Reconciling single-chamber Mg / Ca with whole-shell δ18O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel
- 1Department of Geology and Chemical Oceanography, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, the Netherlands
- 2Faculty of Earth- and Life Sciences, VU University Amsterdam, de Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
- 3Department of Earth Sciences, Faculty of Geosciences, Utrecht University, P.O. Box 80021, 3508TA Utrecht, the Netherlands
- 4Institució Catalana de Recerca i Estudis Avançats (ICREA) and Institut de Ciència i Tecnologia Ambientals, Departament de Física, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain
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 δ18O), which is less for species calcifying below the thermocline. Obtained single-chamber Mg / Ca ratios are combined with single-specimen δ18O and δ13C 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, δ13C and δ18O 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 δ18O 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 δ18O are in agreement with each other and in line with the changes in hydrography induced by eddies.