Abstract
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 none reaches the sea surface. Instead, the methane dissolves and disperses in the ocean where it is ultimately consumed by methane-oxidizing microorganisms. These microorganisms metabolize methane and release carbon dioxide and dissolved organic matter (DOM), which may impact the biogeochemical habitat of CWCs in close vicinity of cold seeps. We investigated the biogeochemistry of carbon, carbon isotopes, nutrients, DOM compositions, and microbial diversity in the water column. Our results indicated that dissolved inorganic carbon concentrations were 29% higher near cold seeps with modified carbon’s isotopic compositions. The hydrophysical parameters and surface-to-bottom control of sinking particles mainly govern water column productivity and nutrient cycle. DOM compositions implied that the seep-associated microbiomes modify DOM’s chemical diversity and isotopic composition at CWCs and the entire water column near cold seeps. Cold seeps and CWCs coexist in Northern Norway’s continental shelves; however, enhanced water temperatures and consequent increase in methane release at cold seeps may modify the carbon cycling in the area, which could mitigate the ecological role and functioning of CWC reefs in the future.
Plain Language Summary
Cold seeps are geological features that release methane from the seabed to the water column. In oxygenated sea water column, seeping methane is consumed by specialized microbes that convert it into carbon dioxide. Although the increase in carbon dioxide can lead to ocean acidification, cold seeps are often found in the Hola trough of Northern Norway near cold-water corals (CWCs), which are vulnerable to changes in ocean acidity. This raises questions about how these features coexist in the same marine ecosystem and how they impact each other. We investigated the carbon exchange between cold seeps and CWCs by analyzing seawater samples. Our data on nutrients, organic matter, and microbial compositions implied cooccurring carbon processes such as methane oxidation and organic matter synthesis. Notably, cold seeps might support CWCs by producing dissolved organic matter that corals feed on. However, this relationship may be valid for a moderate amount of methane release. If methane release increases, consequent acidification may influence the CWC reefs in the future.
Key Points
- Hola trough of Northern Norway is a natural system offering insights into carbon cycling within coexisting marine ecosystems
- Despite their proximity, cold seeps and coral reefs reveal distinct biogeochemical characteristics in the Hola trough
- Cold seeps and methane oxidation impact the inorganic carbon cycle, yet the exchange of organic carbon might be just as significant
Sert M. F., Bernstein H. C., Dølven K. O., Petters S., Kekäläinen T., Jänis J., Corrales-Guerrero J. & Ferré B., 2025. Cold seeps and coral reefs in northern Norway: carbon cycling in marine ecosystems with coexisting features. Journal of Geophysical Research: Biogeosciences 130(3): e2024JG008475. doi: 10.1029/2024JG008475. Article (subscription required).
