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Sample records for changing meltwater flux

  1. Relative impacts of insolation changes, meltwater fluxes and ice sheets on African and Asian monsoons during the Holocene

    NASA Astrophysics Data System (ADS)

    Marzin, Charline; Braconnot, Pascale; Kageyama, Masa

    2013-11-01

    In order to better understand the evolution of the Afro-Asian monsoon in the early Holocene, we investigate the impact on boreal summer monsoon characteristics of (1) a freshwater flux in the North Atlantic from the surrounding melting ice sheets and (2) a remnant ice sheet over North America and Europe. Sensitivity experiments run with the IPSL_CM4 model show that both the meltwater flux and the remnant ice sheets induce a cooling of similar amplitude of the North Atlantic leading to a southward shift of the Inter-Tropical Convergence Zone over the tropical Atlantic and to a reduction of the African monsoon. The two perturbations have different impacts in the Asian sector. The meltwater flux results in a weakening of the Indian monsoon and no change in the East Asian monsoon, whereas the remnant ice sheets induce a strengthening of the Indian monsoon and a strong weakening of the East Asian monsoon. Despite the similar coolings in the Atlantic Ocean, the ocean heat transport is reduced only in the meltwater flux experiment, which induces slight differences between the two experiments in the role of the surface latent heat flux in the tropical energetics. In the meltwater experiment, the southward shift of the subtropical jet acts to cool the upper atmosphere over the Tibetan Plateau and hence to weaken the Indian monsoon. In the ice sheet experiment this effect is overwhelmed by the changes in extratropical stationary waves induced by the ice sheets, which are associated with a larger cooling over the Eurasian continent than in the meltwater experiment. However these sensitivity experiments suggest that insolation is the dominant factor explaining the relative changes of the African, Indian and East Asian monsoons from the early to the mid-Holocene.

  2. Evidence for cooler European summers during periods of changing meltwater flux to the North Atlantic.

    PubMed

    Heiri, Oliver; Tinner, Willy; Lotter, André F

    2004-10-26

    We analyzed fossil chironomids (nonbiting midges) and pollen in two lake-sediment records to reconstruct and quantify Holocene summer-temperature fluctuations in the European Alps. Chironomid and pollen records indicate five centennial-scale cooling episodes during the early- and mid-Holocene. The strongest temperature declines of approximately 1 degrees C are inferred at approximately 10,700-10,500 and 8,200-7,600 calibrated 14C years B.P., whereas other temperature fluctuations are of smaller amplitude. Two forcing mechanisms have been presented recently to explain centennial-scale climate variability in Europe during the early- and mid-Holocene, both involving changes in Atlantic thermohaline circulation. In the first mechanism, changes in meltwater flux from the North American continent to the North Atlantic are responsible for changes in the Atlantic thermohaline circulation, thereby affecting circum-Atlantic climate. In the second mechanism, solar variability is the cause of Holocene climatic fluctuations, possibly triggering changes in Atlantic thermohaline overturning. Within their dating uncertainty, the two major cooling periods in the European Alps are coeval with substantial changes in the routing of North American freshwater runoff to the North Atlantic, whereas quantitatively, our climatic reconstructions show a poor agreement with available records of past solar activity. Thus, our results suggest that, during the early- and mid-Holocene, freshwater-induced Atlantic circulation changes had stronger influence on Alpine summer temperatures than solar variability and that Holocene thermohaline circulation reductions have led to summer-temperature declines of up to 1 degrees C in central Europe. PMID:15492214

  3. Role of Greenland meltwater in the changing Arctic

    NASA Astrophysics Data System (ADS)

    Dukhovskoy, Dmitry; Proshutinsky, Andrey; Timmermans, Mary-Louise; Myers, Paul; Platov, Gennady; Bamber, Jonathan; Curry, Beth; Somavilla, Raquel

    2016-04-01

    Observational data show that the Arctic ocean-ice-atmosphere system has been changing over the last two decades. Arctic change is manifest in the atypical behavior of the climate indices in the 21st century. Before the 2000s, these indices characterized the quasi-decadal variability of the Arctic climate related to different circulation regimes. Between 1948 and 1996, the Arctic atmospheric circulation alternated between anticyclonic circulation regimes and cyclonic circulation regimes with a period of 10-15 years. Since 1997, however, the Arctic has been dominated by an anticyclonic regime. Previous studies indicate that in the 20th century, freshwater and heat exchange between the Arctic Ocean and the sub-Arctic seas were self-regulated and their interactions were realized via quasi-decadal climate oscillations. What physical processes in the Arctic Ocean - sub-Arctic ocean-ice-atmosphere system are responsible for the observed changes in Arctic climate variability? The presented work is motivated by our hypothesis that in the 21st century, these quasi-decadal oscillations have been interrupted as a result of an additional freshwater source associated with Greenland Ice Sheet melt. Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus Greenland freshwater, the amount of which is about a third of the freshwater volume fluxed into the region during the 1970s Great Salinity Anomaly event, can spread and accumulate in the sub-Arctic seas influencing convective processes there. It is not clear, however, whether Greenland freshwater can propagate into the interior convective regions in the Labrador Sea and the Nordic Seas. In order to investigate the fate and pathways of Greenland freshwater in the sub-Arctic seas and to determine how and at what rate Greenland freshwater propagates into the convective regions, several numerical experiments using a passive tracer to

  4. Flocculated meltwater particles control Arctic land-sea fluxes of labile iron

    NASA Astrophysics Data System (ADS)

    Markussen, Thor Nygaard; Elberling, Bo; Winter, Christian; Andersen, Thorbjørn Joest

    2016-04-01

    Glacial meltwater systems supply the Arctic coastal ocean with large volumes of sediment and potentially bioavailable forms of iron, nitrogen and carbon. The particulate fraction of this supply is significant but estuarine losses have been thought to limit the iron supply from land. Here, our results reveal how flocculation (particle aggregation) involving labile iron may increase horizontal transport rather than enhance deposition close to the source. This is shown by combining field observations in Disko Fjord, West Greenland, and laboratory experiments. Our data show how labile iron affects floc sizes, shapes and densities and consequently yields low settling velocities and extended sediment plumes. We highlight the importance of understanding the flocculation mechanisms when examining fluxes of meltwater transported iron in polar regions today and in the future, and we underline the influence of terrestrial hotspots on the nutrient and solute cycles in Arctic coastal waters.

  5. Flocculated meltwater particles control Arctic land-sea fluxes of labile iron.

    PubMed

    Markussen, Thor Nygaard; Elberling, Bo; Winter, Christian; Andersen, Thorbjørn Joest

    2016-01-01

    Glacial meltwater systems supply the Arctic coastal ocean with large volumes of sediment and potentially bioavailable forms of iron, nitrogen and carbon. The particulate fraction of this supply is significant but estuarine losses have been thought to limit the iron supply from land. Here, our results reveal how flocculation (particle aggregation) involving labile iron may increase horizontal transport rather than enhance deposition close to the source. This is shown by combining field observations in Disko Fjord, West Greenland, and laboratory experiments. Our data show how labile iron affects floc sizes, shapes and densities and consequently yields low settling velocities and extended sediment plumes. We highlight the importance of understanding the flocculation mechanisms when examining fluxes of meltwater transported iron in polar regions today and in the future, and we underline the influence of terrestrial hotspots on the nutrient and solute cycles in Arctic coastal waters. PMID:27050673

  6. Flocculated meltwater particles control Arctic land-sea fluxes of labile iron

    PubMed Central

    Markussen, Thor Nygaard; Elberling, Bo; Winter, Christian; Andersen, Thorbjørn Joest

    2016-01-01

    Glacial meltwater systems supply the Arctic coastal ocean with large volumes of sediment and potentially bioavailable forms of iron, nitrogen and carbon. The particulate fraction of this supply is significant but estuarine losses have been thought to limit the iron supply from land. Here, our results reveal how flocculation (particle aggregation) involving labile iron may increase horizontal transport rather than enhance deposition close to the source. This is shown by combining field observations in Disko Fjord, West Greenland, and laboratory experiments. Our data show how labile iron affects floc sizes, shapes and densities and consequently yields low settling velocities and extended sediment plumes. We highlight the importance of understanding the flocculation mechanisms when examining fluxes of meltwater transported iron in polar regions today and in the future, and we underline the influence of terrestrial hotspots on the nutrient and solute cycles in Arctic coastal waters. PMID:27050673

  7. A numerical model for meltwater channel evolution in glaciers

    NASA Astrophysics Data System (ADS)

    Jarosch, A. H.; Gudmundsson, M. T.

    2012-04-01

    Meltwater channels form an integral part of the hydrological system of a glacier. Better understanding of how meltwater channels develop and evolve is required to fully comprehend supraglacial and englacial meltwater drainage. Incision of supraglacial stream channels and subsequent roof closure by ice deformation has been proposed in recent literature as a possible englacial conduit formation process. Field evidence for supraglacial stream incision has been found in Svalbard and Nepal. In Iceland, where volcanic activity provides meltwater with temperatures above 0 °C, rapid enlargement of supraglacial channels has been observed. Supraglacial channels provide meltwater through englacial passages to the subglacial hydrological systems of big ice sheets, which in turn affects ice sheet motion and their contribution to eustatic sea level change. By coupling, for the first time, a numerical ice dynamic model to a hydraulic model which includes heat transfer, we investigate the evolution of meltwater channels and their incision behaviour. We present results for different, constant meltwater fluxes, different channel slopes, different meltwater temperatures, different melt rate distributions in the channel as well as temporal variations in meltwater flux. The key parameters governing incision rate and depth are channel slope, meltwater temperature loss to the ice and meltwater flux. Channel width and geometry are controlled by melt rate distribution along the channel wall. Calculated Nusselt numbers suggest that turbulent mixing is the main heat transfer mechanism in the meltwater channels studied.

  8. Meltwater flux and runoff modeling in the abalation area of jakobshavn Isbrae, West Greenland

    SciTech Connect

    Mernild, Sebastian Haugard; Chylek, Petr; Liston, Glen; Steffen, Konrad

    2009-01-01

    The temporal variability in surface snow and glacier melt flux and runoff were investigated for the ablation area of lakobshavn Isbrae, West Greenland. High-resolution meteorological observations both on and outside the Greenland Ice Sheet (GrIS) were used as model input. Realistic descriptions of snow accumulation, snow and glacier-ice melt, and runoff are essential to understand trends in ice sheet surface properties and processes. SnowModel, a physically based, spatially distributed meteorological and snow-evolution modeling system was used to simulate the temporal variability of lakobshavn Isbrre accumulation and ablation processes for 2000/01-2006/07. Winter snow-depth observations and MODIS satellite-derived summer melt observations were used for model validation of accumulation and ablation. Simulations agreed well with observed values. Simulated annual surface melt varied from as low as 3.83 x 10{sup 9} m{sup 3} (2001/02) to as high as 8.64 x 10{sup 9} m{sup 3} (2004/05). Modeled surface melt occurred at elevations reaching 1,870 m a.s.l. for 2004/05, while the equilibrium line altitude (ELA) fluctuated from 990 to 1,210 m a.s.l. during the simulation period. The SnowModel meltwater retention and refreezing routines considerably reduce the amount of meltwater available as ice sheet runoff; without these routines the lakobshavn surface runoff would be overestimated by an average of 80%. From September/October through May/June no runoff events were simulated. The modeled interannual runoff variability varied from 1.81 x 10{sup 9} m{sup 3} (2001/02) to 5.21 x 10{sup 9} m{sup 3} (2004/05), yielding a cumulative runoff at the Jakobshavn glacier terminus of {approx}2.25 m w.eq. to {approx}4.5 m w.eq., respectively. The average modeled lakobshavn runoff of {approx}3.4 km{sup 3} y{sup -1} was merged with previous estimates of Jakobshavn ice discharge to quantify the freshwater flux to Illulissat Icefiord. For both runoff and ice discharge the average trends are

  9. Meltwater and Abrupt Climate Change in the Gulf of Mexico During the Last Glacial Termination

    NASA Astrophysics Data System (ADS)

    Williams, C.; Flower, B.; Hastings, D.; Randle, N.

    2008-12-01

    During the Last Glacial Termination from 18,000-8,000 cal. yrs B.P., meltwater routing of the Laurentide Ice Sheet (LIS) may have been linked to abrupt climatic events, such as the Younger Dryas. Previous studies show episodic meltwater input from the LIS, via the Mississippi River to the Gulf of Mexico (GOM) several thousand years before the onset of the Younger Dryas until approximately 13,000 cal yrs B.P., when meltwater routing may have switched to a more northern spillway, causing an abrupt change in thermohaline circulation (THC). The exact timing and magnitude of this meltwater input to the GOM is poorly constrained due to the lack of high-resolution data. Also unknown are the detailed relationships between GOM sea surface temperature, sea surface salinity and ice volume, relative to Northern and Southern Hemisphere climate from Greenland and Antarctica ice core records. High sedimentation rates (~40 cm/kyr) from laminated, anoxic Orca Basin core MD02-2550 provide the necessary resolution to assess GOM paleoceanography. Paired Mg/Ca and δ18O values from planktonic Foraminifera species Globigerinoides ruber (pink and white varieties) provide the relative timing of meltwater input and temperature change in the GOM with nearly decadal resolution. δ18Ocalcite results show multiple cool and/or high salinity periods with isotopic excursions of at least 2‰ that coincide with abrupt climatic events in Greenland ice core records, including the Oldest Dryas from 16,200-15,000 cal. yrs B.P. and the Intra-Allerod Cold Period at 13,860-13,560 cal. yrs B.P. Meltwater input to the GOM is seen for several thousand years before the onset of the Younger Dryas with white G. ruber δ18Ocalcite values as low as -4‰. Thirty-three AMS radiocarbon dates and high-resolution δ18O results provide excellent temporal constraints on deglacial climate events, including an abrupt (<200 yrs) cessation of meltwater in the GOM centered at 10,970± 40 radiocarbon yrs B.P., with a δ18O

  10. Similar meltwater contributions to glacial sea level changes from Antarctic and northern ice sheets.

    PubMed

    Rohling, Eelco J; Marsh, Robert; Wells, Neil C; Siddall, Mark; Edwards, Neil R

    2004-08-26

    The period between 75,000 and 20,000 years ago was characterized by high variability in climate and sea level. Southern Ocean records of ice-rafted debris suggest a significant contribution to the sea level changes from melt water of Antarctic origin, in addition to likely contributions from northern ice sheets, but the relative volumes of melt water from northern and southern sources have yet to be established. Here we simulate the first-order impact of a range of relative meltwater releases from the two polar regions on the distribution of marine oxygen isotopes, using an intermediate complexity model. By comparing our simulations with oxygen isotope data from sediment cores, we infer that the contributions from Antarctica and the northern ice sheets to the documented sea level rises between 65,000 and 35,000 years ago were approximately equal, each accounting for a rise of about 15 m. The reductions in Antarctic ice volume implied by our analysis are comparable to that inferred previously for the Antarctic contribution to meltwater pulse 1A (refs 16, 17), which occurred about 14,200 years ago, during the last deglaciation. PMID:15329718

  11. Laurentide Ice Sheet meltwater and abrupt climate change during the last glaciation

    SciTech Connect

    Hill, H W; Flower, B P; Quinn, T M; Hollander, D J; Guilderson, T P

    2005-10-02

    A leading hypothesis to explain abrupt climate change during the last glacial cycle calls on fluctuations in the margin of the North American Laurentide Ice Sheet (LIS), which may have routed freshwater between the Gulf of Mexico (GOM) and North Atlantic, affecting North Atlantic Deep Water (NADW) variability and regional climate. Paired measurements of {delta}O and Mg/Ca of foraminiferal calcite from GOM sediments reveal five episodes of LIS meltwater input from 28-45 thousand years ago (ka) that do not match the millennial-scale Dansgaard-Oeschger (D/O) warmings recorded in Greenland ice. We suggest that summer melting of the LIS may occur during Antarctic warming and likely contributed to sea-level variability during Marine Isotope Stage 3 (MIS 3).

  12. Megaflood erosion and meltwater plumbing changes during last North American deglaciation recorded in Gulf of Mexico sediments

    NASA Astrophysics Data System (ADS)

    Brown, Paul A.; Kennett, James P.

    1998-07-01

    Submicrometer variations in the median diameter of siliciclastic mud in Orca Basin, northern Gulf of Mexico, sensitively monitor Laurentide ice sheet runoff to the gulf during early stages of the last deglaciation. Grain-size data document a prominent pulse of very fine-grained sediment to the northern Gulf from 12.6 to 12.0 ka, corresponding with the well-known sea-surface meltwater spike in δ18O records. Meltwater megafloods at this time eroded and transported large volumes of clay to the Gulf via the Mississippi River system. The nonquartzose megaflood sediments appear to have been derived from clay-rich midcontinental terrace deposits rather than from glacial outwash supplied by the Laurentide ice margin. Sediment grain-size data, in combination with other terrigenous proxies (clay minerals and reworked calcareous nannofossils), indicate substantial variability in deglacial meltwater discharge and associated sediment load of meltwater runoff. This variability reflects changes in continental plumbing consistent with terrestrial records of North American deglaciation.

  13. Seasonal changes of chemical, isotopic and microbiological signatures in meltwater outflows of the West Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Hagedorn, B.; Choquette, K.; Sletten, R. S.; Dieser, M.; Cameron, K. A.; Liu, L.; Harrold, Z.; Christner, B. C.; Junge, K.

    2012-12-01

    characteristics of rain each event allowing quantification of its contribution to bulk meltwater. Meltwater chemistry can be used to identify meltwater routing in and below the ice sheet and changes from sodium and chlorite dominated snowmelt water to calcium, magnesium and sulfate dominated water which is related to mineral weathering processes are seen throughout the season. In addition, strontium isotope ratios and stable isotopes of sulfate can be used to identify solute provenance areas and the contribution of microbial activity in solute sequestration, respectively.

  14. Did Meltwater Drive the Ocean's AMOC?

    NASA Astrophysics Data System (ADS)

    McManus, J. F.; Oppo, D. W.; Curry, W. B.; Praetorius, S. K.

    2008-12-01

    The Atlantic's meridional overturning circulation (AMOC) is climatically important through its transport of heat and moisture to the high-latitude atmosphere. It is also potentially sensitive to perturbation by the increased near-surface buoyancy fluxes associated with intervals or episodes of large meltwater inputs. We have examined the deep-sea sedimentary record of the North Atlantic using multiple proxies for the rate and mode of AMOC since the last ice age. This history of oceanic changes can be compared to records of meltwater discharge in order to piece together the connections between specific melt events and AMOC. The best evidence for large-scale changes in the rate of AMOC occurred during the H1 Heinrich event iceberg discharge and the Younger Dryas millennial cooling. We will also discuss the evidence for AMOC changes associated with other intervals including the H2 Heinrich event, the Last Glacial Maximum (LGM), meltwater pulse (MWP) 1A and 1B, the Older Dryas, and the 8,200 year event.

  15. Hydrologic and Hyporheic Controls on Nutrient and Dissolved Ion Fluxes in Glacial Meltwater Streams at Daily, Seasonal, and Inter-annual Timescales in the McMurdo Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Weaver, M. R.; Gooseff, M. N.; McKnight, D. M.

    2009-12-01

    In the McMurdo Dry Valleys of Antarctica, glaciers are hydrologically linked to closed-basin lakes at the valley floor by glacial meltwater streams. We propose that the dynamics of meltwater generation and sub-stream thaw depth control the potential for the hyporheic zone and benthic communities to influence transport of nutrients and dissolved ions. We analyzed the dynamics of electrical conductivity (EC), nutrient concentration, and discharge at inter-annual and seasonal scales for 8 streams from 1990 to 2008 (the MCMLTER database). Weak logarithmic correlations against instantaneous discharge were found with all dissolved ions with exception to silica, which had a moderately strong negative correlation to instantaneous flow. Within each season EC is observed to respond to changes in discharge. These responses are typically inverse (i.e., EC decreases as discharge increases). In particular, we observe consistent end of season increases in EC during discharge recession suggesting drainage of the hyporheic zone. During the beginning of most flow seasons EC is elevated until fairly high discharges occur with the warming of the glacier surfaces in summer (mid-flow season), at which time EC dampens. The decrease in EC in the mid-flow season may occur because less of the water in the main channel has interacted with the hyporheic alluvium than under low flow conditions. In addition during the 2008-09 field season, we monitored EC, solute concentrations and discharge at upstream and downstream sites of two streams for two diurnal cycles (hourly sampling). These data indicate that diurnal variation in nutrient and dissolved ion fluxes are largely controlled by diurnal fluctuations in discharge, driven by solar position and intensity. Resolving the differences in controls at these different timescales will greatly enhance our understanding of the influence of hyporheic exchange on these stream ecosystems.

  16. Meltwater flooding events in the Gulf of Mexico revisited: Implications for rapid climate changes during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Aharon, Paul

    2003-12-01

    North American freshwater runoff records have been used to support the case that climate flickers were caused by shutdowns of the ocean thermohaline circulation (THC) resulting from reversals of meltwater discharges. Inconsistencies in the documentation of these meltwater switches, however, continue to fuel the debate on the cause/s of the oscillatory nature of the deglacial climate. New oxygen and carbon isotope records from the northern Gulf of Mexico depict in exceptional detail the succession of meltwater floods and pauses through the southern routing during the interval 16 to 8.9 ka (14C years BP; ka, kiloannum). The records underscore the bimodal role played by the Gulf of Mexico as a destination of meltwater discharges from the receding Laurentide Ice Sheet. The evidence indicates that the Gulf of Mexico acted as the principal source of superfloods at 13.4, 12.6, and 11.9 ka that reached the North Atlantic and contributed significantly to density stratification, disruption of ocean ventilation, and cold reversals. Gulf of Mexico lapsed into a "relief valve" position in post-Younger Dryas time, when meltwater discharges were rerouted south at 9.9, 9.7, 9.4, and 9.1 ka, thus temporarily interrupting North Atlantic-bound freshwater discharges from Lake Agassiz. The history of meltwater events in the Gulf of Mexico contradicts the model that meltwater flow via the eastern outlets into the North Atlantic disrupted the ocean THC, causing cooling, while diversions to the Gulf of Mexico via the Mississippi River enhanced THC and warming.

  17. Global Warming And Meltwater

    NASA Astrophysics Data System (ADS)

    Bratu, S.

    2012-04-01

    In order to find new approaches and new ideas for my students to appreciate the importance of science in their daily life, I proposed a theme for them to debate. They had to search for global warming information and illustrations in the media, and discuss the articles they found in the classroom. This task inspired them to search for new information about this important and timely theme in science. I informed my students that all the best information about global warming and meltwater they found would be used in a poster that would help us to update the knowledge base of the Physics laboratory. I guided them to choose the most eloquent images and significant information. Searching and working to create this poster, the students arrived to better appreciate the importance of science in their daily life and to critically evaluate scientific information transmitted via the media. In the poster we created, one can find images, photos and diagrams and some interesting information: Global warming refers to the rising average temperature of the Earth's atmosphere and oceans and its projected evolution. In the last 100 years, the Earth's average surface temperature increased by about 0.8 °C with about two thirds of the increase occurring over just the last three decades. Warming of the climate system is unequivocal, and scientists are more than 90% certain most of it is caused by increasing concentrations of greenhouse gases produced by human activities such as deforestation and burning fossil fuel. They indicate that during the 21st century the global surface temperature is likely to rise a further 1.1 to 2.9 °C for the lowest emissions scenario and 2.4 to 6.4 °C for the highest predictions. An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, and potentially result in expansion of subtropical deserts. Warming is expected to be strongest in the Arctic and would be associated with continuing decrease of

  18. Sensitivity of the Southern Ocean to enhanced regional Antarctic ice sheet meltwater input

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Phipps, S. J.; Turney, C. S. M.; Golledge, N. R.

    2015-10-01

    Despite advances in our understanding of the processes driving contemporary sea level rise, the stability of the Antarctic ice sheets and their contribution to sea level under projected future warming remains uncertain due to the influence of strong ice-climate feedbacks. Disentangling these feedbacks is key to reducing uncertainty. Here we present a series of climate system model simulations that explore the potential effects of increased West Antarctic Ice Sheet (WAIS) meltwater flux on Southern Ocean dynamics. We project future changes driven by sectors of the WAIS, delivering spatially and temporally variable meltwater flux into the Amundsen, Ross, and Weddell embayments over future centuries. Focusing on the Amundsen Sea sector of the WAIS over the next 200 years, we demonstrate that the enhanced meltwater flux rapidly stratifies surface waters, resulting in a significant decrease in the rate of Antarctic Bottom Water (AABW) formation. This triggers rapid pervasive ocean warming (>1°C) at depth due to advection from the original site(s) of meltwater input. The greatest warming is predicted along sectors of the ice sheet that are highly sensitized to ocean forcing, creating a feedback loop that could enhance basal ice shelf melting and grounding line retreat. Given that we do not include the effects of rising CO2—predicted to further reduce AABW formation—our experiments highlight the urgent need to develop a new generation of fully coupled ice sheet climate models, which include feedback mechanisms such as this, to reduce uncertainty in climate and sea level projections.

  19. Meltwater Temperature Variations in Rivers Draining Declining Alpine Glaciers

    NASA Astrophysics Data System (ADS)

    Collins, D. N.

    2015-12-01

    Marked patterns of seasonal and diurnal variations of discharge and temperature characterise meltwater rivers draining from large Alpine glaciers. Meltwater temperature warms with distance downstream, influenced both by energy availability and the volume of meltwater flowing. The amount of meltwater produced depends also on energy availability but also on the area of ice substrate over which melt occurs. As climate warms, meltwater production by ablation in summer will first increase with increasing energy for melting, before decreasing as the area of ice available for melt decreases, off-setting continuing increase in energy availability. Future meltwater temperature changes will depend on the inter-relationship between increasing energy availability and enhancing volume of meltwater produced. Relationships between rates of ice melt, reduction in ice area, and meltwater production will influence melt water temperature changes as climate warms. Meltwater temperature is inversely related to discharge whilst positively related to heat availability. Records of water temperature and discharge of meltwaters in rivers draining from three valley glaciers in Kanton Wallis, Switzerland have been examined. Hourly data for the Massa, Grosser Aletschgletscher, for the period 2003-2014, the Gornera, Gornergletscher , 2007-2014, and Findelenbach, Findelengletscher, 2007-2014 obtained at distances of a few kilometres from the glacier portals have been analysed, for summer months, during which more than 90% of discharge occurs. Distinctive seasonal temperature regimes have highest annual water temperatures during low flows in May., but then as discharge increased with first increasing radiation, increasing ice area as the transient snow line moved up glacier, and higher air temperatures, water temperatures decreased. On a diurnal basis, meltwater temperatures increased with rising radiation ahead of rising discharge (discharge being delayed by flow through time within the glacier

  20. Force sensor using changes in magnetic flux

    NASA Technical Reports Server (NTRS)

    Pickens, Herman L. (Inventor); Richard, James A. (Inventor)

    2012-01-01

    A force sensor includes a magnetostrictive material and a magnetic field generator positioned in proximity thereto. A magnetic field is induced in and surrounding the magnetostrictive material such that lines of magnetic flux pass through the magnetostrictive material. A sensor positioned in the vicinity of the magnetostrictive material measures changes in one of flux angle and flux density when the magnetostrictive material experiences an applied force that is aligned with the lines of magnetic flux.

  1. Greenland Meltwater and Arctic Circulation Regimes

    NASA Astrophysics Data System (ADS)

    Dukhovskoy, D. S.; Proshutinsky, A. Y.; Timmermans, M. L.; Myers, P. G.; Platov, G.

    2015-12-01

    Between 1948 and 1996, wind-driven components of ice drift and surface ocean currents experienced a well-pronounced decadal variability alternating between anticyclonic and cyclonic circulation regimes. During cyclonic regimes, low sea level atmospheric pressure dominated over the Arctic Ocean driving sea ice and the upper ocean clockwise; the Arctic atmosphere was relatively warm and humid and freshwater flux from the Arctic Ocean toward the sub-Arctic seas was intensified. During anticylonic circulation regimes, high sea level pressure dominated over the Arctic driving sea ice and ocean counter-clockwise; the atmosphere was cold and dry and the freshwater flux from the Arctic to the sub-Arctic seas was reduced. Since 1997, however, the Arctic system has been dominated by an anticyclonic circulation regime with a set of environmental parameters that are atypical for these regimes. Of essential importance is to discern the causes and consequences of the apparent break-down in the natural decadal variability of the Arctic climate system, and specifically: Why has the well-pronounced decadal variability observed in the 20th century been replaced by relatively weak interannual changes under anticyclonic circulation regime conditions in the 21st century? We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from Greenland impact environmental conditions and interrupt their decadal variability. In order to test this hypothesis, numerical experiments with several FAMOS (Forum for Arctic Modeling & Observational Synthesis) ice-ocean coupled models have been conducted. In these experiments, Greenland melt freshwater is tracked by passive tracers being constantly released along the Greenland coast. Propagation pathways and time scales of Greenland meltwater within the sub-Arctic seas are discussed.

  2. A Multi-proxy Approach to Distinguish Between Changes in SST and Meltwater Input in the Gulf of Mexico Back to MIS 3.

    NASA Astrophysics Data System (ADS)

    Lodico, J. M.; Hastings, D. W.; Flower, B. P.; Quinn, T. M.

    2002-12-01

    The Gulf of Mexico (GOM) is part of the Western Hemisphere Warm Pool providing a source of heat and moisture to the North American continent and Northern high latitudes. Paleoclimatic records from the GOM can test the hypothesis that the tropical climate system is an important driver of past global climate change. In July 2002, core MD02-2551 was taken by the French research vessel Marion Dufresne at 26°56.78 N 91°21.75 W and recovered 31.79 m of sediment from Orca Basin situated in the northern GOM 290 km south of the present Louisiana coast. The basin is advantageous for high-resolution paleoclimatology because of a brine layer overlying the sediment that preserves sedimentary laminations and high sedimentation rates estimated at greater than 50 cm/1000 yr. A multi-proxy approach using Mg/Ca and δ18O from foraminiferal calcite will isolate past sea surface temperature (SST) and δ18O of sea water (controlled by salinity, and ice volume). Separation of these parameters will help establish the relationship between changing GOM SSTs and meltwater input from the Laurentide Ice Sheet. The chronology of the core is being established using AMS C14 dating. Both white and pink species of the planktonic foraminifera Globigerinoides ruber were analyzed for δ18O and will be analyzed for Mg/Ca. Coarse resolution data from white G. ruber show a mean value of about -1.5 per mil during the Holocene (low variability of <0.5 per mil) and a mean value of about 0.0 per mil at the Last Glacial Maximum (low variability of <0.5 per mil). Marine Isotope Stage Three (MIS 3) indicates a mean value of about -0.75 per mil (high variability of >0.5 per mil). Sea surface temperature and sea surface salinity have distinctly higher variability during MIS 3 in comparison to the Holocene. Foraminiferal Mg data will add an additional constraint for SST. Phasing between GOM SSTs and high latitude temperatures will help assess the role of the tropical climate system on global climate change.

  3. Modelling heterogeneous meltwater percolation on the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Ligtenberg, S.

    2015-12-01

    The Greenland Ice Sheet (GrIS) has experienced an increase of surface meltwater production over the last decades, with the latest record set in the summer of 2012. For current and future ice sheet mass balance assessments, it is important to quantify what part of this meltwater reaches the ocean and contributes to sea level change. Meltwater produced at the surface has several options: it can infiltrate the local firn pack, where it is either stored temporarily or refrozen, or it can run off along the surface or via en-glacial drainage systems. In this study, we focus on the first; more specifically, in which manner meltwater percolates the firn column. Over the past years, GrIS research has shown that meltwater does not infiltrate the firn pack homogeneously (i.e. matrix flow), but that inhomogeneities in horizontal firn layers causes preferential flow paths for meltwater (i.e. piping). Although this process has been observed and studied on a few isolated sites, it has never been examined on the entire GrIS. To do so, we use the firn model IMAU-FDM with new parameterizations for preferential flow, impermeable ice lenses and sub-surface runoff. At the surface, IMAU-FDM is forced with realistic climate data from the regional climate model RACMO2.3. The model results are evaluated with temperatures and density measurements from firn cores across the GrIS. By allowing for heterogeneous meltwater percolation, the model is able to store heat and mass much deeper in the firn column. This is, however, in part counteracted by the inclusion of impermeability of ice lenses, which causes part of the meltwater to run off horizontally.

  4. Assessing the global meltwater spike*1

    NASA Astrophysics Data System (ADS)

    Jones, Glenn A.; Ruddiman, William F.

    1982-03-01

    L. V. Worthington (1968, Meteorological Monographs8, 63-67) hypothesized that a low-salinity lid covered the entire world ocean. By deconvolving isotopic curves from the western equatorial Pacific and equatorial Atlantic, W. H. Berger, R. F. Johnson, and J. S. Killingley (1977), Nature (London)269, 661-663) and W. H. Berger (1978, Deep-Sea Research25, 473-480) reconstructed "meltwater spikes" similar to those actually observed in the Gulf of Mexico and thus apparently confirmed the Worthington hypothesis. It is shown that this conclusion is unwarranted. The primary flaw in the reconstructed meltwater spikes is that the mixing intensity used in the deconvolution operation is overestimated. As a result, structure recorded in the mixed isotopic record becomes exaggerated in the attempt to restore the original unmixed record. This structure can be attributed to variable ice-volume decay during deglaciation, effects of differential solution on planktonic foraminifera, temporal changes in abundance of the foraminifera carrying the isotopic signal, and analytical error. An alternative geographic view to the global low-salinity lid is offered: a map showing portions of the ocean potentially affected by increased deglacial meltwater at middle and high latitudes and by increased precipitation-induced runoff at low and middle latitudes.

  5. Laurentide Ice Sheet meltwater and the Atlantic meridional overturning circulation since the last glacial maximum: A view from the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Flower, B. P.; Williams, C.; Brown, E. A.; Hastings, D. W.; Hendricks, J.; Goddard, E. A.

    2010-12-01

    The influence of ice sheet meltwater on the Atlantic meridional overturning circulation (AMOC) since the last glacial maximum represents an important issue in abrupt climate change. Comparison of Greenland and Antarctic ice core records has revealed a complex interhemispheric linkage and led to different models of ocean circulation including the “bipolar seesaw.” Meltwater input from the Laurentide Ice Sheet has been invoked as a cause of proximal sea-surface temperature (SST) and salinity change in the North Atlantic, and of regional to global climate change via its influence on the AMOC. We present published and new Mg/Ca, Ba/Ca, and δ18O data on the planktic foraminifer Globigerinoides ruber from northern Gulf of Mexico sediment cores that provide detailed records of SST, δ18O of seawater (δ18Osw), and inferred salinity for the 20-8 ka interval. Age control for Orca Basin core MD02-2550 is based on >40 AMS 14C dates on Globigerinoides ruber and documents continuous sedimentation at rates >35 cm/kyr. Early meltwater input is inferred from δ18Osw and Ba/Ca data prior to and during the Mystery Interval, consistent with a high sensitivity to solar insolation and greenhouse forcing. New bulk sediment δ18O data show major spikes reaching -5.5‰ ca. 14.6 and 12.6 ka. We speculate that these excursions represent fine carbonate sediment from Canadian Paleozoic marine carbonates, analogous to detrital carbonate in the North Atlantic which has a δ18O value of -5‰. Partial support for our hypothesis comes from SEM photomicrographs of bulk sediment from this section, which show no coccoliths or foraminifera in contrast to other intervals. The biogenic carbonate flux seems to have been greatly reduced by fine sediment input. Inferred peak meltwater flow appears to have been associated with the Bolling warming and meltwater pulse 1a. Finally, meltwater reduction at the start of the Younger Dryas supports models for a diversion to North Atlantic outlets and AMOC

  6. Supraglacial meltwater runoff from the Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Smith, L. C.; Chu, V.; Yang, K.; Rennermalm, A. K.; Legleiter, C. J.; Gleason, C. J.; Pitcher, L. H.; Moustafa, S.; Overstreet, B. T.; Behar, A.; Tedesco, M.; Forster, R. R.

    2013-12-01

    This presentation summarizes collaborative field and remote sensing research studying Greenland ice sheet meltwater flux through supraglacial rivers flowing over its surface and in proglacial rivers that emerge along its edge. High-resolution visible/near-infrared WorldView-2 satellite images were acquired simultaneously with in situ measurements of river hydraulic properties, including flow velocities from autonomous GPS drifters and ADCP, bathymetric depth soundings, water surface slopes, and hydraulic roughness. High-resolution mapping of supraglacial lake and river depths across the ablation zone were enabled through calibration of WorldView-2 images with in situ field spectra and water depth soundings collected from an unmanned autonomous watercraft. Fusion of these satellite and in situ datasets permits quantitative estimation of meltwater flux flowing over the ice sheet surface and entering moulins, and in situ proglacial measurements enable estimation of total meltwater export leaving the ice sheet. Analysis suggests that these supra- and pro-glacial rivers represent critical pathways for transport of meltwater runoff from the ice sheet surface to the global ocean.

  7. Emerging impact of Greenland meltwater on deepwater formation in the North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Böning, Claus W.; Behrens, Erik; Biastoch, Arne; Getzlaff, Klaus; Bamber, Jonathan L.

    2016-07-01

    The Greenland ice sheet has experienced increasing mass loss since the 1990s. The enhanced freshwater flux due to both surface melt and outlet glacier discharge is assuming an increasingly important role in the changing freshwater budget of the subarctic Atlantic. The sustained and increasing freshwater fluxes from Greenland to the surface ocean could lead to a suppression of deep winter convection in the Labrador Sea, with potential ramifications for the strength of the Atlantic meridional overturning circulation. Here we assess the impact of the increases in the freshwater fluxes, reconstructed with full spatial resolution, using a global ocean circulation model with a grid spacing fine enough to capture the small-scale, eddying transport processes in the subpolar North Atlantic. Our simulations suggest that the invasion of meltwater from the West Greenland shelf has initiated a gradual freshening trend at the surface of the Labrador Sea. Although the freshening is still smaller than the variability associated with the episodic `great salinity anomalies', the accumulation of meltwater may become large enough to progressively dampen the deep winter convection in the coming years. We conclude that the freshwater anomaly has not yet had a significant impact on the Atlantic meridional overturning circulation.

  8. Pathways of Petermann Glacier meltwater, Greenland

    NASA Astrophysics Data System (ADS)

    Heuzé, Céline; Wåhlin, Anna; Johnson, Helen; Münchow, Andreas

    2016-04-01

    Radar and satellite observations suggest that the floating ice shelf of Petermann Glacier loses up to 80% of its mass through basal melting, caused by the intrusion of warm Atlantic Water into the fjord and under the ice shelf. The fate of Petermann's glacial meltwater is still largely unknown. It is investigated here, using hydrographic observations collected during a research cruise on board I/B Oden in August 2015. Two methods are used to detect the meltwater from Petermann: a mathematical one that provides the concentration of ice shelf meltwater, and a geometrical one to distinguish the meltwater from Petermann and the meltwater from other ice shelves. The meltwater from Petermann mostly circulates on the north side of the fjord. At the sill, 0.5 mSv of meltwater leave the fjord, mostly on the northeastern side between 100 and 350 m depth, but also in the central channel, albeit with a lesser concentration. Meltwater from Petermann is found in all the casts in Hall Basin, notably north of the sill by Greenland coast. The geometrical method reveals that the casts closest to the Canadian side mostly contain meltwater from other, unidentified glaciers. As Atlantic Water warms up, it is key to monitor Greenland melting glaciers and track their meltwater to properly assess their impact on the ocean circulation and sea level rise.

  9. The Flow of Buoyant Meltwater Next to Ice Shelves and Icebergs

    NASA Astrophysics Data System (ADS)

    Wells, A. J.; Worster, G.

    2008-12-01

    Melting at the base of an ice shelf can play a significant role in the polar oceans, contributing to the mass balance of the ice shelf and leading to the formation of Ice Shelf Water. Fresh meltwater is relatively buoyant compared to the surrounding ocean and can rise along the ice surface, with the strength of this flow depending critically on the heat and salt fluxes from the ocean to the ice. We justify a simplified theoretical model that describes the coupling of heat and salt fluxes with the buoyancy- driven flow of meltwater, next to both vertical and sloping ice surfaces. The flow develops with distance along the ice surface, and different flow regimes can be obtained depending on the length and the slope of the ice surface. Both the heat and salt fluxes differ between the two regimes. On moderate scales the flow is controlled by buoyancy in a narrow region close to the ice surface. This predicts that the melting rate is independent of distance along the ice surface, consistent with previous laboratory scale measurements of heat transfer. This regime may be important for ablation at the sides of tabular icebergs, and under some regions of ice shelves. Further downstream, the flow is dominated by buoyancy located further from the wall, and can be described by a model similar to those often used to model ice-shelf-water plumes. This predicts that the melting rate increases with distance along the ice surface. Simple analytic solutions are also derived for flow in an unstratified fluid, which indicate the possible sensitivity of the ablation rate to changes in ocean temperature. The predicted variation of the heat and salt fluxes with distance along the ice surface may have important consequences for more complex models of ice-shelf-water flow.

  10. Glacier Changes in the Bhutanese Himalaya - Present and Future

    NASA Astrophysics Data System (ADS)

    Rupper, S.; Schaefer, J. M.; Burgener, L. K.; Maurer, J.; Smith, R.; Cook, E.; Putnam, A. E.; Krusic, P.; Tsering, K.; Koenig, L.

    2012-12-01

    Glacierized change in the Himalayas affects river-discharge, hydro-energy and agricultural production, and Glacial Lake Outburst Flood potential, but its quantification and extent of impacts remains highly uncertain. Here we present conservative, comprehensive and quantitative predictions for glacier area and meltwater flux changes in Bhutan, monsoonal Himalayas. In particular, we quantify the uncertainties associated with the glacier area and meltwater flux changes due to uncertainty in climate data, a critical problem for much of High Asia. Based on a suite of gridded climate data and a robust glacier melt model, our results show that glacier area and meltwater change projections can vary by an order of magnitude for different climate datasets. The most conservative results indicate that, even if climate were to remain at the present-day mean values (1980-2000), almost 10% of Bhutan's glacierized area would vanish and the meltwater flux would drop by as much as 30%. New mapping of glacierized area from 2000-2010 shows a significant change in glacierized area of 4-6%. Thus the conservative steady-state area changes predicted by the model are already being realized. Under the conservative scenario of an additional 1°C regional warming, glacier retreat is predicted to continue until about 25% of Bhutan's glacierized area will have disappeared and the annual meltwater flux, after an initial spike, would drop by as much as 65%.

  11. Oceanic Transport of Surface Meltwater from the Southern Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Luo, Hao; Castelao, Renato M.; Rennermalm, Asa K.; Tedesco, Marco; Bracco, Annalisa; Yager, Patricia L.; Mote, Thomas L.

    2016-01-01

    The Greenland ice sheet has undergone accelerating mass losses during recent decades. Freshwater runoff from ice melt can influence fjord circulation and dynamic1 and the delivery of bioavailable micronutrients to the ocean. It can also have climate implications, because stratification in the adjacent Labrador Sea may influence deep convection and the strength of the Atlantic meridional overturning circulation. Yet, the fate of the meltwater in the ocean remains unclear. Here, we use a high-resolution ocean model to show that only 1-15% of the surface meltwater runoff originating from southwest Greenland is transported westwards. In contrast, up to 50-60% of the meltwater runoff originating from southeast Greenland is transported westwards into the northern Labrador Sea, leading to significant salinity and stratification anomalies far from the coast. Doubling meltwater runoff, as predicted in future climate scenarios, results in a more-than-double increase in anomalies offshore that persists further into the winter. Interannual variability in offshore export of meltwater is tightly related to variability in wind forcing. The new insight that meltwaters originating from the west and east coasts have different fates indicates that future changes in mass loss rates and surface runoff will probably impact the ocean differently, depending on their Greenland origins.

  12. Oceanic transport of surface meltwater from the southern Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Luo, Hao; Castelao, Renato M.; Rennermalm, Asa K.; Tedesco, Marco; Bracco, Annalisa; Yager, Patricia L.; Mote, Thomas L.

    2016-07-01

    The Greenland ice sheet has undergone accelerating mass losses during recent decades. Freshwater runoff from ice melt can influence fjord circulation and dynamics and the delivery of bioavailable micronutrients to the ocean. It can also have climate implications, because stratification in the adjacent Labrador Sea may influence deep convection and the strength of the Atlantic meridional overturning circulation. Yet, the fate of the meltwater in the ocean remains unclear. Here, we use a high-resolution ocean model to show that only 1-15% of the surface meltwater runoff originating from southwest Greenland is transported westwards. In contrast, up to 50-60% of the meltwater runoff originating from southeast Greenland is transported westwards into the northern Labrador Sea, leading to significant salinity and stratification anomalies far from the coast. Doubling meltwater runoff, as predicted in future climate scenarios, results in a more-than-double increase in anomalies offshore that persists further into the winter. Interannual variability in offshore export of meltwater is tightly related to variability in wind forcing. The new insight that meltwaters originating from the west and east coasts have different fates indicates that future changes in mass loss rates and surface runoff will probably impact the ocean differently, depending on their Greenland origins.

  13. Meltwater routing and the Younger Dryas

    PubMed Central

    Condron, Alan; Winsor, Peter

    2012-01-01

    The Younger Dryas—the last major cold episode on Earth—is generally considered to have been triggered by a meltwater flood into the North Atlantic. The prevailing hypothesis, proposed by Broecker et al. [1989 Nature 341:318–321] more than two decades ago, suggests that an abrupt rerouting of Lake Agassiz overflow through the Great Lakes and St. Lawrence Valley inhibited deep water formation in the subpolar North Atlantic and weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC). More recently, Tarasov and Peltier [2005 Nature 435:662–665] showed that meltwater could have discharged into the Arctic Ocean via the Mackenzie Valley ∼4,000 km northwest of the St. Lawrence outlet. Here we use a sophisticated, high-resolution, ocean sea-ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the North Atlantic. Unlike the hypothesis of Broecker et al., freshwater from the St. Lawrence Valley advects into the subtropical gyre ∼3,000 km south of the North Atlantic deep water formation regions and weakens the AMOC by <15%. In contrast, narrow coastal boundary currents efficiently deliver meltwater from the Mackenzie Valley to the deep water formation regions of the subpolar North Atlantic and weaken the AMOC by >30%. We conclude that meltwater discharge from the Arctic, rather than the St. Lawrence Valley, was more likely to have triggered the Younger Dryas cooling. PMID:23129657

  14. Meltwater routing and the Younger Dryas.

    PubMed

    Condron, Alan; Winsor, Peter

    2012-12-01

    The Younger Dryas--the last major cold episode on Earth--is generally considered to have been triggered by a meltwater flood into the North Atlantic. The prevailing hypothesis, proposed by Broecker et al. [1989 Nature 341:318-321] more than two decades ago, suggests that an abrupt rerouting of Lake Agassiz overflow through the Great Lakes and St. Lawrence Valley inhibited deep water formation in the subpolar North Atlantic and weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC). More recently, Tarasov and Peltier [2005 Nature 435:662-665] showed that meltwater could have discharged into the Arctic Ocean via the Mackenzie Valley ~4,000 km northwest of the St. Lawrence outlet. Here we use a sophisticated, high-resolution, ocean sea-ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the North Atlantic. Unlike the hypothesis of Broecker et al., freshwater from the St. Lawrence Valley advects into the subtropical gyre ~3,000 km south of the North Atlantic deep water formation regions and weakens the AMOC by <15%. In contrast, narrow coastal boundary currents efficiently deliver meltwater from the Mackenzie Valley to the deep water formation regions of the subpolar North Atlantic and weaken the AMOC by >30%. We conclude that meltwater discharge from the Arctic, rather than the St. Lawrence Valley, was more likely to have triggered the Younger Dryas cooling. PMID:23129657

  15. Evolving Photospheric Flux Concentrations and Filament Dynamic Changes

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Aulanier, G.; Mein, P.; López Ariste, A.

    2006-11-01

    We analyze the role of weak photospheric flux concentrations that evolve in a filament channel, in the triggering of dynamic changes in the shape of a filament. The high polarimetric sensitivity of THEMIS allowed us to detect weak flux concentrations (few Gauss) associated with the filament development. The synoptic instruments (MDI, SOLIS) even if their sensitivity is much less than THEMIS were useful to follow any subsequent strengthening of these flux concentrations after their identification in the THEMIS magnetograms. We found that (1) the northern part of the filament develops an Hα barb at the same time that weak minority polarity elements develop near a plage; (2) a section in the southern part of the Hα filament gradually disappears and later reforms at the same time that several mixed-polarity magnetic elements appear, then subsequently cancel or spread away from each other. These changes correspond to increases in EUV emission, as observed by TRACE, EIT, and CDS. This suggests that the plasma is temporarily heated along the filament spine. An idealized sequence of force-free models of this filament channel, based on plasma-supporting magnetic dips occurring in the windings of a very weakly twisted flux tube, naturally explains the evolution of its southern part as being due to changes in the topology of the coronal magnetic field as the photospheric flux concentrations evolve.

  16. Recharge of a subglacial lake by surface meltwater in northeast Greenland

    NASA Astrophysics Data System (ADS)

    Willis, Michael J.; Herried, Bradley G.; Bevis, Michael G.; Bell, Robin E.

    2015-02-01

    In a warming climate, surface meltwater production on large ice sheets is expected to increase. If this water is delivered to the ice sheet base it may have important consequences for ice dynamics. For example, basal water distributed in a diffuse network can decrease basal friction and accelerate ice flow, whereas channelized basal water can move quickly to the ice margin, where it can alter fjord circulation and submarine melt rates. Less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets. Here we show that a subglacial lake in Greenland drained quickly, as seen in the collapse of the ice surface, and then refilled from surface meltwater input. We use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the Flade Isblink ice cap in northeast Greenland. During the autumn of 2011, a collapse basin about 70 metres deep and about 0.4 cubic kilometres in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord. Over the next two years, rapid uplift of the floor of the basin (which is approximately 8.4 square kilometres in area) occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake. Our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet. Sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice and alter downstream ice dynamics. Heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate.

  17. Recharge of a subglacial lake by surface meltwater in northeast Greenland.

    PubMed

    Willis, Michael J; Herried, Bradley G; Bevis, Michael G; Bell, Robin E

    2015-02-12

    In a warming climate, surface meltwater production on large ice sheets is expected to increase. If this water is delivered to the ice sheet base it may have important consequences for ice dynamics. For example, basal water distributed in a diffuse network can decrease basal friction and accelerate ice flow, whereas channelized basal water can move quickly to the ice margin, where it can alter fjord circulation and submarine melt rates. Less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets. Here we show that a subglacial lake in Greenland drained quickly, as seen in the collapse of the ice surface, and then refilled from surface meltwater input. We use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the Flade Isblink ice cap in northeast Greenland. During the autumn of 2011, a collapse basin about 70 metres deep and about 0.4 cubic kilometres in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord. Over the next two years, rapid uplift of the floor of the basin (which is approximately 8.4 square kilometres in area) occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake. Our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet. Sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice and alter downstream ice dynamics. Heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate. PMID:25607355

  18. Clouds enhance Greenland ice sheet meltwater runoff

    NASA Astrophysics Data System (ADS)

    van Tricht, K.; Lhermitte, S.; Lenaerts, J. T. M.; Gorodetskaya, I. V.; L'Ecuyer, T. S.; Noël, B.; van den Broeke, M. R.; Turner, D. D.; van Lipzig, N. P. M.

    2016-01-01

    The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (+/-5.2) W m-2. Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise.

  19. Clouds enhance Greenland ice sheet meltwater runoff

    NASA Astrophysics Data System (ADS)

    Van Tricht, Kristof; Lhermitte, Stef; Lenaerts, Jan T. M.; Gorodetskaya, Irina V.; L'Ecuyer, Tristan S.; Noël, Brice; van den Broeke, Michiel R.; Turner, David D.; van Lipzig, Nicole P. M.

    2016-04-01

    The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m‑2. Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise.

  20. Clouds enhance Greenland ice sheet meltwater runoff

    PubMed Central

    Van Tricht, K.; Lhermitte, S.; Lenaerts, J. T. M.; Gorodetskaya, I. V.; L'Ecuyer, T. S.; Noël, B.; van den Broeke, M. R.; Turner, D. D.; van Lipzig, N. P. M.

    2016-01-01

    The Greenland ice sheet has become one of the main contributors to global sea level rise, predominantly through increased meltwater runoff. The main drivers of Greenland ice sheet runoff, however, remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 (±5.2) W m−2. Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models, to better predict future contributions of the Greenland ice sheet to global sea level rise. PMID:26756470

  1. Climate versus geological controls on glacial meltwater micronutrient production in southern Greenland

    NASA Astrophysics Data System (ADS)

    Aciego, S. M.; Stevenson, E. I.; Arendt, C. A.

    2015-08-01

    Low concentrations of micronutrients in subarctic North Atlantic surface waters limit phytoplankton growth. Iron, phosphorous, and silicon are all potentially bio-limiting nutrients; iron is the most well documented in the subarctic North Atlantic. Manganese, nickel, copper and zinc are also essential trace metals for phytoplankton cell function. However, the spatial and temporal variability in the flux of these elements to the subarctic North Atlantic is undercharacterized. Here we show new data from the meltseason peak in 2013 indicating that glacial meltwater from the southern tip of Greenland has elevated dissolved major and trace metal concentrations compared to glacial meltwater draining shorter melt season glacial catchments to the north. Fe concentrations range from 0.13 to 6.97 μM, Zn from 4 to 95 μM, and Si from 4 to 36 μM, all higher than the depleted surface waters of the subarctic North Atlantic. Measured hydrochemical data modeled by PHREEQC indicates meltwater is undersaturated in pyrite and silicate phases but supersaturated with respect to oxyhydroxides, hematite and goethite, all phases that precipitate Fe as colloids, of which the nanoparticle phases should remain biologically available. The variability in geologic units between the sites indicates that subglacial lithology is a minor but not the dominant control on meltwater chemistry. The disparity in concentrations is directly correlated with climate, and an extended melt season, suggesting that future warming in Greenland will lead to increased trace element, and potential micronutrient, flux to the subarctic North Atlantic surface waters.

  2. A catastrophic meltwater flood event and the formation of the Hudson Shelf Valley

    USGS Publications Warehouse

    Thieler, E.R.; Butman, B.; Schwab, W.C.; Allison, M.A.; Driscoll, N.W.; Donnelly, J.P.; Uchupi, E.

    2007-01-01

    The Hudson Shelf Valley (HSV) is the largest physiographic feature on the U.S. mid-Atlantic continental shelf. The 150-km long valley is the submerged extension of the ancestral Hudson River Valley that connects to the Hudson Canyon. Unlike other incised valleys on the mid-Atlantic shelf, it has not been infilled with sediment during the Holocene. Analyses of multibeam bathymetry, acoustic backscatter intensity, and high-resolution seismic reflection profiles reveal morphologic and stratigraphic evidence for a catastrophic meltwater flood event that formed the modern HSV. The valley and its distal deposits record a discrete flood event that carved 15-m high banks, formed a 120-km2 field of 3- to 6-m high bedforms, and deposited a subaqueous delta on the outer shelf. The HSV is inferred to have been carved initially by precipitation and meltwater runoff during the advance of the Laurentide Ice Sheet, and later by the drainage of early proglacial lakes through stable spillways. A flood resulting from the failure of the terminal moraine dam at the Narrows between Staten Island and Long Island, New York, allowed glacial lakes in the Hudson and Ontario basins to drain across the continental shelf. Water level changes in the Hudson River basin associated with the catastrophic drainage of glacial lakes Iroquois, Vermont, and Albany around 11,450 14C year BP (∼ 13,350 cal BP) may have precipitated dam failure at the Narrows. This 3200 km3 discharge of freshwater entered the North Atlantic proximal to the Gulf Stream and may have affected thermohaline circulation at the onset of the Intra-Allerød Cold Period. Based on bedform characteristics and fluvial morphology in the HSV, the maximum freshwater flux during the flood event is estimated to be ∼ 0.46 Sv for a duration of ∼ 80 days.

  3. Multidecadal Fluvial Sediment Fluxes to Deltas under Environmental Change Scenarios

    NASA Astrophysics Data System (ADS)

    Dunn, Frances; Darby, Stephen; Nicholls, Robert

    2016-04-01

    Sediment delivery is vital to sustain delta environments on which over half a billion people live worldwide. Due to factors such as subsidence and sea level rise, deltas sink relative to sea level if sediment is not delivered to and retained on their surfaces. Deltas which sink relative to sea level experience flooding, land degradation and loss, which endangers anthropogenic activities and populations. The future of fluvial sediment fluxes, a key mechanism for sediment delivery to deltas, is uncertain due to complex environmental changes which are predicted to occur over the coming decades. This research investigates fluvial sediment fluxes under environmental changes in order to assess the sustainability of delta environments under potential future scenarios up to 2100. Global datasets of climate change, reservoir construction, and population and GDP as proxies for anthropogenic influence through land use changes are used to drive the catchment numerical model WBMsed, which is being used to investigate the effects of these environmental changes on fluvial sediment delivery. This process produces fluvial sediment fluxes under multiple future scenarios which will be used to assess the future sustainability of a selection of 8 vulnerable deltas, although the approach can be applied to deltas worldwide. By modelling potential future scenarios of fluvial sediment flux, this research contributes to the prognosis for delta environments. The future scenarios will inform management at multiple temporal scales, and indicate the potential consequences for deltas of various anthropogenic activities. This research will both forewarn managers of potentially unsustainable deltas and indicate those anthropogenic activities which encourage or hinder the creation of sustainable delta environments.

  4. Subtropical versus subpolar freshwater routing: The pathways of icebergs and meltwater in the North Atlantic during deglaciation

    NASA Astrophysics Data System (ADS)

    Condron, A.; Hill, J. C.

    2015-12-01

    Marine sediment records reveal episodes of increased ice rafted debris (IRD) to the subpolar N. Atlantic (40N-50N) during deglaciation that are linked to the calving of enormous numbers of icebergs from the Northern Hemisphere ice sheets. There is considerable interest, and uncertainty, as to whether meltwater from these icebergs freshened the ocean sufficiently to weaken the Atlantic Meridional Overturning Circulation (AMOC). Very recently, hundreds of iceberg scours have been observed along the east coast of the United States as far south as Florida. The iceberg scours are oriented SSW along the coast and are observed in water depths up to several hundred meters deep, indicating that massive (up to 300m thick) icebergs once drifted along the east coast of N. America into the subtropics during deglaciation. A newly developed iceberg model (MITberg) is coupled to an eddy-permitting ocean model to show that icebergs are carried south to Florida by coastally-confined meltwater currents caused by the sudden release of large volumes of meltwater from Hudson Bay and/or Gulf of St. Lawrence. When meltwater fluxes exceed 2.5Sv simulated icebergs drift as far south as Miami, Florida, and thousands are carried into the center of the subtropical gyre by narrow meltwater filaments and instabilities along the boundary current. When the meltwater flood ends, icebergs can no longer drift into the subtropics, and quickly become confined to the subpolar gyre where the majority of IRD is found. Our results indicate that icebergs and meltwater from the north did not always directly freshening the subpolar gyre, but were periodically transported south of the main subpolar deep water formation regions that regulate AMOC strength and climate. Dating the observed iceberg scours will tell us exactly how active and persistent this coastally-confined meltwater pathway was during deglaciation and help us unravel why there is not always a clear relationship between increased high latitude

  5. Paleolimnology of Lake Ontario: AN Assessment of Glacial Meltwater Influx

    NASA Astrophysics Data System (ADS)

    Hladyniuk, R.; Longstaffe, F. J.

    2010-12-01

    The timing and extent of glacial meltwater outbursts from the Laurentide Ice Sheet (LIS) may provide insight into their potential role in initiating and/or sustaining the Younger Dryas (YD) cooling event. It has been previously proposed that meltwater from the LIS suppressed thermohaline circulation in the Atlantic Ocean, leading to an abrupt change in climate (Broecker et al. 1989). Several pathways for transport of glacial meltwater to the Atlantic Ocean have been suggested in the past, including eastern flow through the St. Lawrence River system and discharge into the Arctic Ocean via a northwestern outlet (Murton et al. 2010). Glacial meltwater contributions to Lake Ontario and its ancient equivalents during the last ~14,000 cal BP have been evaluated using the oxygen-isotope compositions of ostracode shells from three sediment cores in Lake Ontario. Glacial Lake Iroquois (~12,500 cal BP) δ18O values as low as -18‰ suggest significant contribution of glacial meltwater runoff from the LIS. This glacial sediment is characterized by occasional grains of sand and gravel. These ice-rafted particles indicate how far icebergs floated and suggest close proximity to the LIS. Early Lake Ontario sediment (~12,000 cal BP) exhibits thicker laminations, suggestive of increased winter ice cover and perhaps a colder climate, and is characterized by slightly lower δ18O values (-19.5‰). The end of glacial-dominated sedimentation at ~11,800 cal BP is demarcated by a significant increase in lakewater δ18O values (-12.0‰), reflecting mixing between regional precipitation in the watershed and upstream inflow into Lake Ontario. At ~10,800 cal BP, the δ18O value of Lake Ontario decreased to ~-15‰. This change reflects the main Algonquin highstand in Lake Huron, which flooded into Lake Ontario from both the Fenelon Falls and Port Huron outlets at this time. Shortly thereafter, the opening of the North Bay outlet and isostatic rebound at the Port Huron outlet limited

  6. Sudden flux change studies in high field superconducting accelerator magnets

    SciTech Connect

    Feher, S.; Bordini, B.; Carcagno, R.; Makulski, A.; Orris, D.F.; Pischalnikov, Y.M.; Sylvester, C.; Tartaglia, M.; Tompkins, J.C.; Zlobin, A.V.; /Fermilab

    2004-10-01

    As part of the High Field Magnet Program at Fermilab many magnets have been tested which utilize multi strand Rutherford type cable made of state-of-the art Nb{sub 3}Sn strands. During these magnet tests we observed sudden flux changes by monitoring coil voltages and the magnetic field close to the magnets. These flux changes might be linked to magnet instabilities. The voltage spike signals were correlated with quench antenna signals, a strong indication that these are magnet phenomena. With a new high resolution voltage spike detection system, we were able to observe the detailed structure of the spikes. Two fundamentally different signal shapes were distinguished, most likely generated by different mechanisms.

