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Reconciling single-chamber Mg / Ca with whole-shell d18O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel
Steinhardt, J.; Cléroux, C.; de Nooijer, L.J.; Brummer, G.-J.A.; Zahn, R.; Ganssen, G.; Reichart, G.-J. (2015). Reconciling single-chamber Mg / Ca with whole-shell d18O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel. Biogeosciences 12: 2411-2429. dx.doi.org/10.5194/bg-12-2411-2015
In: Gattuso, J.P.; Kesselmeier, J. (Ed.) Biogeosciences. Copernicus Publications: Göttingen. ISSN 1726-4170, more
Peer reviewed article  

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Authors  Top 
  • Steinhardt, J., more
  • Cléroux, C., more
  • de Nooijer, L.J., more
  • Brummer, G.-J.A., more
  • Zahn, R.
  • Ganssen, G.
  • Reichart, G.-J., more

Abstract
    Most planktonic foraminifera migrate vertically through the water column during life, meeting a range of depth-related conditions as they grow and calcify. For reconstructing past ocean conditions from geochemical signals recorded in their shells, it is therefore necessary to know vertical habitat preferences. Species with a shallow habitat and limited vertical migration will reflect conditions of the surface mixed layer and short-term and mesoscale (i.e. seasonal) perturbations therein. Species spanning a wider range of depth habitats, however, will contain a more heterogeneous, intra-specimen variability (e.g. Mg / Ca and d18O), which is less for species calcifying below the thermocline. Obtained single-chamber Mg / Ca ratios are combined with single-specimen d18O and d13C of the surface-water inhabitant Globigerinoides ruber, the thermocline-dwelling Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, and the deep dweller Globorotalia scitula from the Mozambique Channel. Species-specific Mg / Ca, d13C and d18O data combined with a depth-resolved mass balance model confirm distinctive migration and calcification patterns for each species as a function of hydrography. Whereas single-specimen d18O rarely reflects changes in depth habitat related to hydrography (e.g. temperature), measured Mg / Ca of the last chambers can only be explained by active migration in response to changes in temperature stratification. Foraminiferal geochemistry and modelled depth habitats shows that the single-chamber Mg / Ca and single shell d18O are in agreement with each other and in line with the changes in hydrography induced by eddies.

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