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

Abstract

We present high-resolution records for oxygen isotopes of the planktic foraminifer Globigerinoidesruber (δ18Oruber) and bulk sediment inorganic geochemistry for Holocene-age sediments from the southeastMediterranean. Our δ18Oruberrecord appears to be dominated by Nile discharge rather than basin-scalesalinity/temperature changes. Nile discharge was enhanced in the early to middle Holocene relative to today.The timing of the long-term maximum in Nile discharge during the early Holocene corresponds to thetiming of maximum intensity of the Indian Ocean-influenced Southwest Indian summer monsoon (SIM). Thiscoincidence suggests a major influence of an Indian Ocean moisture source on Nile discharge in the early tomiddle Holocene, while, presently, the Atlantic Ocean is the main moisture source. Nile discharge was highlyvariable on multicentennial time scale during the early to middle Holocene, being strongly influenced byvariable 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. Thissupports the hypothesis that the Indian Ocean moisture source predominantly controlled Nile discharge atthat time. Solar-driven variability in Nile discharge also influenced paleoenvironmental conditions in theeastern Mediterranean. Bulk sediment Ba/Al and V/Al, used as indicators for (export) productivity and redoxconditions, respectively, varied both in response to solar forcing on multicentennial time scales. We suggestthat changes in Nile discharge on these time scales have been concordant with nutrient inputs to, andshallow ventilation of, the eastern Mediterranean.