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A GLOBAL OUTLOOK ON METHANE GAS HYDRATES
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Field studies show dissolved oxygen is strongly depleted in some
coastal areas and marginal seas, such as the Black Sea and Baltic
Sea, as well as at poorly ventilated and highly productive continental
margins. Observational data show the volume of these depleted
water masses has expanded significantly in recent decades
(Stramma
et al.
2008). Models predict the ongoing oxygen loss
at continental margins will be amplified over the coming century
in response to anthropogenic carbon dioxide emissions (Oschlies
et al.
2008). Most fauna living at the sea floor depend on oxygen
and will vanish when dissolved oxygen concentrations in ambient
bottom waters fall below a critical threshold value. The spread of
low-oxygen conditions is, therefore, a serious threat to fauna living
at the sea floor of the affected continental margin areas. Although
field studies have not yet demonstrated significant pH decreases
or oxygen depletions in the vicinity of methane seeps, it is possible
these effects may take a long time to become apparent. Baseline
studies might be needed in order to understand these slow
environmental degradation issues.