title: Effect of different seawater Mg2 +concentrations on calcification in two benthic foraminifers.
abstract: Magnesium, incorporated in foraminiferal calcite (Mg/CaCC), is used intensively to reconstruct past seawater temperatures but, in addition to temperature, the Mg/CaCCof foraminiferal tests also depends on the ratio of Mg and Ca in seawater (Mg/CaSW). The physiological mechanisms responsible for these proxy relationships are still unknown. This culture study investigates the impact of different seawater [Mg2 +] on calcification in two benthic foraminiferal species precipitating contrasting Mg/CaCC:Ammonia aomoriensis, producing low-Mg calcite andAmphistegina lessonii, producing intermediate-Mg calcite. Foraminiferal growth and test thickness were determined and, Mg/Ca was analyzed using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Results show that at present-day seawater Mg/CaSWof ~ 5, both species have highest growth rates, reflecting their adaptation to modern seawater element concentrations. Test thickness is not significantly affected by different Mg/CaSW. The relationship between Mg/CaSWand Mg/CaCCshows a distinct positive y-axis intercept, possibly reflecting at least two processes involved in foraminiferal biomineralization. The associated Mg partition (DMg) changes non-linearly with increasing Mg/CaSW, hence suggesting that the DMgis best described by an exponential function approaching an asymptote.
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, D-27570 Bremerhaven, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Mewes
authors.affiliation: Department of Earth Sciences, Cambridge University, Downing St., Cambridge, CB2 3EQ, UK.
authors.forename: Gerald
authors.initials: G
authors.lastname: Langer
authors.affiliation: Royal Netherlands Institute for Sea Research, Landsdiep 4, 't Horntje, Texel 1797 SZ, The Netherlands.
authors.forename: Lennart Jan
authors.initials: LJ
authors.lastname: de Nooijer
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, D-27570 Bremerhaven, Germany.
authors.forename: Jelle
authors.initials: J
authors.lastname: Bijma
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, D-27570 Bremerhaven, Germany ; Royal Netherlands Institute for Sea Research, Landsdiep 4, 't Horntje, Texel 1797 SZ, The Netherlands ; Department of Earth Sciences, University of Utrecht, Budapestlaan 4, 3584 CD Utrecht, The Netherlands.
authors.forename: Gert-Jan
authors.initials: GJ
authors.lastname: Reichart
keywords: Biomineralization; Culture experiment; LA-ICP-MS; Mg partitioning; Mg/Ca; Proxy