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The dominant landscape process on the Arctic Coastal Plain of northern Alaska is the formation and drainage of thaw lakes. Lakes and drained thaw-lake basins account for approximately 75% of the modern surface expression of the Barrow Peninsula. The thaw-lake cycle usually obliterates lacustrine or peat sediments from previous cycles, which could otherwise be used for paleoecological reconstruction of long-term landscape and vegetation changes. Several possible erosional remnants of a former topographic surface that predates the formation of the thaw lakes have been tentatively identified. These remnants are characterized by a higher elevation, a thick organic layer with very high ground ice content in the upper permafrost and a plant community somewhat atypical of the region. Ten soil cores were collected from one site, and one core was intensively sampled for soil organic carbon content, pollen analysis and 14C dating. The lowest level of the organic sediments represents the earliest phase of plant growth and dates to ca. 9000 cal BP. Palynological evidence indicates the presence of mesic shrub tundra (including sedge, birch, willow and heath vegetation), and microfossil indicators point to wetter eutrophic conditions during this period. Carbon accumulation was rapid due to high net primary productivity in a relatively nutrient-rich environment. These results are interpreted as the local response to ameliorating climate during the early Holocene. The middle Holocene portion of the record contains an unconformity, indicating that between 8200 and 4200 cal BP sediments were eroded from the site, presumably in response to wind activity during a drier period centered around 4500 cal BP. The modern vegetation community of the erosional remnant was established after 4200 cal BP and peat growth resumed. During the late Holocene, carbon accumulation rates (CARs) were greatly reduced in response to the combined effects of declining productivity associated with climatic cooling, and increased nutrient stress as paludification and permafrost aggradation sequestered mineral nutrients.

Thaw lakes and drained thaw lake basins are ubiquitous on the Arctic Coastal Plain of Alaska. Basins are wet depositional environments, ideally suited for the accumulation and preservation of organic material. Much of this soil organic carbon (SOC) is currently sequestered in the near-surface permafrost but, under a warming scenario, could become mobilized. The relative age of 77 basins on the Barrow Peninsula was estimated using the degree of plant community succession and verified by radiocarbon-dating material collected from the base of the organic layer in 21 basins. Using Landsat-7+ imagery of the region, a neural network classifying algorithm was developed from basin age-dependent spectra and texture. About 22% of the region is covered by 592 lakes (>1 ha), and at least 50% of the land surface is covered by 558 drained lake basins. Analysis of cores collected from basins indicates that (1) organic layer thickness and the degree of organic matter decomposition generally increases with basin ...

Net primary productivity (NPP) is a fundamental ecological variable that provides information about the health and status of vegetation communities. The Normalized Difference Vegetation Index, or NDVI, derived from the Advanced Very High Resolution Radiometer (AVHRR) is increasingly being used to model or predict NPP, especially over large remote areas. In this article, seven seasonally based metrics calculated from a seven-year baseline NDVI dataset were used to model NPP over Alaska, USA. For each growing season, they included maximum, mean and summed NDVI, total days, product of total days and maximum NDVI, an integral estimate of NDVI and a summed product of NDVI and solar radiation. Field (plot) derived NPP estimates were assigned to 18 land cover classes from an Alaskan statewide land cover database. Linear relationships between NPP and each NDVI metric were analysed at four scales: plot, 1-km, 10-km and 20-km pixels. Results show moderate to poor relationship between any of the metrics and NPP esti...

Ice cores removed from shallow ice-covered tundra lakes near Barrow, Alaska, and taiga lakes near Anchorage, Alaska, exhibit increasing concentrations of methane with depth. Methane concentrations in the ice cores increased from 0 μM in the top 15 cm sections to a maximum of 23 μM in the lowest 15 cm sections of tundra lake ice and to a maximum of 147 μM in taiga lake ice. Methane concentrations in the water beneath the ice reflect a similar pattern, with values near 5 μM early in the ice-covered season, increasing up to 42 μM in the tundra lakes, and up to 730 μM in the taiga lakes. Methane levels increase in the water beneath the ice during the course of the winter due to decreasing water volume, exclusion from growing ice, and continued methane production in thawed sediments. Since the ice layer prohibits gas exchange with the atmosphere, the methane is not oxidized, as it would be during the summer months, allowing the winter accumulation and storage of methane in the ice and lake waters. Efflux measurements, taken with floating chambers on the taiga lakes, indicated a large pulse of methane released during the period of ice melt and spring turnover. The efflux from one lake ranged from 2.07 g CH4 m−2 in 1995 to 1.49 g CH4 m−2 in 1996 for the 10 day period immediately after ice melt. Estimation of methane efflux using a boundary layer diffusion model and surface water concentrations during the entire ice-free period in 1996 predicted an efflux of 1.79 g CH4 m−2 during the same 10 day period, compared with 2.28 g CH4 m−2 for the remainder of the summer season. This observation suggests that almost as much methane efflux can occur during a brief period immediately after ice melt as occurs during the remainder of the ice-free season. Since measurements of methane efflux from high-latitude-lakes are generally made after this breakup period, the overall contribution to atmospheric methane from high-latitude lakes may be twice that of current estimates.

