Variations in the marine Ca cycle over the past 20 Ma

Journal Article · Wed Mar 23 00:00:00 EST 2005 · Earth&Planetary Science Letters

OSTI ID:894977

Fantle, Matthew S; DePaolo, D

A 20 million year marine Ca isotope record is constructedbased on measurements of 36 nannofossil ooze samples from DSDP Site 590.The Ca isotopic composition (d44Ca, relative to our b bulk EarthQaverage) of carbonate ooze samples varies between ?0.2 and ?0.9, and theinferred d44Ca of seawater calcium varies between +1.1 and +0.4 (modernseawater value is +0.95 on our scale). Fluctuations in the seawater Caisotope ratio occur in 2 to 4 million year intervals and indicate thatthe supply and removal of Ca from the oceans are seldom in balance. TheCa isotope record is used to reconstruct past weathering fluxes andmarine calcium concentrations. The inferred marine concentration of Cafluctuates by about F20 percent on 2-4 million year time scales and byabout F50 percent over the 20 million year record. These variations arepresumably superimposed on the previously inferred 100 million yearvariations. The seawater Ca concentration was about 0.5 times present at20 Ma and generally increased until 6 Ma (1.7 times present). Localmaxima in seawater calcium concentrations occur at 6.4 and 4 Ma,preceding periods of enhanced marine productivity and high massaccumulation rates at Site 590. While the calculated calciumconcentrations are sensitive to the assumed d44Ca value for theweathering flux, the 2-4 million year features of the derived curves arenot.

• Research Organization: COLLABORATION - Collaboration with UCBerkeley
• DOE Contract Number: DE-AC02-05CH11231
• OSTI ID: 894977
• Report Number(s): LBNL-60819
• Journal Information: Earth&Planetary Science Letters, Vol. 237; Related Information: Journal Publication Date: 27 July 2005
• Country of Publication: United States
• Language: English