Calcium isotope (δ^44/40Ca) variations of Neogene planktonic foraminifera

Abstract

Measurements of the calcium isotopic composition (δ44/40Ca) of planktonic foraminifera from the western equatorial Pacific and the Indian sector of the Southern Ocean show variations of about 0.6‰ over the past 24 Myr. The stacked δ44/40Ca record of Globigerinoides trilobus and Globigerina bulloides indicates a minimum in δ44/40Casw (seawater calcium) at 15 to 16 Ma and a subsequent general increase toward the present, interrupted by a second minimum at 3 to 5 Ma. Applying a coupled calcium/carbon cycle model, we find two scenarios that can explain a large portion of the observed δ44/40Casw variations. In both cases, variations in the Ca input flux to the ocean without proportional changes in the carbonate flux are invoked. The first scenario increases the riverine calcium input to the ocean without a proportional increase of the carbonate flux. The second scenario generates an additional calcium flux from the exchange of Ca by Mg during dolomitization. In both cases the calcium flux variations lead to drastic changes in the seawater Ca concentrations on million year timescales. Our δ44/40Casw record therefore indicates that the global calcium cycle may be much more dynamic than previously assumed.

Calcium isotope fractionation in coccoliths of cultured Calcidiscus leptoporus, Helicosphaera carteri, Syracosphaera pulchra and Umbilicosphaera foliosa

“…As a consequence, they are an important link between global calcium (Ca) and carbon (C) cycling. Because they act as a major Ca sink, coccoliths play an important role in determining the isotopic Ca budget of the marine realm, and consequently their isotopic composition is an important parameter for reconstructing the Ca budget of the global ocean (De La Rocha and DePaolo, 2000;Schmitt et al, 2003;Soudry et al, 2004;Heuser et al, 2005;Fantle and DePaolo, 2005). However, previous studies on coccolith oozes have reported a disparate range of seemingly conflicting Ca isotope values.…”

Calcium isotopic composition of high-latitude proxy carrier <i>Neogloboquadrina pachyderma</i> (sin.)

“…Negative values are set to 0-50 m. * δ 18 O Nps ratios from adjacent cores 23 277 and 23 254, see (Simstich et al, 2003). c Summer salinities and SSTs are averaged using depth corresponding hydrographic data from July-September (main planktonic bloom in the Nordic Seas (Kohfeld et al, 1996) variations of seawater Ca isotopic composition observed in the Early Pleistocene and Late Pliocene of ±0.2‰ compared to the modern seawater value (Fantle and DePaolo, 2005;Heuser et al, 2005;Sime et al, 2007) are within the analytical uncertainty and therefore negligible for the purpose of this study.…”

“…Most planktonic foraminifera species studied so far, dwelling in subpolar to subtropical temperate waters, exhibit a shallow slope for their temperature sensitivity (e.g. Gussone et al, 2003;Heuser et al, 2005;Sime et al, 2005Sime et al, , 2007Griffith et al, 2008). A detailed study on the temperature sensitivity of cultured Orbulina universa resulted in a temperature gradient one-order-of-magnitude smaller than that of N. pachyderma (sin.)…”

Stable isotope profiles (Ca, O, C) through modern brachiopod shells of T. septentrionalis and G. vitreus: Implications for calcium isotope paleo-ocean chemistry

“…This information is important as the chemical composition of the ocean itself is closely linked to the atmosphere and to the global climate. In order to reconstruct the calcium isotopic composition of the paleoocean archives such as brachiopods, belemnites, foraminifers, rudists, coccoliths, barites or phosphates are investigated (e.g., Nägler et al, 2000;Schmitt et al, 2003;Gussone et al, 2004;Fantle and DePaolo, 2005;Heuser et al, 2005;Immenhauser et al, 2005;Gussone et al, 2006;Hippler et al, 2006Hippler et al, , 2009Farkaš et al, 2007a,b;Sime et al, 2007;Griffith et al, 2008).…”