Abstract
This thesis aimed to (1) improve our knowledge on existing geochemical methods for detailed reading of the marine archives, and (2) application of the geochemical toolbox to an area that because of its geographical location, its sensitivity to subtle climate-related changes, and the subsequent preservation of relevant paleo-proxies is a
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perfect area for studies of abrupt climate change: the eastern Mediterranean Sea. XRF core scanning is an often applied geochemical approach to produce paleoenvironmental records from sediments on cm-scales. In this study it is shown that during measurement a water film forms generally under the covering foil of the sediment. The water-film thickness underneath the plastic foil is highly variable, causing significant apparent variability in all elements from Al to Fe, through absorption by the water content. The unverified use of these elements in ratios can thus lead to deviations in the paleoenvironmental interpretation. It is shown how to recognize erroneous element (ratio) variability using Cl intensities, and a method is proposed for correcting XRF core-scan data using conventional analytical data of a few discrete samples. To produce even higher resolution (μm-scale) geochemical records from sediments, a laser ablation (LA) -ICP-MS line-scan method is tested by production of artificial sediments spiked with Al, V, Mo, and Ba in a range of concentrations. The data presented indicates that LA-ICP-MS line-scanning has high potential for reliable quantitative analysis of major to trace elements in (laminated) resin-embedded sediments. A standard protocol is described to produce (semi-)quantitative estimates of geochemical proxies on (tens of) μm-scales in sediments. The geochemical tools are subsequently applied to sediments in and around the Nile delta, which generally are deposited at high sedimentation rates. It is shown that Nile discharge during the early to middle Holocene was dominated by Indian Ocean moisture transport. This is indicated by a similar timing (~9.5 ka) as well as similar solar-induced multi-centennial oscillations in Nile discharge, relative to contemporaneous Indian Ocean-derived monsoon records. These solar signals in Nile discharge also influenced paleo-environmental conditions (i.e. productivity and bottom water redox conditions) during sapropel S1 formation. Moreover, the data in the study reveal that rapid sea-level rise can reduce overturning circulation in the eastern Mediterranean, which likely contributes to sapropel formation. This mechanism acts principally in addition to the primary process of excess-evaporation. Impacts of other controlling factors of Mediterranean overturning (e.g. temperature, net evaporation) are, similar to sea-level rise, expected to be higher at larger rates-of-change. Northern hemisphere cold events were therefore probably important for reduced Mediterranean overturning circulation. That is, because more rapid monsoon enhancement and temperature increase occurs immediately after these events, relative to the change that would have been imposed by insolation alone.
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