No abstract

No abstract

Fire is the keystone disturbance in the Alaskan boreal forest and is highly influenced by summer weather patterns. Records from the last 53 years reveal high variability in the annual area burned in Alaska and corresponding high variability in weather occurring at multiple spatial and temporal scales. Here we use multiple linear regression (MLR) to systematically explore the relationships between weather variables and the annual area burned in Alaska. Variation in the seasonality of the atmospheric circulation-fire linkage is addressed through an evaluation of both the East Pacific teleconnection field and a Pacific Decadal Oscillation index keyed to an annual fire index. In the MLR, seven explanatory variables and an interaction term collectively explain 79% of the variability in the natural logarithm of the number of hectares burned annually by lightning-caused fires in Alaska from 1950 to 2003. Average June temperature alone explains one-third of the variability in the logarithm of annual area burned. The results of this work suggest that the Pacific Decadal Oscillation and the East Pacific teleconnection indices can be useful in determining a priori an estimate of the number of hectares that will burn in an upcoming season. This information also provides insight into the link between ocean-atmosphere interactions and the fire disturbance regime in Alaska.

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

Stratigraphic records from lake sediment cores and slope deposits on Rapa Nui document prehistoric human impacts and natural environmental changes. A hiatus in sedimentation in Rano Raraku suggests that this lake basin dried out sometime after 4090–4410 cal yr BP and refilled only decades to centuries before AD 1180–1290. Widespread ecosystem changes caused by forest clearance by Polynesian farmers began shortly after the end of this drought. Terrestrial sections show a chronology of burning and soil erosion similar to the lake cores. Although changing sediment types and shifts in the pollen rain suggest that droughts occurred earlier in the Holocene, as yet there is no evidence for droughts occurring after AD 1180–1290. The timing of the agricultural colonization of Rapa Nui now seems well established at ca. AD 1200 and it was accompanied by rapid deforestation that was probably exacerbated by the island's small size, its droughty climate, and the rarity of primeval fires. Detailed records of a large interval of Rapa Nui's ecological history remain elusive due to the drought hiatus in the Rano Raraku sediment record. We find no evidence for a "rat outbreak impact" on Rapa Nui's vegetation preceding anthropogenic forest clearance.

A glacier complex composed of confluent alpine glaciers, island ice caps, and piedmont lobes covered much of the Alaska Peninsula and Kodiak Island during the last glacial maximum (LGM). Because this glacier complex formed the southeastern border of Beringia, its dynamics may have been important in the timing and feasibility of the northwest coast route for human migration into lower-latitude North America. Radiocarbon dates from stratigraphic sections on Kodiak Island and in the Bristol Bay lowlands bracket the LGM in southwestern Alaska between 23,000 and 14,700 yr B.P. Reconstruction of ice thickness based on glacier trimlines, moraines, and calculations of basal-shear stress depict the Alaska Peninsula Glacier Complex flowing to the outer edge of the continental shelf in the Gulf of Alaska. Equilibrium-line altitudes (ELAs) were 300 to 700 m lower than today and approached sea level on the southwestern Alaska Peninsula. In northeastern areas where ELAs were higher, bedrock topography largely controlled ice flow except where ice saddles bridged straits and inlets.

Eroding permafrost coasts are likely indicators and integrators of changes in the Arctic System as they are susceptible to the combined effects of declining sea ice extent, increases in open water duration, more frequent and impactful storms, sea-level rise, and warming permafrost. However, few observation sites in the Arctic have yet to link decadal-scale erosion rates with changing environmental conditions due to temporal data gaps. This study increases the temporal fidelity of coastal permafrost bluff observations using near-annual high spatial resolution (<1 m) satellite imagery acquired between 2008-2017 for a 9 km segment of coastline at Drew Point, Beaufort Sea coast, Alaska. Our results show that mean annual erosion for the 2007-2016 decade was 17.2 m yr −1 , which is 2.5 times faster than historic rates, indicating that bluff erosion at this site is likely responding to changes in the Arctic System. In spite of a sustained increase in decadal-scale mean annual erosion rates, mean open water season erosion varied from 6.7 m yr −1 in 2010 to more than 22.0 m yr −1 in 2007, 2012, and 2016. This variability provided a range of coastal responses through which we explored the different roles of potential environmental drivers. The lack of significant correlations between mean open water season erosion and the environmental variables compiled in this study indicates that we may not be adequately capturing the environmental forcing factors, that the system is conditioned by long-term transient effects or extreme weather events rather than annual variability, or that other not yet considered factors may be responsible for the increased erosion occurring at Drew Point. Our results highlight an increase in erosion at Drew Point in the 21st century as well as the complexities associated with unraveling the factors responsible for changing coastal permafrost bluffs in the Arctic.

Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; and Gaglioti, Benjamin V., "Ice-age megafauna in Arctic Alaska: extinction, invasion, survival" (2013 a b s t r a c tRadical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6Â more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30Â greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.