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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Paleoceanography | 2/2 | https://en.wikipedia.org/wiki/Paleoceanography | reference | science, encyclopedia | 2026-05-05T07:36:03.665799+00:00 | kb-cron |
=== Ocean circulation === Several proxy methods have been used to infer past ocean circulation and changes to it. They include carbon isotope ratios, cadmium/calcium (Cd/Ca) ratios, protactinium/thorium isotopes (231Pa and 230Th), radiocarbon activity (δ14C), neodymium isotopes (143Nd and 144Nd), and sortable silt (fraction of deep-sea sediment between 10 and 63 μm). Carbon isotope and cadmium/calcium ratio proxies are used because variability in their ratios is due partly to changes in bottom-water chemistry, which is in turn related the source of deep-water formation. These ratios, however, are influenced by biological, ecological, and geochemical processes which complicate circulation inferences. All proxies included are useful in inferring the behavior of the meridional overturning circulation. For example, McManus et al. [2004] used protactinium/thorium isotopes (231Pa and 230Th) to show that the Atlantic Meridional Overturning Circulation had been nearly (or completely) shut off during the last glacial period. 231Pa and 230Th are both formed from the radioactive decay of dissolved uranium in seawater, with 231Pa able to remain supported in the water column longer than 230Th: 231Pa has a residence time ~100–200 years while 230Th has one ~20–40 years. In today's Atlantic Ocean and current overturning circulation, 230Th transport to the Southern Ocean is minimal due to its short residence time, and 231Pa transport is high. This results in relatively low 231Pa / 230Th ratios found by McManus et al. [2004] in a core at 33N 57W, and a depth of 4.5 km. When the overturning circulation shuts down (as hypothesized) during glacial periods, the 231Pa / 230Th ratio becomes elevated due to the lack of removal of 231Pa to the Southern Ocean. McManus et al. [2004] also note a small raise in the 231Pa / 230Th ratio during the Younger Dryas event, another period in climate history thought to have experienced a weakening overturning circulation.
=== Acidity, pH, and alkalinity === Boron isotope ratios (δ11B) can be used to infer both recent as well as millennial time scale changes in the acidity, pH, and alkalinity of the ocean, which is mainly forced by atmospheric CO2 concentrations and bicarbonate ion concentration in the ocean. δ11B has been identified in corals from the southwestern Pacific to vary with ocean pH, and shows that climate variabilities such as the Pacific decadal oscillation (PDO) can modulate the impact of ocean acidification due to rising atmospheric CO2 concentrations. Another application of δ11B in plankton shells can be used as an indirect proxy for atmospheric CO2 concentrations over the past several million years.
== See also == Oceanography – Scientific study of the ocean Paleoclimatology – Study of changes in ancient climate Paleogeography – Study of physical geography of past landscapesPages displaying short descriptions of redirect targets Paleothermometer — Study of ancient temperatures
== References ==
== External links == Media related to Paleoceanography at Wikimedia Commons