ORIGINAL RESEARCH article
Front. Mar. Sci.
Sec. Marine Biology
Volume 12 - 2025 | doi: 10.3389/fmars.2025.1655427
Chronicles in Ivory: Estimating the age of narwhals (Monodon monoceros) through stochastic modelling of seasonally varying trace elements
Provisionally accepted
Lars Nørtoft Reiter1*
Tonny Bernt Thomsen2Benjamin Dominguez Heredia2
Adeline Leclercq Samson3Daniel Kim Peel Wielandt4
Mads Peter Heide-Jørgensen5
Susanne Ditlevsen1Eva Garde5- 1Kobenhavns Universitet, Copenhagen, Denmark
- 2De Nationale Geologiske Undersogelser for Danmark og Gronland, Copenhagen, Denmark
- 3Universite Grenoble Alpes, Saint-Martin-d'Hères, France
- 4Kobenhavns Universitet Statens Naturhistoriske Museum, Copenhagen, Denmark
- 5Greenland Institute of Natural Resources, Copenhagen, Denmark
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Age estimation is an important tool for understanding the life history of animal populations, and 3 several techniques have been developed, each with its own strengths and limitations. In this 4 study, we apply a novel age-estimation method that utilizes trace element signals with seasonal 5 components obtained through laser ablation inductively coupled plasma mass spectrometry 6 (LA-ICP-MS) on tusks of 16 narwhals. We model tusk growth as a stochastic process that, by 7 hypothesis, tracks the number of elapsed annual cycles. For each tusk, we estimate this process 8 in order to derive model-based age estimates. Results are compared with those from other 9 methods, specifically manual counting (visual reading) of growth layers, radiocarbon dating and 10 using aspartic acid racemization. Our model provided age estimates ranging from 16 to 60 years 11 of age, and showed strong agreement with manual counts for 14 of 16 individuals, with two critical 12 exceptions differing by 9 and 14 years respectively. We show that this method provides objective 13 and reproducible age estimates without requiring visually distinguishable growth layers. We also 14 address modeling challenges and discuss deficiencies related to this particular tusk dataset. 15 Although demonstrated on narwhal tusks, this method is applicable to cyclic growth patterns 16 in mineralized tissues across species. Beyond age estimation, the method allows us to assign 17 temporal estimates to spatial measurements, enabling exploration of trace element history and 18 comparison with external environmental datasets.
Keywords: sclerochronology, Stable isotopes, Age Estimation, Time warping, LA-ICP-MS, stochastic process, Growth layer
Received: 27 Jun 2025; Accepted: 11 Sep 2025.
Copyright: © 2025 Reiter, Thomsen, Heredia, Leclercq Samson, Wielandt, Heide-Jørgensen, Ditlevsen and Garde. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Lars Nørtoft Reiter, Kobenhavns Universitet, Copenhagen, Denmark
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