A Novel Approach Using Time-Depth Distortions to Assess Multicentennial Variability in Deep-Sea Oxygen Deficiency in the Eastern Mediterranean Sea During Sapropel S5

Abstract

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.