Modern and fossil pollen analyses have established the local vegetation succession and landscape evolution along the Meade River near Atqasuk, Alaska. Three data sets were analyzed: (1) a 142-cm-long peat deposit on the exposed river bluff face, (2) a short, 13-cm peat monolith from the near-surface sediment, and (3) a modern data set of surface samples collected along a transect representative of a geomorphic gradient of low-center, transitional, and high-center polygons. Pollen-microfossil assemblages changed significantly along this gradient. Detailed analysis of the short pollen profile shows successional vegetation changes over the last 250 years. The long profile, a 9400-year record of past vegetation, indicates that initially, the site was covered by shallow lakes. Eolian activity had a substantial effect on sediment deposition, but a period of rapid peat growth from 8500 to 5000 14C year B.P. is coincident with increased vegetation cover of mixed grass-shrub tundra. Following this period, peat growth slowed, and shrub vegetation was replaced by tussock-forming sedge vegetation.

A group of ice‐cored frost mounds formed during the winter of 1995–1996 near Barrow, Alaska in a drained thaw‐lake basin. Over 20 mounds, ranging from 5 to 20 m across, were observed in mid‐August ...

Factors controlling the flux of the radiatively important trace gas methane (CH4) from boreal wetlands were examined at three sites along a moisture gradient from a treed low-shrub bog to an open floating graminoid bog in Fairbanks, Alaska. In the summer of 1992 average static chamber flux measurements were −0.02, 71.5, and 289 mg CH4/m2/d in dry, wet, and floating mat communities, respectively. In contrast, the warmer, drier 1993 field season flux measurements were −0.02, 42.9 and 407 mg CH4/m2/d. The data indicate that despite net oxidation of CH4 in the dry regions of the bog, the wetland is a net source of CH4, with fluxes ranging across three orders of magnitude between different plant communities. Comparison with water levels suggests that CH4 flux is turned on and off by changes in site hydrology. In sites where sufficient moisture is present for methanogenesis to occur, CH4 flux appears to be temperature limited, responding exponentially to soil temperature changes. The combined effects of hydrology and temperature create hot spots of CH4 flux within boreal wetlands. The plant communities within Lemeta Bog respond differently to changes in temperature and moisture availability, creating both positive and negative feedbacks to potential global climate change.

Hydrological changes, particularly alterations in water table level, may largely overshadow the more direct effects of global temperature increase upon carbon cycling in arctic and subarctic wetlands. Frozen cores (n=40) of intact soils and vegetation were collected from a bog near Fairbanks, Alaska, and fluxes of CO{sub 2}, CH{sub 4}, and Co in response to water table variation were studied under controlled conditions in the Duke University phytotron. Core microcosms thawed to a 20-cm depth over 30 days under a 20 hour photoperiod with a day/night temperature regime of 20/10{degrees}C. After 30 days the water table in 20 microcosms was decreased from the soil surface to -15 cm and maintained at the soil surface in 20 control cores. Outward fluxes of CO{sub 2} (9-16 g m{sup -2}d{sup -1}) and CO (3-4 mg m{sup -2}d{sup -1}) were greatest during early thaw and decreased to near zero for both gases before the water table treatment started. Lower water table tripled CO{sub 2} flux to the atmosphere when compared with control cores. Carbon monoxide was emitted at low rates from high water table cores and consumed by low water table cores. Methane fluxes were low (

Dwight Billings, James B. Duke Professor of Botany at Duke University, eminent ecologist, writer, prolific mentor, original thinker, and master of his discipline, contributed much to our ecological understanding of the Arctic and beyond. His list of honors and accomplishments fills several pages. Dwight passed away at his home in Durham, North Carolina on 4 January 1997, at the age of 86. ... Billings supervised a total of 52 doctoral students in his years at Duke; as a result, his academic progeny shaped much of the modern field of ecology. The clear and straightforward style of his succinct book Plants and the Ecosystem was responsible for awakening the interest of many to the field of ecology. Billings is considered the father of modern physiological ecology. ... Billings' pioneering work on the physiology of alpine plants, along with that of his students, earned him the recognition of being America's foremost authority on alpine tundra. This led naturally to the tundra of the Arctic, and although his interest in everything from deserts to deciduous forests remained keen, most of his later life was devoted to the study of Arctic and high-latitude ecosystems. The body of work of Dwight Billings (and his academic offspring) pertaining to the Arctic is large and well respected. Many of today's Arctic ecologists trace their academic heritage to Dwight Billings, and essentially all others acknowledge some form of Billings' influence.