Variations in the marine Ca cycle over the past 20 million years

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doi: 10.1016/j.epsl.2005.06.024
Author(s): Fantle, Matthew S.; DePaolo, Donald J.
Author Affiliation(s): Primary:
University of California, Department of Earth and Planetary Science, Berkeley, CA, United States
Other:
E. O. Lawrence Berkeley National Laboratory, United States
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 237(1-2), p.102-117. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 46 refs.; illus., incl. 1 table, anals.
Summary: A 20 million year marine Ca isotope record is constructed based on measurements of 36 nannofossil ooze samples from DSDP Site 590. The Ca isotopic composition (δ44Ca, relative to our "bulk Earth" average) of carbonate ooze samples varies between -0.2 and -0.9, and the inferred δ44Ca of seawater calcium varies between +1.1 and +0.4 (modern seawater value is +0.95 on our scale). Fluctuations in the seawater Ca isotope ratio occur in 2 to 4 million year intervals and indicate that the supply and removal of Ca from the oceans are seldom in balance. The Ca isotope record is used to reconstruct past weathering fluxes and marine calcium concentrations. The inferred marine concentration of Ca fluctuates by about ±20% on 2-4 million year time scales and by about ±50% over the 20 million year record. These variations are presumably superimposed on the previously inferred 100 million year variations. The seawater Ca concentration was about 0.5 times present at 20 Ma and generally increased until 6 Ma (1.7 times present). Local maxima in seawater calcium concentrations occur at 6.4 and 4 Ma, preceding periods of enhanced marine productivity and high mass accumulation rates at Site 590. While the calculated calcium concentrations are sensitive to the assumed δ44Ca value for the weathering flux, the 2-4 million year features of the derived curves are not. Abstract Copyright (2005) Elsevier, B.V.
Year of Publication: 2005
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Calcium; Carbonates; Cenozoic; Chemical composition; Clastic sediments; Cyclic processes; DSDP Site 590; Deep Sea Drilling Project; Diagenesis; IPOD; Isotopes; Leg 90; Marine environment; Marine sediments; Mass spectra; Metals; Mixing; Neogene; Ooze; Pacific Ocean; Paleo-oceanography; Paleoclimatology; Productivity; Quaternary; Reconstruction; Sea water; Sediments; South Pacific; Southwest Pacific; Spectra; Stable isotopes; Tasman Sea; Tertiary; Weathering; West Pacific
Coordinates: S311002 S311001 E1632131 E1632130
Record ID: 2006039027
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands