Post-LGM evolution of the Dora Baltea glacial system and paleoclimatic implications in the Western Italian Alps Elena Serra1,2, Pierre G. Valla3,1,2, Natacha Gribenski1,2, Fabio Magrani1,2, Julien Carcaillet3, Philip Deline4

1Institute of Geological Sciences, University of Bern, Switzerland 3Institute of Earth Sciences (ISTerre), Université Grenoble Alps, Université 2Oeschger Centre for Climate Change Research, University of Bern, Switzerland Savoie , CNRS, IRD, IFSTAR, Grenoble, France Email: [email protected] 4EDYTEM Lab, Université de Savoie, CNRS, Le Bourget-du-Lac, France

[12] 5.0° E 10.0° E 15.0° E Fig. 5 2D ice surface proles obtained with Proler v.2 for six Introduction 4478 m a.s.l. Stage 1, τ = 65 kPa Glacial erratic boulder identied LGM-Lateglacial ice stages. Based on geochronological re-

Germany 48.0°N 3500 Stage 2, τ = 65 kPa Glacially polished bedrock sults, geomorphology and relative stratigraphy, DB glacial land- 46.0°N Stage 3, τ = 65 kPa Subglacial till Cou1-4, 10, 11 Fluctuations of mountain glaciers in Monte Rosa Stage 4, τ = 100 kPa Trimline -1.0 forms/deposits were sorted in six groups. 2D ice surface proles were Austria 14.4 +2.4 4634 m a.s.l. 3000 Stage 5, τ = 100 kPa Paraglacial deposit obtained by tting the ice front and surface to the glacial landforms/de- response to climate variations have Switzerland Stage 6, τ = 65 kPa Mont Blanc Trimline posits belonging to the same paleoglacial stage. been widely recognised worldwide, Cou6-9 The represented proles are the ones obtained for the main DB hydro- -0.6

4808 m a.s.l. 46.0°N [1, 2] 2500 13.5 +0.9 graphic channel (bed topography upstream of the conuence in Cour- both for modern and past times . Chapy mayeur was chosen following the Val Veny, Fig. 2A), using dierent gla- Selva Plana Paleoglacial studies have investigat- cier basal shear stress (τ) values. Ice front and surface geomorphic con- Chenez 2000 straints are shown (same legend as for Fig. 1), with their geochronologi- France Chenez ed Alpine glacier responses to cal results (summed kernel density estimates of individual ages), if avail- La Plantaz Valgrisenche BRENVA-9, 10 -0.4 able. 44.0°N -2.8 10.6 post-LGM (Last Glacial Maximum, Verbion 1500 15.4 +0.6 Valgrisenche 0 50 100km Chanton La Plantaz +0.9 [3] Altitude (m a.s.l.) 26.5-19.0 ka ) climatic uctuations. PLAosl_01, 03 Selva Plana -2.7 Courmayeur 21.6 VIL8_01-04 Saint Pierre Legend 1000 IMA hills +2.7 Saint Pierre Several post-LGM ice retreat and -5.0 -0.8 45.7°N -4.5 25.8 PLAosl_02 14.1 [4] Glacial erratic boulder 36.0 +1.6 Verbion +0.6 re-advance (stadials ) stages have Donnas +4.9 -2.8 13.1±1.1 VIL18_08 Glacially polished bedrock 16.7 +2.7 500 11.8±0.5 been identied across the Alps, relat- Glacial till Donnas POY19_01, 02 -1.4 STPosl_01, 02 -0.6 VIL18_06, 09 19.0 -1.8 9.3 Chanton Trimline +1.5 11.2 +0.7 -1.5 ed to periods of climate warming or +1.0 8.5 +0.3 Paraglacial deposit 0 cooling. However, only few studies Present day ice extent 0 40 80 120 160 200 Gran Paradiso Ivrea hills have succeeded in providing de- 4061 m a.s.l. IMA Fig. 1 Study area, with glacial and paraglacial Distance from IMA (km) Ivrea landforms/deposits. In bold are the names of -7 2600 Stage 5 the investigated sites within the DB catchment, 7° E 8° E Stage 6 Stage 6 tailed post-LGM to Holocene degla- 10.6 -3.2 14.1 -0.8 circles from this study, triangles from the litera- + 0.8 11.8±0.5 + 0.6 [5, 6] -8 ciation sequences . 2500 0 10 20 km ture. IMA: Ivrea Morainic Amphitheatre. Stage 4 Top-right inset: location of the DB catchment 15.4 -2.6 +0.5 Stage 2 (red open box) within the European Alps, with -9 Stage 3 25.8 -5.0 45.3°N 7.0°E 7.5°E Plain 8.0°E the LGM ice extent[15]. 19.0 -1.4 +1.6 2400 Aim +1.5 -10

Investigate post-LGM glacial and 10 2300 6.92° E 7.00° E 7.22° E 7.23° E 7.25° E Fig. 3 (left) Be surface-exposure O (‰) 45.7° N A 18 δ

