. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . 10" 10° 10' 102 [C2]/:C2:|] 10= 10" Figure 27-9. Compositional hydrocarbon trajectory dia- gram for Bristol Bay. For comparison, the compositional fields of the Norton Sound gas seep (Cline and Holmes 1977) and the anoxic waters of the Black Sea (Hunt 1974) are indicated. Mixing of Bristol Bay hydrocarbons with various thermogenically derived hydrocarbon mixtures results in a family of mixing trajectories, two of which are shown here (see text). Along one of the dry gas traject
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . 10" 10° 10' 102 [C2]/:C2:|] 10= 10" Figure 27-9. Compositional hydrocarbon trajectory dia- gram for Bristol Bay. For comparison, the compositional fields of the Norton Sound gas seep (Cline and Holmes 1977) and the anoxic waters of the Black Sea (Hunt 1974) are indicated. Mixing of Bristol Bay hydrocarbons with various thermogenically derived hydrocarbon mixtures results in a family of mixing trajectories, two of which are shown here (see text). Along one of the dry gas trajectories, the fraction (%) of ambient water is given, assuming that the hydrocarbons in the source are each about 100 times the ambient levels. 1. These compositional ratios obtain for most of the Alaskan shelf waters and are probably typical of high latitude, pristine coastal waters. On the other hand, anoxic waters in the Black Sea (Hunt 1974) reflect a narrow compositional field characterized by high con- centrations of methane, [Ci ] /[C2 ] +[C3 ] = 500, and relatively high concentrations of ethane, 20 < [C2 ] / [^2:1 ] < 50. Provisionally, it is assumed that the Black Sea represents a model of the hydrocarbon composition to be expected from anoxic marine sources. At this point it becomes useful to consider the compositional trajectories that might be observed if gases of thermogenic origin were mixed with biologi- cally derived hydrocarbons. To accomplish this, four distinct petroleum/natural gas sources were consid- ered from an analysis of gas and oil well data (Moore et al. 1966). The equations that govern the mix- ing trajectories in the [Ci]/[C2] + [C3] and [C2]/ [^2:1 ] plane are: [Ci] [Ci]a+((1-x)/x)[Ci]t [C2]+[C3] [Q]a+[C3]a+((1-x)/x)[C2]t+[C3]t (1) [C2] [C2]a [Calx [Q:i]=[C2:x]a"'^^1-^^/^)[Q:i]a ^2) The fraction of ambient water is x, whereas con- centrations of the individual hydrocarbons are shown in brackets. The two sources, between which mixing
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