Abstract
Abstract. We quantify retreat rates for three alpine glaciers in the Sawatch Range of the southern Rocky Mountains following the Last Glacial Maximum using 10Be ages from ice-sculpted, valley-floor bedrock transects and statistical analysis via the BACON program in R. Glacier retreat in the Sawatch Range from at (100 %) or near (∼83 %) Last Glacial Maximum extents initiated between 16.0 and 15.6 ka and was complete by 14.2–13.7 ka at rates ranging between 35.6 and 6.8 m a−1. Deglaciation in the Sawatch Range commenced ∼2–3 kyr later than the onset of rising global CO2 and prior to rising temperatures observed in the North Atlantic region at the Heinrich Stadial 1–Bølling transition. However, deglaciation in the Sawatch Range approximately aligns with the timing of Great Basin pluvial lake lowering. Recent data–modeling comparison efforts highlight the influence of the large North American ice sheets on climate in the western United States, and we hypothesize that recession of the North American ice sheets may have influenced the timing and rate of deglaciation in the Sawatch Range. While we cannot definitively argue for exclusively North Atlantic forcing or North American ice sheet forcing, our data demonstrate the importance of regional forcing mechanisms for past climate records.
Highlights
Alpine glaciers worldwide underwent substantial retreat in response to climate warming during the last deglaciation (Shakun et al, 2015; Palacios et al, 2020)
Most ages in each valley are in stratigraphic order and fall within the 95 % confidence interval calculated in BACON, except for four ages (Fig. 4)
While most bedrock ages along each valley transect are in stratigraphic order, we find four ages that do not comply with stratigraphic order and fall outside the 95 % confidence interval of the retreat rates calculated from BACON
Summary
Alpine glaciers worldwide underwent substantial retreat in response to climate warming during the last deglaciation (Shakun et al, 2015; Palacios et al, 2020). To thoroughly characterize the influence of these climatic oscillations, their expression throughout the Northern Hemisphere is often investigated using records of mountain glaciation (Ivy-Ochs et al, 2006; Schaefer et al, 2006; Young et al, 2011; Shakun et al, 2015; Marcott et al, 2019; Young et al, 2019). Where deposits are carefully mapped and dated, quantitative retreat or thinning rates of glaciers can be compared to records of climatic forcings. Statistical approaches to quantify retreat and thinning rates have been previously applied to ice sheets (e.g., Johnson et al, 2014; Jones et al, 2015; Koester et al, 2017; Small et al, 2018; Lesnek et al, 2020) but only for a few mountain glaciers (e.g., Hofmann et al, 2019)
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