Arctic rivers transport huge quantities of dissolved organic carbon (DOC) to the Arctic Ocean. The prevailing paradigm is that DOC in arctic rivers is refractory and therefore of little significance ...for the biogeochemistry of the Arctic Ocean. We show that there is substantial seasonal variability in the lability of DOC transported by Alaskan rivers to the Arctic Ocean: little DOC is lost during incubations of samples collected during summer, but substantial losses (20–40%) occur during incubations of samples collected during the spring freshet when the majority of the annual DOC flux occurs. We speculate that restricting sampling to summer may have biased past studies. If so, then fluvial inputs of DOC to the Arctic Ocean may have a much larger influence on coastal ocean biogeochemistry than previously realized, and reconsideration of the role of terrigenous DOC on carbon, microbial, and food‐web dynamics on the arctic shelf will be warranted.
Rapidly, increasing air temperatures across the Arctic are thawing permafrost and exposing vast quantities of organic carbon, nitrogen, and phosphorus to microbial processing. Shifts in the absolute ...and relative supplies of these elements will likely alter patterns of ecosystem productivity and change the way carbon and nutrients are delivered from upland areas to surface waters such as rivers and lakes. The ultra‐oligotrophic nature of surface waters across the Arctic renders these ecosystems particularly susceptible to changes in productivity and food web dynamics as permafrost thaw alters terrestrial‐aquatic linkages. The objectives of this study were to evaluate decadal‐scale patterns in surface water chemistry and assess potential implications of changing water chemistry to benthic organic matter and aquatic food webs. Data were collected from the upper Kuparuk River on the North Slope of Alaska by the U.S. National Science Foundation's Long‐Term Ecological Research program during 1978–2014. Analyses of these data show increases in stream water alkalinity and cation concentrations consistent with signatures of permafrost thaw. Changes are also documented for discharge‐corrected nitrate concentrations (+), discharge‐corrected dissolved organic carbon concentrations (−), total phosphorus concentrations (−), and δ13C isotope values of aquatic invertebrate consumers (−). These changes show that warming temperatures and thawing permafrost in the upland environment are leading to shifts in the supply of carbon and nutrients available to surface waters and consequently changing resources that support aquatic food webs. This demonstrates that physical, geochemical, and biological changes associated with warming permafrost are fundamentally altering linkages between upland and aquatic ecosystems in rapidly changing arctic environments.
Rapidly increasing temperatures across the Arctic are thawing permafrost soils and changing the way carbon and nutrients are delivered from upland areas to surface waters such as rivers and lakes. Analysis of long‐term data from Arctic Alaska show increases in stream water alkalinity and cation concentrations consistent with signatures of permafrost thaw. Changes are also documented for concentrations of nitrate (+),dissolved organic carbon (−), and total phosphorus (−), as well as δ13C isotope values of aquatic invertebrates (−). These changes show that warming temperatures and thawing permafrost are leading to shifts in the supply of carbon and nutrients to aquatic ecosystems and consequently changing resources that support aquatic food webs.
Terrestrial carbon dynamics influence the contribution of dissolved organic carbon (DOC) to river networks in addition to hydrology. In this study, we use a biogeochemical process model to simulate ...the lateral transfer of DOC from land to the Arctic Ocean via riverine transport. We estimate that, over the 20th century, the pan-Arctic watershed has contributed, on average, 32 Tg C/yr of DOC to river networks emptying into the Arctic Ocean with most of the DOC coming from the extensive area of boreal deciduous needle-leaved forests and forested wetlands in Eurasian watersheds. We also estimate that the rate of terrestrial DOC loading has been increasing by 0.037 Tg C/yr
2
over the 20th century primarily as a result of climate-induced increases in water yield. These increases have been offset by decreases in terrestrial DOC loading caused by wildfires. Other environmental factors (CO
2
fertilization, ozone pollution, atmospheric nitrogen deposition, timber harvest, agriculture) are estimated to have relatively small effects on terrestrial DOC loading to Arctic rivers. The effects of the various environmental factors on terrestrial carbon dynamics have both offset and enhanced concurrent effects on hydrology to influence terrestrial DOC loading and may be changing the relative importance of terrestrial carbon dynamics on this carbon flux. Improvements in simulating terrestrial DOC loading to pan-Arctic rivers in the future will require better information on the production and consumption of DOC within the soil profile, the transfer of DOC from land to headwater streams, the spatial distribution of precipitation and its temporal trends, carbon dynamics of larch-dominated ecosystems in eastern Siberia, and the role of industrial organic effluents on carbon budgets of rivers in western Russia.
