Preprints
https://doi.org/10.5194/cp-2023-23
https://doi.org/10.5194/cp-2023-23
27 Apr 2023
 | 27 Apr 2023
Status: a revised version of this preprint was accepted for the journal CP and is expected to appear here in due course.

Evolution of winter precipitation in the Nile-River watershed since the last glacial

Vera Dorothee Meyer, Jürgen Pätzold, Gesine Mollenhauer, and Enno Schefuß

Abstract. Between 11.5 and 5 ka BP, the Sahara was vegetated owing to a wet climate during the African Humid Period (AHP). However, the climatic factors sustaining the “Green Sahara” are still a matter of debate. Particularly the role of winter precipitation is poorly understood. Using the stable hydrogen isotopic composition (δD) of high molecular weight (HMW) n-alkanoic acids in a marine sediment core from the Eastern Mediterranean (EM), we provide a continuous record for winter precipitation in the Nile-River delta spanning the past 18 ka. Pairing the data with regional δD records from HMW n-alkanes, we show that HMW n-alkanoic acids constantly derive from the delta while the HMW n-alkanes also receive significant contributions from the headwaters between ~15–1 ka BP due to enhanced fluvial runoff. This enables us to reconstruct the evolution of Mediterranean (winter) and monsoonal (summer) rainfall in the Nile River watershed in parallel. Heinrich Stadial 1 (HS1) evolved in two phases with a dry spell between ~17.5–16.0 ka BP followed by wet conditions between ~16–14.5 ka BP owing to movements of the Atlantic storm track. Winter rainfall enhanced substantially between 11–6 ka BP lagging behind the intensification of the summer monsoon by ca. 3 ka. Heavy winter rainfall resulted from a southern position of the Atlantic storm track combined with elevated sea-surface temperatures in the EM reinforcing local cyclogenesis. We show that during the “Green Sahara” monsoon precipitation and Mediterranean winter rainfall were simultaneously enhanced and infer that the winter-rainfall zone extended southwards delivering moisture to the Sahara. Our findings corroborate recent hypotheses according to which southward extended winter rains were a crucial addition to the northward displacement of the summer monsoon helping to sustain a “Green Sahara”.

Vera Dorothee Meyer, Jürgen Pätzold, Gesine Mollenhauer, and Enno Schefuß

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-23', Anonymous Referee #1, 31 May 2023
    • AC2: 'Reply on RC1', Vera Meyer, 30 Sep 2023
  • RC2: 'Comment on cp-2023-23', Anonymous Referee #2, 06 Jun 2023
    • AC3: 'Reply on RC2', Vera Meyer, 30 Sep 2023
  • EC1: 'Comment on cp-2023-23', Christo Buizert, 22 Jun 2023
    • AC1: 'Reply on EC1', Vera Meyer, 30 Sep 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2023-23', Anonymous Referee #1, 31 May 2023
    • AC2: 'Reply on RC1', Vera Meyer, 30 Sep 2023
  • RC2: 'Comment on cp-2023-23', Anonymous Referee #2, 06 Jun 2023
    • AC3: 'Reply on RC2', Vera Meyer, 30 Sep 2023
  • EC1: 'Comment on cp-2023-23', Christo Buizert, 22 Jun 2023
    • AC1: 'Reply on EC1', Vera Meyer, 30 Sep 2023
Vera Dorothee Meyer, Jürgen Pätzold, Gesine Mollenhauer, and Enno Schefuß
Vera Dorothee Meyer, Jürgen Pätzold, Gesine Mollenhauer, and Enno Schefuß

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Short summary
The climatic factors sustaining vegetation in the Sahara during the African Humid Period (AHP) are still not fully understood. Using biomarkers in a marine sediment core from the Eastern Mediterranean, we infer variations in Mediterranean (winter) and monsoonal (summer) rainfall in the Nile River watershed around the AHP. We find that winter and summer rain enhanced during the AHP suggesting that Mediterranean moisture supported the monsoon in sustaining the “Green Sahara”.