Processes and Players in Arctic Marine Pelagic Food Webs - Biogeochemistry, Environment and Climate Change

The microbes in the ocean comprise phytoplankton, protozoans, bacteria and virus. They are tiny but are found in huge numbers and grow very fast, and therefore they have large impact on the ecosystem. The microorganisms produce food for larger animals, decompose pollutants, and regulate CO2 uptake from the atmosphere to the ocean. To understand these processes, we need to know how the microbial food web is structured and how it works. Our primary objectives, to provide a better description of the microbial food web and the microbial processes in the Arctic, as well as producing data for improved ecosystem and climate models, has been addressed through five cruises north and west of Svalbard, a fieldwork on Greenland, and a large field experiment on Svalbard. Using electron microscopy we found algal species that are novel to the Arctic, and even a brand new species - Papposphaera heldalii. Fifteen different microalgae have been isolated and deposited in the international culture collection in Roscoff (www.roscoff-culture-collection.org/). The molecular analyses revealed many more details of the algal community, and somewhat surprisingly, the biodiversity was greater in the deep and dark ocean and at wintertime, than at the surface in the spring-summer season when the abundance was higher. Another surprise was the occurrence of the globally important photosynthesizing cyanobacterium Synechococcus as far north as 82.5 degrees. It was active also in the dark winter season and sometimes more abundant than the tiniest algae that normally dominates the area. This witness an «atlantification» of arctic waters in line with reports of mackerel, herring and Atlantic cod in the area. We described community composition of archaea, bacteria and virus by sequencing their genetic material. In the waters around Svalbard we found high concentrations of a group called Thaumarchaeota. They are autotrophic primary produces (like plants) living by oxidising ammonia, and these organisms exhibited pronounced seasonal growth with high concentrations in the deep Arctic water during summer and in the surface water throughout winter. The bacterial community composition seem to be largely driven by light, as the communities found at great depths where darkness reigns, was very similar all year round. During the light Arctic summer, the communities close to the surface were also all very similar. The abundance, composition and diversity of the viral community also varied with season. Opposed to our own expectations we found the largest diversity and highest numbers of virus compared to hosts in winter. This means that viral infections must be as important at wintertime when abundance and activity of algae and bacteria is low, as they are during the productive spring and summer seasons. The Arctic Ocean have higher concentration of dissolved organic material than other oceans. Still, supply of organic material limits the bacterial growth. Much of the DOM in the ocean originates from land, but our results showed that protist grazing on bacteria is an important source of DOM in situ. In addition, the fieldwork at Greenland revealed that although terrestrial DOM is easier to break down compared to the marine DOM, the latter supporting higher bacterial growth rates. The reason seems to be that the dominating bacteria (Glaciecola and SAR92) are specialized in utilizing the DOM created in situ. In 2015 we carried out a field experiment with natural plankton communities at Svalbard to study trophic interactions. The abundance of zooplankton affected abundance and activity of bacteria but their net effect on carbon and nutrient flow in the system was less than expected apparently because the bacterial community composition and thus their food web functioning also changed. This may imply that the foreseen climatic changes in light conditions, DOM supply and zooplankton will affect the microbial part of the food web less than anticipated. The experiment also demonstrated how ocean acidification may be affected by organic carbon supply and the structure of the microbial food web. During the project period we measured the most northerly wintertime properties of the marine carbonate system in the Eurasian Sector of the Arctic Ocean. This is also of great importance to understanding the present framework of ocean acidification and for ground-truthing ocean models. We have already presented some results at conferences and in peer-reviewed papers, but more will be produced in the years to come. Our cruise activity was presented to a broader audience through Facebook, Blog and YouTube, and the field campaign at Svalbard formed the basis for a documentary shown at NRK / Schrødingers Katt in November 2015. We have also communicated results in Aftenposten Innsikt and in a book chapter in the book "At the Edge".

The interaction between the biosphere, the atmosphere and the hydrosphere is mediated by microorganisms being the main drivers of biogeochemical cycles in the ocean and the main producers and consumers of inorganic nutrients, organic carbon and CO2. The M icroPolar [µP] project focuses on marine microbial food webs and biogeochemical cycles in the Arctic Ocean and will provide a better description and understanding of the organisms, the processes, and the feedback mechanisms that shape this interaction. Th e most critical R&D challenges posed by environmental change in the Arctic Ocean concerns the role of microorganisms; "Who are they?", "What are they doing?", "How do they interact?" and "How do they respond to the current climate change?". A project appr oaching these questions calls for interdisciplinary collaboration. State of the art analytical techniques and metagenomics will be used to describe the microbial community and to quantify carbon flow in Arctic microbial food webs during a full annual cyc le. Sensitivity experiments with biogeochemical process studies in mesocosms will be used to inform on the key importance of biogeochemical feedbacks to climate change and rising CO2. The project partners cover a range of disciplines including microbial e cology, climate research, biogeochemistry, marine chemistry, metagenomics and ocean modeling, which all are required to conduct the research and to integrate the results in an Earth system science and environmental management perspective. MicroPolar [µP] will generate a unique dataset, with a potential bioprospecting spin-off. It will improve Earth system models and climate projections, and contribute to the conception needed for a knowledge based management of natural resources and industrial activity in the polar regions.