The stable isotopic composition (37Cl/35Cl) of dissolved chloride in rainwater

The stable isotopic composition of dissolved Cl-Cl- in rainwater was measured from a coastal and an interior location in eastern Canada. At the interior Bonner Lake, Ontario, site the δ37Cl values of dissolved Cl-Cl- in precipitation ranged from −3.5‰ to −1.2‰ (SMOC) with an amount-weighted annual average of −2.3‰. At the coastal site, Bay D’Espoir, Newfoundland, δ37Cl values of dissolved Cl-Cl- values ranged from −3.1‰ to 0.0‰ with an amount-weighted annual average of −1.3‰. These negative δ37Cl values provide evidence that atmospheric HCl is 37Cl depleted, presumably from acidification of sea-salt aerosols. Accordingly, dissolved Cl-Cl- in the headwaters of two montane rivers in Western Canada had similarly depleted δ37Cl values. These results have implications to the interpretation of the isotopic compositions of dissolved Cl-Cl- in surface waters, formation fluids, and groundwaters.