Im November 2013 erschien in den Geophysical Research Letters die Arbeit „Mechanisms of southern Caribbean SST variability over the last two millennia“ eines US-amerikanischen Forscherteams um Jennifer Wurtzel von der US-amerikanischen Stony Brook University. Die Wissenschaftler untersuchten hierzu Sedimentkerne die vor der Küste Venezuelas gewonnen wurden. Anhand des Magnesium-Kalzium-Verhältnisses rekonstruierten Wurtzel und Kollegen die Temperaturgeschichte des Untersuchungsgebietes für die vergangenen 2000 Jahre. Dabei fanden sie für einen 800 Jahre langen Abschnitt eine gute Korrelation der klimatischen Entwicklung mit den Sonnenaktivitätsschwankungen. Interessanterweise hinkten die Klimaänderungen der solaren Kurve um etwa 40 Jahre hinterher. Die Forscher vermuten, dass die Verzögerung durch die Beteiligung träger ozeanischer Prozesse zustande kommt, da atmosphärische Veränderungen schneller ablaufen würden.
Hier die Kurzfassung der Arbeit im englischen Original:
We present a high-resolution Mg/Ca reconstruction of tropical Atlantic sea surface temperatures (SSTs) spanning the last 2000 years using seasonally representative foraminifera from the Cariaco Basin. The range of summer/fall SST over this interval is restricted to 1.5°C, while winter/spring SST varies by 4.5°C over the same time period suggesting that boreal winter variations control interannual SST variability in the tropical North Atlantic. Antiphasing between the two data sets, including a large divergence in the seasonal records circa 900 Common Era, can be explained by changes in Atlantic meridional overturning circulation and associated changes in surface/subsurface temperatures in the tropical North Atlantic as well as resultant changes in trade wind belt location and intensity. A statistically significant but nonlinear relation exists between reconstructed winter/spring temperatures and solar variability.
Die Studie ist Teil der Masterarbeit von Jennifer Wurtzel (pdf hier). Auf Seite 55 schreibt die Autorin:
However, solar variability leads the Cariaco temperature record by 25-40 years, suggesting the linkage between solar variability and tropical SSTs is driven by relatively slow marine processes rather than faster atmospheric ones. The first half of the Mg/Ca record challenges this hypothesis, as the relationship between the Cariaco record and solar variability seems to break down, but that may be attributed to the inconsistency of G. bulloides as either a surface or subsurface temperature indicator. It is also possible that the early portion of the Mg/Ca record may have been dominantly forced by something other than solar variability, with the solar correlation only becoming relevant later in the record. The data sets distinctly diverge in 1950, possibly as a result of anthropogenic influences dominating the more recent tropical SST signal or another shift in the G. bulloides proxy.
