Timing and source of excess freshwater inputs to the Eastern Mediterranean Sea at the origin of water stagnation and Sapropel S1 deposition. - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2021

Timing and source of excess freshwater inputs to the Eastern Mediterranean Sea at the origin of water stagnation and Sapropel S1 deposition.

François Beny
  • Fonction : Auteur
Laurence Vidal
Abel Guihou
  • Fonction : Auteur
Pierre Deschamps
Hartmut Schulz
  • Fonction : Auteur

Résumé

Eastern Mediterranean Sea sediments are marked by organic rich layers called sapropel. The most recent sapropel (S1) formation was principally caused by excess freshwater inputs from the Nile River and the Gibraltar Strait. However, the role of paleodrainage in North Africa and water from northern coast of the Mediterranean Sea are still debated. We analysed Nd isotopic composition of detrital fraction, d18O and d13C on G. ruber, and bulk elementary composition of core SL95 from the Gulf of Sirte to reconstruct possible activation of Libyan Wadis for the past 20 kyr cal. BP (ka). The foraminiferal stable isotopes and Ba peak confirmed the presence of S1 deposition. The detrital eNd present a marked increase from -12 to -11 around 13 ka, and a peak (eNd = -9.5) after the sapropel S1 interruption, during the S1b (8.2-6ka). The new eNd and previously published detrital records indicate an asynchronous shift of the eNd signature toward more radiogenic values at the end of the last deglaciation and the early Holocene. Close to the Nile River mouth, the eNd increased as early as around 14.5ka whereas it is observed during the S1a period (around 10.5-8.2ka) for cores close to the Aegean Sea, and during the S1b period (8.2-6ka) in the Gulf of Sirte. We interpret these shifts as the result of an increased contribution of the sources characterized by radiogenic Nd isotopic composition due to enhanced rainfalls over the regions, in addition to reduced unradiogenic Saharan dust inputs. This suggests that: (1) freshwater from the Blue Nile could have started the East Mediterranean circulation stagnation at the beginning of African Humid Period; (2) a freshwater delivery from the Aegean Sea during S1a is likely due to the enhanced autumn/winter storm track over the northern border of the Mediterranean Sea; (3) the Libyan Wadis were reactivated during the S1b with possible contribution to maintaining reduced ventilation
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Dates et versions

hal-03544783 , version 1 (26-01-2022)

Identifiants

  • HAL Id : hal-03544783 , version 1

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François Beny, Tachikawa Kazuyo, Laurence Vidal, Abel Guihou, Pierre Deschamps, et al.. Timing and source of excess freshwater inputs to the Eastern Mediterranean Sea at the origin of water stagnation and Sapropel S1 deposition.. AGU fall meeting, Dec 2021, New Orleans and Online, United States. ⟨hal-03544783⟩
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