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

   https://doi.org/10.5194/cp-17-2451-2021  

   Braumann, Sandra M. ; Schaefer, Joerg M. ; Neuhuber, Stephanie M. ; Lüthgens, Christopher ; Hidy, Alan J. ; Fiebig, Markus ( January 2021 , Climate of the Past)

   Abstract. Glaciers preserve climate variations in their geologicaland geomorphological records, which makes them prime candidates for climatereconstructions. Investigating the glacier–climate system over the pastmillennia is particularly relevant first because the amplitude andfrequency of natural climate variability during the Holocene provides theclimatic context against which modern, human-induced climate change must beassessed. Second, the transition from the last glacial to the currentinterglacial promises important insights into the climate system duringwarming, which is of particular interest with respect to ongoing climatechange. Evidence of stable ice margin positions that record cooling during the past12 kyr are preserved in two glaciated valleys of the Silvretta Massif in theeastern European Alps, the Jamtal (JAM) and the Laraintal (LAR). We mappedand dated moraines in these catchments including historical ridges usingberyllium-10 surface exposure dating (10Be SED) techniques andcorrelate resulting moraine formation intervals with climate proxy recordsto evaluate the spatial and temporal scale of these cold phases. The newgeochronologies 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 occurredaround 500 CE. The Jamtal and Laraintal moraine chronologies provide evidence thatmillennial-scale EH warming was superimposed by centennial-scale cooling.The timing of EH moraine formation coincides with brief temperature dropsidentified in local and regional paleoproxy records, most prominently withthe Preboreal Oscillation (PBO) and is consistent with moraine depositionin other catchments in the European Alps and in the Arctic region. Thisconsistency points to cooling beyond the local scale and therefore aregional or even hemispheric climate driver. Freshwater input sourced fromthe Laurentide Ice Sheet (LIS), which changed circulation patterns in theNorth Atlantic, is a plausible explanation for EH cooling and moraineformation in the Nordic region and in Europe. 

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2. Moraines in the Austrian Alps record repeated phases of glacier stabilization through the Late Glacial and the Early Holocene

   https://doi.org/10.1038/s41598-022-12477-x  

   Braumann, Sandra M. ; Schaefer, Joerg M. ; Neuhuber, Stephanie ; Fiebig, Markus ( June 2022 , Scientific Reports)

   Climate is currently warming due to anthropogenic impact on the Earth’s atmosphere. To better understand the processes and feedbacks within the climate system that underlie this accelerating warming trend, it is useful to examine past periods of abrupt climate change that were driven by natural forcings. Glaciers provide an excellent natural laboratory for reconstructing the climate of the past as they respond sensitively to climate oscillations. Therefore, we study glacier systems and their behavior during the transition from colder to warmer climate phases, focusing on the period between 15 and 10 ka. Using a combination of geomorphological mapping and beryllium-10 surface exposure dating, we reconstruct ice extents in two glaciated valleys of the Silvretta Massif in the Austrian Alps. The mountain glacier record shows that general deglaciation after the Last Glacial Maximum (LGM) was repeatedly interrupted by glacier stabilization or readvance, perhaps during the Oldest Dryas to Bølling transition (landform age: 14.4 ± 1.0 ka) and certainly during the Younger Dryas (YD; 12.9–11.7 ka) and the Early Holocene (EH; 12–10 ka). The oldest landform age indicates a lateral ice margin that postdates the ‘Gschnitz’ stadial (ca. 17–16 ka) and predates the YD. It shows that local inner-alpine glaciers were more extensive until the onset of the Bølling warm phase (ca. 14.6 ka), or possibly even into the Bølling than during the subsequent YD. The second age group, ca. 80 m below the (pre-)Bølling ice margin, indicates glacier extents during the YD cold phase and captures the spatial and temporal fine structure of glacier retreat during this period. The ice surface lowered approximately 50–60 m through the YD, which is indicative of milder climate conditions at the end of the YD compared to its beginning. Finally, the third age group falls into a period of more substantial warming, the YD–EH transition, and shows discontinuous glacier retreat during the glacial to interglacial transition. The new geochronologies synthesized with pre-existing moraine records from the Silvretta Massif evidence multiple cold phases that punctuated the general post-LGM warming trend and illustrate the sensitive response of Silvretta glaciers to abrupt climate oscillations in the past.

