A reconstruction of Lower Danube-Black Sea climate history. First insights from novel loess-paleosol sequences.

Loess–paleosol sequences (LPS) constitute continuous terrestrial archives of Quaternary climate change, recording both local environmental conditions and large-scale atmospheric dynamics. While LPS have been extensively studied worldwide, those of the Lower Danube–Black Sea (LDBS) region of Romania and Bulgaria remain comparatively underexplored. Situated at the nexus of Mediterranean, central European, and continental western Asian air masses, the LDBS region offers a unique opportunity to investigate large-scale climate shifts and their associated environmental responses.

The LOEs-CLIMBE project, funded by the Swiss National Science Foundation (SNSF) through the Multilateral Academic Projects (MAPS) scheme with support from the Romanian (UEFSCDI) and Bulgarian funding agencies, addresses this gap through a high-resolution, multi-proxy investigation of two key LPS sites: Urluia (Romania) and Kolobar (Bulgaria). Spanning the last ~800 ka, with particular focus on the Mid-Brunhes Event onwards (MBE), the project integrates elemental composition, stable isotope records, and molecular biomarkers within a newly established chronological framework. These proxies support reconstructions of vegetation dynamics, climate variability, and pedogenic processes across multiple glacial–interglacial cycles.

Here, we present preliminary results from both LPS. The site at Urluia, located in southeastern Romania, is a former quarry exposing a >20 m thick, continuous LPS. The sequence comprises multiple complex palaeosols (S1–S5), interpreted as interglacial soils, interbedded with massive loess units deposited during glacial periods.

Near the village of Kolobar, situated in northeastern Bulgaria and distal from both the Danube and the Black Sea, is an active quarry. Here, a ~25 m thick LPS is exposed with ~1.1 m of modern soil on top. Approximately seven major palaeosols (S1–S7) extend back to ~800 ka. Field observations identify a marked stratigraphic shift at S4, from thick loess units with thin palaeosols above to massive palaeosols with thinner loess below. This transition coincides with an increase in bulk density from ~1.41 to 1.61 g cm⁻³ and is interpreted as the onset of the MBE, a transition not represented at Urluia. Carbonate precipitation is observed in all palaeosols above the S7, while loess dolls occur in the L1 and L2. Bioturbation, including crotovinas from mammals and earthworm burrows as well as root traces, is widespread throughout the whole sequence. However, this is present at different depths in different assemblages. Altogether, these field observations argue for an apparent grass steppe vegetation with fluctuating populations of burrowing organisms throughout the last 800 ka, while hydrological and sedimentary conditions have changed considerably between periods with predominant loess sedimentation and stronger soil formation. We will present these first findings and support them with elemental and stable isotope composition alongside organic matter composition gained from infrared spectroscopy measurements.