A Dynamic Marine Calcium Cycle During the Past 28 Million Years
Elizabeth M. Griffith,1,2*
Adina Paytan,2
Ken Caldeira,3
Thomas D. Bullen,4
Ellen Thomas5,6
Multiple lines of evidence have shown that the isotopic composition
and concentration of calcium in seawater have changed over the
past 28 million years. A high-resolution, continuous seawater
calcium isotope ratio curve from marine (pelagic) barite reveals
distinct features in the evolution of the seawater calcium isotopic
ratio suggesting changes in seawater calcium concentrations.
The most pronounced increase in the
44/40Ca value of seawater
(of 0.3 per mil) occurred over roughly 4 million years following
a period of low values around 13 million years ago. The major
change in marine calcium corresponds to a climatic transition
and global change in the carbon cycle and suggests a reorganization
of the global biogeochemical system.
2 Institute of Marine Sciences, University of California, Santa Cruz, CA 95064, USA.
3 Department of Global Ecology, Carnegie Institution of Washington, 260 Panama Street, Stanford, CA 94305, USA.
4 Branch of Regional Research, Water Resources Division, U.S. Geological Survey, MS 420, 345 Middlefield Road, Menlo Park, CA 94025, USA.
5 Department of Geology and Geophysics, Yale University, Post Office Box 208109, New Haven, CT 06520, USA.
6 Department of Earth and Environmental Sciences, Wesleyan University, 265 Church Street, Middletown, CT 06459, USA.
* To whom correspondence should be addressed. E-mail: egriffith{at}ucsc.edu
