O-17/O-16 47 O-18 161 O-18/O-16 3,888 Obliquity of the ecliptic 144 Observations 1,670 Observation wells 57 Observatories 230 Observers 90 Occurrence 297 Ocean 233 Ocean-atmosphere interaction 47 Ocean basins 174 Ocean bottom 1,650 Ocean circulation 3,951 Ocean--Circulation 1,005 Ocean currents 4,223 Ocean--Currents 1,151 OCEAN CURRENTS 131 Ocean Drilling Program 1,504 Ocean Drilling Program--ODP Site 1090 44 Ocean Drilling Program--ODP Site 1095 45 Ocean Drilling Program--ODP Site 1165 52 Ocean Drilling Program--ODP Site 689 44 Ocean Drilling Program--ODP Site 690 69 Ocean environments 4,898 Ocean floors 1,723 Oceanic crust 313 Oceanographic ships 68 Oceanographic surveys 796 Oceanography 3,297 Oceanography - Antarctic regions 50 Oceanography - Arctic regions 58 Oceanography--Instruments 206 Oceanography--Maps and charts 294 Oceanography--Models 349 Oceanography, physical 295 Oceans 142 Ocean--Temperature 1,116 Ocean--Water masses 764 Ocean waves 1,056 Offshore 630 Offshore drilling 1,061 Offshore landforms 87 Offshore structures 2,666 Oil and gas fields 796 Oil recovery 632 Oil spills 1,438 Oil storage 55 Oil wells 341 Oligocene 579 Olivine 194 Olivine group 217 One-dimensional models 446 Onshore 53 Ooze 99 Opal 172 Optical absorption 73 Optically stimulated luminescence 130 Optical phenomena 61 Optical properties 917 Optical spectra 91 Optimization 138 Orbital forcing 417 Orbital observations 64 Orbits 55 Ordinary chondrites 167 Ordovician 373 Organic acids 682 Organic carbon 1,343 Organic compounds 6,287 Organic materials 574 Organic nitrogen 60 Organic nuclei 176 Organic residues 363 Organic soils 414 Organization 54 Organizations 1,200 Organochlorine pesticides 109 Orientation 704 Origin 896 Orogenic belts 127 Orogeny 307 Orthogneiss 52 Orthopyroxene 115 Orthosilicates 687 Oscillations 456 Osteichthyes 151 Ostracoda 270 Otariidae 67 Outcrops 302 Outer planets 329 Outer shelf 91 Outwash 408 Outwash plains 132 Overburden 98 Oxidation 413 Oxides 508 Oxygen 4,851 Oxygen isotopes 365 Ozone 3,463