Sea turtles’ shells act as biological time capsules and record signs of major environmental changes in the ocean according to new research which has carbon dated the shells.

Scutes – the thick, hardened, shield-like plates that form a turtle’s shell – are made from keratin, the same material as a human’s hair. 

This material grows in successive layers and captures chemical information about a turtle’s diet, and the environments they exist in, including how the marine environment is affecting their stress levels.

While researchers have used this “biological record keeping” to understand the ecology of these turtles, they have now applied radiocarbon techniques to historically contextualise these chemical records and trace how environmental changes affect the species.  

The research was led by Bethan Linscott and Amy Wallace, in collaboration with researchers from the University of Florida, the University of Bristol, and Earth Sciences New Zealand.

To determine how quickly the layers form, they analysed shell samples from 24 stranded sea turtles, loggerheads (Caretta caretta) and green turtles (Chelonia mydas), collected along the Florida coast between 2019 and 2022. 

The team removed small circular biopsies from the scutes and sliced them into ultra-thin sections approximately 50 microns thick.

Each layer was radiocarbon dated and compared with the mid-20th-century “bomb pulse,” a spike from nuclear weapons testing that serves as an environmental tracer in the marine environment.

The researchers then used Bayesian age-depth modelling – a statistical approach commonly used in archaeology – to date sediment layers to estimate how quickly the shell tissue accumulated. The results showed that scute growth rates vary among turtles, but on average, each 50-micron layer represents about seven to nine months of growth.

By reconstructing the timelines, scientists have been able to correlate slower shell growth rates, with environmental disturbances in Florida waters – harmful algal blooms known as “red tides” and large Sargassum seaweed events.

Turtles have a long life-span, and spend a lot of their time out in the open ocean, making direct observation of their lives much more difficult.

This new research therefore offers a great insight into how environmental stress affects them, and how we can better protect them.

“These shells are effectively recording environmental stress in the ocean,” Linscott said, “It’s a bit like sea turtle forensics. We can use chemical fingerprints preserved in scutes to detect ecological shifts.”

“Our findings can help scientists better understand how marine ecosystems are changing and how species respond to those changes,” she added.

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