Purpose Follicular lymphoma (FL) is an indolent cancer, with effective but rarely curative treatment options. As a standard study end point for first-line FL therapy, progression-free survival (PFS) ...requires extended follow-up (median PFS, > 7 years). To provide patients with earlier access to newer therapies, an earlier end point to expedite clinical trials is needed. Our objective was to formally assess the complete response rate at 30 months (CR30) after initiation of induction therapy as a potential surrogate end point for PFS in first-line FL therapy. Patients and Methods We analyzed individual patient data from 13 randomized multicenter trials of induction and maintenance regimens in first-line FL therapy published after 1990 and with sufficient data to evaluate whether CR30 could predict treatment effects on PFS. Correlation of the CR30 odds ratio with the PFS hazard ratio was evaluated by both linear regression (R
) and bivariate copula (R
) models. Prespecified criteria for surrogacy required either R
or R
≥ 0.80, with a lower-bound 95% CI > 0.60. Results Data from eight induction and five maintenance randomized trials in 3,837 evaluable patients were analyzed. The prespecified surrogacy threshold was met, with an R
of 0.88 (95% CI, 0.77 to 0.96) and an R
of 0.86 (95% CI, 0.72 to 1.00). Multiple sensitivity and supplemental analyses supported the robustness of the findings. A minimum 11% absolute improvement in CR30 from a 50% control rate predicted a significant treatment effect on PFS (hazard ratio, 0.69). Conclusion This large, prospective, pooled analysis of randomized chemotherapy, immunotherapy, and chemoimmunotherapy trials demonstrates that CR30 is a surrogate end point for PFS in first-line FL treatment trials. Use of this end point may expedite therapeutic development with the intent of bringing novel therapies to this patient population years before PFS results are mature.
While much of the dissolved organic carbon (DOC) within rivers is destined for mineralization to CO2, a substantial fraction of riverine bicarbonate (HCO3−) flux represents a CO2 sink, as a result of ...weathering processes that sequester CO2 as HCO3−. We explored landscape‐level controls on DOC and HCO3− flux in subcatchments of the boreal, with a specific focus on the effect of permafrost on riverine dissolved C flux. To do this, we undertook a multivariate analysis that partitioned the variance attributable to known, key regulators of dissolved C flux (runoff, lithology, and vegetation) prior to examining the effect of permafrost, using riverine biogeochemistry data from a suite of subcatchments drawn from the Mackenzie, Yukon, East, and West Siberian regions of the circumboreal. Across the diverse catchments that we study, controls on HCO3−flux were near‐universal: runoff and an increased carbonate rock contribution to weathering (assessed as riverwater Ca:Na) increased HCO3− yields, while increasing permafrost extent was associated with decreases in HCO3−. In contrast, permafrost had contrasting and region‐specific effects on DOC yield, even after the variation caused by other key drivers of its flux had been accounted for. We used ionic ratios and SO4 yields to calculate the potential range of CO2sequestered via weathering across these boreal subcatchments, and show that decreasing permafrost extent is associated with increases in weathering‐mediated CO2 fixation across broad spatial scales, an effect that could counterbalance some of the organic C mineralization that is predicted with declining permafrost.
Key Points
Controls on bicarbonate flux from boreal catchments are near universal
River HCO3, and CO2 fixed via weathering, decrease with increasing permafrost
Permafrost has a region‐specific effect on DOC flux from boreal catchments
Castleman disease Dham, Anu; Peterson, Bruce A
Current opinion in hematology,
2007-July, Letnik:
14, Številka:
4
Journal Article
PURPOSE OF REVIEWCastleman disease was initially described over 50 years ago as a benign localized mass of lymph nodes found primarily in the mediastinum of asymptomatic patients. Subsequently, ...additional types were recognized that extend the spectrum of this heterogeneous group of diseases. Optimal standard therapies have not been established. Currently, most patients receive treatments derived from past experience with non-Hodgkin lymphoma that are not altogether satisfactory.
RECENT FINDINGSAdvances in understanding the biological basis of Castleman disease have provided new targets for therapeutic exploitation. Recognition of the role of interleukin-6 in disease perpetuation has led to the use of an antihuman interleukin-6 receptor monoclonal antibody, tocilizumab. Rituximab, an anti-CD20 monoclonal antibody, targets CD20-positive B lymphocytes, a prominent component of this disorder. Human herpes virus-8 and angiogenesis, both involved in the pathogenesis of Castleman disease, may provide additional unique therapeutic opportunities.
