Phase associations and lipid distributions in the seasonally ice-covered Arctic estuary of the Mackenzie Shelf

Alkanes, hopane triterpenes, polycyclic aromatic hydrocarbons (PAHs), n-alcohols and sterols have been determined in the suspended particulate (> 0.7 μm) and dissolved (Chromosorb T absorption) phases of samples from the Mackenzie River and shelf in winter, spring and summer. The dissolved phase carries a significant fraction of the alkanes and PAHs in winter and spring and is an important component of the hydrocarbon budget. However, dissolved alkanes and PAHs are only a minor component of the hydrocarbon budget when concentrations of suspended particulate are high during the open water season. At this time nearly all of the alkanes and parent PAHs are associated with the > 1.2 μm particulate size fraction. The colloidal fraction is only a minor component of the PAHs in the Mackenzie River and nearshore, but a larger proportion of the PAH load is apparently borne by the finer particulate fractions in the marine regime. In all seasons the contribution to the dissolved phase decreases in the order diploptene, diagenetic hopanes, sterols and alcohols. Because petrogenic alkanes did not interfere in the higher alkane region, a seasonally independent terrigenous alkane equilibrium between the >0.7 μm particulate reservoir and the dissolved fraction could be observed in the Mackenzie River and estuary. A dissolved phase odd-even predominance (OEP) is found wherever significant higher plant alkanes are present. The loss of this OEP on the mid shelf is most likely caused by a reduction in the particulate associated supply of terrigenous alkanes. The lower molecular-mass (up to 178), more water soluble PAHs predominate in the dissolved phase. Atmospheric PAHs are minor, occur most often in surface water and offshore samples and are present in greater amounts in the dissolved phase and fine particulate fractions