  7. Greenland meltwater storage in firn limited by near-surface ice formation

    NASA Astrophysics Data System (ADS)

    Machguth, Horst; Macferrin, Mike; van As, Dirk; Box, Jason E.; Charalampidis, Charalampos; Colgan, William; Fausto, Robert S.; Meijer, Harro A. J.; Mosley-Thompson, Ellen; van de Wal, Roderik S. W.

    2016-04-01

    Approximately half of Greenland’s current annual mass loss is attributed to runoff from surface melt. At higher elevations, however, melt does not necessarily equal runoff, because meltwater can refreeze in the porous near-surface snow and firn. Two recent studies suggest that all or most of Greenland’s firn pore space is available for meltwater storage, making the firn an important buffer against contribution to sea level rise for decades to come. Here, we employ in situ observations and historical legacy data to demonstrate that surface runoff begins to dominate over meltwater storage well before firn pore space has been completely filled. Our observations frame the recent exceptional melt summers in 2010 and 2012 (refs ,), revealing significant changes in firn structure at different elevations caused by successive intensive melt events. In the upper regions (more than ~1,900 m above sea level), firn has undergone substantial densification, while at lower elevations, where melt is most abundant, porous firn has lost most of its capability to retain meltwater. Here, the formation of near-surface ice layers renders deep pore space difficult to access, forcing meltwater to enter an efficient surface discharge system and intensifying ice sheet mass loss earlier than previously suggested.

  8. Sea-level constraints on the amplitude and source distribution of Meltwater Pulse 1A

    NASA Astrophysics Data System (ADS)

    Liu, Jean; Milne, Glenn A.; Kopp, Robert E.; Clark, Peter U.; Shennan, Ian

    2016-02-01

    During the last deglaciation, sea levels rose as ice sheets retreated. This climate transition was punctuated by periods of more intense melting; the largest and most rapid of these--Meltwater Pulse 1A--occurred about 14,500 years ago, with rates of sea-level rise reaching approximately 4 m per century. Such rates of rise suggest ice-sheet instability, but the meltwater sources are poorly constrained, thus limiting our understanding of the causes and impacts of the event. In particular, geophysical modelling studies constrained by tropical sea-level records suggest an Antarctic contribution of more than seven metres, whereas most reconstructions from Antarctica indicate no substantial change in ice-sheet volume around the time of Meltwater Pulse 1A. Here we use a glacial isostatic adjustment model to reinterpret tropical sea-level reconstructions from Barbados, the Sunda Shelf and Tahiti. According to our results, global mean sea-level rise during Meltwater Pulse 1A was between 8.6 and 14.6 m (95% probability). As for the melt partitioning, we find an allowable contribution from Antarctica of either 4.1 to 10.0 m or 0 to 6.9 m (95% probability), using two recent estimates of the contribution from the North American ice sheets. We conclude that with current geologic constraints, the method applied here is unable to support or refute the possibility of a significant Antarctic contribution to Meltwater Pulse 1A.

  9. Flux change in viscous laminar flow under oscillating boundary condition

    NASA Astrophysics Data System (ADS)

    Ueda, R.; Mikada, H.; Goto, T.; Takekawa, J.

    2012-12-01

    The behavior of interstitial fluid is one of major interest in earth sciences in terms of the exploitation of water resources, the initiation of earthquakes, enhanced oil recovery (EOR), etc. Seismic waves are often known to increase the flux of interstitial fluid but the relationship between the flux and propagating seismic waves have not been well investigated in the past, although seismic stimulation has been applied in the oil industry for enhanced oil recovery (EOR). Many observations indicated that seismic waves could stimulate the oil production due to lowering of apparent viscosity coefficient, to the coalescence and/or the dispersion of droplets of a phase in multiphase fluids. However, the detailed mechanism of seismic stimulation has not been fully understood, either. In this study, We attempt to understand the mechanism of the flux change in viscous laminar flow under oscillating boundary condition for the simulation of interstitial flow. Here, we analyze a monophase flow in a pore throat. We first assume a Hagen-Poiseuille flow of incompressible fluid through a pore-throat in a porous medium. We adopt the Lattice Boltzmann method (LBM) in which the motion of fluid is simulated through the variation of velocity distribution function representing the distribution of discrete particle velocities. We use an improved incompressible LBKG model (d2q9i) proposed in Zou et. al. (1995) to accurately accommodate the boundary conditions of pressure and velocity in the Hagen-Poiseuille flow. We also use an half-way bounce back boundary condition as the velocity boundary condition. Also, we assume a uniform pressure (density) difference between inlet and outlet flow, and the density difference could initiate the flow in our simulation. The oscillating boundary condition is given by the body force acting on fluid particles. In this simulation, we found that the flux change is negligible under small amplitude of oscillation in both horizontal and vertical directions

  10. Dynamic Antarctic ice-sheet response to deglacial meltwater pulses

    NASA Astrophysics Data System (ADS)

    Weber, Michael; Clark, Peter U.; Timmermann, Axel; Lohmann, Gerrit; Kuhn, Gerhard; Sprenk, Daniela; Gladstone, Rupert

    2013-04-01

    Reconstruction of the last global sea level rise faces uncertainties because only a few robust data evidences are available for Antarctic ice sheets. Deglacial dynamics have mostly been inferred from shallow-water cores on the shelf, where decisive changes are either erased by grounding ice or occur in condensed, lithologically complex successions with partially reversed and generally unreliable 14C ages. Previous modeling studies reconstruct a late ice-sheet retreat starting around 12 ka BP and ending around 7 ka BP with a large impact of an unstable West Antarctic Ice Sheet (WAIS) and a small impact of a stable East Antarctic Ice Sheet (EAIS). However, new findings from two deepwater cores from the Scotia Sea challenge these reconstructions and call for a principal revision of the Antarctic deglacial history. The well-dated sites (Weber et al., 2012, Quaternary Science Reviews) provide the first integrative and representative record of Antarctic Ice Sheet instability. They are located in the central transport route of virtually all Antarctic icebergs, the so-called Iceberg Alley, and demonstrate a highly dynamic Antarctic Ice Sheet during the last deglaciation with eight distinct phases of enhanced iceberg routing, dubbed Antarctic Ice Sheet Events (AIE), in contrast to existing models of a late and monotonous ice-sheet retreat which implied only little contribution to the last, natural, sea-level rise 19,000 to 9,000 years ago. We found the first direct evidence for an Antarctic contribution to Meltwater Pulse 1A in the flux rates of ice-rafted debris. Using an ensemble of transient deglacial model simulations we could show that increased export of warmer Circumpolar Deep Water towards Antarctica contributed to Antarctic Ice Sheet melt by ocean thermal forcing (Weber et al., Science, in review). These new findings hold the potential to substantially revise and improve our understanding of the transient response of the ice sheet to external and internal forcings

  11. Sign change of the flux flow Hall effect in HTSC

    SciTech Connect

    Feigel`man, M.V.; Geshkenbein, V.B.; Larkin, A.I.; Vinokur, V.M.

    1996-11-01

    A novel mechanism for the sign change of the Hall effect in the flux flow region is proposed. The difference {delta}{ital n} between the electron density at the center of the vortex core and that far outside the vortex causes the additional contribution to the Hall conductivity {delta}{sigma}{sub xy} = -{delta}{ital nec}/{ital B}. This contribution can be larger than the conventional one in the dirty case {Delta}{ital T}{tau} {lt} 1. If the electron density inside the core exceeds the electron density far outside, a double sign change may occur as a function of temperature.

  12. Lateral mixing across ice meltwater fronts of the Chukchi Sea shelf

    NASA Astrophysics Data System (ADS)

    Lu, K.; Weingartner, T.; Danielson, S.; Winsor, P.; Dobbins, E.; Martini, K.; Statscewich, H.

    2015-08-01

    Summer and fall hydrographic sections in the northeastern Chukchi Sea frequently capture 5-20 m thick intrapycnocline lenses or horizontal plumes of warm, moderately salty summer Bering Sea Water flowing northward from Bering Strait. These features occur within the shallow (~20 m depth) pycnocline separating cold, dilute, surface meltwater from near-freezing, salty, winter-formed waters beneath the pycnocline. An idealized numerical model suggests that the features arise from eddies and meanders generated by instability of the surface front separating meltwater from Bering Sea Water. Warm Bering Sea Water is transported across the front and into the pycnocline by the cross-frontal velocities associated with the instabilities. The accompanying lateral eddy heat fluxes may be important both in summer for promoting ice melt and in fall by delaying the onset of ice formation over portions of this shelf. Lateral heat flux magnitudes depend upon the stratification of the Bering Sea Water.

  13. Detecting regional patterns of changing CO2 flux in Alaska.

    PubMed

    Parazoo, Nicholas C; Commane, Roisin; Wofsy, Steven C; Koven, Charles D; Sweeney, Colm; Lawrence, David M; Lindaas, Jakob; Chang, Rachel Y-W; Miller, Charles E

    2016-07-12

    With rapid changes in climate and the seasonal amplitude of carbon dioxide (CO2) in the Arctic, it is critical that we detect and quantify the underlying processes controlling the changing amplitude of CO2 to better predict carbon cycle feedbacks in the Arctic climate system. We use satellite and airborne observations of atmospheric CO2 with climatically forced CO2 flux simulations to assess the detectability of Alaskan carbon cycle signals as future warming evolves. We find that current satellite remote sensing technologies can detect changing uptake accurately during the growing season but lack sufficient cold season coverage and near-surface sensitivity to constrain annual carbon balance changes at regional scale. Airborne strategies that target regular vertical profile measurements within continental interiors are more sensitive to regional flux deeper into the cold season but currently lack sufficient spatial coverage throughout the entire cold season. Thus, the current CO2 observing network is unlikely to detect potentially large CO2 sources associated with deep permafrost thaw and cold season respiration expected over the next 50 y. Although continuity of current observations is vital, strategies and technologies focused on cold season measurements (active remote sensing, aircraft, and tall towers) and systematic sampling of vertical profiles across continental interiors over the full annual cycle are required to detect the onset of carbon release from thawing permafrost. PMID:27354511

  14. Detecting regional patterns of changing CO2 flux in Alaska

    NASA Astrophysics Data System (ADS)

    Parazoo, Nicholas C.; Commane, Roisin; Wofsy, Steven C.; Koven, Charles D.; Sweeney, Colm; Lawrence, David M.; Lindaas, Jakob; Chang, Rachel Y.-W.; Miller, Charles E.

    2016-07-01

    With rapid changes in climate and the seasonal amplitude of carbon dioxide (CO2) in the Arctic, it is critical that we detect and quantify the underlying processes controlling the changing amplitude of CO2 to better predict carbon cycle feedbacks in the Arctic climate system. We use satellite and airborne observations of atmospheric CO2 with climatically forced CO2 flux simulations to assess the detectability of Alaskan carbon cycle signals as future warming evolves. We find that current satellite remote sensing technologies can detect changing uptake accurately during the growing season but lack sufficient cold season coverage and near-surface sensitivity to constrain annual carbon balance changes at regional scale. Airborne strategies that target regular vertical profile measurements within continental interiors are more sensitive to regional flux deeper into the cold season but currently lack sufficient spatial coverage throughout the entire cold season. Thus, the current CO2 observing network is unlikely to detect potentially large CO2 sources associated with deep permafrost thaw and cold season respiration expected over the next 50 y. Although continuity of current observations is vital, strategies and technologies focused on cold season measurements (active remote sensing, aircraft, and tall towers) and systematic sampling of vertical profiles across continental interiors over the full annual cycle are required to detect the onset of carbon release from thawing permafrost.

  15. Meltwater routing and the Atlantic meridional overturning circulation: A Gulf of Mexico perspective

    NASA Astrophysics Data System (ADS)

    Flower, B. P.; Williams, C.; Randle, N.; Hastings, D. W.

    2008-12-01

    Routing of low-salinity meltwater from the Laurentide Ice Sheet (LIS) into the North Atlantic via eastern outlets (e.g., St. Lawrence and Hudson River systems) and northern outlets (e.g., Hudson Bay and Arctic Ocean) is thought to have reduced Atlantic meridional overturning circulation (AMOC) and thereby triggered rapid regional to global climate change during the last glacial cycle. In contrast, southward meltwater flow to the Gulf of Mexico is generally thought to allow enhanced AMOC and warmer climates in the North Atlantic region. Situated at the outlet of the Mississippi River system, Orca Basin is ideally located to record meltwater input from the LIS. Orca Basin core MD02-2550 collected by the R/V Marion Dufresne in 2002 on IMAGES cruise VIII allows sub-centennial-scale records of Mg/Ca sea-surface temperature (SST) and δ18Oseawater back to ca. 23.9 ka. Accumulation rates average about 40 cm/k.y. Our current data extend from ca. 16.5-7 ka, with age control provided by 40 AMS radiocarbon dates (nearly all in stratigraphic order; calibrated using Calib 5.0.2). We use paired Mg/Ca and oxygen isotope data on Globigerinoides ruber to isolate changes in the oxygen isotopic composition of seawater. Four major episodic δ18O decreases of more than 2 per mil indicate substantial LIS meltwater input. Intervals of major meltwater discharge to the Gulf of Mexico do not appear to match known pulses of global sea level increase. However, abrupt reductions in southward meltwater input to the Gulf of Mexico seem to correlate with abrupt coolings in the North Atlantic region (e.g., Younger Dryas, Intra-Allerod cold period, and Oldest Dryas). In particular, a 3.5 per mil δ18O increase centered at 10,970 radiocarbon years B.P. (the "cessation event") appears to coincide with the onset of the Younger Dryas in European lakes and with Δ14C evidence from Cariaco Basin for AMOC reduction. Furthermore, recent results with the NCAR Community Climate System model (CCSM3) indicate

  16. Greenland ice sheet motion insensitive to exceptional meltwater forcing.

    PubMed

    Tedstone, Andrew J; Nienow, Peter W; Sole, Andrew J; Mair, Douglas W F; Cowton, Thomas R; Bartholomew, Ian D; King, Matt A

    2013-12-01

    Changes to the dynamics of the Greenland ice sheet can be forced by various mechanisms including surface-melt-induced ice acceleration and oceanic forcing of marine-terminating glaciers. We use observations of ice motion to examine the surface melt-induced dynamic response of a land-terminating outlet glacier in southwest Greenland to the exceptional melting observed in 2012. During summer, meltwater generated on the Greenland ice sheet surface accesses the ice sheet bed, lubricating basal motion and resulting in periods of faster ice flow. However, the net impact of varying meltwater volumes upon seasonal and annual ice flow, and thus sea level rise, remains unclear. We show that two extreme melt events (98.6% of the Greenland ice sheet surface experienced melting on July 12, the most significant melt event since 1889, and 79.2% on July 29) and summer ice sheet runoff ~3.9 σ above the 1958-2011 mean resulted in enhanced summer ice motion relative to the average melt year of 2009. However, despite record summer melting, subsequent reduced winter ice motion resulted in 6% less net annual ice motion in 2012 than in 2009. Our findings suggest that surface melt-induced acceleration of land-terminating regions of the ice sheet will remain insignificant even under extreme melting scenarios. PMID:24248343

  17. Predicting Changes in the Radio Emission Fluxes of Extragalactic Sources

    NASA Astrophysics Data System (ADS)

    Sukharev, A. L.; Ryabov, M. I.; Donskikh, G. I.

    2016-06-01

    Data from long-term monitoring with the 26-m University of Michigan radio telescope at a frequency of 14.5 GHz (1974-2011) is used to predict changes in the radio emission fluxes from the extragalactic sources 3C273, 3C120, 3C345, 3C446, 3C454.3, OJ287, OT081, and BLLac. The predictions are based on data on the major periods of variability and their durations obtained by wavelet analysis. The radio emission fluxes from the sources 3C345, 3C446, and 3C454.3, which have complicated variabilities, are predicted using an autoregression linear prediction method. This yields a forecast of the flux variations extending up to 5 years. Harmonic prediction is used for another group of sources, BLLac, OJ287, and OT081, with rapid variability. This approach yielded forecasts extending 4-9 years. For the sources 3C273 and 3C120, which have stable long periods, the harmonic method was also used and yielded a forecast extending up to 16 years. The reliability of the prediction was confirmed by independent observational data from the MOJAVE program for 2011-2015.

  18. Oxygen isotope ratios in the shell of Mytilus edulis: archives of glacier meltwater in Greenland?

    NASA Astrophysics Data System (ADS)

    Versteegh, E. A. A.; Blicher, M. E.; Mortensen, J.; Rysgaard, S.; Als, T. D.; Wanamaker, A. D., Jr.

    2012-12-01

    Melting of the Greenland Ice Sheet (GrIS) is accelerating and will contribute significantly to global sea level rise during the 21st century. Instrumental data on GrIS melting only cover the last few decades, and proxy data extending our knowledge into the past are vital for validating models predicting the influence of ongoing climate change. We investigated a potential meltwater proxy in Godthåbsfjord (West Greenland), where glacier meltwater causes seasonal excursions with lower oxygen isotope water (δ18Ow) values and salinity. The blue mussel (Mytilus edulis) potentially records these variations, because it precipitates its shell calcite in oxygen isotopic equilibrium with ambient seawater. As M. edulis shells are known to occur in raised shorelines and archaeological shell middens from previous Holocene warm periods, this species may be ideal in reconstructing past meltwater dynamics. We investigate its potential as a palaeo-meltwater proxy. First, we confirmed that M. edulis shell calcite oxygen isotope (δ18Oc) values are in equilibrium with ambient water and generally reflect meltwater conditions. Subsequently we investigated if this species recorded the full range of δ18Ow values occurring during the years 2007 to 2010. Results show that δ18Ow values were not recorded at very low salinities (< ~ 19), because the mussels appear to cease growing. This implies that Mytilus edulis δ18Oc values are suitable in reconstructing past meltwater amounts in most cases, but care has to be taken that shells are collected not too close to a glacier, but rather in the mid-region or mouth of the fjord. The focus of future research will expand on the geographical and temporal range of the shell measurements by sampling mussels in other fjords in Greenland along a south-north gradient, and by sampling shells from raised shorelines and archaeological shell middens from prehistoric settlements in Greenland.

  19. Oxygen isotope ratios in the shell of Mytilus edulis: archives of glacier meltwater in Greenland?

    NASA Astrophysics Data System (ADS)

    Versteegh, E. A. A.; Blicher, M. E.; Mortensen, J.; Rysgaard, S.; Als, T. D.; Wanamaker, A. D., Jr.

    2012-09-01

    Melting of the Greenland Ice Sheet (GrIS) is accelerating and will contribute significantly to global sea level rise during the 21st century. Instrumental data on GrIS melting only cover the last few decades, and proxy data extending our knowledge into the past are vital for validating models predicting the influence of ongoing climate change. We investigated a potential meltwater proxy in Godthåbsfjord (West Greenland), where glacier meltwater causes seasonal excursions with lower oxygen isotope water (δ18Ow) values and salinity. The blue mussel (Mytilus edulis) potentially records these variations, because it precipitates its shell calcite in oxygen isotopic equilibrium with ambient seawater. As M. edulis shells are known to occur in raised shorelines and kitchen middens from previous Holocene warm periods, this species may be ideal in reconstructing past meltwater dynamics. We investigate its potential as a palaeo-meltwater proxy. First, we confirmed that M. edulis shell calcite oxygen isotope (δ18Oc) values are in equilibrium with ambient water and generally reflect meltwater conditions. Subsequently we investigated if this species recorded the full range of δ18Ow values occurring during the years 2007 to 2010. Results show that δ18Ow values were not recorded at very low salinities (< ~19), because the mussels appear to cease growing. This implies that M. edulis δ18Oc values are suitable in reconstructing past meltwater amounts in most cases, but care has to be taken that shells are collected not too close to a glacier, but rather in the mid region or mouth of the fjord. The focus of future research will expand on the geographical and temporal range of the shell measurements by sampling mussels in other fjords in Greenland along a south-north gradient, and by sampling shells from raised shorelines and kitchen middens from prehistoric settlements in Greenland.

  20. Sensitivity of simulated hydrological fluxes towards changes in soil properties in response to land use change

    NASA Astrophysics Data System (ADS)

    Huisman, J. A.; Breuer, L.; Frede, H.-G.

    Current model studies on the impact of land use change on water resources often simulate changes in land use without considering changes in the soil properties due to the change in land use. In this study, an artificial study catchment representing the Dill catchment (Germany) was used within the eco-hydrological model SWAT-G to study the sensitivity of SWAT-G simulations towards changes in soil properties during land use change. Since there is little information on these soil-vegetation interactions, we performed a model sensitivity study to investigate the impact of changes in the depth of the top soil layer, bulk density, saturated hydraulic conductivity and available water content on several simulated hydrological fluxes. To assess the significance of the simulated changes due to the changing soil properties, we compared the model sensitivity with the uncertainty in the hydrological fluxes due to the uncertainty in the parameterization of the plant parameters. The results showed that the changes in soil properties due to a land use transition from cropland to pasture only have a minor impact on the simulated mean annual, summer and winter runoff and actual evapotranspiration. Soil-vegetation interactions have a stronger impact on the simulated mean surface runoff, although the absolute contribution of this flux is small in our conceptualization of the Dill catchment. A comparison of the sensitivity and uncertainty of the simulated hydrological fluxes led to the conclusion that changes in soil properties due to land use change are relatively unimportant in our model of the Dill catchment in the light of the low sensitivity of the dominating hydrological fluxes and the large output uncertainty due to the plant parameter uncertainty.

  1. Transport and reaction of iron and iron stable isotopes in glacial meltwaters on Svalbard near Kongsfjorden: From rivers to estuary to ocean

    NASA Astrophysics Data System (ADS)

    Zhang, Ruifeng; John, Seth G.; Zhang, Jing; Ren, Jingling; Wu, Ying; Zhu, Zhuoyi; Liu, Sumei; Zhu, Xunchi; Marsay, Chris M.; Wenger, Fred

    2015-08-01

    Glacial meltwater has been suggested as a significant source of potentially bioavailable iron to the oceans. However, the supply of dissolved iron (dFe) in glacial meltwaters is poorly constrained as few sites have been studied, and because the chemical processing of Fe during transport from glaciers to the adjacent coastal ocean is not well understood. In order to better constrain glacial fluxes of dFe to the ocean, iron concentrations, iron stable isotopes (δ56Fe), and other supporting chemical and physical measurements were made along a ∼4 km long glacial meltwater river on Svalbard and in estuarine waters that it flows into. Dissolved iron concentrations in the Bayelva River decreased from a maximum of 734 nM near the glacier to an average value of 116 nM near the mouth of the river. Measurements in the Kongsfjorden estuary suggest that 3 to 10 nM of dFe from the Bayelva River is stabilized in glacial waters by the time it mixes into the ocean. Incubation of Bayelva River waters over two weeks in both the light and dark show similar results, with the majority of dFe being quickly precipitated and 4 to 7 nM Fe stabilized in the dissolved phase. Evidence suggests that Fe is most likely lost from the dissolved phase by aggregation and adsorption of nanoparticulate and colloidal Fe to particles. Dissolved δ56Fe was between - 0.11 ‰ and + 0.09 ‰ for all river samples and did not vary systematically with dFe concentrations. We infer that the Fe is lost from the dissolved phase by a process that fractionates Fe isotopes by less than 0.05‰, indicating that the Fe bonding environment does not change during precipitation. This is consistent with DOC loss that is much faster than predicted photo-oxidation rates, suggesting that DOC is also lost through adsorption and precipitation. Dissolved Fe concentrations in the Bayelva River (15-734 nM), and Fe concentrations which are stabilized in the dissolved phase (4-7 nM) are much lower than some previous estimates of

  2. Identifying glacial meltwater in the Amundsen Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Biddle, Louise; Heywood, Karen; Jenkins, Adrian; Kaiser, Jan

    2016-04-01

    Pine Island Glacier, located in the Amundsen Sea, is losing mass rapidly due to relatively warm ocean waters melting its ice shelf from below. The resulting increase in meltwater production may be the root of the freshening in the Ross Sea over the last 30 years. Tracing the meltwater travelling away from the ice sheets is important in order to identify the regions most affected by the increased input of this water type. We use water mass characteristics (temperature, salinity, O2 concentration) derived from 105 CTD casts during the Ocean2ice cruise on RRS James Clark Ross in January-March 2014 to calculate meltwater fractions north of Pine Island Glacier. The data show maximum meltwater fractions at the ice front of up to 2.4 % and a plume of meltwater travelling away from the ice front along the 1027.7 kg m-3 isopycnal. We investigate the reliability of these results and attach uncertainties to the measurements made to ascertain the most reliable method of meltwater calculation in the Amundsen Sea. Processes such as atmospheric interaction and biological activity also affect the calculated apparent meltwater fractions. We analyse their effects on the reliability of the calculated meltwater fractions across the region using a bulk mixed layer model based on the one-dimensional Price-Weller-Pinkel model (1986). The model includes sea ice, dissolved oxygen concentrations and a simple respiration model, forced by NCEP climatology and an initial linear mixing profile between Winter Water (WW) and Circumpolar Deep Water (CDW). The model mimics the seasonal cycle of mixed layer warming and freshening and simulates how increases in sea ice formation and the influx of slightly cooler Lower CDW impact on the apparent meltwater fractions. These processes could result in biased meltwater signatures across the eastern Amundsen Sea.

  3. Hydrothermal iron flux variability following rapid sea level changes

    NASA Astrophysics Data System (ADS)

    Middleton, Jennifer L.; Langmuir, Charles H.; Mukhopadhyay, Sujoy; McManus, Jerry F.; Mitrovica, Jerry X.

    2016-04-01

    Sea level changes associated with Pleistocene glacial cycles have been hypothesized to modulate melt production and hydrothermal activity at ocean ridges, yet little is known about fluctuations in hydrothermal circulation on time scales longer than a few millennia. We present a high-resolution record of hydrothermal activity over the past 50 ka using elemental flux data from a new sediment core from the Mir zone of the TAG hydrothermal field at 26°N on the Mid-Atlantic Ridge. Mir sediments reveal sixfold to eightfold increases in hydrothermal iron and copper deposition during the Last Glacial Maximum, followed by a rapid decline during the sea level rise associated with deglaciation. Our results, along with previous observations from Pacific and Atlantic spreading centers, indicate that rapid sea level changes influence hydrothermal output on mid-ocean ridges. Thus, climate variability may discretize volcanic processing of the solid Earth on millennial time scales and subsequently stimulate variability in biogeochemical interactions with volcanic systems.

  4. Miniaturised 'lab-on-a-chip' nitrate analyser applied to high resolution in situ analysis of glacial meltwater

    NASA Astrophysics Data System (ADS)

    Beaton, A.; Mowlem, M.; Wadham, J. L.

    2013-12-01

    In situ chemical measurements of glacial meltwater can provide high temporal and spatial resolution data that allow us to infer biogeochemical processes and calculate export from glacial systems. Despite this, in situ measurements of single chemical parameters in glacial meltwater have so far largely been restricted to pH and dissolved oxygen. The lack of high performance ruggedized in situ sensors for other analytes means that the laboratory-based analysis of manually collected samples is still routine. Microfluidics (through lab-on-a-chip technology) permits the miniaturisation of established chemical analysis techniques so that they can be performed in situ. The advantages of decreased size and low power and reagent consumption make these systems suitable for deployment in extreme and inaccessible environments where regular manual sample collection is logistically difficult. We present data from a novel stand-alone microfluidic wet chemical nitrate analyser that has been deployed to monitor a proglacial meltwater river draining from the Greenland ice sheet. By performing a measurement every 20 minutes, the analyser was able to reveal diurnal fluctuations and short term trends in nitrate concentrations that would not discernible using standard daily sampling. High resolution in situ measurements such as these can allow a more accurate determination of nutrient export fluxes from glacial systems into the polar oceans, and allow enhanced interpretation of water quality datasets. Steps have been taken to ruggedize the system so that it can survive the freeze-thaw conditions, dilute concentrations and high sediment loads that can be associated with cryospheric environments. The system is small, has low power consumption and detects nitrate and nitrite with a limit of detection (LOD) of 0.025 μM, which is sufficient for low nutrient glacial environments. On-going work looks to deploy similar nutrient analysers more widely, not only in glacial systems, but also in

  5. Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, southwest Greenland

    NASA Astrophysics Data System (ADS)

    Clason, C. C.; Mair, D. W. F.; Nienow, P. W.; Bartholomew, I. D.; Sole, A.; Palmer, S.; Schwanghart, W.

    2014-07-01

    Meltwater delivered to the bed of the Greenland Ice Sheet is a driver of variable ice-motion through changes in effective pressure and enhanced basal lubrication. Ice surface velocities have been shown to respond rapidly both to meltwater production at the surface and to drainage of supraglacial lakes, suggesting efficient transfer of meltwater from the supraglacial to subglacial hydrological systems. Although considerable effort is currently being directed towards improved modelling of the controlling surface and basal processes, modelling the temporal and spatial evolution of the transfer of melt to the bed has received less attention. Here we present the results of spatially-distributed modelling for prediction of moulins and lake drainages on the Leverett Glacier in south-west Greenland. The model is run for the 2009 and 2010 ablation seasons, and for future increased melt scenarios. The temporal and spatial patterns of modelled lake drainages are qualitatively comparable with those seen from analyses of satellite imagery. The modelled timings and locations of delivery of meltwater to the bed match well with observed temporal and spatial patterns of ice surface speed ups. This is particularly true for the lower catchment (< 1000 m a.s.l.) where both the model and observations indicate that the development of moulins is the main mechanism for the transfer of surface meltwater to the bed. At higher elevations (e.g. 1250-1500 m a.s.l.) the development and drainage of supraglacial lakes becomes increasingly important. At these higher elevations, the delay between modelled melt generation and subsequent delivery of melt to the bed matches the observed delay between the peak air temperatures and subsequent velocity speed ups. Although both moulins and lake drainages are predicted to increase in number for future warmer climate scenarios, the lake drainages play an increasingly important role in both expanding the area over which melt accesses the bed and in enabling

  6. The influence of meltwater on the Labrador Current in Heinrich event 1 and the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Li, Gang; Piper, David J. W.

    2015-01-01

    The Labrador Current transports freshwater from the Arctic regions to the northern Atlantic and the freshwater flux can influence the meridional overturning circulation. The response of the Labrador Current to meltwater processes is unclear during the deglaciation of the ice sheets around the northwest Atlantic. This study utilized cores from Flemish Pass to monitor variations in the strength of the Labrador Current by using the sortable-silt proxy. The carbonate content, the amount of ice-rafted detritus and XRF chemical data were measured to identify the main meltwater events during the last deglaciation. This study observed a clear enhancement of the flow strength of the Labrador Current in Heinrich Event 1 and the Younger Dryas, with the greatest flow strength during the Younger Dryas event. The onset of the current enhancement was dated at ca 13 cal ka BP, which preceded the enhanced ice-rafted deposition in Hudson Strait by about one thousand years. The current enhancement in Flemish Pass during the Younger Dryas event corresponds to the freshening of the surface water. Thus meltwater preceding significant iceberg supply has an important effect on the Labrador Current in Heinrich events on the Laurentide Ice Sheet margin.

  7. Spreading of Greenland meltwaters in the ocean revealed by noble gases

    NASA Astrophysics Data System (ADS)

    Beaird, Nicholas; Straneo, Fiammetta; Jenkins, William

    2015-09-01

    We present the first noble gas observations in a proglacial fjord in Greenland, providing an unprecedented view of surface and submarine melt pathways into the ocean. Using Optimum Multiparameter Analysis, noble gas concentrations remove large uncertainties inherent in previous studies of meltwater in Greenland fjords. We find glacially modified waters with submarine melt concentrations up to 0.66 ± 0.09% and runoff 3.9 ± 0.29%. Radiogenic enrichment of Helium enables identification of ice sheet near-bed melt (0.48 ± 0.08%). We identify distinct regions of meltwater export reflecting heterogeneous melt processes: a surface layer of both runoff and submarine melt and an intermediate layer composed primarily of submarine melt. Intermediate ocean waters carry the majority of heat to the fjords' glaciers, and warmer deep waters are isolated from the ice edge. The average entrainment ratio implies that ocean water masses are upwelled at a rate 30 times the combined glacial meltwater volume flux.

  8. Simulation of the cold climate event 8200 years ago by meltwater outburst from Lake Agassiz

    NASA Astrophysics Data System (ADS)

    Bauer, E.; Ganopolski, A.; Montoya, M.

    2004-09-01

    The cold climate anomaly about 8200 years ago is investigated with CLIMBER-2, a coupled atmosphere-ocean-biosphere model of intermediate complexity. This climate model simulates a cooling of about 3.6 K over the North Atlantic induced by a meltwater pulse from Lake Agassiz routed through the Hudson strait. The meltwater pulse is assumed to have a volume of 1.6 × 1014 m3 and a period of discharge of 2 years on the basis of glaciological modeling of the decay of the Laurentide Ice Sheet (LIS). We present a possible mechanism which can explain the centennial duration of the 8.2 ka cold event. The mechanism is related to the existence of an additional equilibrium climate state with reduced North Atlantic Deep Water (NADW) formation and a southward shift of the NADW formation area. Hints at the additional climate state were obtained from the largely varying duration of the pulse-induced cold episode in response to overlaid random freshwater fluctuations in Monte Carlo simulations. The model equilibrium state was attained by releasing a weak multicentury freshwater flux through the St. Lawrence pathway completed by the meltwater pulse. The existence of such a climate mode appears essential for reproducing climate anomalies in close agreement with paleoclimatic reconstructions of the 8.2 ka event. The results furthermore suggest that the temporal evolution of the cold event was partly a matter of chance.

  9. Modeling glacial meltwater plume dynamics and sedimentation in high-latitude fjords

    NASA Astrophysics Data System (ADS)

    Mugford, R. I.; Dowdeswell, J. A.

    2011-03-01

    A model, SedPlume, has been developed to simulate marine sediment deposited by glacial meltwater plumes emerging from tidewater glaciers. Turbid meltwater emerging from beneath a glacier into a fjord rises as a buoyant forced plume due to density contrasts with the ambient fjord water. SedPlume assumes that meltwater discharge flows at a constant rate for long enough periods that the plume reaches a steady state. Entrainment of ambient fluid into the turbulent plume is assumed to occur at a rate proportional to the local velocity of the plume. Plume motion is considered in two dimensions: one horizontal dimension (perpendicular to the glacier front) and the vertical dimension. An integral model is formulated for the conservation equations of volume, momentum, buoyancy, and sediment flux along the path of a turbulent plume injected into stably stratified ambient fluid. Sedimentation occurs from the plume when the radial component of the sediment fall velocity exceeds the entrainment velocity. When the plume reaches the surface, it is treated as a radially spreading surface gravity current, for which exact solutions exist for the sediment deposition rate. Flocculation of silt and clay particles is modeled using empirical measurements of particle settling velocities in fjords to adjust the settling velocity of fine-grained sediments. SedPlume has been applied to McBride Inlet, Alaska, a temperate glaciated fjord where the majority of sedimentation originates from meltwater sources. SedPlume produces rates and patterns of sedimentation in good agreement with observations, with calculated peak ice-proximal annual sedimentation rates of approximately 22 m yr-1.

  10. Modelling meltwater delivery to the ice-bed interface through full thickness fractures on outlet glaciers of the western Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Clason, C.; Mair, D.; Nienow, P. W.

    2010-12-01

    Dynamic response to increased supraglacial meltwater generation and subsequent influx to the subglacial hydrological system is well documented in temperate glaciers. Meltwater-enhanced acceleration of ice surface velocities, or ‘spring events’, have also more recently been observed on polythermal glaciers and outlet glaciers of the Greenland Ice Sheet (GrIS). These high velocity events may be a response to increased basal lubrication and basal water pressures when meltwater reaches the subglacial system directly through moulins. Supraglacial meltwater can provide hydrostatic stresses adequate to offset closure due to the lithostatic stress of the ice when streams intersect and enter surface crevasses. A crevasse will continue to propagate through the full ice thickness provided the meltwater head within the crevasse remains sufficient, thereby allowing this flux of meltwater to be delivered to the ice-bed interface. A spatially distributed model for prediction of full ice thickness water-driven fracture and quantification of meltwater delivered to the bed has been produced. The model consists of three major components: the first sub-routine calculates surface tensile stresses from measured ice surface velocities and identifies areas likely to contain crevassing following the Von Mises failure criteria; the second is a degree day melt model and flow routing model run using measured meteorological inputs; the third sub-routine calculates crevasse penetration depths using an established linear elastic fracture mechanics model for propagation of water-filled fractures. The daily outputs of melt modelling weight routing of meltwater across the ice surface, and in turn determine the discharge into crevasses. This allows the supraglacial meltwater head, and thus fracture propagation speed, to vary daily within crevasse depth modelling. The temporal resolution of the model also allows the evolution of moulin formation through the ablation season to be captured. We

  11. Flux correction and the simulation of changing climate

    NASA Astrophysics Data System (ADS)

    Schneider, Edwin K.

    1996-03-01

    A flaw is pointed out in the manner in which flux correction is currently applied to coupled atmosphere-ocean general circulation models. If a transient climate simulation were carried out using perfect initial data and a perfect model, then a perfect simulation would be made. However, if the model were flux corrected so that it is in equilibrium for current conditions, according to current practice, then errors in the simulation would grow initially to a finite amplitude and persist indefinitely. Larger errors would be produced by a simulation with the flux corrected model beginning from pre-industrial conditions than by a simulation beginning from current conditions. An example with a simple linear model is constructed to illustrate this point, and the relationship to the cold start problem is demonstrated. An optimal flux correction for the simple example is shown to be one which would eliminate the error in the current climate from a transient simulation begun sufficiently far in the past.

  12. Deglacial Warming in the Gulf of Mexico Preceded Laurentide Ice Sheet Meltwater Input: Implications for Tropical Climate Forcing

    NASA Astrophysics Data System (ADS)

    Flower, B. P.; Hastings, D. W.; Hill, H. W.; Hollander, D. J.; Lodico, J.; Quinn, T. M.

    2002-12-01

    As part of the Western Hemisphere Warm Pool (WHWP), the Gulf of Mexico is an important source of heat and moisture to the North American continent and the higher latitudes. Orca Basin on the Louisiana slope in the northern Gulf of Mexico is ideally located to record deglacial WHWP sea-surface temperature (SST) warming in relation to meltwater input from the Laurentide Ice Sheet (LIS). Paired δ18O and Mg/Ca data on planktic foraminifera (Globigerinoides ruber, white variety) from cores EN32-PC4 and -PC6 are used to separate deglacial changes in SST and δ18Oseawater due to low-salinity meltwater. In core EN32-PC4, Mg-SST increases from near full-glacial values of about 24°C at ca. 15 ka 14C to >28°C at ca. 12.8 ka 14C, including a sharp increase of >3°C from 14.2-13.3 ka 14C. This warming clearly precedes the peak of meltwater input (minimum Gs. ruber δ18O) by nearly 2 k.y. Furthermore, Mg-SST and global δ18Oseawater changes can be subtracted from Gs. ruber δ18O to isolate the influence of meltwater (ice-volume corrected δ18Oseawater), which can be interpreted in terms of salinity variations. This exercise indicates a peak in meltwater input at 12 ka 14C, close to the timing of meltwater pulse 1A. If confirmed in EN32-PC6, these results suggest that (1) subtropical deglacial SST warming preceded LIS decay, and (2) the origin of sea-level rise during mwp-1A was primarily meltwater derived from the LIS. Extending paired Mg-SST and δ18O data on Gs. ruber into Marine Isotope Stage (MIS) 3 further illuminates the phasing of WHWP changes relative to high-latitude climate variability. Preliminary results indicate significant SST variability that can be correlated to Dansgaard-Oeschger events of the Greenland ice core records. In addition, δ18O data on Gs. ruber (pink variety) indicate at least one interval of significant meltwater input in mid-MIS 3. Our continuing work will test the hypothesis that the tropical/subtropical Atlantic is an important driver of

  13. Bulk meltwater flow and liquid water content of snowpacks mapped using the electrical self-potential (SP) method

    NASA Astrophysics Data System (ADS)

    Thompson, Sarah S.; Kulessa, Bernd; Essery, Richard L. H.; Lüthi, Martin P.

    2016-02-01

    Our ability to measure, quantify and assimilate hydrological properties and processes of snow in operational models is disproportionally poor compared to the significance of seasonal snowmelt as a global water resource and major risk factor in flood and avalanche forecasting. We show here that strong electrical self-potential fields are generated in melting in situ snowpacks at Rhone Glacier and Jungfraujoch Glacier, Switzerland. In agreement with theory, the diurnal evolution of self-potential magnitudes ( ˜ 60-250 mV) relates to those of bulk meltwater fluxes (0-1.2 × 10-6 m3 s-1) principally through the permeability and the content, electrical conductivity and pH of liquid water. Previous work revealed that when fresh snow melts, ions are eluted in sequence and electrical conductivity, pH and self-potential data change diagnostically. Our snowpacks had experienced earlier stages of melt, and complementary snow pit measurements revealed that electrical conductivity ( ˜ 1-5 × 10-6 S m-1) and pH ( ˜ 6.5-6.7) as well as permeabilities (respectively ˜ 9.7 × 10-5 and ˜ 4.3 × 10-5 m2 at Rhone Glacier and Jungfraujoch Glacier) were invariant. This implies, first, that preferential elution of ions was complete and, second, that our self-potential measurements reflect daily changes in liquid water contents. These were calculated to increase within the pendular regime from ˜ 1 to 5 and ˜ 3 to 5.5 % respectively at Rhone Glacier and Jungfraujoch Glacier, as confirmed by ground truth measurements. We conclude that the electrical self-potential method is a promising snow and firn hydrology sensor owing to its suitability for (1) sensing lateral and vertical liquid water flows directly and minimally invasively, (2) complementing established observational programs through multidimensional spatial mapping of meltwater fluxes or liquid water content and (3) monitoring autonomously at a low cost. Future work should focus on the development of self-potential sensor

  14. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Golledge, N. R.; Menviel, L.; Carter, L.; England, M. H.; Cortese, G.; Levy, R. H.

    2014-12-01

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise - `meltwater pulses' - took place. Although the timing and magnitude of these events have become better-constrained, a causal link between ocean stratification, the meltwater pulses, and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.

  15. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning

    NASA Astrophysics Data System (ADS)

    Golledge, N. R.; Menviel, L.; Carter, L.; Fogwill, C. J.; England, M. H.; Cortese, G.; Levy, R. H.

    2014-09-01

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise—meltwater pulses—took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.

  16. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning.

    PubMed

    Golledge, N R; Menviel, L; Carter, L; Fogwill, C J; England, M H; Cortese, G; Levy, R H

    2014-01-01

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise--meltwater pulses--took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat. PMID:25263015

  17. Phasing of deglacial warming and Laurentide Ice Sheet meltwater in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Flower, Benjamin P.; Hastings, David W.; Hill, Heather W.; Quinn, Terrence M.

    2004-07-01

    Evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation. However, existing studies show that deglacial warming was asynchronous across the tropical band, complicating the identification of causal mechanisms. The Orca Basin in the northern Gulf of Mexico is ideally located to record subtropical Atlantic sea-surface temperature (SST) warming in relation to meltwater input from the Laurentide Ice Sheet. Paired δ18O and Mg/Ca data on the planktonic foraminifer Globigerinoides ruber from core EN32-PC6 are used to separate deglacial changes in SST and δ18O of seawater. SST as calculated from Mg/Ca data increased by >3 °C from ca. 17.2 to 15.5 ka in association with Heinrich event 1 and was not in phase with Greenland air temperature. Subtracting temperature effects from δ18O values in G. ruber reveals two excursions representing Laurentide meltwater input to the Gulf of Mexico, one of >1.5‰ from ca. 16.1 to 15.6 ka and a second major spike of >2.5‰ from ca. 15.2 to 13.0 ka that encompassed meltwater pulse 1A and peaked ca. 13.8 ka during the Bølling-Ållerød. Conversion to salinity through the use of a Laurentide meltwater end member of -25‰ indicates that near-surface salinity decreased by 2‰ 4‰ during these spikes. These results suggest that Gulf of Mexico SST warming preceded peak Laurentide Ice Sheet decay and the Bølling-Ållerød interval by >2 k.y. and that heat was retained in the subtropical Atlantic during Heinrich event 1, consistent with modulation of deglacial climate by thermohaline circulation.

  18. Quantification of Seasonal and Interannual Variability of Proglacial Meltwater from a Tidewater Glacier

    NASA Astrophysics Data System (ADS)

    Darlington, E. F.; Hodgkins, R.; Jenkins, A.

    2014-12-01

    Ice - ocean interactions of tidewater glaciers remain poorly understood; yet 39% of the global glaciated area drains directly into the ocean via tidewater glaciers. As the Arctic cryosphere continues to lose mass in response to a warming climate, more detailed observations are needed to increase our understanding of ice - ocean processes, enabling improved model predictions of Arctic change. Svalbard hosts a high proportion of tidewater glaciers, including Kronebreen, the fastest flowing glacier on the archipelago. The proglacial meltwater exiting the base of Kronebreen transports fine grained sediment to Kongsfjorden, entrained in a buoyant plume which spreads laterally and is visible at the surface. In-situ measurements of the concentration and spectral reflectance of these surface sediments were used to calibrate spectral data from the MODIS instruments on the Terra and Aqua satellites. Temperature and salinity in front of the calving face, and throughout the meltwater plume, have been measured using a hand held CTD. The spatial surface pattern of total suspended sediment (TSS; g l-1) and plume area, has been quantified for every cloud free day between 1st June - 30th September from 2002 - 2013. High TSS sediment during the early melt season indicates flushing, whilst sediment exhaustion is apparent at the end. We show that the areal extent of these proglacial plumes responds to atmospheric temperature, with a 12 day lag. An underlying seasonal evolution of plume extent is apparent; plume area is small at the beginning and end of the melt season, peaking mid-July. Wind speed and direction also play a role in dictating the length of plume formation, with katabatic winds originating from the glacier, lengthening plumes. However, the overall extent of the sediment plume is dependent on meltwater inputs. As such, this method enables the daily to interannual quantification of proglacial meltwater release from tidewater glaciers, utilizing remote sensing.

  19. From circumpolar deep water to the glacial meltwater plume on the eastern Amundsen Shelf

    NASA Astrophysics Data System (ADS)

    Nakayama, Y.; Schröder, M.; Hellmer, H. H.

    2013-07-01

    The melting of Pine Island Ice Shelf (PIIS) has increased since the 1990 s, which may have a large impact on ice sheet dynamics, sea-level rise, and changes in water mass properties of surrounding oceans. The reason for the PIIS melting is the relatively warm (˜1.2°C) Circumpolar Deep Water (CDW) that penetrates into the PIIS cavity through two submarine glacial troughs located on the Amundsen Sea continental shelf. In this study, we mainly analyze the hydrographic data obtained during ANTXXVI/3 in 2010 with the focus on pathways of the intruding CDW, PIIS melt rates, and the fate of glacial meltwater. We analyze the data by dividing CTD profiles into 6 groups according to intruding CDW properties and meltwater content. From this analysis, it is seen that CDW warmer than 1.23 °C (colder than 1.23 °C) intrudes via the eastern (central) trough. The temperature is controlled by the thickness of the intruding CDW layer. The eastern trough supports a denser CDW layer than the water mass in Pine Island Trough (PIT). The eastern intrusion is modified on the way into PIT through mixing with the lighter and colder CDW from the central trough. Using ocean transport and tracer transport calculations from the ice shelf front CTD section, the estimated melt rate in 2010 is ˜30myr-1, which is comparable to published values. From spatial distributions of meltwater content, meltwater flows along the bathymetry towards the west. When compared with earlier (2000) observations, a warmer and thicker CDW layer is observed in Pine Island Trough for the period 2007-2010, indicating a recent thickening of the CDW intrusion.

  20. Circulation and meltwater distribution in the Bellingshausen Sea: From shelf break to coast

    NASA Astrophysics Data System (ADS)

    Zhang, Xiyue; Thompson, Andrew F.; Flexas, Mar M.; Roquet, Fabien; Bornemann, Horst

    2016-06-01

    West Antarctic ice shelves have thinned dramatically over recent decades. Oceanographic measurements that explore connections between offshore warming and transport across a continental shelf with variable bathymetry toward ice shelves are needed to constrain future changes in melt rates. Six years of seal-acquired observations provide extensive hydrographic coverage in the Bellingshausen Sea, where ship-based measurements are scarce. Warm but modified Circumpolar Deep Water floods the shelf and establishes a cyclonic circulation within the Belgica Trough with flow extending toward the coast along the eastern boundaries and returning to the shelf break along western boundaries. These boundary currents are the primary water mass pathways that carry heat toward the coast and advect ice shelf meltwater offshore. The modified Circumpolar Deep Water and meltwater mixtures shoal and thin as they approach the continental slope before flowing westward at the shelf break, suggesting the presence of the Antarctic Slope Current. Constraining meltwater pathways is a key step in monitoring the stability of the West Antarctic Ice Sheet.

  1. Late Pleistocene and Holocene meltwater events in the western Arctic Ocean

    USGS Publications Warehouse

    Poore, R.Z.; Osterman, L.; Curry, W.B.; Phillips, R.L.

    1999-01-01

    Accelerator mass spectrometer 14C dated stable isotope data from Neogloboquadrina pachyerma in cores raised from the Mendeleyev Ridge and slope provide evidence for significant influx of meltwater to the western Arctic Ocean during the early part of marine oxygen isotope stage 1 (OIS 1) and during several intervals within OIS 3. The strongest OIS 3 meltwater event occurred before ca. 45 ka (conventional radiocarbon age) and was probably related to the deglaciation at the beginning of OIS 3. Major meltwater input to the western Arctic Ocean during the last deglaciation coincides closely with the maximum rate of global sea-level rise as determined from the Barbados sea-level record, demonstrating a strong link between the global record and changes in the central Arctic Ocean. OIS 2, which includes the last glacial maximum, is very condensed or absent in the cores. Abundance and ??13C values for N. pachyderma in the middle part of OIS 3 are similar to modern values, indicating high productivity and seasonal ice-free areas along the Arctic margin at that time. These records indicate that the Arctic Ocean was a source of heat and moisture to the northern polar atmosphere during parts of OIS 3.

  2. Fast nanoscale heat-flux modulation with phase-change materials

    NASA Astrophysics Data System (ADS)

    van Zwol, P. J.; Joulain, K.; Ben Abdallah, P.; Greffet, J. J.; Chevrier, J.

    2011-05-01

    We introduce a concept for electrically controlled heat-flux modulation. A flux contrast larger than 10 dB is expected with switching time on the order of tens of nanoseconds. Heat-flux modulation is based on the interplay between radiative heat transfer at the nanoscale and phase-change materials. Such large contrasts are not obtainable in solids, or in far field. As such, this opens up new horizons for temperature modulation and actuation at the nanoscale.

  3. Surface expression of subglacial meltwater movement, Bering Glacier, Alaska

    SciTech Connect

    Cadwell, D.H. ); Fleisher, P.J. . Dept. of Earth Sciences); Bailey, P.K. )

    1993-03-01

    Longitudinal topographic profiles (1988--1992) across the thermokarst terminus of the Grindle Hills Ice-tongue and interlobate moraine of the Bering Piedmont Glacier document annual changes in crevasse patterns and fluctuations in surface elevation related to subglacial water movement. A semi-continuous record of aerial photos (1978--1990), plus field observations (1988--1992), reveal the progressive enlargement of two lateral collapse basin on both sides of the thermokarst, connected by a transverse collapse trough. Seasonally generated meltwater at depth rises within the glacier, fills the basins and other depressions and lifts the thermokarst terminus of the ice-tongue a few meters by buoyancy and hydrostatic pressure. The resulting surface tension creates a chaotic crevasse pattern unrelated to normal glacier movement. The crevasses open (2 m wide, 8--10 m deep) in response to increased water accumulation at depth and close during subsidence as the ice-tongue settles following evacuation of subglacier water. A network of open conduits (>10 m diameter), exposed by surface ablation, provides evidence for the scale of englacial passageways beneath the thermokarst and represents a form of subglacial ablation that leads to removal of support and collapse in stagnant glacier masses.

  4. Estimation of surface temperature variations due to changes in sky and solar flux with elevation.

    USGS Publications Warehouse

    Hummer-Miller, S.

    1981-01-01

    Sky and solar radiance are of major importance in determining the ground temperature. Knowledge of their behavior is a fundamental part of surface temperature models. These 2 fluxes vary with elevation and this variation produces temperature changes. Therefore, when using thermal-property differences to discriminate geologic materials, these flux variations with elevation need to be considered. -from Author

  5. Transcriptional regulation is insufficient to explain substrate-induced flux changes in Bacillus subtilis

    PubMed Central

    Chubukov, Victor; Uhr, Markus; Le Chat, Ludovic; Kleijn, Roelco J; Jules, Matthieu; Link, Hannes; Aymerich, Stephane; Stelling, Jörg; Sauer, Uwe

    2013-01-01

    One of the key ways in which microbes are thought to regulate their metabolism is by modulating the availability of enzymes through transcriptional regulation. However, the limited success of efforts to manipulate metabolic fluxes by rewiring the transcriptional network has cast doubt on the idea that transcript abundance controls metabolic fluxes. In this study, we investigate control of metabolic flux in the model bacterium Bacillus subtilis by quantifying fluxes, transcripts, and metabolites in eight metabolic states enforced by different environmental conditions. We find that most enzymes whose flux switches between on and off states, such as those involved in substrate uptake, exhibit large corresponding transcriptional changes. However, for the majority of enzymes in central metabolism, enzyme concentrations were insufficient to explain the observed fluxes—only for a number of reactions in the tricarboxylic acid cycle were enzyme changes approximately proportional to flux changes. Surprisingly, substrate changes revealed by metabolomics were also insufficient to explain observed fluxes, leaving a large role for allosteric regulation and enzyme modification in the control of metabolic fluxes. PMID:24281055

  6. Early Holocene meltwater events in the Labrador Sea

    NASA Astrophysics Data System (ADS)

    Pearce, Christof; Jennings, Anne; Andrews, John; Hillaire-Marcel, Claude; Seidenkrantz, Marit-Solveig; Lewis, Mike

    2016-04-01

    During the early Holocene, the Labrador Sea was strongly influenced by the presence of the remainder of the Laurentide Ice Sheet and its active eastern margin. Glacial advances and retreats lead to episodic release of meltwater and icebergs with potential impact on ocean circulation and climate during the deglaciation. The purpose of this study is to use detrital carbonate (DC) records in the Labrador Sea to study the spatial variability of the carbonate events and inferred sources and routing of glacial meltwater originating from Hudson Strait (HS) as well as potential contributions from Northern Baffin Bay (NBB) ice sheet margins. We use DC in sediment cores as a proxy for glacial meltwater and ice berg drift from these areas. More than 20 sediment cores with published DC, stable oxygen isotope, and radiocarbon stratigraphies provide the data for this study. Our hypothesis is that the complex interplay of current systems, shelf and slope bathymetry and location of meltwater and ice berg injection points will affect the spatial distribution of the DC events. In addition, differences in local ocean reservoir age for shelf, slope and open ocean sites may also contribute to offsets in the apparent ages of DC events. Identification of DC peaks also is influenced by sedimentation rates and sampling resolution. To objectively correlate DC events, we study mostly published core data, removing all earlier assumptions about marine reservoir ages and assess all core chronologies with their associated errors. Our results show that none of the DC events is found in all sites and no record captures all of the DC events. Despite this, some of the larger events occur in several records and allow robust temporal and spatial mapping of the meltwater pathways. Besides the meltwater route due south along the Labrador margin on the shelf, some events show a clear signal in deeper Labrador Sea sites pointing at a more direct injection of freshwater in the subpolar gyre.

  7. Surface Drifters Track the Fate of Greenland Ice Sheet Meltwater

    NASA Astrophysics Data System (ADS)

    Hauri, Claudine; Truffer, Martin; Winsor, Peter; Lennert, Kunuk

    2014-07-01

    Understanding the fate and influence of glacial meltwater in heavily ice-covered fjord systems has proven difficult because previous measurement platforms were con­strained to deeper water to keep instrumentation safe from drifting icebergs. Now, using novel, satellite-tracked devices that can with­ stand multiple collisions with ice blocks (see Figure 1) without incurring much damage, scientists have obtained new and detailed data about the role of Greenland Ice Sheet meltwater and its trajectories through God­thåbsfjord in western Greenland.

  8. High Resolution Photogrammetric Digital Elevation Models Across Calving Fronts and Meltwater Channels in Greenland

    NASA Astrophysics Data System (ADS)

    Le Bel, D. A.; Brown, S.; Zappa, C. J.; Bell, R. E.; Frearson, N.; Tinto, K. J.

    2014-12-01

    Photogrammetric digital elevation models (DEMs) are a powerful approach for understanding elevation change and dynamics along the margins of the large ice sheets. The IcePod system, mounted on a New York Air National Guard LC-130, can measure high-resolution surface elevations with a Riegl VQ580 scanning laser altimeter and Imperx Bobcat IGV-B6620 color visible-wavelength camera (6600x4400 resolution); the surface temperature with a Sofradir IRE-640L infrared camera (spectral response 7.7-9.5 μm, 640x512 resolution); and the structure of snow and ice with two radar systems. We show the use of IcePod imagery to develop DEMs across calving fronts and meltwater channels in Greenland. Multiple over-flights of the Kangerlussaq Airport ramp have provided a test of the technique at a location with accurate, independently-determined elevation. Here the photogrammetric DEM of the airport, constrained by ground control measurements, is compared with the Lidar results. In July 2014 the IcePod ice-ocean imaging system surveyed the calving fronts of five outlet glaciers north of Jakobshavn Isbrae. We used Agisoft PhotoScan to develop a DEM of each calving front using imagery captured by the IcePod systems. Adjacent to the ice sheet, meltwater plumes foster mixing in the fjord, moving warm ocean water into contact with the front of the ice sheet where it can undercut the ice front and trigger calving. The five glaciers provide an opportunity to examine the calving front structure in relation to ocean temperature, fjord circulation, and spatial scale of the meltwater plumes. The combination of the accurate DEM of the calving front and the thermal imagery used to constrain the temperature and dynamics of the adjacent plume provides new insights into the ice-ocean interactions. Ice sheet margins provide insights into the connections between the surface meltwater and the fate of the water at the ice sheet base. Surface meltwater channels are visualized here for the first time using

  9. Meltwater pathways and grain size transformation in a Pleistocene Mediterranean glacial-fluvial system

    NASA Astrophysics Data System (ADS)

    Adamson, Kathryn; Woodward, Jamie; Hughes, Philip

    2013-04-01

    The Pleistocene sedimentary records of Mount Orjen, western Montenegro, have been used to investigate changes in grain size characteristics of fine sediments transported from the glaciated mountains to the fluvial systems downstream. Understanding the particle size characteristics of the fine sediments transported by these cold stage river systems is important for several reasons. The braided rivers draining the glaciated mountains of the western Balkans may have been an important source of loess for example. It is also important to establish the grain size signature of suspended sediment delivered to the marine environment to aid land-marine correlations. The fine-grained component of the tills is dominated by glacially-comminuted limestone particles. Detailed particle size analysis of the fine sediment matrix component (<63 μm) of glacial till and alluvial deposits has been undertaken using multiple samples at 12 sites surrounding the Orjen massif. This limestone karst terrain includes a range of meltwater pathways and depositional contexts, including: river valleys, alluvial fans, poljes, and ice marginal settings. 35 U-series ages and soil development indices have been used to develop a robust geochronology for the Pleistocene records Two dominant surface meltwater and sediment pathways have been identified around Mount Orjen. The particle size distributions reveal that these transportation routes can have distinctive sedimentological signatures. Type 1 pathways deliver meltwater and sediments downstream via bedrock gorges. In these settings, the fine grained alluvial matrix presents a largely bimodal particle size distribution (PSD). Type 2 pathways represent meltwater channels draining directly from the ice margin. Alluvial sediments within these environments more closely resemble the normally distributed PSD of the glacial tills. The transition to bimodal PSDs, downstream of Type 1 meltwater routes, suggests that the glacially-comminuted sediments are

  10. Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, Southwest Greenland

    NASA Astrophysics Data System (ADS)

    Clason, C. C.; Mair, D. W. F.; Nienow, P. W.; Bartholomew, I. D.; Sole, A.; Palmer, S.; Schwanghart, W.

