Speleothem-based hydroclimate proxies and Late-Quaternary paleoclimate in the Western Mediterranean

Hydroclimate variability in the Western Mediterranean is a critical issue under ongoing climate change, as its fluctuations have significant impacts on ecosystems, water resources, and human societies. The regional climate system is highly complex and is strongly influenced by atmospheric and oceanic circulation at both regional and larger spatial scales. To better understand the mechanisms governing hydroclimate variability in this region, paleoclimate records are crucial, as they provide an essential reference and long-term benchmark against which modern and future changes can be evaluated. Speleothems are valuable paleoclimate archives because they provide high-resolution records with well-constrained chronologies and have been widely applied in hydroclimate reconstructions. In the Western Mediterranean, numerous caves have been studied, with substantially more data available from Southern Europe than from Northern Africa. However, the regional hydroclimate system remains complex and is still not fully understood, highlighting the need for additional high-resolution, long-term records. Records from both regions are essential for improving our understanding of climate mechanisms and the spatial structure of the regional climate system. In the first publication of this thesis, a stalagmite record (OV12-5) from Monaco, with an average temporal resolution of 5 years for δ¹⁸O and δ¹³C, was presented, revealing multi-centennial arid events during MIS 5a. These arid events are interpreted to be associated with a northward displacement of the westerlies away from the Western Mediterranean. Possible driving mechanisms include slowdowns of the AMOC, a positive NAO-like circulation pattern, and/or solar forcing. In the second publication, speleothem formation records from Tunisia identify humid and arid periods over the past 300,000 years. Overall, humid phases predominantly occurred during interglacial periods, whereas glacial periods were generally characterized by more arid conditions. The humid intervals are attributed to a southward displacement and intensification of the mid-latitude westerlies and the Mediterranean storm track. These findings provide clear evidence for the significant role of mid-latitude westerlies in driving humid conditions in northernmost Africa over the past 300,000 years. In the final manuscript, a stalagmite record (LAM-2-1) from Tunisia reveals multiple growth interruptions, including three hiatuses and one interval of reduced deposition. The δ¹⁸O record shows pronounced wet–dry alternations during the last glacial period, highlighting the high sensitivity of hydroclimate to rapid climate variability. Combined with climate model simulations, the results indicate that hydroclimate was primarily controlled by orbital forcing and further modulated by AMOC-driven atmospheric reorganizations on multi-centennial to millennial timescales. Taken together, the speleothem records demonstrate a high sensitivity to hydroclimate changes in the Western Mediterranean and indicate that regional hydroclimate variability is strongly linked to the position and strength of the mid-latitude westerlies and the Mediterranean storm track across both Southern Europe and Northern Africa. These results highlight the importance of large-scale atmospheric circulation in controlling moisture transport and precipitation patterns in the region and emphasize the tightly coupled nature of European and Northern African hydroclimate from orbital scales to multi-centennial scales. This integrated perspective provides important constraints for understanding past climate dynamics and for improving projections of future hydroclimate change in the Western Mediterranean region.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2026

Author dc:creator

• Chung, Yun-Chuan

• geosciences

Statement dc:rights

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Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/631010

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F631010