9:15 AM - 9:30 AM
[BPT04-02] Analysis of the relationship between planktic foraminiferal fossils and palaeoenvironmental parameters using micro X-ray CT.
★Invited Papers
Keywords:planktic foraminifers, paleoenvironmental proxy, micro X-ray computed tomography
Various marine organisms, including corals, coccoliths and foraminifers and so on, use the carbonate ions in the surrounding seawater for the production of their skeletons and shells. It has been suggested that the carbonate saturation of seawater strongly affects foraminiferal shells, and that foraminiferal shell production is sensitive to increases in pCO2. The size-normalized weights of foraminiferal shells have been utilized as a means of estimating the surface seawater environment. However, the specific parameters of foraminiferal shells that are reflected in the size-normalized weight remain uncertain. In other words, it is not clear whether the observed changes are attributable to shell thickness, shell volume, shell density, or a combination of these factors. Consequently, the relationship between environmental parameters and foraminiferal shell parameters, particularly three-dimensional parameters such as shell volume and density, remains unclear.
In this study, the shell SNW, shell volume and shell density of the planktic foraminifer Globigerinoides ruber (white) in the MD98-2196 core were measured. Furthermore, the relationship between these shell parameters and environmental parameters (pCO2 and sea surface temperature : SST) was investigated. The potential of each shell parameter as a proxy for estimating palaeoenvironmental conditions was also explored. Precise and quantitative measurements of three-dimensional parameters using high-resolution micro-X-ray computed tomography suggest that both shell weight and shell volume, normalized by shell size, may be negatively correlated with environmental parameters (pCO2 and SST). These two parameters were also found to be more sensitive to pCO2 than SST. Conversely, shell density never showed any change during the 3-100 ka period, suggesting that it remained constant. Consequently, variations in SNW are likely to reflect changes in shell quantity, with not much effect by shell quality (i.e. density). Furthermore, the results suggest that it is possible to use shell volume as an environmental proxy along with the previously used SNW. By contrast, shell density was maintained at a relatively constant level, thus requiring further investigation to elucidate the environmental parameters that influence shell density during foraminifers shell formation (or confirm its complete constancy).
In this study, the shell SNW, shell volume and shell density of the planktic foraminifer Globigerinoides ruber (white) in the MD98-2196 core were measured. Furthermore, the relationship between these shell parameters and environmental parameters (pCO2 and sea surface temperature : SST) was investigated. The potential of each shell parameter as a proxy for estimating palaeoenvironmental conditions was also explored. Precise and quantitative measurements of three-dimensional parameters using high-resolution micro-X-ray computed tomography suggest that both shell weight and shell volume, normalized by shell size, may be negatively correlated with environmental parameters (pCO2 and SST). These two parameters were also found to be more sensitive to pCO2 than SST. Conversely, shell density never showed any change during the 3-100 ka period, suggesting that it remained constant. Consequently, variations in SNW are likely to reflect changes in shell quantity, with not much effect by shell quality (i.e. density). Furthermore, the results suggest that it is possible to use shell volume as an environmental proxy along with the previously used SNW. By contrast, shell density was maintained at a relatively constant level, thus requiring further investigation to elucidate the environmental parameters that influence shell density during foraminifers shell formation (or confirm its complete constancy).