    2015-01-01

    Meltwater delivered to the bed of the Greenland Ice Sheet is a driver of variable ice-motion through changes in effective pressure and enhanced basal lubrication. Ice surface velocities have been shown to respond rapidly both to meltwater production at the surface and to drainage of supraglacial lakes, suggesting efficient transfer of meltwater from the supraglacial to subglacial hydrological systems. Although considerable effort is currently being directed towards improved modelling of the controlling surface and basal processes, modelling the temporal and spatial evolution of the transfer of melt to the bed has received less attention. Here we present the results of spatially distributed modelling for prediction of moulins and lake drainages on the Leverett Glacier in Southwest Greenland. The model is run for the 2009 and 2010 ablation seasons, and for future increased melt scenarios. The temporal pattern of modelled lake drainages are qualitatively comparable with those documented from analyses of repeat satellite imagery. The modelled timings and locations of delivery of meltwater to the bed also match well with observed temporal and spatial patterns of ice surface speed-ups. This is particularly true for the lower catchment (<1000 m a.s.l.) where both the model and observations indicate that the development of moulins is the main mechanism for the transfer of surface meltwater to the bed. At higher elevations (e.g. 1250-1500 m a.s.l.) the development and drainage of supraglacial lakes becomes increasingly important. At these higher elevations, the delay between modelled melt generation and subsequent delivery of melt to the bed matches the observed delay between the peak air temperatures and subsequent velocity speed-ups, while the instantaneous transfer of melt to the bed in a control simulation does not. Although both moulins and lake drainages are predicted to increase in number for future warmer climate scenarios, the lake drainages play an increasingly

  11. Meltwaters in Antarctica: Delineating and Quantifying Sources of Freshwater along the Western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Corbett, D. R.; Null, K. A.; Crenshaw, J.; Lyons, W. B.; Peterson, R. N.; Peterson, L.; Viso, R. F.; Buck, C. S.

    2014-12-01

    The importance of freshwater discharge from glaciers and ice sheets along the Western Antarctic Peninsula (WAP) is now evident, but quantifying the source of freshwater inputs (e.g., calving, ice sheet basal melt, and/or subglacial flow) directly and the associated constituent fluxes have been limited. The mode of freshwater contribution in glacier marine environments can be important to understanding glacial melt dynamics related to climate change and overall influences on the coastal ecosystem. As part of an NSF funded project, we are attempting to quantify for the first time using land-based measurements the rate of freshwater input and the associated flux of nutrients and iron to the coastal waters of the WAP, and the mixing of these constituents across the continental shelf. This research is combining geophysical measurements with established radio- (radium quartet and 222Rn) and stable tracer (18O and 2H) techniques to quantify submarine groundwater discharge (SGD), particularly the freshwater contributions, to the coast and delineate the source of water and dissolved constituents. Nearshore surface water and end member (e.g., streams, groundwater, etc.) tracer data suggest a means of discerning the source of freshwater, with up to 50% of freshwater input from subsurface flow. Time series tracer data in combination with electrical resistivity measurements provide clear observations of SGD and provide insights into tidal influences and the rapid response of subsurface fluid interactions. More broadly, 223Ra and 224Ra activities are elevated in porewaters and glacial meltwaters and decreased in surface water with distance from shore. A preliminary mass balance model estimates SGD at approximately 200 m3 d-1 per m of shoreline during austral summer, comparable to temperate environments. Across the shelf, surface water tracer concentrations suggest rapid cross-shelf mixing (730-14000 m2s-1) that could increase delivery of nearshore freshwater and dissolved

  12. Changes in magnetic flux density around fatigue crack tips of carbon tool steels

    NASA Astrophysics Data System (ADS)

    Honda, Takashi; Kida, Katsuyuki; Santos, Edson C.; Tanabe, Hirotaka

    2010-03-01

    Fatigue failure of steel occurs when small cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components it is important to find the cracks which eventually grow to cause failures. However, at present, it is not easy to distinguish, in the early stages of growth, the cracks which will grow fast and cause failure. We hypothesized that it may be possible to distinguish them by comparing changes in the magnetic flux density around the tips of those cracks that grew large enough to cause failure. In order to measure these changes in magnetic flux density, we developed a scanning Hall probe microscope and observed the fatigue cracks growing from artificial slits in carbon tool steels (JIS SKS93). We also compared the changes in magnetic flux density around crack tips which grew under different loads and found that there is a strong correlation between the magnetic flux density, crack growth and stress intensity factors. In order to understand this relation, we measured the changes in the magnetic flux density and residual tensile stress by using an X-ray system, and found that the magnetic flux density changes not only in the plastic deformation area but also in the area of elastic stress field with increased stress.

  13. Changes in magnetic flux density around fatigue crack tips of carbon tool steels

    NASA Astrophysics Data System (ADS)

    Honda, Takashi; Kida, Katsuyuki; Santos, Edson C.; Tanabe, Hirotaka

    2009-12-01

    Fatigue failure of steel occurs when small cracks form in a component and then continue to grow to a size large enough to cause failure. In order to understand the strength of steel components it is important to find the cracks which eventually grow to cause failures. However, at present, it is not easy to distinguish, in the early stages of growth, the cracks which will grow fast and cause failure. We hypothesized that it may be possible to distinguish them by comparing changes in the magnetic flux density around the tips of those cracks that grew large enough to cause failure. In order to measure these changes in magnetic flux density, we developed a scanning Hall probe microscope and observed the fatigue cracks growing from artificial slits in carbon tool steels (JIS SKS93). We also compared the changes in magnetic flux density around crack tips which grew under different loads and found that there is a strong correlation between the magnetic flux density, crack growth and stress intensity factors. In order to understand this relation, we measured the changes in the magnetic flux density and residual tensile stress by using an X-ray system, and found that the magnetic flux density changes not only in the plastic deformation area but also in the area of elastic stress field with increased stress.

  14. Evidence for Meltwater Pulse 1a in the Gulf of Mexico based on radiogenic isotopes

    NASA Astrophysics Data System (ADS)

    Biller, N. B.; Martin, E. E.; Flower, B. P.

    2011-12-01

    Meltwater pulse 1a (MWP-1a) is associated with a rapid sea level rise of more than 20 m in less than 500 yrs during the last deglaciation. This event has been dated at between 14.17 and 13.6 ka based on U/Th dating of Barbados corals, but other studies suggest it coincided with the onset of the Bolling warm interval at ca 14.6 ka. The contribution of inferred meltwater from the Antarctic ice sheet and Northern Hemisphere ice sheets is under debate. Relative contributions from the northern versus southern hemisphere have implications for variations in ocean surface salinity, North Atlantic Deep Water formation and related climate responses. A study of bulk sediment δ18O values from core MD02-2550 from the anoxic Orca Basin in the Gulf of Mexico produced peak δ18O values of -5.5 % during a foraminifera-barren interval dated at ca. 14.54-14.35 ka based on an age model using >40 AMS 14C dates on Globigerinoides ruber. This δ18O value is unusual for marine sediments and has been interpreted to represent material eroded by the Laurentide Ice Sheet and delivered to the Gulf of Mexico during or just before MWP-1a. This interpretation is consistent with data from detrital carbonate grains recovered from Heinrich Events in the North Atlantic that are believed to represent lower Paleozoic basin sediments from northeastern Canada (Hodell and Curtis, 2008). For this study, we evaluated radiogenic isotopes of Nd and Pb (Sr isotopes will be added in the near future) on dilute 0.1N HCl leachates of bulk sediments from MD02-2550 to identify changes in input sources during the foraminifera-barren interval. There are few data on modern Nd and Pb isotopes for Gulf of Mexico sediments, but limited data support our expectation that leachates of older continental material sourced from Canada should contribute more radiogenic Pb and less radiogenic Nd than leachates of younger sediments derived from the Mississippi River drainage basin. Measured 206Pb/204Pb values are ~19.0 before and

  15. Capturing Greenland Meltwater Plume Dynamics with IcePod Imagery

    NASA Astrophysics Data System (ADS)

    Brown, S.; Le Bel, D. A.; Zappa, C. J.; Porter, D. F.; Tinto, K. J.; Bell, R. E.; Frearson, N.

    2014-12-01

    Meltwater that forms on the surface of the Greenland Ice Sheet and falls to the ice sheet bed eventually emerges at the calving front as tan, turbid plumes of water. Adjacent to the ice, these meltwater plumes foster mixing in the fjord moving warm ocean water into contact with the front of the ice sheet where it can undercut the ice front and trigger calving. The dynamics of meltwater plumes is difficult to study due to their proximity to the steep calving fronts and their intermittent nature. In July 2014 the IcePod, the ice-ocean imaging system mounted on a New York Air National Guard LC-130, surveyed the 5 glaciers just north of Jakobshavn Isbrae, each of which had an active meltwater plume. The IcePod system has core instrumentation that can resolve high-resolution surface elevations with a scanning laser and visual cameras, the temperature of the surface with an infrared camera, and the structure of snow and ice with two radar systems. For the study of plume dynamics, the key IcePod observations include: (1) the morphology of the calving front captured with the visual camera and the scanning laser and (2) thermal structure, velocity and turbulence of the plume water resolved with the infrared camera. In the future, an expanded IcePod capability will include an AXCTD launching system to recovery the hydrography of the fjord and the plumes. The IcePod survey directly crossed 3 of the 5 meltwater plumes on two subsequent days. The plumes sampled multiple times were Sermeq Avangnardleq A that drains into the Jakobshavn Isbrae Fjord, Eqip Sermia and Sermia Kangilerngata. While each of the ice feeding these three adjacent fjords has experienced the same surface melting conditions the structure of the meltwater plumes was very different in each fjords. Sermeq Avangnardleq A had a narrow angular shaped plume nestled in an embayment in the calving front, Eqip Sermia had two broad diffuse plumes and Sermia Kangilerngata had a narrow circular plume in an ice choked

  16. Identities in flux: cognitive network activation in times of change.

    PubMed

    Menon, Tanya; Smith, Edward Bishop

    2014-05-01

    Using a dynamic cognitive model, we experimentally test two competing hypotheses that link identity and cognitive network activation during times of change. On one hand, affirming people's sense of power might give them confidence to think beyond the densest subsections of their social networks. Alternatively, if such power affirmations conflict with people's more stable status characteristics, this could create tension, deterring people from considering their networks' diversity. We test these competing hypotheses experimentally by priming people at varying levels of status with power (high/low) and asking them to report their social networks. We show that confirming identity-not affirming power-cognitively prepares people to broaden their social networks when the world is changing around them. The emotional signature of having a confirmed identity is feeling comfortable and in control, which mediates network activation. We suggest that stable, confirmed identities are the foundation from which people can exhibit greater network responsiveness. PMID:24576631

  17. Limits on Radio Frequency Flux Density Changes in Sgr A*

    NASA Astrophysics Data System (ADS)

    Bower, Geoffrey C.; Brunthaler, Andreas; Falcke, Heino

    2013-04-01

    We report new limits on changes low frequency emission for Sgr A* based on Jansky VLA observations obtained on 2013 April 26. Data were obtained through the NRAO Service Observing program (https://science.nrao.edu/science/service-observing/service-observing). The JVLA is currently in the compact D-configuration, providing low resolution observations in which Sgr A* is heavily confused by diffuse structure associated with Sgr A West and East.

  18. Extending the Record of Greenland Ice Sheet Subsurface Meltwater: Exploring New Applications of Satellite Remote Sensing Data

    NASA Astrophysics Data System (ADS)

    Carter, M.; Reusch, D. B.; Karmosky, C. C.

    2015-12-01

    The discovery of pervasive year-round englacial meltwater in southeastern Greenland by Forster et. al (2012) in the form of a Perennial Firn Aquifer (PFA) with an estimated 140+/120 GT of water (pre-2011 melt season) has significantly changed the understanding of meltwater retention, energy balance models and Greenland hydrology. Prior to this, englacial meltwater was not considered a significant portion of the water budget in Greenland. The cryosphere and hydrology communities are currently observing and studying PFAs through data obtained from the NASA ICEBridge Program. Due to environmental and time constraints, data is limited to a few months each year beginning in 2010. This leaves a significant need to explore new methods of monitoring PFAs both throughout the year and across time in order to improve the understanding of PFA formation and hydrologic consequences. Both passive microwave and infrared radiation have been used to monitor surface melt via satellite remote sensing, are recorded regularly over Greenland, and are available from 1979. While infrared data are confined to the surface, microwaves have been noted to penetrate past the ice sheet surface and return a subsurface melt signal. A combination of microwave and infrared reflectance signals has the potential to identify subsurface meltwater distinct from surface melt throughout the year. This method of identifying englacial meltwater will be compared to recognized data sets, and correlated to meteorological requirements to determine accuracy. If this method proves effective, it could significantly extend the record of PFA location and physical and temporal extent so that hydrologic and climatic results can be better analyzed.

  19. Performance analysis of a PM motor by changing the magnitude and the path of flux

    NASA Astrophysics Data System (ADS)

    Lee, Hyung-Woo; Lee, Ki-Doek; Kim, Mi-Jung; Lee, Jae-Jun; Han, Jung-Ho; Jeong, Tae-Chul; Lee, Ho-Joon; Ryu, Gwang-Hyeon; Park, Hyun-Jong; Lee, Ju

    2013-01-01

    In an electric motor in which permanent magnets are used, the magnetic flux is caused by the magneto-motive force of the permanent magnets of the rotor and the stator winding wire, and the performance of the electric motor is determined by the scale of the magnetic flux and the magnetic circuit. This thesis is aimed at introducing electric motors in which permanent magnets are used and focuses on a performance analysis of said electric motors according to the scale of the magnetic flux and changes in the magnetic circuit. The analysis was carried out by separating the magnetic flux occurring at the stator winding wire into the magnetic flux of axis d and that of q axis, so that the impact of the magnetic flux on the performance of the electric motor could be analyzed. In addition, the impact of changes in the magnetic circuit, which were caused by the magnetic flux at the permanent magnet of the rotator, on the electric motor was analyzed. Finally, the results of the analysis were verified by performing experiments on a model made by using selected analysis results.

  20. Decadal and annual changes in biogenic opal and carbonate fluxes to the deep Sargasso Sea

    USGS Publications Warehouse

    Deuser, W.G.; Jickells, T.D.; Commeau, Judith A.

    1995-01-01

    Analyses of samples from a 14-year series of sediment-trap deployments in the deep Sargasso Sea reveal a significant trend in the ratio of the sinking fluxes of biogenic calcium carbonate and silica. Although there are pronounced seasonal cycles for both flux components, the overall opal/CaCO3 ratio changed by 50% from 1978 to 1991 (largely due to a decrease of opal flux), while total flux had no significant trend. These results suggest that plankton communities respond rapidly to subtle climate change, such as is evident in regional variations of wind speed, precipitation, wintertime ventilation and midwater temperatures. If the trends we observe in the makeup of sinking particulate matter occur on a large scale, they may in turn modify climate by modulating ocean-atmosphere CO2 exchange and albedo over the ocean.

  1. RECONSTRUCTING LAURENTIDE ICE SHEET MELTWATER GEOCHEMISTRY USING COMBINED STABLE ISOTOPE AND LASER ABLATION TRACE ELEMENT ANALYSES

    NASA Astrophysics Data System (ADS)

    Vetter, L.; Spero, H. J.; Eggins, S. M.; Flower, B. P.; Williams, C. C.

    2009-12-01

    Little is known about the oxygen isotope evolution of Northern hemisphere ice sheets during past glacial cycles, with the exception of results from models and calculations based on whole ocean δ18O change. Reconstructing changes in the δ18Owater of the global ocean assumes a homogeneous δ18O value for contributions from Northern hemisphere ice sheets with a mass balance contribution from the Southern hemisphere. Because oceanic δ18Ow forms a crucial baseline for deconvolving the combined signal of temperature and hydrologic changes recorded in foraminiferal calcite, constraints on the contributions of melting ice sheets form a fundamental component of reconstructions of global ocean δ18Ow changes on glacial timescales. Here we present a novel geochemical technique to compute the oxygen isotopic composition of Laurentide Ice Sheet (LIS) meltwater flowing into the Gulf of Mexico during periods of rapid ice sheet melting. The technique combines data from different types of geochemical analyses on individual shells of the planktonic foraminifera Orbulina universa to compute meltwater geochemistry, using laser ablation ICP-MS to measure Mg/Ca (a temperature proxy) and Ba/Ca (a salinity proxy) and isotope ratio mass spectrometry to measure δ18O (a temperature and δ18Owater proxy) on remaining shell material. O. universa has a very large temperature and salinity tolerance (9-30°C; 23-45 psu) and broad depth habitat (0-80 m), so an assemblage of individual shells from a single core interval records a range of water conditions. We have selected deglacial meltwater intervals from core MD02-2550 (26.95°N, 91.35°W, 2245 m water depth), collected from the anoxic Orca Basin in the Gulf of Mexico, for a proof of concept demonstration. From each interval, we combine measurements of Mg/Ca, Ba/Ca, and δ18O on 30-100 individual O. universa. The δ18O from each shell reflects the combined influence of temperature and δ18Owater, where this latter value is a function of

  2. Effect of Rapidly Changing River Stage on Uranium Flux through the Hyporheic Zone

    SciTech Connect

    Fritz, Brad G.; Arntzen, Evan V.

    2007-11-01

    At the Hanford Site, the flux of uranium contaminated groundwater into the Columbia River varies according to the dynamic changes in hydraulic gradient caused by fluctuating river stage. The river stage changes in response to operations of dams on the Columbia River. Piezometers were installed in the hyporheic zone to facilitate long term, high frequency measurement of water and uranium fluxes into the Columbia River in response to fluctuating river stage. In addition, measurement of the water level in the near shore unconfined aquifer enhanced the understanding of the relationship between fluctuating river stage and uranium flux. The changing river stage caused head fluctuations in the unconfined aquifer, and resulted in fluctuating hydraulic gradient in the hyporheic zone. Further, influx of river water into the unconfined aquifer caused reduced uranium concentration in near shore groundwater as a result of dilution. Calculated water flux through the hyporheic zone ranged between 0.3 and -0.5 L/min/m2. The flux of uranium through the hyporheic zone exceeded 30 ug/min/m2 during some time periods, but was generally on the order of 3 to 5 ug/min/m2 over the course of this study. It was also found that at this location, the top 20 cm of the hyporheic zone constituted the most restrictive portion of the aquifer, and controlled the flux of water through the hyporheic zone.

  3. Terminology as a key uncertainty in net land use and land cover change carbon flux estimates

    NASA Astrophysics Data System (ADS)

    Pongratz, J.; Reick, C. H.; Houghton, R. A.; House, J. I.

    2014-03-01

    Reasons for the large uncertainty in land use and land cover change (LULCC) emissions go beyond recognized issues related to the available data on land cover change and the fact that model simulations rely on a simplified and incomplete description of the complexity of biological and LULCC processes. The large range across published LULCC emission estimates is also fundamentally driven by the fact that the net LULCC flux is defined and calculated in different ways across models. We introduce a conceptual framework that allows us to compare the different types of models and simulation setups used to derive land use fluxes. We find that published studies are based on at least nine different definitions of the net LULCC flux. Many multi-model syntheses lack a clear agreement on definition. Our analysis reveals three key processes that are accounted for in different ways: the land use feedback, the loss of additional sink capacity, and legacy (regrowth and decomposition) fluxes. We show that these terminological differences, alone, explain differences between published net LULCC flux estimates that are of the same order as the published estimates themselves. This has consequences for quantifications of the residual terrestrial sink: the spread in estimates caused by terminological differences is conveyed to those of the residual sink. Furthermore, the application of inconsistent definitions of net LULCC flux and residual sink has led to double-counting of fluxes in the past. While the decision to use a specific definition of the net LULCC flux will depend on the scientific application and potential political considerations, our analysis shows that the uncertainty of the net LULCC flux can be substantially reduced when the existing terminological confusion is resolved.

  4. Response of High Latitude Wetland Fluxes of Methane to Changes in Temperature and Water

    NASA Astrophysics Data System (ADS)

    Worden, J.; Bloom, A. A.; Bowman, K. W.; Lee, M.; Frankenberg, C.; Schimel, D.

    2014-12-01

    High latitude methane fluxes represent between 5 - 20% of the total methane budget. This large range in methane emissions estimates are due to poor knowledge of wetland extent, dependency of emissions to temperature and water, the seasonal cycle of freezing and thawing, and a poor measurement network. In turn, these uncertainties limit our ability to predict future methane fluxes in response to a warming climate. Temperature and rainfall at high-latitudes changed dramatically between 2009 and 2010, likely in response to variations in ENSO and the Arctic Anomaly. We might therefore expect that high-latitude methane fluxes significantly changed between 2009 and 2010 because these methane fluxes primarily depend on these environmental parameters. In this study, we implement several wetland models and their corresponding methane fluxes for 2009 and 2010 into the GEOS-Chem global chemistry model. We evaluate whether satellite measurements such as total column measurement from GOSAT or TROP-OMI can distinguish between these models, allowing for better estimates of the magnitude and timing of wetland fluxes and improved process understanding of high-latitude methane emissions.

  5. Investigating the potential impacts of local climate change on the meltwater supply of a small snow-fed mountain river system: A case study of the Animas River, Colorado

    NASA Astrophysics Data System (ADS)

    Day, C. A.

    2010-12-01

    The western US receives up to 80% of its annual streamflow from snowmelt fed river systems during the mid-to-late spring season. Changes in winter and spring air temperature and precipitation patterns have, however, begun to alter this sensitive hydroclimatological process, both in terms of the timing and magnitude of snowmelt events and the responding streamflow. Monitoring and planning for these changes in the future may well prove crucial for local water resource planners who traditionally rely on historical trends or means for water resource planning. Local-level water resource planners also often do not have the data or tools at the right resolution available to them for the same planning purposes. This goal of this research was to identify how changes in the local winter-spring climate may alter the hydrological response of a typical small mountain snowmelt fed river system, the Animas River in SW Colorado. To achieve this, a statistical downscaling technique was applied to increase the resolution of, and build a linear relationship between, historical upper atmospheric reanalysis data to surface level mean air temperature and precipitation for several climate stations located across the basin for 1950-2007. The same technique was then used to increase the resolution of two GCM scenarios from the NCAR CCSM3 model SRES-AR4 data runs (a 'business as usual’ or A1B scenario, and an increase in global greenhouse gas emissions or A2 scenario) using the same relationships between the historical upper atmospheric reanalysis data and the surface station climate data. Snowmelt streamflow magnitude and timing were then projected to 2099 based on their historical relationship to mean monthly winter and spring air temperature and precipitation before being compared to the historical averages. Results indicated a shift in the timing of the snowmelt streamflow to earlier in the spring, and a reduction in the magnitude of peak spring streamflow following increasing spring

  6. Relevance of methodological choices for accounting of land use change carbon fluxes

    NASA Astrophysics Data System (ADS)

    Pongratz, Julia; Hansis, Eberhard; Davis, Steven

    2015-04-01

    To understand and potentially steer how humans shape land-climate interactions it is important to accurately attribute greenhouse gas fluxes from land use and land cover change (LULCC) in space and time. However, such accounting of carbon fluxes from LULCC generally requires choosing from multiple options of how to attribute the fluxes to regions and to LULCC activities. Applying a newly-developed and spatially-explicit bookkeeping model, BLUE ("bookkeeping of land use emissions"), we quantify LULCC carbon fluxes and attribute them to land-use activities and countries by a range of different accounting methods. We present results with respect to a Kyoto Protocol-like ``commitment'' accounting period, using land use emissions of 2008-12 as example scenario. We assess the effect of accounting methods that vary (1) the temporal evolution of carbon stocks, (2) the state of the carbon stocks at the beginning of the period, (3) the temporal attribution of carbon fluxes during the period, and (4) treatment of LULCC fluxes that occurred prior to the beginning of the period. We show that the methodological choices result in grossly different estimates of carbon fluxes for the different attribution definitions. The global net flux in the accounting period varies between 4.3 Pg(C) uptake and 15.2 Pg(C) emissions, depending on the accounting method. Regional results show different modes of variation. This finding has implications for both political and scientific considerations: Not all methodological choices are currently specified under the UNFCCC treaties on land use, land-use change and forestry. Yet, a consistent accounting scheme is crucial to assure comparability of individual LULCC activities, quantify their relevance for the global annual carbon budget, and assess the effects of LULCC policies.

  7. Changes in Carbon Flux at the Duke Forest Hardwood Ameriflux Site Due to Land Cover/Land Use Changes

    NASA Astrophysics Data System (ADS)

    McCombs, A. G.

    2014-12-01

    The Raleigh/Durham, North Carolina metropolitan area has been ranked by Forbes as the fastest growing cities in the United States. As a result of the rapid growth, there has been a significant amount of urban sprawl. The objective of this study was to determine if the changes in land use and land cover have caused a change in the carbon flux near the Duke Forest AmeriFlux station that was active from 2001 to 2008. The land cover and land use were assessed every two years to determine how land cover has changed at the Duke Forest Hardwoods (US-Dk2) AmeriFlux site from 2001 to 2008 using Landsat scenes. The change in land cover and land use was then compared to changes in the carbon footprint that is computed annually from 2001 to 2008. The footprint model for each wind direction determined that there are changes annually and that the research will determine if these changes are due to annual weather patterns or land use and land cover changes.

  8. Evidence of Meltwater Retention within the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Rennermalm, A. K.; Smith, L. C.; Chu, V. W.; Box, J. E.; Forster, R. R.; van den Broeke, M. R.

    2012-12-01

    Greenland ice sheet water release, and the magnitude of sub- and englacial storage, firn densification, internal refreezing and other hydrologic processes that delay or reduce true water export to the global ocean remain poorly understood. This problem is compounded by scant hydrometerological measurements. Here, ice sheet surface meltwater runoff and proglacial river discharge determined between 2008 and 2010 for three sites near Kangerlussuaq, western Greenland were used to establish the water budget for a small ice sheet watershed. The water budget could not be closed in the three years, even when uncertainty ranges were considered. Instead, between 12% and 53% of ice sheet surface runoff is retained within the catchment each melt year (time between onset of ice sheet runoff in two consecutive years) most likely in en- and subglacial storages. Evidence suggests that while some holdover summer meltwater may escape during the cold-season, this water volume is too small to close the budget. Thus, this study indicates that the Greenland ice sheet cryo-hydrologic system may remain active year round, and that meltwater may be retained in the pro glacial area, internally, or in firn layers for prolonged time periods before release to the ocean.

  9. Upstream versus downstream control of meltwater plumes under ice shelves

    NASA Astrophysics Data System (ADS)

    Wells, Andrew

    2013-11-01

    In many locations the Greenland and Antarctic ice sheets discharge into the ocean through ice shelves floating on top of a warm salty ocean. The turbulent buoyancy-driven flow of meltwater beneath the sloping ice-shelf base enhances heat transfer and provides a feedback on ice melting rates, with consequences for ice sheet dynamics and predictions of sea-level rise. Previous steady-state models of meltwater plumes under ice shelves have solved for the development of flow along the slope from an initial source, corresponding to solely upstream control of the plume dynamics. I re-interpret the plume dynamics embedded within the framework of a time-dependent model, and show that the flow exhibits distinct regimes depending on the source conditions. Solutions with upstream control are physically consistent for certain source conditions, but the plume is influenced by a combination of upstream and downstream conditions in other regions of parameter space. The dynamics are illustrated for flow underneath a two-dimensional ice shelf of initially constant basal slope, and stable attracting states are determined. The implications for modelling meltwater flow under ice shelves are discussed.

  10. Relevance of methodological choices for accounting of land use change carbon fluxes

    NASA Astrophysics Data System (ADS)

    Hansis, Eberhard; Davis, Steven J.; Pongratz, Julia

    2015-08-01

    Accounting for carbon fluxes from land use and land cover change (LULCC) generally requires choosing from multiple options of how to attribute the fluxes to regions and to LULCC activities. Applying a newly developed and spatially explicit bookkeeping model BLUE (bookkeeping of land use emissions), we quantify LULCC fluxes and attribute them to land use activities and countries by a range of different accounting methods. We present results with respect to a Kyoto Protocol-like "commitment" accounting period, using land use emissions of 2008-2012 as an example scenario. We assess the effect of accounting methods that vary (1) the temporal evolution of carbon stocks, (2) the state of the carbon stocks at the beginning of the period, (3) the temporal attribution of carbon fluxes during the period, and (4) treatment of LULCC fluxes that occurred prior to the beginning of the period. We show that the methodological choices result in grossly different estimates of carbon fluxes for the different attribution definitions.

  11. Effects of Upstream Human Changes on Nutrient Fluxes to Major Deltas World-Wide

    NASA Astrophysics Data System (ADS)

    Van Cappellen, P.; Dürr, H. H.; Maavara, T.

    2015-12-01

    Major deltas world-wide are connected to large river systems, and while they make up <1% of the shoreline, they are at the receiving end of 25-42% of all discharge, suspended sediment load and nutrient load. Thus, in addition to the pressure from human impact in the deltas, changes far upstream are tightly linked to effects downstream. The Global-NEWS approach has explored scenarios along storylines that influence future nutrient fluxes, and if highlighted for individual delta, reveals large differences in future change, with most of the influence being attributed to factors such as land use change or increased damming. Notably the latter factor has received recent attention with regards to nutrient fluxes, and phosphorus (P) in particular (Maavara et al. in review): the largest increases in P retention by reservoirs, between 2000 and 2030, are expected to occur in the Yangtze, Mekong, Amazon and Ganges-Brahmaputra river basins. Here, we discuss how Global-NEWS and other approaches assess these future changes in nutrient fluxes, and how the expected new boom in dam construction can influence these fluxes to deltas world-wide.

  12. Response of the atmospheric boundary layer to changes in surfaces fluxes

    NASA Astrophysics Data System (ADS)

    Owinoh, A. Z.; Hunt, J. C.; Orr, A.; Clark, P.

    2003-04-01

    The response of the atmospheric boundary layer (ABL) to varying surface fluxes such as surface heat fluxes and roughness changes is a common element in several problems in mesoscale dynamics. We study some of these problems by reducing the complexity of the physical processes that are relevant to mechanism of interest so that analytical solutions can be obtained. Our presentation begins with the examination of the time dependent response and the influence of a 2-D low hill on the flow in a neutral boundary layer to a uniform surface heat flux switched at time, t=0. Analytical solutions for changes in temperature, mean wind and shear stress profiles in the ABL are sought. The modelled profiles are compared with those obtained from the UK Unified Model run on a idealised mode at 12km horizontal resolution. To understand the time and spatial dependence, perturbations are analysed of stratified ABL equations as they pass over areas where there is sharply differing surface heat flux and roughness; a situation freqently observed between rural and urban areas, or across coastline or across sea-ice boundaries. New estimates are derived for the transition distance and how the fluxes, temperature and velocity, vary in the transition distance zone. These simple estimates are compared with Rider et al. (1963) experimental data. Rider N. E., Philip J. R. &Bradley E. F. (1963), The horizontal transport of heat and moisture - A micrometeorological study. Q. J. R. Meteorol. Soc, 89, 507-531.

  13. The deglacial retreat of the Laurentide Ice Sheet's southern margin: Meltwater provenance insights from the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Williams, C.; Brown, E. A.; Hastings, D. W.; Lowell, T. V.; Shiller, A. M.; Shevenell, A.; Flower, B. P.

    2012-12-01

    Northern Gulf of Mexico (GOM) sediments document abrupt millennial-scale variability that may be linked to Laurentide Ice Sheet (LIS) melting and significant changes in Atlantic Meridional Overturning Circulation (AMOC) during the last deglaciation and Holocene (24-7 ka). To investigate the deglacial response of the southern margin of the LIS, the impact of meltwater on the GOM, and the influence of GOM meltwater events on the AMOC, we undertook a multi-proxy (foraminiferal δ18O, Mg/Ca, and Ba/Ca) geochemical study of a high-resolution (45 cm/kyr) sedimentary sequence from core MD02-2550, recovered from Orca Basin (2248 m water depth) in the GOM. Paired G. ruber (white and pink, separately) δ18O and Mg/Ca analyses allow us to use Mg/Ca paleothermometry to remove the temperature component of the δ18O signal, leaving behind a record of seawater δ18O (δ18Osw). After correcting the δ18Osw record for global ice volume, the resulting GOM δ18Oivc-sw record is primarily influenced by LIS meltwater. To assess how meltwater pulses influenced GOM salinity during deglaciation, we paired our δ18Oivc-sw record with a foraminiferal Ba/Ca record that reflects river discharge-induced salinity changes. Mississippi River Ba concentrations are elevated relative to GOM seawater (400 vs. 85 nM) and modern seawater Ba/Ca (Ba/Casw) exhibits a linear relationship with salinity (>20 psu). Because foraminiferal Ba/Ca exhibits a predictable relationship to Ba/Casw, it may be used to calculate changes in salinity arising from deglacial variations in Mississippi River discharge. A complicating factor for Ba/Ca-based salinity interpretations is that Ba concentrations vary spatially throughout the Mississippi River watershed. For example, modern Missouri and Upper Mississippi River Ba concentrations (633 and 436 nM, respectively) are higher than that of the Ohio River (253 nM). Thus, GOM Ba/Ca variability could reflect changes in total Mississippi River input and/or shifts in the dominant

  14. Green house gas flux at high latitudes - constraints and susceptibility to a changing climate

    NASA Astrophysics Data System (ADS)

    Nilsson, M. B.

    2015-12-01

    High latitude boreal forests and peatlands contribute importantly to the land-atmosphere exchange of both carbon dioxide and methane. High latitude biomes are also identified as most vulnerable to changing climate. High latitudes are characterized by a strong seasonality in incoming solar radiation, weather conditions and biogeochemical processes. The strong seasonality in incoming solar radiation, not to change in response to a changing climate, constitute firm constraints on how changes in air temperature, evapotranspiration and precipitation will affect biogeochemical processes underlying the land atmosphere exchange of green house gases. Timing of the soil frost thaw and plant phenology thus constitutes two master controls on how fluxes of both CO2 and CH4 will be affected by weather conditions. In addition also the wintertime conditions importantly affect GHG fluxes both during winter time as well as during the succeeding summer. Examples will primarily be given for peatlands and coniferous forests.

  15. Carbon fluxes resulting from land-use changes in the Tamaulipan thornscrub of northeastern Mexico

    PubMed Central

    Návar-Chaidez, Jose de Jesus

    2008-01-01

    Information on carbon stock and flux resulting from land-use changes in subtropical, semi-arid ecosystems are important to understand global carbon flux, yet little data is available. In the Tamaulipan thornscrub forests of northeastern Mexico, biomass components of standing vegetation were estimated from 56 quadrats (200 m2 each). Regional land-use changes and present forest cover, as well as estimates of soil organic carbon from chronosequences, were used to predict carbon stocks and fluxes in this ecosystem. For the period of 1980–1996, the Tamaulipan thornscrub is presenting an annual deforestation rate of 2.27% indicating that approximately 600 km2 of this plant community are lost every year and that 60% of the original Mexican Tamaulipan thornscrub vegetation has been lost since the 1950's. On the other hand, intensive agriculture, including introduced grasslands increased (4,000 km2) from 32 to 42% of the total studied area, largely at the expense of the Tamaulipan thornscrub forests. Land-use changes from Tamaulipan thornscrub forest to agriculture contribute 2.2 Tg to current annual carbon emissions and standing biomass averages 0.24 ± 0.06 Tg, root biomass averages 0.17 ± 0.03 Tg, and soil organic carbon averages 1.80 ± 0.27 Tg. Land-use changes from 1950 to 2000 accounted for Carbon emissions of the order of 180.1 Tg. Projected land-use changes will likely contribute to an additional carbon flux of 98.0 Tg by the year 2100. Practices to conserve sequester, and transfer carbon stocks in semi-arid ecosystems are discussed as a means to reduce carbon flux from deforestation practices. PMID:18826617

  16. Large climate-induced changes in ultraviolet index and stratosphere-to-troposphere ozone flux

    NASA Astrophysics Data System (ADS)

    Hegglin, Michaela I.; Shepherd, Theodore G.

    2009-10-01

    Now that stratospheric ozone depletion has been controlled by the Montreal Protocol, interest has turned to the effects of climate change on the ozone layer. Climate models predict an accelerated stratospheric circulation, leading to changes in the spatial distribution of stratospheric ozone and an increased stratosphere-to-troposphere ozone flux. Here we use an atmospheric chemistry climate model to isolate the effects of climate change from those of ozone depletion and recovery on stratosphere-to-troposphere ozone flux and the clear-sky ultraviolet radiation index-a measure of potential human exposure to ultraviolet radiation. We show that under the Intergovernmental Panel on Climate Change moderate emissions scenario, global stratosphere-to-troposphere ozone flux increases by 23% between 1965 and 2095 as a result of climate change. During this time, the clear-sky ultraviolet radiation index decreases by 9% in northern high latitudes-a much larger effect than that of stratospheric ozone recovery-and increases by 4% in the tropics, and by up to 20% in southern high latitudes in late spring and early summer. The latter increase in the ultraviolet index is equivalent to nearly half of that generated by the Antarctic `ozone hole' that was created by anthropogenic halogens. Our results suggest that climate change will alter the tropospheric ozone budget and the ultraviolet index, which would have consequences for tropospheric radiative forcing, air quality and human and ecosystem health.

  17. Assessing the influence of historic net and gross land changes on the carbon fluxes of Europe.

    PubMed

    Fuchs, Richard; Schulp, Catharina J E; Hengeveld, Geerten M; Verburg, Peter H; Clevers, Jan G P W; Schelhaas, Mart-Jan; Herold, Martin

    2016-07-01

    Legacy effects of land cover/use on carbon fluxes require considering both present and past land cover/use change dynamics. To assess past land use dynamics, model-based reconstructions of historic land cover/use are needed. Most historic reconstructions consider only the net area difference between two time steps (net changes) instead of accounting for all area gains and losses (gross changes). Studies about the impact of gross and net land change accounting methods on the carbon balance are still lacking. In this study, we assessed historic changes in carbon in soils for five land cover/use types and of carbon in above-ground biomass of forests. The assessment focused on Europe for the period 1950 to 2010 with decadal time steps at 1-km spatial resolution using a bookkeeping approach. To assess the implications of gross land change data, we also used net land changes for comparison. Main contributors to carbon sequestration between 1950 and 2010 were afforestation and cropland abandonment leading to 14.6 PgC sequestered carbon (of which 7.6 PgC was in forest biomass). Sequestration was highest for old-growth forest areas. A sequestration dip was reached during the 1970s due to changes in forest management practices. Main contributors to carbon emissions were deforestation (1.7 PgC) and stable cropland areas on peaty soils (0.8 PgC). In total, net fluxes summed up to 203 TgC yr(-1) (98 TgC yr(-1) in forest biomass and 105 TgC yr(-1) in soils). For areas that were subject to land changes in both reconstructions (35% of total area), the differences in carbon fluxes were about 68%. Overall for Europe the difference between accounting for either gross or net land changes led to 7% difference (up to 11% per decade) in carbon fluxes with systematically higher fluxes for gross land change data. PMID:26668087

  18. Steering epitaxial alignment of Au, Pd, and AuPd nanowire arrays by atom flux change.

    PubMed

    Yoo, Youngdong; Seo, Kwanyong; Han, Sol; Varadwaj, Kumar S K; Kim, Hyun You; Ryu, Ji Hoon; Lee, Hyuck Mo; Ahn, Jae Pyoung; Ihee, Hyotcherl; Kim, Bongsoo

    2010-02-10

    We have synthesized epitaxial Au, Pd, and AuPd nanowire arrays in vertical or horizontal alignment on a c-cut sapphire substrate. We show that the vertical and horizontal nanowire arrays grow from half-octahedral seeds by the correlations of the geometry and orientation of seed crystals with those of as-grown nanowires. The alignment of nanowires can be steered by changing the atom flux. At low atom deposition flux vertical nanowires grow, while at high atom flux horizontal nanowires grow. Similar vertical/horizontal epitaxial growth is also demonstrated on SrTiO(3) substrates. This orientation-steering mechanism is visualized by molecular dynamics simulations. PMID:20050692

  19. Suspended sediment fluxes in an Indonesian river draining a rainforested basin subject to land cover change

    NASA Astrophysics Data System (ADS)

    Buschman, F. A.; Hoitink, A. J. F.; de Jong, S. M.; Hoekstra, P.

    2011-07-01

    Forest clearing for reasons of timber production, open pit mining and the establishment of oil palm plantations generally results in excessively high sediment loads in the tropics. The increasing sediment fluxes pose a threat to coastal marine ecosystems such as coral reefs. This study presents observations of suspended sediment fluxes in the Berau river (Indonesia), which debouches into a coastal ocean that can be considered the preeminent center of coral diversity. The Berau is an example of a small river draining a mountainous, relatively pristine basin that receives abundant rainfall. Flow velocity was measured over a large part of the river width at a station under the influence of tides, using a Horizontal Acoustic Doppler Current Profiler (HADCP). Surrogate measurements of suspended sediment concentration were taken with an Optical Backscatter Sensor (OBS). Tidally averaged suspended sediment concentration increases with river discharge, implying that the tidally averaged suspended sediment flux increases non-linearly with river discharge. Averaged over the 6.5 weeks observations covered by the benchmark survey, the tidally averaged suspended sediment flux was estimated at 2 Mt y-1. Considering the wet conditions during the observation period, this figure may be considered as an upper limit of the yearly averaged flux. This flux is significantly smaller than what could have been expected from the characteristics of the catchment. The consequences of ongoing clearing of rainforest were explored using a plot scale erosion model. When rainforest, which still covered 50-60 % of the basin in 2007, is converted to production land, soil loss is expected to increase with a factor between 10 and 100. If this soil loss is transported seaward as suspended sediment, the increase in suspended sediment flux in the Berau river would impose a severe sediment stress on the global hotspot of coral reef diversity. The impact of land cover changes will largely depend on the

  20. Suspended sediment fluxes in an Indonesian river draining a rainforested basin subject to land cover change

    NASA Astrophysics Data System (ADS)

    Buschman, F.; Hoitink, A.; de Jong, S.; Hoekstra, P.

    2011-12-01

    Forest clearing in the tropics for reasons of timber production, open pit mining and the establishment of oil palm plantations generally results in excessively high sediment loads. The increasing sediment fluxes pose a threat to coastal marine ecosystems such as coral reefs. This study presents observations of suspended sediment fluxes in the Berau river (Indonesia), which debouches into a coastal ocean that can be considered the preeminent center of coral diversity. The Berau is an example of a small river draining a mountainous, relatively pristine basin that receives abundant rainfall. Flow velocity was measured over a large part of the river width at a station under the influence of tides, using a Horizontal Acoustic Doppler Current Profiler (HADCP). Surrogate measurements of suspended sediment concentration were taken with an Optical Backscatter Sensor (OBS). Tidally averaged suspended sediment concentration increases with river discharge, implying that the tidally averaged suspended sediment flux increases non-linearly with river discharge. Averaged over the 6.5 weeks covered by the benchmark survey, the tidally averaged suspended sediment flux was estimated at 2 Mt/y. Considering the wet conditions during the observation period, this figure may be considered as an upper limit of the yearly averaged flux. This flux is significantly smaller than what could have been expected from the characteristics of the catchment. Furthermore, the consequences of ongoing clearing of rainforest were explored using a plot scale erosion model. When rainforest, which still covered 50 - 60 % of the basin in 2007, is converted to production land, soil loss is expected to increase with a factor between 10 and 100. If this soil loss is transported seaward as suspended sediment, the increase in suspended sediment flux in the Berau river would impose a severe sediment stress on the global hotspot of coral reef diversity. The impact of land cover changes will largely depend on the

  1. Dependence of Large-Scale Global Poynting Flux on IMF By Polarity Change

    NASA Astrophysics Data System (ADS)

    Humberset, B. K.; Gjerloev, J. W.

    2014-12-01

    In this study we present the dependence of the global Poynting flux on the IMF By polarity change. The amount of energy that enters the magnetosphere from the solar wind is a function of the solar wind speed and pressure and the IMF orientation and magnitude. All the various published coupling models show that the polarity of the IMF By component does not change the energy input. In contrast the global convection patterns, and thus the ionospheric Pedersen currents, depend on IMF By polarity. This seems to imply that the ionospheric energy deposition is a function of IMF By polarity. Thus, there appear to be a fundamental difference between the input (from the solar wind) and the output (energy dissipating Pedersen currents). We, therefore, ask the question: To what extend is the global Poynting flux dependent on the IMF By polarity? We have performed a statistical study evaluating 59 abrupt transitions in the IMF By component (polarity changes) as measured by the ACE spacecraft. The effect of other solar wind coupling parameters, such as the IMF Bz component, are minimized by selecting events where these are nearly constant. We use electric field distributions from SuperDARN and field-aligned current distributions from AMPERE to calculate the global distribution of the Poynting Flux. To minimize the effect of magnetospheric energy unloading we focus on the 06-18 MLT region. We further investigate the dependence on solar induced conductivity. We find that the Poynting flux is slightly larger for positive IMF By compared to negative By conditions. For a low conductivity (not sunlit) ionosphere the Poynting flux is smaller than in the high conductivity (sunlit) ionosphere and we find a smaller dependence on IMF By polarity. The study emphasizes the global dynamic behavior of the ionosphere in its response to changes in the external driver (IMF).

  2. Antropogenically induced changes in sediment and biogenic silica fluxes in Chesapeake Bay

    USGS Publications Warehouse

    Colman, Steven M.; Bratton, J.F.

    2003-01-01

    Sediment cores as long as 20 m, dated by 14C, 210Pb, and 137Cs methods and pollen stratigraphy, provide a history of diatom productivity and sediment-accumulation rates in Chesapeake Bay. We calculated the flux of biogenic silica and total sediment for the past 1500 yr for two high-sedimentation-rate sites in the mesohaline section of the bay. The data show that biogenic silica flux to sediments, an index of diatom productivity in the bay, as well as its variability, were relatively low before European settlement of the Chesapeake Bay watershed. In the succeeding 300-400 yr, the flux of biogenic silica has increased by a factor of 4 to 5. Biogenic silica fluxes still appear to be increasing, despite recent nutrient-reduction efforts. The increase in diatom-produced biogenic silica has been partly masked (in concentration terms) by a similar increase in total sediment flux. This history suggests the magnitude of anthropogenic disturbance of the estuary and indicates that significant changes had occurred long before the twentieth century.

  3. Anthropogenically induced changes in sediment and biogenic silica fluxes in Chesapeake Bay

    USGS Publications Warehouse

    Colman, Steven M.; Bratton, John F.

    2003-01-01

    Sediment cores as long as 20 m, dated by 14C, 210Pb, and 137Cs methods and pollen stratigraphy, provide a history of diatom productivity and sediment-accumulation rates in Chesapeake Bay. We calculated the flux of biogenic silica and total sediment for the past 1500 yr for two high-sedimentation-rate sites in the mesohaline section of the bay. The data show that biogenic silica flux to sediments, an index of diatom productivity in the bay, as well as its variability, were relatively low before European settlement of the Chesapeake Bay watershed. In the succeeding 300–400 yr, the flux of biogenic silica has increased by a factor of 4 to 5. Biogenic silica fluxes still appear to be increasing, despite recent nutrient-reduction efforts. The increase in diatom-produced biogenic silica has been partly masked (in concentration terms) by a similar increase in total sediment flux. This history suggests the magnitude of anthropogenic disturbance of the estuary and indicates that significant changes had occurred long before the twentieth century.

  4. Carbon Flux to the Atmosphere from Land-Use Changes: 1850 to 1990

    SciTech Connect

    Houghton, R.A.

    2001-02-22

    The database documented in this numeric data package, a revision to a database originally published by the Carbon Dioxide Information Analysis Center (CDIAC) in 1995, consists of annual estimates, from 1850 through 1990, of the net flux of carbon between terrestrial ecosystems and the atmosphere resulting from deliberate changes in land cover and land use, especially forest clearing for agriculture and the harvest of wood for wood products or energy. The data are provided on a year-by-year basis for nine regions (North America, South and Central America, Europe, North Africa and the Middle East, Tropical Africa, the Former Soviet Union, China, South and Southeast Asia, and the Pacific Developed Region) and the globe. Some data begin earlier than 1850 (e.g., for six regions, areas of different ecosystems are provided for the year 1700) or extend beyond 1990 (e.g., fuelwood harvest in South and Southeast Asia, by forest type, is provided through 1995). The global net flux during the period 1850 to 1990 was 124 Pg of carbon (1 petagram = 10{sup 15} grams). During this period, the greatest regional flux was from South and Southeast Asia (39 Pg of carbon), while the smallest regional flux was from North Africa and the Middle East (3 Pg of carbon). For the year 1990, the global total net flux was estimated to be 2.1 Pg of carbon.

  5. Identification of glacial meltwater runoff in a karstic environment and its implication for present and future water availability

    NASA Astrophysics Data System (ADS)

    Finger, D.; Hugentobler, A.; Huss, M.; Voinesco, A.; Wernli, H.; Fischer, D.; Weber, E.; Jeannin, P.-Y.; Kauzlaric, M.; Wirz, A.; Vennemann, T.; Hüsler, F.; Schädler, B.; Weingartner, R.

    2013-08-01

    Glaciers all over the world are expected to continue to retreat due to the global warming throughout the 21st century. Consequently, future seasonal water availability might become scarce once glacier areas have declined below a certain threshold affecting future water management strategies. Particular attention should be paid to glaciers located in a karstic environment, as parts of the meltwater can be drained by underlying karst systems, making it difficult to assess water availability. In this study tracer experiments, karst modeling and glacier melt modeling are combined in order to identify flow paths in a high alpine, glacierized, karstic environment (Glacier de la Plaine Morte, Switzerland) and to investigate current and predict future downstream water availability. Flow paths through the karst underground were determined with natural and fluorescent tracers. Subsequently, geologic information and the findings from tracer experiments were assembled in a karst model. Finally, glacier melt projections driven with a climate scenario were performed to discuss future water availability in the area surrounding the glacier. The results suggest that during late summer glacier meltwater is rapidly drained through well-developed channels at the glacier bottom to the north of the glacier, while during low flow season meltwater enters into the karst and is drained to the south. Climate change projections with the glacier melt model reveal that by the end of the century glacier melt will be significantly reduced in the summer, jeopardizing water availability in glacier-fed karst springs.

  6. Influence of glacial meltwater and humidity on evaporation of two Tibetan lakes indicated by delta 18O

    NASA Astrophysics Data System (ADS)

    Gao, J.

    2009-04-01

    delta 18O and model results are adopted to study the affects of glacial meltwater and relative humidity in two lake basins (Lakes Yamdrok-tso and Puma Yum-tso) at two different elevations on the southern Tibetan Plateau. Temporally, the lake water delta 18O of Yamdrok-tso Lake displays a seasonal fluctuation, whereas the lake water delta 18O is stable in Puma Yum-tso Lake in whole year. Spatially, the delta 18O value in Yamdrok-tso Lake is 2‰ higher than that in Puma Yum-tso Lake. delta 18O values in the two lake basins increase by 10‰ from the termini of glaciers to the lake shores, by about 1‰ from the lakeshores to the lake center, by 0.4‰ from the water surface to depth in these lakes. The largest difference, from the terminus of the Qiangyong Glacier to the depth of 35 m, is 14.1‰ and demonstrates the importance of glacial meltwater. Evaporation alters the changes of delta 18O in the two lake basins. Model results show that relative humidity is a major controlling factor of evaporation. delta 18O values of both Yamdrok-tso and Puma Yum-tso Lakes are at their steady condition, but Puma Yum-tso Lake has taken a longer time to approach the current condition, which might be attributed to higher humidity and more glacial meltwater at the lake.

  7. Culturable bacteria in glacial meltwater at 6,350 m on the East Rongbuk Glacier, Mount Everest.

    PubMed

    Liu, Yongqin; Yao, Tandong; Jiao, Nianzhi; Kang, Shichang; Huang, Sijun; Li, Qiang; Wang, Kejuan; Liu, Xiaobo

    2009-01-01

    Culturable bacteria in the glacial meltwater in the ablation zones of glacier at high altitude (6,350 m) on Mt Everest were isolated and identified by 16S rRNA amplification and sequencing. The obtained sequences revealed the presence of members of alpha, beta, and gamma-Proteobacteria, Actinobacteria, and Firmicutes, with the Actinobacteria dominant in the studied habitat. All 16S rRNA sequences were similar to previously determined sequences, ranging from 97 to 99% identical values. The strains isolated from meltwater were distinctly different from those recovered from a cryoconite hole and under glacier habitat. The majority of the isolates' nearest neighbors were from the permafrost, dust, soil, plant, and aqueous environments. The Biolog bioassay and growth test under different temperatures suggested that the culturable bacteria in glacial meltwater could be divided into three categories in terms of their survival strategies: Group I sensitive to temperature change but versatile in utilization of carbon substrates (capable of utilization of about 70% of the Biolog carbon substrates); Group II tolerant to variable temperature and less capable of carbon utilization (less than half of the Biolog carbon species can be used); Group III slow in growth and weak in carbon utilization (only a few Biolog carbon substrates can be used). PMID:19015814

  8. A case study of carbon fluxes from land change in the southwest Brazilian Amazon

    USGS Publications Warehouse

    Barrett, K.; Rogan, J.; Eastman, J.R.

    2009-01-01

    Worldwide, land change is responsible for one-fifth of anthropogenic carbon emissions. In Brazil, three-quarters of carbon emissions originate from land change. This study represents a municipal-scale study of carbon fluxes from vegetation in Rio Branco, Brazil. Land-cover maps of pasture, forest, and secondary growth from 1993, 1996, 1999, and 2003 were produced using an unsupervised classification method (overall accuracy = 89%). Carbon fluxes from land change over the decade of imagery were estimated from transitions between land-cover categories for each time interval. This article presents new methods for estimating emissions reductions from carbon stored in the vegetation that replaces forests (e.g., pasture) and sequestration by new (>10-15 years) forests, which reduced gross emissions by 16, 15, and 22% for the period of 1993-1996, 1996-1999, and 1999-2003, respectively. The methods used in the analysis are broadly applicable and provide a comprehensive characterization of regional-scale carbon fluxes from land change.

  9. Hydrology of melt-water channels in southwestern Minnesota

    USGS Publications Warehouse

    Thompson, Gerald L.

    1965-01-01

    Melt-water channel deposits are among the most important aquifers in southwestern Minnesota, but permeable zones within the deposits are difficult to locate. Interpretation of the depositional history of proglacial channel deposits from aerial photographs and test-hole samples indicates the position of the permeable zones. Generally, the coarse-grained deposits are in headwater areas, near the confluence of two channels, in bends, or at the junction of sluiceways. Locally, these deposits yield as much as 1,000 gallons per minute to wells.

  10. Laurentide-Cordilleran Ice Sheet saddle collapse as a contribution to meltwater pulse 1A

    NASA Astrophysics Data System (ADS)

    Gomez, N.; Gregoire, L. J.; Mitrovica, J. X.; Payne, A. J.

    2015-05-01

    The source or sources of meltwater pulse 1A (MWP-1A) at ~14.5 ka, recorded at widely distributed sites as a sea level rise of ~10-20 m in less than 500 years, is uncertain. A recent ice modeling study of North America and Greenland has suggested that the collapse of an ice saddle between the Laurentide and Cordilleran ice sheets, with a eustatic sea level equivalent (ESLE) of ~10 m, may have been the dominant contributor to MWP-1A. To test this suggestion, we predict gravitationally self-consistent sea level changes from the Last Glacial Maximum to the present day associated with the ice model. We find that a combination of the saddle collapse scenario and melting outside North America and Greenland with an ESLE of ~3 m yields sea level changes across MWP-1A that are consistent with far-field sea level records at Barbados, Tahiti, and Sunda Shelf.

  11. Deglacial meltwater pulse 1B and Younger Dryas sea levels revisited with boreholes at Tahiti.

    PubMed

    Bard, Edouard; Hamelin, Bruno; Delanghe-Sabatier, Doriane

    2010-03-01

    Reconstructing sea-level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets. The resolution of the few sea-level records covering the critical time interval between 14,000 and 9,000 calendar years before the present is still insufficient to draw conclusions about sea-level changes associated with the Younger Dryas cold event and the meltwater pulse 1B (MWP-1B). We used the uranium-thorium method to date shallow-living corals from three new cores drilled onshore in the Tahiti barrier reef. No significant discontinuity can be detected in the sea-level rise during the MWP-1B period. The new Tahiti sea-level record shows that the sea-level rise slowed down during the Younger Dryas before accelerating again during the Holocene. PMID:20075212

  12. Preliminary investigation of changes in x-ray multilayer optics subjected to high radiation flux

    SciTech Connect

    Hockaday, M.P.; Blake, R.L.; Grosso, J.S.; Selph, M.M.; Klein, M.M.; Matuska, W. Jr.; Palmer, M.A.; Liefeld, R.J.

    1985-01-01

    A variety of metal multilayers was exposed to high x-ray flux using Sandia National Laboratories' PROTO II machine in the gas puff mode. Fluxes incident on the multilayers above 700 MW/cm/sup 2/ in total radiation, in nominal 20 ns pulses, were realized. The neon hydrogen- and helium-like resonance lines were used to probe the x-ray reflectivity properties of the multilayers as they underwent change of state during the heating pulse. A fluorescer-fiber optic-streak camera system was used to monitor the changes in x-ray reflectivity as a function of time and irradiance. Preliminary results are presented for a W/C multilayer. Work in progress to model the experiment is discussed. 13 refs., 4 figs.

  13. Land-Use Change, Soil Process and Trace Gas Fluxes in the Brazilian Amazon Basin

    NASA Technical Reports Server (NTRS)

    Melillo, Jerry M.; Steudler, Paul A.

    1997-01-01

    We measured changes in key soil processes and the fluxes of CO2, CH4 and N2O associated with the conversion of tropical rainforest to pasture in Rondonia, a state in the southwest Amazon that has experienced rapid deforestation, primarily for cattle ranching, since the late 1970s. These measurements provide a comprehensive quantitative picture of the nature of surface soil element stocks, C and nutrient dynamics, and trace gas fluxes between soils and the atmosphere during the entire sequence of land-use change from the initial cutting and burning of native forest, through planting and establishment of pasture grass and ending with very old continuously-pastured land. All of our work is done in cooperation with Brazilian scientists at the Centro de Energia Nuclear na Agricultura (CENA) through an extant official bi-lateral agreement between the Marine Biological Laboratory and the University of Sao Paulo, CENA's parent institution.

  14. Methane and carbon dioxide fluxes in a hydrologically changed wetland in Canada

    NASA Astrophysics Data System (ADS)

    Fleischer, Elisa; Berger, Sina; Burger, Magdalena; Forsyth, Jordan; Goebel, Marie; Wagner-Riddle, Claudia; Blodau, Christian; Klemm, Otto

    2015-04-01

    Northern peatlands store about 30 % of the global soil carbon and account for a significant contribution to methane emissions from natural sources. The carbon cycle in peatland ecosystems is very sensitive to hydrological changes so that it is important to quantify and analyze the direction and magnitude of carbon fluxes under such conditions. For example, increased water levels might decrease the carbon dioxide uptake and increase methane emissions. The Luther Bog in Ontario, Canada, has been flooded to create a reservoir in 1952. This changed the hydrological regime of the adjacent areas and the question arises whether the changed ecosystem acts as a sink or source for carbon, and how it affects global warming. In 2014, an eddy covariance measurement station was operated there from May to October to quantify the exchange of water vapor, carbon dioxide and methane between the bog and the atmosphere. The station was located in an area that got wetter through the construction of the dam. The magnitude and direction of the methane fluxes were independent from daily patterns. The constantly high water level excluded the effect of temperature changes on the methane production. A seasonal variation with increased emissions during the summer period was visible despite the slightly decreased water level. However, the difference was small. The study site was found to be a clear methane source. The carbon dioxide fluxes showed typical diurnal courses. Their magnitude was relatively constant during the measurement period apart from a slight decrease in fall. The uptake of carbon clearly overweighed the carbon loss, meaning that the bog is sequestering carbon. However, considering the global warming potential of carbon dioxide and methane the effect on climate change is only slightly negative. This points out that even changed wetland ecosystems can keep their important function of sequestering carbon and thereby counteract global warming. A comparison and combination of this

  15. The distribution of glacial meltwater in the Amundsen Sea, Antarctica, revealed by excess helium and neon

    NASA Astrophysics Data System (ADS)

    Kim, I.; Hahm, D.; Rhee, T. S.; Lee, S.

    2014-12-01

    Noble gases in seawater are useful tracers of glacial melting around Antarctica because the dissolution of the air bubbles trapped in glacial ice produces significant saturation anomalies of noble gases. To evaluate the significance of glacial meltwater (GMW) fluxes, we measured the two noble gases, helium (He) and neon (Ne), in the water column of the Amundsen Sea, Antarctica in 2011 and 2012. The measured saturation anomalies of He and Ne (ΔHe = (He/Heeq - 1) × 100% and ΔNe = (Ne/Neeq - 1) × 100%, where Heeq and Neeq are at equilibrium with the atmosphere) were in the range of 4 - 25% and 2 - 15% (n = 85), respectively, near the Getz and Dotson Ice Shelves (GIS and DIS). The dissolved He and Ne in the upper 500 m of this region were largely supersaturated up to 16% and 13%, respectively, with respect to the background seawater (open ocean water). The maximum values of ΔHe and ΔNe were observed in 400 - 500 m depth where the warm Circumpolar Deep Water (CDW) melts the base of the ice shelves. These large excess He and Ne were even appeared nearly 200 km away the ice shelves, suggesting that GMW can be transported up to several hundred kilometers offshore. The calculated meltwater fraction in GIS, DIS, and continental shelf regions, based on the excess He, were 0.4 - 0.8% and 0.5 - 1.2%, 0.2 - 1.0%, respectively. The largest GMW fraction (almost 2%) was observed in the western side of the DIS due to an intensified outflow from the western side of the DIS. In 2012, the GMW fraction decreased by approximately 30 - 40% compared to 2011, demonstrating significant inter-annual variability in glacial melting. For an estimated He residence time of 0.4 - 0.9 yr on the shelf region, the GMW flux from the GIS and DIS were estimated to be about 45 - 110 Gt yr-1, corresponding basal melting rate of 3 - 8 m yr-1. Our regional melting rate is comparable to recent satellite- or heat flux based estimates.

