Early Holocene cold snaps and their expression in the moraine record of the eastern European Alps

Abstract

Abstract. Glaciers preserve climate variations in their geological and geomorphological records, which makes them prime candidates for climate reconstructions. Investigating the glacier–climate system over the past millennia is particularly relevant first because the amplitude and frequency of natural climate variability during the Holocene provides the climatic context against which modern, human-induced climate change must be assessed. Second, the transition from the last glacial to the current interglacial promises important insights into the climate system during warming, which is of particular interest with respect to ongoing climate change. Evidence of stable ice margin positions that record cooling during the past 12 kyr are preserved in two glaciated valleys of the Silvretta Massif in the eastern European Alps, the Jamtal (JAM) and the Laraintal (LAR). We mapped and dated moraines in these catchments including historical ridges using beryllium-10 surface exposure dating (10Be SED) techniques and correlate resulting moraine formation intervals with climate proxy records to evaluate the spatial and temporal scale of these cold phases. The new geochronologies indicate the formation of moraines during the early Holocene (EH), ca. 11.0 ± 0.7 ka (n = 19). Boulder ages along historical moraines (n = 6) suggest at least two glacier advances during the Little Ice Age (LIA; ca. 1250–1850 CE) around 1300 CE and in the second half of the 18th century. An earlier advance to the same position may have occurred around 500 CE. The Jamtal and Laraintal moraine chronologies provide evidence that millennial-scale EH warming was superimposed by centennial-scale cooling. The timing of EH moraine formation coincides with brief temperature drops identified in local and regional paleoproxy records, most prominently with the Preboreal Oscillation (PBO) and is consistent with moraine deposition in other catchments in the European Alps and in the Arctic region. This consistency points to cooling beyond the local scale and therefore a regional or even hemispheric climate driver. Freshwater input sourced from the Laurentide Ice Sheet (LIS), which changed circulation patterns in the North Atlantic, is a plausible explanation for EH cooling and moraine formation in the Nordic region and in Europe.

Moraines in the Austrian Alps Record Repeated Phases of Glacier Stabilization through the Late Glacial and the Early Holocene

“…The ice margin geomorphology another level below denoted as J5 (Figure 4d), differs from J6 in the absence of a distinct ridge and in the abundance of boulders of which two were selected for dating and yield ages of 11.6 ± 0.2 ka and 11.8 ± 0.2 ka. Two boulders in the main valley embedded in lateral and in terminal moraines (J3-4, Figure 3c-d) give ages of 10.4 ± 0.2 ka and 11.6 ± 0.2 ka and extend the Holocene moraine chronology published for the valley by Braumann, et al 9 .…”

“…For the period between ca. 12 and 10 ka, moraine chronologies from different places in the Alps, including data presented in this study, have shown that ice retreat and therefore warming was not linear, but was interrupted by centennial-scale cooling [8][9][10][11] . For the (pre-)Bølling period, it is still unclear whether ice retreat was steady and of such magnitude that most glaciers in the European Alps retreated to the highest cirques or disappeared altogether 7 .…”

“…The link between the deglaciation of the Laurentide ice sheet, resulting in freshwater input into the North Atlantic, and cooling in Europe has been suggested as an explanation for abrupt centennial-scale cooling in the context of the YD-Holocene transition 44,45 . Moraine formation as a result of this teleconnection during the YD-Holocene transition has recently been proposed by Young, et al 46 for the Greenland ice sheet, by Protin, et al 8 for mountain glaciers in the French Alps, and by Braumann, et al 9 for the Austrian Alps. Comparing the warming during the pre-Bølling to Bølling transition and during the YD-Holocene transition (Figure 6e), we tentatively suggest brief episodes of an AMOC weakening and subsequent cooling in Europe.…”

“…The new early Holocene terminus of Jamtal glacier marked by JAM-20-27 (Figure 3d) is located only around 900 m outboard the Holocene/LIA moraine (Figure 7c). J3-4 is interpreted as the equivalent of the right lateral early Holocene moraine set (JR3-4) that was mapped and dated in a previous study 9 , which in concert with the adjacent EH Laraintal chronology indicates moraine deposition and thus glacier stabilization ca. 11.0 ± 0.7 ka (Figures 6f, 7b, and S1).…”

“…The pre-existing geomorphological maps were updated and supplemented with information gained during several eld campaigns in the summers of 2018 to 2021, from remote sensing data 74,75 and drone imagery. Glacier reconstructions of Jamtal glacier for the Holocene including corresponding maps are presented in Braumann, et al 9 . With this study, we extend the Jamtal glacier chronology into the LG and focus on landforms that evidence glacier oscillations during that period by mapping and dating margins outboard the Holocene moraines.…”