Carbon cycling in coexisting marine ecosystems: Cold seeps and coral reefs in Northern Norway

Cold seeps and cold water corals (CWCs) coexist on Northern Norway's continental shelf at the Hola trough between Lofoten and Vesterålen. Here, cold seeps release methane from the seabed, yet only a limited amount reaches the atmosphere. The remaining methane dissolves and disperses in nearby seeps. Methane is unreactive for most microorganisms in the water column, yet it is a unique energy and carbon source for methane-oxidizing bacteria (MOB). MOBs metabolize methane and release carbon dioxide as the end product of oxidation. Increasing carbon dioxide may constrain pH-sensitive CWCs in the region. We investigated the biogeochemistry of carbon, carbon isotopes, nutrients, dissolved organic matter (DOM) compositions and microbial diversity through water column profiles and water samples collected in June 2022. Preliminary results indicated that elevated methane increases dissolved inorganic carbon concentrations and modifies carbon isotopic compositions. Additionally, DOM compositions implied a positive correlation between prokaryotic diversity and protein-like DOM components at cold seeps and the entire water column near CWCs, suggesting analogous microbial modifications. Our preliminary conclusion suggests cold seeps and CWCs symbiotically coexist in Northern Norway continental shelves; however, enhanced water temperatures and consequent increase in methane release at cold seeps may mitigate the functioning of CWCs in future. This study is supported by the Research Council of Norway, project number 320100, through the project EMAN7 (Environmental impact of Methane seepage and sub-seabed characterization at LoVe-Node 7).