Exploring the past: reconstructing ancient coastal environments

Uncovering 7,800 years of history in southern Spain

Our coastlines are full of hidden stories, and my doctoral research explores just that: reconstructing the paleoenvironment of San Juan de los Terreros, a saltpan in the coastal zone of Almería, Spain, covering the last 7,800 years. The Holocene witnessed significant changes in climate, sea level, and human activity (Ortiz et al., 2020, 2021, 2022; Torres et al., 2020, 2022; Gil-García et al., 2022). Understanding these changes helps archaeologists, geologists, and environmentalists to interpret past societies and their relationship with the environment.

How do we reconstruct ancient environments?

For the reconstruction of the environmental history of this area, a combination of advanced and classical methods was used:

• Sedimentology, Paleontology and Mineralogy: Using sedimentological, paleontological analysis and X-ray diffraction, we identify sediment types, biodiversity and minerals that reconstruct conditions like lagoon salinity and dryness.
• Amino Acid Racemization: By examining the transformation of amino acids in ostracod shells (Cyprideis torosa), the sediments can be accurately dated, offering a powerful complement to radiocarbon dating when organic materials are scarce. There are only three laboratories in the world performing this technique.
• Radiocarbon Dating: A classical tool, this technique helps cross-check sediment ages, especially in ancient environments.
• Biomarker Analysis: These molecular fossils indicate where the organic matter came from (plants, algae, or bacteria), allowing us to infer past climate, vegetation, and water conditions.
• Palynology: The study of fossil pollen offers a window into ancient plant communities, shedding light on shifts between mesophytic phases and periods of dryness.
• Trace Element Analysis: Detecting high concentrations of some metals (Pb, Cu, Zn) suggests early mining or metallurgical activities, highlighting how ancient populations affected the environment some millennia ago.

Main findings

From the sediment core, we reconstructed the chronological framework, dating back to 7,800 years, showing clay-rich layers with abundant gypsum, a signature of extremely dry conditions and limited water availability. Biomarker analyses allowed us to define five geochemical units, each marking subtle changes in water availability. In addition, through pollen analysis, we defined three main pollen zones, highlighting a period of mesophytic optimal conditions followed by a trend towards increasing aridity, closely aligning with the geochemical findings. Notably, around 3,660 years ago, high lead concentrations pointed towards significant human influence, likely to be linked with mining activity, a result that aligns with archaeological evidence of early metallurgy in the region (Manteca et al., 2017; Ortiz et al., 2021, 2022; Murillo-Barroso et al., 2024).

Applying these methods beyond Spain

My research also took me to France. From Jalès (the Archéorient laboratory in Ardèche), I collected stored samples from Orbetello (Italy) and Olbia (France) lagoons in order to apply these techniques to the study of these sedimentary records. These Mediterranean lagoons provide a broader perspective for comparing how natural changes and human activity have shaped coastal environments over time. By using amino acid racemization and biomarker analysis, we aim to build chronologies and reconstruct the environmental histories that will enrich both the archaeological interpretation and our understanding of past landscape dynamics.

I would like to acknowledge le programme IDEX Thalassocraties, as well as the IMU URBO and IMU-ZooNosoi programs for their support. Special thanks also go to the CCF (Carotteurs Continental Français) for their technical expertise during core extraction.

Why it matters

Reconstructing past environments helps us to understand how climate, geography, and human societies interacted during past times, a crucial step for archaeologists seeking to understand ancient settlements, and for geologists and environmental scientists to understand past changes in order to anticipate future changes. The lessons learned in San Juan de los Terreros are helping us explore new sites and unravel stories that connect different shores of the Mediterranean.

Each environment, each lagoon, each sediment layer, is a chapter in our shared story.

This work was made possible by funding from the Spanish Ministry of Science and Innovation (MCIN/ AEI/10.13039/501100011033) project PID2021-123549NB-I00. Santiago Romero was supported by a ‘Formación de Personal Investigador’ fellowship PRE2022-105248 funded by MCIN/ AEI/10.13039/501100011033 and FSE+.

The author

Santiago Alejandro Romero García is a doctoral researcher specializing in coastal paleoenvironmental reconstruction. His work focuses on Mediterranean lagoon systems, combining geochemical, biological, and sedimentological approaches to better understand past environmental changes and human–environment interactions.

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