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This paper explores paleoenvironmental and paleoecological information that may be obtained from small‐mammal assemblages recovered at central Alaska archaeological sites dated to the terminal Pleistocene and early Holocene (14,500–8,000 cal B.P.). Small‐mammal remains in these open‐air sites are primarily related to deposition by natural death causes and as such provide information on site paleoenvironments and landscape heterogeneity. Their presence within archaeological occupations likely relates to anthropogenic disturbance and features that would have favored burrow construction. The co‐occurrence of small‐mammal remains and archaeological occupations provides a chronological framework of presence in the locality for most recorded small‐mammal species. Small‐mammal remains document faunal turnover between Pleistocene and Holocene communities. The near‐contemporaneity of species that strongly differ in their ecological requirements suggest that the terminal Pleistocene and early Holocene in central Alaska was a period of dynamic change that may have been characterized by patchy vegetation distribution, rather than the climax communities seen today. In addition to the biogeographical value of small‐mammal remains the paleoenvironmental information that they provide help to characterize the ecology of early human settlers in the region and the processes behind human dispersal in Beringia and the Americas at the end of the Ice Age. [ABSTRACT FROM AUTHOR]

Recent decades of warmer climate have brought drying wetlands and falling lake levels to southern Alaska. These recent changes can be placed into a longer-term context of postglacial lake-level fluctuations that include low stands that were as much as 7 m lower than present at eight lakes on the Kenai Lowland. Closed-basin lakes on the Kenai Lowland are typically ringed with old shorelines, usually as wave-cut scarps, cut several meters above modern lake levels; the scarps formed during deglaciation at 25–19 ka in a kettle moraine topography on the western Kenai Lowland. These high-water stands were followed by millennia of low stands, when closed-basin lake levels were drawn down by 5–10 m or more. Peat cores from satellite fens near or adjoining the eight closed-basin lakes show that a regional lake level rise was underway by at least 13.4 ka. At Jigsaw Lake, a detailed study of 23 pairs of overlapping sediment cores, seismic profiling, macrofossil analysis, and 58 AMS radiocarbon dates reveal rapidly rising water levels at 9–8 ka that caused large slabs of peat to slough off and sink to the lake bottom. These slabs preserve an archive of vegetation that had accumulated on a lakeshore apron exposed during the preceding drawdown period. They also preserve evidence of a brief period of lake level rise at 4.7–4.5 ka. We examined plant succession using in situ peat sequences in nine satellite fens around Jigsaw Lake that indicated increased effective moisture between 4.6 and 2.5 ka synchronous with the lake level rise. Mid- to late-Holocene lake high stands in this area are recorded by numerous ice-shoved ramparts (ISRs) along the shores. ISRs at 15 lakes show that individual ramparts typically record several shove events, separated by hundreds or thousands of years. Most ISRs date to within the last 5200 years and it is likely that older ISRs were erased by rising lake levels during the mid- to late Holocene. This study illustrates how data on vegetation changes in hydrologically coupled satellite-fen peat records can be used to constrain the water level histories in larger adjacent lakes. We suggest that this method could be more widely utilized for paleo-lake level reconstruction. [ABSTRACT FROM AUTHOR]

Despite extensive paleoenvironmental research on the postglacial history of the Kenai Peninsula, Alaska, uncertainties remain regarding the region's deglaciation, vegetation development, and past hydroclimate. To elucidate this complex environmental history, we present new proxy datasets from Hidden and Kelly lakes, located in the eastern Kenai lowlands at the foot of the Kenai Mountains, including sedimentological properties (magnetic susceptibility, organic matter, grain size, and biogenic silica), pollen and macrofossils, diatom assemblages, and diatom oxygen isotopes. We use a simple hydrologic and isotope mass balance model to constrain interpretations of the diatom oxygen isotope data. Results reveal that glacier ice retreated from Hidden Lake's headwaters by ca. 13.1 cal ka BP, and that groundwater was an important component of Kelly Lake's hydrologic budget in the Early Holocene. As the forest developed and the climate became wetter in the Middle to Late Holocene, Kelly Lake reached or exceeded its modern level. In the last ca. 75 years, rising temperature caused rapid changes in biogenic silica content and diatom oxygen isotope values. Our findings demonstrate the utility of mass balance modeling to constrain interpretations of paleolimnologic oxygen isotope data, and that groundwater can exert a strong influence on lake water isotopes, potentially confounding interpretations of regional climate. [ABSTRACT FROM AUTHOR]