SUMMARYRational approaches to the treatment of Castleman disease have begun to have an impact on disease management; however, the role of these new agents remains to be established. As the complexity of Castleman disease is more fully understood, additional targets for new innovative therapies undoubtedly will be identified.
Luminosity functions and their integrated luminosity densities are presented for the 6-degree Field Galaxy Survey (6dFGS). This ongoing survey ultimately aims to measure around 150 000 redshifts and ...15 000 peculiar velocities over almost the entire southern sky at |b| > 10°. The main target samples are taken from the 2-Micron All-Sky Survey (2MASS) Extended Source Catalog and the SuperCOSMOS Sky Survey catalogue, and comprise 138 226 galaxies complete to (K, H, J, rF, bJ) = (12.75, 13.00, 13.75, 15.60, 16.75). These samples are comparable in size to the optically selected Sloan Digital Sky Survey and 2-degree Field Galaxy Redshift Survey (2dFGRS) samples, and improve on recent near-infrared-selected redshift surveys by more than an order of magnitude in both number and sky coverage. The partial samples used in this paper contain a little over half of the total sample in each band and are ∼90 per cent complete. Luminosity distributions are derived using the 1/Vmax, Sandage–Tammann–Yahil (STY) and step-wise maximum likelihood (SWML) estimators, and probe 1–2 absolute magnitudes fainter in the near-infrared than previous surveys. The effects of magnitude errors, redshift incompleteness and peculiar velocities have been taken into account and corrected throughout. Generally, the 6dFGS luminosity functions are in excellent agreement with those of similarly sized surveys. Our data are of sufficient quality to demonstrate that a Schechter function is not an ideal fit to the true luminosity distribution, due to its inability to simultaneously match the faint-end slope and rapid bright-end decline. Integrated luminosity densities from the 6dFGS are consistent with an old stellar population and moderately declining star formation rate.
Circumpolar synchrony in big river bacterioplankton Crump, Byron C; Peterson, Bruce J; Raymond, Peter A ...
Proceedings of the National Academy of Sciences - PNAS,
12/2009, Letnik:
106, Številka:
50
Journal Article
Recenzirano
Odprti dostop
Natural bacterial communities are extremely diverse and highly dynamic, but evidence is mounting that the compositions of these communities follow predictable temporal patterns. We investigated these ...patterns with a 3-year, circumpolar study of bacterioplankton communities in the six largest rivers of the pan-arctic watershed (Ob', Yenisey, Lena, Kolyma, Yukon, and Mackenzie), five of which are among Earth's 25 largest rivers. Communities in the six rivers shifted synchronously over time, correlating with seasonal shifts in hydrology and biogeochemistry and clustering into three groups: winter/spring, spring freshet, and summer/fall. This synchrony indicates that hemisphere-scale variation in seasonal climate sets the pace of variation in microbial diversity. Moreover, these seasonal communities reassembled each year in all six rivers, suggesting a long-term, predictable succession in the composition of big river bacterioplankton communities.
Several recent publications have documented changes in river discharge from arctic and subarctic watersheds. Comparison of these findings, however, has been hampered by differences in time periods ...and methods of analysis. Here we compare changes in discharge from different regions of the pan‐arctic watershed using identical time periods and analytical methods. Discharge to the Arctic Ocean increased by 5.6 km3/y/y during 1964–2000, the net result of a large increase from Eurasia moderated by a small decrease from North America. In contrast, discharge to Hudson/James/Ungava Bays decreased by 2.5 km3/y/y during 1964–2000. While this evaluation identifies an overall increase in discharge (∼120 km3/y greater discharge at the end of the time period as compared to the beginning for Hudson/James/Unvaga Bays and the Arctic Ocean combined), the contrasting regional trends also highlight the need to understand the consequences of adding/removing freshwater from particular regions of the arctic and subarctic oceans.
Synthesis of river-monitoring data reveals that the average annual discharge of fresh water from the six largest Eurasian rivers to the Arctic Ocean increased by 7% from 1936 to 1999. The average ...annual rate of increase was 2.0 ± 0.7 cubic kilometers per year. Consequently, average annual discharge from the six rivers is now about 128 cubic kilometers per year greater than it was when routine measurements of discharge began. Discharge was correlated with changes in both the North Atlantic Oscillation and global mean surface air temperature. The observed large-scale change in freshwater flux has potentially important implications for ocean circulation and climate.
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