332 research outputs found
A circumpolar perspective on fluvial sediment flux to the Arctic ocean
Quantification of sediment fluxes from rivers is fundamental to understanding landâocean linkages in the Arctic. Numerous publications have focused on this subject over the past century, yet assessments of temporal trends are scarce and consensus on contemporary fluxes is lacking. Published estimates vary widely, but often provide little accessory information needed to interpret the differences. We present a panâarctic synthesis of sediment flux from 19 arctic rivers, primarily focusing on contributions from the eight largest ones. For this synthesis, historical records and recent unpublished data were compiled from Russian, Canadian, and United States sources. Evaluation of these data revealed no longâterm trends in sediment flux, but did show stepwise changes in the historical records of two of the rivers. In some cases, old values that do not reflect contemporary fluxes are still being reported, while in other cases, typographical errors have been propagated into the recent literature. Most of the discrepancy among published estimates, however, can be explained by differences in years of records examined and gauging stations used. Variations in sediment flux from year to year in arctic rivers are large, so estimates based on relatively few years can differ substantially. To determine best contemporary estimates of sediment flux for the eight largest arctic rivers, we used a combination of newly available data, historical records, and literature values. These estimates contribute to our understanding of carbon, nutrient, and contaminant transport to the Arctic Ocean and provide a baseline for detecting future anthropogenic or natural change in the Arctic
Coordination and Sustainability of River Observing Activities in the Arctic
To understand and respond to changes in the worldâs northern regions, we need a coordinated system of long-term Arctic observations. River networks naturally integrate across landscapes and link the terrestrial and ocean domains. Changes in river discharge reflect changes in the terrestrial water balance, whereas changes in water chemistry are linked to changes in biogeochemical processes and water flow paths. Sustained measurements of river water discharge and water chemistry are therefore essential components of an Arctic observing network. As we strive to establish and sustain long-term observations in the Arctic, these two measurements must be coupled. Although river discharge and chemistry measurements are already coupled to some extent within national boundaries, this is not done in a consistent and coordinated fashion across the pan-Arctic domain. As a consequence, data quality and availability vary widely among regions. International coordination of river discharge and chemistry measurements in the Arctic would be greatly facilitated by formal commitments to maintain a set of core sites and associated measurements that are mutually agreed upon among pan-Arctic nations. Involvement of the agencies currently operating river discharge gauges around the Arctic and establishment of an overarching coordination entity to implement shared protocols, track data quality, and manage data streams would be essential in this endeavor. Focused studies addressing scale-dependent relationships between watershed characteristics and water chemistry, in-stream processes, and estuarine and coastal dynamics are also needed to support interpretation and application of Arctic river observing data as they relate to land and ocean change
Development of tandem cells consisting of GaAs single crystal and CuInSe2/CdZnS polycrystalline thin films
The tandem cells consisting of GaAs single crystal and CuInSe2 polycrystalline thin films are being developed under the joint program of the Boeing Co. and Kopin Corp. to meet the increasing power needs for future spacecraft. The updated status of this program is presented along with experimental results such as cell performance, and radiation resistance. Other cell characteristics including the specific power of and the interconnect options for this tandem cell approach are also discussed
Differentiating Writing Inks Using Direct Analysis in Real Time Mass Spectrometry
Writing ink analysis is used in establishing document authenticity and the sources and relative ages of written entries. Most analytical methods require removing samples or visibly altering the document. Nondestructive, in situ analysis of writing inks on paper without visible alteration is possible using mass spectrometry with a new ion source called Direct Analysis in Real Time. Forty-three different black and blue ballpoint, black fluid, and black gel inks were examined. Both dyes and persistent but thermally labile components of the inks contribute to the mass spectra, principally as protonated molecules [M1H]1. Numerous ink components were identified from the spectra. The spectra were placed in a searchable library, which was then challenged with two spectra from each of the 43 inks. The best match for each of the challenge spectra was correct for all but one ink, which matched with a very similar ink by the same manufacturer
Coordination and Sustainability of River Observing Activities in the Arctic