  16. Consequences and feedbacks on CO2 fluxes of climate change impacts on alpine vegetation

    NASA Astrophysics Data System (ADS)

    Cannone, N.; Guglielmin, M.

    2009-04-01

    The vegetation in a high alpine site of the European Alps experienced changes in area between 1953 and 2003 as a result of climate change (Cannone et al. 2007). Shrubs showed rapid expansion rates of 5.6% per decade at altitudes between 2400 m and 2500 m. Above 2500 m, vegetation coverage exhibited unexpected patterns of regression associated with increased precipitation and permafrost degradation. The warming of air temperature induced a cascade effect, with changes in the all ecological series (from the shrubland to the nival snowbed vegetation), with the arrival of the alpine shrubland and upward displacement of the alpine grassland (especially between 2230 and 2500 m). During the growing season 2008 (since the late-spring snowmelt to the start of the continuous snow cover in fall) we analyzed and measured the CO2 fluxes associated to the vegetation types exhibiting the highest changes since 1953 until today. In particular, we monitored two different ecological types of shrubland vegetations (the chionophilous alpine shrubs dominated by Rhododendron ferrugineum and the wind-swept community of dwarf shrubs dominated by Loiseleuria procumbens), the climax alpine grassland (dominated by Carex curvula), the pioneer discontinuous alpine vegetation, the snowbed vegetation (dominated by Salix herbacea) and the barren ground. CO2 fluxes (i.e. net ecosystem exchange, ecosystem photosynthesis and ecosystem respiration), biomass, soil C and N were measured for all these vegetation types. Implications of the changes occurred to the CO2 fluxes above 2200 m a.s.l. in response to the areal changes of spatial distribution of the investigated vegetation types and their potential feedbacks are discussed. Nicoletta Cannone, Sergio Sgorbati, and Mauro Guglielmin 2007. Unexpected impacts of climate change on alpine vegetation. Front Ecol Environ 2007; 5(7): 360-364

  17. Understanding ecosystems' sub-daily water and carbon flux changes during dry-down events

    NASA Astrophysics Data System (ADS)

    Nelson, Jacob; Jung, Martin; Carvalhais, Nuno; Migliavacca, Mirco; Reichstein, Markus

    2016-04-01

    Sub-daily water and carbon flux patterns give important and sometimes overlooked information about ecosystem processes and land-atmosphere feedbacks. While models often perform well down to daily timescales, they can be uncertain with respect to the diurnal courses, especially during dry-down events where the fraction of T to ET is shifting. We analyzed events from multiple locations for unique pattern changes that were robust across sites. Of particular interest were the divergence of water and carbon fluxes during high radiation periods, which indicates changes in water use efficiency as drought conditions intensified. The validity of attributing the signatures to ecosystem transitions such as changes in phenology, switches in soil evaporation vs transpiration dominance, and physiological stress were evaluated by comparing to site specific sap flow, soil moisture, and remote sensing data. Going forward, these findings can be used to further understand ecosystem physiology under drought conditions, and can also be used to partition of water fluxes and better constrain future models.

  18. Laurentide Ice Sheet meltwater δ18O from paired LA-ICPMS and IRMS analyses on single foraminifers

    NASA Astrophysics Data System (ADS)

    Vetter, L.; Spero, H. J.; Eggins, S. M.; Flower, B. P.; Williams, C.

    2012-12-01

    The oxygen isotope composition of past continental ice sheets can be estimated from modeling results and computations from whole-ocean deglacial δ18Owater change. Reconstructions of the glacial-interglacial rate of change in the δ18Owater of the global ocean assume a homogeneous δ18O value for contributions from individual ice sheets, such as the Laurentide Ice Sheet (LIS). However, observations of the modern Greenland and Antarctic ice sheets indicate dynamic and highly variable melting of different parts of these ice sheets. Computing the oxygen isotopic value of meltwater from the LIS could provide a powerful tool for exploring the dynamics of ice sheet melting during the last deglaciation. Here we present a record of the oxygen isotopic composition of LIS meltwater entering the Gulf of Mexico during discrete time slices of the last deglaciation (18 - 11 ka). We employ a novel technique that combines laser ablation ICP-MS and oxygen isotope analyses on individual shells of the planktic foraminifer Orbulina universa to quantify the instantaneous δ18Owater value of ice sheet meltwater. For each individual O. universa shell we quantify Mg/Ca (a temperature proxy) and Ba/Ca (a salinity proxy) with LA-ICP-MS, and then analyze the same O. universa for δ18O using the remaining material from the same shell. From these proxies, we compute δ18Owater and salinity for each individual foraminifer. A regression of all the data points obtained from the same core interval yields a δ18Owater:salinity relationship whose y-intercept is the freshwater end-member. We analyzed 28 core intervals from 17.5 ka to 13 ka (10-40 individual foraminifers per interval) and one Holocene core top interval from Gulf of Mexico Orca Basin core MD02-2550. Our data suggest that prior to 15 ka, Mississippi River outflow into the Gulf of Mexico was dominated by regional precipitation, and that LIS meltwater did not play a significant role in salinity variation over the Orca Basin. From 15 to 13

  19. A fully automated meltwater monitoring and collection system for spatially distributed isotope analysis in snowmelt-dominated catchments

    NASA Astrophysics Data System (ADS)

    Rücker, Andrea; Boss, Stefan; Von Freyberg, Jana; Zappa, Massimiliano; Kirchner, James

    2016-04-01

    In many mountainous catchments the seasonal snowpack stores a significant volume of water, which is released as streamflow during the melting period. The predicted change in future climate will bring new challenges in water resource management in snow-dominated headwater catchments and their receiving lowlands. To improve predictions of hydrologic extreme events, particularly summer droughts, it is important characterize the relationship between winter snowpack and summer (low) flows in such areas (e.g., Godsey et al., 2014). In this context, stable water isotopes (18O, 2H) are a powerful tool for fingerprinting the sources of streamflow and tracing water flow pathways. For this reason, we have established an isotope sampling network in the Alptal catchment (46.4 km2) in Central-Switzerland as part of the SREP-Drought project (Snow Resources and the Early Prediction of hydrological DROUGHT in mountainous streams). Samples of precipitation (daily), snow cores (weekly) and runoff (daily) are analyzed for their isotopic signature in a regular cycle. Precipitation is also sampled along a horizontal transect at the valley bottom, and along an elevational transect. Additionally, the analysis of snow meltwater is of importance. As the sample collection of snow meltwater in mountainous terrain is often impractical, we have developed a fully automatic snow lysimeter system, which measures meltwater volume and collects samples for isotope analysis at daily intervals. The system consists of three lysimeters built from Decagon-ECRN-100 High Resolution Rain Gauges as standard component that allows monitoring of meltwater flow. Each lysimeter leads the meltwater into a 10-liter container that is automatically sampled and then emptied daily. These water samples are replaced regularly and analyzed afterwards on their isotopic composition in the lab. Snow melt events as well as system status can be monitored in real time. In our presentation we describe the automatic snow lysimeter

  20. Neoproterozoic cap-dolostone deposition in stratified glacial meltwater plume

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Wang, Zhengrong; Raub, Timothy D.; Macdonald, Francis A.; Evans, David A. D.

    2014-10-01

    Neoproterozoic cap carbonates host distinctive geochemical and sedimentological features that reflect prevailing conditions in the aftermath of Snowball Earth. Interpretation of these features has remained contentious, with hypotheses hinging upon timescale and synchronicity of deposition, and whether or not geochemical signatures of cap carbonates represent those of a well-mixed ocean. Here we present new high-resolution Sr and Mg isotope results from basal Ediacaran cap dolostones in South Australia and Mongolia. Least-altered Sr and Mg isotope compositions of carbonates are identified through a novel incremental leaching technique that monitors the purity of a carbonate sample and the effects of diagenesis. These data can be explained by the formation of these cap dolostones involving two chemically distinct solutions, a glacial meltwater plume enriched in radiogenic Sr, and a saline ocean residue with relatively lower 87Sr/86Sr ratios. Model simulations suggest that these water bodies remained dynamically stratified during part of cap-dolostone deposition, most likely lasting for ∼8 thousand years. Our results can potentially reconcile previous conflicts between timescales estimated from physical mixing models and paleomagnetic constraints. Geochemical data from cap carbonates used to interpret the nature of Snowball Earth and its aftermath should be recast in terms of a chemically distinct meltwater plume.

  1. Seasonal changes in Fe along a glaciated Greenlandic fjord.

    NASA Astrophysics Data System (ADS)

    Hopwood, Mark; Connelly, Douglas; Arendt, Kristine; Juul-Pedersen, Thomas; Stinchcombe, Mark; Meire, Lorenz; Esposito, Mario; Krishna, Ram

    2016-03-01

    Greenland's ice sheet is the second largest on Earth, and is under threat from a warming Arctic climate. An increase in freshwater discharge from Greenland has the potential to strongly influence the composition of adjacent water masses with the largest impact on marine ecosystems likely to be found within the glaciated fjords. Here we demonstrate that physical and chemical estuarine processes within a large Greenlandic fjord are critical factors in determining the fate of meltwater derived nutrients and particles, especially for non-conservative elements such as Fe. Concentrations of Fe and macronutrients in surface waters along Godthåbsfjord, a southwest Greenlandic fjord with freshwater input from 6 glaciers, changed markedly between the onset and peak of the meltwater season due to the development of a thin (<10 m), outflowing, low-salinity surface layer. Dissolved (<0.2 µm) Fe concentrations in meltwater entering Godthåbsfjord (200 nM), in freshly melted glacial ice (mean 38 nM) and in surface waters close to a land terminating glacial system (80 nM) all indicated high Fe inputs into the fjord in summer. Total dissolvable (unfiltered at pH <2.0) Fe was similarly high with concentrations always in excess of 100 nM throughout the fjord and reaching up to 5.0 µM close to glacial outflows in summer. Yet, despite the large seasonal freshwater influx into the fjord, Fe concentrations near the fjord mouth in the out-flowing surface layer were similar in summer to those measured before the meltwater season. Furthermore, turbidity profiles indicated that sub-glacial particulate Fe inputs may not actually mix into the outflowing surface layer of this fjord. Emphasis has previously been placed on the possibility of increased Fe export from Greenland as meltwater fluxes increase. Here we suggest that in-fjord processes may be effective at removing Fe from surface waters before it can be exported to coastal seas.

  2. The role of vegetation change on surface energy partitioning: insights from a global flux monitoring network

    NASA Astrophysics Data System (ADS)

    Stoy, Paul; Juang, Jehn-Yih; Siqueira, Mario; Novick, Kim; Katul, Gabriel

    2010-05-01

    Vegetation contributes to the absorption and partitioning of energy at the Earth's surface and the surface-atmosphere flux of important greenhouse gases. Changes to vegetation alter the surface energy balance and biogeochemical fluxes. Recent publications have stressed the need to quantify both biogeochemical and biogeophysical effects of land cover change on regional and global climate using a combination of observations and models. This presentation focuses on the observational record by synthesizing surface-atmosphere radiation balance characteristics - including surface albedo and the fluxes of latent and sensible heat - across global ecosystems in the FLUXNET database. We present characteristic seasonal courses of energy balance components across globally distributed ecosystems and demonstrate the impacts of vegetation change on the surface energy balance. We then perform a perturbation analysis on the energy balance equation to quantify the effects of land cover change on surface radiometric and aerodynamic temperatures in paired eddy covariance towers across the globe. Results emphasize the importance of evapotranspiritive cooling in addition to alterations in albedo on surface temperature change. For example, in the Duke Forest experiment, increases in albedo during a shift from abandoned field to pine or hardwood forest warmed the surface by ca. 1° C on an annual basis, but enhanced evapotranspiration cooled the surface by ca. 2 to 3° C such that reforestation induced a net surface cooling. Results using a general methodology agreed with previous results (Juang et al., 2007, Geophysical Research Letters, L21408). Global modeling exercises may underemphasize the role of evaporative cooling versus that of albedo in surface energy balance studies.

  3. Recent changes in sea ice area flux through the Beaufort Sea during the summer

    NASA Astrophysics Data System (ADS)

    Howell, Stephen E. L.; Brady, Michael; Derksen, Chris; Kelly, Richard E. J.

    2016-04-01

    Over the annual cycle, sea ice is sequestered from the Canadian Basin and transported through the Beaufort Sea toward the Chukchi Sea. In recent years, the Beaufort Sea has experienced considerable ice loss during the summer, which may be indicative of recent changes to this process. In order to investigate this, we quantify the sea ice area flux using RADARSAT from 1997 to 2014 at three gates in Beaufort Sea: the Canadian Basin (entrance), mid-Beaufort (midpoint), and Chukchi (exit). There was a mean annual flux of 42 ± 56 × 103 km2 at the Canadian Basin gate, 94 ± 92 × 103 km2 at the mid-Beaufort gate and -83 ± 68 × 103 km2 at the Chukchi gate (positive and negative flux signs correspond to ice inflow and outflow, respectively). The majority of ice transport in Beaufort Sea was found to occur from October to May providing replenishment for ice lost during the summer months. The cross-strait gradient in sea level pressure explains ˜40% of the variance in the ice area flux at the gates. Remarkably, the mean July-October net sea ice area flux at the Chukchi gate decreased by ˜80% from 2008 to 2014 relative to 1997-2007 and became virtually ice-free every year since 2008. This reduction was associated with younger (thinner) ice that was unable to survive the summer melt season when either being sequestered from the Canadian Basin and transported through Beaufort Sea during the melt season (2008-2011) or remaining immobile and present in the vicinity of the Chukchi gate during the melt season (2012-2014).

  4. The Effect of Satellite Observing System Changes on MERRA Water and Energy Fluxes

    NASA Technical Reports Server (NTRS)

    Robertson, Franklin R.; Bosilovich, M. G.; Chen, J.; Miller, t. L.

    2010-01-01

    Because reanalysis data sets offer state variables and fluxes at regular space / time intervals, atmospheric reanalyses have become a mainstay of the climate community for diagnostic purposes and for driving offline ocean and land models. Although one weakness of these data sets is the susceptibility of the flux products to uncertainties because of shortcomings in parameterized model physics, another issue, perhaps less appreciated, is the fact that continual but discreet changes in the evolving observational system, particularly from satellite sensors, may also introduce artifacts in the time series of quantities. In this paper we examine the ability of the NASA MERRA (Modern Era Retrospective Analysis for Research and Applications) and other recent reanalyses to determine variability in the climate system over the satellite record (approximately the last 30 years). In particular we highlight the effect on the reanalysis of discontinuities at the junctures of the onset of passive microwave imaging (Special Sensor Microwave Imager) in late 1987 as well as improved sounding and imaging with the Advanced Microwave Sounding Unit, AMSU-A, in 1998. We first examine MERRA fluxes from the perspective of how physical modes of variability (e.g. ENSO events, Pacific Decadal Variability) are contaminated by artificial step-like trends induced by the onset of new moisture data these two satellite observing systems. Secondly, we show how Redundancy Analysis, a statistical regression methodology, is effective in relating these artifact signals in the moisture and temperature analysis increments to their presence in the physical flux terms (e.g. precipitation, radiation). This procedure is shown to be effective greatly reducing the artificial trends in the flux quantities.

  5. The Effect of Satellite Observing System Changes on MERRA Water and Energy Fluxes

    NASA Technical Reports Server (NTRS)

    Robertson, Franklin R.; Bosilovich, M. G.; Chen, J.; Miller, T. L.

    2011-01-01

    Because reanalysis data sets offer state variables and fluxes at regular space / time intervals, atmospheric reanalyses have become a mainstay of the climate community for diagnostic purposes and for driving offline ocean and land models. Although one weakness of these data sets is the susceptibility of the flux products to uncertainties because of shortcomings in parameterized model physics, another issue, perhaps less appreciated, is the fact that continual but discreet changes in the evolving observational system, particularly from satellite sensors, may also introduce artifacts in the time series of quantities. In this paper we examine the ability of the NASA MERRA (Modern Era Retrospective Analysis for Research and Applications) and other recent reanalyses to determine variability in the climate system over the satellite record (approx. the last 30 years). In particular we highlight the effect on the reanalysis of discontinuities at the junctures of the onset of passive microwave imaging (Special Sensor Microwave Imager) in late 1987 and, more prominently, with improved sounding and imaging with the Advanced Microwave Sounding Unit, AMSU-A, in 1998. We first examine MERRA fluxes from the perspective of how physical modes of variability (e.g. ENSO events, Pacific Decadal Variability) are contained by artificial step-like trends induced by the onset of new moisture data these two satellite observing systems. Secondly, we show how Redundancy Analysis, a statistical regression methodology, is effective in relating these artifact signals in the moisture and temperature analysis increments to their presence in the physical flux terms (e.g. precipitation, radiation). This procedure is shown to be effective greatly reducing the artificial trends in the flux quantities.

  6. Changing trends of rainfall and sediment fluxes in the Kinta River catchment, Malaysia

    NASA Astrophysics Data System (ADS)

    Ismail, W. R.; Hashim, M.

    2015-03-01

    The Kinta River, draining an area of 2566 km2, originates in the Korbu Mountain in Perak, Malaysia, and flows through heterogeneous, mixed land uses ranging from extensive forests to mining, rubber and oil palm plantations, and urban development. A land use change analysis of the Kinta River catchment was carried out together with assessment of the long-term trend in rainfall and sediment fluxes. The Mann-Kendall test was used to examine and assess the long-term trends in rainfall and its relationship with the sediment discharge trend. The land use analysis shows that forests, water bodies and mining land declined whilst built and agricultural land use increased significantly. This has influenced the sediment flux of the catchment. However, most of the rainfall stations and river gauging stations are experiencing an increasing trends, except at Kinta river at Tg. Rambutan. Sediment flux shows a net erosion for the period from 1961 to 1969. The total annual sediment discharge in the Kinta River catchment was low with an average rate of 1,757 t/km2/year. From 1970 to 1985, the annual sediment yield rose to an average rate of 4062 t/km2/year. Afterwards, from 1986 to 1993, the total annual sediment discharge decreased to an average rate of 1,306 t/km2/year and increased back during the period 1994 to 2000 to 2109 t/km2/year. From 2001 to 2006 the average sediment flux rate declined to 865 t/km2/year. The decline was almost 80% from the 1970s. High sediment flux in the early 1970s is partly associated with reduced tin mining activities in the area. This decreasing trend in sediment delivery leaving the Kinta River catchment is expected to continue dropping in the future.

  7. Seasonal changes in soil water repellency and their effect on soil CO2 fluxes

    NASA Astrophysics Data System (ADS)

    Urbanek, Emilia; Qassem, Khalid

    2016-04-01

    Soil water repellency (SWR) is a seasonally variable phenomenon controlled by moisture content and at the same time a regulator of the distribution and conductivity of water in the soil. The distribution and availability of water in soil is also an important factor for microbial activity, decomposition of soil organic matter and exchange of gases like CO2 and CH4 between the soil and the atmosphere. It has been therefore hypothesised that SWR by restricting water availability in soil can affect the production and the transport of CO2 in the soil and between the soil and the atmosphere. This study investigates the effect of seasonal changes in soil moisture and water repellency on CO2 fluxes from soil. The study was conducted for 3 year at four grassland and pine forest sites in the UK with contrasting precipitation. The results show the temporal changes in soil moisture content and SWR are affected by rainfall intensity and the length of dry periods between the storms. Soils exposed to very high annual rainfall (>1200mm) can still exhibit high levels of SWR for relatively long periods of time. The spatial variation in soil moisture resulting from SWR affects soil CO2 fluxes, but the most profound effect is visible during and immediately after the rainfall events. Keywords: soil water repellency, CO2 flux, hydrophobicity, preferential flow, gas exchange, rainfall

  8. North Atlantic overturning and climate response to meltwater forcing during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Muschitiello, Francesco; Dokken, Trond; Väliranta, Minna; Björck, Svante; Davies, Siwan; Luoto, Tomi; Schenk, Frederik; Smittenberg, Rienk; Reimer, Paula; Wohlfarth, Barbara

    2016-04-01

    The last deglaciation (˜18-11 kyr BP) is an important analog to investigate the response of the Atlantic Meridional Overturning Circulation (AMOC) to future ice-sheet melting and its impact on regional climate change. In this study we present synchronised terrestrial and marine proxy records that provide insight into freshwater run-off and climate variability in the eastern North Atlantic during the last deglaciation. The reconstructions show that atmospheric circulation rather than freshwater forcing primarily controls the stability of the AMOC. However, catastrophic meltwater drainage from the Scandinavian continent may have solicited complex feedbacks necessary to account for the rapid large-scale hydro-climate shifts and the major weakening of the overturning circulation system at the onset of the Younger Dryas stadial.

  9. Reaction path modelling used to explore the relationship between secondary mineral precipitation and low Si content in the meltwaters of a polythermal surge-type glacier

    NASA Astrophysics Data System (ADS)

    Crompton, J. W.; Flowers, G. E.; Kirste, D. M.; Hagedorn, B.

    2014-12-01

    The subglacial chemical weathering environment is characterized by low temperatures and the hydrolysis and carbonation of freshly comminuted mineral surfaces. Such conditions motivate the hypothesis that relatively low silica fluxes should be found in glacierized basins. Additionally, it is often assumed that glacier meltwaters are far from saturation and that the water chemistry is controlled solely by the dissolution of primary silicates and trace quantities of sulphide and carbonate minerals. Alternatively, we propose that the formation of secondary minerals and precipitates in the delayed drainage system play an important role in controlling the low silica fluxes observed in subglacial envrionments. Borehole and proglacial meltwater samples were collected from a polythermal surge-type glacier overlying granodiorite bedrock in the St. Elias Mountains of Yukon, Canada. The meltwater chemistry, along with the mineralogy of the bedrock and suspended sediments indicate the presence of mineral precipitation accompanied by substantial basal freeze-on. This is supported by field evidence of debris rich basal ice at the terminus and at the base of a borehole. The surplus of Cl- above the supraglacial input is used to calculate the amount of basal freeze-on in the delayed drainage system, and the amount of mixing between the delayed and fast drainage systems. We use Geochemist's Workbench for reaction path modelling with a focus on the silica composition to simulate the chemical evolution of glacial meltwater from (1) the initial water rock contact, (2) basal freeze on, and (3) mixing and post mixing reactions. Unless there is a substantial degree of non-stoichiometric dissolution, we find that the observed proglacial water chemistry at the terminus is largely controlled by the hydrochemistry of water in the delayed drainage system. Lastly, we use this model to explore the relationship between the proglacial water chemistry and the daily glacier surface velocities for

  10. Long-term lysimeter experiment to analyze the influence of the climate change on matter fluxes

    NASA Astrophysics Data System (ADS)

    Pütz, Thomas; Groh, Jannis; Wollschläger, Ute; Gerke, Horst; Priesack, Eckart; Kiese, Ralf; Borg, Erik; Vereecken, Harry

    2015-04-01

    Based on the TERENO SoilCan infrastructure, a long-term large-scale experiment was designed to study the effects of climate change on terrestrial systems. The water and matter fluxes in soil are the main focuses of SoilCan. In the frame of SoilCan, fully automated lysimeter systems were installed on several highly equipped experimental field sites of the TERENO-observatories and the relevant status variables of each ecosystem were monitored (e.g. climate, hydrology, biosphere-atmosphere exchange, biodiversity, etc.). In total, 90 lysimeters (1.5 m depth, 1m2 surface) were filled with soil monoliths at the four TERENO-observatories and were instrumented with TDRs, tensiometers, temperature sensors, soil heat flux plates, and CO2 sensors. For the controlling of the lower boundary condition, suction candle rakes were installed into the lysimeter bottoms. In combination with bi-directional pumps and tanks, the water content of the lysimeters was adjusted to the surrounded original field sites. To simulate the expected climate change, 48 lysimeters were transferred along temperature and rainfall gradients within the respective observatories and between the observatories, based on the principle 'Space for Time'. In case of the "Rur" observatory, three intensively instrumented field sites ("Wüstebach", "Rollesbroich" und "Selhausen") were equipped with lysimeter stations. These three field sites include different land uses, "Wüstebach" as a forest site, "Rollesbroich" as a grassland and "Selhausen" as an arable site. In order to standardize the agronomic management, the crop rotation at the arable lysimeters comprised winter wheat - winter rye - winter barley - oats. For investigation of the matter flux, soil solutions and leachates were regularly sampled. The water balances and the dynamics of the carbon and nitrogen fluxes in the first two years of the experiment will be presented.

  11. Representing moisture fluxes and phase changes in glacier debris cover using a single-reservoir approach

    NASA Astrophysics Data System (ADS)

    Collier, E.; Nicholson, L. I.; Brock, B. W.; Maussion, F.; Essery, R.; Bush, A. B. G.

    2014-03-01

    Due to the complexity of treating moisture in supraglacial debris, surface energy balance models to date have neglected moisture infiltration and phase changes in the debris layer. The latent heat flux (QL) is also often excluded due to the uncertainty in determining the surface vapour pressure. To quantify the importance of moisture on the surface energy and climatic mass balance (CMB) of debris-covered glaciers, we developed a simple, single-reservoir parameterization for the debris ice and water content, as well as an estimation of the latent heat flux. The parameterization was incorporated into a sophisticated CMB model adapted for debris-covered glaciers. We perform two point simulations using both our new "moist" and the conventional "dry" approaches, on the Miage Glacier, Italy, during summer 2008 and fall 2011. The former simulation coincides with available in situ glaciological and meteorological measurements, including the first eddy-covariance measurements of the turbulent fluxes over supraglacial debris, while the latter contains two refreeze events that permit evaluation of the influence of phase changes. The simulations demonstrate a clear influence of moisture on the glacier energy and mass dynamics. Heat transmission to the underlying ice is lower, as the effective thermal diffusivity of the debris is reduced by increases in the weighted density and specific heat capacity when water and ice are considered. In combination with surface heat extraction by QL, sub-debris ice melt is reduced by 2.3% in 2008 and by 2.8% in 2011 when moisture effects are included. However, mass loss due to surface vapour fluxes more than compensates for the reduction in ice melt, such that the total accumulated ablation increased by 5.3% in 2008 and by 2.8% in 2011. Although the parameterization is a simplified representation of the moist physics of glacier debris, it is a novel attempt at including moisture in a numerical model of debris-covered glaciers and opens up

  12. Modeling CO2 sediment-water flux variations connected with changes of redox conditions

    NASA Astrophysics Data System (ADS)

    Yakushev, Evgeniy; Protsenko, Elizaveta

    2013-04-01

    Changes of bottom redox conditions from oxic to hypoxic, suboxic and anoxic affect rates of sediment-water fluxes of chemical parameters, i.e. oxygen, nutrient (including carbon), redox metals. Chemosynthetic organic matter production in suboxic and anoxic conditions additionally affects transformation of carbon. This work aimed in estimation of a potential influence of changes of the bottom redox conditions on the sediment -water fluxes of carbon. We use a 1-dimensional C-N-P-Si-O-S-Mn-Fe vertical transport-reaction model describing both the sediments and bottom boundary layers coupled with biogeochemical block simulating changeable redox conditions, and the carbonate system processes block. A biogeochemical block is based on ROLM (RedOx Layer Model), that was constructed to simulate basic features of the water column biogeochemical structure changes in oxic, anoxic and changeable conditions (Yakushev et al., 2007). Organic matter formation and decay, reduction and oxidation of species of nitrogen, sulfur, manganese, iron, and the transformation of phosphorus species are parameterized in the model. The model includes blocks for phytoplankton, zooplankton, aerobic autotrophic and heterotrophic bacteria and anaerobic autotrophic and heterotrophic bacteria. In this study we additionally parameterized transformation of Si and C and forms of alkalinity. We simulate changes in the bottom boundary layer pH in different redox conditions under the same leakage scenario.

  13. Diachronic Impacts of Land Use Change on Water Fluxes in the Sahel, West Africa

    NASA Astrophysics Data System (ADS)

    Favreau, G.; Cappelaere, B.; Demarty, J.; Ibrahim, M.; Lecoz, M.; Nazoumou, Y.; Ngounou-Ngatcha, B.; Velluet, C.

    2012-12-01

    The water cycle in the Sahel region is known to be subject to great variability, from infra-rainfall time scale during the West African monsoon (e.g., surface runoff surveys) to century or even millennium time periods (i.e., for large sedimentary aquifers). Detailed hydrological and heat flow surveys, using a large set of instrumental methods or approaches have increased our understanding of eco-hydrological processes leading to the observed changes in green (soil moisture) and "blue" (surface and ground water) resources. In semiarid SW Niger, change from fallow to rainfed millet crop had a important impact on the water cycle, increasing runoff on sandy slopes and focused recharge through endoreic ponds and gullies, but also deep drainage and direct recharge below crop fields. As a consequence, evapotranspiration fluxes decreased, both during the dry and rainy seasons. Conversion from semi-natural dryland savannah to rainfed crop production reversed fluxes from upward (small discharge from deep rooted ligneous species) to downward (net recharge) in the Lake Chad basin aquifer. Moreover, the use of irrigation using river water increased drainage in the river plains and hence, increased aquifer recharge, decreasing evapotranspiration fluxes and river discharge. In endoreic, large sedimentary basins of the Sahel region, ground water represents the terrestrial outlet of the system and changes may be recorded in long-term water table fluctuations. A detailed analysis of trends in aquifer reserves in the Sahel indicates that it matches diachronic changes in land use, both in time and space. This further suggests, in turn, diachronic retroaction and feedback of the terrestrial water cycle to the atmosphere.

  14. Modelling Multidecadal Fluvial Sediment Fluxes to Deltas Under Future Environmental Change

    NASA Astrophysics Data System (ADS)

    Dunn, F. E.; Darby, S. E.; Nicholls, R. J.

    2015-12-01

    As low lying coastal regions deltas are prone to land loss, degradation, and flooding due to relative sea level rise. These processes endanger delta populations and infrastructure, a situation which is increasingly exacerbated by anthropogenic activities. The flux of fluvial sediment to deltas is a first order control on delta aggradation and thus the potential for the surface elevation of a delta to be maintained or rise relative to sea level. Aggradation may occur without anthropogenic interference, but it can also be induced by controlled flooding. This research investigates how future environmental changes through to 2100 will influence fluvial sediment delivery to a selection of 10 vulnerable deltas, thereby contributing to the understanding of relative sea level change projections for these fragile coastal systems. The key environmental changes investigated in this study include anthropogenic climate change, reservoir construction, and land cover changes induced by changes in agricultural practices and vegetation cover. The effects of these environmental changes on fluvial sediment delivery are being evaluated using the catchment numerical model WBMsed, which is being calibrated for the selection of deltas using historical reference data. As a test case, the inputs for modelling current and future sediment fluxes to the Ganges-Brahmaputra-Meghna delta are refined using economic and population projections as proxies for anthropogenic influences on delta catchments. This research will contribute to the prognosis for vulnerable deltas and inform their short- and long-term management by indicating the consequences of anthropogenic activities which affect delta elevation and sustainability via altering fluvial sediment processes. While this could give forewarning for the residents and managers of unsustainable deltas, it could also be used as an argument for or against various anthropogenic activities.

  15. Longitudinal Inter-Comparison of Modeled and Measured West Greenland Ice Sheet Meltwater Runoff Losses (2004-2014)

    NASA Astrophysics Data System (ADS)

    Moustafa, S.; Rennermalm, A. K.; Tedesco, M.; Mote, T. L.; Koenig, L.; Smith, L. C.; Hagedorn, B.; Overeem, I.; Sletten, R. S.; Mikkelsen, A. B.; Hasholt, B.; Hall, D. K.

    2015-12-01

    Increased surface meltwater runoff, that exits the Greenland ice sheet (GrIS) margin via supra-, en-, and sub-glacial drainage networks into fjords, pro-glacial lakes and rivers, accounts for half or more of total mass loss. Despite its importance, modeled meltwater runoff fluxes are poorly constrained, primarily due to a lack of direct in situ observations. Here, we present the first ever longitudinal (north-south) inter-comparison of a multi-year dataset (2004-2014) of discharge for four drainage basins - Watson, Akuliarusiarsuup Kuua, Naujat Kuat, and North Rivers - along West Greenland. These in situ hydrologic measurements are compared with modeled runoff output from Modèle Atmosphérique Régional (MAR) regional climate model, and the performance of the model is examined. An analysis of the relationship between modeled and actual ice sheet runoff patterns is assessed, and provides insight into the model's ability to capture inter-annual and intra-annual variability, spatiotemporal patterns, and extreme melt events. This study's findings will inform future development and parameterization of ice sheet surface mass balance models.

  16. Nutrient treatments alter microbial mat colonization in two glacial meltwater streams from the McMurdo Dry Valleys, Antarctica.

    PubMed

    Kohler, Tyler J; Van Horn, David J; Darling, Joshua P; Takacs-Vesbach, Cristina D; McKnight, Diane M

    2016-04-01

    Microbial mats are abundant in many alpine and polar aquatic ecosystems. With warmer temperatures, new hydrologic pathways are developing in these regions and increasing dissolved nutrient fluxes. In the McMurdo Dry Valleys, thermokarsting may release both nutrients and sediment, and has the potential to influence mats in glacial meltwater streams. To test the role of nutrient inputs on community structure, we created nutrient diffusing substrata (NDS) with agar enriched in N, P and N + P, with controls, and deployed them into two Dry Valley streams. We found N amendments (N and N + P) to have greater chlorophyll-a concentrations, total algal biovolume, more fine filamentous cyanobacteria and a higher proportion of live diatoms than other treatments. Furthermore, N treatments were substantially elevated in Bacteroidetes and the small diatom, Fistulifera pelliculosa. On the other hand, species richness was almost double in P and N + P treatments over others, and coccoid green algae and Proteobacteria were more abundant in both streams. Collectively, these data suggest that nutrients have the potential to stimulate growth and alter community structure in glacial meltwater stream microbial mats, and the recent erosion of permafrost and accelerated glacial melt will likely impact resident biota in polar lotic systems here and elsewhere. PMID:26940086

  17. Deglacial Record in the Illinois River Valley Explains Asynchronous Phases of Meltwater Pulses and Clay Mineral Excursions in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Wang, H.

    2014-12-01

    One prominent event of the Bølling/Allerød (B/A) interstadial was the large meltwater release to global oceans. The Laurentide Ice Sheet (LIS) is usually considered the main source. But, the large LIS meltwater discharge conflicts with the marine record showing an active North Atlantic meridional overturning circulation (AMOC) during the B/A interval. Continuous dune-lacustrine successions in the Illinois River Valley (IRV) have shown complete records of the last deglacial chronozones. Their grain-size distributions and accurate B/A age 14C dates of plant fossils from 15 m deep lacustrine sediment in the IRV suggest that most of the IRV and parts of the adjacent upland were inundated by water. The inundation was caused by a sediment dam interpreted to have been constructed and followed by a breach at the confluence of the Mississippi and Illinois Rivers during the B/A interval due to sediment mobilization by the large meltwater release. The grain size distributions correlate with meltwater pulses and mineralogical excursions in sediments from the Gulf of Mexico (GOM) very well. The blockage and release of illite and chlorite rich fine-grained sediments from the Lake Michigan basin changed the relative abundance of clay minerals and thus the ratio of smectite/(illite + chlorite) in the sediment of the GOM. This finding explains why the meltwater episodes from the LIS and the associated detrital discharges are not synchronous in the sediments in the GOM. The finding also ties meltwater pulses and associated detrital discharges in the GOM closely to the LIS discharges via the Mississippi River Valley on chronozonal scales. Three arguments can be made from this result: 1) unaffected AMOC during B/A interval resulted potentially from the hyperpycnal inflow into the GOM floor; 2) limited volume of the meltwater discharge did not significantly influence the AMOC; and 3) the freshwater input into the GOM from the LIS at this particular location did not significantly

  18. Decadal Vegetation Changes in a Northern Peatland,Greenhouse gas Fluxes and net Radiative Forcing

    NASA Astrophysics Data System (ADS)

    Johansson, T.; Malmer, N.; Christensen, T. R.; Kerman, H. J.

    2004-05-01

    Today the sub-Arctic permafrost thaws with an accelerating rate. This has implications for the stability of the northern peatland ecosystems that are underlain by permafrost and eventually for the energy balance of the Earth. These ecosystems are unique in the world; while at the same time considered to have been net carbon sinks since the last glacial termination they have the ability to release large amounts of methane. During the last 30 years the vegetation of northernmost Swedish peatlands have undergone change. Dry ombrotrophic systems have become wet and nutrient rich reflecting the close connection between vegetation and permafrost status. The objective of this study was to analyse how the vegetation change since 1970 on Stordalen mire (a mixed mire complex in northern Sweden, 68° 20' N, 19\\deg02' E) may have changed the net exchange of greenhouse gases CO2 and CH4. Color infrared aerial images (CIR) of the entire mire from 1970 and 2000 were used. We estimated the large-scale vegetation change on the Stordalen mire, and used available and published data on plot scale C-fluxes to calculate exchanges in total C- equivalents (C-CO2 and C-CH4). These were then scaled to the whole mire to estimate the effect vegetation change has had on the radiative forcing of the entire mire. The derived vegetation maps of the central part of Stordalen mire (15 ha) clearly show a decadal change in vegetation composition between 1970-2000. The areal extension of dry elevated ombrotrophic areas has decreased by 11- 36% or expressed in hectares, an approximate loss of 1 to 3 hectares. Accordingly dwarf shrub vegetation with a high abundance of bare peat and lichens in the bottom layer and associated species in the field layer are nowadays less abundant on the mire. During the same time period the total CO2 and CH4 flux changed by 1- 11% (sink) and 19- 66% (source) respectively. When calculating the flux as total C-equivalents, using IPCC's GWP (Global Warming Potentials) for

  19. Glacial Meltwater Streams of the McMurdo Dry Valleys, Antarctica: Ecosystems Waiting for Water

    NASA Astrophysics Data System (ADS)

    McKnight, D. M.; Gooseff, M.; Cozzetto, K.

    2007-12-01

    The McMurdo Dry Valleys of Antarctica contain many glacial meltwater streams that flow for 6 to 12 weeks during the austral summer and link the glaciers to the lakes on the valley floors. Dry valley streams gain solutes longitudinally through weathering reactions and microbial processes occurring in the hyporheic zone, evident as a damp area underneath and adjacent to the stream. The lower boundary of the hyporheic zone is determined by the depth to permafrost. On sunny days, stream temperatures can reach 15 °C, and advection of this warm water can erode the frozen lower boundary of the hyporheic zone. In cold summers, streamflow is fed mostly by melt from the faces of the source glaciers and a large portion of this meltwater may be stored in the hyporheic zone and then lost through sublimation, rather than discharged to the lakes. Some streams have thriving microbial mats composed of cyanobacteria and diatoms. These mats are freeze-dried through the winter and begin photosynthesizing with the onset of flow. To evaluate the longer term persistence of cynaobacterial mats, we diverted flow to an abandoned channel, which had not received substantial flow for approximately two decades. We observed that cyanobacterial mats became abundant in the reactivated channel within a week, indicating that the mats had been preserved in a cryptobiotic state in the channel. Over the next several years, these mats had high rates of productivity and nitrogen fixation compared to mats from other streams. These stream-scale experimental results indicate that the cryptobiotic preservation of cyanobacterial mats in abandoned channels in the dry valleys allows for rapid response of stream ecosystems to climatic and geomorphological change.

  20. Model support for forcing of the 8.2 ka event by meltwater from the Hudson Bay ice dome

    NASA Astrophysics Data System (ADS)

    Wagner, Amy J.; Morrill, Carrie; Otto-Bliesner, Bette L.; Rosenbloom, Nan; Watkins, Kelsey R.

    2013-12-01

    Previous model experiments of the 8.2 ka event forced by the drainage of Lake Agassiz often do not produce climate anomalies as long as those inferred from proxies. In addition to the Agassiz forcing, there is new evidence for significant amounts of freshwater entering the ocean at 8.2 ka from the disintegration of the Laurentide ice sheet (LIS). We use the Community Climate System Model version 3 (CCSM3) to test the contribution of this additional meltwater flux. Similar to previous model experiments, we find that the estimated freshwater forcing from Lake Agassiz is capable of sustaining ocean and climate anomalies for only two to three decades, much shorter than the event duration of ~150 years in proxies. Using new estimates of the LIS freshwater flux (~0.13 Sv for 100 years) from the collapse of the Hudson Bay ice dome in addition to the Agassiz drainage, the CCSM3 generates climate anomalies with a magnitude and duration that match within error those from proxies. This result is insensitive to the duration of freshwater release, a major uncertainty, if the total volume remains the same. An analysis of the modeled North Atlantic freshwater budget indicates that the Agassiz drainage is rapidly transported out of the North Atlantic while the LIS contribution generates longer-lasting freshwater anomalies that are also subject to recirculation by the subtropical gyre back into the North Atlantic. Thus, the meltwater flux originating from the LIS appears to be more important than the Agassiz drainage in generating 8.2 ka climate anomalies and is one way to reconcile some model-data discrepancies.

  1. Modeling impacts of changes in temperature and water table on C gas fluxes in an Alaskan peatland

    NASA Astrophysics Data System (ADS)

    Deng, Jia; Li, Changsheng; Frolking, Steve

    2015-07-01

    Northern peatlands have accumulated a large amount of organic carbon (C) in their thick peat profile. Climate change and associated variations in soil environments are expected to have significant impacts on the C balance of these ecosystems, but the magnitude is still highly uncertain. Verifying and understanding the influences of changes in environmental factors on C gas fluxes in biogeochemical models are essential for forecasting feedbacks between C gas fluxes and climate change. In this study, we applied a biogeochemical model, DeNitrification-DeComposition (DNDC), to assess impacts of air temperature (TA) and water table (WT) on C gas fluxes in an Alaskan peatland. DNDC was validated against field measurements of net ecosystem exchange of CO2 (NEE) and CH4 fluxes under manipulated surface soil temperature and WT conditions in a moderate rich fen. The validation demonstrates that DNDC was able to capture the observed impacts of the manipulations in soil environments on C gas fluxes. To investigate responses of C gas fluxes to changes in TA and soil water condition, we conducted a series of simulations with varying TA and WT. The results demonstrate that (1) uptake rates of CO2 at the site were reduced by either too colder or warmer temperatures and generally increased with increasing soil moisture; (2) CH4 emissions showed an increasing trend as TA increased or WT rose toward the peat surface; and (3) the site could shift from a net greenhouse gas (GHG) sink into a net GHG source under some warm and/or dry conditions. A sensitivity analysis evaluated the relative importance of TA and WT to C gas fluxes. The results indicate that both TA and WT played important roles in regulating NEE and CH4 emissions and that within the investigated ranges of the variations in TA and WT, changes in WT showed a greater impact than changes in TA on NEE, CH4 fluxes, and net C gas fluxes at the study fen.

  2. Seasonal Change Of CO2 Flux At Tundra Vegetation In Interior Alaska

    NASA Astrophysics Data System (ADS)

    Nojiri, A.; Harazono, Y.; Ohtaki, E.; Iwata, T.

    2003-12-01

    CO2 flux and micrometeorology have been measured to reveal the responses of forest at permafrost to climate change since October in 2002. The vegetation was black spruce and tussock tundra located in the campus (147° 51'W, 64° 51N) of the University of Alaska Fairbanks, Alaska. There have been significant gaps of flux measurements in the interior Alaska where it is generally warmer in summer and has different climate conditions. CO2 uptake started in March when the tussock tundra was still under snow cover. CO2 uptake increased after spring thaw in mid April that ranged -0.3mg/m2/s and increased gradually until early May (DOY135). After that, daily maximum CO2 uptake kept almost upper-limit level of -1mg/m2/s during summer (June and July). Day-length was longer at the site so the nighttime CO2 respiration was defined as CO2 efflux when PAR was less than 10 mol/m2/s. Averages of CO2 respiration were 0.042mg/m2/s in mid April (DOY100-109), 0.021mg/m2/s in mid May (DOY130-139), 0.15mg/m2/s in mid June (DOY160-169), and 0.15mg/m2/s in mid July (DOY190-199), respectively. Air temperature in mid summer did not changed remarkably and daily average temperature in June and July were almost the same as between 10 and 20. These were caused by lower solar radiation and higher level of precipitation in 2003 summer than the normal year. Observed CO2 flux was limited period and the CO2 budget over tussock tundra in interior Alaska was a source from spring to summer in 2003. Long term CO2 budget study is demanded to reveal whether anthropogenic or natural variation is major effect on climate change, thus it is important to continue the flux measurements and to reveal the relationships between the atmosphere and the vegetation.

  3. Motion and Magnetic Flux Changes of Coronal Bright Points Relative to Supergranular Cell Boundaries

    NASA Astrophysics Data System (ADS)

    Yousefzadeh, M.; Safari, H.; Attie, R.; Alipour, N.

    2016-01-01

    To calculate the magnetic flux and the horizontal movement of coronal bright points (CBPs) in relation to supergranular cell boundaries, the time series of the SDO/HMI visible-light continuum images and SDO/AIA EUV images for 13 February 2011 have been studied. The supergranular lanes were detected in HMI continuum images using the automatic supergranular cell recognition method. The automatic identification and tracking method was applied for detecting the CBPs in AIA 193 Å images. By applying the ball-tracking method on HMI continuum images, the underlying flow fields were determined. By using the velocity fields and the automatic supergranular cell recognition method, the lanes and boundaries were detected. The locations of CBPs were projected on the photospheric co-spatial and co-temporal images. We found that about 90 % of the locations of CBPs correspond to the lane of the supergranular cell boundaries (network CBPs or NCBPs) of which about 40 % of them appeared at junctions. The remaining 10 % appeared within the supergranular regions (internetwork CBPs or INCBPs). The horizontal velocities for NCBPs and INCBPs were about 1.6±0.1 km s^{-1} and 1.7±0.1 km s^{-1}, respectively. Using the magnetic field extrapolation, we were able to detect the bipoles underlying CBPs, and we studied their magnetic evolution. The orientation of CBPs observed in the 171, 193, and 211 Å images and the orientation of their magnetic bipoles are positively correlated. For out of 50 INCBPs, 54 % showed cancellation, 32 % emergence, and 12 % complex flux changes. Out of 90 NCBPs, 60 % presented cancellation, 20 % showed emergence, and 20 % showed complex flux changes.

  4. Extreme Ultraviolet Radiation Flux Changes and Total Electron Content Enhancement During Solar Flares

    NASA Astrophysics Data System (ADS)

    Kelley, T. P.; Zhang, S.; Coster, A. J.

    2011-12-01

    Solar flares induce sudden changes in X-ray irradiance and EUV flux. The possibility of a correlation between these changes and the daytime global value of total electron content (TEC) is investigated through the use of data from the GPS, SOHO, and GOES satellites. The Millstone Hill Incoherent Scatter Radar (ISR) is used to investigate the altitude stratification of the flare induced TEC enhancement. A study is conducted for the months of October 2002 and September 2005 as they had 329 and 114 flares, respectively. The amount of TEC enhancement due to a solar flare is found to be dependent on solar activity, solar flare strength, and the background TEC. On average, October 2002 had solar flares of less strength and higher solar activity. Flare effects were more evident in September 2005 which had on average, a small background TEC (10-15 TECu) and prominent (~2 TECu) TEC enhancements. In addition, a high and positive correlation between X-ray irradiance and EUV flux was seen during solar flare events. Through the comparison of the different data sets, it is found that the majority of the TEC enhancement is in the E and F regions (100-150 km) which corresponds to the portion of the ionosphere ionized by EUV radiation.

  5. Changes in SO2 flux degassing regime prior to the 2014 Stromboli eruption

    NASA Astrophysics Data System (ADS)

    Tamburello, Giancarlo; Delle Donne, Dario; Ripepe, Maurizio; Bitetto, Marcello; Cosenza, Paolo; Giudice, Gaetano; Riccobono, Giuseppe; Aiuppa, Alessandro

    2015-04-01

    Volcanic eruptions are often accompanied by release of huge amounts of magmatic SO2. Capturing sizeable precursory SO2 flux variations prior to eruption has revealed far more challenging, instead, in spite of the recent progresses in instrumental gas monitoring. Here, we report on the SO2 fluxes variations we detected at Stromboli volcano prior to the effusive eruption started on the 6th August 2014. The SO2 fluxes were regularly quantified at high-rate (0.5 Hz) using two fully autonomous permanent SO2 camera devices installed - within the framework the ERC-FP7 project "Bridge"- at two sites located at 0.5 km (Roccette) and 1.75 km (Sciara del Fuoco rim) distance from the crater terrace. This system provided sufficient spatial resolution, (~0.4 m) to allow for separate evaluation of gas emissions from the centrals/NE craters (CC and NEC, ~150 t/d on average) and from the northern hornitos (NH, ~15 t/d on average) that was active in summer 2014. Notwithstanding its marginal contribution to the total SO2 flux, the NH was vigorously active before the effusive eruption onset, and produced a large number of ash-free explosions, which individual SO2 output was easily measurable at high sampling rate with the SO2 cameras. From the beginning of June 2014, the NH exhibited a progressive increase of its explosive SO2 release (from ~1 t/d up to ~5 t/d) which culminated in correspondence with a sequence of lava overflows on the beginning of July 2014. A notable correlation between the explosive degassing pattern and co-acquired acoustic pressure and satellite-derived Volcanic Radiative Power was observed. The relative contributions of the individual degassing craters to the total gas emissions varied in response to the displacement of the magma level within the conduits, with the largest SO2 fluxes being observed during lava overflows. Our results here indicate detectable changes in the relative gas contribution from the different craters and in their degassing modes, although

  6. Stratospheric O3 changes during 2001-2010: the small role of solar flux variations in a CTM

    NASA Astrophysics Data System (ADS)

    Dhomse, S. S.; Chipperfield, M. P.; Feng, W.; Ball, W. T.; Unruh, Y. C.; Haigh, J. D.; Krivova, N. A.; Solanki, S. K.; Smith, A. K.

    2013-05-01

    Solar spectral fluxes (or irradiance) measured by the SOlar Radiation and Climate Experiment (SORCE) show different variability at ultraviolet (UV) wavelengths compared to other irradiance measurements and models (e.g. NRL-SSI, SATIRE-S). Some modelling studies have suggested that stratospheric/lower mesospheric O3 changes during solar cycle 23 (1996-2008) can only be reproduced if SORCE solar fluxes are used. We have used a 3-D chemical transport model (CTM), forced by meteorology from the European Centre for Medium-Range Weather Forecasts (ECMWF), to simulate middle atmospheric O3 using three different solar flux datasets (SORCE, NRL-SSI and SATIRE-S). Simulated O3 changes are compared with Microwave Limb Sounder (MLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite data. Modelled O3 anomalies from all solar flux datasets show good agreement with the observations, despite the different flux variations. The off-line CTM reproduces these changes through dynamical information contained in the analyses. A notable feature during this period is a robust positive solar signal in the tropical middle stratosphere due to changes in stratospheric dynamics. Ozone changes in the lower mesosphere cannot be used to discriminate between solar flux datasets due to large uncertainties and the short time span of the observations. Overall this study suggests that, in a CTM, the UV variations detected by SORCE are not necessary to reproduce observed stratospheric O3 changes during 2001-2010.

  7. Stratospheric O3 changes during 2001-2010: the small role of solar flux variations in a chemical transport model

    NASA Astrophysics Data System (ADS)

    Dhomse, S. S.; Chipperfield, M. P.; Feng, W.; Ball, W. T.; Unruh, Y. C.; Haigh, J. D.; Krivova, N. A.; Solanki, S. K.; Smith, A. K.

    2013-10-01

    Solar spectral fluxes (or irradiance) measured by the SOlar Radiation and Climate Experiment (SORCE) show different variability at ultraviolet (UV) wavelengths compared to other irradiance measurements and models (e.g. NRL-SSI, SATIRE-S). Some modelling studies have suggested that stratospheric/lower mesospheric O3 changes during solar cycle 23 (1996-2008) can only be reproduced if SORCE solar fluxes are used. We have used a 3-D chemical transport model (CTM), forced by meteorology from the European Centre for Medium-Range Weather Forecasts (ECMWF), to simulate middle atmospheric O3 using three different solar flux data sets (SORCE, NRL-SSI and SATIRE-S). Simulated O3 changes are compared with Microwave Limb Sounder (MLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite data. Modelled O3 anomalies from all solar flux data sets show good agreement with the observations, despite the different flux variations. The off-line CTM reproduces these changes through dynamical information contained in the analyses. A notable feature during this period is a robust positive solar signal in the tropical middle stratosphere, which is due to realistic dynamical changes in our simulations. Ozone changes in the lower mesosphere cannot be used to discriminate between solar flux data sets due to large uncertainties and the short time span of the observations. Overall this study suggests that, in a CTM, the UV variations detected by SORCE are not necessary to reproduce observed stratospheric O3 changes during 2001-2010.

  8. Modeling Subglacial Meltwater Plumes across Greenland's Outlet Glaciers: Implications for Ice-Ocean Coupling in a Warming Climate

    NASA Astrophysics Data System (ADS)

    Carroll, D.; Sutherland, D.; Moon, T. A.; Hudson, B.; Noel, B.; Felikson, D.; Catania, G. A.; Nash, J. D.; Shroyer, E.; Bartholomaus, T.; Stearns, L. A.; van den Broeke, M.

    2015-12-01

    Meltwater accumulated on the Greenland Ice Sheet (GrIS) drains to glacier beds, often discharging into outlet glacier fjords hundreds of meters below sea level. The injection of buoyant meltwater at depth drives a turbulent plume that entrains warm bottom water as it rises along the ice face, resulting in increased submarine melt rates. Recent studies have used remotely sensed data to identify distinct seasonal flow patterns in GrIS outlet glacier dynamics, suggesting some glaciers are especially sensitive to changes at the terminus. However, we currently lack an understanding of the corresponding regional patterns in near-glacier circulation that are a first-order control on submarine melt rates and indirectly modulate the resultant estuarine exchange flow and mixing of fjord waters. In this study, we use a buoyant plume model combined with a synthesis of shipboard hydrography, moored observations, estimates of subglacial discharge, and remotely sensed data on glacier characteristics, to provide an estimate of plume properties across GrIS outlet glaciers in both time and space. We validate our model results with detailed ice-ocean measurements from neighboring outlet glacier fjords in Uummannaq Bay, west Greenland. Model and observations agree that strongly stratified fjords with deep outlet glaciers result in warm, subsurface plumes, while shallow fjords result in surface-intensified plumes that retain their cold meltwater signature. We compare these results to a high-resolution ocean model to provide an estimate of submarine melt rates during peak summer discharge. One advantage of our approach is the rapid characterization of distinct plume regimes across GrIS outlet glacier parameter space. Finally, we compare these plume regimes with characteristics of glacier behavior (ice velocity, surface elevation, terminus position), over decadal and seasonal time-scales. This comparison allows us to investigate which outlet glacier systems might be more sensitive to

  9. The ionospheric signatures of flux transfer events and solar wind dynamic pressure changes

    NASA Technical Reports Server (NTRS)

    Lockwood, M.; Cowley, S. W. H.; Sandholt, P. E.; Lepping, R. P.

    1990-01-01

    Recent observations of vortical flow patterns in the dayside auroral ionosphere are discussed in terms of two alternative mechanisms: (1) the time-dependent magnetic reconnection in 'flux transfer events' (FTEs); and (2) the action of solar wind dynamic pressure changes at the magnetopause. It is argued that the ionospheric flow signature of an FTE should be a twin vortex, with the mean flow velocity in the central region of the pattern being equal to the velocity of the pattern as a whole. On the other hand, the pulse of enhanced or reduced dynamic pressure is also expected to produce a twin vortex, but with the central plasma flow being generally different in speed from (and almost orthogonal to) the motion of the whole pattern. It is found that, while none of the events discussed here are consistent with the theories of the effects of the dynamic pressure changes, all are well explained in terms of the ionospheric signatures of FTEs.

  10. Biochar-Induced Changes in Soil Hydraulic Conductivity and Dissolved Nutrient Fluxes Constrained by Laboratory Experiments

    PubMed Central

    Barnes, Rebecca T.; Gallagher, Morgan E.; Masiello, Caroline A.; Liu, Zuolin; Dugan, Brandon

    2014-01-01

    The addition of charcoal (or biochar) to soil has significant carbon sequestration and agronomic potential, making it important to determine how this potentially large anthropogenic carbon influx will alter ecosystem functions. We used column experiments to quantify how hydrologic and nutrient-retention characteristics of three soil materials differed with biochar amendment. We compared three homogeneous soil materials (sand, organic-rich topsoil, and clay-rich Hapludert) to provide a basic understanding of biochar-soil-water interactions. On average, biochar amendment decreased saturated hydraulic conductivity (K) by 92% in sand and 67% in organic soil, but increased K by 328% in clay-rich soil. The change in K for sand was not predicted by the accompanying physical changes to the soil mixture; the sand-biochar mixture was less dense and more porous than sand without biochar. We propose two hydrologic pathways that are potential drivers for this behavior: one through the interstitial biochar-sand space and a second through pores within the biochar grains themselves. This second pathway adds to the porosity of the soil mixture; however, it likely does not add to the effective soil K due to its tortuosity and smaller pore size. Therefore, the addition of biochar can increase or decrease soil drainage, and suggests that any potential improvement of water delivery to plants is dependent on soil type, biochar amendment rate, and biochar properties. Changes in dissolved carbon (C) and nitrogen (N) fluxes also differed; with biochar increasing the C flux from organic-poor sand, decreasing it from organic-rich soils, and retaining small amounts of soil-derived N. The aromaticity of C lost from sand and clay increased, suggesting lost C was biochar-derived; though the loss accounts for only 0.05% of added biochar-C. Thus, the direction and magnitude of hydraulic, C, and N changes associated with biochar amendments are soil type (composition and particle size) dependent

  11. Biochar-induced changes in soil hydraulic conductivity and dissolved nutrient fluxes constrained by laboratory experiments.

    PubMed

    Barnes, Rebecca T; Gallagher, Morgan E; Masiello, Caroline A; Liu, Zuolin; Dugan, Brandon

    2014-01-01

    The addition of charcoal (or biochar) to soil has significant carbon sequestration and agronomic potential, making it important to determine how this potentially large anthropogenic carbon influx will alter ecosystem functions. We used column experiments to quantify how hydrologic and nutrient-retention characteristics of three soil materials differed with biochar amendment. We compared three homogeneous soil materials (sand, organic-rich topsoil, and clay-rich Hapludert) to provide a basic understanding of biochar-soil-water interactions. On average, biochar amendment decreased saturated hydraulic conductivity (K) by 92% in sand and 67% in organic soil, but increased K by 328% in clay-rich soil. The change in K for sand was not predicted by the accompanying physical changes to the soil mixture; the sand-biochar mixture was less dense and more porous than sand without biochar. We propose two hydrologic pathways that are potential drivers for this behavior: one through the interstitial biochar-sand space and a second through pores within the biochar grains themselves. This second pathway adds to the porosity of the soil mixture; however, it likely does not add to the effective soil K due to its tortuosity and smaller pore size. Therefore, the addition of biochar can increase or decrease soil drainage, and suggests that any potential improvement of water delivery to plants is dependent on soil type, biochar amendment rate, and biochar properties. Changes in dissolved carbon (C) and nitrogen (N) fluxes also differed; with biochar increasing the C flux from organic-poor sand, decreasing it from organic-rich soils, and retaining small amounts of soil-derived N. The aromaticity of C lost from sand and clay increased, suggesting lost C was biochar-derived; though the loss accounts for only 0.05% of added biochar-C. Thus, the direction and magnitude of hydraulic, C, and N changes associated with biochar amendments are soil type (composition and particle size) dependent

  12. Representing moisture fluxes and phase changes in glacier debris cover using a reservoir approach

    NASA Astrophysics Data System (ADS)

    Collier, E.; Nicholson, L. I.; Brock, B. W.; Maussion, F.; Essery, R.; Bush, A. B. G.

    2014-08-01

    Due to the complexity of treating moisture in supraglacial debris, surface energy balance models to date have neglected moisture infiltration and phase changes in the debris layer. The latent heat flux (QL) is also often excluded due to the uncertainty in determining the surface vapour pressure. To quantify the importance of moisture on the surface energy and climatic mass balance (CMB) of debris-covered glaciers, we developed a simple reservoir parameterization for the debris ice and water content, as well as an estimation of the latent heat flux. The parameterization was incorporated into a CMB model adapted for debris-covered glaciers. We present the results of two point simulations, using both our new "moist" and the conventional "dry" approaches, on the Miage Glacier, Italy, during summer 2008 and fall 2011. The former year coincides with available in situ glaciological and meteorological measurements, including the first eddy-covariance measurements of the turbulent fluxes over supraglacial debris, while the latter contains two refreeze events that permit evaluation of the influence of phase changes. The simulations demonstrate a clear influence of moisture on the glacier energy and mass-balance dynamics. When water and ice are considered, heat transmission to the underlying glacier ice is lower, as the effective thermal diffusivity of the saturated debris layers is reduced by increases in both the density and the specific heat capacity of the layers. In combination with surface heat extraction by QL, subdebris ice melt is reduced by 3.1% in 2008 and by 7.0% in 2011 when moisture effects are included. However, the influence of the parameterization on the total accumulated mass balance varies seasonally. In summer 2008, mass loss due to surface vapour fluxes more than compensates for the reduction in ice melt, such that the total ablation increases by 4.0%. Conversely, in fall 2011, the modulation of basal debris temperature by debris ice results in a decrease

  13. Assessment of climate change impacts on diffuse nutrient and pesticide fluxes at the watershed scale

    NASA Astrophysics Data System (ADS)

    Arabi, M.; Records, R.; Ahmadi, M.

