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Reconstructing millennial- to centennial-scale climate variability for the Eemian—an interval with estimated sea surface temperatures ~0.5 °C warmer than “preindustrial”—requires records with high temporal resolution. Sapropel S5 sediments, deposited under anoxic conditions in the Eastern Mediterranean Sea, offer the rare opportunity to assess multicentennial climate variability during this time. Here we present high-resolution S5 piston core data from the Nile delta region. Specifically, we focus on Ba/Ti, Br/Ti, and Mo/Ti, as they are proxies for paleo-productivity, marine organic carbon, and sediment anoxia, respectively. A high correlation between our Ba/Ti values in core 64PE-406-E1 and well-dated Ba records of nearby cores (LC21 and ODP967) was found. We, therefore, tuned our data to these cores obtaining an initial age model. A time-frequency analyses indicated significant frequency content in the multicentennial band, although the frequency components drifted over time. Assuming spectral simplicity, we corrected for sedimentation rate changes on a multicentennial time scale. This novel approach grants a higher-resolution age model. The resulting variability in sedimentation rate is similar to records of monsoon variability, indicating a possible link between sedimentation at the core location and low-latitude monsoon variability, linked via the River Nile. Moreover, the periodicities found in the sapropel time series are similar to the frequency content of total solar irradiance and sunspot records known for the Holocene, at least at high frequencies (~50–150 years). Hence, our data suggest cyclic intrasapropel variability, at least during the deposition of sapropel S5, may be linked to solar cycles.

International audience; Over the past 13 ka, the hydrology for the southeastern Mediterranean was mainly regulated by Nile River runoff, which in turn was controlled by climate forcing. Being affected by orbital forcing, and the position of the Intertropical Convergence Zone (ITCZ), planktic foraminiferal data (assemblages, stable isotopes, and size properties) indicate three major periods. (1) From 13.0 to 11.5 ka, the upper water column was well-mixed, cold, and productive. (2) From 11.5 to 6.4 ka, hydrology and foraminifers were affected by intensified monsoonal circulation. The enhanced size of Globigerinoides ruber is interpreted as a response to environmental stress caused by low-saline waters. (3) After 6.4 ka, the southward retreat of the ITCZ caused a decrease in freshwater discharge and hence a return to ecological equilibrium. A drop in foraminifer diversity from 2.9 to 1.1 ka was related to more arid conditions, and limited supply of nutrients from the Nile River. We suggest a link to a negative North Atlantic Oscillation (NAO) marking the Roman Humid Period in the western Mediterranean, and in anti-phase with the southeastern Mediterranean aridity. Because Nile River runoff exerted major control on surface hydrology, a connection to Indian and Pacific climate systems partially controlling precipitation over the Nile catchment area is hypothesized. From 1.1 to 0.54 ka, high foraminifer diversity indicates humid conditions synchronous to the Medieval Climate Anomaly under a positive NAO state. Over the past 0.54 ka encompassing the Little Ice Age, another arid period is indicated by a drop in foraminifer diversity.

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 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.

The formation of Eastern Mediterranean organic matter rich deposits known as sapropels is the results of two mechanisms: (enhanced) marine productivity and preservation of organic material at depth. However, their relative contribution and their leads and lags with respect to each other remain elusive. Here, we address these questions by studying sediments deposited prior to, during, and after the most recent sapropel (S1, ∼10–6 calibrated ka before present, BP) with an integrated marine and terrestrial palynological approach, combined with existing and newly generated geochemical data. The studied core was retrieved from an area under strong influence of the Nile outflow and has high average sediment accumulation rates allowing a high temporal resolution (of several decades to centuries). Marine productivity, as reconstructed with total dinocyst accumulation rates (ARs) and biogenic CaCO3 content, starts to increase ∼1 ka prior to sapropel formation. A shift in the dinocyst taxa contributing to the productivity signal at sapropel onset indicates the rapid development of (seasonal) water column stratification. Pollen and spore ARs also increase prior to sapropel onset, but a few centuries after the increase in marine productivity. Hence, the first shift to a high marine productivity system before sapropel deposition may have been mostly favoured by the injection of nutrients via shoaling of the nutricline with a minor contribution of nutrients from land via river input and flooding of the shelves. Pollen assemblages indicate a gradual change across the sapropel onset from a savanna-like, through coastal marsh expansion, toward an open woodland assemblage, which is consistent with enhanced Nile influence and delta development. At sapropel onset a marked shift in pollen ARs could suggest increased preservation under anoxia. However, major shifts in pollen assemblages and signs of selective- or partial decomposition of terrestrial palynomorphs are absent. We therefore suggest that the high pollen ARs largely result from an increased influx of pollen by enhanced Nile discharge and extension of the freshwater plume. Three centuries after the sapropel onset, dinocyst ARs and CaCO3 content indicate that marine productivity starts to decrease, while sapropel deposition continued. Organic carbon content decreased only later and less dramatically. This may be explained by a shift in the dominance of the organisms contributing to marine productivity, to an enhanced preservation of organic matter, or a combination of both.