Carbon and Oxygen Isotope Records from Tridacna derasa Shells: Toward Establishing a Reliable Proxy for Sea Surface Environments

Abstract

We report the carbon (δ13C) and oxygen (δ18O) isotope records of three modern Tridacna derasa shells from Ishigaki-jima, southwestern Japan. The high-resolution δ13C profiles of samples from the inner shell layer on cross-sections fall within similar narrow ranges and display no regular variations or trends, such as an ontogenetic trend or abrupt short-term drops likely to be related to reproductive activity. This suggests that the calcification site of this species is not likely affected by photosynthetic CO2 uptake or CO2 incorporation during respiration. The δ18O profiles show distinct seasonal cycles. The intraspecific variability in the δ18O values is small in parts of the shell precipitated in the adult stage, but is not negligible in the juvenile and senescent stages. The differences in the monthly and seasonally resolved δ18O values among shells are less than 0.51‰ and 0.76‰, respectively. The shell δ18O values are nearly identical or close to the δ18O values for aragonite precipitated in oxygen isotope equilibrium with ambient seawater (δ18OEA). The largest differences between the shell δ18O and δ18OEA values calculated from the monthly and seasonally resolved data correspond to an overestimate of the seawater temperature by as much as 1.7°C and 2.3°C, respectively. However, these differences are smaller in the adult stage (<0.25‰) than in the other stages. This small difference allows an accurate reconstruction of the seawater temperature with an error of <1.1°C. Consequently, we recommend that multiple shell records be obtained because of the non-negligible intraspecific variations in their δ18O values. Growth banding, composed of alternating narrow white bands and wide light-grey bands, is discernible on cross-sections of the inner shell layer. The δ18Oshell data indicate that they were formed in winter and the other seasons, respectively.

Стабильные изотопы углерода и азота в органическом матриксе раковин чужеродных моллюсков Viviparus viviparus (Linnaeus, 1758) Новосибирского водохранилища

“…Литературные сведения о возможных онтогенетических изменениях изотопного состава раковин противоречивы. Ряд исследований, выполненных на двустворчатых моллюсках, показал, что изменения δ13С в раковинах не проявляли статистически значимых различий у особей разного возраста (Aharon 1991;Elliot et al 2009;Yamanashi et al 2016). В то же время у многих как морских, так и пресноводных моллюсков было обнаружено отчетливое снижение δ13С в течение жизни (McConnaughey and Gillikin 2008;Lartaud et al 2011;Chauvaud et al 2011).…”

Unexpected isotopic variability in biogenic aragonite: A user issue or proxy problem?

“…Whether this variability arises from natural heterogeneity among samples, sampling artifacts (e.g. Yamanashi et al, 2016), or a combination of both of these sources remains an open question. To date, this "unexpected"  18 O variability, larger than that of typical analytical uncertainty, has not been fully investigated.…”

“…Sample replication is generally recommended for paleoclimate proxies as a means to reduce error associated with proxy noise in isotopic composition among individual specimens/samples (e.g., corals -Stephans, 2004, Suzuki et al, 2005, DeLong et al, 2013otoliths -Darnaude et al, 2014;speleothems -Denniston et al, 2013;trees -Loader et al, 2013;bivalves -Gillikin et al, 2005, Yamanashi et al, 2016. Less focus has been placed on the component of isotopic variability related to human error involved in isotope sampling.…”

Evidence of intense climate variation and reduced ENSO activity from δ&lt;sup&gt;18&lt;/sup&gt;O of &lt;i&gt;Tridacna&lt;/i&gt; 3700 years ago

“…Nonetheless, the SST and SSS influence on δ 18 O shell is uncertainties due to the distinct variation of temperature and salinity in different area. For example, δ 18 O shell of the Tridacna from southwestern Japan could be directly used as a proxy of SST (Yamanashi et al, 2016), while δ 18 O shell of Indonesian Tridacna were interpreted to be contributed 71.4 % by SST and 28.6 % by SSS (Arias-Ruiz et al, 2017). Thus, local calibration from modern Tridacna is important to determine the relationship of δ 18 O shell , SST and SSS.…”