Pristane–phytane ratios may also be affected slightly at low stages of biodegradation. At moderate levels these compounds are removed completely (left figure). The right figure below shows whole-oil gas chromatograms of three oils from the offshore Mackenzie Delta, northwestern Canada, showing a modest decrease in the pristane–phytane ratio, apparently as the result of minor biodegradation. | Pristane–phytane ratios may also be affected slightly at low stages of biodegradation. At moderate levels these compounds are removed completely (left figure). The right figure below shows whole-oil gas chromatograms of three oils from the offshore Mackenzie Delta, northwestern Canada, showing a modest decrease in the pristane–phytane ratio, apparently as the result of minor biodegradation. |