    2012-12-01

    The study aims to assess the potential impacts of the changing climate on pollutant fluxes including sediment, phosphorus, nitrogen, and atrazine at the watershed scale over the 21st century. Specific objectives are (i) to understand changes in climatic conditions under a comprehensive set of 112 climate projections consistent with Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (IPCC-SRES) emission pathways and models; (ii) to fully enumerate and synthesize hydrologic and water quality responses to projected climate scenarios; and (iii) to investigate changes in dissolved and particulate water quality constituents. These objectives were investigated in a predominantly agricultural watershed in the Midwestern United States. The hydrologic model Soil and Water Assessment Tool (SWAT) was utilized to represent processes governing hydrology and water quality within the watershed. The SWAT model was driven with a suite of 112 distinct dynamically downscaled climate projections representing IPCC-SERES low, moderate, and high greenhouse gas emission pathways. Statistical downscaling procedures were used to derive daily climatic values for meteorological stations in the study area from grid-based dynamically downscaled monthly predictions. Predicted changes in hydroclimatic, nutrient, and pesticide fluxes under the 112 distinct simulations were then analyzed by emission pathway ensemble and characterized over early-, mid-, and late-century assessment periods (2015-2034, 2045-2064, and 2080-2099). Clear warming trends were apparent for temperature, while increases in precipitation were insignificant. Stream discharge, sediment yield, and total nutrient yields did not differ significantly between assessment periods, although atrazine yields were predicted to be slightly greater by late-century. However, the proportion of dissolved to total nutrients increased, with nitrate and soluble phosphorus yields increasing significantly between early

  14. Quantitative Estimation of Terrigenous Supply in the Gulf of Mexico during the Meltwater Pulse 1A

    NASA Astrophysics Data System (ADS)

    Bout-Roumazeilles, V.; Sionneau, T.; Meunier, G.; Montero Serrano, J.

    2013-05-01

    The contribution of the Laurentide Ice Sheet to the sea-level rise associated with the Meltwater Pulse-1A (MWP1A) through its southern outlet (Gulf of Mexico via the Mississippi River) is still questioning, especially because the Atlantic Meridional Overturning Circulation does not show any evidence of freshwater discharge out flowing from the Gulf of Mexico (GOM) (McManus et al., 2004). A recent study helps refining both the chronology of the MWP1A and the amplitude of the associated sea level rise (Deschamps et al., 2012). Moreover, comparison of data established respectively in Tahiti and Barbados, in agreement with isostatic adjustment models (Clark, 2002; Bassett, 2005; 2007) suggests an important contribution of Antarctica ice sheet without excluding a contribution from northern ice-sheets (Peltier, 2006; Carlson, 2009). Mineralogical characteristics of terrigenous sediments deposited in the northwestern GOM during the major deglacial meltwater spike give some new insights on these questions (Montero et al., 2009; 2010; 2011; Sionneau et al., 2008; 2010). The compilation of data from a series of cores along a West-East transect across the northern GOM allows constraining the origin and propagation of the detrital supply associated with the most prominent freshwater discharge. Our results suggest that the detrital plume may have propagated eastward as hyperpycnal flow(s) but did not extend westward whereas the isotopic signal reached the western part of the basin via buoyancy processes or hypopycnal flows. Comparison of these sedimentary evidences with modeled freshwater flows in the GOM allows evaluating the consistency between modeling and observations (Peltier, 2005; Stanford et al., 2006; Meckler et al., 2008; Montero et al., 2009; Sionneau et al., 2010). The reconstructed freshwater flux associated with the MWS flowing through the southern outlet is one order of magnitude higher than present-day averaged annual flow of the Mississippi River (Licciardi et

  15. Carbon exchange fluxes over peatlands in Western Siberia: Possible feedback between land-use change and climate change.

    PubMed

    Fleischer, Elisa; Khashimov, Ilhom; Hölzel, Norbert; Klemm, Otto

    2016-03-01

    The growing demand for agricultural products has been leading to an expansion and intensification of agriculture around the world. More and more unused land is currently reclaimed in the regions of the former Soviet Union. Driven by climate change, the Western Siberian grain belt might, in a long-term, even expand into the drained peatland areas to the North. It is crucial to study the consequences of this land-use change with respect to the carbon cycling as this is still a major knowledge gap. We present for the first time data on the atmosphere-ecosystem exchange of carbon dioxide and methane of an arable field and a neighboring unused grassland on peat soil in Western Siberia. Eddy covariance measurements were performed over one vegetation period. No directed methane fluxes were found due to an effective drainage of the study sites. The carbon dioxide fluxes appeared to be of high relevance for the global carbon and greenhouse gas cycles. They showed very site-specific patterns resulting from the development of vegetation: the persistent plants of the grassland were able to start photosynthesizing soon after snow melt, while the absence of vegetation on the managed field lead to a phase of emissions until the oat plants started to grow in June. The uptake peak of the oat field is much later than that of the grassland, but larger due to a rapid plant growth. Budgeting the whole measurement period, the grassland served as a carbon sink, whereas the oat field was identified to be a carbon source. The conversion from non-used grasslands on peat soil to cultivated fields in Western Siberia is therefore considered to have a positive feedback on climate change. PMID:26748007

  16. Drivers of potential GHG fluxes under bioenergy land use change in the UK

    NASA Astrophysics Data System (ADS)

    Parmar, Kim; Keith, Aidan M.; Perks, Mike; Rowe, Rebecca; Sohi, Saran; McNamara, Niall

    2013-04-01

    The greatest contributors to global greenhouse gases (GHG's) are CO2 emissions from fossil fuel use and following land use change (LUC). Globally, soils contain three times more carbon than the atmosphere and have the potential to act as GHG sources or sinks. A significant amount of land may be converted to bioenergy production to help meet UK 2050 renewable energy and GHG emissions reduction targets. This raises considerable sustainability concerns with respect to the effects of LUC on soil carbon (C) conservation and GHG emissions. Forests are a key component in the global C cycle and when managed effectively can reduce atmospheric GHG concentrations. Together with other dedicated bioenergy crops, Short Rotation Forestry (SRF) could be used to meet biomass requirements. SRF is defined as high density plantations of fastgrowing tree species grown on short rotational lengths (8-20 years) for biomass (McKay 2011). As SRF is likely to be an important domestic source of biomass for energy it is imperative that we gain an understanding of the implications for large-scale commercial application on soil C and the GHG balance. We utilized a paired-site approach to investigate how LUC to SRF could potentially alter the underlying processes of soil GHG production and consumption. This work was linked to a wider soil C stock inventory for bioenergy LUC, so our major focus was on changes to soil respiration. Specifically, we examined the relative importance of litter, soil, and microbial properties in determining potential soil respiration, and whether these relationships were consistent at different soil temperatures (10 ° C and 20 ° C). Soils were sampled to a depth of 30 cm from 30 LUC transitions across the UK and incubated under controlled laboratory conditions, with gas samples taken over a seven day enclosure period. CO2, N2O and CH4 gas fluxes were measured by gas chromatography and were examined together with other soil properties measured in the field and

  17. Stratospheric O3 changes during 2001-2010: The small role of solar flux variations in a CTM

    NASA Astrophysics Data System (ADS)

    Dhomse, Sandip; Chipperfield, Martyn; Feng, Wuhu; Ball, William; Unruh, Yvonne; Haigh, Joanna; Krivova, Natalie; Solanki, Sami

    2013-04-01

    Solar spectral fluxes (or irradiance) measured by the SOlar Radiation and Climate Experiment (SORCE) shows different variability at ultraviolet (UV) wavelengths compared to other irradiance measurements and models (e.g. NRL, SATIRE-S). Some modelling studies have suggested that stratospheric O3 changes during solar cycle 23 (1996-2008) can only be reproduced if SORCE solar fluxes are used. We have used a 3-D chemical transport model (CTM), forced by meteorology from the European Centre for Medium-Range Weather Forecasts (ECMWF), to simulate stratospheric O3 using 3 different solar flux datasets (SORCE, NRL-SSI and SATIRE-S). Simulated O3 changes are compared with Microwave Limb Sounder (MLS) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite data. Modelled O3 anomalies using all solar flux datasets show good agreement with the observations, despite the different flux variations. A notable feature during this period is a robust positive solar signal in the tropical middle stratosphere. The CTM reproduces these changes through dynamical information contained in the analyses. Changes in the upper stratosphere cannot be used to discriminate between solar flux datasets due to large uncertainties in the O3 observations. Overall this study suggests that the UV variations detected by SORCE are not necessary to reproduce observed stratospheric O3 changes during 2001-2010.

  18. Temporal changes in soil water repellency linked to the soil respiration and CH4 and CO2 fluxes

    NASA Astrophysics Data System (ADS)

    Qassem, Khalid; Urbanek, Emilia; van Keulen, Geertje

    2014-05-01

    Soil water repellency (SWR) is known to be a spatially and temporally variable phenomenon. The seasonal changes in soil moisture lead to development of soil water repellency, which in consequence may affect the microbial activity and in consequence alter the CO2 and CH4 fluxes from soils. Soil microbial activity is strongly linked to the temperature and moisture status of the soil. In terms of CO2 flux intermediate moisture contents are most favourable for the optimal microbial activity and highest CO2 fluxes. Methanogenesis occurs primarily in anaerobic water-logged habitats while methanotrophy is a strictly aerobic process. In the study we hypothesise that the changes in CO2 and CH4 fluxes are closely linked to critical moisture thresholds for soil water repellency. This research project aims to adopt a multi-disciplinary approach to comprehensively determine the effect of SWR on CO2 and CH4 fluxes. Research is conducted in situ at four sites exhibiting SWR in the southern UK. Flux measurements are carried out concomitant with meteorological and SWR observations Field observations are supported by laboratory measurements carried out on intact soil samples collected at the above identified field sites. The laboratory analyses are conducted under constant temperatures with controlled changes of soil moisture content. Methanogenic and Methanotrophic microbial populations are being analysed at different SWR and moisture contents using the latest metagenomic and metatranscriptomic approaches. Currently available data show that greenhouse gas flux are closely linked with soil moisture thresholds for SWR development.

  19. Regional carbon fluxes from land use and land cover change in Asia, 1980–2009

    NASA Astrophysics Data System (ADS)

    Calle, Leonardo; Canadell, Josep G.; Patra, Prabir; Ciais, Philippe; Ichii, Kazuhito; Tian, Hanqin; Kondo, Masayuki; Piao, Shilong; Arneth, Almut; Harper, Anna B.; Ito, Akihiko; Kato, Etsushi; Koven, Charlie; Sitch, Stephen; Stocker, Benjamin D.; Vivoy, Nicolas; Wiltshire, Andy; Zaehle, Sönke; Poulter, Benjamin

    2016-07-01

    We present a synthesis of the land-atmosphere carbon flux from land use and land cover change (LULCC) in Asia using multiple data sources and paying particular attention to deforestation and forest regrowth fluxes. The data sources are quasi-independent and include the U.N. Food and Agriculture Organization-Forest Resource Assessment (FAO-FRA 2015; country-level inventory estimates), the Emission Database for Global Atmospheric Research (EDGARv4.3), the ‘Houghton’ bookkeeping model that incorporates FAO-FRA data, an ensemble of 8 state-of-the-art Dynamic Global Vegetation Models (DGVM), and 2 recently published independent studies using primarily remote sensing techniques. The estimates are aggregated spatially to Southeast, East, and South Asia and temporally for three decades, 1980–1989, 1990–1999 and 2000–2009. Since 1980, net carbon emissions from LULCC in Asia were responsible for 20%–40% of global LULCC emissions, with emissions from Southeast Asia alone accounting for 15%–25% of global LULCC emissions during the same period. In the 2000s and for all Asia, three estimates (FAO-FRA, DGVM, Houghton) were in agreement of a net source of carbon to the atmosphere, with mean estimates ranging between 0.24 to 0.41 Pg C yr‑1, whereas EDGARv4.3 suggested a net carbon sink of ‑0.17 Pg C yr‑1. Three of 4 estimates suggest that LULCC carbon emissions declined by at least 34% in the preceding decade (1990–2000). Spread in the estimates is due to the inclusion of different flux components and their treatments, showing the importance to include emissions from carbon rich peatlands and land management, such as shifting cultivation and wood harvesting, which appear to be consistently underreported.

  20. Estimating nocturnal ecosystem respiration from the vertical turbulent flux and change in storage of CO2

    SciTech Connect

    Gu, Lianhong; Van Gorsel, Eva; Leuning, Ray; Delpierre, Nicolas; Black, Andy; Chen, Baozhang; Munger, J. William; Wofsy, Steve; Aubinet, M.

    2009-11-01

    Micrometeorological measurements of nighttime ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397 403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (FC) and change in storage (FS) of CO2 in the few hours after sundown. The sum of FC and FS reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration RRmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of Fc + Fs extrapolated to zero light, RLRC, and (3) with a detailed process-based forest ecosystem model, Rcast. At most sites respiration rates estimated using the u*-filter, Rust, were smaller than RRmax and RLRC. Agreement of our approach with independent measurements indicates that RRmax provides an excellent estimate of nighttime

  1. Vatnajökull meltwater discharge variability: a Holocene climate sensor in the Nordic Seas

    NASA Astrophysics Data System (ADS)

    Striberger, J.; Björck, S.; Ingólfsson, Ó.; Kjær, K.; Sandgren, P.; Snowball, I.

    2009-04-01

    The Holocene glacial history of Vatnajökull and its many outlet glaciers is rather poorly known, even though it is one of the largest ice caps outside Antarctica and Greenland. Vatnajökull is positioned in the centre of the Nordic Seas, the region for North Atlantic Deep Water formation and it is influenced by humid-bearing cyclone systems from the southwest. Thus, it can be regarded as a sensor for a combination of different climatic driven processes. Lake Lögurinn (53 km2, 20 m a.s.l), situated northeast of Vatnajökull, is part of the drainage system of Eyjabakkajökull, one of the most conspicuous surging outlet glaciers of the ice cap. In addition to glacial meltwater, the lake also receives discharge from rivers that drain non-glaciated catchments. The mix of glacial and non-glacial suspension makes the sediments suitable for analyses of how the fluvial regime has varied over time and how this relates to meltwater discharge, fluvial discharge and general changes in climate and hydrology. A total of 17.8 m of sediment was obtained from the central part of the northernmost sub-basin in Lake Lögurinn at water depths of 38 and 16 m, respectively. The sediments are laminated in most parts of the sequence. 137Cs analyses of the surface core have confirmed that the laminated couplets are varves. Tephra horizons have been used as time markers throughout the sediments, and X-ray fluorescence and X-ray analyses as well as visual observations have been used in order to identify varves in the uppermost 3.8 m of the sequence. This section covers the time period AD 1262-2005. The sediment contains 610 varves for the periods AD 1262-1476 and AD 1603-2005 (a total of 618 years). A significant change in sedimentation rate is observed between AD 1477-1602 (from 5.9 mm/yr to 1.2 mm/yr). For this period only 18 varves are found. This abrupt change is likely related to a lower discharge rate, or to more turbulent conditions in the lake. The sedimentation rate of the

  2. The ionospheric signatures of flux transfer events and solar wind dynamic pressure changes

    SciTech Connect

    Lockwood, M. Imperial College, London ); Cowley, S.W.H. ); Sandholt, P.E. ); Lepping, R.P. )

    1990-10-01

    The generation of flow and current vortices in the dayside auroral ionosphere has been predicted for two processes occurring at the dayside magnetopause. The first of these mechanisms is time-dependent magnetic reconnection, in flux transfer events (FTEs); the second is the action of solar wind dynamic pressure changes. The ionospheric flow signature of an FTE should be a twin vortex, with the mean flow velocity in the central regon of the pattern equal ot the velocity of the pattern as a whole. On the other hand, a pulse of enhanced or reduced dynamic pressure is also expected to produce a twin vortex, but with the central plasma flow being generally different in speed from, and almost orthogonal to, the motion of the whole pattern. In this paper, the authors make use of this distinction to discuss recent observations of vortical flow patterns in the dayside auroral ionosphere in terms of one or other of the proposed mechanisms. They conclude that some of the observatons reported are consistent only with the predicted signature of FTEs. They then evaluate the dimensions of the open flux tubes required to explain some recent simultaneous radar and auroral observatons and infer that they are typically 300 km in north-south extent but up to 2,000 km in longitudinal extent (i.e., roughly 5 hours of MLT). Hence these observations suggest that recent theories of FTEs which invoke time-varying reconnecton at an elongated neutral line may be correct.

  3. Siderophore-promoted transfer of rare earth elements and iron from volcanic ash into glacial meltwater, river and ocean water

    NASA Astrophysics Data System (ADS)

    Bau, Michael; Tepe, Nathalie; Mohwinkel, Dennis

    2013-02-01

    The rare earth elements (REE) are a group of trace elements that have short marine residence times and that in river, lake and marine surface waters are typically associated with organic and inorganic particles. Explosive volcanic eruptions, such as the 2010 eruptions of Eyjafjallajökull volcano in Iceland, produce volcanic ash particles which can be an important source of iron and other nutrients for aquatic organisms. To become bioavailable, however, this iron needs to be solubilized by complexing agents, such as siderophores. A well-studied example of such a chelator is the biogenic siderophore desferrioxamin-B (DFOB). Based on results from incubation experiments with glacial meltwater-rich river waters from southern Iceland, which are rich in suspended volcanic ash and that had been incubated with and without DFOB, respectively, we here show that siderophores not only enhance the release of iron, but also promote the mobilization of REE from these particles. In the presence of DFOB, partial dissolution of volcanic ash (and presumably other lithic particles) produces a flux of dissolved REE into ambient waters, that is characterized by depletion of the light REE over the middle REE and by selective enrichment of cerium, due to the formation of dissolved Ce(IV)-DFOB complexes. In siderophore-rich environments, this siderophore-bound REE flux has the potential to modify the concentrations and distribution of the dissolved REE and of the isotopic composition of dissolved Nd in glacial meltwaters, river waters and seawater and might be a component of the boundary effects between shelf sediments and seawater, which are assumed to account for the “missing Nd flux” to seawater. Thermodynamic data further suggest that siderophore-promoted element mobilization could also be important for other polyvalent (trace) elements, such as Hf.

  4. New insights on the late-stage history of glacial Lake Ojibway: implications for meltwater discharges of the last deglaciation

    NASA Astrophysics Data System (ADS)

    Roy, Martin; Veillette, Jean J.; Godbout, Pierre-Marc

    2016-04-01

    located east of James Bay that preserve a well-developed drainage unit. There, the microfossil content and associated stable isotope geochemistry of the underlying Ojibway rhythmites indicate that the final drawdown of the lake was preceded by episodic subglacial drainage events. Radiocarbon dating of the sequence has also refined the timing of the final lake drainage. This event is also present deeper within the southeastern Ojibway basin where the grain size and geochemical composition of thinly bedded rhythmites, as well as the oxygen isotope of ostacods, document an anomalously thick and coarse-grained marker bed that records the abrupt termination of the lake in this region. Taken together, these results indicate that the late-stage history of Lake Ojibway was marked by significant changes in the areal extent and depth of the lake, which likely implied routing events into newly deglaciated regions and/or (subglacial) meltwater discharges into the North Atlantic. Our investigations also identify the James Bay region as a major drainage pathway for meltwater at the end of the last deglaciation. The elevation, extent and chronology of the Ojibway shoreline sequence are currently being refined in order to improve paleogeographic reconstructions and estimates of meltwater volumes, all aspects that are critically needed to evaluate the impact of freshwater discharges on ocean circulation.

  5. Warming alters food web-driven changes in the CO2 flux of experimental pond ecosystems.

    PubMed

    Atwood, T B; Hammill, E; Kratina, P; Greig, H S; Shurin, J B; Richardson, J S

    2015-12-01

    Evidence shows the important role biota play in the carbon cycle, and strategic management of plant and animal populations could enhance CO2 uptake in aquatic ecosystems. However, it is currently unknown how management-driven changes to community structure may interact with climate warming and other anthropogenic perturbations to alter CO2 fluxes. Here we showed that under ambient water temperatures, predators (three-spined stickleback) and nutrient enrichment synergistically increased primary producer biomass, resulting in increased CO2 uptake by mesocosms in early dawn. However, a 3°C increase in water temperatures counteracted positive effects of predators and nutrients, leading to reduced primary producer biomass and a switch from CO2 influx to efflux. This confounding effect of temperature demonstrates that climate scenarios must be accounted for when undertaking ecosystem management actions to increase biosequestration. PMID:26631247

  6. Role of land use change in landslide-related sediment fluxes in tropical mountain regions

    NASA Astrophysics Data System (ADS)

    Guns, M.; Vanacker, V.; Demoulin, A.

    2012-04-01

    Tropical mountain regions are characterised by high denudation rates. Landslides are known to be recurrent phenomena in active mountain belts, but their contribution to the overall sedimentary fluxes is not yet well known. Previous studies on sedimentary cascades have mostly focused on natural environments, without considering the impact of human and/or anthropogenic disturbances on sedimentary budgets. In our work, we hypothesise that human-induced land use change might alter the sediment cascade through shifts in the landslide magnitude-frequency relationship. We have tested this assumption in the Virgen Yacu catchment (approximately 11km2), in the Ecuadorian Cordillera Occidental. Landslide inventories and land use maps were established based on a series of sequential aerial photos (1963, 1977, 1984 and 1989), a HR Landsat image (2001) and a VHR WorldView2 image (2010). Aerial photographs were ortho-rectified, and coregistred with the WorldView2 satellite image. Field campaigns were realised in 2010 and 2011 to collect field-based data on landslide type and geometry (depth, width and length). This allowed us to establish an empirical relationship between landslide area and volume, which was then applied to the landslide inventories to estimate landslide-related sediment production rates for various time periods. The contribution of landslides to the overall sediment flux of the catchment was estimated by comparing the landslide-related sediment production to the total sediment yield. The empirical landslide area-volume relationship established here for the Ecuadorian Andes is similar to that derived for the Himalayas. It suggests that landslides are the main source of sediment in this mountainous catchment. First calculations indicate that human-induced land use change alters the magnitude-frequency relationship through strong increase of small landslides.

  7. Dynamics of Flow Over A Low Hill Caused By Change In Surface Heat Flux

    NASA Astrophysics Data System (ADS)

    Owinoh, A. Z.; Hunt, J. C. R.; Orr, A.; Klein, R.

    Our understanding of flow over complex terrain has been shaped partially by the theo- retical work of Hunt and colleagues (e.g. Hunt et al., 1988) which is based on the tech- niques of asymptotic matching. The boundary layer is divided into three sub-layers, each with essentially different flow dynamics. The dynamics of the lowest layer (the inner layer) are modified by turbulence generated by surface properties. In the middle layer, the flow is inviscid but rotational. In the outer layer, turbulent friction is rela- tively unimportant and one can treat the flow as essentially inviscid. In this talk, we present the dynamics of the inner region of flow over low hill, on whose surface there is an abrupt (t > 0), but uniform, change in heat flux. The leading order perturbation to the basic flow equations are solved analytically. The solutions show how an initially neutral turbulent flow (Lmo = +) responds to change in heat flux by making a tran- sition (in time) to stable (Lmo > 0) and unstable flows (Lmo < 0), where Lmo is the Monin-Obukhov length. In doing so |Lmo| decreases to the length of the inner layer. Buoyancy forces have large effect on the down slope flow (e.g. recirculating wake and increased vertical shear). Features of the solutions are compared with Scorer's (1955) observations and with experimental results obtained from two numerical weather fore- cast models, namely, UK Met. Office Unified Model and the German Weather Service (DWD) Lokall-Modell. Hunt, J. C. R., Leibovich, S. &Richards K. J., 1988, `Turbulent shear flow over low hills'. Q. J. R. Meteorol. Soc, 114, 1435-1470. Scorer, R. S. 1955, `Theory of airflow over mountains: IV - Separation of flow from the surface', Q. J. R. Meteorol. Soc., 81, 340-350.

  8. Impact of climate change on greenhouse gas fluxes of (pre-) alpine grassland soils

    NASA Astrophysics Data System (ADS)

    Lu, Haiyan; Diaz-Pines, Eugenio; Fu, Jin; Butterbach-Bahl, Klaus; Kiese, Ralf

    2013-04-01

    Embedded into the German Helmholtz Society funded infrastructure project TERENO IMK-IFU is running the (Pre-) Alpine Observatory covering several research sites in the Ammer catchment, South-Bavaria, Germany. TERENO was designed to study long term effects of climate change on terrestrial ecosystems. Due to cool and moist climatic conditions alpine grassland soils of moderate elevation (app. 1000m) are rich in soil organic carbon and associated nitrogen. In the framework of an in-situ climate change experiment we test the hypothesis that soil organic carbon and nitrogen are either volatilized (GHG emissions) or leached with seepage water due to increase in temperature. Field investigations are carried out in the (Pre-) Alpine TERENO Observatory covering several research sites in South-Bavaria, Germany. IMK-IFU has installed 36 lysimeters with undisturbed intact grassland soil cores (diameter 1m, depth 1.4m, 2-3 t of soil) and is operating them at three sites differing in altitude (Graswang 850m, Rottenbuch 750m, Fendt 600m). Lysimeters were partly translocated from higher elevation to sites at lower elevation and other soil cores still staying at the sites as controls. Along the altitudinal gradient mean annual temperature differences are δ1.5°C Graswang-Rottenbuch and δ 2.5°C Graswang-Fendt and slightly lower mean annual rainfall with decreasing altitude. We will present the first full year datasets of soil CO2, N2O and CH4 emissions measured by manual as well as automatic chambers via a new developed robot system. Comparing emissions at the controls sites, and comparing the translocated soil cores, showed that the most significant differences were found for CO2 and CH4 fluxes and less for N2O fluxes. Higher temperatures generally stimulated CO2 and N2O emissions and lead to increased uptake rates of atmospheric CH4. Different dynamics of snow pack formation at the three sites investigated, caused pronounced differences in frost-thaw driven N2O emissions which

  9. Developing an Understanding of Vegetation Change and Fluvial Carbon Fluxes in Semi-Arid Environments

    NASA Astrophysics Data System (ADS)

    Puttock, A. K.; Dungait, J.; Bol, R.; MacLeod, C. J.; Brazier, R.

    2011-12-01

    Dryland environments are estimated to cover around 40% of the global land surface (Okin et al, 2009) and are home to approximately 2.5 billion people (Reynolds et al. 2007). Many of these areas have recently experienced extensive land degradation. One such area and the focus of this project is the semi-arid US Southwest, where degradation over the past 150 years has been characterized by the invasion of woody vegetation into grasslands. Transition from grass to woody vegetation results in a change in ecosystem structure and function (Turnbull et al, 2008). Structural change is typically characterised by an increased heterogeneity of soil and vegetation resources, associated with reduced vegetation coverage and an increased vulnerability to soil erosion and the potential loss of key nutrients to adjacent fluvial systems. Such loss of resources may impact heavily upon the amount of carbon that is sequestered by these environments and the amount of carbon that is lost as the land becomes more degraded. Therefore, understanding these vegetation transitions is significant for sustainable land use and global biogeochemical cycling. This project uses an ecohydrological approach, monitoring natural rainfall-runoff events over six bounded plots with different vegetation coverage. The experiment takes advantage of a natural abundance stable 13C isotope shift from C3 piñon-juniper (Pinus edulis-Juniperus monosperma) mixed stand through a C4 pure-grass (Bouteloua eriopoda) to C3 shrub (Larrea tridentate). Data collected quantify fluvial fluxes of sediment and associated soil organic matter and carbon that is lost from across the grass-to-shrub and grass-to-woodland transition (where change in space is taken to indicate a similar change through time). Results collected during the 2010 and 2011 monsoon seasons will be presented, illustrating that soil and carbon losses are greater as the ecosystem becomes more dominated by woody plants. Additionally this project utilises novel

  10. Determination of the magnetocaloric entropy change by field sweep using a heat flux setup

    SciTech Connect

    Monteiro, J. C. B. Reis, R. D. dos; Mansanares, A. M.; Gandra, F. G.

    2014-08-18

    We report on a simple setup using a heat flux sensor adapted to a Quantum Design Physical Property Measurement System to determine the magnetocaloric entropy change (ΔS). The major differences for the existing setups are the simplicity of this assembly and the ease to obtain the isothermal entropy change either by a field sweep or a temperature sweep process. We discuss the use of these two processes applied to Gd and Gd{sub 5}Ge{sub 2}Si{sub 2} samples. The results are compared to the temperature sweep measurements and they show the advantages of this setup and of the field sweep procedure. We found a significant reduction of ΔS and on the refrigerating cooling power (RCP) at low field changes in a field sweep process when the sample is not driven to the same initial state for each temperature. We show that the field sweep process without any measuring protocol is the only correct way to experimentally determine ΔS and RCP for a practical regenerative refrigerator.

  11. A Double Dusty Dilemma - IRAC Flux Changes in Circumbinary Debris Disk

    NASA Astrophysics Data System (ADS)

    Parsons, Steven; Farihi, Jay; Gaensicke, Boris

    2015-10-01

    We have serendipitously discovered the first metal-polluted white dwarf with what appears to be a circumbinary dust disk. Both the atmospheric metals and infrared excess were found by our team a few years ago, but only recently did we (surprisingly!) identify a spectroscopic periodicity of 2.27 hr which unambiguously identifies this peculiar system as a close binary. Most remarkable for this proposal is that the system must be dynamically unstable, as a companion and canonical (flat, opaque) dust disk occupy overlapping orbital regions. We thus strongly suspected the system must be in a state of relatively rapid change, and recent DDT observations confirmed our hypothesis. We now propose to observe the system over a complete binary orbit to further constrain the changes in infrared flux, and to distentangle dust emission variability from any changes induced by the binary orbit itself. Micron-size dust grains should be subject to PR drag within a decade, and imply dust depletion on yearly timescales -- consistent with the DDT data. Our third epoch observations will provide an direct test by searching for a continuing decrease in dust emission. If such a decrease is not confirmed, it would imply the circumbinary dust reservoir is being replenished on yearly timescales.

  12. Changes in water and solute fluxes in the vadose zone after switching crops

    NASA Astrophysics Data System (ADS)

    Turkeltaub, Tuvia; Dahan, Ofer; Kurtzman, Daniel

    2015-04-01

    Switching crop type and therefore changing irrigation and fertilization regimes leads to alternation in deep percolation and concentrations of solutes in pore water. Changes of fluxes of water, chloride and nitrate under a commercial greenhouse due to a change from tomato to green spices were observed. The site, located above the a coastal aquifer, was monitored for the last four years. A vadose-zone monitoring system (VMS) was implemented under the greenhouse and provided continuous data on both the temporal variation in water content and the chemical composition of pore water at multiple depths in the deep vadose zone (~20 m). Chloride and nitrate profiles, before and after the crop type switching, indicate on a clear alternation in soil water solutes concentrations. Before the switching of the crop type, the average chloride profile ranged from ~130 to ~210, while after the switching, the average profile ranged from ~34 to ~203 mg L-1, 22% reduction in chloride mass. Counter trend was observed for the nitrate concentrations, the average nitrate profile before switching ranged from ~11 to ~44 mg L-1, and after switching, the average profile ranged from ~500 to ~75 mg L-1, 400% increase in nitrate mass. A one dimensional unsaturated water flow and chloride transport model was calibrated to transient deep vadose zone data. A comparison between the simulation results under each of the surface boundary conditions of the vegetables and spices cultivation regime, clearly show a distinct alternation in the quantity and quality of groundwater recharge.

  13. Influence of stem temperature changes on heat pulse sap flux density measurements.

    PubMed

    Vandegehuchte, Maurits W; Burgess, Stephen S O; Downey, Alec; Steppe, Kathy

    2015-04-01

    While natural spatial temperature gradients between measurement needles have been thoroughly investigated for continuous heat-based sap flow methods, little attention has been given to how natural changes in stem temperature impact heat pulse-based methods through temporal rather than spatial effects. By modelling the theoretical equation for both an ideal instantaneous pulse and a step pulse and applying a finite element model which included actual needle dimensions and wound effects, the influence of a varying stem temperature on heat pulse-based methods was investigated. It was shown that the heat ratio (HR) method was influenced, while for the compensation heat pulse and Tmax methods changes in stem temperatures of up to 0.002 °C s(-1) did not lead to significantly different results. For the HR method, rising stem temperatures during measurements led to lower heat pulse velocity values, while decreasing stem temperatures led to both higher and lower heat pulse velocities, and to imaginary results for high flows. These errors of up to 40% can easily be prevented by including a temperature correction in the data analysis procedure, calculating the slope of the natural temperature change based on the measured temperatures before application of the heat pulse. Results of a greenhouse and outdoor experiment on Pinus pinea L. show the influence of this correction on low and average sap flux densities. PMID:25145698

  14. Deglaciation, lake levels, and meltwater discharge in the Lake Michigan basin

    USGS Publications Warehouse

    Colman, Steven M.; Clark, J.A.; Clayton, L.; Hansel, A.K.; Larsen, C.E.

    1994-01-01

    The deglacial history of the Lake Michigan basin, including discharge and routing of meltwater, is complex because of the interaction among (1) glacial retreats and re-advances in the basin (2) the timing of occupation and the isostatic adjustment of lake outlets and (3) the depositional and erosional processes that left evidence of past lake levels. In the southern part of the basin, a restricted area little affected by differential isostasy, new studies of onshore and offshore areas allow refinement of a lake-level history that has evolved over 100 years. Important new data include the recognition of two periods of influx of meltwater from Lake Agassiz into the basin and details of the highstands gleaned from sedimentological evidence. Major disagreements still persist concerning the exact timing and lake-level changes associated with the Algonquin phase, approximately 11,000 BP. A wide variety of independent data suggests that the Lake Michigan Lobe was thin, unstable, and subject to rapid advances and retreats. Consequently, lake-level changes were commonly abrupt and stable shorelines were short-lived. The long-held beliefs that the southern part of the basin was stable and separated from deformed northern areas by a hinge-line discontinuity are becoming difficult to maintain. Numerical modeling of the ice-earth system and empirical modeling of shoreline deformation are both consistent with observed shoreline tilting in the north and with the amount and pattern of modern deformation shown by lake-level gauges. New studies of subaerial lacustrine features suggest the presence of deformed shorelines higher than those originally ascribed to the supposed horizontal Glenwood level. Finally, the Lake Michigan region as a whole appears to behave in a similar manner to other areas, both local (other Great Lakes) and regional (U.S. east coast), that have experienced major isostatic changes. Detailed sedimentological and dating studies of field sites and additional

  15. Validation of the THIRMAL-1 melt-water interaction code

    SciTech Connect

    Chu, C.C.; Sienicki, J.J.; Spencer, B.W.

    1995-09-01

    The THIRMAL-1 computer code has been used to calculate nonexplosive LWR melt-water interactions both in-vessel and ex-vessel. To support the application of the code and enhance its acceptability, THIRMAL-1 has been compared with available data from two of the ongoing FARO experiments at Ispra and two of the Corium Coolant Mixing (CCM) experiments performed at Argonne. THIRMAL-1 calculations for the FARO Scoping Test and Quenching Test 2 as well as the CCM-5 and -6 experiments were found to be in excellent agreement with the experiment results. This lends confidence to the modeling that has been incorporated in the code describing melt stream breakup due to the growth of both Kelvin-Helmholtz and large wave instabilities, the sizes of droplets formed, multiphase flow and heat transfer in the mixing zone surrounding and below the melt metallic phase. As part of the analysis of the FARO tests, a mechanistic model was developed to calculate the prefragmentation as it may have occurred when melt relocated from the release vessel to the water surface and the model was compared with the relevant data from FARO.

  16. Transient nature of Arctic spring systems driven by subglacial meltwater

    NASA Astrophysics Data System (ADS)

    Scheidegger, J. M.; Bense, V. F.; Grasby, S. E.

    2012-06-01

    In the High Arctic, supra- and proglacial springs occur at Borup Fiord Pass, Ellesmere Island. Spring waters are sulfur bearing and isotope analysis suggests springs are fed by deeply circulating glacial meltwater. However, the mechanism maintaining spring flow is unclear in these areas of thick permafrost which would hamper the discharge of deep groundwater to the surface. It has been hypothesized that fracture zones along faults focus groundwater which discharges initially underneath wet-based parts of the ice. With thinning ice, the spring head is exposed to surface temperatures, tens of degrees lower than temperatures of pressure melting, and permafrost starts to develop. Numerical modeling of coupled heat and fluid flow suggest that focused groundwater discharge should eventually be cut off by permafrost encroaching into the feeding channel of the spring. Nevertheless, our model simulations show that these springs can remain flowing for millennia depending on the initial flow rate and ambient surface temperature. These systems might provide a terrestrial analog for the possible occurrence of Martian springs recharged by polar ice caps.

  17. Can we reconcile differences in estimates of carbon fluxes from land-use change and forestry for the 1990s?

    NASA Astrophysics Data System (ADS)

    Ito, A.; Penner, J. E.; Prather, M. J.; de Campos, C. P.; Houghton, R. A.; Kato, T.; Jain, A. K.; Yang, X.; Hurtt, G. C.; Frolking, S.; Fearon, M. G.; Chini, L. P.; Wang, A.; Price, D. T.

    2008-02-01

    The effect of Land Use Change and Forestry (LUCF) on terrestrial carbon fluxes can be regarded as a carbon credit or debit under the UNFCCC, but scientific uncertainty in the estimates for LUCF remains large. Here, we assess the LUCF estimates by examining a variety of models of different types with different land cover change maps in the 1990s. Annual carbon pools and their changes are separated into different components for separate geographical regions, while annual land cover change areas and carbon fluxes are disaggregated into different LUCF activities and the biospheric response due to CO2 fertilization and climate change. We developed a consolidated estimate of the terrestrial carbon fluxes that combines book-keeping models with process-based biogeochemical models and inventory estimates and yields an estimate of the global terrestrial carbon flux that is within the uncertainty range developed in the IPCC 4th Assessment Report. We examined the USA and Brazil as case studies in order to assess the cause of differences from the UNFCCC reported carbon fluxes. Major differences in the litter and soil organic matter components are found for the USA. Differences in Brazil result from assumptions about the LUC for agricultural purposes. The effects of CO2 fertilization and climate change also vary significantly in Brazil. Our consolidated estimate shows that the small sink in Latin America is within the uncertainty range from inverse models, but that the sink in the USA is significantly smaller than the inverse models estimates. Because there are different sources of errors at the country level, there is no easy reconciliation of different estimates of carbon fluxes at the global level. Clearly, further work is required to develop data sets for historical land cover change areas and models of biogeochemical changes for an accurate representation of carbon uptake or emissions due to LUC.

  18. Can we reconcile differences in estimates of carbon fluxes from land-use change and forestry for the 1990s?

    NASA Astrophysics Data System (ADS)

    Ito, A.; Penner, J. E.; Prather, M. J.; de Campos, C. P.; Houghton, R. A.; Kato, T.; Jain, A. K.; Yang, X.; Hurtt, G. C.; Frolking, S.; Fearon, M. G.; Chini, L. P.; Wang, A.; Price, D. T.

    2008-06-01

    The effect of Land Use Change and Forestry (LUCF) on terrestrial carbon fluxes can be regarded as a carbon credit or debit under the UNFCCC, but scientific uncertainty in the estimates for LUCF remains large. Here, we assess the LUCF estimates by examining a variety of models of different types with different land cover change maps in the 1990s. Annual carbon pools and their changes are separated into different components for separate geographical regions, while annual land cover change areas and carbon fluxes are disaggregated into different LUCF activities and the biospheric response due to CO2 fertilization and climate change. We developed a consolidated estimate of the terrestrial carbon fluxes that combines book-keeping models with process-based biogeochemical models and inventory estimates and yields an estimate of the global terrestrial carbon flux that is within the uncertainty range developed in the IPCC 4th Assessment Report. We examined the USA and Brazil as case studies in order to assess the cause of differences from the UNFCCC reported carbon fluxes. Major differences in the litter and soil organic matter components are found for the USA. Differences in Brazil result from assumptions about the LUC for agricultural purposes. The effects of CO2 fertilization and climate change also vary significantly in Brazil. Our consolidated estimate shows that the small sink in Latin America is within the uncertainty range from inverse models, but that the sink in the USA is significantly smaller than the inverse models estimates. Because there are different sources of errors at the country level, there is no easy reconciliation of different estimates of carbon fluxes at the global level. Clearly, further work is required to develop data sets for historical land cover change areas and models of biogeochemical changes for an accurate representation of carbon uptake or emissions due to LUC.

  19. Gulf of Mexico Sea-Surface Temperatures and Laurentide Meltwater Input During MIS 3: Implications for High/Low Latitude Linkages

    NASA Astrophysics Data System (ADS)

    Hill, H. W.; Flower, B. P.; Hastings, D. W.; Hollander, D. J.; Lodico, J.; Quinn, T. M.

    2002-12-01

    A new sediment core from the Orca Basin, Gulf of Mexico, will be helpful in determining the role of low latitude ocean dynamics in rapid climate change. The 31.79-m core (MD02-2551; 26o56.78'N, 91o21.75'W), obtained in July 2002 aboard the R/V Marion Dufrense will provide, for the first time, an opportunity to study Gulf of Mexico sea-surface temperature (SST) and sea-surface salinity (SSS), as well as meltwater input from the Laurentide Ice Sheet (LIS) during the Dansgaard-Oeschger (D-O) cycles found in Marine Isotope Stage (MIS) 3, 24-57 ka. The anoxic Orca Basin, which sits 290 km south of the Mississippi Delta, is filled with a hypersaline brine resulting in undisturbed laminations and excellent preservation of planktonic foraminifera. A coarse resolution isotope stratigraphy of the core using Globigerinoides ruber (pink and white variety) with a size fraction from 250-355 microns and faunal abundances suggests the oldest sediments are from MIS 3, resulting in an average sedimentation rate of >50 cm/1000 years. A distinct negative isotope anomaly, reaching δ18O -4 ‰ based on pink G. ruber, occurs at 2625 cm, which is best explained by increased meltwater input from the LIS. More detailed work on the core, including AMS 14C age control, will demonstrate how SST and meltwater input relate to D-O events. Multi-proxy data, including δ18O, Mg/Ca and Uk'37, make it possible to deconvolve SST and SSS. Understanding the relationship between subtropical SST, Greenland air temperatures and high latitude SST, in addition to LIS meltwater input, will test the hypothesis that subtropical SST changes lead high-latitude climate change.

  20. Observing and diagnosing biological fluxes and canopy mechanisms with implications for climate change and ecosystem disturbance

    NASA Astrophysics Data System (ADS)

    Reed, David E.

    Improving our predictions of ecosystem responses is an important challenge in ecological science due to the increasing number of stresses applied to biological systems. The assumption that ecosystems are operating in steady-state conditions at annual and longer time scales is far too simple of a model as ecosystems are an integral part of the earth system. Anthropogenic and non-anthropogenic forces acting on ecosystems within the earth system are numerous and include broad external factors such as climate change to specific internal factors such as infestations causing disturbance. This research quantifies changes in biogeochemical cycling and increases understanding of the mechanisms that control these cycles across two major ecosystems of the intermountain west with the broad goal of better predictive power of ecosystem responses. Eddy covariance methods were used to quantify carbon, water and energy fluxes at two different field sites in sagebrush ecosystems and one field site in a lodgepole pine ecosystem, in south-east Wyoming and northern Colorado. These measurements were supported with environmental and micrometeorological measurements in order to better understand physical mechanisms and canopy processes that control these biological fluxes. Results from the sagebrush component of this dissertation show how semi-arid sagebrush canopies interact with the lower atmosphere in ways that can alter environmental control of water loss with changing leaf area. This feedback has large implications combined with the large land area of these ecosystems and predictions of a dryer and more variable precipitation regime in the future. At the higher elevation lodgepole pine site, the ecosystem is undergoing a major mortality disturbance due to native bark beetles. Interestingly, even with ˜80% mortality of the canopy, few changes are observed to carbon and water cycling, as well as water use efficiency and energy cycling at the ecosystem scale. This calls into question

  1. Last Interglacial (MIS5e) hydrographic shifts linked to meltwater discharges from the East Greenland margin

    NASA Astrophysics Data System (ADS)

    Zhuravleva, Anastasia; Bauch, Henning A.; Van Nieuwenhove, Nicolas

    2016-04-01

    The East Greenland Current (EGC) plays a key role in transporting polar water from the Arctic to convectional sites of the Iceland and Labrador seas. Ongoing melting of the Greenland Ice Sheet (GIS) as well as the Arctic sea ice prompts freshening of the EGC and accumulation of low-density water in the subpolar North Atlantic, thus affecting the stabilities of water mass overturning and subsequent northward heat transfer. To assess natural eastern GIS dynamics and possible freshwater-induced regional oceanic reorganizations we analyzed several sediment sequences from the poorly investigated area along the eastern Greenland margin and the western Nordic Seas. Records span the last interglacial (LIG, MIS5e) cycle, including deglacial Termination 2 and the LIG climatic optimum. On a global scale, the latter is believed to have been warmer than present, with a higher sea level, and may, therefore, serve as a promising analogue for future hydrographic changes. Based on various proxy data (stable isotopes, planktic foraminiferal assemblages, ice-rafted debris) our reconstructions support the notion of a "two-step development" of Termination 2 which underwent severe surface freshening in the subpolar North Atlantic. This is shown in extremely light oxygen isotopic values registered all along the eastern Greenland margin during early MIS5e, which are indicative for pronounced eastern/central GIS retreat and a further propagation of the resulting meltwater southward via the EGC. In addition, we find compelling evidence for at least two separate meltwater episodes in proximity of the eastern GIS during early MIS5e. The climatic episode in between is correlated with an early LIG warm peak, which may be linked to enhanced presence of Atlantic water in the central Nordic Seas (Bauch et al., 2012) and further downstream along southern Greenland (Hillaire-Marcel et al., 1994, Irvali et al., 2012). Our data, therefore, reveal a complex and variable dynamic of the EGC during MIS5e

  2. A High-Resolution Record of Meltwater Discharge and Deglacial Warming in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Gilbert, M. L.; Hastings, D. W.; Flower, B. P.; Quinn, T. M.

    2005-12-01

    Sea surface temperature (SST) and δ18Osw records from the Gulf of Mexico (GOM) during the last deglaciation will help distinguish different mechanisms for abrupt climate change. Orca Basin is an ideal location to study climate changes in the GOM and to record the timing of meltwater discharge events through the Mississippi River; the anoxic hypersaline bottom water prevents bioturbation and results in finely laminated sediments. We sampled core MD 02-2550 at 0.5 cm resolution which, given sedimentation rates of greater than 30 cm/ka, corresponds to ~20 yr resolution. We analyzed Mg/Ca ratios on Globigerinoides ruber (white) to generate a SST record using the calibration of Anand et al. (2003). The record presented here extends from ca. 13 to 10.4 ka BP. The average temperatures at the beginning of the record from 13 to 12.5 ka BP are 26.3°C, with a variability of 1.0°C (1 σ). A major SST decrease of 3.0°C is recorded in two steps at 12.5 ka and 12.2 that lasts ca. 500 years. Within this transition, a more rapid cooling of ~2.0°C in less than 100 years is observed starting at ca. 12.2 ka. A reciprocal warming is observed in three stages from 12.0 to 11.0 ka: first a warming of 1.3°C over 300 years, relatively constant temperatures for 400 years, and a final warming of 1.7°C over 300 years returning to the same average SST as before the cold period. These cooler temperatures persisted for ca. 1500 yrs and likely corresponds to the Younger Dryas stadial. The annual SST in the GOM today is the same as the average temperature preceding and following the cold period. These trends represent the most detailed Mg/Ca SST records of the B/A Younger Dryas oscillation observed in the GOM. Paired with the Mg/Ca-derived SST, δ18O data will be generated to produce a δ18Osw record. This will enable us to ascertain the timing and precise phasing of deglacial warming relative to Laurentide ice sheet meltwater input into the GOM.

  3. Atmospheric water vapor flux, bifurcation of the thermohaline circulation, and climate change

    SciTech Connect

    Wang, H.; Birchfield, G.E.

    1992-10-01

    Latitudinal heat transport in the ocean and atmosphere represents a fundamental process of the Earth`s climate system. The ocean component of heat transport is effected by the thermohaline circulation. Changes in this circulation have a significant effect on global climate. Paleoclimate evidence from the Greenland ice and deep sea sediment core suggests during much of glacial time the climate system oscillated between two different states. The role of atmospheric hydrological cycle on the global thermohaline circulation and the feedback to the climate system through changes in the ocean`s latitudinal heat transport, with a simple coupled ocean-atmosphere energy-salt balance model is addressed here. Two components of the atmospheric hydrological cycle, i.e., latitudinal water vapor transport and the net flux of water vapor from the Atlantic to the Pacific Ocean appear to play separate roles. If the inter-basin transport is sufficiently large, small changes in water vapor transport over the North Atlantic can effect bifurcation or a rapid transition between two different equilibria in the global thermohaline circulation. If the inter-basin transport is from the Pacific to the Atlantic and sufficiently large, latitudinal vapor transport in the North Pacific controls the bifurcations. For intermediate values of inter-basin transport, no rapid transitions occur in either basin. For estimated values of water vapor transport for the present climate the model asserts that while vapor transport from the Atlantic to the Pacific Ocean is sufficiently large to make the North Atlantic the dominant region for deep water production, latitudinal water vapor transport is sufficiently low that the thermohaline circulation appears stable, i.e., far from a bifurcation point. This conclusion is supported to some extent by the fact that the high latitude temperature of the atmosphere as recorded in the Greenland ice cores has changes little over the last 9000 years. 31 refs., 5 figs.

  4. Non-linearities in hydrological connectivity and microbiological flux in nested catchments - implications of environmental change

    NASA Astrophysics Data System (ADS)

    Tetzlaff, D.; Soulsby, C.; Birkel, C.; Capell, R.; Speed, M.

    2009-12-01

    The non-linearities of catchment hydrological behaviour are strongly influenced by the connectivity of hillslopes and channel networks, particularly where overland flow is an important runoff mechanism. Such surface connectivity also controls the flux of microbiological pollutants (coliform bacteria) from areas of live stock grazing which can have serious health implications for potable water supplies. We report a nested catchment study where hydrological and tracer monitoring over a two year period has been coupled with regular sampling for faecal indicator organisms (FIOs). The study has been based in catchments with mixed landuse where FIOs are derived from livestock (sheep and cows) in agricultural land and wild animals (red deer) on moorlands. At all scales (3-1800km2), high levels of FIO were transient and episodic and strongly correlated with periods of high hydrological connectivity. We show how this non-linearity in connectivity can be captured within a dynamic hydrological model. The model was used, along with climate change predictions, to assess possible scenarios of change in connectivity and microbiological contamination in catchments with different land use.

  5. Wind farm induced changes in wind speed and surface fluxes over the North Sea

    NASA Astrophysics Data System (ADS)

    Chatterjee, Fabien; van Lipzig, Nicole; Meyers, Johan

    2016-04-01

    Offshore wind farm deployment in the North Sea is foreseen to expand dramatically in the coming years. The strong expansion of offshore wind parks is likely to affect the regional climatology on the North Sea. We assess this impact by conducting a regional climate model simulation over future wind farms built near the German coast. In order to achieve this, the wind farm parameterisation of Fitch et al. 2012, where wind farms are parameterised as elevated sources of turbulent kinetic energy and sinks of momentum ( Blahak et al 2010 and Fitch et al 2012) is implemented in COSMO-CLM at a 1.5 km resolution. As a first step, COSMO-CLM's ability to reproduce wind profiles over the North Sea is evaluated using wind speed data from the FINO1 meteorological mast, toghether with QuikScat scatterometer data, for a time period of 2000-2008. Subsequently, the impact of windfarms on the regional climate over a period of ten years (1999-2008) is assessed. A large scale wind farm can create wakes which depending on the wind direction could affect the power production of a neighbouring farm. Furthermore, wind farms decelerate the flow and create a vertical circulation in the inflow region. As a result, changes in vertical fluxes of moisture are observed. This leads to enhanced low level cloud cover which may trigger changes in precipitation.

  6. Numerical Simulation and Sensitivity Analysis of Subglacial Meltwater Plumes: Implications for Ocean-Glacier Coupling in Rink Isbrae, West Greenland

    NASA Astrophysics Data System (ADS)

    Carroll, D.; Sutherland, D.; Shroyer, E.; Nash, J. D.

    2014-12-01

    The rate of mass loss from the Greenland Ice Sheet quadrupled over the last two decades and may be due in part to changes in ocean heat transport to marine-terminating outlet glaciers. Meltwater commonly discharges at the grounding line in these outlet glacier fjords, generating a turbulent upwelling plume that separates from the glacier face when it reaches neutral density. This mechanism is the current paradigm for setting the magnitude of net heat transport in Greenland's glacial fjords. However, sufficient observations of meltwater plumes are not available to test the buoyancy-driven circulation hypothesis. Here, we use an ocean general circulation model (MITgcm) of the near-glacier field to investigate how plume water properties, terminal height, centerline velocity and volume transport depend on the initial conditions and numerical parameter choices in the model. These results are compared to a hydrodynamic mixing model (CORMIX), typically used in civil engineering applications. Experiments using stratification profiles from the continental shelf quantify the errors associated with using far-field observatons to initialize near-glacier plume models. The plume-scale model results are then integrated with a 3-D fjord-scale model of the Rink Isbrae glacier/fjord system in west Greenland. We find that variability in the near-glacier plume structure can strongly control the resulting fjord-scale circulation. The fjord model is forced with wind and tides to examine how oceanic and atmospheric forcing influence net heat transport to the glacier.

  7. Quantitative evaluation on the influence from cryosphere meltwater on runoff in an inland river basin of China

    NASA Astrophysics Data System (ADS)

    Zongxing, Li; Qi, Feng; Wang, Q. J.; Song, Yong; Jianguo, Li; Yongge, Li; Yamin, Wang

    2016-08-01

    Under climate warming, increasing attention is being directed towards high altitude regions where glaciers are shrinking and frozen soil is in degrading. This study, taken Taolai river in Qilian Mountains as an example, is to quantify the relative contributions of cryosphere meltwater to outlet river, based on 221 water samples from precipitation, river, groundwater and meltwater during 2013-2014. The results indicated that cryosphere meltwater accounted for 49% of the total runoff in the source region, and this contribution rate decreased to 21% at the outlet of basin. In addition, precipitation and meltwater from cryosphere belt has contributed up to 78% of the outlet river runoff. An inverse altitude effect of stable isotopes for river water and groundwater is likely to occur, which is caused by the relatively larger contribution rate of frozen soil meltwater in the source region. The results could provide a comprehensive overview on the influence from cryosphere meltwater to hydrologic process in cold basins.

  8. Isotopically nonstationary 13C flux analysis of changes in Arabidopsis thaliana leaf metabolism due to high light acclimation.

    PubMed

    Ma, Fangfang; Jazmin, Lara J; Young, Jamey D; Allen, Doug K

    2014-11-25

    Improving plant productivity is an important aim for metabolic engineering. There are few comprehensive methods that quantitatively describe leaf metabolism, although such information would be valuable for increasing photosynthetic capacity, enhancing biomass production, and rerouting carbon flux toward desirable end products. Isotopically nonstationary metabolic flux analysis (INST-MFA) has been previously applied to map carbon fluxes in photoautotrophic bacteria, which involves model-based regression of transient (13)C-labeling patterns of intracellular metabolites. However, experimental and computational difficulties have hindered its application to terrestrial plant systems. We performed in vivo isotopic labeling of Arabidopsis thaliana rosettes with (13)CO2 and estimated fluxes throughout leaf photosynthetic metabolism by INST-MFA. Plants grown at 200 µmol m(-2)s(-1) light were compared with plants acclimated for 9 d at an irradiance of 500 µmol⋅m(-2)⋅s(-1). Approximately 1,400 independent mass isotopomer measurements obtained from analysis of 37 metabolite fragment ions were regressed to estimate 136 total fluxes (54 free fluxes) under each condition. The results provide a comprehensive description of changes in carbon partitioning and overall photosynthetic flux after long-term developmental acclimation of leaves to high light. Despite a doubling in the carboxylation rate, the photorespiratory flux increased from 17 to 28% of net CO2 assimilation with high-light acclimation (Vc/Vo: 3.5:1 vs. 2.3:1, respectively). This study highlights the potential of (13)C INST-MFA to describe emergent flux phenotypes that respond to environmental conditions or plant physiology and cannot be obtained by other complementary approaches. PMID:25368168

  9. Meltwater Origin of the 2005 Mount Steller Landslide Confirmed by Analysis of Global Fiducials Program Imagery

    NASA Astrophysics Data System (ADS)

    Molnia, B. F.; Angeli, K.

    2012-12-01

    roof of the west wall channel tunnel had collapsed and its path could be discerned in the remaining ice and snow; (3) several near-summit depressions remained that suggested liquid water may have existed and been temporarily stored; (4) the surface on which the slide occurred had a slope that was >50 degrees; (5) the slide mass had many unique components suggesting a complex series of related failures; and (6) there was an absence of large rock bodies in the slide debris, suggesting that much of the failed material may have previously been fractured by freeze-thaw processes. The timely collection of GFP imagery confirmed the continued presence of meltwater near the point of origin of this slide. Coupled with the September 15 oblique photography, interpretation of these images suggests that a large volume of water had recently been flowing on Steller's east summit ridge and that the water might have had a role in triggering the landslide. The presence of a large volume of water close to the summit raises questions about climate change and its role in the future generation of high elevation landslides. Although Mt. Steller is tens of kilometers from the closest human infrastructure, there are numerous other settings around the world where mountains with similar elevations, hanging glaciers, and sun-facing orientations are in close proximity to human infrastructure.

  10. Geomorphological evidence of channelized subglacial meltwater drainage under the Scandinavian Ice Sheet

    NASA Astrophysics Data System (ADS)

    Adamczyk, Aleksander; Wysota, Wojciech; Sobiech, Marcin; Piotrowski, Jan A.

    2016-04-01

    The impact of subglacial meltwater erosion on shaping glacial landscapes is contentious and often difficult to constrain due to the lack of unequivocal diagnostic criteria. The same holds for the role of subglacial meltwater in glacier movement processes and sediment transport and deposition. Here we present new evidence of widespread channelized erosion under the southern, soft-bedded fringe of the last Scandinavian Ice Sheet (SIS) based on high-resolution terrain analysis with LiDAR imagery. We identify several tens of sites with "glacial curvilineation" landscapes first recognized by Lesemann et al. (2010, 2014) and considered as evidence of erosion by turbulent meltwater flows at the ice/bed interface. The "glacial curvilineation" landscapes mapped here consist of sets of parallel, winding ridges typically several metres high and up to several kilometres long occupying glacial overdeepenings and tunnel valleys. The ridges are aligned approximately perpendicular to the past ice sheet margins and they are composed of various deposits often pre-dating the last ice advance. We interpret them as erosional remnants of older landscapes dissected by high-energy subglacial meltwater flows. These findings suggest that the palaeoglaciological significance of meltwater drainage under the southern portion of SIS may have been grossly underestimated. References Lesemann, J.-E., Piotrowski, J.A. and Wysota, W., 2010. „Glacial curvilineations": New glacial landforms produced by longitudinal vortices in subglacial meltwater flows. Geomorphology 120, 153-161. Lesemann, J.-E., Piotrowski, J.A. and Wysota, W., 2014. Genesis of the "glacial curvilineation" landscape by meltwater processes under the former Scandinavian Ice Sheet, Poland. Sedimentary Geology 312, 1-18.

  11. Changes in Streamflow and the Flux of Nutrients in the Mississippi-Atchafalaya River Basin, USA, 1980-2007

    USGS Publications Warehouse

    Battaglin, William A.; Aulenbach, Brent T.; Vecchia, Aldo; Buxton, Herbert T.

    2010-01-01

    decreased. However, the flux of total phosphorus between the baseline period and subsequent 5-year periods has increased. The average spring (April, May, and June) streamflow and fluxes of silica, total nitrogen, nitrate, and orthophosphate to the Gulf of Mexico also decreased, whereas the spring flux of total phosphorus has increased. Similar changes in streamflow and nutrient flux were observed at many sites Buxtonwithin the basin. The inputs of water, total nitrogen, and total phosphorus from the major subbasins of the Mississippi-Atchafalaya River Basin as a percentage of the to-the-gulf totals have increased from the Ohio River Basin, decreased from the Missouri River Basin, and remained relatively unchanged from the Upper Mississippi, Red, and Arkansas River Basins. Changes in streamflow and nutrient fluxes are related, but short-term variations in sources of streamflow and nutrients complicate the interpretation of factors that affect nutrient delivery to the Gulf of Mexico. Parametric time-series models are used to try and separate natural variability in nutrient flux from changes due to other causes. Results indicate that the decrease in annual nutrient fluxes that has occurred between the 1980-1996 baseline period and more recent years can be largely attributed to natural causes (climate and streamflow) and not management actions or other human controlled activities in the Mississippi-Atchafalaya River Basin. The downward trends in total nitrogen, nitrate, ammonium, and orthophosphate that were detected at either the Mississippi River near St. Francisville, La., or the Atchafalaya River at Melville, La., occurred prior to 1995. In spite of the general decrease in nutrient flux, the average size of the Gulf of Mexico hypoxic zone has increased between 1997 and 2007. The reasons for this are not clear but could be due to the type or nature of nutrient delivery. Whereas the annual flux of total nitrogen to the Gulf of Mexico has decreased, the proporti

  12. Changes in fluxes of heat, H2O, CO2 caused by a large wind farm

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Crop Wind Energy Experiment (CWEX) provides a platform to investigate the effect of wind turbines and large wind farms on surface fluxes of momentum, heat, moisture and carbon dioxide (CO2). In 2010 and 2011, eddy covariance flux stations were installed between two lines of turbines at the south...

