Abstract
Nearly 13,000 years ago, the warming trend into the Holocene was sharply interrupted by a reversal to near glacial conditions. Climatic causes and ecological consequences of the Younger Dryas (YD) have been extensively studied, however proxy archives from the Mediterranean basin capturing this period are scarce and do not provide annual resolution. Here, we report a hydroclimatic reconstruction from stable isotopes (δ18O, δ13C) in subfossil pines from southern France. Growing before and during the transition period into the YD (12 900–12 600 cal BP), the trees provide an annually resolved, continuous sequence of atmospheric change. Isotopic signature of tree sourcewater (δ18Osw) and estimates of relative air humidity were reconstructed as a proxy for variations in air mass origin and precipitation regime. We find a distinct increase in inter-annual variability of sourcewater isotopes (δ18Osw), with three major downturn phases of increasing magnitude beginning at 12 740 cal BP. The observed variation most likely results from an amplified intensity of North Atlantic (low δ18Osw) versus Mediterranean (high δ18Osw) precipitation. This marked pattern of climate variability is not seen in records from higher latitudes and is likely a consequence of atmospheric circulation oscillations at the margin of the southward moving polar front.
Highlights
During the abrupt and intense climate change from the Allerød warm phase to the YD cold reversal in the North Hemisphere[1,2] sea-ice production and drifting enhanced[3], alpine glaciers advanced[4], storm intensity strengthened[5], and a reorganization of the atmosphere[6,7] may have occurred
Model simulations specify that this summer-dry/winter-wet regime persisted at the Last Glacial Maximum (LGM) when climate-forcing mechanisms were substantially different[17]
The region surrounding Barbiers is situated within a transitional climatic zone that is influenced by warm Mediterranean, cool Atlantic and mixing of air masses from both origins
Summary
Maren Pauly[1,2], Gerhard Helle 1,2, Cécile Miramont[3], Ulf Büntgen[4,5,6], Kerstin Treydte[5], Frederick Reinig[5], Frédéric Guibal[3], Olivier Sivan[7], Ingo Heinrich[1,11], Frank Riedel[2], Bernd Kromer[8], Daniel Balanzategui[1], Lukas Wacker[9], Adam Sookdeo9 & Achim Brauer[1,10]. Isotopic signature of tree sourcewater (δ18Osw) and estimates of relative air humidity were reconstructed as a proxy for variations in air mass origin and precipitation regime. The observed variation most likely results from an amplified intensity of North Atlantic (low δ18Osw) versus Mediterranean (high δ18Osw) precipitation This marked pattern of climate variability is not seen in records from higher latitudes and is likely a consequence of atmospheric circulation oscillations at the margin of the southward moving polar front. We present carbon and oxygen isotope chronologies from tree-ring cellulose (δ13Ccell, δ18Ocell) used to develop the first annually resolved, biochemical climate proxy for reconstructing the abrupt cooling transition to the YD in the Mediterranean, thereby extending the latitudinal transect of annually-resolved records southward from Greenland[6] and western Germany[5]. In a multi-parameter approach, tree ring-width, δ18Ocell and δ13Ccell (Fig. S3) were utilized in combination with NGRIP δ18O-derived annually resolved temperature[6] to (a) reconstruct local sourcewater δ18O (δ18O*SW, predominately reflecting oxygen isotopes of precipitation; Fig. 2b and (b) to estimate relative humidity, both based on leaf-level dual-isotope theory[26,27]
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