Paleoceanography

(oceanography) The study of the history of the circulation, chemistry, biogeography, fertility, and sedimentation of the oceans.

The study of the history of the ocean with regard to circulation, chemistry, biology, and patterns of sedimentation. The source of information is largely the biogenous deep-ocean sediments, so the field may be considered a branch of sedimentology or paleontology. However, there are also strong links to geophysics, marine geochemistry, and mathematical modeling. Geophysical sciences are called upon for reconstruction of geography (position of continents, horizontal motion of the ocean floor), topography (changing depth patterns in the ocean, general subsidence of any given piece of sea floor), and dating (radioisotopes, magnetic patterns on the sea floor and in sediments). Geochemical analyses deliver information on sediment composition (stable and unstable isotopes; major and minor components such as carbonate, opal, and trace elements). Such information is useful in correlating sedimentary sequences and, when combined with geochemical arguments, yields insights about the dynamics of carbon and nutrient cycles. Mathematical modeling introduces a strong quantitative element. It draws upon the knowledge reservoir of modern oceanography and climatology. See also Climatology; Geochemistry; Geophysics; Paleontology; Sedimentology.

The study of marine sediments on land is as old as geology itself. Modern paleoceanography is set apart by the study of sediments recovered from the ocean, especially the deep ocean, and by the use of concepts developed by oceanographers (controls on ocean currents and upwelling, vertical stratification, heat budget, nutrient and carbon cycles, pelagic biogeography, and water masses). Important early studies were on cores raised by the United States cable ship Lord Kelvin (1936) in the North Atlantic. The glacial debris zones noted in the Kelvin cores are now commonly referred to as Heinrich layers; they are witness to sporadic input of iceberg armadas during the last glacial epoch. See also Glacial epoch.

Comparisons of climate-related changes between major ocean basins became possible through the systematic recovery of long cores by the circumglobal Swedish Deep Sea Expedition (1947–1949) on the research vessel Albatross. The expedition retrieved cores up to 15 m (45 ft) long, with records reaching back 500,000–1,000,000 years. Many fundamental paleoceanographic concepts were established by the geologists who analyzed these cores, including the role of trade winds in promoting glacial-age upwelling, the changing supply of North Atlantic Deep Water, the cyclicity of climatic change in the late Quaternary, and large-scale shifts in biogeographic boundaries. See also Climate modeling; Paleoclimatology; Quaternary.

A quantum jump in paleoceanographic research resulted from the initiation of deep-sea drilling using the research vessel Glomar Challenger (1968). Enormous blank regions on the world's map suddenly became accessible for detailed exploration far back into geologic time, that is, into the Early Cretaceous. Highlights of the first decade of drilling results include the documentation of cooling steps as the planet moved into the present ice age; the reconstruction of long-term fluctuations in the carbonate compensation depth; the documentation of large-scale salt deposition in an isolated Mediterranean basin; and the discovery of temporary anoxic conditions in the Cretaceous deep sea. See also Cretaceous.

For the journal, see Paleoceanography (journal).

Paleoceanography is the study of the history of the oceans in the geologic past with regard to circulation, chemistry, biology, geology and patterns of sedimentation.

Source of information

The source of information is largely the biogenous deep-ocean sediments, so the field is closely related to sedimentology or paleontology. Paleoceanographic research is also intimately tied to paleoclimatology.

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