Decadal sea surface temperature variability in the Eastern Mediterranean during the Last Interglacial

Abstract:

The Last Interglacial (LIG; ~130,000 to 116,000 years ago) is the most recent period from the past with warmer-than-present climate. Thus, climate reconstructions from the LIG provide an excellent opportunity to evaluate current and projected future climatic trends against natural climate variability from the warmer world. However, long and continuous records of LIG climate at subdecadal resolution have been elusive due to a small number of suitable geological records and limitations of conventional methodologies for estimating past climate. We circumvented these issues by applying submillimeter-resolution Mass Spectrometry Imaging of organic compounds on finely laminated sapropel sediment deposited during the LIG in the Eastern Mediterranean. The resulting time-series of alkenone-based sea surface temperature (SST) covers ~4.800 years in 1-4 year resolution. This unique regional climatic record reveals prominent decadal SST oscillations with a ~60-years cyclicity, suggesting a similar decadal mode of climate variability as in the current warm period. The rates of decadal SST change during the LIG often exceeded the range recorded in the same region during the instrumental era, indicating higher variability of the decadal LIG regional climate. However, the decadal trends were short-lived when compared to projected 21^st century warming. Looking on the LIG centennial SST trends as the potential analogous for the 21^st century climate warming, only the highest centennial SST increase observed in the LIG record is comparable in magnitude to the 21^st century SST increase projected under the medium-low-emissions RCP4.5 scenario. On the other hand, the high-emission RCP8.5 scenario projects future SST rise to outpace any of the LIG centennial SST increases in our record already within the next few decades.