Cold seeps: climate relevance and anthropogenic impacts

Cold seeps are deep-sea benthic features which emit hydrocarbon-rich fluids (primarily methane), representing notable conduits for carbon from long-term geologic stores to the hydrosphere. Methane is a potent greenhouse gas with substantial implications for earth’s climate. Due to their global distribution, cold seeps and their associated ecosystems have a potentially significant, and often overlooked, role in global carbon cycling. Cold seeps host extensive chemosynthetic communities with cascading ecological impacts to nearby deep-sea ecosystems and provide carbon-regulating (“blue carbon”) services. Herein, we view cold seeps through the blue carbon lens, highlighting their climate-regulating services, which include: 1) geologic carbon reservoirs in methane hydrates and carbonate minerals; 2) natural carbon emission reduction through chemoautotrophic methane oxidation and the physical blockage of vents; and 3) carbon recycling and sequestration mediated by diverse biological communities which store carbon as biomass, recycle methane-derived carbon, and enhance carbon burial. Our perspective also considers anthropogenic stressors, such as bottom contact fishing, ecosystem engineering projects, and climate-driven changes (warming, deoxygenation, acidification), that may threaten these services. These activities can destroy cold seep ecosystems, alter fluid emissions, disturb benthic sediments, damage vulnerable benthic habitats, and destabilize carbon reservoirs, consequently impairing carbon storage, natural emission reduction, and recycling processes at cold seeps. This new perspective discusses the carbon-cycling services of cold seeps and their ecosystems and underscores their potential liability as climate-relevant methane sources, if they are damaged by human activities. For these reasons, future research is needed to better quantify the blue carbon services of cold seeps, to advance management and conservation.