Centennial Resolution Palaeoceanography of the Aegean Sea

Abstract

This thesis provides detailed multi-proxy records from six sediment cores in the Aegean Sea Levantine Basin, including high-resolution (1 cm to 0.5 cm) faunal records of planktonic foraminifera; stable isotope data for oxygen and carbon based on the same samples; and inorganic geochemistry records. The study interprets changes in palaeo-circulation as the result of climatic change, acting on several different time scales. This approach combines glacial inter-glacial warming, procession driven monsoon variation and cooling events acting on the 1450 year and 2300 year cycles.

It investigates longer-term variability during the Late Glacial and Holocene, in particular that associated with the deposition of the early Holocene dysoxic/anoxic sapropel S1. Concentrating on the onset of sapropel-forming conditions we identify the start of 'seasonal' stratification and highlight a lag in δ¹⁸O response of the planktonic foraminifer N. pachyderma to Termination T1b as identified in the δ¹⁸O record of G. ruber. By use of a simple model, it is determined that this offset cannot be a function of bioturbation effects. The lag is in the order of 1 kyr and suggests that isolation of intermediate/deep-water preceded the start of sapropel formation by up to 1.5 kyr. Using this discovery, the author proposes an explanation for the major unresolved problem in sapropel studies, namely the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition. It is suggested that nutrients had been accumulating in a stagnant basin for 1 -1.5 kyr and that these accumulated resources were utilized during the deposition of S1. In addition, the study provides a first quantitative estimate of the diffusive (1/e) mixing time scale for the eastern Mediterranean in its "stratified" sapropel mode, which is of the order of 450 years.

Using four high sedimentation-rate marine cores with suppressed bioturbation effects, recovered along the northern margin of the eastern Mediterranean. It is demonstrated that the study region, central to the development of modern civilisation, was substantially affected throughout the Holocene by a distinct cycle of cooling events on the order of 2 C-degrees.

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