Genetic analyses of permafrost and temperate sediments reveal that plant and animal DNA may be preserved for long periods, even in the absence of obvious macrofossils. In Siberia, five permafrost cores ranging from 400,000 to 10,000 years old contained at least 19 different plant taxa, including the oldest authenticated ancient DNA sequences known, and megafaunal sequences including mammoth, bison, and horse. The genetic data record a number of dramatic changes in the taxonomic diversity and composition of Beringian vegetation and fauna. Temperate cave sediments in New Zealand also yielded DNA sequences of extinct biota, including two species of ratite moa, and 29 plant taxa characteristic of the prehuman environment. Therefore, many sedimentary deposits may contain unique, and widespread, genetic records of paleoenvironments.

The results of the International Permafrost Association's International Polar Year Thermal State of Permafrost (TSP) project are presented based on field measurements from Russia during the IPY years (2007-09) and collected historical data. Most ground temperatures measured in existing and new boreholes show a substantial warming during the last 20 to 30 years. The magnitude of the warming varied with location, but was typically from 0.58C to 28C at the depth of zero annual amplitude. Thawing of Little Ice Age permafrost is ongoing at many locations. There are some indications that the late Holocene permafrost has begun to thaw at some undisturbed locations in northeastern Europe and northwest Siberia. Thawing of permafrost is most noticeable within the discontinuous permafrost domain. However, permafrost in Russia is also starting to thaw at some limited locations in the continuous permafrost zone. As a result, a northward displacement of the boundary between continuous and discontinuous permafrost zones was observed. This data set will serve as a baseline against which to measure changes of near-surface permafrost temperatures and permafrost boundaries, to validate climate model scenarios, and for temperature reanalysis.

Metabolic activity was measured in the laboratory at temperatures between 5 and ؊20°C on the basis of incorporation of 14 C-labeled acetate into lipids by samples of a natural population of bacteria from Siberian permafrost (permanently frozen soil). Incorporation followed a sigmoidal pattern similar to growth curves. At all temperatures, the log phase was followed, within 200 to 350 days, by a stationary phase, which was monitored until the 550th day of activity. The minimum doubling times ranged from 1 day (5°C) to 20 days (؊10°C) to ca. 160 days (؊20°C). The curves reached the stationary phase at different levels, depending on the incubation temperature. We suggest that the stationary phase, which is generally considered to be reached when the availability of nutrients becomes limiting, was brought on under our conditions by the formation of diffusion barriers in the thin layers of unfrozen water known to be present in permafrost soils, the thickness of which depends on temperature.In numerous previously published articles the authors described microbial metabolic activity at subzero temperatures. In more recent reviews (6,9,14,22), the authors agree that earlier reports of microbial activity (mostly bacterial activity) at temperatures below Ϫ12°C were unsubstantiated. Microbial growth or metabolic activity has been reported in permafrost bacteria at Ϫ10°C (11) and in the antarctic cryptoendolithic microbial community at temperatures between Ϫ5 and Ϫ10°C (7, 28), and the temperature limit of bacterial growth in frozen food is generally considered to be Ϫ8°C (9). In arctic and antarctic lichens, photosynthetic activity has been observed in a similar temperature range (12) and, more recently, at Ϫ17°C (23). However, no quantitative measurements of the dynamics of metabolic activity or of growth have been described. We attempted to quantify metabolic activity at subzero temperatures in the native bacterial population of Siberian permafrost by measuring the incorporation of sodium acetate into lipids over a 550-day period.Significant numbers of viable bacteria (10 2 to 10 8 cells g Ϫ1 ) are known to be present in permafrost that is 1 to 3 million years old in the arctic (10,21,24,29) 1996, abstr. 60, 1996); all of the bacteria that have been characterized so far have been psychrotrophs (psychrotolerant mesophiles). The ratio of aerobic bacteria to anaerobic bacteria seems to vary according to the geological history. Comparative quantitative studies have not been performed. Permafrost sediments of alluvial, lake, and marine origin that formed under anoxic conditions contain high numbers of anaerobes (compared to total cell counts), like the samples studied by Rivkina et al. (21), whereas other samples, like the samples described by Shi et al. (24) or the sample used in the present study, seem to be dominated by aerobes. Although the exact number of anaerobes in our sample is not known, the anaerobes that were present, which were unable to metabolize under the conditions used in the experiment, obviously did n...

[1] Changes in active layer thickness (ALT) over northern high-latitude permafrost regions have important impacts on the surface energy balance, hydrologic cycle, carbon exchange between the atmosphere and the land surface, plant growth, and ecosystems as a whole. This study examines the 20th century variations of ALT for the Ob, Yenisey, and Lena River basins. ALT is estimated from historical soil temperature measurements from 17 stations , Lena basin only), an annual thawing index based on both surface air temperature data and numerical modeling . The latter two provide spatial fields. Based on the thawing index, the long-term average ALT is about 1.87 m in the Ob, 1.67 in the Yenisey, and 1.69 m in the Lena basin. Over the past several decades, ALT over the three basins shows positive trends, but with different magnitudes. Based on the 17 stations, ALT increased about 0.32 m between 1956 and 1990 in the Lena. To the extent that results based on the soil temperatures represent ground ''truth,'' ALT obtained from both the thawing index and numerical modeling is underestimated. It is widely believed that ALT will increase with global warming. However, this hypothesis needs further refinement since ALT responds primarily to summer air temperature while observed warming has occurred mainly in winter and spring. It is also shown that ALT exhibits complex and inconsistent responses to variations in snow cover.Citation: Zhang, T., et al. (2005), Spatial and temporal variability in active layer thickness over the Russian Arctic drainage basin,