Central Alaska and Yukon represent the longest continuously inhabited region in the Americas, with a rich record of research on technology, subsistence, and decision-making spanning over 14,000 years. Still, archaeologists debate whether the changes observed in the material and paleodemographic record can be interpreted as the result of environmental influences. This paper presents a multivariate analysis of regional occupation chronology, paleodemography, site placement, and climate data to investigate how past populations were affected by climate change. This research shows that populations were larger than expected at some of the earliest periods and that significant climatic and environmental events do not correspond with significant population decreases as researchers have previously argued. Changes in land use were gradual and unidirectional, with decreases in average site slope, increases in average site size, and consistent average site elevation through time. Trends in land use and paleodemography correspond to cultural phases assigned by regional experts, though environmental shifts undoubtedly played a role in shaping land use and culture throughout the past. This research has possible implications for our understanding of important cultural moments in the region's history, such as initial and subsequent migrations throughout the Americas. • Modeling climate impacts on land use and paleodemography in central Alaska and Yukon using settlement patterning data. • Long-term trends in human population from the late Pleistocene to the late Holocene (14,000–100 calibrated years BP). • Comparison of continuous and categorical data shows gradual changes in land use, population size, and climate. • Cultural intervals align with changes in land use and settlement patterning. [ABSTRACT FROM AUTHOR]

We present evidence of land‐level change resulting from the 2016 Mw 7.6 Chiloé earthquake from tidal wetlands along the southern coastline of Isla de Chiloé, Chile, to test criteria for the detection of low‐level, <0.1 m, coseismic land‐level change. In order to record coseismic land‐level change in tidal wetland sediments, both the creation and preservation thresholds must be exceeded. High‐resolution diatom analyses of sediment blocks at two tidal marshes reveal that the 2016 earthquake exceeded the creation threshold and a statistically significant change in diatom assemblage is recorded. In contrast, the preservation threshold was not exceeded and the record of coseismic land‐level motion is not preserved at any location visited. After nine months, interseismic and coseismic changes are statistically indistinguishable. The most sensitive part of the tidal wetland is not consistent between research locations, possibly as a result of changes in sedimentation after the earthquake. We compare records of change from great earthquakes in Alaska with the record from the Chiloé earthquake to explore the detection limit. We propose that coastal palaeoseismological records are highly likely to underestimate the frequency of major (Mw 7–8) earthquakes, with important implications for recurrence intervals and assessment of future seismic hazards. [ABSTRACT FROM AUTHOR]

The middle Tanana Valley of central Alaska contains a well‐preserved record of human occupation and paleoenvironmental change since the Late Glacial period (c. 16,000 cal yr BP) and is a critical region for understanding human dispersal into the Americas. Micromorphology analysis of soils and sediments from six archaeological sites yields valuable information about soil formation processes and landscape evolution during the Late Glacial and into the Holocene. At the macroscale, site stratigraphies are very similar, and thin organic‐rich layers (locally known as "stringers") are commonly interpreted as buried soils. However, at the microscale, these layers exhibit significant differences in the degree of bioturbation, organic matter humification, and boundary abruptness, indicating that pedogenesis was not the sole process at every site. In this way, our microscale analysis addresses issues of equifinality related to site formation interpretations, a persistent problem with subarctic and high‐latitude stratigraphy. Additionally, this study reveals a certain level of landform and landscape instability within a broader trend of regional increases in pedogenesis and vegetation coverage, adding to the existing model of heterogeneity across this subarctic landscape. Here we demonstrate the utility of micromorphology to test field interpretations and improve models of Late Glacial landscape evolution in high‐latitude contexts. [ABSTRACT FROM AUTHOR]

Stratigraphic records extending to Marine Oxygen Isotope Stage (MIS) 3 (57,000–29,000 cal yr BP) or older in Beringia are extremely rare. Three stratigraphic sections in interior western Alaska show near continuous sedimentological and environmental progressions extending from at least MIS 3, if not older, through MIS 1 (14,000 cal yr BP–present). The Kolmakof, Sue Creek, and VABM (vertical angle bench mark) Kuskokwim sections along the central Kuskokwim River, once a highland landscape at the fringe of central and eastern Beringia, contain aeolian deposition and soil sequences dating beyond 50,000 14C yr BP. Thick peaty soil, shallow lacustrine, and tephra deposits represent the MIS 3 interstade (or older). Sand sheet and loess deposits, wedge cast development, and very thin soil development mark the later MIS 3 period and the transition into the MIS 2 stade (29,000–14,000 cal yr BP). Loess accumulation with thicker soil development occurred between ~16,000–13,500 cal yr BP at the MIS 2 and MIS 1 transition. After ~13,500 cal yr BP, loess accumulation waned and peat development increased throughout MIS 1. These stratigraphic sequences represent transitions between a warm and moist period during MIS 3, to a cooler and more arid period during MIS 2, then a return to warmer and moister climates in MIS 1. [ABSTRACT FROM AUTHOR]

