Climatic reconstruction for the Younger Dryas/Early Holocene transition and the Little Ice Age based on paleo-extents of Argentière glacier (French Alps)

Abstract

Investigation of Holocene extents of mountain glaciers along with the related naturally-driven climate conditions helps improve our understanding of glacier sensitivity to ongoing climate change. Here, we present the first Holocene glacial chronology in the Mont-Blanc massif (Argentière glacier) in the French Alps, based on 25 in situ-produced cosmogenic 10 Be dates of moraines and glacial bedrocks. The obtained ages from mapped sequences of moraines at three locations reveal that the glacier was retreating from its Lateglacial extent and oscillating several times between ~11.7 ka and ~10.4 ka, i.e. during the Younger Dryas/Early Holocene (YD/EH) transition, before substantially retreating at ~10.4 ka. Climate conditions corresponding to the past extents of Argentière glacier during the YD/EH transition (~ 11 ka) and the Little Ice Age (LIA) were modelled with two different approaches: by determining summer temperature differences from reconstructed ELA-rises and by using a Positive Degree Day (PDD) mass-balance model coupled with a dynamic ice flow model. The ELArise reconstructions yield a possible range of summer temperatures for the YD/EH transition that were cooler by between 3.0 and 4.8°C compared to the year 2008, depending on the choice of the ELA sensitivity to summer temperature. The results from the PDD model indicate temperatures cooler by ~3.6 to 5.5°C during the YD/EH transition than during the 1979-2002 period. For the LIA, our findings highlight that the role of local precipitation changes, superimposed on the dominant temperature signal, is important in the detailed evolution of the glacier. Overall, this study highlights the challenge that remains in accurately inferring paleoclimate conditions from past glacier extents.

Postglacial erosion of bedrock surfaces and deglaciation timing: New insights from the Mont Blanc massif (western Alps)

“…4D; Table DR2). These results agree with known deglaciation scenarios for the Alps (Ivy-Ochs, 2015; Wirsig et al, 2016;Protin et al, 2019). Indeed, ice-surface lowering starting at 16.6 ± 0.6 ka at an elevation of 2550 masl coincides with TCN dating from the southern side of the Mont Blanc massif (Wirsig et al, 2016).…”

“…Using modern records, a rock surface at 1800 masl spends 8% of the year in the FCW (−3 °C to −8 °C; Matsuoka and Murton, 2008), or 14% and 21% at 2400 and 3200 masl, respectively. This trend also holds for the Younger Dryasearly Holocene transition, assuming the temperature was 4.5 °C less than today (3.6-5.5 °C, Protin et al, 2019) and that the summer-winter difference was similar to today. The observed decrease in erosion rates with elevation is also too pronounced to be explained by chemical weathering alone.…”

Paired 10Be sampling of polished bedrock and erratic boulders to improve dating of glacial landforms: an example from the Western Alps

“…Glaciers are still present at high altitude in the Mont Blanc Massif. The mapping and dating of moraines in this area indicate that deglaciation took place in several steps during the Late Glacial (Coutterand and Nicoud, 2005;Protin et al, 2019).…”

“…Several examples of this complexity have been observed for past glacial valleys in the Alps and in the Pyrenees (Fabel et al, ; Delmas et al, ; Chenet et al, ; Protin et al, ). Erratic boulders with exposure cosmogenic ages from the last glacial period lie on older polished surfaces (Delmas et al, ).…”

Glacier fluctuations during the Late Glacial and Holocene on the Ariège valley, northern slope of the Pyrenees and reconstructed climatic conditions

“…This LIA extent on the southern slopes of the Central Pyrenean cirques may correspond to the maximum glacier advance during the Holocene (Palacios et al 2017) as recently documented in the Maladeta massif (Crest et al 2017). This contrasts with several places in the Alps (Schimmelpfennig et al 2012(Schimmelpfennig et al , 2014Solomina et al 2015;Protin et al 2019) where an early Holocene period leads to observed glacier advance larger than that of the LIA.…”