U need to express knowledge of low oxygen due to lack of light in deep ocean which means no photosynthesis. U also need to express knowledge of the rduction of concentrations of gases as depth increases and increase in pressure. Then come to a logic conclusion that under these coditions corrosion is not expected to occur. Then u may need a case study to show the existence of corrosion in deep sea water. U may need to also show the change in conc of salts as depth decreases. Graphs may b key to your response. Then discuss bacterial corrosion givin specific reasons y corrosion occurs. possible 7 marker.