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Solar forcing of Nile discharge and sapropel S1 formation in the early- to mid-Holocene eastern Mediterranean

April 30, 2014

We present high-resolution records for oxygen isotopes of the planktic foraminifer Globigerinoides ruber (δ18Oruber), and bulk sediment inorganic geochemistry for Holocene-age sediments from the southeast Mediterranean. Our δ18Oruber record appears to be dominated by Nile discharge rather than basin-scale salinity/temperature changes. Nile discharge was enhanced in the early- to mid-Holocene relative to today.

The timing of the long-term maximum in Nile discharge during the early-Holocene corresponds to the timing of maximum intensity of the Indian Ocean-influenced Southwest Indian summer Monsoon (SIM). This coincidence suggests a major influence of an Indian Ocean moisture source on Nile discharge in the early- to mid-Holocene, while, presently, the Atlantic Ocean is the main moisture source. Nile discharge was highly variable on multi-centennial timescale during the early- to mid-Holocene, being strongly influenced by variable solar activity. This solar-driven variability is also recorded in contemporaneous SIM records, however not observed in an Atlantic Ocean-derived West African summer monsoon record from the Holocene. This supports the hypothesis that the Indian Ocean moisture source predominantly controlled Nile discharge at that time. Solar-driven variability in Nile discharge also influenced paleoenvironmental conditions in the eastern Mediterranean. Bulk sediment Ba/Al and V/Al, used as indicators for (export) productivity and redox conditions, respectively, varied both in response to solar forcing on multi-centennial timescales. We suggest that changes in Nile discharge on these timescales have been concordant with nutrient inputs to, and shallow ventilation of, the eastern Mediterranean.

Hennekam R, Jilbert T, Schnetger B, de Lange GJ, in press: olar forcing of Nile discharge and sapropel S1 formation in the early- to mid-Holocene eastern Mediterranean, Paleoceanography, doi:10.1002/2013PA002553. Article (subscription required).

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