The distribution of formulas in van Krevelen space was typical for a marine sample , with the majority of formulas in the region H/C 1 -1.5 and O/C 0.3 -0.7 (Figure ). This is where the most recalcitrant DOM is typically found, namely 'Island of Stability' molecules and CRAM formulas . These data are consistent with the NMR findings (Section 3.4), and suggest that the TRM sample is a useful and otherwise unavailable reference mixture for relatively aged, recalcitrant marine DOM.