Climate change and the permafrost carbon feedback.

Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.

A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch.

Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch. However, the same thermokarst lakes can also sequester carbon, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene carbon accumulation in 20 lake sediments (47 ± 10 grams of carbon per square metre per year; mean ± standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160 petagrams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears, potentially negating the climate stabilization provided by thermokarst lakes during the late Holocene.

Upland Yedoma taliks are an unpredicted source of atmospheric methane.

Landscape drying associated with permafrost thaw is expected to enhance microbial methane oxidation in arctic soils. Here we show that ice-rich, Yedoma permafrost deposits, comprising a disproportionately large fraction of pan-arctic soil carbon, present an alternate trajectory. Field and laboratory observations indicate that talik (perennially thawed soils in permafrost) development in unsaturated Yedoma uplands leads to unexpectedly large methane emissions (35-78 mg m-2 d-1 summer, 150-180 mg m-2 d-1 winter). Upland Yedoma talik emissions were nearly three times higher annually than northern-wetland emissions on an areal basis. Approximately 70% emissions occurred in winter, when surface-soil freezing abated methanotrophy, enhancing methane escape from the talik. Remote sensing and numerical modeling indicate the potential for widespread upland talik formation across the pan-arctic Yedoma domain during the 21st and 22nd centuries. Contrary to current climate model predictions, these findings imply a positive and much larger permafrost-methane-climate feedback for upland Yedoma.

Subsea permafrost organic carbon stocks are large and of dominantly low reactivity.

Subsea permafrost carbon pools below the Arctic shelf seas are a major unknown in the global carbon cycle. We combine a numerical model of sedimentation and permafrost evolution with simplified carbon turnover to estimate accumulation and microbial decomposition of organic matter on the pan-Arctic shelf over the past four glacial cycles. We find that Arctic shelf permafrost is a globally important long-term carbon sink storing 2822 (1518-4982) Pg OC, double the amount stored in lowland permafrost. Although currently thawing, prior microbial decomposition and organic matter aging limit decomposition rates to less than 48 Tg OC/yr (25-85) constraining emissions due to thaw and suggesting that the large permafrost shelf carbon pool is largely insensitive to thaw. We identify an urgent need to reduce uncertainty in rates of microbial decomposition of organic matter in cold and saline subaquatic environments. Large emissions of methane more likely derive from older and deeper sources than from organic matter in thawing permafrost.

Thawing Yedoma permafrost is a neglected nitrous oxide source.

In contrast to the well-recognized permafrost carbon (C) feedback to climate change, the fate of permafrost nitrogen (N) after thaw is poorly understood. According to mounting evidence, part of the N liberated from permafrost may be released to the atmosphere as the strong greenhouse gas (GHG) nitrous oxide (N2O). Here, we report post-thaw N2O release from late Pleistocene permafrost deposits called Yedoma, which store a substantial part of permafrost C and N and are highly vulnerable to thaw. While freshly thawed, unvegetated Yedoma in disturbed areas emit little N2O, emissions increase within few years after stabilization, drying and revegetation with grasses to high rates (548 (133-6286) µg N m-2 day-1; median with (range)), exceeding by 1-2 orders of magnitude the typical rates from permafrost-affected soils. Using targeted metagenomics of key N cycling genes, we link the increase in in situ N2O emissions with structural changes of the microbial community responsible for N cycling. Our results highlight the importance of extra N availability from thawing Yedoma permafrost, causing a positive climate feedback from the Arctic in the form of N2O emissions.

Author Correction: Remote sensing quantifies widespread abundance of permafrost region disturbances across the Arctic and Subarctic.

The original version of this Article contained an error in the author affiliations. Affiliation 5 incorrectly read 'Tyumen State Oil and Gas University, Tyumen, Tyument. Oblast, Russian Federation, 625000'.This has now been corrected in both the PDF and HTML versions of the Article.

Century-scale time since permafrost thaw affects temperature sensitivity of net methane production in thermokarst-lake and talik sediments.

