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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ACCELERATE (ArChaeological and Climatic data from ELEmental ratios using Rapid Analysis of shell carbonaTE)

Teaser

Summary

ACCELERATE aimed to 1) develop a rapid and affordable technique to analyse palaeoclimatic information preserved in the elemental composition of shell carbonates; and 2) establish standardised ways of applying these techniques to large samples of marine molluscs from coastal shell-midden deposits around the world in order to reconstruct climate change and patterns of prehistoric of coastal subsistence.
This kind of research has a long history and from the very beginning struggled with high sample costs and as a result with small datasets.
We address these issues using Laser Induced Breakdown Spectroscopy (LIBS), a method which rapidly acquires elemental spectra and is able to accurately map geochemical patterns within shells.
Within ACCELERATE, we built an analytical LIBS system from old and new parts (some twenty years old) that is customised to work with mollusc shells from archaeological and geological contexts.
Through collaborations and extensive experimental testing, we acquired preliminary data from dozens of mollusc species around the world to really see how we can practically address the variety of shells that can be found. This included not just size and shape, but also mineralogical differences and differences in growth rate and structure.
Most importantly, we focused on species that are widely found in archaeological sites and that have a long history and climate studies. As such, we built a dataset around the limpet species Patella caerulea, that can be found in archaeological sites across the Mediterranean, and across time. This species has been dated to early human occupations from before the Ice Age, Roman periods, but also historical periods, which makes this species hugely interesting in terms of studying ecological changes and how human exploitation has influenced its populations throughout time.
With our newly developed method we provide the tool to study climate at less than a percent of the cost of earlier studies and also on a much wider range and with a higher statistical robustness. This is invaluable for future decisions on how to prepare for and fight against climate change, how to protect coastal resources most efficiently, and also for the understanding of our shared past.

Work performed

Within the first year we finished the setup of the customised Laser Spectroscopy system, which included the automated sampling as well as the instant spectral analysis to gain climatic data.
We applied the method to mollusc shells from around the world and published elemental maps of oysters, clams and gastropods in the Journal of Analytical Atomic Spectroscopy (Hausmann et al. 2017).

The customised systems was then applied to a well established proxy for sea surface temperature in the Red Sea, Conomurex fasciatus.
However, the mollusc failed to produce sufficiently reliable elemental data for climate reconstruction. A comparison of the stable oxygen isotope values, which reflect sea surface temperature, and the Mg/Ca and Sr/Ca ratios has been accepted for publication by Springer, in the edited volume: Geological Setting of the Red Sea, by Najeeb Rasul and Ian Stewart.

The second year aimed to find other mollusc species to carry out climate reconstructions. By expanding our collaborative network to the US, Ireland, Australia, and Taiwan, we gained access to promising mollusc species, which yield high-resolution climatic data.
The most promising results were found in limpets and oysters.
The results of these collaborations are currently being written up and we aim to publish them in high impact journals (i.e. Nature Geoscience, PNAS).

Final results

Most importantly, we improved sampling times for mollusc climate archives by a factor of >10 and conceived a way to improve it by up to 100.
This directly translates into 10â€“100 times as many samples that can be included in ecological and climatic models.
In addition, we provide a fast way of creating elemental maps instead of only line scans, and thus literally introduced a second dimension to the analysis of shell climate records.