USGS · 70260137
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William J. Neal, Alan Werner, Christopher F. Waythomas. 2023-09-06. Memorial to Norman W. Ten Brink (1943–2023). https://doi.org/10.1080/15230430.2023.2248844
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Pollen analysis of samples from a coastal exposure near Teller, southwestern Seward Peninsula, Alaska, provides a record of vegetation and climate spanning the Last Glacial Maximum (LGM) through the Holocene. The site is near the center of the former Bering Land Bridge (BLB). The oldest pollen-bearing sediment unit is a loess deposit of LGM age, with pollen assemblages that closely resemble LGM assemblages from other key sites in central Beringia spanning 16° of latitude. These fossil assemblages represent vegetation composed primarily of grasses, sedges, Artemisia , willows, and forbs and are interpreted to represent steppe–tundra, associated with dry climates and summer temperatures cooler than at present. LGM mosses did not accumulate insulating layers of peat; the summer active soil layer was deeper than at present. Permafrost with ice wedges and loess deposition were widespread. A regional transition from steppe–tundra vegetation to a dwarf shrub–sedge–moss mesic-to-wetland vegetation began in central Beringia with the onset of Bølling–Allerød (B-A) warming at 14,700 cal yr BP. Warming events of the B-A and early Holocene resulted in widespread development of thermokarst terrain on the BLB and on ice-rich terrain in Western Alaska. Mesic climates and vegetation developed on the BLB during the marine transgression and because of B-A and early Holocene warming. Early Holocene warming allowed some boreal forest species such as alders to begin colonizing Western Alaska from the interior.
Loess is the most widespread surficial deposit in the state of Alaska. Although loess of last glacial age is common in mid-continental North America, records of last glacial loess in Alaska have been elusive. Here we report a record of last glacial loess on the Seward Peninsula, along with studies of a transect of loess localities also thought to date to the last glacial period. Highly diverse hypotheses on the origin of loess on the Seward Peninsula include local volcanic rocks and mountain ranges to the north and south, as well as offshore deposits. We present particle size and mineralogical and geochemical data that indicate that the most likely sources for loess in this part of eastern Beringia are glaciogenic silt particles of the Kobuk River and Noatak River, both of which drain the Brooks Range to the northeast. Northeasterly paleowinds were therefore responsible for loess on the Seward Peninsula. Such winds probably occurred during late summer or early autumn, when river discharge was at a minimum but temperatures were still above freezing. Northeasterly winds during the last glacial period are in good agreement with a recent paleoclimate model.
Collared pikas ( Ochotona collaris ) are cold adapted alpine lagomorphs of western Canada and Alaska, USA, that are vulnerable to direct and indirect effects of climate change. However, how and to what extent such changes influence persistence for this species is not well understood, particularly at fine spatial scales. Our goal was to evaluate how microclimate and microhabitat characteristics influence occupancy of collared pikas. We quantified thermal conditions during both summer and winter to test hypotheses about potential drivers of pika persistence. We recorded den occupancy and territory characteristics, including in situ measurements of den microclimate, across three study areas with contrasting climate gradients in southcentral and interior Alaska during 2017–2022. We examined changes in pika den occurrence by estimating annual colonization and extinction rates with a Bayesian dynamic occurrence model with forage availability, rock size, and multiple den temperature metrics as the explanatory variables. Our top model indicated that daily maximum temperature during both summer and winter best predicted den persistence and larger rocks had a moderating effect on warm summer den temperatures. This information helps to advance understanding about the mechanistic links between climate and population persistence for small mammal species under a rapidly changing arctic climate.