An Incidence of Multi-Year Sediment Storage on Channel Snowpack in the Canadian High Arctic

During June 2005, we identified the presence of sediment buried within multi-year channel snowpack of a small river located near Cape Bounty, Melville Island, Nunavut (74°55' N, 109°35' W). Photographic evidence indicates that the sediment was deposited during the 2003 season by the initial meltwater flowing on the snowpack, which was dammed by snow upstream of a channel constriction. The resulting pond covered a minimum area of 180 m2 and contained an estimated minimum 27 Mg of sediment. Suspended sediment measurements during the 2003 season indicate that deposition on the snowpack at this location represented 49%–65% of the sediment transport prior to the ponding and emplacement of the sediment on the snow, and approximately 20% of the measured sediment flux for the entire season. Multi-year snow accumulations immediately downstream exhibited similar sediment deposition on snow, but no evidence of multi-year sediment storage was present. By contrast, a similar stream in an adjacent watershed channelized rapidly, with minimal sediment deposition on the snow, and delivered a large pulse of sediment to the downstream lake. These results provide quantitative evidence for the magnitude of sediment storage on snowpack and point to the unique role that snow plays in the fluvial geomorphology of High Arctic watersheds.En juin 2005, nous avons dénoté la présence de sédiment enterré dans une plaque de neige datant de plusieurs années d’une petite rivière située près de cap Bounty, sur l’île Melville, au Nunavut (74°55' N, 109°35' O). D’après des preuves photographiques, le sédiment a été déposé pendant la saison 2003 par l’eau de fusion initiale s’écoulant sur la plaque de neige, qui avait été endiguée par la neige en amont d’un canal confiné. L’étang qui en a découlé recouvrait une aire minimale de 180 m2 et contenait, selon les estimations, au moins 27 Mg de sédiment. Les mesures de sédiment en suspension pendant la saison 2003 indiquent que ce dépôt sur la plaque de neige à cet endroit représentait entre 49 % et 65 % du transport de sédiment avant l’accumulation d’eau et l’emplacement de sédiment sur la neige, et environ 20 % du flux de sédiment mesuré pour toute la saison. Les accumulations de neige de plusieurs années immédiatement en aval comptaient des dépôts de sédiment semblables sur la neige, quoi qu’aucun emmagasinage de sédiment sur plusieurs années n’était présent. Par contraste, un cours d’eau similaire d’un bassin hydrographique adjacent s’est canalisé rapidement, avec peu de dépôts de sédiment sur la neige, puis a laissé une grande quantité de sédiment au lac en aval. Ces résultats fournissent des preuves quantitatives quant à l’ampleur de l’emmagasinage de sédiment sur la plaque de neige et laissent envisager le rôle unique que joue la neige sur la géomorphologie fluviale des bassins hydrographiques de l’Extrême-Arctique

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Seasonal fluxes and age of particulate organic carbon exported from Arctic catchments impacted by localized permafrost slope disturbances

Projected warming is expected to alter the Arctic permafrost regime with potential impacts on hydrological fluxes of particulate organic carbon (POC) and sediment. Previous work has focused on large Arctic basins and revealed the important contribution of old carbon in river POC, but little is known about POC fluxes from smaller coastal watersheds, particularly where widespread postglacial raised marine sediments represent a potential source of old soil carbon that could be mobilized by permafrost disturbance. To evaluate these processes, the characteristics of POC, particulate nitrogen (PN) and suspended sediment transport from paired small coastal Arctic watersheds subject to recent permafrost disturbance were investigated at the Cape Bounty Arctic Watershed Observatory (CBAWO) in the Canadian High Arctic. Approximately 2% of the total suspended sediment load from both watersheds was composed of POC and the majority of the sediment and POC fluxes occurred during the spring snowmelt period. Radiocarbon analysis of POC indicates recent permafrost disturbances deliver substantially older POC to the aquatic system. Localized permafrost slope disturbances have a measurable influence on downstream POC age and dominate (estimated up to 78% of POC) sediment fluxes during summer baseflow. The elevation of disturbances and Holocene emergence data show limited age sensitivity of POC to the location of disturbance and suggest slope failures are likely to deliver carbon with a relatively similar age range to the aquatic system, regardless of landscape location