To understand and respond to changes in the worldâs northern regions, we need a coordinated system of long-term Arctic observations. River networks naturally integrate across landscapes and link the terrestrial and ocean domains. Changes in river discharge reflect changes in the terrestrial water balance, whereas changes in water chemistry are linked to changes in biogeochemical processes and water flow paths. Sustained measurements of river water discharge and water chemistry are therefore essential components of an Arctic observing network. As we strive to establish and sustain long-term observations in the Arctic, these two measurements must be coupled. Although river discharge and chemistry measurements are already coupled to some extent within national boundaries, this is not done in a consistent and coordinated fashion across the pan-Arctic domain. As a consequence, data quality and availability vary widely among regions. International coordination of river discharge and chemistry measurements in the Arctic would be greatly facilitated by formal commitments to maintain a set of core sites and associated measurements that are mutually agreed upon among pan-Arctic nations. Involvement of the agencies currently operating river discharge gauges around the Arctic and establishment of an overarching coordination entity to implement shared protocols, track data quality, and manage data streams would be essential in this endeavor. Focused studies addressing scale-dependent relationships between watershed characteristics and water chemistry, in-stream processes, and estuarine and coastal dynamics are also needed to support interpretation and application of Arctic river observing data as they relate to land and ocean change.Pour comprendre les changements qui sâopĂšrent dans les rĂ©gions nordiques du monde et y rĂ©agir, nous devons nous doter dâun systĂšme coordonnĂ© dâobservation Ă long terme dans lâArctique. Les rĂ©seaux fluviaux sâintĂšgrent naturellement dans les paysages et relient le domaine terrestre au domaine ocĂ©anique. Les changements qui sâexercent dans les rĂ©seaux fluviaux sont le reflet des changements dans lâĂ©quilibre hydrique terrestre, tandis que les changements qui sâexercent sur lâhydrochimie sont liĂ©s aux changements caractĂ©risant les processus biogĂ©ochimiques et les parcours dâĂ©coulement de lâeau. Par consĂ©quent, un rĂ©seau dâobservation arctique devrait essentiellement ĂȘtre assorti de mesures durables dâĂ©vacuation des eaux fluviales et dâhydrochimie. Au moment oĂč nous nous efforçons dâĂ©tablir et de soutenir des observations Ă long terme dans lâArctique, ces deux types de mesures doivent ĂȘtre suivies en parallĂšle. Bien que les mesures de lâĂ©vacuation fluviale et les mesures chimiques soient dĂ©jĂ , dans une certaine mesure, suivies en parallĂšle Ă lâintĂ©rieur des frontiĂšres nationales, cela ne se fait pas de maniĂšre uniforme et coordonnĂ©e Ă la grandeur du domaine panarctique, et en consĂ©quence, la qualitĂ© et la disponiÂbilitĂ© des donnĂ©es varient beaucoup dâune rĂ©gion Ă lâautre. La coordination internationale des mesures dâĂ©vacuation fluviale et chimiques dans lâArctique serait grandement facilitĂ©e par lâexistence dâengagements officiels visant Ă maintenir une sĂ©rie dâemplacements fondamentaux et de mesures connexes fixĂ©es par entente mutuelle au sein des nations panarctiques. La particÂipation des agences qui gĂšrent les manomĂštres dâĂ©vacuation fluviale dans lâArctique et lâĂ©tablissement dâune entitĂ© de coordiÂnation gĂ©nĂ©rale mettant en oeuvre des protocoles partagĂ©s, vĂ©rifiant la qualitĂ© des donnĂ©es et gĂ©rant les flux de donnĂ©es seraient Ă©galement essentiels. Des Ă©tudes ciblĂ©es portant sur les relations influencĂ©es par lâĂ©chelle entre les caractĂ©ristiques du bassin hydrographique et lâhydrochimie, sur les processus sâopĂ©rant Ă lâintĂ©rieur des cours dâeau et sur la dynamique des estuaires et des rives sâavĂšrent Ă©galement nĂ©cessaires pour Ă©tayer lâinterprĂ©tation et lâapplication des donnĂ©es dâobservation fluviale de lâArctique en matiĂšre de changement terrestre et ocĂ©anique
Recent changes in nitrate and dissolved organic carbon export from the upper Kuparuk River, North Slope, Alaska
Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): G04S60, doi:10.1029/2006JG000371.Export of nitrate and dissolved organic carbon (DOC) from the upper Kuparuk River between the late 1970s and early 2000s was evaluated using long-term ecological research (LTER) data in combination with solute flux and catchment hydrology models. The USGS Load Estimator (LOADEST) was used to calculate JuneâAugust export from 1978 forward. LOADEST was then coupled with a catchment-based land surface model (CLSM) to estimate total annual export from 1991 to 2001. Simulations using the LOADEST/CLSM combination indicate that annual nitrate export from the upper Kuparuk River increased by ~5 fold and annual DOC export decreased by about one half from 1991 to 2001. The decrease in DOC export was focused in May and was primarily attributed to a decrease in river discharge. In contrast, increased nitrate export was evident from May to September and was primarily attributed to increased nitrate concentrations. Increased nitrate concentrations are evident across a wide range of discharge conditions, indicating that higher values do not simply reflect lower discharge in recent years but a significant shift to higher concentration per unit discharge. Nitrate concentrations remained elevated after 2001. However, extraordinarily low discharge during June 2004 and JuneâAugust 2005 outweighed the influence of higher concentrations in determining export during these years. The mechanism responsible for the recent increase in nitrate concentrations is uncertain but may relate to changes in soils and vegetation associated with regional warming. While changes in nitrate and DOC export from arctic rivers reflect changes in terrestrial ecosystems, they also have significant implications for Arctic Ocean ecosystems.This work was supported by the Arctic