  13. Simulations of ice flux through Totten Glacier as ice shelf calving changes

    NASA Astrophysics Data System (ADS)

    Moore, John; Sun, Sainan; Åström, Jan

    2016-04-01

    Totten glacier is one of the most important ocean portals for the East Antarctic ice sheet. Melt rates under the ice shelf in front of the glacier are very high, and the ice shelf seems to suffer from extensive basal melt-induced calving. The ice shelf is underlain by a relatively narrow and convoluted cavity, which recent resurveying suggests maybe substantially different from Bedmap2 geometry. Here we use the BISICLES ice flow model and ice shelf buttressing derived from inverse modeling to simulate present day ice dynamics. We then use a discrete particle model so simulate ice shelf fracturing to simulate how the ice shelf geometry, calving patterns and buttressing force could evolve. The new ice shelf geometry is then used with the continuum model to asses ice flux through the region 50 years into the future. The results suggest considerable changes in glacier-ice shelf configuration, but which are sensitive to ice shelf pinning points and sub-shelf cavity geometry.

  14. Moisture flux changes and trends for the entire Arctic in 2003-2011 derived from EOS Aqua data

    NASA Astrophysics Data System (ADS)

    Boisvert, L. N.; Markus, T.; Vihma, T. P.

    2013-12-01

    The Arctic sea ice acts as a barrier between the ocean and lower atmosphere, reducing the exchange of heat and moisture. In recent years the ice pack has undergone many changes, in particular a rapid reduction in sea ice extent and compactness in summer and autumn. This, along with modeling studies, would cause one to believe that the moisture flux would be increasing. We estimate the daily moisture flux from 2003-2011 using geophysical data from multiple sensors onboard NASA's Aqua satellite, taking advantage of observations being collected at the same time and along the same track. Our findings show the moisture flux, averaged over the entire Arctic, has had large interannual variations. Increases in air specific humidity tend to reduce the moisture flux, whereas the decrease in sea ice cover tends to increase the flux. Statistically significant seasonal decreasing trends are seen in December, January and February because of the dominating effect of increase in 2m air specific humidity increasing, reducing the surface-air specific humidity difference by -0.0547 kg/kg in the Kara/Barents Seas, E. Greenland Sea and Baffin Bay regions where there is some open water year round. Our results also show that the contribution of the sea ice zone to the total moisture flux has increased by 3.6% because the amount of open water within the sea ice has increased by 4.3%.

  15. Transverse Eskers in the Irish Midlands: Implications for Meltwater Pathways in Ice Sheets

    NASA Astrophysics Data System (ADS)

    Delaney, Cathy

    2013-04-01

    Large eskers in the Irish Midlands, formed during the last Glacial Termination (MIS 2) are thought to have formed time-transgressively in subglacial conduits feeding to a subaqueous margin, where conduit orientation was controlled by the ice sheet surface gradient in this area, and parallels ice flow direction as indicated by drumlinoid features. However, three eskers systems (the Ballyduff Esker, Kilcormac Esker and Streamstown Esker) have sections with orientations at up to 90 degrees to the dominant ridge orientation, over distances of up to 5km. These shifts in orientation are associated with a change in esker morphology from one or two continuous ridges to anabranching and fragmented ridges and small kames. Exposures in the Ballyduff and Kilcormac Eskers indicate water flow was both parallel and perpendicular to ridge orientation during formation, and that deposition occurred en- or supra-glacially. Deposition of the Streamstown ridges occurred subglacially. In all cases the shift in ridge orientation indicates the diversion of meltwater drainage into transverse crevasse systems, reflecting a temporary phase of extensional ice flow.

  16. Biogeochemistry of glacial meltwater streams in the McMurdo Dry Valleys

    NASA Astrophysics Data System (ADS)

    McKnight, D. M.; Jaros, C.; Gooseff, M.; Lyons, W. B.

    2003-04-01

    The McMurdo Dry Valleys of Antarctica contain many glacial melt water streams which connect glaciers, soils, and lakes. Although flow occurs in the austral summers for only 6 to 12 weeks, these streams are important landscape features influencing the response of the lakes to changing climate. Some of these streams have thriving mat communities composed of cyanobacteria, which are in a freeze-dried state during winter. The streams are composed of an open channel and hyporheic zone, which is visible as a wetted area adjacent to the stream. The hyporheic zone becomes saturated as the flow advances downstream and can correspond to a substantial storage zone for meltwater. During cold summers, the water loss through evaporation form the stream and the hyporheic zone is substantial. Tracer injection experiments show that the porosity of the unconsolidated alluvium results in rapid hyporheic exchange in dry valley streams. Study of nutrient uptake through tracer experiments shows rapid nitrate and phosphate assimilation by the mats, as well as some denitrification. The hyporheic zone is also a zone of active weathering reactions enhanced possibly by microbial growth on mineral surfaces, and thus hyporheic exchange strongly influences stream chemistry and ecology.

  17. Teasing Apart Regional Climate and Meltwater Influences on Florida Straits Sea Surface Temperature and Salinity over the past 40 kyr

    NASA Astrophysics Data System (ADS)

    Schmidt, M. W.; Lynch-Stieglitz, J.

    2008-12-01

    Recent reconstructions of North Atlantic salinity variability over the last glacial cycle show that abrupt climate events are linked to major reorganizations in the low-latitude hydrologic cycle, affecting large-scale changes in evaporation minus precipitation (E-P) patterns. Although there is general agreement that the Intertropical Convergence Zone (ITCZ) migrates southward during cold stadials, it remains unclear how this shift affects the net E-P budget in the North Atlantic. In order to reconstruct a high resolution record of past sea surface temperature (SST) and salinity (SSS) in the Florida Straits across abrupt climate events of the last 40 kyr, we combine Mg/Ca paleothermometry and δ18O measurements in shells from the surface-dwelling foraminifera Globigerinoides ruber in cores KNR166-2-JPC29 (24°17'N, 83°16'W; 648 m depth; 8-20 cm/kyr sed. rate) and JPC26 (24°19.61'N, 83°15.14'W; 546 m depth; 18-240 cm/kyr sed. rate) and calculate δ18OSEAWATER (δ18OSW) variability. Removal of the δ18OSW signal due to continental ice volume variation results in the ice volume-free (IVF) δ18OSW record (a proxy for SSS variability). Although most waters flowing through the Florida Straits today originate in the tropical western Atlantic, major meltwater discharges from the Mississippi River across the last deglacial period also influenced SST and SSS in the Florida Straits. To constrain periods of increased meltwater discharge, we measured Ba/Ca ratios in G. ruber from select intervals. Because riverine waters have a much higher dissolved Ba+2 concentration relative to seawater, foraminifera Ba/Ca ratios can be used as an additional proxy to constrain periods of increase riverine discharge. Initial results suggest the hydrographic history of the Florida Straits is influenced by both meltwater discharge and regional climate variability linked to the high-latitude North Atlantic. Both the IVF- δ18OSW and Ba/Ca records reveal a prolonged period from 16.0-13.0 kyr

  18. Late Pleistocene-Holocene ground surface heat flux changes reconstructed from borehole temperature data (the Urals, Russia)

    NASA Astrophysics Data System (ADS)

    Demezhko, D. Y.; Gornostaeva, A. A.

    2015-04-01

    We use geothermal reconstruction of the ground surface temperature (GST) history early obtained in the Middle Urals to determine the surface heat flux (SHF) history over the past 35 kyr. A new algorithm of GST-SHF transformation was applied to solve this problem. The timescale of geothermal reconstructions has been corrected by comparing the estimated heat flux and annual insolation at the latitude of 60° N. The consistency of SHF and insolation changes on the interval 35-6 kyr BP with the linear correlation coefficient R = 0.99 points to orbital factors as the main cause of climatic changes during the Pleistocene-Holocene transition. The amplitude of SHF variations is about 1.3% of the insolation change amplitude. The increase of carbon dioxide concentrations lagged by 2-3 kyr from the SHF increase and occurred synchronously with GST changes.

  19. Partitioning CO2 Fluxes in Transitional Bioenergy CROPS:EFFECT of Land Use Change

    NASA Astrophysics Data System (ADS)

    Zenone, T.; Chen, J.; Hamilton, S. K.; Robertson, G. P.

    2010-12-01

    The demand for alternatives to petroleum is increasing the production of bioenergy. Undisturbed ecosystems in different part of the globe were converted to bioenergy cultivations. In this study we examined the effect of land conversion on C Pools and fluxes using the Eddy Covariance (EC) technique in seven sites in southwestern Michigan undergoing such conversions. Of the seven sites, four had been managed for the Conservation Reserve Program (CRP) during the last 20 years to maintain them as grasslands. The other three were cultivated in a corn/soybean rotation. The effects of land use change were studied during 2009 when six of the fields (three CRP and three crop fields) were converted to soybean cultivation, with the 7th site remained as a grassland reference. Daytime estimates of ecosystem respiration (Reco) were obtained from the night NEE-temperature relationship. An Arrhenius-type model was used to describe the temperature dependence of Reco. The Gross Primary Productivity (GPP) was then obtained by subtracting Reco from NEE. Soil CO2 fluxes (SRR) were measured in all sites with a portable EGM-4 infrared gas analyzer (PP-Systems, UK). SRR, soil temperature, and soil moisture were analyzed using a two-way ANOVA with repeated measures analyses on one factor. SRR was modeled using a nonlinear regression function to describe SRR as dependant on soil temperature and soil moisture, expressed as soil water content relative to the soil water content at field capacity (RSWC). Standard errors of nonlinear regression parameters were estimated by a bootstrapping algorithm. During winter the agricultural sites were essentially carbon (C) neutral while the grasslands were C sources, with average emissions of 15 g C m-2 month-1. The annual NEP at sites converted from CRP to soybeans had a net emission of 156 (± 25) - 128 (± 27) g C m-2 year-1. The sites previously cultivated as corn/soybean rotation was a net C uptake, with NEP ranging from -91 (± 26) to -57 (± 21) g

  20. Pink marine sediments reveal rapid ice melt and Arctic meltwater discharge during Dansgaard-Oeschger warmings.

    PubMed

    Rasmussen, Tine L; Thomsen, Erik

    2013-01-01

    The climate of the last glaciation was interrupted by numerous abrupt temperature fluctuations, referred to as Greenland interstadials and stadials. During warm interstadials the meridional overturning circulation was active transferring heat to the north, whereas during cold stadials the Nordic Seas were ice-covered and the overturning circulation was disrupted. Meltwater discharge, from ice sheets surrounding the Nordic Seas, is implicated as a cause of this ocean instability, yet very little is known regarding this proposed discharge during warmings. Here we show that, during warmings, pink clay from Devonian Red Beds is transported in suspension by meltwater from the surrounding ice sheet and replaces the greenish silt that is normally deposited on the north-western slope of Svalbard during interstadials. The magnitude of the outpourings is comparable to the size of the outbursts during the deglaciation. Decreasing concentrations of ice-rafted debris during the interstadials signify that the ice sheet retreats as the meltwater production increases. PMID:24264767

  1. Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay

    NASA Astrophysics Data System (ADS)

    Jansen, J. D.; Codilean, A. T.; Stroeven, A. P.; Fabel, D.; Hättestrand, C.; Kleman, J.; Harbor, J. M.; Heyman, J.; Kubik, P. W.; Xu, S.

    2014-05-01

    The century-long debate over the origins of inner gorges that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial forms cut beneath ice. Here we apply cosmogenic nuclide exposure dating to seven inner gorges along ~500 km of the former Fennoscandian ice sheet margin in combination with a new deglaciation map. We show that the timing of exposure matches the advent of ice-free conditions, strongly suggesting that gorges were cut by channelized subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting. The lack of postglacial river erosion in our seven gorges implicates subglacial meltwater as a key driver of valley deepening on the Baltic Shield over multiple glacial cycles.

  2. Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay.

    PubMed

    Jansen, J D; Codilean, A T; Stroeven, A P; Fabel, D; Hättestrand, C; Kleman, J; Harbor, J M; Heyman, J; Kubik, P W; Xu, S

    2014-01-01

    The century-long debate over the origins of inner gorges that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial forms cut beneath ice. Here we apply cosmogenic nuclide exposure dating to seven inner gorges along ~500 km of the former Fennoscandian ice sheet margin in combination with a new deglaciation map. We show that the timing of exposure matches the advent of ice-free conditions, strongly suggesting that gorges were cut by channelized subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting. The lack of postglacial river erosion in our seven gorges implicates subglacial meltwater as a key driver of valley deepening on the Baltic Shield over multiple glacial cycles. PMID:24809336

  3. The influence of glacial meltwater on alpine aquatic ecosystems: a review.

    PubMed

    Slemmons, Krista E H; Saros, Jasmine E; Simon, Kevin

    2013-10-01

    The recent and rapid recession of alpine glaciers over the last 150 years has major implications for associated aquatic communities. Glacial meltwater shapes many of the physical features of high altitude lakes and streams, producing turbid environments with distinctive hydrology patterns relative to nival systems. Over the past decade, numerous studies have investigated the chemical and biological effects of glacial meltwater on freshwater ecosystems. Here, we review these studies across both lake and stream ecosystems. Focusing on alpine regions mainly in the Northern Hemisphere, we present examples of how glacial meltwater can affect habitat by altering physical and chemical features of aquatic ecosystems, and review the subsequent effects on the biological structure and function of lakes and streams. Collectively or separately, these factors can drive the overall distribution, diversity and behavior of primary producers, triggering cascading effects throughout the food web. We conclude by proposing areas for future research, particularly in regions where glaciers are soon projected to disappear. PMID:24056713

  4. Abnormal changes in the density of thermal neutron flux in biocenoses near the earth surface.

    PubMed

    Plotnikova, N V; Smirnov, A N; Kolesnikov, M V; Semenov, D S; Frolov, V A; Lapshin, V B; Syroeshkin, A V

    2007-04-01

    We revealed an increase in the density of thermal neutron flux in forest biocenoses, which was not associated with astrogeophysical events. The maximum spike of this parameter in the biocenosis reached 10,000 n/(sec x m2). Diurnal pattern of the density of thermal neutron flux depended only on the type of biocenosis. The effects of biomodulation of corpuscular radiation for balneology are discussed. PMID:18214289

  5. Moisture flux changes and trends for the entire Arctic in 2003-2011 derived from EOS Aqua data

    NASA Astrophysics Data System (ADS)

    Boisvert, Linette N.; Markus, Thorsten; Vihma, Timo

    2013-10-01

    The Arctic sea ice acts as a barrier between the ocean and lower atmosphere, reducing the exchange of heat and moisture. In recent years the ice pack has undergone many changes, in particular a rapid reduction in sea ice extent and compactness in summer and autumn. This, along with modeling studies, would cause one to believe that the moisture flux would be increasing. We estimate the daily moisture flux from 2003 to 2011 using geophysical data from multiple sensors onboard NASA's Aqua satellite, taking advantage of observations being collected at the same time and along the same track. Our findings show the moisture flux, averaged over the entire Arctic, has had large interannual variations, with smallest fluxes in 2010, 2003, and 2004, and largest ones in 2007, 2008, and 2005. Increases in air specific humidity tend to reduce the moisture flux, whereas the decrease in sea ice cover tends to increase the flux. Statistically significant seasonal decreasing trends are seen in December, January, and February because of the dominating effect of increase in 2 m air specific humidity increasing, reducing the surface-air specific humidity difference by -0.0547 kg/kg in the Kara/Barents Seas, E. Greenland Sea, and Baffin Bay regions where there is some open water year round. Our results also show that the contribution of the sea ice zone to the total moisture flux (from the open ocean and sea ice zone) has increased by 3.6% because the amount of open water within the sea ice zone has increased by 4.3%.

  6. In-situ biofilm characterization in membrane systems using Optical Coherence Tomography: formation, structure, detachment and impact of flux change.

    PubMed

    Dreszer, C; Wexler, A D; Drusová, S; Overdijk, T; Zwijnenburg, A; Flemming, H-C; Kruithof, J C; Vrouwenvelder, J S

    2014-12-15

    Biofouling causes performance loss in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane operation for process and drinking water production. The development of biofilm formation, structure and detachment was studied in-situ, non-destructively with Optical Coherence Tomography (OCT) in direct relation with the hydraulic biofilm resistance and membrane performance parameters: transmembrane pressure drop (TMP) and feed-channel pressure drop (FCP). The objective was to evaluate the suitability of OCT for biofouling studies, applying a membrane biofouling test cell operated at constant crossflow velocity (0.1 m s(-1)) and permeate flux (20 L m(-2)h(-1)). In time, the biofilm thickness on the membrane increased continuously causing a decline in membrane performance. Local biofilm detachment was observed at the biofilm-membrane interface. A mature biofilm was subjected to permeate flux variation (20 to 60 to 20 L m(-2)h(-1)). An increase in permeate flux caused a decrease in biofilm thickness and an increase in biofilm resistance, indicating biofilm compaction. Restoring the original permeate flux did not completely restore the original biofilm parameters: After elevated flux operation the biofilm thickness was reduced to 75% and the hydraulic resistance increased to 116% of the original values. Therefore, after a temporarily permeate flux increase the impact of the biofilm on membrane performance was stronger. OCT imaging of the biofilm with increased permeate flux revealed that the biofilm became compacted, lost internal voids, and became more dense. Therefore, membrane performance losses were not only related to biofilm thickness but also to the internal biofilm structure, e.g. caused by changes in pressure. Optical Coherence Tomography proved to be a suitable tool for quantitative in-situ biofilm thickness and morphology studies which can be carried out non-destructively and in real-time in transparent membrane biofouling monitors. PMID:25282092

  7. Milliarcsecond Change of IM Pegasi Radio Position in 1 Hour Coincident with Sharp Rise in Flux Density

    NASA Astrophysics Data System (ADS)

    Lebach, D. E.; Ratner, M. I.; Shapiro, I. I.; Ransom, R. R.; Bietenholz, M. F.; Bartel, N.; Lestrade, J.-F.

    1999-05-01

    Continuum VLBI observations at 3.6 cm of the RS CVn binary star IM Pegasi (HR 8703) for ~16 hr beginning on 1997 January 16 revealed an apparent motion of the star's radio position that coincided temporally with a large relative change in its flux density. Specifically, a rise in flux density from 18 to 46 mJy in 1.4 hr coincided with a detected position change over that interval of (Δα, Δδ)=(-0.68+/-0.15, 0.55+/-0.20) mas. The magnitude of this position change is much larger than can be explained by parallax, proper motion, and orbital motion and is about two-thirds the estimated angular diameter of the primary component of the binary.

  8. Effects of CO[sub 2] and climate change on forest trees: Shoot growth and gas flux responses

    SciTech Connect

    Olszyk, D.M.; Wise, C.M.; Tingey, D.T.; Rygiewicz, P.T. ); Waschmann, R.S. )

    1994-06-01

    Critical questions regarding effects of rising atmospheric CO[sub 2] and climate change on forested systems include: Will shoot growth change in response to elevated CO[sub 2] and temperature . Will net carbon and water fluxes change in response to elevated CO[sub 2] and temperature Initial shoot growth and gas flux data are presented for Pseudotsuga menziesii seedlings continuously exposed for one year to target environments of ambient or ambient +200 ppm CO[sub 2], and ambient or ambient + 4[degrees]C air temperature in closed chambers. Changes in stem diameter, height, terminal shoot and bud length, are reported. Whole canopy and single branch level gas flux data used to calculate photosynthetic, respiration, and transpiration rates also are reported. The experiment is continuing so that longer-term impacts of CO[sub 2] and temperature on the seedlings can be determined and data obtained for process-based modeling of tree growth. The aboveground effects will be related to belowground processes to evaluate whole system responses to atmospheric CO[sub 2] and climate change.

  9. Meltwater input to the southern ocean during the last glacial maximum

    SciTech Connect

    Shemesh, A.; Burckle, L.H.; Hays, J.D.

    1994-12-02

    Three records of oxygen isotopes in biogenic silica from deep-sea sediment cores from the Atlantic and Indian sectors of the Southern Ocean reveal the presence of isotopically depleted diatomaceous opal in sediment from the last glacial maximum. This depletion is attributed to the presence of lids of meltwater that mixed with surface water along certain trajectories in the Southern Ocean. An increase in the drainage from Antarctica or extensive northward transport of icebergs are among the main mechanisms that could have produced the increase in meltwater input to the glacial Southern Ocean. Similar isotopic trends were observed in older climatic cycles at the same cores.

  10. Satellite observation of winter season liquid meltwater storage within Greenland's firn aquifer: 1992-2014

    NASA Astrophysics Data System (ADS)

    Miller, J. Z.; Forster, R. R.; Long, D. G.; Scambos, T. A.; Kuipers Munneke, P.; van den Broeke, M. R.

    2014-12-01

    It has long been known that the microwave response is sensitive to near-surface (~5 m) liquid meltwater within ice sheets. Since the beginning of the satellite-era, active and passive microwave instruments have frequently been used to detect what have been assumed to be melt processes from space. Microwave melt models are typically threshold-based binary detections - liquid meltwater is either present or it is not. The recent discovery of substantial quantities (~140±20 Gt) of liquid meltwater stored within Greenland's extensive firn aquifer highlights evolving knowledge of melt and retention processes within the upper layers (< ~35 m) of the percolation facies of the Greenland ice sheet, as well as limitations in current microwave melt models. Firn aquifers form as the result of high melt rates that saturate snow and firn layers with liquid meltwater during the melt season, and high snow accumulation rates that thermally insulates this saturated layer during the winter season - allowing it to be stored in liquid form at decreasing depths as refreeze propagates from the ice sheet surface downward. While subsurface liquid meltwater is known to influence the microwave response, current microwave melt models do not distinguish between the introduction of liquid meltwater controlled by melt processes and the continued presence of liquid meltwater controlled by the retention process. This research exploits the multidecadal (1992-2014) satellite-borne active (ERS, ASCAT) and passive (AMSR-E) microwave climate record to provide the first long-term, spatiotemporally continuous, observational evidence of winter season meltwater storage within Greenland's firn aquifer. We use multi-frequency backscatter and brightness temperature image time series reconstructed at enhanced resolution (~12 km), and a microwave signature algorithm derived from a coupled two-layer radiative transfer model, to characterize both melt and retention processes using simple, time

  11. Can we reconstruct meltwater supplies from ice-sheet to the ocean from proxies ?

    NASA Astrophysics Data System (ADS)

    de Vernal, A.; Hillaire-Marcel, C.

    2006-12-01

    The transfer of water from ice sheets to the ocean occurs through iceberg or meltwater discharge. In the first case, sedimentary tracers provide information on source areas and dispersal patterns, but do not permit quantifying the volume of freshwater release. In the second case, sedimentary tracers can help identifying catastrophic discharge that are accompanied by turbulent flow and gravity currents on sea-floor. Otherwise, continuous input of freshwater from ice margins (or from river) into the ocean results in stratification in upper waters that is controlled by discharge rates up to some threshold of turbulence. In this situation, sedimentary tracers are not much helpful informative, but biogenic remains, their isotopic and elemental contents can provide relevant information. They allow identifying salinity anomalies related to the mixing of freshwater in surface water layers. However, the associated changes in the upper water mass structure have an impact on pelagic ecosystems. Most stenohaline organisms are affected and decrease in abundance unless they are able to migrate along the halocline to find suitable salinity conditions. In theory, the analysis of fossil assemblage permits to infer changes in salinity and/or in the stratification of the upper water masses, and through transfer function, to make quantitative reconstructions. This exercise has been tempted with biological tracers such as dinocysts. Other proxies should also reveal informative, notably diatoms that occur in all salinity domains. In theory also, if a given species is able to keep its depth habitat despite changes in salinity and/or water mass structure, isotopic or geochemical tracers allow identifying changes in water-mass properties. This assumption is however debatable. Thus, reconstructing freshwater discharge is a challenge and requires combining complementary tracers. Here, we examine records of the last deglaciation with special attention to the Younger Dryas (YD) and "8.2 ka

  12. Modeling the impacts of temperature and precipitation changes on soil CO2 fluxes from a Switchgrass stand recently converted from cropland.

    PubMed

    Lai, Liming; Kumar, Sandeep; Chintala, Rajesh; Owens, Vance N; Clay, David; Schumacher, Joseph; Nizami, Abdul-Sattar; Lee, Sang Soo; Rafique, Rashad

    2016-05-01

    Switchgrass (Panicum virgatum L.) is a perennial C4 grass native to North America and successfully adapted to diverse environmental conditions. It offers the potential to reduce soil surface carbon dioxide (CO2) fluxes and mitigate climate change. However, information on how these CO2 fluxes respond to changing climate is still lacking. In this study, CO2 fluxes were monitored continuously from 2011 through 2014 using high frequency measurements from Switchgrass land seeded in 2008 on an experimental site that has been previously used for soybean (Glycine max L.) in South Dakota, USA. DAYCENT, a process-based model, was used to simulate CO2 fluxes. An improved methodology CPTE [Combining Parameter estimation (PEST) with "Trial and Error" method] was used to calibrate DAYCENT. The calibrated DAYCENT model was used for simulating future CO2 emissions based on different climate change scenarios. This study showed that: (i) the measured soil CO2 fluxes from Switchgrass land were higher for 2012 which was a drought year, and these fluxes when simulated using DAYCENT for long-term (2015-2070) provided a pattern of polynomial curve; (ii) the simulated CO2 fluxes provided different patterns with temperature and precipitation changes in a long-term, (iii) the future CO2 fluxes from Switchgrass land under different changing climate scenarios were not significantly different, therefore, it can be concluded that Switchgrass grown for longer durations could reduce changes in CO2 fluxes from soil as a result of temperature and precipitation changes to some extent. PMID:27155405

  13. Biogenic CO2 fluxes, changes in surface albedo and biodiversity impacts from establishment of a miscanthus plantation.

    PubMed

    Jørgensen, Susanne V; Cherubini, Francesco; Michelsen, Ottar

    2014-12-15

    Depletion in oil resources and environmental concern related to the use of fossil fuels has increased the interest in using second generation biomass as alternative feedstock for fuels and materials. However, the land use and land use change for producing second generation (2G) biomass impacts the environment in various ways, of which not all are usually considered in life cycle assessment. This study assesses the biogenic CO2 fluxes, surface albedo changes and biodiversity impacts for 100 years after changing land use from forest or fallow land to miscanthus plantation in Wisconsin, US. Climate change impacts are addressed in terms of effective forcing, a mid-point indicator which can be used to compare impacts from biogenic CO2 fluxes and albedo changes. Biodiversity impacts are assessed through elaboration on two different existing approaches, to express the change in biodiversity impact from one human influenced state to another. Concerning the impacts from biogenic CO2 fluxes, in the case of conversion from a forest to a miscanthus plantation (case A) there is a contribution to global warming, whereas when a fallow land is converted (case B), there is a climate cooling. When the effects from albedo changes are included, both scenarios show a net cooling impact, which is more pronounced in case B. Both cases reduce biodiversity in the area where the miscanthus plantation is established, though most in case A. The results illustrate the relevance of these issues when considering environmental impacts of land use and land use change. The apparent trade-offs in terms of environmental impacts further highlight the importance of including these aspects in LCA of land use and land use changes, in order to enable informed decision making. PMID:25194521

  14. Quantifying the magnitude, spatiotemporal variation and age of aquatic CO2 fluxes in western Greenland

    NASA Astrophysics Data System (ADS)

    Long, Hazel; Waldron, Susan; Hoey, Trevor; Garnett, Mark; Newton, Jason

    2015-04-01

    High latitude regions are experiencing accelerated atmospheric warming, and understanding the terrestrial response to this is of crucial importance as: a) permafrost soils hold vast amounts (1672 Pg; Tarnocai et al., 2009) of carbon (C) which may be released and feedback to climate change; and, b) ice sheet melt in this region is accelerating, and whilst this will cause albedo and heat flux changes, the role of this in atmospheric gas release is poorly known. To understand how sensitive arctic environments may respond to future warming, we need measurements that document current C flux rates and help to understand C cycling pathways. Although it has been widely hypothesised that Arctic regions may become increasingly significant C sources, the contribution of aquatic C fluxes which integrate catchment-wide sources has been little studied. Using a floating chamber method we directly measured CO2 fluxes from spatially distributed freshwaters (ice sheet melt, permafrost melt, and lakes/ponds) in the Kangerlussuaq region of western Greenland during the early part of the summer 2014 melt season. Fluxes from freshwaters with permafrost sources were in the range -3.15 to +1.28 μmol CO2 m-2 s-1. Fluxes from a river draining the ice sheet and the Russell Glacier were between -2.19 and +4.31 μmol CO2 m-2 s-1. These ranges show the systems can be both sources (efflux) and sinks (influx) of CO2. Much freshwater data worldwide shows CO2 efflux, and recording river/stream systems being a CO2 sink is unusual. Analysis of dissolved inorganic carbon (DIC) concentrations of the water sources revealed higher concentrations of DIC in the meltwater of permafrost systems (0.66-1.92 mmol) than the ice melt system (0.07 to 0.17 mmol), as well as differences in the carbon stable isotope ratio ranges (δ13C permafrost-melt, -9.5 to -1.2 permil; δ13C ice-melt, -11.7 to 7.3 permil). Where we recorded CO2 efflux we collected effluxed CO2 for radiocarbon analysis, and here we will present

  15. Regional flux analysis for discovering and quantifying anatomical changes: An application to the brain morphometry in Alzheimer's disease.

    PubMed

    Lorenzi, M; Ayache, N; Pennec, X

    2015-07-15

    In this study we introduce the regional flux analysis, a novel approach to deformation based morphometry based on the Helmholtz decomposition of deformations parameterized by stationary velocity fields. We use the scalar pressure map associated to the irrotational component of the deformation to discover the critical regions of volume change. These regions are used to consistently quantify the associated measure of volume change by the probabilistic integration of the flux of the longitudinal deformations across the boundaries. The presented framework unifies voxel-based and regional approaches, and robustly describes the volume changes at both group-wise and subject-specific level as a spatial process governed by consistently defined regions. Our experiments on the large cohorts of the ADNI dataset show that the regional flux analysis is a powerful and flexible instrument for the study of Alzheimer's disease in a wide range of scenarios: cross-sectional deformation based morphometry, longitudinal discovery and quantification of group-wise volume changes, and statistically powered and robust quantification of hippocampal and ventricular atrophy. PMID:25963734

  16. Increased Fluvial Dissolved Organic Carbon Fluxes over 130 Years of Land-Use Change in the Thames Basin

    NASA Astrophysics Data System (ADS)

    Noacco, V.; Howden, N. J. K.; Wagener, T.; Worrall, F.

    2014-12-01

    This study investigates drivers of changing dissolved organic carbon (DOC) export in the UK's River Thames basin between 1881 and 2011. Specifically, we consider how impacts of land-use change drive increases in DOC concentrations and fluxes at the basin outlet. First, we estimate soil organic carbon (SOC) stocks in the Thames basin for the period. Second, SOC losses due to land-use change are partitioned into DOC lost to surface waters through runoff, DOC leached into deeper soils and groundwater, and losses to the atmosphere as CO2. SOC stocks for each year are calculated from a large database of typical SOC levels for land-uses present in the Thames basin and are combined with literature values of transition times for SOC to adjust to a new level following land-use change. We also account for climate change effects on SOC stock due to temperature increases, which reduces SOC stocks as soil organic matter turnover rates increase. Soil carbon fluxes are calculated as the inter-annual change in SOC. We use a 130 year record of DOC concentration in the Thames, and parameters from previous long-term nitrate modeling, to constrain estimates of fluvial DOC rises caused by SOC losses. We developed a sewage model to evaluate the relative contribution of point and diffuse sources to the total DOC flux. The results show that sewage effluent point sources do not contribute to DOC concentration at the monitoring point, except for isolated periods of exceptionally low flow. Our work shows for the majority of years, diffuse sources are the main contributor to annual DOC loads. Moreover even though there are many small inter-annual variations in DOC concentration, the major change in both estimated SOC storage and fluvial DOC export occurred during WWII due to substantial changes in land-use, the legacy of which continues to date.

  17. Validating hydro-meteorological fluxes using GRACE-derived water storage changes - a global and regional perspective

    NASA Astrophysics Data System (ADS)

    Eicker, Annette; Springer, Anne; Kusche, Jürgen; Jütten, Thomas; Diekkrüger, Bernd; Longuevergne, Laurent

    2016-04-01

    Atmospheric and terrestrial water budgets, which represent important boundary conditions for both climate modeling and hydrological studies, are linked by evapotranspiration (E) and precipitation (P). These fields are provided by numerical weather prediction models and atmospheric reanalyses such as ERA-Interim and MERRA-Land; yet, in particular the quality of E is still not well evaluated. Via the terrestrial water budget equation, water storage changes derived from products of the Gravity Recovery and Climate Experiment (GRACE) mission, combined with runoff (R) data can be used to assess the realism of atmospheric models. While on short temporal scales (inter-annual down to sub-seasonal) the modeled fluxes agree remarkably well with GRACE water storage changes, the models exhibit large biases and fail to capture the long-term flux trends in P-E-R corresponding to GRACE accelerations (Eicker et al. 2016). This leads to the assumption that despite the short time span of available gravity field observations, GRACE is able to provide new information for constraining the long-term evolution of water fluxes in future atmospheric reanalyses. In this contribution we will investigate the agreement of GRACE water storage changes with P-E-R flux time series from different (global and regional) atmospheric reanalyses, land surface models, as well as observation-based data sets. We will perform a global analyses and we will additionally focus on selected river basins. The investigations will be carried out for various temporal scales, focussing on the short-term fluxes (month-to-month variations), for which models and GRACE agree well with correlations of the de-trended and de-seasoned fluxes time series reaching up to 0.8 and more. We will furthermore extent the study towards even higher temporal frequencies, investigating whether the modeled and observed fluxes show sub-monthly variability that can be detected in daily GRACE time series. Eicker, A., E. Forootan, A. Springer

  18. Major Subglacial Meltwater Channels Reveal Former Dynamic Ice Sheet in West Antarctica

    NASA Astrophysics Data System (ADS)

    Rose, Kathryn; Ross, Neil; Bingham, Robert; Corr, Hugh; Ferraccioli, Fausto; Jordan, Tom; LeBrocq, Anne; Rippin, David; Siegert, Martin

    2014-05-01

    The Eocene-Oligocene boundary (ca. 34 Ma) marks the onset of widespread, continental-scale glaciation in Antarctica, due to declining atmospheric carbon dioxide levels and the opening of the Drake Passage. The marine-based West Antarctic Ice Sheet (WAIS) is considered highly susceptible to change, experiencing numerous oscillations since its formation. In order to assess how past changes to the WAIS are relevant for understanding its future behaviour, it is important to comprehend the glaciological processes involved in those changes. Central to this is an appreciation of climate and ice flow regimes, in particular the extent to which former ice sheets have experienced surface melting (as in Greenland today). Geomorphic analysis of subglacial topography has played a key role in reconstructing the nature of former ice masses in Antarctica, as landscape form can be linked to glacial process. While radio-echo sounding (RES) is the primary tool used to map boundary conditions beneath ice sheets, recent developments have demonstrated that satellite imagery of the ice surface can provide insights into subglacial topography, where RES is unavailable. Using this combination of datasets, we have identified a series of major, elongate subglacial features, which we interpret as preserved subglacial channels, developed through the action of water. They are incised into a subglacial plateau in the region between the Möller and Foundation ice streams (MIS and FIS, respectively), in West Antarctica. The channels are observed across an area of ~17,700 km2 and extend 200 km inland from the grounding line. They are located below sea level and track over present-day reverse slopes, indicating a subglacial (rather than pre-glacial) fluvial origin. In order to form, these channels require significant, probably periodic (seasonal), meltwater inputs to the base of the ice sheet. We suggest the channels are the result of meltwater inputs to the subglacial environment from the ice surface

  19. 21st century projections of terrestrial carbon fluxes over Northern Eurasia: the role of land legacy, future land use change and future climate change

    NASA Astrophysics Data System (ADS)

    Monier, Erwan; Kicklighter, David; Sokolov, Andrei

    2015-04-01

    Northern Eurasia is a major player in the global carbon budget because of boreal forests and peatlands. Circumpolar boreal forests alone contain more than five times the amount of carbon of temperate forests and almost double the amount of carbon of the world's tropical forests. In this study, we investigate possible changes in terrestrial fluxes of carbon dioxide over Northern Eurasia over the 21st century. We estimate the contributions of land legacy, future land use change and future climate change. We present three sets of simulations of terrestrial fluxes of carbon dioxide over Northern Eurasia from 1500 to 2100 using the MBL Terrestrial Ecosystem Model (TEM), a process-based ecosystem/biogeochemistry model: (1) fixed land cover corresponding to year 2005; (2) historical land use land cover change from 1500 to 2005 and fixed land cover corresponding to year 2005 until 2100; (3) historical land use land cover change from 1500 to 2005 and RCP land use land cover change scenarios until 2100. Each set of simulations is forced by a large ensemble of climate simulations using the MIT IGSM-CAM model, which accounts for the uncertainty in projections of future climate change in order to obtain robust estimates of the contribution of land legacy, land use change and climate change. The climate ensemble consists of: two emissions scenarios, a "business as usual" unconstrained emissions scenario and a stabilization scenario, similar to, respectively, the RCP8.5 and RCP4.5 scenarios; three values of climate sensitivity (2.0°C, 2.5°C and 4.5°C corresponding to the 5th percentile, median, and 95th percentile of the marginal posterior probability density function with uniform prior) and associated net aerosol forcing chosen to best reproduce observed climate change; and five different representations of natural variability. The results of this study provide new insight on projections of future terrestrial carbon fluxes over Northern Eurasia.

  20. No minimum threshold for ozone-induced changes in soybean canopy fluxes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Tropospheric ozone concentrations [O3] are increasing at rates that exceed any other pollutant. This highly reactive gas drives reductions in plant productivity and canopy water use while also increasing canopy temperature and sensible heat flux. It is not clear whether a minimum threshold of ozone ...

  1. Vadose zone monitoring strategies to control water flux dynamics and changes in soil hydraulic properties.

    NASA Astrophysics Data System (ADS)

    Valdes-Abellan, Javier; Jiménez-Martínez, Joaquin; Candela, Lucila

    2013-04-01

    ROSETTA based on soil textural fractions. Simulation of water flow using automatic and non-automatic date was carried out by HYDRUS-1D independently. A good agreement from collected automatic and non-automatic data and modelled results can be recognized. General trend was captured, except for the outlier values as expected. Slightly differences were found between hydraulic properties obtained from laboratory determinations, and from inverse modelling from the two approaches. Differences up to 14% of flux through the lower boundary were detected between the two strategies According to results, automatic sensors have more resolution and then they're more appropriated to detect subtle changes of soil hydraulic properties. Nevertheless, if the aim of the research is to control the general trend of water dynamics, no significant differences were observed between the two systems.

  2. In Situ Data Suggest Supra-, En- and/or Subglacial Meltwater Retention in Southwest Greenland

    NASA Astrophysics Data System (ADS)

    Rennermalm, A. K.; Mikkelsen, A. B.; van As, D.; Overeem, I.; Smith, L. C.; Chu, V.; Nienow, P. W.; Tedstone, A.

    2013-12-01

    To accurately determine the Greenland ice sheet contribution to raising global sea levels, a better understanding of how much surface meltwater is retained is needed. It is possible to calculate catchment meltwater retention from land-terminating outlet glaciers with an input/output method. In this paper, this method is used to determine meltwater retention within the large Watson River catchment in Southwest Greenland using runoff calculated with a surface energy balance model relying on input data from three on-ice automatic weather stations, and river discharge datasets from three nested ice sheet catchments (60 - 9750 km2) for 2008 - 2012. By using data from three nested basins of different sizes, an understanding of spatial distribution can be obtained. This analysis indicates that meltwater retention in supra-, en-, and/or subglacial environments may take place both below 800 m a.s.l, near the margin, and above 800 m a.s.l, in the interior region of the ice sheet.

  3. Deformation, warming and softening of Greenland’s ice by refreezing meltwater

    NASA Astrophysics Data System (ADS)

    Bell, Robin E.; Tinto, Kirsteen; Das, Indrani; Wolovick, Michael; Chu, Winnie; Creyts, Timothy T.; Frearson, Nicholas; Abdi, Abdulhakim; Paden, John D.

    2014-07-01

    Meltwater beneath the large ice sheets can influence ice flow by lubrication at the base or by softening when meltwater refreezes to form relatively warm ice. Refreezing has produced large basal ice units in East Antarctica. Bubble-free basal ice units also outcrop at the edge of the Greenland ice sheet, but the extent of refreezing and its influence on Greenland’s ice flow dynamics are unknown. Here we demonstrate that refreezing of meltwater produces distinct basal ice units throughout northern Greenland with thicknesses of up to 1,100 m. We compare airborne gravity data with modelled gravity anomalies to show that these basal units are ice. Using radar data we determine the extent of the units, which significantly disrupt the overlying ice sheet stratigraphy. The units consist of refrozen basal water commonly surrounded by heavily deformed meteoric ice derived from snowfall. We map these units along the ice sheet margins where surface melt is the largest source of water, as well as in the interior where basal melting is the only source of water. Beneath Petermann Glacier, basal units coincide with the onset of fast flow and channels in the floating ice tongue. We suggest that refreezing of meltwater and the resulting deformation of the surrounding basal ice warms the Greenland ice sheet, modifying the temperature structure of the ice column and influencing ice flow and grounding line melting.

  4. Meltwater flood landforms created beneath a Miocene ice sheet, Transantarctic Mountains

    NASA Astrophysics Data System (ADS)

    Sugden, D.; Denton, G.

    2005-12-01

    We illustrate spectacular meltwater landforms associated with an ice sheet that overrode the Transantarctic Mountains in southern Victoria Land around 14 million years ago. Subglacial channels systems commonly originate near divides and converge downhill toward the northeast. One channel system in the Convoy Range is more than 30 km long and drops about 1000 m in elevation. High-elevation divides in sandstone cols show ice sculpturing, with flow toward the northeast. Bedrock in leeside slopes and platforms is commonly stripped of unconsolidated deposits and bears corrugations, potholes, plunge pools and scabland. We conclude that a major Antarctic Ice Sheet submerged the area as it flowed northeastward toward the outer Antarctic continental shelf. The meltwater landforms and scabland with preserved patches of regolith are best explained by the breaching of cold-based ice on the mountain rim by subglacial meltwater outbursts. Melt from warm-based ice, along with subglacial lakes trapped upstream of the mountain rim, are possible sources of the meltwater necessary to form the channel systems and scablands.

  5. Chemical characterisation of meltwater draining from Gangotri Glacier, Garhwal Himalaya, India

    NASA Astrophysics Data System (ADS)

    Singh, Virendra Bahadur; Ramanathan, Al; Pottakkal, Jose George; Sharma, Parmanand; Linda, Anurag; Azam, Mohd Farooq; Chatterjee, C.

    2012-06-01

    A detailed analytical study of major cations (Ca2 + , Mg2 + , Na + , K + ) and anions (SO4^{2-}, HCO3-, Cl - , NO3-) of meltwater draining from Gangotri Glacier was carried out to understand major ion chemistry and to get an insight into geochemical weathering processes controlling hydrochemistry of the glacier. In the meltwater, the abundance order of cations and anions varied as follows: Ca2 + > Mg2 + > K + > Na + and SO4^{2-} > HCO3- > Cl - > NO3-, respectively. Calcium and magnesium are dominant cations while sulphate and bicarbonate are dominant anions. Weathering of rocks is the dominant mechanism controlling the hydrochemistry of drainage basin. The relative high contribution of (Ca+Mg) to the total cations (TZ + ), high (Ca+Mg)/(Na+K) ratio (2.63) and low (Na+K)/TZ + ratio (0.29) indicate the dominance of carbonate weathering as a major source for dissolved ions in the glacier meltwater. Sulphide oxidation and carbonation are the main proton supplying geochemical reactions controlling the rock weathering in the study area. Statistical analysis was done to identify various factors controlling the dissolved ionic strength of Gangotri Glacier meltwater.

  6. Solute, Discharge, and Nutrient Dynamics at Sub-daily Timescales in Glacial Meltwater Streams of the McMurdo Dry Valleys

    NASA Astrophysics Data System (ADS)

    Bernzott, E. D.; Gooseff, M. N.; McKnight, D. M.

    2011-12-01

    In the McMurdo Dry Valleys, Antarctica, streams and their hyporheic zones are responsible for the translation and evolution of meltwater, solutes, and nutrients from glacier sources to closed basin lakes. Streamflow in the Dry Valleys is highly variable on a sub-daily timescale due to fluctuating meteorological conditions, particularly the availability of solar radiation for meltwater generation. Flow seasons last for 6-12 weeks and there is substantial variability in daily discharge cycles throughout the season. Dissolved nitrate in Dry Valley streams comes from mineralization and atmospheric deposition, and is taken up by benthic algal mats and hyporheic microbes. We propose that stream discharge and hyporheic exchange are primary controls on stream nutrient concentrations. We calculated solute fluxes using long-term discharge and electrical conductivity data, reported at 15-minute intervals, at several permanent gauge sites in Taylor Valley. Relationships between nitrate concentrations and discharge were computed using samples retrieved approximately weekly throughout each flow season. These data were supplemented by 2-3 day deployments of a Submersible Nitrate Analyzer (SUNA) in several streams, which recorded nitrate concentrations on 15-minute intervals. Solute concentrations generally increased with increasing discharge, indicating a strong hyporheic interaction at higher discharges. Analysis of fluctuations in nitrate concentrations indicates a more complex relationship. Algal mats respond differently to wetting as the season progresses, adding a seasonal component to the relationship. This is complicated further by the compound effects of solar radiation on photosynthesis and melt, which are sub-daily fluctuations occurring at different timescales.

  7. Is the Wilkins Ice Shelf a Firn Aquifer? Spaceborne Observation of Subsurface Winter Season Liquid Meltwater Storage on the Antarctic Peninsula using Multi-Frequency Active and Passive Microwave Remote Sensing

    NASA Astrophysics Data System (ADS)

    Miller, J.; Scambos, T.; Forster, R. R.; Long, D. G.; Ligtenberg, S.; van den Broeke, M.; Vaughan, D. G.

    2015-12-01

    Near-surface liquid meltwater on ice shelves has been inferred to influence ice shelf stability if it induces hydrofracture and is linked to disintegration events on the Larsen B and the Wilkins ice shelves on the Antarctic Peninsula during the summer months. While the initial Wilkins disintegration event occurred in March of 2009, two smaller disintegration events followed in May and in July of that year. It has long been assumed meltwater refreezes soon after surface melt processes cease. Given this assumption, an earlier hypothesis for the two winter season disintegration events was hydrofracture via a brine infiltration layer. Two lines of evidence supported this hypothesis 1) early airborne radar surveys did not record a reflection from the bottom of the ice shelf, and 2) a shallow core drilled in 1972 on the Wilkins encountered liquid water at a depth of ~7 m. The salinity of the water and the temperature at the base of the core, however, were not described. The recent discovery of winter season liquid meltwater storage on the Greenland ice sheet has changed perceptions on meltwater longevity at depth in firn. Evidence of Greenland's firn aquifer includes liquid meltwater encountered in shallow firn cores at 5 m depth and a lack of reflections from the base of the ice sheet in airborne surveys. Thus, previous lines of evidence suggesting brine infiltration may alternatively suggest the presence of a perennial firn aquifer. We recently demonstrated the capability for observation of Greenland's firn aquifer from space using multi-frequency active and passive microwave remote sensing. This research exploits the retrieval technique developed for Greenland to provide the first spaceborne mappings of winter season liquid meltwater storage on the Wilkins. We combine L-band brightness temperature and backscatter data from the MIRAS instrument (1.4 GHz) aboard ESA's Soil Moisture and Ocean Salinity mission and the radar (1.3 GHZ) and radiometer(1.4 GHz) aboard NASA

  8. Changes In CO2 Gas Flux And Soil Temperatures Induced By A Vibratory Seismic Source At Solfatara (Phlegrean Fields, Italy).

    NASA Astrophysics Data System (ADS)

    Vandemeulebrouck, J.; Gresse, M.; Chiodini, G.; Byrdina, S.; Woith, H.; Bruno, P. P.

    2014-12-01

    Solfatara, the most active crater of Phlegrean Fields (Italy) is characterized by a fumarolic activity and an intense diffuse degassing, with 1500 tons of CO2 and > 3000 tons of water vapor released per day. A major part of the emitted water vapor is condensed at the near surface producing a thermal power flux around 100 MW, and contributing substantially to the total water input into the hydrothermal system. On May 2014, during a seismic experiment (RICEN) in the frame of the MED-SUV European project, a Minivib vibratory seismic source was used to generate a frequency modulated seismic signal at different points of Solfatara. We performed CO2 flux measurements at a few meters from the seismic source during the vibrations. In certain points, the vibrations induced a remarkable increase in the CO2 diffuse degassing, with a flux that doubled during the low-frequency seismic vibrations and returned to previous values afterwards. The observed CO2 flux increase could be due to permeability enhancement in the sub-surface soil layers during the seismic vibrations. Close to Fangaia mud pool, we also monitored the soil temperature at different levels above the condensation depth and observed transient temperature changes during the vibrations but also outside the vibration periods. Seismic vibrations likely favor the triggering of thermal instabilities of gravitational or convective origin in the liquid-saturated condensate layer.

  9. Riverine nutrients fluxes to the North Sea and harmful algal blooms, what changed since 1984 ?

    NASA Astrophysics Data System (ADS)

    Passy, Paul; Gypens, Nathalie; Billen, Gilles; Garnier, Josette; Thieu, Vincent; Rousseau, Véronique; Callens, Julie; Parent, Jean-Yves; Lancelot, Christiane

    2013-04-01

    Nutrients fluxes delivered to the coastal zones reflect human activities taking place within watersheds. Silica (Si) fluxes mainly originate from soils and rocks weathering, so they are few impacted by human activities. On the contrary, nitrogen (N) and phosphorus (P) fluxes are dramatically impacted by human activities. N originates from urban waste water but mainly from agricultural activities. P originates mostly from urban and industrial waste waters. The enrichment of the hydrosystems in N and P leads to an imbalance between N and P in one hand and Si in the other hand. This imbalance leads to harmful algal blooms, which are damaging aquatic ecosystems, fishing activities and touristic activities. In 1992, the OSPAR convention was signed by 15 European States and targets to decrease the N and P fluxes delivered to the European coastal zones by 50 % with respect to the reference year of 1985. Focusing on the Seine, Somme and Scheldt watersheds (France and Belgium) and the adjacent coastal zone of the North Sea, we developed a retrospective modelling from 1984 to 2007 calculating nutrients fluxes from watersheds and Phaeocystis blooms occurring in the coastal zone. We coupled the biogeochemical deterministic model Seneque/Riverstrahler depicting processes occurring within hydrological networks with the marine model MIRO simulating Phaeocystis blooms in the coastal zone. The evolution of N and P fluxes were highly dissimilar. Indeed, P mainly originates from point sources. Thereby the banishment of P from the washing powders during the nineties, the development of sewage and the improvement of WWTP in terms of waste water treatment lead to a decrease of P fluxes delivered to the coastal zone. This decrease can be observed for the three watersheds. The P OSPAR objective is achieved since the middle of the 2000's years. On the other side, N, mostly originating from agricultural diffuse sources, did not decrease over the period. The fluxes even increased at the

  10. Water Resources in a Peruvian Mountain Watershed: Hydrochemical Tracing of Groundwater and Glacier Meltwater Impact on Streamflow

    NASA Astrophysics Data System (ADS)

    McKenzie, J. M.; Mark, B. G.

    2005-12-01

    The Callejon de Huaylas, Peru, is a large (~5000 km2; elevation range from ~1800 to 1650 masl) drainage basin for the Rio Santa, which is fed by the glacierized Cordillera Blanca and the non-glacierized Cordillera Negra. The region is well-populated, with extensive agricultural diversity and natural resources, but currently receding glaciers are threatening the future water supply. During the dry season (May to September) glacial melt water from the Cordillera Blanca partially buffers stream-flow, although the magnitude of this effect is not easily measured. We attempt to evaluate the relative contribution of glacier meltwater and groundwater to the regional stream discharge, from 1st order basins to the whole watershed. In July, 2004 and July, 2005 we collected 89 water samples from streams, springs, and groundwater within the Callejon de Huaylas and analyzed for major dissolved ions and the isotopes of oxygen and hydrogen. The water generally has a Ca-Mg-HCO3 chemical signal, consistent with the regional geology. Preliminary δ18O and δD values range from -15.6‰ to -4.9‰ and -113‰ to -51.3‰ respectively. Transects of surface water samples from Cordillera Blanca glaciers to the Rio Santa show isotopic enrichment with lower elevation. We sampled 14 groundwater wells and springs, and found the isotopic composition of the water to be isotopically enriched and very similar to surface water within the Cordillera Negra. The Rio Santa is a mixture of Cordillera Blanca and Cordillera Negra surface waters, and the down gradient transect becomes relatively depleted with lower elevation, possibly due to the distribution of glacier mass in the Cordillera Blanca. This research is the beginning of a long term water sampling and monitoring program to identify unique geochemical end-members for quantification of glacier meltwater and groundwater contributions and to assess changes in the hydrologic balance within the Callejon de Huaylas as a result of glacier recession.

  11. Measuring Bedload Sediment Flux in Large Rivers: New Data from the Mekong River and Its Applications in Assessing Geomorphic Change

    NASA Astrophysics Data System (ADS)

    Best, J.; Hackney, C. R.; Parsons, D. R.; Darby, S. E.; Leyland, J.; Aalto, R. E.; Nicholas, A. P.

    2014-12-01

    Many large rivers are undergoing renewed and increasing anthropogenic-induced change as water diversions, new dams and greater water demands place enhanced stresses on these river basins. Examples of rivers undergoing significant change include the Amazon, Madeira, Nile, Yangtze and Mekong, with considerable ongoing debate raging as to the long-term geomorphic and ecological effects of major anthropogenic interventions. Assessing the effects of such change in large rivers is demanding, one reason being that sediment transport is often exceedingly difficult to measure, and thus data needed to inform the debate on the impact of anthropogenic change is frequently lacking. Here, we report on one aspect of research being undertaken as part of STELAR-S2S - Sediment Transfer and Erosion on Large Alluvial Rivers - that is seeking to better understand the relationship between climate, anthropogenic impacts and sediment transport in some of the world's largest rivers. We are using the Lower Mekong River as our study site, with the Mekong delta being one of only three in the world classified by the IPCC as 'extremely vulnerable' to future changes in climate. Herein, we describe details of bedload sediment flux estimation using repeated high-resolution multibeam echo sounder (MBES) bathymetric mapping along the Lower Mekong and Tonle Sap rivers in Cambodia. We are using MBES to quantify the spatial variation in sediment transport both along and also across the river at 11 sites in the study area. Predicted increases in the extraction of sediment from the river through sand dredging are thought likely to cause a significant decrease in downstream sediment flux, and future dam construction along the Mekong main channel potentially offers another source of significant change. These field results will be set in the light of these anthropogenic drivers on sediment flux in the Mekong River and their possible future effects on bar formation and channel migration.

  12. Subglacial source of meltwater discharge in an emerging ice-marginal channel, Bering Glacier, Alaska

    SciTech Connect

    Priscott, G.; Fleisher, P.J. . Dept. of Earth Sciences)

    1993-03-01

    The retreating eastern margin of Bering Piedmont Glacier terminates in two ice-contact lakes separated by an island that has been uncovered in the last decade. A semi-continuous aerial photo record (1978--1991) and field observations (1992) confirms a newly-developed ice-marginal channel linking these two lakes that is fed by a persistent subglacial conduit system. This investigation documents channel characteristic, discharge, turbidity, water temperature and the location of the present ice margin. Bathymetry along the channel reveals a highly irregular profile consisting of low-gradient reaches 3--5 m deep interrupted by shallow sills (< 1 m) of grounded, subaqueous ice and a 40 m basin among ice islands. Channel dimensions measured in 5 cross section reveal abrupt, small-scale changes typical of sub-bottom ice. Discharge varies from 72.24 cms near a node of upwelling to 40.38 cms 2 km down stream, then back up to 42.25 cms within 0.4 km, where the channel enters a lake. Turbidity values between 1.67 g/l and 4.20 g/l, of 10 water samples vary irregularly along the channel and with depth at-a-station. Early July water temperatures from 7 widely-spaced locations indicate the thermocline occurs at depths from 1 to 3 m and separates surface water at +1.1 C from supercooled water at [minus]1.0 C. Clusters of in situ platy frazil ice crystals several centimeters in diameter were observed on floating ice in the area of upwelling supercooled water. The presence of upwelling, highly-turbid, supercooled water indicates that the primary meltwater source is a subglacial conduit network at the ice margin, from which flow separates and discharges through a leaky channel into both lakes.

  13. Changes in deep-sea carbonate-hosted microbial communities associated with high and low methane flux

    NASA Astrophysics Data System (ADS)

    Case, D. H.; Steele, J. A.; Chadwick, G.; Mendoza, G. F.; Levin, L. A.; Orphan, V. J.

    2012-12-01

    Methane seeps on continental shelves are rich in authigenic carbonates built of methane-derived carbon. These authigenic carbonates are home to micro- and macroscopic communities whose compositions are thus far poorly constrained but are known to broadly depend on local methane flux. The formation of authigenic carbonates is itself a result of microbial metabolic activity, as associations of anaerobic methane oxidizing archaea (ANME) and sulfate reducing bacteria (SRB) in the sediment subsurface increase both dissolved inorganic carbon (DIC) and alkalinity in pore waters. This 1:1 increase in DIC and alkalinity promotes the precipitation of authigenic carbonates. In this study, we performed in situ manipulations to test the response of micro- and macrofaunal communities to a change in methane flux. Methane-derived authigenic carbonates from two locations at Hydrate Ridge, OR, USA (depth range 595-604 mbsl), were transplanted from "active" cold seep sites (high methane flux) to "inactive" background sites (low methane flux), and vise versa, for one year. Community diversity surveys using T-RFLP and 16S rRNA clone libraries revealed how both bacterial and archaeal assemblages respond to this change in local environment, specifically demonstrating reproducible shifts in different ANME groups (ANME-1 vs. ANME-2). Animal assemblage composition also shifted during transplantation; gastropod representation increased (relative to control rocks) when substrates were moved from inactive to active sites and polychaete, crustacean and echinoderm representation increased when substrates were moved from active to inactive sites. Combined with organic and inorganic carbon δ13C measurements and mineralogy, this unique in situ experiment demonstrates that authigenic carbonates are viable habitats, hosting microbial and macrofaunal communities capable of responding to changes in external environment over relatively short time periods.

  14. Changes of soil carbon dioxide, methane, and nitrous oxide fluxes in relation to land use/cover management.

    PubMed

    Kooch, Yahya; Moghimian, Negar; Bayranvand, Mohammad; Alberti, Giorgio

    2016-06-01

    Conversions of land use/cover are associated with changes in soil properties and biogeochemical cycling, with implications for carbon (C), nitrogen (N), and trace gas fluxes. In an attempt to provide a comprehensive evaluation of the significance of different land uses (Alnus subcordata plantation, Taxodium distichum plantation, agriculture, and deforested areas) on soil features and on the dynamics of greenhouse gas (GHG) fluxes at local scale, this study was carried out in Mazandaran province, northern Iran. Sixteen samples per land use, from the top 10 cm of soil, were taken, from which bulk density, texture, water content, pH, organic C, total N, microbial biomass of C and N, and earthworm density/biomass were determined. In addition, the seasonal changes in the fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were monitored over a year. Our results indicated that the different land uses were different in terms of soil properties and GHG fluxes. Even though the amount of the GHG varied widely during the year, the highest CO2 and CH4 fluxes (0.32 mg CO2 m(-2) day(-1) and 0.11 mg CH4 m(-2) day(-1), respectively) were recorded in the deforested areas. N2O flux was higher in Alnus plantation (0.18 mg N2O m(-2) day(-1)) and deforested areas (0.17 mg N2O m(-2) day(-1)) than at agriculture site (0.05 mg N2O m(-2) day(-1)) and Taxodium plantation (0.03 mg N2O m(-2) day(-1)). This study demonstrated strong impacts of land use change on soil-atmosphere trace gas exchanges and provides useful observational constraints for top-down and bottom-up biogeochemistry models. PMID:27173683

  15. Changing fluxes of carbon and other solutes from the Mekong River

    PubMed Central

    Li, Siyue; Bush, Richard T.

