16،000 سال تغییر محیط زیستی از ناحیه دریاچه Petersschrader، منطقه شمال شرقی بروکس، آلاسکا
:عنوان
Abstract: Paleoclimate reconstructions are essential to contextualize recent warming that is affecting the Arctic region faster than anywhere else on Earth. To better understand this rapidly changing landscape, I used sedimentological evidence from Lake Peters and Lake Schrader in the northeastern Brooks Range to infer changing environmental conditions over the past 16,000 years (16 ka). Across five core sites, distinct changes in the visual stratigraphy and physical sediment properties including sediment bulk density, organic-matter content, and grain-size distributions record changing environmental conditions. The oldest sediments accumulated rapidly and contain little organic matter, interpreted to represent a landscape dominated by glacial and paraglacial processes associated with the rapid upvalley retreat of glaciers. No robust evidence was found for a climate fluctuation concurrent with the Younger Dryas. A peak in organic-matter abundance between 12–10 ka is attributed to a maximum in Northern Hemisphere summer insolation and accords with other regional paleoclimate reconstructions. Following this, conditions appear to have become drier as indicated by sediments with high density and low organic content until 5 ka. Alternatively, these sediments could represent a glacial advance, but this is unlikely as regional evidence for cooler conditions is absent. From 5–2 ka, organic matter consistently increases in several cores and is attributed to increased river discharge, which carried terrestrial organic matter into the lakes, or to increased summer temperatures, which led to higher productivity, or both. After 2 ka, sediments increase in density and decrease in organic content, which suggests the growth of glaciers within the catchment. Moraine mapping and lichenometry confirm previous studies and accord with changes in lake sediments. Rhizocarpon geographicum thallus diameters on boulders located on the outermost moraine crest suggest the maximum Holocene glacial extent is associated with increased moraine frequency from elsewhere in the Brooks Range dating to 2.5–1.9 ka. New measurements from a distinct moraine crest from an additional valley show consistency within the basin and are likely associated with a regional increase in moraine frequency from 1.1–1.0 ka. Increased sedimentation rates and organic productivity in both lakes may record glacier retreat during the last century. This study provides a framework for future research and fills an important gap in paleoenvironmental records for the northeastern Brooks Range.
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