A Dynamic Marine Calcium Cycle During the Past 28 Million Years

Abstract

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 delta44/40Ca 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.

The Ca isotopic composition of dust-producing regions: Measurements of surface sediments in the Black Rock Desert, Nevada

“…Such is the case for the calcium isotope proxy, which has been proposed to elucidate paleo-sea surface temperatures (e.g., Nägler et al, 2000;Bö hm et al, 2006;Langer et al, 2007) and/or variations in Ca cycling in the geological past (e.g., De La Rocha and DePaolo, 2000;DePaolo, 2004;Fantle and DePaolo, 2005;Heuser et al, 2005;Farkas et al, 2007;Sime et al, 2007;Griffith et al, 2008;Fantle, 2010). In both cases, knowing the isotopic composition of seawater is fundamental to successful utilization of the proxy.…”

Exploring the controls on element ratios in middle Eocene samples of the benthic foraminifera <i>Oridorsalis umbonatus</i>

“…However, it is difficult to conceive that seawater [Ca 2+ ] could be decoupled over million year periods from calcite compensation. Griffith et al (2008) suggest that changes in the rate of dolomitization and/or the Ca 2+ :HCO − 3 of riverine inputs are possible processes to decouple the Ca and C cycle, but additional work is required to evaluate these hypotheses. Shortterm (< 1 Myr) variations in the X/Ca at Site 1209, if solely due to changes in seawater [Ca 2+ ], would require extremely large and unrealistic changes over a geologically rapid time (∼ 15 % in [Ca 2+ ] in < 400 kyr).…”

“…Sequence stratigraphic and geochemical proxy reconstructions support highly variable sea level during the middle Eocene (Browning et al, 1996;Miller et al, 2005;). An increase in the Ca 2+ flux from continental weathering when unaccompanied by carbonate compensation is a mechanism of lowering seawater X/Ca, and has been proposed as one way to account for the apparent increase in seawater [Ca 2+ ] during the middle Miocene glacial expansion (Griffith et al, 2008). During the Neogene the magnitude of seawater [Ca 2+ ] variations on timescales of 2-4 Myr is ∼ 20 % (Fantle and DePaolo, 2005), which is similar to the long-term variability in the middle Eocene Sr/Ca and Mg/Ca records at Site 1209.…”

Temporal variability in chemical cycling of the subterranean estuary and associated chemical loading to the coastal ocean

“…van Keywords: submarine groundwater discharge; subterranean estuary; karst; barium; radium; uranium; strontium; manganese; Yucatan Peninsula Variability in oceanic Ca isotopes may be related to changes in ocean carbon cycling on long time scales (Griffith et al, 2008) and Ra is used extensively as a tracer of groundwater discharge . Uranium serves as a proxy of ocean redox state …”