    2015-01-01

    Rivers are an important aquatic conduit that connects terrestrial sources of dissolved inorganic carbon (DIC) and other elements with oceanic reservoirs. The Mekong River, one of the world’s largest rivers, is firstly examined to explore inter-annual fluxes of dissolved and particulate constituents during 1923–2011 and their associated natural or anthropogenic controls. Over this period, inter-annual fluxes of dissolved and particulate constituents decrease, while anthropogenic activities have doubled the relative abundance of SO42−, Cl− and Na+. The estimated fluxes of solutes from the Mekong decrease as follows (Mt/y): TDS (40.4) > HCO3− (23.4) > Ca2+ (6.4) > SO42− (3.8) > Cl− (1.74)~Na+ (1.7) ~ Si (1.67) > Mg2+ (1.2) > K+ (0.5). The runoff, land cover and lithological composition significantly contribute to dissolved and particulate yields globally. HCO3− and TDS yields are readily predicted by runoff and percent of carbonate, while TSS yield by runoff and population density. The Himalayan Rivers, including the Mekong, are a disproportionally high contributor to global riverine carbon and other solute budgets, and are of course underlined. The estimated global riverine HCO3− flux (Himalayan Rivers included) is 34014 × 109 mol/y (0.41 Pg C/y), 3915 Mt/y for solute load, including HCO3−, and 13553 Mt/y for TSS. Thereby this study illustrates the importance of riverine solute delivery in global carbon cycling. PMID:26522820

  16. Changing fluxes of carbon and other solutes from the Mekong River.

    PubMed

    Li, Siyue; Bush, Richard T

    2015-01-01

    Rivers are an important aquatic conduit that connects terrestrial sources of dissolved inorganic carbon (DIC) and other elements with oceanic reservoirs. The Mekong River, one of the world's largest rivers, is firstly examined to explore inter-annual fluxes of dissolved and particulate constituents during 1923-2011 and their associated natural or anthropogenic controls. Over this period, inter-annual fluxes of dissolved and particulate constituents decrease, while anthropogenic activities have doubled the relative abundance of SO4(2-), Cl(-) and Na(+). The estimated fluxes of solutes from the Mekong decrease as follows (Mt/y): TDS (40.4) > HCO3(-) (23.4) > Ca(2+) (6.4) > SO4(2-) (3.8) > Cl(-) (1.74)~Na(+) (1.7) ~ Si (1.67) > Mg(2+) (1.2) > K(+ 0.5). The runoff, land cover and lithological composition significantly contribute to dissolved and particulate yields globally. HCO3(-) and TDS yields are readily predicted by runoff and percent of carbonate, while TSS yield by runoff and population density. The Himalayan Rivers, including the Mekong, are a disproportionally high contributor to global riverine carbon and other solute budgets, and are of course underlined. The estimated global riverine HCO3(-) flux (Himalayan Rivers included) is 34,014 × 10(9) mol/y (0.41 Pg C/y), 3915 Mt/y for solute load, including HCO3(-), and 13,553 Mt/y for TSS. Thereby this study illustrates the importance of riverine solute delivery in global carbon cycling. PMID:26522820

  17. Changing fluxes of carbon and other solutes from the Mekong River

    NASA Astrophysics Data System (ADS)

    Li, Siyue; Bush, Richard T.

    2015-11-01

    Rivers are an important aquatic conduit that connects terrestrial sources of dissolved inorganic carbon (DIC) and other elements with oceanic reservoirs. The Mekong River, one of the world’s largest rivers, is firstly examined to explore inter-annual fluxes of dissolved and particulate constituents during 1923-2011 and their associated natural or anthropogenic controls. Over this period, inter-annual fluxes of dissolved and particulate constituents decrease, while anthropogenic activities have doubled the relative abundance of SO42-, Cl- and Na+. The estimated fluxes of solutes from the Mekong decrease as follows (Mt/y): TDS (40.4) > HCO3- (23.4) > Ca2+ (6.4) > SO42- (3.8) > Cl- (1.74)~Na+ (1.7) ~ Si (1.67) > Mg2+ (1.2) > K+ (0.5). The runoff, land cover and lithological composition significantly contribute to dissolved and particulate yields globally. HCO3- and TDS yields are readily predicted by runoff and percent of carbonate, while TSS yield by runoff and population density. The Himalayan Rivers, including the Mekong, are a disproportionally high contributor to global riverine carbon and other solute budgets, and are of course underlined. The estimated global riverine HCO3- flux (Himalayan Rivers included) is 34014 × 109 mol/y (0.41 Pg C/y), 3915 Mt/y for solute load, including HCO3-, and 13553 Mt/y for TSS. Thereby this study illustrates the importance of riverine solute delivery in global carbon cycling.

  18. Fluxes of N2O and CH4 from forest and grassland lysimeter soils in response to simulated climate change

    NASA Astrophysics Data System (ADS)

    Weymann, Daniel; Brueggemann, Nicolas; Puetz, Thomas; Vereecken, Harry

    2015-04-01

    Central Europe is expected to be exposed to altered temperature and hydrological conditions, which will affect the vulnerability of nitrogen and carbon cycling in soils and thus production and fluxes of climate relevant trace gases. However, knowledge of the response of greenhouse gas fluxes to climate change is limited so far, but will be an important basis for future climate projections. Here we present preliminary results of an ongoing lysimeter field study which aims to assess the impact of simulated climate change on N2O and CH4 fluxes from a forest and a fertilized grassland soil. The lysimeters are part of the Germany-wide research infrastructure TERENO, which investigates feedbacks of climate change to the pedosphere on a long-term scale. Lysimeters (A = 1m2) were established in 2010 at high elevated sites (HE, 500 and 600 m.a.s.l.) and subsequently transferred along an altitudinal gradient to a low elevated site (LE, 100 m.a.s.l.) within the Eifel / Lower Rhine Valley Observatory in Western Germany, thereby resulting in a temperature increase of 2.3 K whereas precipitation decreased by 160 mm during the present study period. Systematic monitoring of soil-atmosphere exchange of N2O and CH4 based on weekly manual closed chamber measurements at HE and LE sites has started in August 2013. Furthermore, we routinely determine dissolved N2O and CH4 concentrations in the seepage water using a headspace equilibration technique and record water discharge in order to quantify leaching losses of both greenhouse gases. Cumulative N2O fluxes clearly responded to simulated climate change conditions and increased by 250 % and 600 % for the forest and the grassland soil, respectively. This difference between the HE and LE sites was mainly caused by an exceptionally heavy precipitation event in July 2014 which turned the LE site sustainably to a consistently higher emission level. Nonetheless, emissions remained rather small and ranged between 20 and 40 μg m-2 h-1. In

  19. History of Laurentide meltwater flow to the Gulf of Mexico during the last deglaciation, as revealed by reworked calcareous nannofossils

    NASA Astrophysics Data System (ADS)

    Marchitto, Thomas M.; Wei, Kuo-Yen

    1995-09-01

    The history of meltwater flow from the Laurentide Ice Sheet to the Gulf of Mexico during the last deglaciation, which holds possible implications for the cause of the Younger Dryas cold episode, is not well understood. We propose a new chronology based on using the percentage of reworked calcareous nannofossils in Orca Basin sediments as a proxy for erosion. The period of greatest meltwater flow to the gulf was between 12.7 and 12.1 ka (during the Bølling warm interval), and flow remained high until the beginning of the Younger Dryas cold episode at 11.3 ka; this corresponds to meltwater pulse IA. A sharp meltwater decrease at 12.2 ka may represent the Older Dryas glacial readvance. Little or no meltwater is inferred to have flowed to the gulf from ˜10 to 9 ka, which is the time of the second major meltwater pulse, IB. Therefore, meltwater must have been permanently diverted away from the Gulf of Mexico at the beginning of the Younger Dryas.

  20. How can research on anthropogenic greenhouse gas flux quantification be better aligned with US climate change policy needs?

    NASA Astrophysics Data System (ADS)

    Gurney, K. R.

    2014-12-01

    Scientific research on quantification of anthropogenic greenhouse gas emissions at national and sub-national scales within the US has advanced considerably in the last decade. Large investment has been made in building systems capable of observing greenhouse gases in the atmosphere at multiple scales, measuring direct anthropogenic fluxes near sources and modeling the linkages between fluxes and observed concentrations. Much of this research has been focused at improving the "verification" component of "monitoring, reporting, and verification" and indeed, has achieved successes in recent years. However, there are opportunities for ongoing scientific research to contribute critical new information to policymakers. In order to realize this contribution, additional but complementary, research foci must be emphasized. Examples include more focus on anthropogenic emission drivers, quantification at scales relevant to human decision-making, and exploration of cost versus uncertainty in observing/modeling systems. I will review what I think are the opportunities to better align scientific research with current and emerging US climate change policymaking. I will then explore a few examples of where expansion or alteration of greenhouse gas flux quantification research focus could better align with current and emerging US climate change policymaking such as embodied in the proposed EPA rule aimed at reducing emissions from US power plants, California's ongoing emissions reduction policymaking and aspirational emission reduction efforts in multiple US cities.

  1. Seasonal to interannual depth-dependent changes in phosphorus flux in Cariaco Basin, Venezuela

    NASA Astrophysics Data System (ADS)

    Benitez-Nelson, C. R.; O'Neill, L.; Thunell, R.

    2004-12-01

    One of the major removal pathways of phosphorus (P) from the water column is through the formation, sinking, and burial of particles formed during marine biological production. Yet the flux of P containing particles to the seafloor remains one of the least studied components of the P cycle. In this study, particulate inorganic P (PIP) and particulate organic P (POP) fluxes were measured in a series of samples collected from sediment traps ranging in depth from 275 to 1255 m from November 1995 - November 2002 in Cariaco Basin, Venezuela. PIP concentrations averaged 40- 60 % (depending on depth) of the total particulate P (TPP) measured in the traps. PIP fluxes decreased by 75 % between the surface and deep waters, from a median of 28.6 to 6.3 \\mu mol m-2 d-1, whereas POP fluxes decreased by only 50 %, from 17.2 to 8.5 \\mu mol m-2 d-1. TPP, PIP and POP all vary seasonally and higher fluxes follow higher production during the upwelling season from late January to April. The relationship between particulate organic C (POC) and POP is relatively constant (POC:POP = 283) throughout the entire water column over the entire period (r2 = 0.58). However, there is a much tighter relationship between POP and POC in upwelling (January through April, r2 = 0.85) versus non upwelling (May through December, r2 = 0.40) seasons. Furthermore, upwelling, and hence higher production appears to be associated with higher POC:POP ratios (327 versus 258 in non upwelling periods). Higher than Redfield POC:POP ratios may indicate that preferential release of P containing organic matter is occurring, but if true, it is restricted to the upper 250 m of the water column above the shallowest sediment trap. An alternative explanation may be that the composition of plankton in the Cariaco Basin does not conform to the Redfield-ratio. Plankton tow samples collected over the upper 200 m with a > 200 um mesh had POC:POP ratios of 294 +/- 38. However, there is no other evidence that the euphotic zone

  2. Changes in Moisture Flux over the Tibetan Plateau during 1979-2011: Insights from a High Resolution Simulation

    SciTech Connect

    Gao, Yanhong; Leung, Lai-Yung R.; Zhang, Yongxin; Cuo, Lan

    2015-05-15

    Net precipitation (precipitation minus evapotranspiration, P-E) changes between 1979 and 2011 from a high resolution regional climate simulation and its reanalysis forcing are analyzed over the Tibet Plateau (TP) and compared to the global land data assimilation system (GLDAS) product. The high resolution simulation better resolves precipitation changes than its coarse resolution forcing, which contributes dominantly to the improved P-E change in the regional simulation compared to the global reanalysis. Hence, the former may provide better insights about the drivers of P-E changes. The mechanism behind the P-E changes is explored by decomposing the column integrated moisture flux convergence into thermodynamic, dynamic, and transient eddy components. High-resolution climate simulation improves the spatial pattern of P-E changes over the best available global reanalysis. High-resolution climate simulation also facilitates new and substantial findings regarding the role of thermodynamics and transient eddies in P-E changes reflected in observed changes in major river basins fed by runoff from the TP. The analysis revealed the contrasting convergence/divergence changes between the northwestern and southeastern TP and feedback through latent heat release as an important mechanism leading to the mean P-E changes in the TP.

  3. A coupled carbon and plant hydraulic model to predict ecosystem carbon and water flux responses to disturbance and environmental change

    NASA Astrophysics Data System (ADS)

    Mackay, D. S.; Ewers, B. E.; Roberts, D. E.; McDowell, N. G.; Pendall, E.; Frank, J. M.; Reed, D. E.; Massman, W. J.; Mitra, B.

    2011-12-01

    Changing climate drivers including temperature, humidity, precipitation, and carbon dioxide (CO2) concentrations directly control land surface exchanges of CO2 and water. In a profound way these responses are modulated by disturbances that are driven by or exacerbated by climate change. Predicting these changes is challenging given that the feedbacks between environmental controls, disturbances, and fluxes are complex. Flux data in areas of bark beetle outbreaks in the western U.S.A. show differential declines in carbon and water flux in response to the occlusion of xylem by associated fungi. For example, bark beetle infestation at the GLEES AmeriFlux site manifested in a decline in summer water use efficiency to 60% in the year after peak infestation compared to previous years, and no recovery of carbon uptake following a period of high vapor pressure deficit. This points to complex feedbacks between disturbance and differential ecosystem reaction and relaxation responses. Theory based on plant hydraulics and extending to include links to carbon storage and exhaustion has potential for explaining these dynamics with simple, yet rigorous models. In this spirit we developed a coupled model that combines an existing model of canopy water and carbon flow, TREES [e.g., Loranty et al., 2010], with the Sperry et al., [1998] plant hydraulic model. The new model simultaneously solves carbon uptake and losses along with plant hydraulics, and allows for testing specific hypotheses on feedbacks between xylem dysfunction, stomatal and non-stomatal controls on photosynthesis and carbon allocation, and autotrophic and heterotrophic respiration. These are constrained through gas exchange, root vulnerability to cavitation, sap flux, and eddy covariance data in a novel model complexity-testing framework. Our analysis focuses on an ecosystem gradient spanning sagebrush to subalpine forests. Our modeling results support hypotheses on feedbacks between hydraulic dysfunction and 1) non

  4. Thermal Conductivity Change Kinetics of Ceramic Thermal Barrier Coatings Determined by the Steady-State Laser Heat Flux Technique

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.

    2000-01-01

    A steady-state laser heat flux technique has been developed at the NASA Glenn Research Center at Lewis Field to obtain critical thermal conductivity data of ceramic thermal barrier coatings under the temperature and thermal gradients that are realistically expected to be encountered in advanced engine systems. In this study, thermal conductivity change kinetics of a plasma-sprayed, 254-mm-thick ZrO2-8 wt % Y2O3 ceramic coating were obtained at high temperatures. During the testing, the temperature gradients across the coating system were carefully measured by the surface and back pyrometers and an embedded miniature thermocouple in the substrate. The actual heat flux passing through the coating system was determined from the metal substrate temperature drop (measured by the embedded miniature thermocouple and the back pyrometer) combined with one-dimensional heat transfer models.

  5. Physicochemical impacts of dust particles on alpine glacier meltwater at the Laohugou Glacier basin in western Qilian Mountains, China.

    PubMed

    Dong, Zhiwen; Qin, Dahe; Chen, Jizu; Qin, Xiang; Ren, Jiawen; Cui, Xiaoqing; Du, Zhiheng; Kang, Shichang

    2014-09-15

    This work discusses the temporal variation of various physicochemical species in the meltwater runoff of Laohugou Glacier No. 12 (4260 ma.s.l.) in central Asia, and their correlation with dust particles, based on a two-year field observation in summer 2012 and 2013, mainly focusing on dust concentration and size distribution, meltwater chemistry, particles SEM-EDX analysis in the meltwater, and MODIS atmospheric optical depth fields around the Qilian Mountains in central Asia. We find that, the volume-size distribution of dust particles in the meltwater is mainly composed of three parts, which includes fine aerosol particles (with diameter of 0~3.0 μm, mainly PM 2.5), atmospheric dust (with diameter of 3.0~20 μm), and local dust particles (20~100 μm), respectively. Comparison of dust particles in the snowpack and meltwater runoff indicates that, large part of dust particles in the meltwater may have originated from atmospheric dust deposition to the snow and ice on the glacier, and transported into the meltwater runoff. Moreover, temporal variation of dust and major ions (especially crustal species) is very similar with each other, showing great influence of dust particles to the chemical constituents of the glacier meltwater. SPM and TDS implied significant influences of dust to the physical characteristics of the glacier meltwater. Results showed that, accelerated glacier melting may affect physicochemical characteristics of the meltwater at an alpine basin under global warming. MODIS atmospheric optical depth (AOD) fields derived using the Deep Blue algorithm, showed great influence of regional dust transportation over western Qilian Mountains in springtime. SEM-EDX analysis shows that dust particles in the glacier meltwater contain Si-, Al-, Ca-, K-, and Fe-rich materials, such as quartz, albite, aluminate, and fly ash, similar to that deposited in snowpack. These results showed great and even currently underestimated influences of atmospheric dust

  6. Multi-model prediction of climate-induced changes in ozone and reactive nitrogen fluxes into the troposphere

    NASA Astrophysics Data System (ADS)

    Hegglin, M. I.; Shepherd, T. G.; Ccmval Modelling Team

    2010-12-01

    Chemistry-Climate Models (CCMs) consistently predict a strengthening of the stratospheric Brewer-Dobson circulation due to climate change. The associated changes in the distribution of stratospheric ozone and reactive nitrogen will affect not only the flux of those tracers into the troposphere, but also the amount of ultra-violet radiation reaching the troposphere. While the contribution of stratospheric ozone to the total tropospheric ozone budget is only about 10%, it strongly affects ozone concentrations in the upper troposphere, where ozone has a relatively long lifetime (about one month) and its largest impact on radiative forcing. At the same time, changes in reactive nitrogen and UV radiation may influence the efficacy of chemical processes in the troposphere, and have adverse effects on human beings and the ecosystem. We present new results from a multi-model comparison of predicted changes in stratospheric ozone and reactive nitrogen fluxes using state-of-the-art CCMs, and the role of ozone depletion and recovery in modulating them. In order to gain confidence in the model predictions, we also evaluate the models’ capabilities to represent dynamical and chemical processes in the lower stratosphere through process-oriented diagnostics using both aircraft and satellite data.

  7. Changes in Moisture Flux Over the Tibetan Plateau During 1979-2011: Insights from a High Resolution Simulation

    SciTech Connect

    Gao, Yanhong; Leung, Lai-Yung R.; Zhang, Yongxin; Cuo, Lan

    2015-05-01

    Net precipitation (precipitation minus evapotranspiration, P-E) changes from a high resolution regional climate simulation and its reanalysis forcing are analyzed over the Tibet Plateau (TP) and compared to the global land data assimilation system (GLDAS) product. The mechanism behind the P-E changes is explored by decomposing the column integrated moisture flux convergence into thermodynamic, dynamic, and transient eddy components. High-resolution climate simulation improves the spatial pattern of P-E changes over the best available global reanalysis. Improvement in simulating precipitation changes at high elevations contributes dominantly to the improved P-E changes. High-resolution climate simulation also facilitates new and substantial findings regarding the role of thermodynamics and transient eddies in P-E changes reflected in observed changes in major river basins fed by runoff from the TP. The analysis revealed the contrasting convergence/divergence changes between the northwestern and southeastern TP and feedback through latent heat release as an important mechanism leading to the mean P-E changes in the TP.

  8. Seasonal Changes in Plankton Food Web Structure and Carbon Dioxide Flux from Southern California Reservoirs

    PubMed Central

    Adamczyk, Emily M.; Shurin, Jonathan B.

    2015-01-01

    Reservoirs around the world contribute to cycling of carbon dioxide (CO2) with the atmosphere, but there is little information on how ecosystem processes determine the absorption or emission of CO2. Reservoirs are the most prevalent freshwater systems in the arid southwest of North America, yet it is unclear whether they sequester or release CO2 and therefore how water impoundment impacts global carbon cycling. We sampled three reservoirs in San Diego, California, weekly for one year. We measured seasonal variation in the abundances of bacteria, phytoplankton, and zooplankton, as well as water chemistry (pH, nutrients, ions, dissolved organic carbon [DOC]), which were used to estimate partial pressure of CO2 (pCO2), and CO2 flux. We found that San Diego reservoirs are most often undersaturated with CO2 with respect to the atmosphere and are estimated to absorb on average 3.22 mmol C m-2 day-1. pCO2 was highest in the winter and lower in the summer, indicating seasonal shifts in the magnitudes of photosynthesis and respiration associated with day length, temperature and water inputs. Abundances of microbes (bacteria) peaked in the winter along with pCO2, while phytoplankton, nutrients, zooplankton and DOC were all unrelated to pCO2. Our data indicate that reservoirs of semi-arid environments may primarily function as carbon sinks, and that carbon flux varies seasonally but is unrelated to nutrient or DOC availability, or the abundances of phytoplankton or zooplankton. PMID:26473601

  9. Differences Between ERBE and CERES Tropical Means Fluxes: ENSO, Climate Change of Calibration?

    NASA Technical Reports Server (NTRS)

    Wielicki, Bruce A.; Wong, Takmeng; Young, David F.; Barkstrom, Bruce R.; Lee, R. B., III; Haeffelin, Martial

    1999-01-01

    Verner E. Soumi was the father of radiation budget measurements from space. He directed the team at the University of Wisconsin that developed the first radiation budget measurements on the Iota (Explorer VII) coverage) spacecraft in 1959. The first data published was from hand calculations of night-time long-wave fluxes, with absolute accuracy estimated as better than 10 percent, and the data shown as hand drawn maps with lines of equal "long-wave radiation loss, in Langleys per minute X 10(exp -3) (isolangleys)". The first comparisons of the new radiation data with nephanalyses showed that clouds dominated the radiation patterns. Soumi immediately proposed using the radiation fields to help understand the atmospheric heat sources necessary to drive the atmospheric circulation. This early work already pointed to the relationship between the outgoing longwave radiation at the top of the atmosphere and the vertical flux divergence of infrared radiation within the atmosphere. In the next 30 years, global satellite observations of the radiation balance of the planet have advanced both in accuracy, stability, and in their ability to address cause and effect in the climate system. The purpose of the present paper is to examine early results of the new Clouds and the Earth's Radiant Energy System (CERES) data on Tropical Rainfall Measuring System (TRMM) which started data collection in January, 1998. CERES is a direct descendant of the legacy of Soumi's foresight on understanding the global energetics using satellite observations of broadband radiation.

  10. Differences between ERBE and CERES Tropical Mean Fluxes: ENSO, Climate Change or Calibration?

    NASA Technical Reports Server (NTRS)

    Wielicki, Bruce A.; Wong, Takmeng; Young, David F.; Barkstrom, Bruce R.; Lee, R. B., III; Haeffelin, Martial

    2005-01-01

    Verner E. Soumi was the father of radiation budget measurements from space. He directed the team at the University of Wisconsin that developed the first radiation budget measurements on the Iota (Explorer VII) coverage) spacecraft in 1959. The first data published was from hand calculations of night-time long-wave fluxes, with absolute accuracy estimated as better than 10 percent, and the data shown as hand drawn maps with lines of equal "long-wave radiation loss, in Langleys per minute X 10(exp -3) (isolangleys)". The first comparisons of the new radiation data with nephanalyses showed that clouds dominated the radiation patterns. Soumi immediately proposed using the radiation fields to help understand the atmospheric heat sources necessary to drive the atmospheric circulation. This early work already pointed to the relationship between the outgoing longwave radiation at the top of the atmosphere and the vertical flux divergence of infrared radiation within the atmosphere. In the next 30 years, global satellite observations of the radiation balance of the planet have advanced both in accuracy, stability, and in their ability to address cause and effect in the climate system. The purpose of the present paper is to examine early results of the new Clouds and the Earth's Radiant Energy System (CERES) data on Tropical Rainfall Measuring System (TRMM) which started data collection in January, 1998. CERES is a direct descendant of the legacy of Soumi's foresight on understanding the global energetics using satellite observations of broadband radiation.

  11. Seasonal Changes in Plankton Food Web Structure and Carbon Dioxide Flux from Southern California Reservoirs.

    PubMed

    Adamczyk, Emily M; Shurin, Jonathan B

    2015-01-01

    Reservoirs around the world contribute to cycling of carbon dioxide (CO2) with the atmosphere, but there is little information on how ecosystem processes determine the absorption or emission of CO2. Reservoirs are the most prevalent freshwater systems in the arid southwest of North America, yet it is unclear whether they sequester or release CO2 and therefore how water impoundment impacts global carbon cycling. We sampled three reservoirs in San Diego, California, weekly for one year. We measured seasonal variation in the abundances of bacteria, phytoplankton, and zooplankton, as well as water chemistry (pH, nutrients, ions, dissolved organic carbon [DOC]), which were used to estimate partial pressure of CO2 (pCO2), and CO2 flux. We found that San Diego reservoirs are most often undersaturated with CO2 with respect to the atmosphere and are estimated to absorb on average 3.22 mmol C m(-2) day(-1). pCO2 was highest in the winter and lower in the summer, indicating seasonal shifts in the magnitudes of photosynthesis and respiration associated with day length, temperature and water inputs. Abundances of microbes (bacteria) peaked in the winter along with pCO2, while phytoplankton, nutrients, zooplankton and DOC were all unrelated to pCO2. Our data indicate that reservoirs of semi-arid environments may primarily function as carbon sinks, and that carbon flux varies seasonally but is unrelated to nutrient or DOC availability, or the abundances of phytoplankton or zooplankton. PMID:26473601

  12. Surface morphology changes and deuterium retention in Toughened, Fine-grained Recrystallized Tungsten under high-flux irradiation conditions

    NASA Astrophysics Data System (ADS)

    Oya, M.; Lee, H. T.; Ueda, Y.; Kurishita, H.; Oyaidzu, M.; Hayashi, T.; Yoshida, N.; Morgan, T. W.; De Temmerman, G.

    2015-08-01

    Surface morphology changes and deuterium (D) retention in Toughened, Fine-Grained Recrystallized Tungsten (TFGR W) with TaC dispersoids (W-TaC) and pure tungsten exposed to D plasmas to a fluence of 1026 D/m2 s were studied as a function of the D ion flux (1022-1024 D/m2 s). As the flux increased from 1022 D/m2 s to 1024 D/m2 s, the numbers of blisters increased for both materials. However, smaller blisters were observed on W-TaC compared to pure W. In W-TaC, cracks beneath the surface along grain boundaries were observed, which were comparable to the blister sizes. The reason for the smaller blister sizes may arise from smaller grain sizes of W-TaC. In addition, reduction of the D retention in W-TaC was observed for higher flux exposures. D depth profiles indicate this reduction arises due to decrease in trapping in the bulk.

  13. Seasonal changes of nutrient fluxes in the Upper Changjiang basin: An example of the Longchuanjiang River, China

    NASA Astrophysics Data System (ADS)

    Lu, X. X.; Li, Siyue; He, Min; Zhou, Yue; Bei, Rongta; Li, Li; Ziegler, Alan D.

    2011-08-01

    SummaryFluxes of dissolved and particulate nitrogen (N) and phosphorus (P) variables were measured monthly from September 2007 to March 2009 in the upper Longchuanjiang River (Yunnan Province, China) to determine annual loads and seasonal variability. Dissolved N (DN) and particle associated P (PAP) contributed 56% and 99% of the total nitrogen (TN) and total phosphorus (TP) yields of 549 and 608 kg/km 2/yr. Fluxes of particulate N (PN), dissolved P (DP), PAP and TP exhibited great seasonality because they were highly correlated with water discharge. Areal export rates of NH4+-N, PN, PAP and TP were higher than in the main channel and most tributaries of the Changjiang River. High particulate loads were contributed to erosion of phosphorus-rich soils during heavily rains in the wet season. Median measured concentrations of TN, NH4+-N and TP exceeded the maximum permissible limit for domestic and recreational use in China. High nitrogen and phosphorus concentrations draw attention to the potential for additional nutrient loading to foster the formation of algal blooms in locations where free-flowing river sections are changing into cascades of reservoirs. Importantly, the great seasonality in the data shows necessity of sufficient sampling for determining annual fluxes.

  14. Global Ocean Sensitivity to Local Geologically Short-Term Variability of Freshwater Fluxes

    NASA Astrophysics Data System (ADS)

    Seidov, D.; Haupt, B. J.

    2004-12-01

    The geologic record and computer modeling indicate that the transitions between cold and warm climates during the last deglaciation , driven by internal climate dynamics, were geologically very fast, lasting for only decades or shorter. The THC is, perhaps, the only viable candidate for driving these kinds of abrupt changes. Current perception of how the THC may become an agent of abrupt climate change is that the THC is rather sensitive to changes in freshwater fluxes in the high-latitudes, also known as major meltwater events. Our recent numerical experiments challenge the idea of the high-latitudinal meltwater events as the only possible cause of THC alteration. These experiments suggest that the inter-basin sea surface salinity contrasts caused by disparity of freshwater fluxes over the world ocean can also be a very potent factor in THC dynamics. To address the role of changes in both high-latitudinal and inter-basin freshwater fluxes in altering the global THC, we performed several simple numerical experiments. First, we ran the atmospheric control experiment using the NCAR Community Climate Model (CCM) with observed sea surface temperature (SST) and salinity to get the present-day control atmospheric state, that is, the wind stress, SST, and freshwater fluxes across the sea surfaces. Next, we ran the oceanic control experiment using the GFDL Modular Ocean Model (MOM) with these sea surface conditions from the CCM. In the first series of experiments, we specified idealized anomalies of freshwater fluxes in the northern North Atlantic, the Southern Ocean, and the subtropical North Atlantic and North Pacific. These experiments gave us insight on the relative importance of high-latitudinal and inter-basin short-term fluctuations in freshwater balance for the THC dynamics. In the second series of experiments, we simulated the disruption of the freshwater regime in the northern North Atlantic caused by freshwater floods from Lake Agassiz (a glacial lake that

  15. Evidence of Microbial Regulation of Biogeochemical Cycles from a Study on Methane Flux and Land Use Change

    PubMed Central

    Nazaries, Loïc; Pan, Yao; Bodrossy, Levente; Baggs, Elizabeth M.; Millard, Peter; Murrell, J. Colin

    2013-01-01

    Microbes play an essential role in ecosystem functions, including carrying out biogeochemical cycles, but are currently considered a black box in predictive models and all global biodiversity debates. This is due to (i) perceived temporal and spatial variations in microbial communities and (ii) lack of ecological theory explaining how microbes regulate ecosystem functions. Providing evidence of the microbial regulation of biogeochemical cycles is key for predicting ecosystem functions, including greenhouse gas fluxes, under current and future climate scenarios. Using functional measures, stable-isotope probing, and molecular methods, we show that microbial (community diversity and function) response to land use change is stable over time. We investigated the change in net methane flux and associated microbial communities due to afforestation of bog, grassland, and moorland. Afforestation resulted in the stable and consistent enhancement in sink of atmospheric methane at all sites. This change in function was linked to a niche-specific separation of microbial communities (methanotrophs). The results suggest that ecological theories developed for macroecology may explain the microbial regulation of the methane cycle. Our findings provide support for the explicit consideration of microbial data in ecosystem/climate models to improve predictions of biogeochemical cycles. PMID:23624469

  16. Polygonal tundra geomorphological change in response to warming alters future CO2 and CH4 flux on the Barrow Peninsula.

    PubMed

    Lara, Mark J; McGuire, A David; Euskirchen, Eugenie S; Tweedie, Craig E; Hinkel, Kenneth M; Skurikhin, Alexei N; Romanovsky, Vladimir E; Grosse, Guido; Bolton, W Robert; Genet, Helene

    2015-04-01

    The landscape of the Barrow Peninsula in northern Alaska is thought to have formed over centuries to millennia, and is now dominated by ice-wedge polygonal tundra that spans drained thaw-lake basins and interstitial tundra. In nearby tundra regions, studies have identified a rapid increase in thermokarst formation (i.e., pits) over recent decades in response to climate warming, facilitating changes in polygonal tundra geomorphology. We assessed the future impact of 100 years of tundra geomorphic change on peak growing season carbon exchange in response to: (i) landscape succession associated with the thaw-lake cycle; and (ii) low, moderate, and extreme scenarios of thermokarst pit formation (10%, 30%, and 50%) reported for Alaskan arctic tundra sites. We developed a 30 × 30 m resolution tundra geomorphology map (overall accuracy:75%; Kappa:0.69) for our ~1800 km² study area composed of ten classes; drained slope, high center polygon, flat-center polygon, low center polygon, coalescent low center polygon, polygon trough, meadow, ponds, rivers, and lakes, to determine their spatial distribution across the Barrow Peninsula. Land-atmosphere CO2 and CH4 flux data were collected for the summers of 2006-2010 at eighty-two sites near Barrow, across the mapped classes. The developed geomorphic map was used for the regional assessment of carbon flux. Results indicate (i) at present during peak growing season on the Barrow Peninsula, CO2 uptake occurs at -902.3 10(6) gC-CO2 day(-1) (uncertainty using 95% CI is between -438.3 and -1366 10(6) gC-CO2 day(-1)) and CH4 flux at 28.9 10(6) gC-CH4 day(-1) (uncertainty using 95% CI is between 12.9 and 44.9 10(6) gC-CH4 day(-1)), (ii) one century of future landscape change associated with the thaw-lake cycle only slightly alter CO2 and CH4 exchange, while (iii) moderate increases in thermokarst pits would strengthen both CO2 uptake (-166.9 10(6) gC-CO2 day(-1)) and CH4 flux (2.8 10(6) gC-CH4 day(-1)) with geomorphic change from low

  17. Compensatory Flux Changes within an Endocytic Trafficking Network Maintain Thermal Robustness of Notch Signaling

    PubMed Central

    Shimizu, Hideyuki; Woodcock, Simon A.; Wilkin, Marian B.; Trubenová, Barbora; Monk, Nicholas A.M.; Baron, Martin

    2014-01-01

    Summary Developmental signaling is remarkably robust to environmental variation, including temperature. For example, in ectothermic animals such as Drosophila, Notch signaling is maintained within functional limits across a wide temperature range. We combine experimental and computational approaches to show that temperature compensation of Notch signaling is achieved by an unexpected variety of endocytic-dependent routes to Notch activation which, when superimposed on ligand-induced activation, act as a robustness module. Thermal compensation arises through an altered balance of fluxes within competing trafficking routes, coupled with temperature-dependent ubiquitination of Notch. This flexible ensemble of trafficking routes supports Notch signaling at low temperature but can be switched to restrain Notch signaling at high temperature and thus compensates for the inherent temperature sensitivity of ligand-induced activation. The outcome is to extend the physiological range over which normal development can occur. Similar mechanisms may provide thermal robustness for other developmental signals. PMID:24855951

  18. Microbial limitation in a changing world: A stoichiometric approach for predicting microbial resource limitation and fluxes

    NASA Astrophysics Data System (ADS)

    Midgley, M.; Phillips, R.

    2014-12-01

    Microbes mediate fluxes of carbon (C), nitrogen (N), and phosphorus (P) in soils depending on ratios of available C, N, and P relative to microbial demand. Hence, characterizing microbial C and nutrient limitation in soils is critical for predicting how ecosystems will respond to human alterations of climate and nutrient availability. Here, we take a stoichiometric approach to assessing microbial C, N, and P limitation by using threshold element ratios (TERs). TERs enable shifting resource limitation to be assessed by matching C, N and P ratios from microbial biomass, extracellular enzyme activities, and soil nutrient concentrations. We assessed microbial nutrient limitation in temperate forests dominated by trees that associate with one of two mycorrhizal symbionts: arbsucular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi. We found that both ECM and AM microbial communities were co-limited by C and N, supporting conventional wisdom that microbes are C-limited and temperate forests are N-limited. However, AM microbial communities were relatively more C-limited than ECM communities (P=0.001). In response to chronic field N fertilization, both AM and ECM communities became relatively more P-limited (P=0.011), but they remained N- and C-limited overall. Thus, realistic levels of N deposition may not dampen microbial N limitation. Reflecting differences in relative limitation, N mineralization rates were higher in AM soils than in ECM soils (P=0.004) while C mineralization rates were higher in ECM soils than in AM soils (P=0.023). There were no significant differences in P flux between AM and ECM soils or detectable mineralization responses to N addition, indicating that mineralization rates are closely tied to C and nutrient limitation. Overall, we found that 1) microbial resource limitation can be detected without resource addition; and 2) TERs and ratios of labile resources are viable tools for predicting mineralization responses to resource additions.

  19. Radiative Flux Changes by Aerosols from North America, Europe, and Africa over the Atlantic Ocean: Measurements and Calculations from TARFOX and ACE-2

    NASA Technical Reports Server (NTRS)

    Russell, P. B.; Hignett, P.; Livingston, J. M.; Schmid, B.; Chien, A.; Bergstrom, R.; Durkee, P. A.; Hobbs, P. V.; Bates, T. S.; Quinn, P. K.; Condon, Estelle (Technical Monitor)

    1998-01-01

    Aerosol effects on atmospheric radiative fluxes provide a forcing function that is a major source of uncertainty in understanding the past climate and predicting climate change. To help reduce this uncertainty, the 1996 Tropospheric Aerosol Radiative Forcing Experiment (TARFOX) and the 1997 second Aerosol Characterization Experiment (ACE-2) measured the properties and radiative effects of American, European, and African aerosols over the Atlantic. In TARFOX, radiative fluxes and microphysics of the American aerosol were measured from the UK C-130 while optical depth spectra, aerosol composition, and other properties were measured by the University of Washington C-131A and the CIRPAS Pelican. Closure studies show that the measured flux changes agree with those derived from the aerosol measurements using several modelling approaches. The best-fit midvisible single-scatter albedos (approx. 0.89 to 0.93) obtained from the TARFOX flux comparisons are in accord with values derived by independent techniques. In ACE-2 we measured optical depth and extinction spectra for both European urban-marine aerosols and free-tropospheric African dust aerosols, using sunphotometers on the R/V Vodyanitskiy and the Pelican. Preliminary values for the radiative flux sensitivities (Delta Flux / Delta Optical depth) computed for ACE-2 aerosols (boundary layer and African dust) over ocean are similar to those found in TARFOX. Combining a satellite-derived optical depth climatology with the aerosol optical model validated for flux sensitivities in TARFOX provides first-cut estimates of aerosol-induced flux changes over the Atlantic Ocean.

  20. Organizational Routines in Flux: A Case Study of Change in Recording and Monitoring Student Attendance

    ERIC Educational Resources Information Center

    Conley, Sharon; Enomoto, Ernestine K.

    2009-01-01

    Using an organizational theory to study how people can actually change routines, this study examined alterations made to two aspects of a high school's attendance procedures over 5 years. The authors drew primarily from interviews and school documents to describe and analyze changes made by administrators, faculty, and staff. Organizing questions…

  1. TERRECO: A Flux-Based Approach to Understanding Landscape Change, Potentials of Resilience and Sustainability in Ecosystem Services

    NASA Astrophysics Data System (ADS)

    Tenhunen, J. D.; Kang, S.

    2011-12-01

    The Millenium Assessment has provided a broad perspective on the ways and degree to which global change has stressed ecosystems and their potential to deliver goods and services to mankind. Management of natural resources at regional scale requires a clear understanding of the ways that ongoing human activities modify or create new system stressors, leading to net gains or losses in ecosystem services. Ever since information from the International Biological Program (IBP) was summarized in the 1960s, we know that ecosystem stress response, recovery and resilience are related to changes in ecosystem turnover of materials, nutrient retention or loss, resource use efficiencies, and additional ecosystem properties that determine fluxes of carbon, water and nutrients. At landscape or regional scale, changes in system drivers influence land-surface to atmosphere gas exchange (water, carbon and trace gas emissions), the seasonal course of soil resource stores, hydrology, and transport of nutrients and carbon into and through river systems. In today's terminology, shifts in these fluxes indicate a modification of potential ecosystem services provided to us by the landscape or region of interest, and upon which we depend. Ongoing modeling efforts of the TERRECO project carried out in S. Korea focus on describing landscape and regional level flow networks for carbon, water, and nutrients, but in addition monetary flows associated with gains and losses in ecosystem services (cf. Fig. 1). The description is embedded within a framework which examines the trade-offs between agricultural intensification versus yield of high quality water to reservoirs for drinking water supply. The models also quantify hypothetical changes in flow networks that would occur in the context of climate, land use and social change scenarios.

  2. Meltwater Runoff and Storage Based on Dielectric Properties of the Supraglacial Snowpack on Haig Glacier, Canadian Rocky Mountains.

    NASA Astrophysics Data System (ADS)

    Samimi, S.; Marshall, S. J.

    2015-12-01

    Meltwater refreezing and storage in the supraglacial snowpack can reduce and delay meltwater runoff on temperate alpine glaciers, but models of glacier runoff that are used to examine mass balance and glacier water resources do not generally account for this storage. Past studies on Haig Glacier in the Canadian Rocky Mountains show a consistent over-estimate of the amount of summer runoff from the glacier, based on modeled melt vs. measured discharge. We hypothesized that much of the 'missing runoff' was associated with overnight refreezing of meltwater that is ponded on the glacier surface and stored in pore space of the seasonal snowpack. Additional energy is required to melt this refrozen water each day, such that a large fraction of the meltwater that is generated on the glacier is 'recycled' water. To test this idea, we measured the temperature and meltwater content in the upper 40 cm of the supraglacial snowpack of Haig Glacier in spring and summer 2015. Thermistors and TDR probes were installed at 10-cm intervals at two sites in the glacier accumulation area. A Denoth meter was used to make point measurements for comparison with the TDR inferences of snowpack dielectric properties. These data are supplemented by automatic weather station data, used to calculate surface melt rates, and discharge measurements in the glacier outlet stream. We observed a strong diurnal cycle in snow water content, with the snowpack drying out overnight, but contrary to what we expected, there was negligible subsurface meltwater refreezing during our study. Overnight refreezing was restricted to a thin surface layer of the snowpack, while overnight drying was likely due to meltwater drainage to the snow-ice interface. We use our observations to calibrate and test a model of meltwater runoff from the glacier from summer 2015.

  3. Seasonal variation of the solute and suspended sediment load in Gangotri glacier meltwater, central Himalaya, India

    NASA Astrophysics Data System (ADS)

    Singh, Virendra Bahadur; Ramanathan, AL.; Pottakkal, Jose George; Kumar, Manoj

    2014-01-01

    A systematic study on the seasonal variation of major cations and anions was carried out to understand the source of dissolved ions as well as the geochemical weathering processes controlling the meltwater chemistry of Gangotri glacier. Calcium and magnesium are the major cations while sulphate is the dominant anion followed by bicarbonate. The high ratios of (Ca + Mg)/(Na + K), Ca/Na, Mg/Na, HCO3/Na and low ratio of (Na + K)/TZ+ for pre-monsoon, monsoon and post-monsoon seasons indicate the dominance of carbonate weathering, which is a major source of the dissolved ions in the meltwater of Gangotri glacier followed by silicate weathering. High equivalent ratios of Na/Cl and K/Cl as compared to sea water indicate relatively lesser contribution from atmospheric input to the chemical composition of meltwater. Correlation matrix and factor analysis were used to identify various factors controlling the major ion chemistry. Marked seasonal and diurnal variations were observed in the dissolved ions and suspended sediment concentration. Daily mean suspended sediment concentration for pre-monsoon, monsoon and post-monsoon was observed as 1719, 3281 and 445 mgl-1, respectively. Highest suspended sediment load was observed in monsoon season followed by pre-monsoon and post-monsoon seasons. The cation denudation rates of Gangotri glacier meltwater were calculated to be 42.2, 46.5 and 15.9 t km-2 y-1 for pre-monsoon (June only), monsoon and post-monsoon respectively. These values are higher than that of other Himalayan glaciers. Whereas physical weathering rate of the Gangotri glacier catchment was observed to be 7056, 15,344 and 588 t km-2 y-1 for pre-monsoon (June only), monsoon and post-monsoon respectively, much higher than the Indian and world averages of river.

  4. Seasonal and short term fluctuations of iceberg flux from Hans Glacier Spitsbergen

    NASA Astrophysics Data System (ADS)

    Jania, Jacek; Blaszczyk, Malgorzata; Cieply, Michal; Grabiec, Mariusz; Budzik, Tomasz; Ignatiuk, Dariusz; Uszczyk, Aleksander; Tymrowska, Patrycja; Majchrowska, Elzbieta; Prominska, Agnieszka; Walczowski, Waldemar; Pastusiak, Tadeusz; Petlicki, Michal; Puczko, Dariusz

    2016-04-01

    Glacier iceberg flux due to calving might be an important source of freshwater deliver to Arctic fjords. Mass loss due to calving gives also significant contribution of glacier mass budget. Seasonal changes of dynamics of tidewater glaciers is generally known. After advance of glacier front during winter, summer recession occurs thanks to higher calving in the warmer period of the year. Nevertheless, annual course of iceberg flux intensity is not calculated frequently. Observations and survey of glacier dynamics were conducted on Hans Glacier a polythermal glacier ending down into Hornsund Fiord in Southern Spitsbergen. They provide information for discernment of seasonal calving intensity and iceberg supply to the fiord as a source of freshwater seasonally and in shorter periods of time. Source data on glacier front geometry, bathymetry of the fore bay, seasonal fluctuation of ice-cliff position and glacier velocity were obtained by different field survey and remote sensing methods. Time lapse photos, repeated terrestrial laser scanning and measurements of sea water temperature, salinity and dynamics as well, together with record from meteorological stations were used to determine factors of calving intensity. Calving flux from the glacier to Hornsund Fjord was calculated for short-period events and selected summer seasons between 2007 and 2015. Interannual differences in calving flux were also estimated. Ratios of meltwater to iceberg freshwater supply to the fiord was preliminarily estimated as well.

  5. Subglacial hydraulic conditions of the former Barents Sea Ice Sheet inferred from meltwater landforms

    NASA Astrophysics Data System (ADS)

    Shackleton, Calvin; Bjarnadóttir, Lilja; Winsborrow, Monica; Esteves, Mariana; Andreassen, Karin

    2016-04-01

    A large multibeam dataset acquired by the MAREANO programme covering over 24,000 km2 at 5 m horizontal resolution has uncovered abundant subglacial meltwater landforms in the central Barents Sea. These landforms provide unprecedented insights into the nature of hydrological systems operating at the bed of the former Barents Sea Ice Sheet, helping us to understand the subglacial environments of marine based ice sheets as a whole. Large sinuous features up to 3.5 km wide and over 40 km long, with depths up to 40 m are interpreted as braided tunnel valleys, which would have drained vast amounts of water at the base of the ice sheet. Dendritic channels are also common, up to 42 km long and 24 m deep, along with several anastomosing channels and numerous complex esker systems. These features document that a wide range of subglacial hydraulic conditions and a well-established meltwater system existed beneath the former Barents Sea Ice Sheet. In conjunction with mapping of glacial landforms, these meltwater features provide the basis for a reconstruction of the subglacial drainage systems in the central Barents Sea and their interaction with the dynamic activity of the overlying ice sheet.

  6. Influence of glacial meltwater on equilibrium process of two Tibetan lakes indicated by δ18O

    NASA Astrophysics Data System (ADS)

    Gao, J.

    2009-12-01

    δ18O measurements based on systematic sampling and isotopic model have been adopted to study the affects of glacial meltwater in two lake basins (Lakes Yamdrok-tso and Puma Yum-tso) at two different elevations on the southern Tibetan Plateau. Temporally, δ18O values in precipitation and lake water display a seasonal fluctuation in both lakes. Spatially, δ18O values in the two lake basins increase by 10‰ from the termini of glaciers to the lake shores, by about 1‰ from the lakeshores to the lake center, by 0.4‰ from the water surface to depth in these lakes. The obvious annual δ18O variations indicate that lake water mixes sufficient in a short time. Model results show that glacial meltwater is an important factor on lake water equilibrium process. Equilibrium δ18O values decrease 0.8‰ for Yamdrok-tso Lake and 0.6‰ for Puma Yum-tso Lake when contributions of glacial meltwater to these lakes shrink by 60%. δ18O increases rapidly during the initial stages and then it takes a long time to approach the equilibrium value. The modeled results also show that the surface lake water temperature has only a little impact on this process.

  7. Basal crevasses on the Larsen C Ice Shelf, Antarctica: Implications for meltwater ponding and hydrofracture

    NASA Astrophysics Data System (ADS)

    McGrath, Daniel; Steffen, Konrad; Rajaram, Harihar; Scambos, Ted; Abdalati, Waleed; Rignot, Eric

    2012-08-01

    A key mechanism for the rapid collapse of both the Larsen A and B Ice Shelves was meltwater-driven crevasse propagation. Basal crevasses, large-scale structural features within ice shelves, may have contributed to this mechanism in three important ways: i) the shelf surface deforms due to modified buoyancy and gravitational forces above the basal crevasse, creating >10 m deep compressional surface depressions where meltwater can collect, ii) bending stresses from the modified shape drive surface crevassing, with crevasses reaching 40 m in width, on the flanks of the basal-crevasse-induced trough and iii) the ice thickness is substantially reduced, thereby minimizing the propagation distance before a full-thickness rift is created. We examine a basal crevasse (4.5 km in length, ∼230 m in height), and the corresponding surface features, in the Cabinet Inlet sector of the Larsen C Ice Shelf using a combination of high-resolution (0.5 m) satellite imagery, kinematic GPS and in situ ground penetrating radar. We discuss how basal crevasses may have contributed to the breakup of the Larsen B Ice Shelf by directly controlling the location of meltwater ponding and highlight the presence of similar features on the Amery and Getz Ice Shelves with high-resolution imagery.

  8. Routing of meltwater from the Laurentide Ice Sheet during the Younger Dryas cold episode

    NASA Astrophysics Data System (ADS)

    Broecker, Wallace S.; Kennett, James P.; Flower, Benjamin P.; Teller, James T.; Trumbore, Sue; Bonani, Georges; Wolfli, Willy

    1989-09-01

    ROOTH1 proposed that the Younger Dryas cold episode, which chilled the North Atlantic region from 11,000 to 10,000 yr BP, was initiated by a diversion of meltwater from the Mississippi drainage to the St Lawrence drainage system. The link between these events is postulated to be a turnoff, during the Younger Dryas cold episode, of the North Atlantic's conveyor-belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the North Atlantic region2. This turnoff is attributed to a reduction in surface-water salinity, and hence also in density, of the waters in the region where North Atlantic Deep Water (NADW) now forms. Here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from Orca Basin core EN32-PC4 which reveal a significant reduction in meltwater flow through the Mississippi River to the Gulf of Mexico from about 11,200 to 10,000 radiocarbon years ago. This finding is consistent with the record for Lake Agassiz which indicates that the meltwater from the southwestern margin of the Laurentide Ice Sheet was diverted to the northern Atlantic Ocean through the St Lawrence valley during the interval from ~11,000 to 10,000 years before present (yr BP).

  9. Tracing Pleistocene to Holocene meltwater events and provenance of sediments in Baffin Bay using radiogenic isotope signals

    NASA Astrophysics Data System (ADS)

    Kirillova, Valeriia; Kasemann, Simone A.; Lucassen, Friedrich

    2016-04-01

    Large meltwater discharge is the principal carrier of detritus from the continent into the ocean and the dispersion of this detritus by ocean currents is a measure for the spatially focused addition of freshwater in the ocean in the high latitude areas. To trace Greenland ice sheet dynamics and freshwater routing during late Pleistocene to Holocene climate transition, we generate strontium (Sr), neodymium (Nd) and lead (Pb) isotope records on sediment cores in the Baffin Bay: GeoTÜ SL 170, covering the last 18.000 years of climate history and GeoTÜ SL 174, covering 40.000 years. Sr, Nd and Pb isotopes are used as proxies for the provenance of continental detritus and seawater sources. Isotope analyses were performed on two separated fractions from the sedimentary core material: the chemically leached fraction and the remaining detritus. Leachates are supposed to represent Fe-Mn coatings formed on the surface of the sediment grains and to reflect the bottom water signal. The detrital fraction acts as a tracer for the meltwater event and weathering regime of the nearby continental masses. For the detrital fraction of the core SL 170, a pronounced shift can be observed in all three isotope systems at ˜ 12 ka, what coincides with the Younger Dryas cold event. For the detrital fraction the 87Sr/86Sr is around ˜0,72 before the event and reaches up to ˜0,74 after. Nd isotope composition (ɛNd) changed from ˜-26 to ˜-32. The shift suggests a change in the continental sources from West and West-South Greenland to the Baffin Island and Canadian Archipelago. It can be explained by the ice sheet melting processes. The 206Pb/204Pb values for the detrital fraction range from ˜17 before the shift to ˜18 after. On the contrary, the leachates show pronounced radiogenic signatures with values changing from ˜21 to ˜23. The reason for such an unusual high values is most likely in the composition of the leached material, which doesn't seem to show the presence of Fe

  10. On the relationship between the energetic particle flux morphology and the change in the magnetic field magnitude during substorms

    NASA Technical Reports Server (NTRS)

    Lopez, R. E.; Lui, A. T. Y.; Sibeck, D. G.; Takahashi, K.; Mcentire, R. W.

    1989-01-01

    The relationship between the morphology of energetic particle substorm injections and the change in the magnetic field magnitude over the course of the event is examined. Using the statistical relationships between the magnetic field during the growth phase and the change in the field magnitude during substorms calculated by Lopez et al. (1988), a limited number of dispersionless ion injections observed by AMPTE CCE are selected. It is argued that this limited set is representative of a large set of events and that the conclusions drawn from examining those events are valid for substorms in general in the inner magnetosphere. It is demonstrated that in an event when CCE directly observed the disruption of the current sheet, the particle and field data show that the region of particle acceleration was highly turbulent and was temporally, and perhaps spatially, limited and that the high fluxes of energetic particles are qualitatively associated with intense inductive electric fields.

  11. Spatial variations in xylem sap flux density in the trunk of orchard-grown, mature mango trees under changing soil water conditions.

    PubMed

    Lu, Ping; Müller, Warren J.; Chacko, Elias K.

    2000-05-01

    Circumferential and radial variations in xylem sap flux density in trunks of 13-year-old mango (Mangifera indica L.) trees were investigated with Granier sap flow sensor probes under limiting and non-limiting soil water conditions. Under non-limiting soil water conditions, circumferential variation was substantial, but there was no apparent relationship between sap flux density and aspect (i.e., the radial position of the sensor probes on the trunk relative to the compass). Hourly sap flux densities over 24 hours at different aspects were highly pair-wise correlated. The relationships between different aspects were constant during well-watered periods but highly variable under changing soil water conditions. Sap flux density showed marked radial variation within the trunk and a substantial flux was observed at the center of the trunk. For each selected aspect on each tree, changes in sap flux densities over time at different depths were closely correlated, so flux at a particular depth could be extrapolated as a multiple of flux from 0 to 2 cm beneath the cambium. However, depth profiles of sap flux density differed between trees and even between aspects within a tree, and also varied in an unpredictable manner as soil water conditions changed. Nevertheless, over a period of non-limiting soil water conditions, depth profiles remained relatively constant. Based on the depth profiles obtained during these periods, a method is described for calculating total sap flow in a mango tree from sap flux density at 0-2 cm beneath the cambium. Total daily sap flows obtained were consistent with water use estimated from soil water balance. PMID:12651518

  12. How deep does a typical crevasse in western Greenland carry meltwater?

    NASA Astrophysics Data System (ADS)

    Poinar, K.; Joughin, I. R.

    2013-12-01

    A flurry of recent work has shown that cryo-hydrologic warming, the transfer of latent heat from meltwater back to the ice sheet, may significantly increase the velocity of large regions of slow-moving ice-sheet ice, particularly in western Greenland. This suggests that as the ablation zone continues to expand up the ice sheet, so too may the influence of cryo-hydrologic warming, which would cause additional sea level rise. A key assumption of the recent cryo-hydrologic models is that crevasses penetrate deep into the ice sheet, typically all the way to the bed. We test the applicability of this assumption: although it has long been known that crevasses in locations with sufficient water volume to maintain a high hydraulic head, such as under supraglacial lakes, can hydrofracture through the full ice thickness, we note that lakes are hardly typical at the scale required by the cryo-hydrologic models over large regions (every ~100 meters), which suggests that full-ice-sheet penetration by every crevasse is not a certainty. Given a field of crevasses with typically observed spacing (~20 to 100 meters), the annual rate of meltwater production, and the far-field tensile stress, how deep can the meltwater drive these crevasses, and if they can reach the bed, how many years does that take? We answer these questions by coupling a viscoelastic model for crevasse shape, depth, and volume, which accounts for elastic opening and creep closure rates, to a thermal model for the ambient ice sheet temperature, which gives us refreezing rates within the crevasse. Over time, the elastic opening, creep closure, and healing by refreezing evolve in tandem with crevasse depth and ice temperature. We find that the large volume of meltwater limits creep closure rates, allowing crevasses to reach large widths and depths over multi-decadal periods. The modeled crevasse widths (~2 meters at the surface) are significantly larger than we observe in western Greenland (tens of centimeters), but

  13. Cordilleran Ice Sheet meltwater delivery to the coastal waters of the northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Hendy, I. L.; Taylor, M.; Gombiner, J. H.; Hemming, S. R.; Bryce, J. G.; Blichert-Toft, J.

    2014-12-01

    Cordilleran Ice Sheet (CIS) delivered meltwater to the NE Pacific Ocean off BC and WA via glacial lake outburst floods (GLOFs), ice rafting and subglacial meltwater discharge. A deglacial glaciomarine sedimentation record is preserved in the well dated ~50-kyr core MD02-2496 (48˚58.47' N, 127˚02.14' W, water depth 1243 m), collected off Vancouver Island. To understand the history of the relationship between the CIS, climate and meltwater discharge, high resolution, multi-proxy geochemical records from the interval that captures the Fraser Glaciation (~30-10 ka) were generated. These proxies include Mg/Ca temperatures and δ18Oseawater from planktonic foraminiferal sp. N. pachyderma and G. bulloides, elemental and organic carbon (Corg) geochemistry of bulk sediments, ɛNd and K/Ar dating of the <63µm fraction. A detailed reconstruction of CIS retreat has been generated based on the source of glaciomarine sediments and ice rafted debris (IRD), as well as evidence for processes such as GLOF events and iceberg discharge. At the Fraser Glaciation initiation (~30 ka) <63µm glaciomarine sediments deposited at MD02-2496 had a ~100 Ma volcanic rock source. The CIS passed over the Vancouver Island continental shelf at Tofino at ~20 ka ~75 km from the site dramatically increasing sedimentation. From ~19 to 17.3 ka GLOFs created cyclic (~80 year) sedimentary packages of ~300 Ma (ɛNd of ~-8) shale associated with terrestrial Corg, and ~100 Ma (ɛNd of ~-3) volcanic sediment associated with marine Corg. The GLOFs were likely to be associated with glacial lake Missoula outburst flooding, occurring during the interval of the coolest ocean temperatures (2-4°C) and most depleted δ18Oseawater (-1.75‰). At 17.3 ka as ocean temperatures increased by ~3°C and δ18Oseawater increased to ~0‰, IRD deposition increased dramatically at the site, terminating abruptly at 16.2 ka. At the Bølling, ocean temperatures rose by > 3°C to 10-12°C in association with an additional IRD

  14. Gross nitrogen fluxes in intact beech-soil-microbe systems under experimentally simulated climate change

    NASA Astrophysics Data System (ADS)

    Tejedor, Javier; Bilela, Silvija; Gasche Gasche, Rainer; Gschwendtner, Silvia; Leberecht, Martin; Bimüller, Carolin; Kögel-Knabner, Ingrid; Polle, Andrea; Schloter, Michael; Rennenberg, Heinz; Dannenmann, Michael

    2013-04-01

    The vulnerability of beech forests of Central Europe to projected climate change conditions is a current matter of debate and concern. In order to investigate the response of N cycling in a typical beech forest to projected climate change conditions, we transplanted small lysimeters with intact beech-soil systems from a slope with N-exposure (representing present day climate conditions) to a slope with S exposure (serving as a warmer and drier model climate for future conditions). Lysimeters transfers within the N exposure served as control. After an equilibration period of 1 year, three isotope labeling/harvest cycles were performed: (1) comparison between N and S slopes under ambient conditions; (2) comparison between N and S slopes after intensified drought at S exposure; (3) rewetting after the drought period. Homogenous triple isotope labeling (15N/13C glutamine, 15NH4+, 15NO3-) in combination with 15N tracing and -pool dilution approaches as well as molecular analyses of nitrogen cycling genes and mycorrhiza morphotyping allowed to simultaneously quantify all N turnover processes in the intact beech-soil-microbe system. Nitrate was the major N source of beech seedlings with little importance of ammonium and no importance of glutamine. Experimental simulation of climate change resulted in significantly reduced gene copies of ammonia oxidizing bacteria in soil (AOB), a dramatic attenuation of microbial gross nitrate production from 252±83 mg N m-2 day-1 for the control treatment to 49±29 mg N m-2 day-1 for the climate change treatment and associated strong declines in soil nitrate concentrations as well as nitrate uptake by microorganisms and beech, which could not be compensated by uptake of ammonium or glutamine. Therefore, N content of beech seedlings was strongly reduced in the climate change treatment. Hence our data provide a microbial mechanism to explain nutritional limitations of beech under higher temperatures and drought and raise questions about

  15. Historical changes in air temperature are evident in temperature fluxes measured in the sub-soil.

    NASA Astrophysics Data System (ADS)

    Fraser, Fiona; McCormick, Benjamin; Hallett, Paul; Wookey, Philip; Hopkins, David

    2013-04-01

    Warming trends in soil temperature have implications for a plethora of soil processes, including exacerbated climate change through the net release of greenhouse gases. Whereas long-term datasets of air temperature changes are abundant, a search of scientific literature reveals a lack of information on soil temperature changes and their specific consequences. We analysed five long-term data series collected in the UK (Dundee and Armagh) and Canada (Charlottetown, Ottawa and Swift Current). They show that the temperatures of soils at 5 - 20 cm depth, and sub-soils at 30 - 150 cm depth, increased in line with air temperature changes over the period 1958 - 2003. Differences were found, however, between soil and air temperatures when data were sub-divided into seasons. In spring, soil temperature warming ranged from 0.19°C at 30 cm in Armagh to 4.30°C at 50 cm in Charlottetown. In summer, however, the difference was smaller and ranged from 0.21°C at 10 cm in Ottawa to 3.70°C at 50 cm in Charlottetown. Winter temperatures were warmer in soil and ranged from 0.45°C at 5 cm in Charlottetown to 3.76°C at 150 cm in Charlottetown. There were significant trends in changes to soil temperature over time, whereas air temperature trends tended only to be significant in winter (changes range from 1.27°C in Armagh to 3.35°C in Swift Current). Differences in the seasonal warming patterns between air and soil temperatures have potential implications for the parameterization of models of biogeochemical cycling.