Permafrost thaw subjects previously frozen soil organic carbon (SOC) to microbial degradation to the greenhouse gases carbon dioxide (CO2) and methane (CH4). Emission of these gases constitutes a positive feedback to climate warming. Among numerous uncertainties in estimating the strength of this permafrost carbon feedback (PCF), two are: (i) how mineralization of permafrost SOC thawed in saturated anaerobic conditions responds to changes in temperature and (ii) how microbial communities and temperature sensitivities change over time since thaw. To address these uncertainties, we utilized a thermokarst-lake sediment core as a natural chronosequence where SOC thawed and incubated in situ under saturated anaerobic conditions for up to 400 years following permafrost thaw. Initial microbial communities were characterized, and sediments were anaerobically incubated in the lab at four temperatures (0 °C, 3 °C, 10 °C, and 25 °C) bracketing those observed in the lake's talik. Net CH4 production in freshly-thawed sediments near the downward-expanding thaw boundary at the base of the talik were most sensitive to warming at the lower incubation temperatures (0 °C to 3 °C), while the overlying sediments which had been thawed for centuries had initial low abundant methanogenic communities (< 0.02%) and did not experience statistically significant increases in net CH4 production potentials until higher incubation temperatures (10 °C to 25 °C). We propose these observed differences in temperature sensitivities are due to differences in SOM quality and functional microbial community composition that evolve over time; however further research is necessary to better constrain the roles of these factors in determining temperature controls on anaerobic C mineralization.

Remote sensing quantifies widespread abundance of permafrost region disturbances across the Arctic and Subarctic.

Local observations indicate that climate change and shifting disturbance regimes are causing permafrost degradation. However, the occurrence and distribution of permafrost region disturbances (PRDs) remain poorly resolved across the Arctic and Subarctic. Here we quantify the abundance and distribution of three primary PRDs using time-series analysis of 30-m resolution Landsat imagery from 1999 to 2014. Our dataset spans four continental-scale transects in North America and Eurasia, covering ~10% of the permafrost region. Lake area loss (-1.45%) dominated the study domain with enhanced losses occurring at the boundary between discontinuous and continuous permafrost regions. Fires were the most extensive PRD across boreal regions (6.59%), but in tundra regions (0.63%) limited to Alaska. Retrogressive thaw slumps were abundant but highly localized (<10-5%). Our analysis synergizes the global-scale importance of PRDs. The findings highlight the need to include PRDs in next-generation land surface models to project the permafrost carbon feedback.

Embryonic and postnatal development of the serotonergic raphe system and its target regions in 5-HT1A receptor deletion or overexpressing mouse mutants.

The neurotransmitter 5-HT regulates early developmental processes in the CNS. In the present study we followed the embryonic and postnatal development of serotonergic raphe neurons and catecholaminergic target systems in the brain of 5-HT1A receptor knockout (KO) and overexpressing (OE) in comparison with wild-type (WT) mice from embryonic day (E) 12.5 to postnatal day (P) 15.5. Up to P15.5 no differences were apparent in the differentiation and distribution of serotonergic neurons in the raphe area as revealed by the equal number of serotonergic neurons in the dorsal raphe in all three genotypes. However, the establishment of serotonergic projections to the mesencephalic tegmentum and hypothalamus was delayed at E12.5 in KO and OE animals and projections to the cerebral cortex between E16.5 and E18.5 were delayed in OE mice. This delay was only transient and did not occur in other brain areas including septum, hippocampus and striatum. Moreover, OE mice caught up with WT and KO animals postnatally such that at P1.5 serotonergic innervation of the cortex was more extensive in the OE than in KO and WT mice. Tissue levels of 5-HT and of its main metabolite 5-hydroxyindoleacetic acid as well as 5-HT turnover were considerably higher in brains of OE mice and slightly elevated in KO mice in comparison with the WT, starting at E16.5 through P15.5. The initial differentiation of dopaminergic neurons and fibers in the substantia nigra at E12.5 was transiently delayed in KO and OE mice as compared with WT mice, but no abnormalities in noradrenergic development were apparent in later stages. The present data indicate that 5-HT1A receptor deficiency or overexpression is associated with increased 5-HT synthesis and turnover in the early postnatal period. However, they also show that effects of 5-HT1A KO or OE on the structural development of the serotonergic system are at best subtle and transient. They may nonetheless contribute to the establishment of increased or reduced anxiety-like behavior, respectively, in adult mice.

