Auch in Afrika hat die Sonne in den letzten 10.000 Jahren kräftig bei der Klimagestaltung mitgemischt. Beispiel Ägypten: Im Mai 2014 erschien im Fachblatt Paleoceanography eine Studie einer Gruppe der Universitäten Utrecht und Oldenburg um Rick Hennekam. Die Forscher untersuchten die Zeit von 11.000-6.000 Jahre vor heute anhand von Mikrofossilien und anderen klimarelevanten Parametern. Dabei fanden sie, dass die Abflussmenge des Nils während dieser Zeit stark schwankte, und zwar im Takte der Sonnenaktivität. Neben den Niederschlägen und dem Wasservolumen beeinflusste die Sonne zudem auch den Sauerstoffgehalt in systematischer Weise. Hier der Abstract:
Solar forcing of Nile discharge and sapropel S1 formation in the early to middle Holocene eastern Mediterranean
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 middle 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 middle Holocene, while, presently, the Atlantic Ocean is the main moisture source. Nile discharge was highly variable on multicentennial time scale during the early to middle 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 multicentennial time scales. We suggest that changes in Nile discharge on these time scales have been concordant with nutrient inputs to, and shallow ventilation of, the eastern Mediterranean.
Hierzu passt auch eine Arbeit von Jiménez-Espejo, die im Mai 2014 im Fachblatt Chemical Geology publiziert wurde. Anhand einer Sedimentabfolge in einem See in Südspanien rekonstruierten die Autoren den aus der Sahara herüberwehenden Staubeintrag. Dabei fanden die Wissenschaftler charakteristische Millenniumszyklen im Bereich von 2600-2200, die sie dem solaren Hallstatt-Zyklus zuordneten. Zudem trat ein 1500-1400 Jahreszyklus auf. Hier der Abstract:
Saharan aeolian input and effective humidity variations over western Europe during the Holocene from a high altitude record
Saharan dust inputs affect present day ecosystems and biogeochemical cycles at a global scale. Previous Saharan dust input reconstructions have been mainly based on marine records from the African margin, nevertheless dust reaching western-central Europe is mainly transported by high-altitude atmospheric currents and requires high altitude records for its reconstruction. The organic and inorganic geochemical study of sediments from a southern Iberia alpine lacustrine record has provided an exceptional reconstruction of Saharan dust impact and regional climatic variations during the Holocene. After the last deglaciation, results indicate that Saharan dust reached Western Europe in a stepwise fashion from 7.0 to 6.0 cal. kyr BP and increased since then until present, promoting major geochemical changes in the lacustrine system. Effective humidity reconstruction indicates wetter conditions during the early Holocene and progressive aridification during middle–late Holocene time, boosting abrupt changes in the lacustrine system. Cyclostratigraphic analyses and transport mechanisms both point to solar irradiance and aridity as major triggering factors for dust supply over Western Europe during the Holocene.
Siehe auch Besprechung des Artikels auf The Hockeschtick.
