Release of toxic-metal acid-brines related to permafrost thaw driven slumping of Cretaceous mudstones – Smoking Hills (Ingniryuat), Arctic Canada

The Smoking Hills (Ingniryuat) is a polar desert of Arctic Canada, which contains naturally occurring streams and ponds of hyper-acidic (pH < −2) metal-rich brines (total dissolved solids up to 394,000 mg/L). Acid waters are formed though oxidation of pyrite and metal-rich mudstones of the Late Cretaceous Smoking Hills Formation. Water in contact with the mudstones rapidly changes chemistry, becoming acidic, metal-rich, and opaque orange due to precipitation of Fe-sulfates. Acid generation occurs through mass wasting of Smoking Hills Formation mudstones due to permafrost thaw and ground ice melt in addition to coastal erosion and stream undercutting.  Fluvial incision through bedrock strata also leads to acid generation. These hyper-acidic metal-rich waters discharge to larger river systems and are transported to the Arctic Ocean, increasing some metal concetrations to exceed health guidelines for drinking water and skin contact. Climate warming will likely increase slumping rates and associated debris flows, impounding more surface ponds and stream courses, generating more acid waters, amplifying toxic metal flux to the environment, and drive river ‘rusting’.