Supplementary Material S1. Review of Airborne Arctic Methane measurements CH4 concentration profiles over the Arctic Ocean were measured on five flights during the HIAPER Pole-to-Pole Observations (HIPPO) campaign (Kort et al., 2012; Wofsy, 2011) and produced evidence of sea surface CH4 emissions from the northern Chukchi and Beaufort Seas in most profiles, up to 82°N. Enhanced concentrations near the sea surface were common over fractured floating ice in sample profiles collected on 2 Nov.