Circumpolar distribution and carbon storage of thermokarst landscapes.

Thermokarst is the process whereby the thawing of ice-rich permafrost ground causes land subsidence, resulting in development of distinctive landforms. Accelerated thermokarst due to climate change will damage infrastructure, but also impact hydrology, ecology and biogeochemistry. Here, we present a circumpolar assessment of the distribution of thermokarst landscapes, defined as landscapes comprised of current thermokarst landforms and areas susceptible to future thermokarst development. At 3.6 × 106 km2, thermokarst landscapes are estimated to cover ∼20% of the northern permafrost region, with approximately equal contributions from three landscape types where characteristic wetland, lake and hillslope thermokarst landforms occur. We estimate that approximately half of the below-ground organic carbon within the study region is stored in thermokarst landscapes. Our results highlight the importance of explicitly considering thermokarst when assessing impacts of climate change, including future landscape greenhouse gas emissions, and provide a means for assessing such impacts at the circumpolar scale.

Expression of Kv1 potassium channels in mouse hippocampal primary cultures: development and activity-dependent regulation.

Excitability and discharge behavior of neurons depends on the highly variable expression pattern of voltage-dependent potassium (Kv) channels throughout the nervous system. To learn more about distribution, development, and activity-dependent regulation of Kv channel subunit expression in the rodent hippocampus, we studied the protein expression of members of the Kv1 subfamily in mouse hippocampus in situ and in primary cultures. In adult hippocampus, Kv1 (1-6) channel alpha-subunits were present, whereas at postnatal day 2, none of these proteins could be detected in CA1-CA3 and dentate gyrus. Kv1.1 was the first channel to be observed at postnatal day 6. The delayed postnatal expression and most of the subcellular distribution observed in hippocampal sections were mimicked by cultured hippocampal neurons in which Kv channels appeared only after 10 days in vitro. This developmental upregulation was paralleled by a dramatic increase in total K(+) current, as well as an elevated GABA release in the presence of 4-aminopyridine. Thus, the developmental profile, subcellular localization, and functionality of Kv1 channels in primary culture of hippocampus closely resembles the in situ situation. Impairing secretion by clostridial neurotoxins or blocking activity by tetrodotoxin inhibited the expression of Kv1.1, Kv1.2, and Kv1.4, whereas the other Kv1 channels still appeared. This activity-dependent depression was only observed before the initial appearance of the respective channels and lost after they had been expressed. Our data show that hippocampal neurons in culture are a convenient model to study the developmental expression and regulation of Kv1 channels. The ontogenetic regulation and the activity-dependent expression of Kv1.1, Kv1.2, and Kv1.4 indicate that neuronal activity plays a crucial role for the development of the mature Kv channel pattern in hippocampal neurons.

A simplified, data-constrained approach to estimate the permafrost carbon-climate feedback.

We present an approach to estimate the feedback from large-scale thawing of permafrost soils using a simplified, data-constrained model that combines three elements: soil carbon (C) maps and profiles to identify the distribution and type of C in permafrost soils; incubation experiments to quantify the rates of C lost after thaw; and models of soil thermal dynamics in response to climate warming. We call the approach the Permafrost Carbon Network Incubation-Panarctic Thermal scaling approach (PInc-PanTher). The approach assumes that C stocks do not decompose at all when frozen, but once thawed follow set decomposition trajectories as a function of soil temperature. The trajectories are determined according to a three-pool decomposition model fitted to incubation data using parameters specific to soil horizon types. We calculate litterfall C inputs required to maintain steady-state C balance for the current climate, and hold those inputs constant. Soil temperatures are taken from the soil thermal modules of ecosystem model simulations forced by a common set of future climate change anomalies under two warming scenarios over the period 2010 to 2100. Under a medium warming scenario (RCP4.5), the approach projects permafrost soil C losses of 12.2-33.4 Pg C; under a high warming scenario (RCP8.5), the approach projects C losses of 27.9-112.6 Pg C. Projected C losses are roughly linearly proportional to global temperature changes across the two scenarios. These results indicate a global sensitivity of frozen soil C to climate change (γ sensitivity) of -14 to -19 Pg C °C(-1) on a 100 year time scale. For CH4 emissions, our approach assumes a fixed saturated area and that increases in CH4 emissions are related to increased heterotrophic respiration in anoxic soil, yielding CH4 emission increases of 7% and 35% for the RCP4.5 and RCP8.5 scenarios, respectively, which add an additional greenhouse gas forcing of approximately 10-18%. The simplified approach presented here neglects many important processes that may amplify or mitigate C release from permafrost soils, but serves as a data-constrained estimate on the forced, large-scale permafrost C response to warming.

