New paper finds solar activity an important influence on climate during the Medieval Warm Period

A paper published today in The Holocene reconstructs sea surface temperatures [SSTs] of the Southern Adriatic Sea during the Medieval Warm Period and finds "clear" evidence of solar influence on climate change. The authors find sea surface temperatures varied closely with 11 year solar cycles. According to the authors, "We observe a clear 11.4 year cyclicity in the reconstructed SST series. Furthermore, there is a good matching between SST and global ¹⁴C [temperature proxy] anomalies. This suggests that solar activity might have had an important influence on the local climate during Medieval time."

Top graph shows the "clear 11.4 yr cyclicity in the reconstructed SST series"  [pink] corresponding to the solar cycle

Paleoclimate of the Southern Adriatic Sea region during the ‘Medieval Climate Anomaly’ reflected by organic walled dinoflagellate cysts

Liang Chen1

1. Karin AF Zonneveld1,2
2. Gerard JM Versteegh2

1. ¹Fachbereich Geowissenschaften, Universität Bremen, Germany
2. ²MARUM, Universität Bremen, Germany

1. Liang Chen, Fachbereich Geowissenschaften, Universität Bremen, Postfach 330440, D-28334 Bremen, Germany. Email: lichen@uni-bremen.de

Abstract

To obtain insight into the character and forcing of southern Italian climate change during the ‘Medieval Climate Anomaly’ (c. ad 900–1200), marine sediments deposited between ad 990 and 1200 from the Gulf of Taranto have been analyzed for their dinoflagellate cyst content with a 3.5 yr resolution. The reconstructed sea surface temperature (SST) appears to be lower than today [note the paper shows temperatures only ~0.1C lower than the 20th century mean, and that the 20th century mean was  ~0.1C lower than during the Roman Warm Period]. We observe a clear 11.4 yr cyclicity in the reconstructed SST series. Furthermore, there is a good matching between SST and global ¹⁴C anomalies. This suggests that solar activity might have had an important influence on the local climate during Medieval time. Short-term fluctuations in accumulation rates of aerobic degradation resistant species that react sensitively on the trophic state of the upper waters and/or are characteristic for river plume waters indicate that the trophic state of the upper waters is closely linked to river discharge, which in turn is strongly related to precipitation in Italy. We reconstruct low river discharge/precipitations in the Adriatic area synchronous to widespread drought events in other nearby subtropical regions. We attribute this to NAO and ENSO related large-scale ocean–atmosphere circulation shifts during the Medieval period. Furthermore, we suggest that eruptions of southern Italian volcanoes might have influenced the local upper water nutrient conditions as well.

Full paper here [chapter 6]