Active layer slope disturbances affect seasonality and composition of dissolved nitrogen export from High Arctic headwater catchments

This study investigates the impacts of active layer detachments (ALDs) on nitrogen in seasonal runoff from High Arctic hillslope catchments. We examined dissolved nitrogen in runoff from an undisturbed catchment (Goose; GS) and one that was disturbed (Ptarmigan; PT) by ALDs, prior to disturbance (2007) and five years after disturbance (2012). The seasonal dynamics of N species concentrations and fluxes were similar in both catchments in 2007, but the mean seasonal nitrate concentration and mass flux from the disturbed catchment were on the order of 30 times higher relative to the undisturbed catchment in 2012. Stormflow yielded 45% and 60% of the 2012 TDN flux in GS and PT, respectively, although rainfall runoff provided less than 25% of seasonal discharge. Results support that through the combined effects of increased disturbance and rainfall, climate change stands to significantly enhance the export of nitrate from High Arctic watersheds. This study highlights that the increase in the delivery of nitrate from disturbance is especially pronounced late in the season when downstream productivity and the biological demand for this often limiting nutrient is high. Our results also demonstrate that the impact of ALDs on nitrate export can persist more than five years following disturbance.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Multi-year impacts of permafrost disturbance and thermal perturbation on High Arctic stream chemistry

Permafrost disturbances (such as active layer detachment (ALD) slides) and thermal perturbation (deep ground thaw from high soil temperatures) alters Arctic surface water chemistry. However, the potential multi-year impacts on water chemistry and the ultimate recovery time are not well understood. This study evaluates the impacts and recovery following disturbance of a High Arctic catchment in 2007 from ALDs. We measured ion concentrations and stable isotopes in surface waters collected between 2006 and 2014 from paired catchments - one disturbed and the other not. 2007 and 2012 were exceptionally warm and represent unusual thermal perturbation for both catchments. Results indicate that the exposure and mobilization of soluble ions in near surface soil is a key control over dissolved ion concentrations and composition following ALDs. Runoff in the disturbed catchment shows increased total dissolved solute (TDS) concentrations and seasonal TDS fluxes, and changes to the composition of individual ions. These impacts persist seven years after disturbance, and are consistent with the thawing of the solute-rich transient layer and upper permafrost. Thermal perturbation increased TDS concentrations and seasonal fluxes in runoff for up to two years as ions released from ground thaw appear to be available for flushing in subsequent summers.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Redistribution of soil organic matter by permafrost disturbance in the Canadian High Arctic

This is an accepted manuscript of a published article.With increased warming in the Arctic, permafrost thaw may induce localized physical disturbance of slopes. These disturbances, referred to as active layer detachments (ALDs), redistribute soil across the landscape, potentially releasing previously unavailable carbon (C). In 2007–2008, widespread ALD activity was reported at the Cape Bounty Arctic Watershed Observatory in Nunavut, Canada. Our study investigated organic matter (OM) composition in soil profiles from ALD-impacted and undisturbed areas. Solid-state 13C nuclear magnetic resonance (NMR) and solvent-extractable biomarkers were used to characterize soil OM. Throughout the disturbed upslope profile, where surface soils and vegetation had been removed, NMR revealed low O-alkyl C content and biomarker analysis revealed low concentrations of solvent-extractable compounds suggesting enhanced erosion of labile-rich OM by the ALD. In the disturbed downslope region, vegetation remained intact but displaced material from upslope produced lateral compression ridges at the surface. High O-alkyl content in the surface horizon was consistent with enrichment of carbohydrates and peptides, but low concentrations of labile biomarkers (i.e., sugars) suggested the presence of relatively unaltered labile-rich OM. Decreased O-alkyl content and biomarker concentrations below the surface contrasted with the undisturbed profile and may indicate the loss of well-established pre-ALD surface drainage with compression ridge formation. However, pre-ALD profile composition remains unknown and the observed decreases may result from nominal pre-ALD OM inputs. These results are the first to establish OM composition in ALD-impacted soil profiles, suggesting reallocation of permafrost-derived soil C to areas where degradation or erosion may contribute to increased C losses from disturbed Arctic soils

An Incidence of Multi-Year Sediment Storage on Channel Snowpack in the Canadian High Arctic

