Interpolar methane gradient (IPG) data from ice cores suggest the "switching on" of a major Northern Hemisphere methane source in the early Holocene. Extensive data from Russia's West Siberian ...Lowland show (i) explosive, widespread peatland establishment between 11.5 and 9 thousand years ago, predating comparable development in North America and synchronous with increased atmospheric methane concentrations and IPGs, (ii) larger carbon stocks than previously thought (70.2 Petagrams, up to approximately 26% of all terrestrial carbon accumulated since the Last Glacial Maximum), and (iii) little evidence for catastrophic oxidation, suggesting the region represents a long-term carbon dioxide sink and global methane source since the early Holocene.
Climate change and the northern Russian treeline zone MacDonald, G.M; Kremenetski, K.V; Beilman, D.W
Philosophical transactions of the Royal Society of London. Series B. Biological sciences,
07/2008, Letnik:
363, Številka:
1501
Journal Article
Recenzirano
Odprti dostop
The Russian treeline is a dynamic ecotone typified by steep gradients in summer temperature and regionally variable gradients in albedo and heat flux. The location of the treeline is largely ...controlled by summer temperatures and growing season length. Temperatures have responded strongly to twentieth-century global warming and will display a magnified response to future warming. Dendroecological studies indicate enhanced conifer recruitment during the twentieth century. However, conifers have not yet recolonized many areas where trees were present during the Medieval Warm period (ca AD 800-1300) or the Holocene Thermal Maximum (HTM; ca 10 000-3000 years ago). Reconstruction of tree distributions during the HTM suggests that the future position of the treeline due to global warming may approximate its former Holocene maximum position. An increased dominance of evergreen tree species in the northern Siberian forests may be an important difference between past and future conditions. Based on the slow rates of treeline expansion observed during the twentieth century, the presence of steep climatic gradients associated with the current Arctic coastline and the prevalence of organic soils, it is possible that rates of treeline expansion will be regionally variable and transient forest communities with species abundances different from today's may develop.
Extinction of the woolly mammoth in Beringia has long been subject to research and speculation. Here we use a new geo-referenced database of radiocarbon-dated evidence to show that mammoths were ...abundant in the open-habitat of Marine Isotope Stage 3 (∼45-30 ka). During the Last Glacial Maximum (∼25-20 ka), northern populations declined while those in interior Siberia increased. Northern mammoths increased after the glacial maximum, but declined at and after the Younger Dryas (∼12.9-11.5 ka). Remaining continental mammoths, now concentrated in the north, disappeared in the early Holocene with development of extensive peatlands, wet tundra, birch shrubland and coniferous forest. Long sympatry in Siberia suggests that humans may be best seen as a synergistic cofactor in that extirpation. The extinction of island populations occurred at ∼4 ka. Mammoth extinction was not due to a single cause, but followed a long trajectory in concert with changes in climate, habitat and human presence.
The West Siberian Lowland (WSL) contains the world's most extensive peatlands and a substantial fraction of the global terrestrial carbon pool. Despite its recognition as a carbon reservoir of great ...significance, the extent, thickness, and carbon content of WSL peatlands have not been analyzed in detail. This paper compiles a wide array of data into a geographic information system (GIS) to create a high‐resolution, spatially explicit digital inventory of all WSL peatlands and their associated physical properties. Detailed measurements for nearly 10,000 individual peatlands (patches) are based on compilation of previously unpublished Russian field and ancillary map data, satellite imagery, previously published depth measurements, and our own field depth and core measurements taken throughout the region during field campaigns in 1999, 2000, and 2001. At the patch level, carbon storage is estimated as the product of peatland area, depth, and carbon content. Estimates of peatland area are validated from RESURS‐01 satellite images, and the quality of the Russian peatland depth and carbon content data is independently confirmed by laboratory analysis of core samples. Through GIS‐based spatial analysis of the peat areal extent, depth, and carbon content data, we conservatively estimate the total area of WSL peatlands at 592,440 km2, the total peat mass at 147.82 Pg, and the total carbon pool at 70.21 Pg C. Our analysis concludes that WSL peatlands are more extensive and represent a substantially larger carbon pool than previously thought: Previous studies report 9,440–273,440 km2 less peatland area and 15.11–30.19 Pg less carbon than found in this analysis. The complete digital database is freely available for scientific use at http://arcss.colorado.edu/data/arcss131.html.
Our ability to reliably use radiocarbon (14C) dates of mollusk shells to estimate calendar ages may depend on the feeding preference and habitat of a particular species and the geology of the region. ...Gastropods that feed by scraping are prone to incorporation of carbon from the substrate into their shells as evidenced by studies comparing the radiocarbon dates of shells and flesh from different species on different substrates (Dye 1994; Hogg et al. 1998). Limpet shells (Patella sp.) are commonly found in prehistoric midden deposits in the British Isles and elsewhere, however these shells have largely been avoided for radiocarbon dating in regions of limestone outcrops. Results from limpets (Patella vulgata) collected alive on limestone and volcanic substrates on the coasts of Ireland indicate that the shells were formed in equilibrium with the seawater, with no significant 14C offsets. Limpets collected from the east coast of Northern Ireland have elevated 14C due to the output of Sellafield nuclear fuel reprocessing plant. In all locations, the flesh was depleted in 14C compared to the shells. The results will have an important consequence for radiocarbon dating of midden deposits as well as the bone of humans and animals who fed on the limpets.
