9:30 AM - 9:45 AM
[HTT16-08] Combined analysis of stable oxygen isotope and trace elements in the statolith of Todarodes pacificus (Japanese flying squid) to establish new reliable geochemical tracers
Keywords:trace elements, oxygen isotope, Todarodes pacificus , MICAL3c + IsoPrime, LA-ICPMS
The stable oxygen isotope (δ18O) and the trace elements of biogenic calcium carbonates are representative geochemical tracers for reconstructing environmental conditions and biological processes. In the field of fisheries science, those geochemical tracers in the cephalopod statolith and fish otolith are employed to reconstruct the bio-environmental conditions during their growth because statolith and otolith grow by accreting calcium carbonate (aragonite: CaCO3) during their growth (e.g., Campana 1999). The oxygen isotope fractionation coefficient between water and calcium carbonate has been determined for various biogenic carbonates (e.g., Grossman and Ku 1986). Therefore, δ18O has been regarded as a reliable geochemical proxy of water temperature. Other geochemical proxies of water temperature reported in previous studies are trace element concentrations such as magnesium (Mg), strontium (Sr), and barium (Ba). Although they have been applied independently of δ18O analysis for estimating water temperature due to their analytical simplicity and high spatial resolution, it is reported that vital effects and environmental concentrations of each trace element significantly influence the trace element composition of statolith and otolith (Hussy et al. 2022). Therefore, a direct comparison between the δ18O data reflecting water temperature and the trace element concentration can be used to evaluate the availability of trace element concentrations as water temperature proxies. However, no study has reported combining trace element concentration analysis with δ18O analysis of statolith and otoliths at the same level of high spatial resolution.
At Kyoto University, the combination of the ultra-sensitive isotope ratio mass spectrometer (MICAL3c + IsoPrime) with LA-ICPMS (Raijin-α + Agilent 8900) enables the comparison of oxygen isotope and trace element compositions in biogenic carbonate with equivalent high spatial resolution. In this study, we performed high-sensitivity δ18O analysis and trace element composition (Mg, Ca, Sr, Ba) concentration analysis from the core to the margin of statolith in the same individual of Todarodes pacificus (Japanese flying squid). The samples were collected in Hokkaido in June, August, and November 2022 (near the Tsugaru Strait). We present the results of verifying whether trace element concentrations in statolith can be utilized as water temperature proxies, as well as the potential of trace elements as a new geochemical proxy for estimating migration areas of squid.
Individuals in June showed constant δ18O values from the core to the margin (δ18O = +0.3 ± 0.3‰, 1s). δ18O values of individuals in August increased from +0.4‰ at the core to +1.4‰~+1.7‰ with growth, then decreased to +0.4‰ towards the margin. For individuals in November, δ18O values exhibit the monotonic increase from the core (-1.1‰) to the margin (-0.1‰). These δ18O patterns imply that individuals collected each month experienced different water temperature histories. Trace element concentrations (Mg, Sr, Ba) showed a decreasing trend from the core to the margin regardless of the collected month. This trend of trace elements shows no correlation with the δ18O pattern, suggesting that the trace element concentrations in the statolith of T. pacificus will not be suitable as a proxy for water temperature. Focusing on trace element ratios, Sr/Mg and Ba/Mg show a weak correlation with δ18O. This is expected to reflect variations in the element partitioning depending on water temperature. The trace element ratios such as Li/Mg and Sr-U have been reported to be useful as water temperature proxies for corals (Ross et al. 2019). However, in the statolith of T. pacificus, the changes in the trace element ratio do not match the changes in the δ18O value. Therefore, we conclude that it is difficult to use Sr/Mg and Ba/Mg as quantitative temperature proxies.
On the other hand, Sr/Ba may be a geochemical proxy for discriminating the migration area. Because the isothermal region extends in the east-west direction of the ocean, it is difficult to estimate the migration region in the east-west direction by temperature records of δ18O. Sr and Ba have similar chemical behavior to Ca, and they are incorporated into Ca sites in the crystal lattice via inorganic and organic complexes during biomineralization. Therefore, the Sr/Ba of statolith would reflect the variation of Sr/Ba in each migration region in the east-west direction. By conducting further analyses, we would establish an identification index of migration regions using Sr/Ba.
At Kyoto University, the combination of the ultra-sensitive isotope ratio mass spectrometer (MICAL3c + IsoPrime) with LA-ICPMS (Raijin-α + Agilent 8900) enables the comparison of oxygen isotope and trace element compositions in biogenic carbonate with equivalent high spatial resolution. In this study, we performed high-sensitivity δ18O analysis and trace element composition (Mg, Ca, Sr, Ba) concentration analysis from the core to the margin of statolith in the same individual of Todarodes pacificus (Japanese flying squid). The samples were collected in Hokkaido in June, August, and November 2022 (near the Tsugaru Strait). We present the results of verifying whether trace element concentrations in statolith can be utilized as water temperature proxies, as well as the potential of trace elements as a new geochemical proxy for estimating migration areas of squid.
Individuals in June showed constant δ18O values from the core to the margin (δ18O = +0.3 ± 0.3‰, 1s). δ18O values of individuals in August increased from +0.4‰ at the core to +1.4‰~+1.7‰ with growth, then decreased to +0.4‰ towards the margin. For individuals in November, δ18O values exhibit the monotonic increase from the core (-1.1‰) to the margin (-0.1‰). These δ18O patterns imply that individuals collected each month experienced different water temperature histories. Trace element concentrations (Mg, Sr, Ba) showed a decreasing trend from the core to the margin regardless of the collected month. This trend of trace elements shows no correlation with the δ18O pattern, suggesting that the trace element concentrations in the statolith of T. pacificus will not be suitable as a proxy for water temperature. Focusing on trace element ratios, Sr/Mg and Ba/Mg show a weak correlation with δ18O. This is expected to reflect variations in the element partitioning depending on water temperature. The trace element ratios such as Li/Mg and Sr-U have been reported to be useful as water temperature proxies for corals (Ross et al. 2019). However, in the statolith of T. pacificus, the changes in the trace element ratio do not match the changes in the δ18O value. Therefore, we conclude that it is difficult to use Sr/Mg and Ba/Mg as quantitative temperature proxies.
On the other hand, Sr/Ba may be a geochemical proxy for discriminating the migration area. Because the isothermal region extends in the east-west direction of the ocean, it is difficult to estimate the migration region in the east-west direction by temperature records of δ18O. Sr and Ba have similar chemical behavior to Ca, and they are incorporated into Ca sites in the crystal lattice via inorganic and organic complexes during biomineralization. Therefore, the Sr/Ba of statolith would reflect the variation of Sr/Ba in each migration region in the east-west direction. By conducting further analyses, we would establish an identification index of migration regions using Sr/Ba.