Responses of an arctic landscape to Lateglacial and early Holocene climatic changes: the importance of moisture

Abstract

Many of the physical and biological processes that characterize arctic ecosystems are unique to high latitudes, and their sensitivities to climate change are poorly understood. Stratigraphic records of land-surface processes and vegetation change in the Arctic Foothills of northern Alaska reveal how tundra landscapes responded to climatic changes between 13,000 and 8000 14 C yr BP. Peat deposition began and shrub vegetation became widespread ca. 12,500 14 C yr BP, probably in response to the advent of warmer and wetter climate. Increased slope erosion caused rapid alluviation in valleys, and Populus trees spread northward along braided floodplains before 11,000 14 C yr BP. Lake levels fell and streams incised their floodplains during the Younger Dryas (YD) (11,000-10,000 14 C yr BP). A hiatus in records of Populus suggest that its geographic range contracted, and pollen records of other species suggest a cooler and drier climate during this interval. Basal peats dating to the YD are rare, suggesting that rates of paludification slowed. Immediately after 10,000 14 C yr BP, lake levels rose, streams aggraded rapidly again, intense solifluction occurred, and Populus re-invaded the area. Moist acidic tundra vegetation was widespread by 8500 14 C yr BP along with wet, organic-rich soils. Most of these landscape-scale effects of climatic change involved changes in moisture. Although low temperature is the most conspicuous feature of arctic climate, shifts in effective moisture may be the proximate cause for many of the impacts that climate change has in arctic regions. r

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

“…This was Guthrie's (1990Guthrie's ( , 2001) basic hypothesis, and it fits with how post-glacial changes in climate affected the biophysical processes that he asserts were important in maintaining the Mammoth Steppe. We know that paludification began on the North Slope ca 16 cal ka BP (Jones and Yu, 2010) and that the present-day tundra vegetation types were in place, at least in the Arctic Foothills, by 9e10.5 cal ka BP (Mann et al, 2002). This chronology is consistent with the estimated extinction dates of horse, bison, and mammoth on the North Slope (Figs.…”

“…As sea level rose in postglacial times, maritime air masses invaded northern Alaska more frequently, transforming summer climate from sunny, dry, and warm to its present state of cloudy, damp, and relatively cold (Mann et al, 2001). Paleoenvironmental records from arctic Alaska lend support to Guthrie's ideas in the form of evidence for sweeping changes in hillslope erosion, floodplain dynamics, and vegetation e all triggered by increases in effective moisture during the PleistoceneeHolocene transition (Mann et al, 2002(Mann et al, , 2010. Mesice hydric vegetation dominated by sedges and shrubs spread across the region early in post-glacial times (Oswald et al, 1999), replacing the formerly dominant graminoids and forbs (Zazula et al, 2006, and probably lowering soil temperatures (Blok et al, 2010).…”

Lateglacial and Holocene isotopic and environmental history of northern coastal Alaska – Results from a buried ice-wedge system at Barrow

“…The YD stadial is known from pollen records of southern Alaska, but rarely found in northern Alaska (Mann et al, 2002;Kokorowski et al, 2008). In our pollen record of the Barrow site, the YD is not well pronounced.…”

“…Paleoenvironmental reconstructions for this critical transitional period are limited for northern Alaska, but may add important information to regional and global, spatial and temporal correlations. Mann et al (2002) provide stratigraphic evidence from an Alaskan Arctic Foothill site for the tundra landscape responses to climatic change for the period 13e8 kyr BP. Eisner et al (2005) document an early phase of high productive plant growth at ca 8 kyr BP from an erosional remnant on the northern Arctic Coastal Plain.…”

Life and extinction of megafauna in the ice-age Arctic

“…As sea level rose across Alaska's continental shelves and storm tracks shifted poleward, maritime air masses invaded more frequently, transforming the North Slope's summer climate from sunny, dry, and relatively warm to its present state of cloudy, damp, and relatively cool (29,30). Guthrie (14,18) identified paludification, the spread of peat and organic soil horizons across previously well-drained landscapes, as the proximate cause of the demise of the mammoth steppe (31).…”