[M-IS16] Paleoclimatology and paleoceanography

[MIS16-08] Effects of environmental changes on planktic foraminiferal shells assessed by the investigation of micro-X-ray CT.

*Shunichi Kinoshita¹, Quan Wang², Azumi Kuroyanagi³, Masafumi MURAYAMA⁴, Yurika Ujiie⁵, Hodaka Kawahata² (1.Department of Geology and Paleontology National Museum of Nature and Science, 2.Atmosphere Ocean Research Institute, the University of Tokyo, 3.Tohoku University Museum, The Center for Academic Resources and Archives, Tohoku University, 4.Faculty of Agriculture and Marine Science, Kochi University, 5.Center for Advanced Marine Core Research, Kochi University)

Keywords:atmospheric pCO₂, Globigerinoides ruber, shell density, shell volume, size-normalized weight, SST

Ocean acidification is in progress, and the main reason of this environmental problem is that the ocean has taken in about half of pCO₂ originating in human activity after the pre-industrial era. Various organisms living in the sea such as corals, coccolithophorids, and foraminifers produce their shells with carbonate ions which present in the seawaters around them. There are some evidences that the carbonate saturation state affects on the planktic foraminiferal shells, and it is known that the production rate of foraminiferal shells sensitively reacts to increasing of pCO₂. The size-normalized weight of foraminiferal shells is used to estimate the surface carbonate system. However, it is unsolved that which shell parameters has been reflect to size-normalized weight. It is considered ambiguously to be attributed to shell wall thickness or shell density, or both. Therefore, it is still unclear that the relationships between foraminiferal shell parameters and environmental ones, especially three-dimensional parameters such as shell volume (which could be reflect mean shell thickness) and density.
In this study, we measured the shell size-normalized weight, shell volume, and shell density of planktic foraminifer Globigerinoides ruber (white) in the core MD98-2196 to elucidate the relationship between those shell parameters and environmental parameters (pCO₂ and SST). We used high-resolution micro-X-ray computed tomography for assessed the shell volume and shell density. The results suggested that the shell size-normalized weight and shell volume might be negatively correlated to marine environmental parameters (pCO₂ and SST). In addition, these two parameters might be more affected by pCO₂ than SST. On the other hand, since the shell density showed no changes in 3-100ka, it could be interpreted to be constant. Thus, it is suggested that future ocean acidification and warming will cause negative effects on carbonate productivity of planktic foraminiferal even though it will not affect on shell density.