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The mineralogy and isotopic compositions of subglacially precipitated carbonate crusts (SPCCs) provide information on conditions and processes beneath former glaciers and ice sheets. Here we describe SPCCs formed on gneissic bedrock at the bed of the Laurentide Ice Sheet (LIS) during the last glacial maximum on central Baffin Island. Geochemical data indicate that the Ca in the crusts was likely derived from the subglacial chemical weathering Ca-bearing minerals in the local bedrock. C and Sr isotopic analyses reveal that the C in the calcite was derived predominantly from older plant debris. The δ18O values of the SPCCs suggest that these crusts formed in isotopic equilibrium with basal ice LIS preserved in the Barnes Ice Cap (BIC). Columnar crystal fabric and the predominance of sparite over micrite in the SPCCs are indicative of carbonate precipitation under open-system conditions. However, the mean δ18O value of the calcite crusts is ~ 10‰ higher than those of primary LIS ice preserved in the BIC, demonstrating that SPCCs record the isotopic composition of only basal ice. Palynomorph assemblages preserved within the calcite and basal BIC ice include species last endemic to the Arctic in the early Tertiary. The source of these palynomorphs remains enigmatic.
Understanding the timing of mountain glacier and paleolake expansion and retraction in the Great Basin region of the western United States has important implications for regional-scale climate change during the last Pleistocene glaciation. The relative timing of mountain glacier maxima and the well-studied Lake Bonneville highstand has been unclear, however, owing to poor chronological limits on glacial deposits. Here, this problem is addressed by applying terrestrial cosmogenic 10Be exposure dating to a classic set of terminal moraines in Little Cottonwood and American Fork Canyons in the western Wasatch Mountains. The exposure ages indicate that the main phase of deglaciation began at 15.7 ± 1.3 ka in both canyons. This update to the glacial chronology of the western Wasatch Mountains can be reconciled with previous stratigraphic observations of glacial and paleolake deposits in this area, and indicates that the start of deglaciation occurred during or at the end of the Lake Bonneville hydrologic maximum. The glacial chronology reported here is consistent with the growing body of data suggesting that mountain glaciers in the western U.S. began retreating as many as 4 ka after the start of northern hemisphere deglaciation (at ca. 19 ka).
During the last glacial maximum (LGM), the western Uinta Mountains of northeastern Utah were occupied by the Western Uinta Ice Field. Cosmogenic10Be surface-exposure ages from the terminal moraine in the North Fork Provo Valley and paired26Al and10Be ages from striated bedrock at Bald Mountain Pass set limits on the timing of the local LGM. Moraine boulder ages suggest that ice reached its maximum extent by 17.4±0.5 ka (± 2σ).10Be and26Al measurements on striated bedrock from Bald Mountain Pass, situated near the former center of the ice field, yield a mean26Al/10Be ratio of 5.7±0.8 and a mean exposure age of 14.0±0.5 ka, which places a minimum-limiting age on when the ice field melted completely. We also applied a mass/energy-balance and ice-flow model to investigate the LGM climate of the western Uinta Mountains. Results suggest that temperatures were likely 5 to 7°C cooler than present and precipitation was 2 to 3.5 times greater than modern, and the western-most glaciers in the range generally received more precipitation when expanding to their maximum extent than glaciers farther east. This scenario is consistent with the hypothesis that precipitation in the western Uintas was enhanced by pluvial Lake Bonneville during the last glaciation.
Historical records, photographs, maps and measurements were used to determine changes in the length, geometry and volume of Rabots Glaciär, Sweden, in response to a ∼1°C warming that occurred early in the 20th century. The glacier’s initial rate of retreat from its 1910 maximum was ~2.0 m a–1. After a sharp increase to ∼11.7 m a–1 between 1933 and 1946, the mean retreat rate decreased to ∼5.5 m a-1 between 1946 and 1959. Thereafter the rate of retreat increased to ∼11.0 m a-1 and has remained relatively constant to the present time. Concomitant decreases in ice volume were estimated to be 77.3 × 106m3 between 1910 and 1959, 51.1 × 106m3 between 1959 and 1980, at least 10.4 × 106m3 between 1980 and 1989, and 14.4 × 106m3 between 1989 and 2003. The total volume change over the last 93 years is estimated at ∼153.2 × 106m3 corresponding to 1.6 × 106m3a–1.. The magnitude of the ongoing changes in length and volume suggests that Rabots Glaciär has not yet completed its response to the earlier climatic warming. In contrast, several nearby glaciers, most notably Storglaciären, have completed their adjustments and established new steady-state profiles as a result of having shorter response times.
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