Changes in Holocene sediment deposition in the Aegean Sea: climatic versus early anthropogenic forcing

Since the Lateglacial, the Eastern Mediterranean region has been subject to repeated climatic and environmental change. It is also home to some of the earliest cultural centres in human history. These cultures have closely interacted with their environment, but it is still unclear to what extent climatic change has influenced their evolution. At the same time, the onset and extent of early anthropogenic impact on terrestrial and notably in marine ecosystems is still poorly constrained. In order to decipher the impact of early societies on sediment deposition in the Aegean Sea versus climatically driven changes in sedimentation, we have analyzed five sediment cores from coastal settings in the Aegean Sea retrieved during METEOR expeditions M144 (in 2017/18) and M195 (2023), as well as Eurofleets+ cruise ‘MYRTOON’ (2021). Spanning the entire Holocene and partially even dating back to ~13 ka, these cores exhibit extraordinarily high sedimentation rates. We have carried out grain-size analysis at decadal resolution to obtain insight into the different processes underlying sediment transport and deposition (e.g., fluvial versus aeolian, naturally versus anthropogenically induced).

For all cores, the application of end-member modelling shows clusters of grain-size distributions of c. 2 µm and 21 µm with distinct variability over time linked to changes in fluvial  and dust input. The finer grain-size end-member is interpreted to represent fluvial input, with the coarser material having been deposited proximally near the river mouths and the finer fraction remaining in suspension and being transported over longer distances into more distal settings. We find finer sediments during the deposition of sapropel S1 at ~10–6 ka BP, suggesting higher fluvial input into the Aegean Sea during that time. In contrast, a stronger prevalence of coarser-grained sediments from ~6 ka BP onwards suggest a decrease in fluvial input at that time. Notably, intervals with finer sediments appear during the past ~4 ka at sites located closer to the coast, whereas such intervals do not occur at sites from more distal settings. This suggests that the proximal sites are sensitive recorders of early anthropogenic forcing during the Late Holocene, as a result of erosion due to deforestation. These sedimentological results are currently augmented by ongoing x-ray fluorescence (XRF) core scanning and x-ray diffraction (XRD) analyses that will provide element geochemical insight into changes in detrital input connected to sediment provenance.