45.85° N -11 paraglacial history of the Dora Baltea and luminescence ages in Saint ELA(m a.s.l.) STP19_01: STP19_04: 15.4±0.7 ka 13.3±1.2 ka Pierre site. Samples STP19_01-06 (DB) catchment (southwestern Alps, constrain the ice front position of 2200 CHAP19_01: 3.2±0.3 ka Val FerretCou10: 14.3±0.7 ka STP19_03: 15.9±0.6 ka STP19_05: -12 45.72° N Brenva CHAP19_02: 2.6±0.2 ka Cou11: 14.2±1.1 ka 12.9±0.7 ka Stage 4. Italy; Fig. 1), in response to post-LGM glacier CHAP19_03: 1.9±0.3 ka STP19_06: 15.1±0.6 ka STP19_02: 10.3±0.5 ka AABR ELA: 2428 m a.s.l. 2100 to Holocene climatic uctuations. AAR ELA: 2428 m a.s.l. -13 Cou8: 13.1±0.6 ka Fig. 4 (below) Luminescence THAR ELA: 2405 m a.s.l. event 1 Allerød Interstadial Bølling Interstadial Younger Dryas Cou1: 16.5±0.6 ka Heinrich Cou9: 13.7±0.6 ka Saint Pierre Cou2: 14.9±0.7 ka dating from the uvioglacial sed- 4808 m a.s.l. Holocene Lateglacial LGM Cou3: 17.1±0.7 ka BRENVA-9: 0 10 20 km Cou6: 14.2±0.9 ka 803 m a.s.l. 45.3° N -14 2000 Cou4: 13.2±0.7 ka 10.8±0.6 ka Cou7: 13.4±0.6 ka STPosl_01: 10.0±1.4 ka iments of La Plantaz, interpreted 8 10 12 14 16 18 20 22 24 26 28 30 BRENVA-10: Methods 45.80° N STPosl_02: 11.5±1.0 ka as kame terrace deposit. The red Older Dryas 10.6±0.4 ka Courmayeur Age (ka) Fig. 5b 10 Miage Val Veny Grand Eyvia dashed line denes the unconform- glacier - Geochronology: Be surface-expo- Glacial erratic boulder Fig. 6 3D ice surface reconstructions and ELA estimates of ice Stage 4. Fig. 7 Dora Baltea paleoglacial stages and ELA estimates in comparison with Alpine LGM 0 0.5 1 km ity between the lodgement till at 45.70° N Glacially polished bedrock 3D ice congurations of the six identied paleoglacial stages were ob- to early Holocene climatic record (speleothems δ18O[17, 18, 19]). Chronology of the dierent ice Glacial erratic boulder Paraglacial deposit POY19_01: 9.4±0.7 the base and the uvioglacial strata sure and luminescence dating of gla- Glacially polished bedrock MIA01: 4.2±0.3 ka POY19_02: 9.2±0.6 tained through interpolation of 2D ice surfaces reconstructed along the stages is based on the dating constraints from landforms/deposits associated to specic ice 0 1.5 3 km on top. MIA02: 2.7±0.3 ka 1.5 3 DB valley and the main tributarie (Fig. 5). stage conguration (Fig. 5). Ice Stage 1 is not included, because of its pre-LGM age. For Stage 6, cial and paraglacial landforms/de- MIA03: 3.2±0.2 ka MIA04: 3.1±0.1 ka ELA values were estimated by using the THAR, AAR and AABR methods[16]. two possible chronology estimates are reported. ELA results are calculated with the AABR posits, in combination with dating 6.964° E 6.967° E 10 method. B Fig. 2 Compilation of Be sur- PLAosl_03: 21.7±2.9 ka [7, 8, 9, 10, 11] face-exposure ages in the up- PLAosl_02: 13.1±1.1 ka from the literature . 45.800° N stream DB catchment, from this Conclusion - 2D and 3D paleoglacial recon- VIL18_04: VIL18_06: 14.0±0.6 ka 8.6±0.4 ka study (circles) and from the lit- Six LGM to early Holocene paleoglacial stages were reconstructed along the DB valley, consistent with structions and equilibrium-line alti- VIL18_08: erature (triangles). A) Ages of er- VIL18_03: 11.8±0.5 ka ratic boulders and polished bed- 13.3±0.6 ka VIL18_09: post-LGM glacier uctuations identied in other Alpine sectors. tude (ELA) calculations: semi-auto- VIL18_02: 7.4±0.7 ka rocks from literature studies and 14.4±0.6 ka 45.797° N 45.797° N from the Chapy morainic ridge. PLAosl_01: A potential connection appears between DB glacier oscillations and post-LGM Alpine climatic variability. matic ArcGIS routine, similar to the VIL18_01: B) Polished bedrock knob and er- 14.2±0.6 ka 21.5±2.6 ka Two slope collapse events following DB glacier retreat were chronologically constrained. approach of the GlaRe ArcGIS tool- ratic boulders from the two mo- 0 1.5 3 m [12, 13, 14] rainic ridges of Courmayeur, con- box . 0 0.1 0.2 km straining ice front of Stages 5-6. References: 1Oerlemans (2005), 2Mackintosh et al. (2017), 3Clark et al. (2019), 4Ivy-Ochs et al. (2007), [5]Federici et al. (2016), [6]Wirsig et al. (2016a), [7]Gianotti et al. (2008), [8]Gianotti et al. (2015), [9]Le Roy (2012), [10]Deline et al. (2015), [11]Wirsig et al. (2016b), [12]Benn and Hulton (2010), [13]Pellitero et al. (2015), [14]Pellitero et al. (2016), [15]Ellers and Gibbard (2004), [16]Benn and Lehmkuhl (2000), [17]Luetscher et al. (2015), [18]Li et al. (2021), [19]Regattieri et al. (2019).