Evaluation of palaeoenvironmental changes during the last 18,000 years in the Myrtoon basin, SW Aegean Sea

Abstract

High-resolution Last Glacial Maximum to Holocene palaeoenvironmental changes corresponding to a time interval between 200 and 500 years are examined in the Myrtoon basin in the SW Aegean Sea, using the abundance variation in foraminifera and pollen in relation to accelerator mass spectrometry 14C dating and limited oxygen isotope data. Foram abundance variation shows that from 18 ka to the Late Glacial–Holocene boundary at around 10.5 to 9.5 ka the sea surface was cold. During this period two intervals of relatively high and low sea surface temperature (SST) were observed. The first high SST occurred at around 14.2 ka, whereas the second high SST was centred at around 12.8 ka and appears to correspond to the Termination 1A event. The first low SST was centred at around 13.7 ka and the second low SST occurred between 11.8 and 10.8 ka. The former event may correspond to the Heinrich 1 event and the latter to the Younger Dryas chronozone. The Holocene started with a sharp warming of sea surface water, reaching present-day levels and probably associated with a reduction in salinity. The formation of the sapropel sequence in the Myrtoon basin started at about 10 ka, about the same time as the sapropel formation in the other Aegean basins, which means that the environmental conditions became suitable for the formation of sapropels in the Aegean about 800 years earlier than in the Adriatic, Ionian and Levantine basins. Within the sapropel sequence there are two high organic carbon (Corg) content sublayers S-1 a (9–7.9 ka) and S-1 b (7.3–6.9 ka) separated by a lower Corg content sublayer, indicating variation in the oceanographic and climatic conditions prevailing in the area during the sapropel sequence formation. The depositions of S-1 a and S-1 b coincide with an increase in SST. Increased temperature and enhanced fresh water inputs from the outflowing rivers in to the Aegean Sea, which later was supplemented by the overflowing of the Black Sea, lowered the sea surface density and reduced the vertical water masses circulation resulting in reduced bottom water ventilation. The reduction of O 2 supply to the seabed in combination with increased fluxes of terrigenous and/or marine organic matter were responsible for the creation of dysoxic to anoxic conditions in the seabed, which led to the formation of sapropel S-1. The sapropel formation ended at 5.2 ka and about the same time the SST attained present-day levels. During the Last Glacial Maximum and Late Glacial periods the pollen source area was providing a suitable environment for the growth and survival of arboreal taxa. The source area was apparently ice free and was characterized by sufficient humidity and non-lethal low temperatures, probably only a few degrees colder than present day.