Warm summers during the Younger Dryas cold reversal

Abstract

The Younger Dryas (YD) cold reversal interrupts the warming climate of the deglaciation with global climatic impacts. The sudden cooling is typically linked to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) in response to meltwater discharges from ice sheets. However, inconsistencies regarding the YD-response of European summer temperatures have cast doubt whether the concept provides a sufficient explanation. Here we present results from a high-resolution global climate simulation together with a new July temperature compilation based on plant indicator species and show that European summers remain warm during the YD. Our climate simulation provides robust physical evidence that atmospheric blocking of cold westerly winds over Fennoscandia is a key mechanism counteracting the cooling impact of an AMOC-slowdown during summer. Despite the persistence of short warm summers, the YD is dominated by a shift to a continental climate with extreme winter to spring cooling and short growing seasons.

Deglaciation history of Lake Ladoga (northwestern Russia) based on varved sediments

“…The simultaneous increase in EM 3 (representing coarse silt and fine sand), associated with an increase in Zr and a decrease in K, and Fe deposition, may be indicative of a particularly fast ice retreat during this stage, as suggested by Punkari (1997). A climate-model study by Schenk et al (2018) suggests that summer temperatures in Europe during the YD were comparably high as during the Allerød but also somewhat short-lived. A very small variability in the varve thicknesses in our record implies rather constant interannual summer temperatures for this period.…”

“…During the initial stage (c. 12.3 to 11.9 cal. A climate-model study by Schenk et al (2018) suggests that summer temperatures in Europe during the YD were comparably high as during the Allerød but also somewhat short-lived. Low meltwater supply was probably due to low temperatures, as suggested by regional pollen-based climate reconstructions (Subetto et al 2002;Wohlfarth et al 2004) as well as ice-core data (e.g.…”

Late Pleistocene climate of the northern Iberian Peninsula: New insights from palaeoglaciers at Fuentes Carrionas (Cantabrian Mountains)

“…Climate cooling at the YD is considered to have affected more winter than summer temperatures, which remained warm thorough the event, hence producing a high seasonality climate. Likewise, enhanced snowfall and a shorter growing season have been modelled for Western Europe during the event (Schenk et al , ), whereas westerlies would have driven a moist climate (Rodrigo‐Gámiz et al , ). These conclusions are confirmed by our precipitation and temperature anomaly results for the YD.…”

Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly

“…A common explanation for the YD involves meltwaterinduced weakening of Atlantic Meridional Overturning Circulation (AMOC) (Berger, 1990;Alley, 2000;Broecker et al, 2010;Johnson and McClure, 1976;Schenk et al, 2018). Initial support for this theory included elevated δ 18 O values in Gulf of Mexico sediment dating from the early YD (implying that meltwater was rerouted elsewhere) (Broecker et al, 1988;Flower and Kennett, 1990;Teller, 1990).…”

“…Red circles represent petrologic estimates of SO 2 release, and orange triangles represent estimated actual values, calculated from either satellite or ice core data (Shinohara, 2008). The grey bar represents the range of values for the Laacher See eruption as suggested by Textor et al (2003), Schenk et al (2018), and Bahr et al (2018), and the blue triangle in the Laacher See column represents the total estimated SO 2 emitted by the Laacher See eruption (83.6 Mt) assuming that the actual SO 2 emitted is 20.9 times the petrologic estimate, calculated here as the mean value of 17 non-basaltic explosive eruptions (the 16 listed in Shinohara (2008) plus the AD 1257 Samalas eruption; Vidal et al, 2016). amounts are well correlated (Oppenheimer, 2003;Carn et al, 2016), and therefore magnitude is often used as a surrogate for sulfur yield. However, variability of almost 3 orders of magnitude exists in the amount of sulfur released amongst equivalently sized explosive eruptions (Carn et al, 2016), and consequently eruption size is not the only predictor of total sulfur released.…”