Anomalous depth profiles of hydrocarbon tracers of thermogenic origin have been reported at various marine locations, including Ragay Gulf, the Philippines. Until now the origin of such profiles remained unexplained. We present a quantitative numerical model in which the bottom-water anomalies are interpreted as transient states of the hydrocarbon plume intermittently seeping from the ocean floor and mixing with the stratified water. An anomalous midwater plume forms because of different mixing regimes in the water column. For typical values of the vertical and horizontal mixing coefficients in the ocean, the anomalies may persist for periods up to ∼1 yr.

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