[MIS08-P08] The paleo ocean temperature recorded in carbonate clumped isotope of early Pleistocene fish otolith fossils from the Dainichi Formation of the Kakegawa Group, Shizuoka
Keywords:Pleistocene, Fish otolith, Paleo ocean temperature, Carbonate clumped isotope
The Dainichi Formation of Kakegawa Group distributed in southwestern Shizuoka Prefecture is shallow sea sediment of early Pleistocene (~2 Ma) and contains various marine fish otoliths. Otolith is calcium carbonate structure in the inner ear of vertebrates and used as balance indicator. Otolith of teleost fish especially grows large and many of them weigh over ~10 milligrams. They often keep firm structure in stratums. We analyzed the bulk and clumped isotopes of fossil and modern otoliths of several species including Sillago sp. Nibea sp. Apogonichthys sp. in order to examine their potential for the ancient temperature archive.
The carbonate clumped isotopes thermometry is a technique to reconstruct the temperature of mineral precipitation without the isotopic information of the parent water. The abundance anomaly of 47CO2 (Δ47) generated by acid digestion of calcite is an index of temperature (Ghosh et al. 2006). There are few studies about otolith Δ47 value although its rigid microstructure is tolerant against diagenetic alternation. The temperature calibration of fish otolith Δ47 value by Ghosh et al. (2007) is marginally different from the original calibration of Ghosh et al. (2006). The small discrepancy might reflect a vital effect, or systematic error in temperature estimation of fish growth (Eiler, 2011). We used temperature calibration depending on synthetic calcites developed by Kato et al. (2019).
The Δ47 values were 0.709–0.723‰ (13.0–17.4°C) for fossil Sillago, 0.717–0.719‰ (14.0–14.7°C) for fossil Nibea and 0.724‰ (12.4°C) for fossil Apogonichthys with typical measurement error of ± 0.01‰. While the modern otoliths yield Δ47 temperatures well reproducing the modern ocean temperature. The result of paleo temperature reconstruction is ~5°C colder than Δ47 temperatures from modern otoliths. The paleo water δ18O value reconstructed from fossil otolith δ18O corrected by Δ47 temperature was −1–−2‰VSMOW. This value is significantly lower than present ocean δ18O and may indicate strong influence of fresh water in the depositional setting of the lower Pleistocene Dainichi Formation.
References;
Eiler (2011) Quat. Sci. Rev. 30, 3575–3588.
Ghosh et al. (2006) Geochim. Cosmochim. Acta 70, 1439–1456.
Ghosh et al. (2007) Geochim. Cosmochim. Acta 71, 2736–2744.
Kato et al. (2019) Geochim. Cosmochim. Acta 244, 548–564.
The carbonate clumped isotopes thermometry is a technique to reconstruct the temperature of mineral precipitation without the isotopic information of the parent water. The abundance anomaly of 47CO2 (Δ47) generated by acid digestion of calcite is an index of temperature (Ghosh et al. 2006). There are few studies about otolith Δ47 value although its rigid microstructure is tolerant against diagenetic alternation. The temperature calibration of fish otolith Δ47 value by Ghosh et al. (2007) is marginally different from the original calibration of Ghosh et al. (2006). The small discrepancy might reflect a vital effect, or systematic error in temperature estimation of fish growth (Eiler, 2011). We used temperature calibration depending on synthetic calcites developed by Kato et al. (2019).
The Δ47 values were 0.709–0.723‰ (13.0–17.4°C) for fossil Sillago, 0.717–0.719‰ (14.0–14.7°C) for fossil Nibea and 0.724‰ (12.4°C) for fossil Apogonichthys with typical measurement error of ± 0.01‰. While the modern otoliths yield Δ47 temperatures well reproducing the modern ocean temperature. The result of paleo temperature reconstruction is ~5°C colder than Δ47 temperatures from modern otoliths. The paleo water δ18O value reconstructed from fossil otolith δ18O corrected by Δ47 temperature was −1–−2‰VSMOW. This value is significantly lower than present ocean δ18O and may indicate strong influence of fresh water in the depositional setting of the lower Pleistocene Dainichi Formation.
References;
Eiler (2011) Quat. Sci. Rev. 30, 3575–3588.
Ghosh et al. (2006) Geochim. Cosmochim. Acta 70, 1439–1456.
Ghosh et al. (2007) Geochim. Cosmochim. Acta 71, 2736–2744.
Kato et al. (2019) Geochim. Cosmochim. Acta 244, 548–564.