This study presents geomorphological, paleoenvironmental, and archaeological data from the upland upper Susitna River basin in the central Alaska Range. The goal of this study is to establish the landscape history and record of human use of the study area and test regional land‐use models. The results indicate that the upper Susitna was first occupied in the early Holocene at least 2,000 years after the end of full‐glacial conditions and 1,000 years after evidence of landscape recovery. Early Holocene land‐use consisted of short‐term task‐specific camps occupied by highly mobile groups on logistical forays. Upland land use intensified in the middle and late Holocene after modern vegetation patterns were established; during this time hunter‐gatherers occupied both residential and task‐specific camps in the study area in a logistical land‐use system. These results support a shift in land use in the early Holocene to include upland landscapes and intensification of upland landscape use in the late–middle Holocene. A shift in residential base camp location in the late Holocene may be tied to changing subsistence activities. There is evidence for a hiatus in human occupation following Holocene tephra fall, but it is unclear whether this was related to tephra deposition or broader climate instability. [ABSTRACT FROM AUTHOR]

Wildfire activity in boreal forests is anticipated to increase dramatically, with far-reaching ecological and socioeconomic consequences. Paleorecords are indispensible for elucidating boreal fire regime dynamics under changing climate, because fire return intervals and successional cycles in these ecosystems occur over decadal to centennial timescales. We present charcoal records from 14 lakes in the Yukon Flats of interior Alaska, one of the most flammable ecoregions of the boreal forest biome, to infer causes and consequences of fire regime change over the past 10,000 y. Strong correspondence between charcoal-inferred and observational fire records shows the fidelity of sedimentary charcoal records as archives of past fire regimes. Fire frequency and area burned increased ~6,000-3,000 y ago, probably as a result of elevated landscape flammability associated with increased Picea mariana in the regional vegetation. During the Medieval Climate Anomaly (MCA; ~1,000-500 cal B.P.), the period most similar to recent decades, warm and dry climatic conditions resulted in peak biomass burning, but severe fires favored less-flammable deciduous vegetation, such that fire frequency remained relatively stationary. These results suggest that boreal forests can sustain high-severity fire regimes for centuries under warm and dry conditions, with vegetation feedbacks modulating climate-fire linkages. The apparent limit to MCA burning has been surpassed by the regional fire regime of recent decades, which is characterized by exceptionally high fire frequency and biomass burning. This extreme combination suggests a transition to a unique regime of unprecedented fire activity. However, vegetation dynamics similar to feedbacks that occurred during the MCA may stabilize the fire regime, despite additional warming. [ABSTRACT FROM AUTHOR]

Peatland records of Holocene palaeoclimate have been widely used in Europe. Their potential in western North America remains largely unexploited despite an abundance of candidate sites. Peat humification analysis is a widely used technique for palaeoclimatic inference from peatlands. This study attempts to demonstrate a climatic role in determining peat humification by comparing low-resolution peat humification records from five mires in south-east Alaska. Humification was determined by alkali extraction and colorimetry and records dated by radiocarbon and tephrochronology. Testate amoebae analysis was carried out across a major humification-inferred wet shift in three of the sites. The humification results show variability down the length of the cores but there is only limited agreement between records from different sites. Many general trends in the data appear to be out of phase and periods of proxy 'complacency' are shown. This study does not provide strong evidence for climatic forcing of humification in these sites. Methodological issues including possible problems with the age-depth models and the role of a peat-forming plant species signal in the humification data are discussed. The results support previous studies in suggesting the value of employing a multi-proxy, multi-site, and possibly multi-core approach in peat-based palaeoclimatology. [ABSTRACT FROM AUTHOR]

