Micro XRF elemental mapping for paleoclimate reconstruction in the Indian Ocean -to find exact timings of climate change-

Non-destructive, high-resolution measurement of sediment cores are useful to reveal sediment feature which reflect climatic or oceanographic changes. Such non-destructive measurement (e.g. XRF core scanner measurement) could be reveal sediment feature in finer scale than discrete sample measurement. Although elemental mapping is also useful to reveal 2-dimentional structure of half split core surface, elemental mapping of large materials such as archive half core sections were usually difficult.

In this study, we utilize recently released micro-XRF (M6 JETSTREAM provided by Bruker Corporation) which could measure archive half core directly and could make high-resolution element maps. The fine scale sediment feature which reflecting exact timings of drastic climate changes were revealed by micro-XRF using sediments obtained by following two Sites.

Using the Neogene sediments obtained from DSDP Site 266, located at the high-latitude of Indian ocean close to the Antarctica, the distinctive chemical markers of IRD were observed in specific sections of Site 266. IRD is primarily distinguished by its characteristic iron-rich signature, and the identified fragments measure between 4.2 and 6.4 millimeters in length along their longest axis. Traditionally, these individual particles could only be discerned through destructive analysis. The large-scale micro-XRF capabilities of the JETSTREAM now enable us to non-destructively quantify and fingerprint IRD. The drastic changes of primary producer from the calcareous plankton to the siliceous plankton was also suggested from elemental mapping results.

The sediments obtained from ODP Site 752, located on an isolated ridge in the Indian Ocean contained concretion at Paleogene age when hiatus or lower sedimentation rate was suggested by age model. We measured the concretion and the surrounding sediments together using specialized method of JETSTREAM, and revealed high-resolution elemental maps of concretion and surroundings sediments. The maps clearly shows that each element (Ca, Fe, Mn) is concentrated on different part on and around the concretion. The Ca concentration is higher at an interval above a concretion, which may suggest high calcareous productivity during the sedimentation period.

In this study, we used legacy cores (archive halves) stored at Kochi Core Center (KCC), as the member of ReCoRD program (ReC23-01). Our measurement clearly shows reanalysis of previously obtained core materials by new technics reveals new feature of sediments which is useful to reconstruct past climate changes.