During June 2005, we identified the presence of sediment buried within multi-year channel snowpack of a small river located near Cape Bounty, Melville Island, Nunavut (74°55' N, 109°35' W). Photographic evidence indicates that the sediment was deposited during the 2003 season by the initial meltwater flowing on the snowpack, which was dammed by snow upstream of a channel constriction. The resulting pond covered a minimum area of 180 m2 and contained an estimated minimum 27 Mg of sediment. Suspended sediment measurements during the 2003 season indicate that deposition on the snowpack at this location represented 49%–65% of the sediment transport prior to the ponding and emplacement of the sediment on the snow, and approximately 20% of the measured sediment flux for the entire season. Multi-year snow accumulations immediately downstream exhibited similar sediment deposition on snow, but no evidence of multi-year sediment storage was present. By contrast, a similar stream in an adjacent watershed channelized rapidly, with minimal sediment deposition on the snow, and delivered a large pulse of sediment to the downstream lake. These results provide quantitative evidence for the magnitude of sediment storage on snowpack and point to the unique role that snow plays in the fluvial geomorphology of High Arctic watersheds.En juin 2005, nous avons dénoté la présence de sédiment enterré dans une plaque de neige datant de plusieurs années d’une petite rivière située près de cap Bounty, sur l’île Melville, au Nunavut (74°55' N, 109°35' O). D’après des preuves photographiques, le sédiment a été déposé pendant la saison 2003 par l’eau de fusion initiale s’écoulant sur la plaque de neige, qui avait été endiguée par la neige en amont d’un canal confiné. L’étang qui en a découlé recouvrait une aire minimale de 180 m2 et contenait, selon les estimations, au moins 27 Mg de sédiment. Les mesures de sédiment en suspension pendant la saison 2003 indiquent que ce dépôt sur la plaque de neige à cet endroit représentait entre 49 % et 65 % du transport de sédiment avant l’accumulation d’eau et l’emplacement de sédiment sur la neige, et environ 20 % du flux de sédiment mesuré pour toute la saison. Les accumulations de neige de plusieurs années immédiatement en aval comptaient des dépôts de sédiment semblables sur la neige, quoi qu’aucun emmagasinage de sédiment sur plusieurs années n’était présent. Par contraste, un cours d’eau similaire d’un bassin hydrographique adjacent s’est canalisé rapidement, avec peu de dépôts de sédiment sur la neige, puis a laissé une grande quantité de sédiment au lac en aval. Ces résultats fournissent des preuves quantitatives quant à l’ampleur de l’emmagasinage de sédiment sur la plaque de neige et laissent envisager le rôle unique que joue la neige sur la géomorphologie fluviale des bassins hydrographiques de l’Extrême-Arctique

Diversity, Abundance, and Potential Activity of Nitrifying and Nitrate-Reducing Microbial Assemblages in a Subglacial Ecosystem

Subglacial sediments sampled from beneath Robertson Glacier (RG), Alberta, Canada, were shown to harbor diverse assemblages of potential nitrifiers, nitrate reducers, and diazotrophs, as assessed by amoA, narG, and nifH gene biomarker diversity. Although archaeal amoA genes were detected, they were less abundant and less diverse than bacterial amoA, suggesting that bacteria are the predominant nitrifiers in RG sediments. Maximum nitrification and nitrate reduction rates in microcosms incubated at 4°C were 280 and 18.5 nmol of N per g of dry weight sediment per day, respectively, indicating the potential for these processes to occur in situ. Geochemical analyses of subglacial sediment pore waters and bulk subglacial meltwaters revealed low concentrations of inorganic and organic nitrogen compounds. These data, when coupled with a C/N atomic ratio of dissolved organic matter in subglacial pore waters of ∼210, indicate that the sediment communities are N limited. This may reflect the combined biological activities of organic N mineralization, nitrification, and nitrate reduction. Despite evidence of N limitation and the detection of nifH, we were unable to detect biological nitrogen fixation activity in subglacial sediments. Collectively, the results presented here suggest a role for nitrification and nitrate reduction in sustaining microbial life in subglacial environments. Considering that ice currently covers 11% of the terrestrial landmass and has covered significantly greater portions of Earth at times in the past, the demonstration of nitrification and nitrate reduction in subglacial environments furthers our understanding of the potential for these environments to contribute to global biogeochemical cycles on glacial-interglacial timescales