Geochemistry of reduced fluids from shallow cold vents hosting chemosynthetic communities (Comau Fjord, Chilean Patagonia, ∼42°S)

•Shallow “cold-vents” are evidenced in the vicinities of a volcano’s hot springs in a Chilean fjord.•Meteoric water influences the chemistry of venting fluids, especially after the melting ice season.•High methane and sulfide concentrations in fluids support dense mats of chemosynthetic bacteria.•Reduced compounds from vent fluids probably caused massive mortalities of cold water coral colonies.•Low fluid flow rates and a fast oxidation of elements limit the vent influence in adjacent bottom waters.