<Table> <Tr> <Td> Photosynthesis (land) Photosynthesis (ocean) Photolysis of N O Photolysis of H O </Td> <Td> 16,500 13,500 1.3 0.03 </Td> </Tr> <Tr> <Td> Total gains </Td> <Td> ~ 30,000 </Td> </Tr> <Tr> <Td_colspan="2"> Losses - respiration and decay </Td> </Tr> <Tr> <Td> Aerobic respiration Microbial oxidation Combustion of fossil fuel (anthropogenic) Photochemical oxidation Fixation of N by lightning Fixation of N by industry (anthropogenic) Oxidation of volcanic gases </Td> <Td> 23,000 5,100 1,200 600 12 10 </Td> </Tr> <Tr> <Td_colspan="2"> Losses - weathering </Td> </Tr> <Tr> <Td> Chemical weathering Surface reaction of O </Td> <Td> 50 12 </Td> </Tr> <Tr> <Td> Total losses </Td> <Td> ~ 30,000 </Td> </Tr> </Table> <Tr> <Td> Photosynthesis (land) Photosynthesis (ocean) Photolysis of N O Photolysis of H O </Td> <Td> 16,500 13,500 1.3 0.03 </Td> </Tr> <Tr> <Td> Total gains </Td> <Td> ~ 30,000 </Td> </Tr> <Tr> <Td_colspan="2"> Losses - respiration and decay </Td> </Tr>

What are the sources of oxygen in the atmosphere