System Science Program of the National Science Foundation (OPP-
0436118) and by NSF funding for the Arctic LTER through a series of
grants from 1987 to present
Trajectory shifts in the Arctic and Subarctic freshwater cycle
Author Posting. © The Author(s), 2006. This is the author's version of the work. It is posted here by permission of American Association for the Advancement of Science for personal use, not for redistribution. The definitive version was published in Science 313 (2006): 1061-1066, doi:10.1126/science.1122593.Manifold changes in the freshwater cycle of high-latitude lands and oceans have
been reported in the past few years. A synthesis of these changes in sources of freshwater and in ocean freshwater storage illustrates the complementary and synoptic temporal pattern and magnitude of these changes over the past 50 years. Increasing river discharge anomalies and excess net precipitation on the ocean contributed ~20,000 km3 of fresh water to the Arctic and high latitude North Atlantic oceans from lows in the 1960s to highs in the 1990s. Sea ice attrition provided another ~15,000 km3, and glacial melt added ~2000 km3.
The sum of anomalous inputs from these freshwater sources matched the amount and rate at which fresh water accumulated in the North Atlantic during much of the period from
1965 through 1995. The changes in freshwater inputs and ocean storage occurred in
conjunction with the amplifying North Atlantic Oscillation and rising air temperatures.
Fresh water may now be accumulating in the Arctic Ocean and will likely be exported
southward if and when the North Atlantic Oscillation enters into a new high phase.Funding was provided by
NSF (grants OPP-0229302, OPP- 0436118, OPP-0327664, OPP-0352754, OPP-0519840, OCE-
0326778), ONR (grant N00014-02-1-0305) and NASA (grant IDS-03-0000-0145)
River export of nutrients and organic matter from the North Slope of Alaska to the Beaufort Sea
Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Water Resources Research 50 (2014): 1823â1839, doi:10.1002/2013WR014722.While river-borne materials are recognized as important resources supporting coastal ecosystems around the world, estimates of river export from the North Slope of Alaska have been limited by a scarcity of water chemistry and river discharge data. This paper quantifies water, nutrient, and organic matter export from the three largest rivers (Sagavanirktok, Kuparuk, and Colville) that drain Alaska's North Slope and discusses the potential importance of river inputs for biological production in coastal waters of the Alaskan Beaufort Sea. Together these rivers export âŒ297,000 metric tons of organic carbon and âŒ18,000 metric tons of organic nitrogen each year. Annual fluxes of nitrate-N, ammonium-N, and soluble reactive phosphorus are approximately 1750, 200, and 140 metric tons per year, respectively. Constituent export from Alaska's North Slope is dominated by the Colville River. This is in part due to its larger size, but also because constituent yields are greater in the Colville watershed. River-supplied nitrogen may be more important to productivity along the Alaskan Beaufort Sea coast than previously thought. However, given the dominance of organic nitrogen export, the potential role of river-supplied nitrogen in support of primary production depends strongly on remineralization mechanisms. Although rivers draining the North Slope of Alaska make only a small contribution to overall river export from the pan-arctic watershed, comparisons with major arctic rivers reveal unique regional characteristics as well as remarkable similarities among different regions and scales. Such information is crucial for development of robust river export models that represent the arctic system as a whole.Funding for this project was
provided by a grant from the National
Science Foundation Office of Polar
Programs (NSF-OPP-0436118) as part
of the Arctic System Science (ARCSS)
Study of the Northern Alaska Coastal
System (SNACS) effort.2014-08-2
A pan-arctic evaluation of changes in river discharge during the latter half of the 20th century
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 33 (2006): L06715, doi:10.1029/2006GL025753.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.This work was supported by the Arctic System Science Program of the National Science Foundation (NSF-OPP-0229302, NSF-OPP-0230211, NSF-OPP-0519840) and by the National Oceanic and Atmospheric Administration (NA17RJ2612)
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