[B-PT03] Biomineralization and Geochemistry of Proxies

[BPT03-02] Effects on shell quality of large benthic foraminifers under different temperature conditions

★Invited Papers

*Shunichi Kinoshita¹, Azumi Kuroyanagi², Hiroshi Nishi³, Kazuhiko Fujita⁴, Atsushi Suzuki⁵, Hodaka Kawahata⁶ (1.Department of Geology and Paleontology, National Museum of Nature and Science, 2.Tohoku University Museum, The Center for Academic Resources and Archives, Tohoku University, 3.Fukui Prefectural University, 4.Department of Physics and Earth Sciences, University of the Ryukyus, 5.Geological Survey of Japan National Institute of Advanced Industrial Science and Technology (AIST), 6.Atmosphere Ocean Research Institute, the University of Tokyo)

Keywords:Large benthic foraminifer, micro CT, shell density, laboratory experiments, global warming

Large benthic foraminifera that produce calcium carbonate shells are important single celled organisms in coral reefs. Recent anthropogenic ocean warming has affected their growth, and there is concern that shell production may be negatively affected. Since it has already been reported that LBFs growth would decrease when they grow at higher or lower than optimal water temperatures, quantity of their shell should be negatively affected by ocean warming. On the other hand, it is still remained unknown the effects of growth temperature on quality of their shell (i.e., shell density). Micro focused X-ray CT (MicroCT) is one of the latest technologies used in morphological studies. Its greatest advantages are the non-destructive acquisition of internal structures and the easy quantification of three-dimensional morphology such as size and volume. In addition, improvements in the hardware and software of CT scanners have made it possible to perform high-resolution and short-duration scans, making them suitable for LBF. Thus, 3D visualization of LBF is a very significant advancement in morphometric studies. In this study, to determine how their shell density would be affected by growth temperature, we cultured two species of LBFs which calcifying systems are different (porcelaneous LBF Sorites orbiculus and hyaline LBF Calcarina gaudichaudii) under six different temperature situations (19°C−29°C). After three months culturing, their shells were scanned by MicroCT. The results of this study showed that the growth (shell volume and weight) of both species was suppressed at higher water temperatures, as previously reported, although the optimum water temperatures differed. On the other hand, the shell density of both species was almost constant, indicating that the quality of the shells was maintained under different water temperatures regardless of the differences in the type of shell formation. Thus, MicroCT provided both quantitative and qualitative insights into the water temperature response of LBFs. The current marine environment is rapidly changing not only in terms of global warming but also acidification, and deoxygenation, among many other environmental factors. In the future, it is necessary to elucidate the response to complex environmental factors.