ShellChron 0.4.0: a new tool for constructing chronologies in accretionary carbonate archives from stable oxygen isotope profiles

Abstract

Abstract. This work presents ShellChron, a new model for generating accurate internal age models for high-resolution paleoclimate archives, such as corals, mollusk shells, and speleothems. Reliable sub-annual age models form the backbone of high-resolution paleoclimate studies. In the absence of independent sub-annual growth markers in many of these archives, the most reliable method for determining the age of samples is through age modeling based on stable oxygen isotope or other seasonally controlled proxy records. ShellChron expands on previous solutions to the age model problem by fitting a combination of a growth rate and temperature sinusoid to model seasonal variability in the proxy record in a sliding window approach. This new approach creates smoother, more precise age–distance relationships for multi-annual proxy records with the added benefit of allowing assessment of the uncertainty in the modeled age. The modular script of ShellChron allows the model to be tailored to specific archives, without being limited to oxygen isotope proxy records or carbonate archives, with high flexibility in assigning the relationship between the input proxy and the seasonal cycle. The performance of ShellChron in terms of accuracy and computation time is tested on a set of virtual seasonality records and real coral, mollusk, and speleothem archives. The result shows that several key improvements in comparison to previous age model routines enhance the accuracy of ShellChron on multi-annual records while limiting its processing time. The current full working version of ShellChron enables the user to model the age of 10-year-long high-resolution (16 samples yr−1) carbonate records with monthly accuracy within 1 h of computation time on a personal computer. The model is freely accessible on the CRAN database and GitHub. Members of the community are invited to contribute by adapting the model code to suit their research topics and encouraged to cite the original work of Judd et al. (2018) alongside this work when using ShellChron in future studies.

Amplified seasonality in western Europe in a warmer world

“…For each mollusk specimen, samples were internally dated relative to the seasonal cycle using ShellChron ( 75 ), after which measurements within a specimen were grouped in four 3-monthly bins (“seasons”). Summer was defined as the consecutive 3-month period with the lowest mean Δ 47 value, calculated separately for each specimen (see section S3.2 and figs.…”

Implications of submonthly oxygen and carbon isotope variations in late Pleistocene Melanopsis shells for regional and local hydroclimate in the upper Jordan River valley

“…The ShellChron model package (de Winter, 2022) includes a script to generate a modeled δ 18 O shell record from sinusoidally varying temperature and δ 18 O water curves, which was used to validate the data generated from the modern shell assessed in this study and from modern shells in nearby locations analyzed by Zaarur et al (2016). Temperature and δ 18 O water values reported in the literature were used to generate this record (Gat, 1970; Gat and Dansgaard, 1972; Gil'ad and Bonne, 1990; Litaor et al, 2008; Gophen et al, 2016; Zaarur et al, 2016; Supplementary Text S1).…”

Making sense of variation in sclerochronological stable isotope profiles of mollusks and fish otoliths from the early Eocene southern North Sea Basin

“…The ShellChron 0.4.0 model (De Winter, 2022), based on the approach of Judd et al (2018), was used in R (R version 4.3.1, Rstudio version 2023.06.0 build 421) to transfer δ 18 Oc data to the time domain (Julian days), using a combination of growth rate and temperature sinusoid models on the isotope records while applying a sliding window approach. For this, the model makes the assumption that growth and temperature follow quasi-sinusoidal patterns (De Winter, 2022).…”

“…The ShellChron 0.4.0 model (De Winter, 2022), based on the approach of Judd et al (2018), was used in R (R version 4.3.1, Rstudio version 2023.06.0 build 421) to transfer δ 18 Oc data to the time domain (Julian days), using a combination of growth rate and temperature sinusoid models on the isotope records while applying a sliding window approach. For this, the model makes the assumption that growth and temperature follow quasi-sinusoidal patterns (De Winter, 2022). Since variability in δ 18 Ow is comparatively limited in most fully marine environments (Rohling, 2013), the δ 18 Oc record preserved in the accretionary shells of extra-tropical mollusks can offer a good approximation of seasonal temperature fluctuations so long as season of growth is taken into account (Judd et al, 2018;Ivany and Judd, 2022;De Winter, 2022).…”

“…For this, the model makes the assumption that growth and temperature follow quasi-sinusoidal patterns (De Winter, 2022). Since variability in δ 18 Ow is comparatively limited in most fully marine environments (Rohling, 2013), the δ 18 Oc record preserved in the accretionary shells of extra-tropical mollusks can offer a good approximation of seasonal temperature fluctuations so long as season of growth is taken into account (Judd et al, 2018;Ivany and Judd, 2022;De Winter, 2022).…”