The Arctic Ocean is undergoing unprecedented changes as the Earth warms due to climate change. Increasing global temperatures are resulting in increased rates of glacial melting and retreat, thawing of the permafrost and a steady trend towards reduced sea ice extent in winter. Inputs of freshwater into the Arctic Ocean are also increasing as a result of the increased melting rates.
As the sea ice retreats, the reflective surface of the ice is replaced by absorptive ‘dark’ ocean, and results in a greater absorption of incoming sunlight and heat energy, thus driving up the rate of global temperature increase. However, this picture is too simplistic, and there are many physical and biological processes taking place within the Arctic Ocean water and sea ice which we do not fully understand, but which could affect our projections of changes within the Arctic Ocean. In Autumn 2019, the German Icebreaker FS Polarstern is undertaking a unique expedition, to sail to the edge of the Arctic sea ice in the Russian Laptev Sea, and allow the sea ice to form around the ship. The ship will then drift with the ice pack, close to the North Pole, and exit the sea ice in Autumn 2020 near the east coast of Greenland. This opportunity will allow scientists access to newly formed ‘first year’ sea ice, as well as older ‘multi-year’ ice, and allow them to study all aspects of the Arctic environment across an entire year and all the seasonal changes: physical interactions between atmosphere, sea ice and water column, and the biological activities taking place in all three environments. It is essential we work towards gathering this information now, as it will allow us much better understanding of the processes taking place, and allow us to improve our model predictions of how the Arctic will change over the coming decades. This project has been designed as a key part of this expedition, and will study the formation of a gas called dimethylsulfide (DMS), a key ingredient in the cocktail of gases that makes up the ‘smell of the sea’. It is produced worldwide by single celled algae and bacteria in both freshwater and saltwater environments, but our previous research has shown that sea-ice-dwelling algae produce concentrations of DMS tens to hundreds of times higher than in the water. While only a small proportion (up to 16%) of this DMS is released into the atmosphere, once there it forms cloud-seeding compounds which can influence our weather and climate. When it rains, sulfur compounds are deposited back into the soils of our continents. The remainder of the DMS formed in the oceans stays there, facing consumption by marine microbes and incorporation into the oceanic sulfur cycle. As we know that sea ice is an important source of DMS, the reduction in sea-ice extent with increasing climate change will have significant effects on the volume of DMS entering the atmosphere. Our project aims to investigate the changes in the microbial (bacterial and algal) community across the seasonal changes in the Arctic, and to look at how these changes affect the production rates of DMS and associated organic sulfur compounds. To this end, we will undertake 2 months stationed on FS Polarstern during the boreal spring, and form international collaborations to extend our sample availability to over 6 months through spring to summer. We will continue our research in the home laboratory by studying so-called ‘model micro-organisms’ which we will collect during our time at sea (or in the ice!). All our data collected in the Arctic will be compared to our previous studies in the Antarctic, to give a much clearer picture of the importance of the polar regions as a source of DMS, and how climate change will affect our global climate as these areas change.