Spongiform encephalopathy in AIDS dementia complex: report of five cases.

We describe the morphological findings in the brain of five AIDS patients who died with a clinical diagnosis of dementia. We have found a spongiform change (small rounded vacuoles) in different parts of the brain and a similar but morphologically different sponginess, the status spongiosus, characterized by looser and coarser microcystic cavitations of the grey matter in which the tiny cysts and vacuoles are enmeshed by glial fibrils. At the ultrastructural level, round and oval clear spaces, divided by septae into several smaller ones, appeared in the neuropil. The pathogenesis of the majority of the vacuoles and cavitations is not clear yet but a focal loss of cortical neurons was evident and furthermore some of the vacuoles were identified as remnants of dendrites. The light and electron microscopic findings can not be interpreted as artefacts or as a simple edema of the brain and also can not be explained by the different infective complications. We have found spongiform alterations in all cases of clinically diagnosed dementia and therefore it seems obvious that these findings are quite frequent in AIDS dementia.

Deltamethrin differentially affects neuronal subtypes in hippocampal primary culture.

The effects of deltamethrin on neuronal development and survival were studied using primary mouse hippocampal neurons in culture. Repeated applications of deltamethrin (between 2 nM and 2000 nM) decreased the number of neurons by 16-40%, respectively. Neuronal death was accompanied by an overall decrease of synaptic proteins. Deltamethrin treatment increased the K(+)-stimulated release of amino acid transmitters, GABA and glutamate. The release of the latter might also contribute to neuronal damage. A considerable number of neurons survived treatment with high concentrations of deltamethrin (200-2000 nM) and still displayed characteristics of mature neurons such as synaptic contacts or the expression of members of the Kv1 channel family. When analyzing subtypes of neurons calbindin- as well as somatostatin-positive neurons decreased by 50% after repeated treatment with 2 nM deltamethrin. Under the same conditions neuropeptide Y-positive neurons were up-regulated by 250%.Taken together these data show that deltamethrin at concentrations relevant in human toxicology differentially affects survival of neuronal subtypes by exerting either deleterious or supportive effects. We conclude that deltamethrin disturbs fine-tuning of neuronal efficiency in neuronal networks and might also interfere with the correct wiring during development.

Vacuolar myelopathy in AIDS. A morphological analysis.

Between 1986 and 1988 we studied the spinal cord of 40 patients dying of AIDS. Transverse and longitudinal sections from a minimum of four levels of the spinal cord were examined by means of conventional histology, immunohistochemistry and electron microscopy. Out of 22 cases there were 6 showing a mild, 11 a moderate and 5 a severe myelopathy. Among these cases with severe myelopathy, vacuolar degeneration of the posterior, lateral, and anterior columns of the white matter, which are typical findings of vacuolar myelopathy (VM), were present. Cervical and thoracic cords were affected in all cases, the lumbal cord, however, in only two. Fusiform vacuoles, 30 to 180 microns in diameter and 200 to 500 microns in length, could be seen rising between the axolemma and the myelin sheath. Most of them were still containing an axon cylinder. Foamy phagocytic cells, phagocytosing axons of apparently preserved structure were found within the vacuoles. These foamy macrophages contained rests of axons in their cytoplasm. However, only one case with severe tissue disruption exhibited myelin debris as well. Our morphological findings suggest that in VM of AIDS a process of phagocytosis directed against the axon cylinders occurs simultaneously with vacuolar degeneration of the white matter of the spinal cord. The results suggest furthermore that VM, especially its moderate form, appears to be a more frequent condition than previously assumed.

