Reconciling single-chamber Mg / Ca with whole-shell δ 18 O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel
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 p...
Published in: | Biogeosciences |
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Main Authors: | , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Copernicus Publications
2015
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Subjects: | |
Online Access: | https://doi.org/10.5194/bg-12-2411-2015 https://doaj.org/article/3773ed655c1b4f50b7983eba30b6bbd7 |
Summary: | 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 δ 18 O), which is less for species calcifying below the thermocline. Obtained single-chamber Mg / Ca ratios are combined with single-specimen δ 18 O and δ 13 C 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, δ 13 C and δ 18 O 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 δ 18 O 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 δ 18 O are in agreement with each other and in line with the changes in hydrography induced by eddies. |
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