HR: 0800h
AN: PP51A-0581    [Abstracts]
TI: Evaporites and the Salinity of the Ocean During the Phanerozoic: Implications for Climate, Ocean Circulation and Life
AU: * Floegel, S
EM: sfloegel@ifm-geomar.de
AF: IFM-GEOMAR Leibniz-Institute of Marine Sciences, Wischhofstrasse 1-3, Kiel, SH 24148 Germany
AU: Hay, W W
EM: whay@gmx.de
AF: private, 2045 Windcliff Dr., Estes Park, CO 80517 United States
AU: Migdisov, A
EM: Migdisov@Geokhi.ru
AF: Vernadski Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin 19, Moscow, 119991 Russian Federation
AU: Balukhovsky, A N
EM: Balukhov@Geokhi.ru
AF: Vernadski Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin 19, Moscow, 119991 Russian Federation
AU: Wold, C N
EM: chris@platte.com
AF: Platte River Associates, 2790 Valmont Road, Boulder, CO 80304 United States
AU: Soeding, E
EM: esoeding@iodp-mi-sapporo.org
AF: Integrated Ocean Drilling Program Management International, Inc., Sapporo Office, Creative Research Initiative "Sousei" (CRIS), N21W10 Kitaku, Sapporo, 001-0021 Japan
AB: A compilation of data on volumes and masses of evaporite deposits is used as the basis for reconstruction of the salinity of the ocean in the past. Chloride is tracked as the only ion essentially restricted to the ocean, and past salinities are calculated from reconstructed chlorine content of the ocean. Models for ocean salinity through the Phanerozoic are developed using maximal and minimal estimates of the volumes of existing evaporite deposits, and constant and declining volumes of ocean water through the Phanerozoic. We conclude that there have been significant changes in the mean salinity of the ocean accompanying a general decline throughout the Phanerozoic. The greatest changes are related to major extractions of salt into the ocean basins which developed during the Mesozoic as Pangaea broke apart. Unfortunately, the sizes of these salt deposits are also the least well known. The last major extractions of salt from the ocean occurred during the Miocene, shortly after the large scale extraction of water from the ocean to form the ice cap of Antarctica. However, these two modifications of the masses of H₂O and salt in the ocean followed in sequence and did not cancel each other out. Accordingly, salinities during the Early Miocene were reconstructed to be between 37‰ and 39‰. The Mesozoic was a time of generally declining salinity associated with the deep sea salt extractions of the North Atlantic and Gulf of Mexico (Middle to Late Jurassic) and South Atlantic (Early Cretaceous). The earliest of the major extractions of the Phanerozoic occurred during the Permian. There were few large extractions of salt during the earlier Paleozoic. The models suggest that this was a time of relatively stable but slowly increasing salinities ranging through the upper 40‰'s into the lower 50‰'s. Higher salinities for the world ocean had profound consequences for the thermohaline circulation of the ocean in the past. In the modern ocean, with an average salinity of about 34.7‰, the density of water is only slightly affected by cooling as it approaches the freezing point. Consequently, salinization through sea-ice formation or evaporation is usually required to make water dense enough to sink into the ocean interior. At salinities above about 40‰ water continues to become more dense as it approaches the freezing point, and salinization is not required. The energy-consuming phase changes involved in sea-ice formation and evaporation would not be required for vertical circulation in the ocean. The hypothesized major declines in salinity correspond closely to the evolution of both planktonic foraminifera and calcareous nannoplankton. Both groups were restricted to shelf regions in the Jurassic and early Cretaceous, but spread into the open ocean in the mid Cretaceous. The modeling also suggests that there was a major salinity decline in from the late Precambrian to the Cambrian, and it is tempting to speculate that this may have been a factor in the Cambrian explosion of life.
DE: 4271 Physical and chemical properties of seawater
DE: 4825 Geochemistry
DE: 4835 Marine inorganic chemistry (1050)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005