Severe toxoplasmic ventriculomeningoencephalomyelitis in two AIDS patients following treatment of cerebral toxoplasmic granuloma.

Two patients with acquired immunodeficiency syndrome (AIDS) who were successfully treated for cerebral toxoplasmosis presented a few weeks later with neurologic abnormalities. Brain CT scan showed ventricular dilatation, ependymitis, and meningoencephalitis. Both patients died despite extensive treatment. Neuropathological examination showed enlargement of the cerebral ventricles, severe ventriculoencephalitis with large ependymal and subependymal necrosis, and numerous pseudomembranes within the ventricle lumen. Microscopic examination revealed severe necrotizing ventriculoencephalitis, meningoencephalitis and myelitis. Immunohistochemical studies revealed the presence of miriads of tachyzoites within and around the necrotic areas. Such form of toxoplasmosis as a diffuse meningo-encephalo-ventriculo-myelitis appear unique to AIDS and, to our knowledge, have not been previously documented.

[67Ga scintigraphy in retroperitoneal fibrosis (RPF): indications, application and clinical relevance--report of five patients]. / 67Ga-Szintigraphie bei retroperitonealer Fibrose (RPF): Indikation, Durchführung und klinische Bedeutung.

AIM: The aim of the study was to evaluate the indication for 67Ga-citrate imaging and its clinical impact on patients with retroperitoneal fibrosis (RPF). METHOD: The scanning with ventral and dorsal projections was done 48 an 72 h after i.v.-injection of 370 Mbq 67Ga-citrate. RESULTS: In the 5 patients with idiopathic RPF included in the study, there was a remarkably high correlation between the clinical symptoms, the surgical and histologic findings, the activity of the disease and the results of 67Ga-scintigraphy. CONCLUSION: While CT and--maybe even better--MRI might perfectly show the extension, shape and contour of the fibrotic tissue, Gallium-67 scan appears to be superior in assessing the intensity and activity of the disease process.

Anergic disseminated toxoplasmosis in a patient with the acquired immunodeficiency syndrome.

Cerebral toxoplasmosis is the most common cause of focal brain disease in patients with the acquired immunodeficiency syndrome. A 24-year-old human immunodeficiency virus-infected woman with two previous episodes of Pneumocystis carinii pneumonia presented with diarrhea and fever. Despite antibiotic treatment, septic shock developed, and she died 3 weeks after the symptoms began. Histologic and histochemical studies revealed an anergic toxoplasmosis with dissemination in all examined organs. There were multiple foci of toxoplasmic cysts and free tachyzoites, sometimes with minute areas of necrosis, but no inflammatory reaction at all. Since effective treatment of toxoplasmosis is available, the occurrence of this rare form of toxoplasmosis should be kept in mind.

[Carcinosarcoma of the urinary bladder]. / Zum Karzinosarkom der Harnblase.

A female patient is presented who had a large carcinosarcoma of the urinary bladder that became clinically manifest only 2 months before treatment. The initial treatment by transurethral resection was followed by radical cystectomy; 7 months postoperatively the patient died of local tumour recurrence with widespread metastases. Carcinosarcoma of the urinary bladder is a rare tumour with a poor prognosis. The majority of such tumours are not diagnosed until tumour growth is already far advanced. Owing to the small number of cases there is no clinically proven form of management. In contrast with superficial transitional cell carcinoma of the bladder, superficial carcinosarcoma of the bladder has always invaded the lamina propria, since in addition to the carcinomatous degeneration of the mucosa, sarcomatous degeneration of the underlying submucosal stroma is also present. Any local surgical treatment, such as TUR or partial cystectomy, involves the risk of incomplete tumor removal, because the sarcomatous elements typically invade the submucosa while the overlying mucosa remains intact. Therefore, radical cystectomy appears to be the treatment of choice for both superficial and invasive carcinosarcoma of the urinary bladder.