The Arctic Ocean is currently facing the consequences of the long-term warming trend largely caused by anthropogenic forcing, with a dramatic decrease in the Summer Sea Ice extent in the last 35 years, approximately 50% since 1950s (ParKinson et al. 2013, Lannuzel et al. 2020).

Numerous studies have exemplified the implications of these remarkable environmental changes on the hydrography and physical properties of the Arctic water masses with consequent impacts on nutrients redistribution and shis on the whole biological compartment (Barber et al. 2015, Dybwad et al. 2021, Assmy et al. 2017, Duarte et al. 2022). Nitrogen (N) is a fundamental element for living organisms and its biogeochemical cycle includes highly diverse microorganisms that make N compounds available for biological production (Kuypers et al. 2018).

Previous studies from our research team suggested that prokaryotic communities involved in N-biogeochemistry strongly respond to environmental shis across the Winter to Summer Arctic transition and that ammonia oxidizers assume a keystone function in promoting the recycling of N in the Arctic Ocean (Müller et al. 2018, Sousa et al. 2019). In this project we propose to extend previous observations in a complete study to understand the fixed-N sources and recycling pathways in the Arctic sea-ice changing scenario. We hypothesize that the fast retreat of sea ice will promote new N metabolic microbial functional regimes with transversal ecosystem implications. Previous studies were not able to test this hypothesis by being limited in producing baseline knowledge of the temporal dynamics of Arctic microbial communities, due to the scarcity of biological data on this remote region. In our study, we will uncover this limitation by integrating ongoing monitoring projects, and combining extensive Arctic microbiome and biogeochemical data sets (genomic / metagenomic / metatranscriptomic / biogeochemical / metadata) through the participation in a year base in Arctic expeditions and by bringing together interdisciplinary researchers. Innovative microbiome monitoring technologies (autonomous eDNA sampler) developed by our research team (Martins et al. 2016, Ribeiro et al. 2019) will be also tested and implemented to extend microbiome data sets in Arctic remote environments.

In N-MicroARCTIC project will use unique environmental observations, from 11 years of Arctic expeditions, experiments, and global data analysis in an international effort to produce reliable results and innovative science to understand the Arctic Ocean climate change perturbations on key microbial communities and their metabolism. This include i) novel knowledge to understand the sources of N (e.g. N-fixation, Nitrification) in the contemporary and future Arctic Ocean, which is still under debate without sufficient data that supports an effective answer (Müller et al. 2018, Sousa et al. 2019) ii) new and solid scientific understanding on the response of N microbiome and its functions on Arctic manifestations to climate changes, currently limited by the lack of biological long-term monitoring programs (Duarte et al. 2017, 2022), and only achievable by undertaken the level of interdisciplinarity and completeness of our Arctic Ocean data set; iii) provide a comprehensive new picture on the environmental drivers of N cycle in diverse Arctic environments (fjord, shelf and oceanic domains).

The results from N-MicroARCTIC will represent a major step forward regarding Arctic ecosystem functioning, by filing critical gaps concerning the ecological role of N cycle in sustaining changes in Arctic productivity, diversity and their biological resources. This is crucial because there are some dramatic changes happening on physical and chemical properties of the Arctic Ocean, governed for example by the ice retreat (e.g. ParKinson et al. 2013), increased heat influx of North Atlantic water (e.g. Lannuzel et al. 2020), potential disappearance of ice associated organisms (e.g. Barber et al. 2015), but witch environmental forces impact N microplankton communities are still far from being identified. The proposed scientific plan will also promote inter-crossing of different disciplines (microbial ecology / genetic and megasequence technologies / biogeochemical / bioinformatics / bigdata analysis) leading to breakthroughs in our understanding on how climate change govern the transformations of N in the Arctic Ocean.