ABSTRACT
Our ability to reliably use radiocarbon (
14
C) dates of mollusk shells to estimate calendar ages may depend on the feeding preference and habitat of a particular species and the geology of ...the region. Gastropods that feed by scraping are prone to incorporation of carbon from the substrate into their shells as evidenced by studies comparing the radiocarbon dates of shells and flesh from different species on different substrates (Dye 1994; Hogg et al. 1998). Limpet shells (
Patella sp
.) are commonly found in prehistoric midden deposits in the British Isles and elsewhere, however these shells have largely been avoided for radiocarbon dating in regions of limestone outcrops. Results from limpets (
Patella vulgata
) collected alive on limestone and volcanic substrates on the coasts of Ireland indicate that the shells were formed in equilibrium with the seawater, with no significant
14
C offsets. Limpets collected from the east coast of Northern Ireland have elevated
14
C due to the output of Sellafield nuclear fuel reprocessing plant. In all locations, the flesh was depleted in
14
C compared to the shells. The results will have an important consequence for radiocarbon dating of midden deposits as well as the bone of humans and animals who fed on the limpets.
Significance Antiretroviral therapy (ART) effectively suppresses HIV replication; however, treatment cannot be stopped, because latently infected CD4+ T cells will rekindle infection. As one estimate ...of the size of the pool of latently infected cells that must be purged for cure, we asked whether recrudescent infection is the result of reactivation from one or a larger number latently infected cells. We briefly stopped ART in fully suppressed patients to see how widespread new infections were in the lymphoid tissues (LTs) and how diverse rebounding/founder viruses were in peripheral blood. Recrudescent infection was detectable in multiple different LTs, and the population was genetically diverse, consistent with reactivation from a larger number of cells. These findings underscore the challenges facing strategies to eradicate HIV infection.
Antiretroviral therapy (ART) suppresses HIV replication in most individuals but cannot eradicate latently infected cells established before ART was initiated. Thus, infection rebounds when treatment is interrupted by reactivation of virus production from this reservoir. Currently, one or a few latently infected resting memory CD4 T cells are thought be the principal source of recrudescent infection, but this estimate is based on peripheral blood rather than lymphoid tissues (LTs), the principal sites of virus production and persistence before initiating ART. We, therefore, examined lymph node (LN) and gut-associated lymphoid tissue (GALT) biopsies from fully suppressed subjects, interrupted therapy, monitored plasma viral load (pVL), and repeated biopsies on 12 individuals as soon as pVL became detectable. Isolated HIV RNA-positive (vRNA+) cells were detected by in situ hybridization in LTs obtained before interruption in several patients. After interruption, multiple foci of vRNA+ cells were detected in 6 of 12 individuals as soon as pVL was measureable and in some subjects, in more than one anatomic site. Minimal estimates of the number of rebounding/founder (R/F) variants were determined by single-gene amplification and sequencing of viral RNA or DNA from peripheral blood mononuclear cells and plasma obtained at or just before viral recrudescence. Sequence analysis revealed a large number of R/F viruses representing recrudescent viremia from multiple sources. Together, these findings are consistent with the origins of recrudescent infection by reactivation from many latently infected cells at multiple sites. The inferred large pool of cells and sites to rekindle recrudescent infection highlights the challenges in eradicating HIV.
The richness and ecological roles of yeasts in peatlands are largely unknown. This paper presents a review of the literature on yeasts in peatlands and also provides new data with species isolated ...from peatlands in Saskatchewan, Canada, and West Siberia, Russia. To date, 75 yeast taxa have been reported from peatlands, including 46 identified species and 29 isolates identified only to genus or not at all. This represents 5%–10% of known yeasts and about 10% of all peatland fungi. Cryptococcus, Candida, Pichia, and Rhodotorula are the most prevalent genera, accounting for 58% of known peatland yeast species. We obtained 34 isolates from western Canadian and West Siberian bog and fen peat, including 12 identified species and eight unidentified taxa. Identified taxa comprised mostly species of Candida, Cryptococcus, and Rhodotorula. Unidentified taxa were described based on physiology and morphology. Globally, more species have been reported from bogs than fens (41 vs. 13 taxa), and the species composition differs between the two peatland classes. The effect of depth within the acrotelm on yeast abundance and species composition varies among peatlands. Physiological profiling of the yeasts from our study showed that they can use (poly)saccharides (primarily D-glucose, maltotriose, n-acetyl glucosamine, trehalose, and sucrose), organic acids (primarily D-gluconic acid, fumaric acid, malic acid, and succinic acid), sugar alcohols (primarily D-arabitol, D-mannitol, and D-sorbitol), glycosides (primarily arbutin and salicin), and amino acids (primarily L-glutamic acid) as carbon and nitrogen sources. Based on these profiles, yeasts likely access simple polymers that leach from senesced and/or dead plant materials in peatlands and probably play important roles during the initial stages of organic matter decomposition.
PDF
