Oceans oxygen isotope record

Fig. 18-1 Benthic foraminiferal oxygen isotope record from 3477 m water depth in the eastern tropical Pacific ocean from Ocean Drilling Program site 677 (Shackleton et al, 1990). ratios are expressed in the S...

Figure 2 Comparison of annual mean coral oxygen isotope records in the Pacific and Indian Ocean region extending back more than 100 yr (Gagan et al., 2000) (reproduced by permission of Elsevier from Quat. ScL Rev. 2000,19, 45-64). These records demonstrate the considerable potential of this approach for documenting historical...

Shemesh A., Burckle L. H., and Hays J. D. (1995) Late Pleistocene oxygen isotope records of biogenic silica from the Atlantic sector of the Southern Ocean. Paleoceanography 10(2), 179-196. 

Over the long term, the Cenozoic deep-sea oxygen isotope record is dominated by two important features that relate to major shifts in mean climatic state. The first is a rise in values from 53 to 35. This trend, which is mostly gradual but punctuated by several steps, is an expression of the Eocene transition from greenhouse to icehouse conditions. In the Early Eocene (—53 Ma) the deep sea was relatively warm, —7 °C warmer than present, and there were no ice sheets. Over the next 20 Myr. the ocean cools, and the first large ice sheets appear on Antarctica. The latter event is reflected by the relatively sharp l.2%o increase in 5 0 at 33.4 Ma. This pattern reverses... 

Fig. 5.43 Oxygen isotopic record and stages from sedimentary carbonate at ODP site 677 (eastern equatorial Pacific Ocean after Shackleton et al. 1995).

Boersma, a., Shackleton, N. j. Given, Q. 1979. Carbon and oxygen isotopic records at DSDP Site 384 (North Atlantic) and some Paleocene paleotem-peratures and carbon isotope variations in the Atlantic Ocean. Initial Reports of the Deep Sea Drilling Project, 43, 695-717. 

Railsback, L.B., 1990. Influence of changing deep ocean circulation on the Phanerozoic oxygen isotopic record. Geochimica et Cosmochimica Acta 54 1501-1509. 

Figure 7. (a) Vostok ice core CO2 record reported as ppmv (part per million by volumbe) (9). (b) Ocean sediment core (G. ruber, a species of foraminifera) oxygen isotope record reported as the deviation in parts per thousand from the marine carbonate standard V-PDB (both sea-surface temperature and changes in the bulk seawater oxygen isotope composition affect this record) (49), and boron isotope based pH values reported relative to the seawater pH scale (large squares) (50). (c). Continental ice volume signal from seawater reported... 

Of special geological interest is the isotopic analyses of coeval carbonate-phosphate pairs (Wenzel et al. 2000), which helps to distinguish primary marine signals from secondary alteration effects and sheds light on the causes for 5 0 variations of fossil ocean water. Wenzel et al. (2000) compared Silurian cal-citic brachiopods with phosphatic brachiopods and conodonts from identical stratigraphic horizons. They showed that primary marine oxygen isotope compositions are better preserved in conodonts than in brachiopod shell apatite and suggested that conodonts record paleotemperature and ratios of Silurian sea water. 

Reconstruction of faunal records in deep-sea sediments and oxygen isotope measurements have been yielding useful information of the ocean s paleotemperature. However, the lack of these tools in the case of continents has hampered the estimation of paleotemperature in continents. The latter estimate has mainly been made on somehow indirect approach such as pollen data, periglacial feature, and soil carbonate, all of which suffer from considerable uncertainty stemming from the assumption that must be made to convert the observation to temperature. The advantage of the noble gas thermometer, as compared to the other paleotemperature methods, is that it is based on the relatively simple physical principle that directly relates noble gas concentration to the ambient temperature (see Stute Schlosser, 1993, for a recent review of the noble gas paleotemperature method). However, in actual practice, we need some cautions. 

Veizer J., Fritz P. and Jones B. (1986) Geochemistry of brachiopods Oxygen and carbon isotopic records of Paleozoic oceans. Geochem. Cosmochim. Acta 50, 1679-1696. 

Two methods of sea-level reconstruction have been successful. The hrst involves direct recon-stmction of sea level at individual localities by dating features that record past sea level. The second involves determining the history of variations in the oxygen isotopic composition of the ocean. 

Following Emiliani s (1955) discovery, other laboratories established the capability to apply oxygen isotope variations to oceanic temperature history. It is worth a brief mention of two further major advances relevant to Urey s original conception. In 1967, Nicholas Shackleton of Cambridge University reported the first systematic down-core variations in benthic foraminifera (Shackleton, 1967). He argued that benthic fauna, because they lived in the near-freezing bottomwaters of the ocean, would mainly record... 

Despite these caveats, oxygen isotopic ratios are probably the most widely used climate proxy in ocean history research. Reasons for this widespread use relate to the history of oxygen isotopes in geological research (see Section 6.14.2), the fact that they can be measured quite precisely by mass spectrometry and are relatively immune, at least in younger deposits, to secondary effects, the fact that records tend to be quite reproducible and clearly record climate variability, and finally, because records have proven so useful for stratigraphic and chronological purposes. 

---