and secure water and food supply.