Over the past ~20 years, deep-ocean scientists have paid keen interest to ultramafic-influenced seafloor hydrothermal systems, guided by theoretical predictions that they have the capacity to stimulate the synthesis of simple organic compounds through purely geological processes. The compounds detected to-date include some that are often considered as essential stepping stones on the path to life. In all such systems found to date, where abiotic synthesis does appear to occur, the vent-fluids also exhibit high dissolved hydrogen concentrations. This has proven particularly intriguing given the detection, in Cassini Mission data, for evidence that plumes of frozen matter emitted from the South Pole of Enceladus contain organic compounds, hydrogen, and mineralogical indicators of submarine venting. In our most recent Earth discoveries, however, one of the most hydrogen-rich vent sites we have yet encountered, beneath Arctic sea-ice, shows no sign of generating those same 'pre-biotic' molecules. Our presentation will seek to explain why that should be and whether this one 'false positive' on Earth can be considered the exception that proves the rule.