Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

Abstract

a b s t r a c tA terrestrial sediment sequence exposed in an eroding pingo provides insights into the late-Quaternary environmental history of the northern Seward Peninsula, Alaska. We have obtained the first radiocarbondated evidence for a mid-Wisconsin thermokarst lake, demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods. High values of Picea pollen and the presence of Larix pollen in sediments dated to 50e40 ka BP strongly suggest the presence of forest or woodland early in MIS 3; the trees grew within a vegetation matrix dominated by grass and sedge, and there is indirect evidence of grazing animals. Thus the interstadial ecosystem was different in structure and composition from the Holocene or from the preceding Last Interglacial period. An early Holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa. Multiple extralimital plant taxa suggest mean July temperatures above modern values. The local presence of spruce during the early Holocene warm interval is evident from a radiocarbon-dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line. The first direct evidence of spruce in Northwest Alaska during the early Holocene has implications for the presence of forest refugia in Central Beringia and previously assumed routes and timing of post-glacial forest expansion in Alaska.

Impacts of shore expansion and catchment characteristics on lacustrine thermokarst records in permafrost lowlands, Alaska Arctic Coastal Plain

“…Aside from other permafrost paleo-records such as ice wedges (Siberia: Meyer et al [59]; Alaska: Meyer at al. [60] and terrestrial deposits (e.g., Siberia: Wetterich et al [84]; Canada: Murton et al [68], Fritz et al [28]; Alaska: Kanevskiy et al [48], Wetterich et al [83]), thermokarst lake sediments are important paleo-archives for reconstructing environmental changes on millennial time scales. Numerous studies have focused on general paleo-limnological investigations of Late Quaternary lake sediments by using various sediment and biogeochemical proxies (Lenz et al [55]; diatoms: Biskaborn et al [8]; plant macrofossils: Gaglioti et al [31]).…”

Consideration of dispersal processes and northern refugia can improve our understanding of past plant migration rates in North America

“…A Berigian refugium for white spruce ( Picea glauca ) has been confirmed using phylogeography, pollen and macrofossils (Anderson et al ., ; Zazula et al ., ; Wetterich et al ., ; Edwards et al ., ). It is difficult to compare perceived migration rates for species which spread into their current distribution by colonizing the land from both the north side and south side of the glacial ice sheet.…”

Life and extinction of megafauna in the ice-age Arctic

“…In northwest Alaska, peat layers and elevated percentages of spruce pollen suggest that paludification accompanied the intermittent presence of forests there between 40 and 60 calendar ka B.P. (49). On Siberia's Lena River Delta, buried peat layers date to 32-52 calendar ka B.P.…”