Caldeira Lab Research:Paleoclimate and geochemical cycles

A Dynamic Marine Calcium Cycle During the Past 28 Million Years

Elizabeth M. Griffith, Adina Paytan, Ken Caldeira, Thomas D. Bullen & Ellen Thomas

Climatic changes over the past 28 million years has affected the isotopic ratio of calcium in the Earth's oceans. Here we try to understand what calcium isotopes can tell us about Earth's climate evolution.

Griffith, EM; Paytan, A; Caldeira, K; Bullen, TD; Thomas, E, 2008. A Dynamic Marine Calcium Cycle During the Past 28 Million Years, Science 322 (5908):1671-1674, DOI: 10.1126/Science.1163614

Time varying isotopic composition of the calcium input flux to the oceans (δ44/40Cain) and isotopic fractionation during calcium carbonate precipitation before sedimentation (Δ44/40Cased) in per mil used in the numerical models (top). Calculated ratio of amount of calcium in the oceans [NCa(t)], relative to the present value [NCa(modern)] constrained using data (open diamonds) from (7). Solid black line is NCa(t) / NCa(modern); dashed black line is Phanerozoic trend (7) (bottom). Numerical model assuming (A) constant Δ44/40Cased or (B) varying Δ44/40Cased calculated from the difference between seawater δ44/40Ca (this study) and measured contemporaneous bulk nannofossil ooze carbonates.


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 δ44/40 Ca 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.