3 research outputs found
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Glacier maxima in Baffin Bay during the Medieval Warm Period coeval with Norse settlement
The climatic mechanisms driving the shift from the Medieval Warm Period (MWP) to the Little Ice Age (LIA) in the North Atlantic region are debated. We use cosmogenic beryllium-10 dating to develop a moraine chronology with century-scale resolution over the last millennium and show that alpine glaciers in Baffin Island and western Greenland were at or near their maximum LIA configurations during the proposed general timing of the MWP. Complimentary paleoclimate proxy data suggest that the western North Atlantic region remained cool, whereas the eastern North Atlantic region was comparatively warmer during the MWP—a dipole pattern compatible with a persistent positive phase of the North Atlantic Oscillation. These results demonstrate that over the last millennium, glaciers approached their eventual LIA maxima before what is considered the classic LIA in the Northern Hemisphere. Furthermore, a relatively cool western North Atlantic region during the MWP has implications for understanding Norse migration patterns during the MWP. Our results, paired with other regional climate records, point to nonclimatic factors as contributing to the Norse exodus from the western North Atlantic region
Pinedale Glacial History of the Upper Arkansas River Valley: New Moraine Chronologies, Modeling Results and Geologic Mapping
This field trip guidebook chapter outlines the glacial history of the upper Arkansas River valley, Colorado, and builds on a previous GSA field trip to the same area in 2010. The following will be presented: (1) new cosmogenic 10Be exposure ages of moraine boulders from the Pinedale and Bull Lake glaciations (Marine Isotope Stages 2 and 6, respectively) located adjacent to the Twin Lakes Reservoir, (2) numerical modeling of glaciers during the Pinedale glaciation in major tributaries draining into the upper Arkansas River, (3) discharge estimates for glacial-lake outburst floods in the upper Arkansas River valley, and (4) 10Be ages on flood boulders deposited downvalley from the moraine sequences. This research was stimulated by a new geologic map of the Granite 7.5’ quadrangle, in which the mapping of surficial deposits was revised based in part on the interpretation of newly acquired LiDAR data and field investigations. The new 10Be ages of the Pinedale terminal moraine at Twin Lakes average 21.8 ± 0.7 ka (n=14), which adds to nearby Pinedale terminal moraine ages of 23.6 ± 1.4 ka (n=5), 20.5 ± 0.2 ka (n=3) and 16.6 ± 1.0 ka, and downvalley outburst flood terraces that date to 20.9 ± 0.9 ka (n=4) and 19.0 ± 0.6 ka (n=4). This growing chronology leads to improved understanding of the controls and timing of glaciation in the western U.S., the modeling of glacial-lake outburst flooding, and the reconstruction of paleo-temperature through glacier modeling