Several studies have noted a relationship between vegetation type and fire frequency, yet despite the importance of ecosystem processes such as fire the long-term relationships between disturbance, climate and vegetation type are incompletely understood. We analysed pollen, plant macrofossils and sedimentary charcoal from three lakes within the Kenai lowlands to determine postglacial relationships between disturbance, climate and vegetation for the Boreal forest of southwest Alaska. An herb tundra was established in the lowlands following deglaciation by 13 000 cal. BP. Salix, Alnus and probably Betula kenaica, expanded in the area after 10 700 cal. BP, followed by Picea glauca by 8500 cal. BP. Picea mariana became established by 4600 cal. BP. The early Holocene was probably the driest time during the postglacial, as determined by aquatic plant macrofossils and climate models. Lake levels reached near-modern conditions by at least 8000 cal. BP. Mean Fire Intervals (MFI) were longest during the shrub–herb tundra phase (138±65 yr), decreased after expansion of B. kenaica, Salix and Populus (77±49 yr) and Picea glauca (81±41 yr), and increased again with the arrival of P. mariana (130±66 yr). Unlike previous studies, our data demonstrate the highest fire frequencies during the early to mid-Holocene and less frequent fire during the late Holocene when P. mariana forests dominated the lowlands. Early Holocene forests of P. glauca and B. kenaica existed in summers that were longer and drier than today, while the increasingly wetter and cooler climates of the late Holocene probably hindered forest fire around Paradox Lake, perhaps because of less frequent summer drought. [ABSTRACT FROM AUTHOR]

We synthesize recent results from lake-sediment studies of Holocene fire-climate-vegetation interactions in Alaskan boreal ecosystems. At the millennial time scale, the most robust feature of these records is an increase in fire occurrence with the establishment of boreal forests dominated by Picea mariana: estimated mean fire-return intervals decreased from ≥300 yrs to as low as ∼80 yrs. This fire-vegetation relationship occurred at all sites in interior Alaska with charcoal-based fire reconstructions, regardless of the specific time of P. mariana arrival during the Holocene. The establishment of P. mariana forests was associated with a regional climatic trend toward cooler/wetter conditions. Because such climatic change should not directly enhance fire occurrence, the increase in fire frequency most likely reflects the influence of highly flammable P. mariana forests, which are more conducive to fire ignition and spread than the preceding vegetation types (tundra, and woodlands/forests dominated by Populus or Picea glauca). Increased lightning associated with altered atmospheric circulation may have also played a role in certain areas where fire frequency increased around 4000 calibrated years before present (BP) without an apparent increase in the abundance of P. mariana. When viewed together, the paleo-fire records reveal that fire histories differed among sites in the same modern fire regime and that the fire regime and plant community similar to those of today became established at different times. Thus the spatial array of regional fire regimes was non-static through the Holocene. However, the patterns and causes of the spatial variation remain largely unknown. Advancing our understanding of climate-fire-vegetation interactions in the Alaskan boreal biome will require a network of charcoal records across various ecoregions, quantitative paleoclimate reconstructions, and improved knowledge of how sedimentary charcoal records fire events. [ABSTRACT FROM AUTHOR]

Pollen, stomates and macrofossils were analysed from a 3.63 m sediment core at Jan Lake, east-central Alaska, in order to improve spatial resolution of patterns of vegetation history in this region. The chronology was based on 19 AMS 14C dates on plant macrofossils and concentrated pollen. Zone Jan-I (12 400–11 600 yr BP) records a unique herb-tundra pollen assemblage, particularly high in Chenopodiaceae, adding supporting evidence for a spatial mosaic of lateglacial vegetation in east-central Alaska. Unexpected pollen of Picea, Betula and Alnus in lateglacial sediments appears to arise from reworking of older pollen-bearing deposits, according to a radiocarbon date of 22 180 yr BPon a pollen sample. Shrub Betula tundra dominates zone Jan-II (11 600–10 000 yr BP), with indications of climatic amelioration. Tree species (Populus, Picea glauca, Betula papyrifera) began to arrive in zone Jan-IIIa (9200–6600 yr BP), and the modern boreal forest, including Alnus and Picea mariana, became established during zone Jan-IIIb (6600–0 yr BP). Fossil stomates appear to be an effective indicator of initial local occurrence of Picea at Jan Lake. Picea arrival at Jan Lake is within 300 years of its arrival at other AMS-dated sites across eastern and central Alaska. A migration route into Alaska through the drainages of the Tanana or Yukon Rivers is hypothesized. Evidence is found for a slight mid-Holocene Picea decline at Jan Lake, intermediate in magnitude between Picea pollen records showing no decline to the east and a larger decline to the west in Alaska. [ABSTRACT FROM AUTHOR]