    

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3. Late Holocene glacier and climate fluctuations in the Mackenzie and Selwyn mountain ranges, northwestern Canada

   https://doi.org/10.5194/tc-17-4381-2023  

   Hawkins, Adam C. ; Menounos, Brian ; Goehring, Brent M. ; Osborn, Gerald ; Pelto, Ben M. ; Darvill, Christopher M. ; Schaefer, Joerg M. ( January 2023 , The Cryosphere)

   Abstract. Over the last century, northwestern Canada experienced some of the highest rates of tropospheric warming globally, which caused glaciers in the region to rapidly retreat. Our study seeks to extend the record of glacier fluctuations and assess climate drivers prior to the instrumental record in the Mackenzie and Selwyn mountains of northwestern Canada. We collected 27 10Be surface exposure ages across nine cirque and valley glacier moraines to constrain the timing of their emplacement. Cirque and valley glaciers in this region reached their greatest Holocene extents in the latter half of the Little Ice Age (1600–1850 CE). Four erratic boulders, 10–250 m distal from late Holocene moraines, yielded 10Be exposure ages of 10.9–11.6 ka, demonstrating that by ca. 11 ka, alpine glaciers were no more extensive than during the last several hundred years. Estimated temperature change obtained through reconstruction of equilibrium line altitudes shows that since ca. 1850 CE, mean annual temperatures have risen 0.2–2.3 ∘C. We use our glacier chronology and the Open Global Glacier Model (OGGM) to estimate that from 1000 CE, glaciers in this region reached a maximum total volume of 34–38 km3 between 1765 and 1855 CE and had lost nearly half their ice volume by 2019 CE. OGGM was unable to produce modeled glacier lengths that match the timing or magnitude of the maximum glacier extent indicated by the 10Be chronology. However, when applied to the entire Mackenzie and Selwyn mountain region, past millennium OGGM simulations using the Max Planck Institute Earth System Model (MPI-ESM) and the Community Climate System Model 4 (CCSM4) yield late Holocene glacier volume change temporally consistent with our moraine and remote sensing record, while the Meteorological Research Institute Earth System Model 2 (MRI-ESM2) and the Model for Interdisciplinary Research on Climate (MIROC) fail to produce modeled glacier change consistent with our glacier chronology. Finally, OGGM forced by future climate projections under varying greenhouse gas emission scenarios predicts 85 % to over 97 % glacier volume loss by the end of the 21st century. The loss of glaciers from this region will have profound impacts on local ecosystems and communities that rely on meltwater from glacierized catchments.

    

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4. 10Be age constraints on latest Pleistocene and Holocene cirque glaciation across the western United States

   https://doi.org/10.1038/s41612-019-0062-z  

   Marcott, Shaun A. ; Clark, Peter U. ; Shakun, Jeremy D. ; Brook, Edward J. ; Davis, P. Thompson ; Caffee, Marc W. ( January 2019 , npj Climate and Atmospheric Science)

   Well-dated records of alpine glacier fluctuations provide important insights into the temporal and spatial structure of climate variability. Cirque moraine records from the western United States have historically been interpreted as a resurgence of alpine glaciation in the middle-to-late Holocene (i.e., Neoglaciation), but these moraines remain poorly dated because of limited numerical age constraints at most locations. Here we present 130¹⁰Be ages on 19 moraines deposited by 14 cirque glaciers across this region that have been interpreted as recording these Neoglacial advances. Our¹⁰Be chronology indicates instead that these moraines were deposited during the latest Pleistocene to earliest Holocene, with several as old as 14–15ka. Our results thus show that glaciers retreated from their Last Glacial Maximum (LGM) extent into cirques relatively early during the last deglaciation, experienced small fluctuations during the Bølling–Allerød–Younger Dryas interval, and remained within the maximum limit of the Little Ice Age (LIA) advance of the last several centuries throughout most of the Holocene. Climate modeling suggests that increasing local summer insolation and greenhouse gases were the primary controls on early glacier retreat from their LGM positions. We then infer that subsequent intrinsic climate variability and Younger Dryas cooling caused minor fluctuations during the latest Pleistocene, while the LIA advance represents the culmination of a cooling trend through the Holocene in response to decreasing boreal summer insolation.

    

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5. Early Holocene ice retreat from Isle Royale in the Laurentian Great Lakes constrained with 10 Be exposure-age dating

   https://doi.org/10.5194/gchron-5-413-2023  

   Portenga, Eric W. ; Ullman, David J. ; Corbett, Lee B. ; Bierman, Paul R. ; Caffee, Marc W. ( January 2023 , Geochronology)

   Abstract. The timing of the Laurentide Ice Sheet's final retreat from North America's Laurentian Great Lakes is relevant to understanding regional meltwater routing, changing proglacial lake levels, and lake-bottom stratigraphy following the Last Glacial Maximum. Recessional moraines on Isle Royale, the largest island in Lake Superior, have been mapped but not directly dated. Here, we use the mean of 10 new 10Be exposure ages of glacial erratics from two recessional moraines (10.1 ± 1.1 ka, one standard deviation; excluding one anomalously young sample) to constrain the timing of Isle Royale's final deglaciation. This 10Be age is consistent with existing minimum-limiting 14C ages of basal organic sediment from two inland lakes on Isle Royale, a sediment core in Lake Superior southwest of the island, and an estimated deglaciation age of the younger of two subaqueous moraines between Isle Royale and Michigan's Keweenaw Peninsula. Relationships between Isle Royale's landform ages and Lake Superior bottom stratigraphy allow us to delineate the retreat of the Laurentide ice margin across and through Lake Superior in the early Holocene. We suggest that Laurentide ice was in contact with the southern shorelines of Lake Superior later than previously thought.

    

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