Reconciling single-chamber Mg / Ca with whole-shell δ18O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel

[摘要] Most planktonic foraminifera migrate vertically through the water columnduring life, meeting a range of depth-related conditions as they grow andcalcify. For reconstructing past ocean conditions from geochemical signalsrecorded in their shells, it is therefore necessary to know vertical habitatpreferences. Species with a shallow habitat and limited vertical migrationwill reflect conditions of the surface mixed layer and short-term and mesoscale(i.e. seasonal) perturbations therein. Species spanning a wider range ofdepth habitats, however, will contain a more heterogeneous, intra-specimenvariability (e.g. Mg / Ca and δ¹⁸O), which is less for speciescalcifying below the thermocline. Obtained single-chamber Mg / Ca ratios are combinedwith single-specimen δ¹⁸O and δ¹³C of the surface-water inhabitant Globigerinoides ruber, the thermocline-dwelling Neogloboquadrina dutertreiand Pulleniatina obliquiloculata, and the deep dweller Globorotalia scitula fromthe Mozambique Channel. Species-specific Mg / Ca, δ¹³C andδ¹⁸O data combined with a depth-resolved mass balance modelconfirm distinctive migration and calcification patterns for each species asa function of hydrography. Whereas single-specimen δ¹⁸O rarelyreflects changes in depth habitat related to hydrography (e.g. temperature),measured Mg / Ca of the last chambers can only be explained by activemigration 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 eachother and in line with the changes in hydrography induced by eddies.

[学科分类] 地球化学与岩石