Late Holocene multisource material input into the Aegean Sea: depositional and post-depositional processes

Abstract

The upper ~50 cm sediments in the deep-sea Aegean Sea were generally deposited through hemipelagic rain as indicated by paucity of terrigenous sand-sized particles, abundance of clay-sized materials and lack of turbiditic beds. However, quartz sand-sized grains, black debris, higher C org content and C/N ratio attest to a significant river-borne supply in the North Aegean Trough. Recurrent gravity-induced transfers from the shelf break are evidenced through various markers of coastal deposition dating back the last low-stand (Characea oogons, Elphidium crispum, Ammonia beccarii, glauconitic grains, evolved organic matter). Especially, this deposition induced significant rise of the C/N ratio of successive layers. The top of ash layers of the Minoan eruption was reached in several sample cores giving opportunity for an estimation of sedimentation rate. The rate values (7–15 cm per kyear) in the southern basin are not significantly lower than those (4–23 cm per kyear) in the northern basin in spite of a lower terrigenous supply. This is due to the abundance of cemented Mg-calcite clasts and nodules throughout the cores of the Cretan Basin and North Skiros Basin rising the carbonate content up to 60%. It is suggested that this high carbonate concentration participates in the relative preservation of the most labile components of the organic matter in a large southern part of the basin characterised by low C/N ratio (5.5–8). Around 2000–1200 year BP, thin darks layers were deposited and are not yet completely oxidised. They would attest to a very beginning stage of sapropelic sediment formation during times of stagnant bottom water probably related to the enhanced Black Sea water circulation.