  16. Greenland meltwater impacts on the 234U/238U composition of seawater, the role of subglacial residence time.

    NASA Astrophysics Data System (ADS)

    Arendt, C. A.; Aciego, S.; Sims, K. W. W.; Stevenson, E. I.

    2014-12-01

    The chemical composition of seawater depends on the sources and sinks of the constituent elements, including those derived from continental weathering and transported by rivers. Glacial melt rivers compose a significant percentage of contributing water in the high latitudes, and potentially impact the overall composition of seawater. The magnitude of the chemical changes glacial melt can have on adjacent seawater depends on the composition of glacial melt, which is directly influenced by the subglacial residence time of meltwater. Long residence times correlate to subglacial water with both high cation concentrations and 234U/238U isotopic compositions. Thus, the residence time of subglacial water and corresponding subglacial geochemistry impacts the 234U/238U composition of proximal seawater and potentially global seawater. To test the influence of subglacial water residence times on seawater chemistry we examined the U-series composition of four outlet glaciers directly connected to the Southern Greenland Ice Sheet located near Narsarsuaq, Ilulissat, Nuuk and Kulusuk, and adjacent seawater at each site. All outlet glaciers in this study are located within three of the five primary drainage basins beneath the Greenland Ice Sheet, each in varying stages of subglacial hydrologic evolution, resulting in unique chemical compositions of meltwater draining from each location. At these four locations we found subglacial water residence time values of 10-1000 years. In regions where the U concentration, 234U/238U isotopic composition and residence times were high (1.01 ppb, 1.263 and ~1,000 years in Narsarsuaq) the adjacent seawater 234U/238U composition was elevated (1.152) compared to regions where the U concentration, 234U/238U isotopic composition and residence times were low (0.05 ppb, 1.008 and ~10 years in Illulisat) the adjacent seawater 234U/238U composition remained around the assumed seawater average (1.145). Through this study we observed a direct impact of

  17. /sup 10/Be in polar ice: Data reflect changes in cosmic ray flux or polar meteorology

    SciTech Connect

    Lal, D.

    1987-08-01

    We have theoretically estimated the expected changes in the global cosmic ray production of /sup 10/Be in the atmosphere with changes in solar activity, and the consequent variations in its fallout in the polar regions. The global /sup 10/Be production rate is found to be about 20% higher during periods of very low solar activity, compared to the average solar modulation level observed during the past 3 solar cycles. The stratospheric /sup 10/Be fallout pattern has been derived using the fallout data for /sup 90/Sr as an analog. This fallout shows an amplitude attenuation by a factor of about three at 70/sup 0/; the higher the latitude, the higher the attenuation. The results have been compared with the long time series available for /sup 10/Be in polar ice in Greenland and in Antarctica, 70/sup 0/--78/sup 0/ latitude. It is concluded that the observed variations in /sup 10/Be concentrations in ice cores are primarily due to climatic changes, for both short and long period variations. Thus /sup 10/Be data can be used as a proxy for climate induced meteorological changes in the polar region. copyright American Geophysical Union 1987

  18. Contemporary limnological and sedimentary analyses to investigate anthropogenic changes in nutrient fluxes at Lake Baikal, Siberia

    NASA Astrophysics Data System (ADS)

    Roberts, S.; McGowan, S.; Swann, G. E. A.; Mackay, A. W.; Panizzo, V.; Vologina, E.

    2014-12-01

    Large tectonic freshwater lakes face serious threats to their water quality, biological diversity and endemism through pollution and global warming. Lake Baikal is an important example as anthropogenic stressors (industrial pollution and cultural eutrophication) along with climate change could greatly affect the lake's unique ecosystem and pristine water conditions. Phosphorus, nitrogen and silica are thought to control phytoplankton development, however recent changes in nutrient impacts on Lake Baikal's phytoplankton remains unproven. This research aims to investigate the effect of anthropogenic and environmentally-driven changes on this large and biodiverse lake through seasonal sampling of the phytoplankton community (determined by chlorophyll and carotenoid pigments), chemical parameters (total phosphorus, dissolved organic carbon, silicate, nitrate and other major ions) and vertical profiles of pH, temperature and photosynethetically active radiation. Results show seasonal, vertical and spatial variability in the lake's phytoplankton biomass and composition with higher summer mixed-layer pigment concentrations in the south basin resulting in higher light attenuation coefficients and lower photic zone depths (R2=0.86, p < 0.05). Redundancy analysis shows that this distribution is primarily influenced by average dissolved organic carbon concentrations within the mixing layer, with the strongest negative correlation between picoplankton biomarkers and dissolved organic carbon concentrations (R2=-0.60, p < 0.05). Geochemical biomarkers (pigments and organic carbon [δ13Corganic]) from several sediment cores place these modern day observations within an historical context and allow the impact of past environmental changes on Lake Baikal's primary productivity over the last 60 years and natural climate-driven trends in past centuries to be assessed. These results show clear spatial and temporal changes between sites over this interval with greater increases in

  19. Assessing the impacts of climate change and socio-economic changes on flow and phosphorus flux in the Ganga river system.

    PubMed

    Jin, L; Whitehead, P G; Sarkar, S; Sinha, R; Futter, M N; Butterfield, D; Caesar, J; Crossman, J

    2015-06-01

    Anthropogenic climate change has impacted and will continue to impact the natural environment and people around the world. Increasing temperatures and altered rainfall patterns combined with socio-economic factors such as population changes, land use changes and water transfers will affect flows and nutrient fluxes in river systems. The Ganga river, one of the largest river systems in the world, supports approximately 10% global population and more than 700 cities. Changes in the Ganga river system are likely to have a significant impact on water availability, water quality, aquatic habitats and people. In order to investigate these potential changes on the flow and water quality of the Ganga river, a multi-branch version of INCA Phosphorus (INCA-P) model has been applied to the entire river system. The model is used to quantify the impacts from a changing climate, population growth, additional agricultural land, pollution control and water transfers for 2041-2060 and 2080-2099. The results provide valuable information about potential effects of different management strategies on catchment water quality. PMID:25892033

  20. Limits on Low Frequency Radio Flux Density Changes for Sgr A*

    NASA Astrophysics Data System (ADS)

    Brunthaler, Andreas; Falcke, Heino

    2013-06-01

    We report new limits on changes low frequency emission for Sgr A* based on Jansky VLA observations obtained on 2013 June 09 (ATEL #5153) . Data were obtained through the NRAO Service Observing program (https://science.nrao.edu/science/service-observing/service-observing). The JVLA is currently in the compact C-configuration, providing low resolution observations in which Sgr A* is heavily confused by diffuse structure associated with Sgr A West and East.

  1. Ocean-atmosphere dynamics changes associated with prominent ocean surface turbulent heat fluxes trends during 1958-2013

    NASA Astrophysics Data System (ADS)

    Yang, Hu; Liu, Jiping; Lohmann, Gerrit; Shi, Xiaoxu; Hu, Yongyun; Chen, Xueen

    2016-03-01

    Three prominent features of ocean surface turbulent heat fluxes (THF) trends during 1958-2013 are identified based on the Objectively Analyzed air-sea Fluxes (OAFlux) data set. The associated ocean-atmosphere dynamics changes are further investigated based on the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. First, the THF are enhanced over the mid-latitude expansions of the subtropical western boundary currents (WBCs). An intensified oceanic heat transport, forced by stronger near-surface zonal wind, is likely to be the cause of such THF tendency. Second, the THF are reduced over the tropical eastern Pacific Ocean, which is primarily caused by the decreasing near-surface wind speed and sea surface temperature (SST), associated with a local coupled ocean-atmosphere cooling mode. Finally, the THF are reduced over the northern tropical Atlantic Ocean, which is attributed to the decreasing air-sea humidity and temperature differences as a result of the convergence of near-surface air and the divergence of ocean currents (upwelling).

  2. Land-use change and carbon flux between 1970s and 1990s in central highlands of Chiapas, Mexico

    SciTech Connect

    Jong, B.H.J. de; Ramirez-Marcial, N.; Ochoa-Gaona, S.; Mendoza-Vega, J.; Gonzalez-Espinosa, M.; March-Mifsut, I.; Cairns, M.A.; Haggerty, P.K.

    1999-04-01

    The authors present results of a study in an intensively impacted and highly fragmented landscape in which they apply field-measured carbon (C) density values to land-use/land-cover (LU/LC) statistics to estimate the flux of C between terrestrial ecosystems and the atmosphere from the 1970s and 1990s. Carbon densities were assigned to common LU/LC classes on vegetation maps produced by Mexican governmental organizations and, by differencing areas and C pools, net C flux was calculated from the central highlands of Chiapas, Mexico, during a 16-year period. The total area of closed forests was reduced by half while degraded and fragmented forests expanded 56% and cultivated land and pasture areas increased by 8% and 30%, respectively. Total mean C densities ranged from a high of 504 tons C/ha in the oak and evergreen cloud forests class to a low of 147 tons C/ha in the pasture class. The differences in total C densities among the various LU/LC classes were due to changes in biomass while soil organic matter C remained similar. The authors estimate that a total of 19.99 {times} 10{sup 6} tons C were released to the atmosphere during the period of time covered by the study, equal to approximately 34% of the 1975 vegetation C pool. The Chiapas highlands, while comprising just 0.3% of Mexico`s surface area, contributed 3% of the net national C emissions.

  3. Land use change effects on trace gas fluxes in the forest margins of Central Sulawesi, Indonesia

    NASA Astrophysics Data System (ADS)

    Veldkamp, Edzo; Purbopuspito, Joko; Corre, Marife D.; Brumme, Rainer; Murdiyarso, Daniel

    2008-06-01

    Land use changes and land use intensification are considered important processes contributing to the increasing concentrations of the greenhouse gases nitrous oxide (N2O) and methane (CH4) and of nitric oxide (NO), a precursor of ozone. Studies on the effects of land use changes and land use intensification on soil trace gas emissions were mostly conducted in Latin America and only very few in Asia. Here we present results from Central Sulawesi where profound changes in land use and cultivation practices take place: traditional agricultural practices like shifting cultivation and slash-and-burn agriculture are replaced by permanent cultivation systems and introduction of income-generating cash crops like cacao. Our results showed that N2O emissions were higher from cacao agroforestry (35 ± 10 μg N m-2 h-1) than maize (9 ± 2 μg N m-2 h-1), whereas intermediate rates were observed from secondary forests (25 ± 11 μg N m-2 h-1). NO emissions did not differ among land use systems, ranging from 12 ± 2 μg N m-2 h-1 for cacao agroforestry and secondary forest to 18 ± 2 μg N m-2 h-1 for maize. CH4 uptake was higher for maize (-30 ± 4 μg C m-2 h-1) than cacao agroforestry (-18 ± 2 μg C m-2 h-1) and intermediate rates were measured from secondary forests (-25 ± 4 μg C m-2 h-1). Combining these data with results from other studies in this area, we present chronosequence effects of land use change on trace gas emissions from natural forest, through maize cultivation, to cacao agroforestry (with or without fertilizer). Compared to the original forests, this typical land use change in the study area clearly led to higher N2O emissions and lower CH4 uptake with age of cacao agroforestry systems. We conclude that this common land use sequence in the area combined with the increasing use of fertilizer will strongly increase soil trace gas emissions. We suggest that the future hot spot regions of high N2O (and to a lesser extend NO) emissions in the tropics are those

  4. Climate and air quality impacts of altered BVOC fluxes from land cover change in Southeast Asia 1990 - 2010

    NASA Astrophysics Data System (ADS)

    Harper, Kandice; Yue, Xu; Unger, Nadine

    2016-04-01

    Large-scale transformation of the natural rainforests of Southeast Asia in recent decades, driven primarily by logging and agroforestry activities, including rapid expansion of plantations of high-isoprene-emitting oil palm (Elaeis guineensis) trees at the expense of comparatively low-emitting natural dipterocarp rainforests, may have altered the prevailing regime of biogenic volatile organic compound (BVOC) fluxes from this tropical region. Chemical processing of isoprene in the atmosphere impacts the magnitude and distribution of several short-lived climate forcers, including ozone and secondary organic aerosols. Consequently, modification of the fluxes of isoprene and other BVOCs from vegetation serves as a mechanism by which tropical land cover change impacts both air quality and climate. We apply satellite-derived snapshots of land cover for the period 1990 - 2010 to the NASA ModelE2-Yale Interactive Terrestrial Biosphere (ModelE2-YIBs) global carbon-chemistry-climate model to quantify the impact of Southeast Asian land cover change on atmospheric chemical composition and climate driven by changes in isoprene emission. NASA ModelE2-YIBs features a fully interactive land carbon cycle and includes a BVOC emission algorithm which energetically couples isoprene production to photosynthesis. The time-slice simulations are nudged with large-scale winds from the GMAO reanalysis dataset and are forced with monthly anthropogenic and biomass burning reactive air pollution emissions from the MACCity emissions inventory. Relative to the year 1990, regional isoprene emissions in 2010 increased by 2.6 TgC/yr from the expansion of Southeast Asian oil palm plantations and decreased by 0.7 TgC/yr from the loss of regional dipterocarp rainforest. Considering only the impact of land-cover-change-induced isoprene emission changes in Southeast Asia over this period, we calculate a spatially heterogeneous impact on regional seasonal surface-level ozone concentrations (minimum: -1

  5. Land cover change in the zone of sporadic permafrost causes shift in landscape-scale turbulent energy fluxes

    NASA Astrophysics Data System (ADS)

    Helbig, M.; Wischnewski, K.; Kljun, N.; Chasmer, L.; Quinton, W. L.; Detto, M.; Sonnentag, O.

    2015-12-01

    Boreal forests in the sporadic permafrost zone have been shown to decline at the expense of wetlands following permafrost disappearance. These land cover changes cause shifts in ecosystem properties and affect biosphere-atmosphere interactions. The goal of our study is to examine the effects of permafrost disappearance on landscape-scale sensible (H) and latent heat fluxes (LE) and related potential feedbacks on regional air temperatures (Ta) We use a combination of nested eddy covariance flux towers, flux footprint and planetary boundary layer (PBL) dynamic modelling, and MOderate-resolution Imaging Spectroradiometer (MODIS) remote sensing products to resolve spatio-temporal dynamics in H and LE at the landscape scale at Scotty Creek, NWT (61º18' N; 121º18' W) and in radiometric land surface temperatures (LST) at the regional scale across the southern Taiga Plains in the sporadic permafrost zone of northwestern Canada. The heterogeneous landscape comprises boreal forests with permafrost and permafrost-free wetlands. Our results show that H above the heterogeneous landscape was about twice as high as above a nearby treeless, permafrost-free bog. In contrast, landscape-scale LE was only about 50 % of LE over the bog. These differences were primarily driven by higher heat transfer efficiency of the aerodynamically rougher forest and lower albedo of the forest compared to the bog (about 10 % lower during summer and about 40 % lower during late winter). Aerodynamic LST increased with the fraction of forest in the flux footprints. This effect was strongest (r2 = 0.55, slope = 0.06 K per % forest) at the end of winter when contrasts in albedo are largest. Bulk surface conductance increased with the fraction of wetlands in the footprints. On a regional scale, radiometric MODIS LST increased with tree cover during the snow cover period (0.06 K per % tree cover), but decreased during the summer (-0.04 K per % tree cover). Modelling results showed that a shift from the

  6. Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya

    NASA Astrophysics Data System (ADS)

    Wulf, H.; Bookhagen, B.; Scherler, D.

    2012-07-01

    The sediment flux through Himalayan rivers directly impacts water quality and is important for sustaining agriculture as well as maintaining drinking-water and hydropower generation. Despite the recent increase in demand for these resources, little is known about the triggers and sources of extreme sediment flux events, which lower water quality and account for extensive hydropower reservoir filling and turbine abrasion. Here, we present a comprehensive analysis of the spatiotemporal trends in suspended sediment flux based on daily data during the past decade (2001-2009) from four sites along the Sutlej River and from four of its main tributaries. In conjunction with satellite data depicting rainfall and snow cover, air temperature and earthquake records, and field observations, we infer climatic and geologic controls of peak suspended sediment concentration (SSC) events. Our study identifies three key findings: First, peak SSC events (≥ 99th SSC percentile) coincide frequently (57-80%) with heavy rainstorms and account for about 30% of the suspended sediment flux in the semi-arid to arid interior of the orogen. Second, we observe an increase of suspended sediment flux from the Tibetan Plateau to the Himalayan Front at mean annual timescales. This sediment-flux gradient suggests that averaged, modern erosion in the western Himalaya is most pronounced at frontal regions, which are characterized by high monsoonal rainfall and thick soil cover. Third, in seven of eight catchments, we find an anticlockwise hysteresis loop of annual sediment flux variations with respect to river discharge, which appears to be related to enhanced glacial sediment evacuation during late summer. Our analysis emphasizes the importance of unconsolidated sediments in the high-elevation sector that can easily be mobilized by hydrometeorological events and higher glacial-meltwater contributions. In future climate change scenarios, including continuous glacial retreat and more frequent

  7. Dynamic volume changes in astrocytes are an intrinsic phenomenon mediated by bicarbonate ion flux.

    PubMed

    Florence, Clare M; Baillie, Landon D; Mulligan, Sean J

    2012-01-01

    Astrocytes, the major type of non-neuronal cells in the brain, play an important functional role in extracellular potassium ([K(+)](o)) and pH homeostasis. Pathological brain states that result in [K(+)](o) and pH dysregulation have been shown to cause astrocyte swelling. However, whether astrocyte volume changes occur under physiological conditions is not known. In this study we used two-photon imaging to visualize real-time astrocyte volume changes in the stratum radiatum of the hippocampus CA1 region. Astrocytes were observed to swell by 19.0±0.9% in response to a small physiological increase in the concentration of [K(+)](o) (3 mM). Astrocyte swelling was mediated by the influx of bicarbonate (HCO(3-)) ions as swelling was significantly decreased when the influx of HCO(3-) was reduced. We found: 1) in HCO(3-) free extracellular solution astrocytes swelled by 5.4±0.7%, 2) when the activity of the sodium-bicarbonate cotransporter (NBC) was blocked the astrocytes swelled by 8.3±0.7%, and 3) in the presence of an extracellular carbonic anhydrase (CA) inhibitor astrocytes swelled by 11.4±0.6%. Because a significant HCO(3-) efflux is known to occur through the γ-amino-butyric acid (GABA) channel, we performed a series of experiments to determine if astrocytes were capable of HCO(3-) mediated volume shrinkage with GABA channel activation. Astrocytes were found to shrink -7.7±0.5% of control in response to the GABA(A) channel agonist muscimol. Astrocyte shrinkage from GABA(A) channel activation was significantly decreased to -5.0±0.6% of control in the presence of the membrane-permeant CA inhibitor acetazolamide (ACTZ). These dynamic astrocyte volume changes may represent a previously unappreciated yet fundamental mechanism by which astrocytes regulate physiological brain functioning. PMID:23226475

  8. Origin of dc voltage in type II superconducting flux pumps: field, field rate of change, and current density dependence of resistivity

    NASA Astrophysics Data System (ADS)

    Geng, J.; Matsuda, K.; Fu, L.; Fagnard, J.-F.; Zhang, H.; Zhang, X.; Shen, B.; Dong, Q.; Baghdadi, M.; Coombs, T. A.

    2016-03-01

    Superconducting flux pumps are the kind of devices which can generate direct current into superconducting circuit using external magnetic field. The key point is how to induce a dc voltage across the superconducting load by ac fields. Giaever (1966 IEEE Spectr. 3 117) pointed out flux motion in superconductors will induce a dc voltage, and demonstrated a rectifier model which depended on breaking superconductivity. van de Klundert et al (1981 Cryogenics 21 195, 267) in their review(s) described various configurations for flux pumps all of which relied on inducing the normal state in at least part of the superconductor. In this letter, following their work, we reveal that a variation in the resistivity of type II superconductors is sufficient to induce a dc voltage in flux pumps and it is not necessary to break superconductivity. This variation in resistivity is due to the fact that flux flow is influenced by current density, field intensity, and field rate of change. We propose a general circuit analogy for travelling wave flux pumps, and provide a mathematical analysis to explain the dc voltage. Several existing superconducting flux pumps which rely on the use of a travelling magnetic wave can be explained using the analysis enclosed. This work can also throw light on the design and optimization of flux pumps.

  9. Younger Dryas sea level and meltwater pulse 1B recorded in Barbados reef crest coral Acropora palmata

    NASA Astrophysics Data System (ADS)

    Abdul, N. A.; Mortlock, R. A.; Wright, J. D.; Fairbanks, R. G.

    2016-02-01

    The Younger Dryas climate event occurred during the middle of the last deglacial cycle and is marked by an abrupt shift in the North Atlantic polar front almost to its former glacial position, trending east to west. Using high-precision and high-accuracy U-Th-dated Barbados reef crest coral, Acropora palmata, we generate a detailed sea level record from 13.9 to 9000 years before present (kyr B.P.) and reconstruct the ice volume response to the Younger Dryas cooling. From the mid-Allerød (13.9 kyr B.P.) to the end of the Younger Dryas (11.65 kyr B.P.), rates of sea level rise decreased smoothly from 20 mm yr-1 to 4 mm yr-1, culminating in a 400 year "slow stand" before accelerating into meltwater pulse 1B (MWP-1B). The MWP-1B event at Barbados is better constrained as beginning by 11.45 kyr B.P. and ending at 11.1 kyr B.P. during which time sea level rose 14 ± 2 m and rates of sea level rise reached 40 mm yr-1. We propose that MWP-1B is the direct albeit lagged response of the Northern Hemisphere ice sheets to the rapid warming marking the end of the Younger Dryas coinciding with rapid warming in the circum-North Atlantic region and the polar front shift from its zonal to meridional position 11.65 kyr B.P. As predicted by glaciological models, the ice sheet response to rapid North Atlantic warming was lagged by 400 years due to the thermal inertia of large ice sheets. The regional circum-North Atlantic Younger Dryas climate event is elevated to a global response through sea level changes, starting with the global slowdown in sea level rise during the Younger Dryas and culminating with MWP-1B. No meltwater pulses are evident at the initiation of the Younger Dryas climate event as is often speculated.

  10. Moisture Flux Convergence in Regional and Global Climate Models: Implications for Droughts in the Southwestern United States Under Climate Change

    SciTech Connect

    Gao, Yanhong; Leung, Lai-Yung R.; Salathe, E.; Dominguez, Francina; Nijssen, Bart; Lettenmaier, D. P.

    2012-05-10

    The water cycle of the southwestern United States (SW) is dominated by winter storms that maintain a positive annual net precipitation. Analysis of the control and future climate from four pairs of regional and global climate models (RCMs and GCMs) shows that the RCMs simulate a higher fraction of transient eddy moisture fluxes because the hydrodynamic instabilities associated with flow over complex terrain are better resolved. Under global warming, this enables the RCMs to capture the response of transient eddies to increased atmospheric stability that allows more moisture to converge on the windward side of the mountains by blocking. As a result, RCMs simulate enhanced transient eddy moisture convergence in the SW compared to GCMs, although both robustly simulate drying due to enhanced moisture divergence by the divergent mean flow in a warmer climate. This enhanced convergence leads to reduced susceptibility to hydrological change in the RCMs compared to GCMs.

  11. Increasing confidence in model predictive capabilities under climate change through diagnosis of consistency of internal fluxes and storages

    NASA Astrophysics Data System (ADS)

    Jackson, B. M.; McMillan, H. K.; Poyck, S.

    2009-12-01

    As part of research to quantify the effects of climate change on soil conditions, river flow and flood risk, we present a critical examination of the internal consistency of states and fluxes within the physically based catchment scale conceptual model TopNet. TopNet is a New Zealand developed adaption of TOPMODEL, the well-known variable contributing area conceptual modelling framework. As the model is physically based, many parameters can in theory be related back to field measurements but in practice most applications are calibrated with extremely limited information. In such cases TopNet, like most models, is susceptible to parameter interdependence where an unrealistic value in one parameter can compensate for an unrealistic value in another parameter. Therefore, internal catchment processes can be poorly represented while still providing "good" streamflow simulations for the basin as a whole. This issue seriously compromises our confidence in models reacting correctly to novel meteorological conditions under a changed climate. Here, we test TopNet to check that it is giving the ‘right answers for the right reasons’, i.e. that the internal model fluxes and storage (overland flow, soil storage, shallow groundwater flow, saturated zone extent, etc) are a reasonable simulation of reality. We present results from the flood prone Uawa catchment in the Gisborne region of New Zealand, interrogating internal TopNet states against a detailed high resolution model of surface and subsurface flow and additionally examining both models and their recommended calibration ranges against national scale and detailed hillslope scale soil hydraulic data. Measurements of infiltration capacity and soil profiling to 1m depth including particle size analysis, bulk density and organic matter fractions have been obtained from the site and related to soil moisture characteristics. Inconsistencies between these, the national scale soil and land use data that are otherwise used to

  12. Estuarine removal of glacial iron and implications for iron fluxes to the ocean

    NASA Astrophysics Data System (ADS)

    Schroth, Andrew W.; Crusius, John; Hoyer, Ian; Campbell, Robert

    2014-06-01

    While recent work demonstrates that glacial meltwater provides a substantial and relatively labile flux of the micronutrient iron to oceans, the role of high-latitude estuary environments as a potential sink of glacial iron is unknown. Here we present the first quantitative description of iron removal in a meltwater-dominated estuary. We find that 85% of "dissolved" Fe is removed in the low-salinity region of the estuary along with 41% of "total dissolvable" iron associated with glacial flour. We couple these findings with hydrologic and geochemical data from Gulf of Alaska (GoA) glacierized catchments to calculate meltwater-derived fluxes of size and species partitioned Fe to the GoA. Iron flux data indicate that labile iron in the glacial flour and associated Fe minerals dominate the meltwater contribution to the Fe budget of the GoA. As such, GoA nutrient cycles and related ecosystems could be strongly influenced by continued ice loss in its watershed.

  13. A dynamic model to predict fat and protein fluxes and dry matter intake associated with body reserve changes in cattle.

    PubMed

    Tedeschi, Luis O; Fox, Danny G; Kononoff, Paul J

    2013-04-01

    The objective of this paper was to develop the structure and concepts of a dynamic model to simulate dry matter intake (DMI) pattern and the fluxes of fat and protein in the body reserves of cattle associated with changes in body condition score (BCS) for application within the structure of applied nutrition models. This model was developed to add the capability of evaluating the effects of factors affecting pre- and postcalving DMI, daily energy and protein balances, and changes in BCS over a reproductive cycle. Input variables are average DMI, diet metabolizable energy, and animal information (body weight, BCS, milk production, and calf birth body weight) from each diet fed over the reproductive cycle. Because the depletion and repletion of body reserves in cattle is a complex system of coordinated metabolic processes that reflect hormonal and physiological changes caused by negative or positive energy balances, the system dynamics modeling methodology was used to develop this model. The model was used to evaluate the effect of the dynamic interactions between dietary supply and animal requirements for energy and protein on the fluxes of body fat and body protein of dairy cows over the reproductive cycle and Monte Carlo simulations were used to assess the sensitivity of the parameters. The main long-term factor affecting DMI pattern was the growth of the gravid uterus causing an increase in the volume of abdominal organs and a compression of the rumen, consequentially reducing feed intake. Changes in body reserves (fat and protein) were computed based on metabolizable energy balance, assuming different efficiency of utilization coefficients for fat and protein during repletion and mobilization. The model was evaluated with data from 37 dairy cows individually fed 3 different diets over the lactation and dry periods. The model was successful in simulating the observed pattern of DMI (mean square error was 3.59, 3.97, and 3.66 for diets A, B, and C, respectively

  14. Ocean Response to Possible Southern Meltwater Pulses During Eocene-Oligocene Cooling Climate Trend: A Sensitivity Ocean Modeling Study

    NASA Astrophysics Data System (ADS)

    Haupt, B. J.; Seidov, D.

    2003-12-01

    Understanding ocean circulation and sea level change in the past (and foreseeable future) is one of the focal points of paleoceanography. Sea level may change due to several primary causes, including the meltdown of the major ice sheets, sea ice melting, and changes in the thermohaline structure of the oceans. The sensitivity of the past ocean circulation to meltwater impacts may have been different from the present-day. We still have only a vague understanding of how ocean basin geography may influence the freshwater impacts in different oceans; the role of geography is important for reconstructing variability of past climates with substantially different land-sea distributions. As freshwater impacts in past geologic eras having different basins configurations may have been different from the present-day pattern, the sensitivity of the ocean circulation to sea surface density impacts and climate change could have been different as well. We use the Eocene-Oligocene geometry and climate to address the past ocean and sea level long-term internal variability because this time slice provides a substantially different geometry and for a strong sea ice impact that can be seen in the geologic record. The Eocene epoch is crucial as a transition from the warm Cretaceous ocean to cooler oceans that may have been subject to bi-polar millennial-scale oscillations of the deep ocean circulation caused by freshwater pulses of the developing southern cryosphere. In a series of numerical experiments, sea ice melting and sea water freezing around Antarctica were simulated by superimposing freshwater layers over zonally-averaged sea surface salinity. Eocene sea surface temperature and sea surface salinity are specified based on the paleoclimatic record and modeling. In our simulations, the Eocene ocean circulation is indeed sensitive to freshwater impacts in the Southern Hemisphere. There are noticeable sea level changes caused by the restructuring of the deep ocean thermal and

  15. Measuring Bathymetry, Runup, and Beach Volume Change during Storms: New Methodology Quantifies Substantial Changes in Cross-Shore Sediment Flux

    NASA Astrophysics Data System (ADS)

    Brodie, K. L.; McNinch, J. E.

    2009-12-01

    Accurate predictions of beach change during storms are contingent upon a correct understanding of wave-driven sediment exchange between the beach and nearshore during high energy conditions. Conventional storm data sets use “pre” (often weeks to months prior) and “post” (often many days after the storm in calm conditions) collections of beach topography and nearshore bathymetry to characterize the effects of the storm. These data have led to a common theory for wave-driven event response of the nearshore system, wherein bars and shorelines are smoothed and straightened by strong alongshore currents into two-dimensional, linear forms. Post-storm, the shoreline accretes, bars migrate onshore, and three-dimensional shapes begin to build as low-energy swell returns. Unfortunately, these approaches have left us with a knowledge gap of the extent and timing of erosion and accretion during storms, arguably the most important information both for scientists trying to model storm damage or inundation, and homeowners trying to manage their properties. This work presents the first spatially extensive (10 km alongshore) and temporally high-resolution (dt = 12 hours) quantitative data set of beach volume and nearshore bathymetry evolution during a Nor’easter on North Carolina’s Outer Banks. During the Nor’easter, significant wave height peaked at 3.4 m, and was greater than 2 m for 37 hours, as measured by the Duck FRF 8 m array. Data were collected using CLARIS: Coastal Lidar and Radar Imaging System, a mobile system that couples simultaneous observations of beach topography from a Riegl laser scanner and nearshore bathymetry (out to ~1 km offshore) from X-Band radar-derived celerity measurements (BASIR). The merging of foreshore lidar elevations with 6-min averages of radar-derived swash runup also enables mapping of maximum-runup elevations alongshore during the surveys. Results show that during the storm, neither the shoreline nor nearshore bathymetry returned

  16. Quantum theory of atoms in molecules/charge-charge flux-dipole flux models for fundamental vibrational intensity changes on H-bond formation of water and hydrogen fluoride

    SciTech Connect

    Silva, Arnaldo F.; Richter, Wagner E.; Bruns, Roy E.; Terrabuio, Luiz A.; Haiduke, Roberto L. A.

    2014-02-28

    The Quantum Theory of Atoms In Molecules/Charge-Charge Flux-Dipole Flux (QTAIM/CCFDF) model has been used to investigate the electronic structure variations associated with intensity changes on dimerization for the vibrations of the water and hydrogen fluoride dimers as well as in the water-hydrogen fluoride complex. QCISD/cc-pVTZ wave functions applied in the QTAIM/CCFDF model accurately provide the fundamental band intensities of water and its dimer predicting symmetric and antisymmetric stretching intensity increases for the donor unit of 159 and 47 km mol{sup −1} on H-bond formation compared with the experimental values of 141 and 53 km mol{sup −1}. The symmetric stretching of the proton donor water in the dimer has intensity contributions parallel and perpendicular to its C{sub 2v} axis. The largest calculated increase of 107 km mol{sup −1} is perpendicular to this axis and owes to equilibrium atomic charge displacements on vibration. Charge flux decreases occurring parallel and perpendicular to this axis result in 42 and 40 km mol{sup −1} total intensity increases for the symmetric and antisymmetric stretches, respectively. These decreases in charge flux result in intensity enhancements because of the interaction contributions to the intensities between charge flux and the other quantities. Even though dipole flux contributions are much smaller than the charge and charge flux ones in both monomer and dimer water they are important for calculating the total intensity values for their stretching vibrations since the charge-charge flux interaction term cancels the charge and charge flux contributions. The QTAIM/CCFDF hydrogen-bonded stretching intensity strengthening of 321 km mol{sup −1} on HF dimerization and 592 km mol{sup −1} on HF:H{sub 2}O complexation can essentially be explained by charge, charge flux and their interaction cross term. Atomic contributions to the intensities are also calculated. The bridge hydrogen atomic contributions alone

  17. The impacts of land use changes in the mercury flux in the Madeira River, Western Amazon.

    PubMed

    Lacerda, Luiz D; Bastos, Wanderley R; Almeida, Marcelo D

    2012-03-01

    Changes in hydrochemistry and Hg distribution in the Madeira River from Porto Velho to the confluence with the Amazon River were studied in two cruises in 1997 and 2002. Water conductivity was similar in both periods, but the pH was significantly higher in 2002, in particular along the middle reaches of the river. Total suspended matter concentrations also increased from 1997 to 2002 along the same river portion, which is a result of forest conversion to other land uses, in particular pastures and agriculture accelerated during the interval between the cruises. Dissolved Hg concentrations were similar along the river in both cruises, but particulate Hg concentrations increased significantly along the middle portion of the river, although the suspended matter from 2002 was relatively poorer in Hg compared to that from 1997. Since particulate Hg represents more than 90% of the total Hg present in the river water, there was a significant increase in the total Hg transport in the Madeira River. Although gold mining has nearly ceased to exist in the region, the remobilization of Hg from forest soils through conversion to other land uses is responsible for maintaining relatively high Hg content in the Madeira River environment. PMID:22441596

  18. Evidence for a substantial West Antarctic ice sheet contribution to meltwater pulses and abrupt global sea level rise

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Turney, C. S.; Golledge, N. R.; Etheridge, D. M.; Rubino, M.; Thornton, D.; Woodward, J.; Winter, K.; van Ommen, T. D.; Moy, A. D.; Curran, M. A.; Rootes, C.; Rivera, A.; Millman, H.

    2015-12-01

    During the last deglaciation (21,000 to 7,000years ago) global sea level rise was punctuated by several abrupt meltwater spikes triggered by the retreat of ice sheets and glaciers world-wide. However, the debate regarding the relative timing, geographical source and the physical mechanisms driving these rapid increases in sea level has catalyzed debate critical to predicting future sea level rise and climate. Here we present a unique record of West Antarctic Ice Sheet elevation change derived from the Patriot Hills blue ice area, located close to the modern day grounding line of the Institute Ice Stream in the Weddell Sea Embayment. Combined isotopic signatures and gas volume analysis from the ice allows us to develop a record of local ice sheet palaeo-altitude that is assessed against independent regional high-resolution ice sheet modeling studies, allowing us to demonstrate that past ice sheet elevations across this sector of the WSE were considerably higher than those suggested by current terrestrial reconstructions. We argue that ice in the WSE had a significant influence on both pre and post LGM sea level rise including MWP-1A (~14.6 ka) and during MWP-1B (11.7-11.6 ka), reconciling past sea level rise and demonstrating for the first time that this sector of the WAIS made a significant and direct contribution to post LGM sea level rise.

  19. Benthic microbial communities of coastal terrestrial and ice shelf Antarctic meltwater ponds

    PubMed Central

    Archer, Stephen D. J.; McDonald, Ian R.; Herbold, Craig W.; Lee, Charles K.; Cary, Craig S.

    2015-01-01

    The numerous perennial meltwater ponds distributed throughout Antarctica represent diverse and productive ecosystems central to the ecological functioning of the surrounding ultra oligotrophic environment. The dominant taxa in the pond benthic communities have been well described however, little is known regarding their regional dispersal and local drivers to community structure. The benthic microbial communities of 12 meltwater ponds in the McMurdo Sound of Antarctica were investigated to examine variation between pond microbial communities and their biogeography. Geochemically comparable but geomorphologically distinct ponds were selected from Bratina Island (ice shelf) and Miers Valley (terrestrial) (<40 km between study sites), and community structure within ponds was compared using DNA fingerprinting and pyrosequencing of 16S rRNA gene amplicons. More than 85% of total sequence reads were shared between pooled benthic communities at different locations (OTU0.05), which in combination with favorable prevailing winds suggests aeolian regional distribution. Consistent with previous findings Proteobacteria and Bacteroidetes were the dominant phyla representing over 50% of total sequences; however, a large number of other phyla (21) were also detected in this ecosystem. Although dominant Bacteria were ubiquitous between ponds, site and local selection resulted in heterogeneous community structures and with more than 45% of diversity being pond specific. Potassium was identified as the most significant contributing factor to the cosmopolitan community structure and aluminum to the location unique community based on a BEST analysis (Spearman's correlation coefficient of 0.632 and 0.806, respectively). These results indicate that the microbial communities in meltwater ponds are easily dispersed regionally and that the local geochemical environment drives the ponds community structure. PMID:26074890

  20. Benthic microbial communities of coastal terrestrial and ice shelf Antarctic meltwater ponds.

    PubMed

    Archer, Stephen D J; McDonald, Ian R; Herbold, Craig W; Lee, Charles K; Cary, Craig S

    2015-01-01

    The numerous perennial meltwater ponds distributed throughout Antarctica represent diverse and productive ecosystems central to the ecological functioning of the surrounding ultra oligotrophic environment. The dominant taxa in the pond benthic communities have been well described however, little is known regarding their regional dispersal and local drivers to community structure. The benthic microbial communities of 12 meltwater ponds in the McMurdo Sound of Antarctica were investigated to examine variation between pond microbial communities and their biogeography. Geochemically comparable but geomorphologically distinct ponds were selected from Bratina Island (ice shelf) and Miers Valley (terrestrial) (<40 km between study sites), and community structure within ponds was compared using DNA fingerprinting and pyrosequencing of 16S rRNA gene amplicons. More than 85% of total sequence reads were shared between pooled benthic communities at different locations (OTU0.05), which in combination with favorable prevailing winds suggests aeolian regional distribution. Consistent with previous findings Proteobacteria and Bacteroidetes were the dominant phyla representing over 50% of total sequences; however, a large number of other phyla (21) were also detected in this ecosystem. Although dominant Bacteria were ubiquitous between ponds, site and local selection resulted in heterogeneous community structures and with more than 45% of diversity being pond specific. Potassium was identified as the most significant contributing factor to the cosmopolitan community structure and aluminum to the location unique community based on a BEST analysis (Spearman's correlation coefficient of 0.632 and 0.806, respectively). These results indicate that the microbial communities in meltwater ponds are easily dispersed regionally and that the local geochemical environment drives the ponds community structure. PMID:26074890

  1. Pathways and transit time of meltwater in the englacial drainage system of Rabots Glacier, Kebnekaise, Sweden

    NASA Astrophysics Data System (ADS)

    Coch, Caroline; Clason, Caroline; Rosqvist, Gunhild; Jarsjö, Jerker; Brugger, Keith

    2014-05-01

    Following the crash of a Norwegian Hercules plane in the Kebnekaise mountain range in March 2012, a field campaign was initiated in order to assess the fate of the hydrocarbon pollution in the glacial system. Monitoring of pollution was conducted in the snow pack of Rabots glacier, as well as in the proglacial stream, and the preferential pathways for transport of pollutants were assessed. Since it is likely that soluble components of the aircraft fuel are transported within the glacial meltwater, our study focuses on constraining the likely transit time and dispersion of these components. The hydrologic configuration of Rabots glacier was thus studied during the 2013 ablation season by means of dye tracing experiments and discharge monitoring in the proglacial stream. The analyses of the dye return curves and stream monitoring suggest different hydrological configurations on the north and south side of the glacier, perhaps influenced by shading and the ice thermal structure. The system on the north side seems to be distributed, with extensive interaction of meltwater with the bed, as typified in the turbid proglacial outlet. The distinct peaks of the return curves on the south side indicate efficient transport, perhaps largely through englacial channels, given the relatively clear nature of the proglacial outlet. The evaluation of transit speed along a longitudinal profile contributed to the understanding of drainage efficiency with distance upglacier. The higher up the injection location on the glacier, the more distributed and less efficient the system. The seasonal evolution of efficiency was also assessed, showing an increase inefficiency with time. Furthermore, we hypothesize a disconnect in the glacial hydrological systems on the north and south side of the glacier. Pollution that is transported with the meltwater down from the crash site on the southern side most likely does not reach the drainage system on the northern side. Besides revealing potential

  2. Short-term changes in particulate fluxes measured by drifting sediment traps during end summer oligotrophic regime in the NW Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Marty, J. C.; Goutx, M.; Guigue, C.; Leblond, N.; Raimbault, P.

    2009-01-01

    Short-term changes in the flux of particulate matter were determined in the central north western Mediterranean Sea (near DYFAMED site) using drifting sediment traps at 200 m depth in the course of the DYNAPROC 2 cruise (14 September-17 October, 2004). In this period of marked water column stratification, POC fluxes varied by an order of magnitude, in the range of 0.03-0.29 mg C m-2 h-1 over the month and showed very rapid and high variations. Particulate carbon export represented less than 5% of integrated primary production, suggesting that phytoplankton production was essentially sustained by internal recycling of organic matter and retained within the photic zone. While PON and POP fluxes paralleled one another, the elemental ratios POC/PON and POC/POP, varied widely over short-term periods. Values were always higher than the conventional Redfield ratio indicating that the settling material was in part degraded. This was confirmed by the very low chlorophyll-a flux recorded in the traps (mean 0.017 μg m-2 h-1), the high phaeopigment and free lipid concentrations of the settling material, which all together indicated that the organic matter reaching 200 m depth was reworked (by grazing, fecal pellets production, degradation, . . .) and that algal sinking made a small contribution to the downward flux. Over time, the relative abundance of individual lipid classes in organic matter (OM) changed from glycolipids-dominated to neutral (wax esters, triglycerides) and phospholipids-dominated, suggesting ecosystem maturation as well as rapid and continual exchanges between dissolved, suspended and sinking pools. Our most striking result was documenting the rapid change in fluxes of the various measured parameters. In the situation encountered here, with dominant regenerated production, the effect of wind events was a decrease of fluxes (probably through reduction of grazing). But fluxes increased as soon as calm conditions settle.

  3. The Ponto-Caspian basin as a final trap for southeastern Scandinavian Ice-Sheet meltwater

    NASA Astrophysics Data System (ADS)

    Tudryn, Alina; Leroy, Suzanne A. G.; Toucanne, Samuel; Gibert-Brunet, Elisabeth; Tucholka, Piotr; Lavrushin, Yuri A.; Dufaure, Olivier; Miska, Serge; Bayon, Germain

    2016-09-01

    This paper provides new data on the evolution of the Caspian Sea and Black Sea from the Last Glacial Maximum until ca. 12 cal kyr BP. We present new analyses (clay mineralogy, grain-size, Nd isotopes and pollen) applied to sediments from the river terraces in the lower Volga, from the middle Caspian Sea and from the western part of the Black Sea. The results show that during the last deglaciation, the Ponto-Caspian basin collected meltwater and fine-grained sediment from the southern margin of the Scandinavian Ice Sheet (SIS) via the Dniepr and Volga Rivers. It induced the deposition of characteristic red-brownish/chocolate-coloured illite-rich sediments (Red Layers in the Black Sea and Chocolate Clays in the Caspian Sea) that originated from the Baltic Shield area according to Nd data. This general evolution, common to both seas was nevertheless differentiated over time due to the specificities of their catchment areas and due to the movement of the southern margin of the SIS. Our results indicate that in the eastern part of the East European Plain, the meltwater from the SIS margin supplied the Caspian Sea during the deglaciation until ∼13.8 cal kyr BP, and possibly from the LGM. That led to the Early Khvalynian transgressive stage(s) and Chocolate Clays deposition in the now-emerged northern flat part of the Caspian Sea (river terraces in the modern lower Volga) and in its middle basin. In the western part of the East European Plain, our results confirm the release of meltwater from the SIS margin into the Black Sea that occurred between 17.2 and 15.7 cal kyr BP, as previously proposed. Indeed, recent findings concerning the evolution of the southern margin of the SIS and the Black Sea, show that during the last deglaciation, occurred a westward release of meltwater into the North Atlantic (between ca. 20 and 16.7 cal kyr BP), and a southward one into the Black Sea (between 17.2 and 15.7 cal kyr BP). After the Red Layers/Chocolate Clays deposition in both seas

  4. Release of uranium from rock matrix--a record of glacial meltwater intrusions?

    PubMed

    Rasilainen, Kari; Suksi, Juhani; Ruskeeniemi, Timo; Pitkänen, Petteri; Poteri, Antti

    2003-03-01

    Uranium release observed in a rock matrix around water-carrying fractures was studied using U-series disequilibrium (USD) modelling and mass balance calculations. Several release scenarios were tested, with specific attention to the glacial aspects. The release appears to have occurred in two or three violent episodes during the last 300 ky. A release after the last glaciation can be excluded on mass flow grounds. Continuous release for more than 300 ky can be excluded on radioactive disequilibrium grounds. Repeated inflows of oxic glacial meltwater seem to have triggered the release episodes. PMID:12598107

  5. Revision of Ernst Antevs' New England Varve Chronology: A Record of Meltwater Production and Southeastern LIS Recession: 18.2-12.5 kyr BP (Invited)

    NASA Astrophysics Data System (ADS)

    Ridge, J. C.

    2013-12-01

    New varve cores and 54 radiocarbon ages, have allowed the correction, closure of a gap, calibration, and expansion of Ernst Antevs' (1922) New England Varve Chronology from sediments of glacial Lake Hitchcock and it's successors in the Connecticut Valley of western New England (northeastern U.S.A.). The continuous 5659-yr chronology (18.2-12.5 kyr BP) has been renumbered as the North American Varve Chronology. Glacial varve thickness (18.2-13.7 kyr BP) documents abrupt changes in meltwater production related to varying ablation rate (summer climate) that is linked to ice sheet recession rates and advances, i.e. cold intervals are times of thin varves and slower ice recession or glacial readvances. To take advantage of the varve-climate relationship it is necessary to identify non-climatic events that can cause varve thickness to change. This includes sudden changes in lake level and flood events triggered by the abrupt drainage of tributary glacial lakes. A chronology of ice recession for intervals terminated by four stillstands and readvances of 1-2 century durations have been determined for the Connecticut Valley (from S to N): 50-100 m/yr in northern Connecticut to southern Massachusetts; Chicopee Readvance; 30-40 m/yr in central Mass.; Hatfield event; 80-90 m/yr from northern Mass. to central New Hampshire; North Charlestown end moraines; 300 m/yr to northern N.H.; Littleton Readvance; >300 m/yr to Quebec. Meltwater produced by ice recession of 300 m/yr modeled as a receding 1-bar ice sheet profile (from 100 km up ice near ELA to margin, valley width of 80 km, glacier flow rate of 200 m/yr at ELA) would be a minimum glacial meltwater discharge in the Connecticut Valley of ~90 x 109 m3/yr. This is ~10X the modern Conn. River discharge at Walpole, NH compressed almost entirely to the melt season. Non-glacial varves deposited after ice receded from the basin (13.7-12.5 kyr BP) also document climate change as a result of varve thickness varying with changes in

  6. Post Wildfire Changes in Plant Functioning and Vegetation Dynamics: Implications for Water Fluxes in Re-sprouting Forests

    NASA Astrophysics Data System (ADS)

    Nolan, R. H.; Lane, P. N.; Mitchell, P. J.; Bradstock, R. A.

    2011-12-01

    Fire induced changes to the vegetation dynamics in temperate forests have been demonstrated to affect evapotranspiration (Et) rates through increases in plant size and density and stand-level transpiration and interception. In many cases these transient changes in forest structure result in substantial declines in stream flow for protracted periods after the disturbance. However to date research has focused on the wetter 'ash' forests of south-eastern Australia which solely regenerate via seedlings, it is unknown what changes in Et may occur in those forests which re-sprout post-fire. We hypothesize that Et fluxes track post-fire changes in sapwood area and leaf area index (L) in re-sprouting temperate forests, increasing as the forest regenerates. Following the 2009 Black Saturday wildfires in Victoria, we monitored Et rates for over a year in both damp and dry re-sprouting forest, incorporating a range of fire severity classes. Components of Et including overstorey transpiration, rainfall interception loss and forest floor Et were measured in conjunction with changes in L, sapwood area and leaf physiology. The monitoring period began one year post-fire with a typical hot, dry summer, at which stage Et rates in burnt forest were similar or less than those in unburnt forest. During the following summer, which was one of the wettest on record, Et increased across all monitoring plots but particularly so in the burnt forest where seedling regeneration resulted in an understorey L nearly twice that of unburnt forest. Forest floor Et was up to 46% higher in burnt forest, and rainfall interception values accounted for approximately 25% of rainfall compared to 15% in unburnt forest. The greatest increase in canopy transpiration rates over this period occurred in those trees subject to a low intensity fire where most of the canopy remained intact but there was also fire-triggered sprouting of new leaves along the trunk and main branches. In these trees rates of sapflow

  7. A comparison of mercury fluxes across a range of Canadian subarctic streams: Implications for climate and land-use change

    NASA Astrophysics Data System (ADS)

    Branfireun, B. A.; Price, J. S.

    2011-12-01

    It is well established that peatlands are important modifiers of downstream water quality in any catchment where they are found. Although small headwater peatlands are very important in controlling downstream water quality, there have been no attempts to scale up the process-based knowledge that we have about mercury cycling in small peatlands to the larger extensive peatland systems of the world. The Hudson Bay Lowlands (HBL) is the second largest peatland complex in the world with a total area of approximately 320000 sq km. In light the importance of the carbon stock and predictions of significant climate change impacts, research effort has gone into studying the carbon dynamics of the HBL peatlands however there has been no research on the role of the HBL peatlands in governing the water quality or quantity of the important tributaries of Hudson Bay. The published importance of mercury loading to the Hudson Bay/James Bay in terms of ecosystem and human impact stands in stark contrast with the limited data available for major tributaries. Perhaps of greatest importance are emerging concerns over land-use and/or climate changes in the HBL that affect peat hydrology and mercury dynamics; these concerns are based solely on conjecture because of the absence of empirical data. As part of a study of a broader study of the hydrology and biogeochemistry of the region, we have been investigating mercury and methylmercury fluxes across a wide range of catchments. Regular budget sampling (weekly to biweekly) for total mercury, methylmercury, and other solutes was undertaken over four years (2008-2011) in subcatchments of the Attiwapiskat River, spanning a wide range of catchment areas (~100, ~1000 sq. km) as well as the main stem of the Attiwapiskat, with an upstream catchment area of ~50 000 sq. km. Stream flows were measured nearly continuously (some interruptions due to ice impacts) using a combination of methods, depending on stream size. Our results over nearly four

  8. Surface and sub-surface multi-proxy reconstruction of middle to late Holocene palaeoceanographic changes in Disko Bugt, West Greenland

    NASA Astrophysics Data System (ADS)

    Moros, Matthias; Lloyd, Jeremy M.; Perner, Kerstin; Krawczyk, Diana; Blanz, Thomas; de Vernal, Anne; Ouellet-Bernier, Marie-Michele; Kuijpers, Antoon; Jennings, Anne E.; Witkowski, Andrzej; Schneider, Ralph; Jansen, Eystein

    2016-01-01

    We present new surface water proxy records of meltwater production (alkenone derived), relative sea surface temperature (diatom, alkenones) and sea ice (diatoms) changes from the Disko Bugt area off central West Greenland. We combine these new surface water reconstructions with published proxy records (benthic foraminifera - bottom water proxy; dinocyst assemblages - surface water proxy), along with atmospheric temperature from Greenland ice core and Greenland lake records. This multi-proxy approach allows us to reconstruct centennial scale middle to late Holocene palaeoenvironmental evolution of Disko Bugt and the Western Greenland coastal region with more detail than previously available. Combining surface and bottom water proxies identifies the coupling between ocean circulation (West Greenland Current conditions), the atmosphere and the Greenland Ice Sheet. Centennial to millennial scale changes in the wider North Atlantic region were accompanied by variations in the West Greenland Current (WGC). During periods of relatively warm WGC, increased surface air temperature over western Greenland led to ice sheet retreat and significant meltwater flux. In contrast, during periods of cold WGC, atmospheric cooling resulted in glacier advances. We also identify potential linkages between the palaeoceanography of the Disko Bugt region and key changes in the history of human occupation. Cooler oceanographic conditions at 3.5 ka BP support the view that the Saqqaq culture left Disko Bugt due to deteriorating climatic conditions. The cause of the disappearance of the Dorset culture is unclear, but the new data presented here indicate that it may be linked to a significant increase in meltwater flux, which caused cold and unstable coastal conditions at ca. 2 ka BP. The subsequent settlement of the Norse occurred at the same time as climatic amelioration during the Medieval Climate Anomaly and their disappearance may be related to harsher conditions at the beginning of the

  9. Thermal erosion of ice-wedge polygon terrains changes fluxes of energy and matter of permafrost geosystems

    NASA Astrophysics Data System (ADS)

    Fortier, D.; Godin, E.; Lévesque, E.; Veillette, A.; Lamarque, L.

    2015-12-01

    Subsurface thermal erosion is triggered by convective heat transfers between flowing water and permafrost. Heat advection due to infiltration of run-off in the massive ice wedges and the ice-rich upper portion of permafrost creates sink holes and networks of interconnected tunnels in the permafrost. Mass movements such as collapse of tunnel's roof, retrogressive thaw-slumping and active layer detachment slides lead to the development of extensive gully networks in the landscape. These gullies drastically change the hydrology of ice-wedge polygon terrains and the fluxes of heat, water, sediment, nutrients and carbon within the geosystem. Exportation of sediments out of gullies are positive mechanical feed-back that keep channels active for decades. Along gully margins, drainage of disturbed polygons and ponds, slope drainage, soil consolidation, gully walls colonization by vegetation and wet to mesic plant succession change the thermal properties of the active layer and create negative feedback effects that stabilize active erosion processes and promote permafrost recovery in gully slopes and adjacent disturbed polygons. On Bylot Island (Nunavut), over 40 gullies were monitored to characterize gully geomorphology, thermal and mechanical processes of gully erosion, rates of gully erosion over time within different sedimentary deposits, total volume of eroded permafrost at the landscape scale and gully hydrology. We conducted field and laboratory experiments to quantify heat convection processes and speed of ice wedge ablation in order to derive empirical equations to develop model of permafrost thermal erosion. We used data, collected over 10 years, of geomorphological gully monitoring and regional climate scenarios to evaluate the potential response of ice-wedge polygon terrains to changes in snow, permafrost thermal regime and hydrological conditions over the coming decades and its implication for the short and long term dynamics of arctic permafrost geosystems.

  10. Spatial characterization of the meltwater field from icebergs in the Weddell Sea.

    PubMed

    Helly, John J; Kaufmann, Ronald S; Vernet, Maria; Stephenson, Gordon R

    2011-04-01

    We describe the results from a spatial cyberinfrastructure developed to characterize the meltwater field around individual icebergs and integrate the results with regional- and global-scale data. During the course of the cyberinfrastructure development, it became clear that we were also building an integrated sampling planning capability across multidisciplinary teams that provided greater agility in allocating expedition resources resulting in new scientific insights. The cyberinfrastructure-enabled method is a complement to the conventional methods of hydrographic sampling in which the ship provides a static platform on a station-by-station basis. We adapted a sea-floor mapping method to more rapidly characterize the sea surface geophysically and biologically. By jointly analyzing the multisource, continuously sampled biological, chemical, and physical parameters, using Global Positioning System time as the data fusion key, this surface-mapping method enables us to examine the relationship between the meltwater field of the iceberg to the larger-scale marine ecosystem of the Southern Ocean. Through geospatial data fusion, we are able to combine very fine-scale maps of dynamic processes with more synoptic but lower-resolution data from satellite systems. Our results illustrate the importance of spatial cyberinfrastructure in the overall scientific enterprise and identify key interfaces and sources of error that require improved controls for the development of future Earth observing systems as we move into an era of peta- and exascale, data-intensive computing. PMID:21444769

  11. Characterisation of bacterioplankton communities in the meltwater ponds of Bratina Island, Victoria Land, Antarctica.

    PubMed

    Archer, Stephen D J; McDonald, Ian R; Herbold, Craig W; Cary, Stephen C

    2014-08-01

    A unique collection of Antarctic aquatic environments (meltwater ponds) lies in close proximity on the rock and sediment-covered undulating surface of the McMurdo Ice Shelf, near Bratina Island (Victoria Land, Antarctica). During the 2009-10 mid-austral summer, sets of discrete water samples were collected across the vertical geochemical gradients of five meltwater ponds (Egg, P70E, Legin, Salt and Orange) for geochemical and microbial community structure analysis. Bacterial DNA fingerprints (using Automated Ribosomal Intergenic Spacer Analysis) statistically clustered communities within ponds based on anosim (R = 0.766, P = 0.001); however, one highly stratified pond (Egg) had two distinct depth-related bacterial communities (R = 0.975, P = 0.008). 454 pyrosequencing at three depths within Egg also identified phylum level shifts and increased diversity with depth, Bacteroidetes being the dominant phyla in the surface sample and Proteobacteria being dominant in the bottom two depths. best analysis, which attempts to link community structure and the geochemistry of a pond, identified conductivity and pH individually, and to a lesser extent Ag(109) , NO2 and V(51) as dominant influences to the microbial community structure in these ponds. Increasing abundances of major halo-tolerant OTUs across the strong conductivity gradient reinforce it as the primary driver of community structure in this study. PMID:24862286

  12. Microbial community structure in moraine lakes and glacial meltwaters, Mount Everest.

    PubMed

    Liu, Yongqin; Yao, Tandong; Jiao, Nianzhi; Kang, Shichang; Zeng, Yonghui; Huang, Sijun

    2006-12-01

    The bacterial diversity and abundance in two moraine lakes and two glacial meltwaters (5140, 5152, 5800 and 6350 m above sea level, respectively) in the remote Mount Everest region were examined through 16S rRNA gene clone library and flow cytometry approaches. In total, 247 clones were screened by RFLP and 60 16S rRNA gene sequences were obtained, belonging to the following groups: Proteobacteria (8% alpha subdivision, 21% beta subdivision, and 1% gamma subdivision), Cytophaga-Flavobacteria-Bacteroides (CFB) (54%), Actinobacteria (4%), Planctomycetes (2%), Verrucomicrobia (2%), Fibrobacteres (1%) and Eukaryotic chroloplast (3%), respectively. The high dominance of CFB distinguished the Mount Everest waters from other mountain lakes. The highest bacterial abundance and diversity occurred in the open moraine lake at 5152 m, and the lowest in the glacial meltwater at 6350 m. Low temperature at high altitude is considered to be critical for component dominancy. At the same altitude, nutrient availability plays a role in regulating population structure. Our results also show that the bacteria in Mount Everest may be derived from different sources. PMID:17107422

  13. Spatial characterization of the meltwater field from icebergs in the Weddell Sea

    PubMed Central

    Helly, John J.; Kaufmann, Ronald S.; Vernet, Maria; Stephenson, Gordon R.

    2011-01-01

    We describe the results from a spatial cyberinfrastructure developed to characterize the meltwater field around individual icebergs and integrate the results with regional- and global-scale data. During the course of the cyberinfrastructure development, it became clear that we were also building an integrated sampling planning capability across multidisciplinary teams that provided greater agility in allocating expedition resources resulting in new scientific insights. The cyberinfrastructure-enabled method is a complement to the conventional methods of hydrographic sampling in which the ship provides a static platform on a station-by-station basis. We adapted a sea-floor mapping method to more rapidly characterize the sea surface geophysically and biologically. By jointly analyzing the multisource, continuously sampled biological, chemical, and physical parameters, using Global Positioning System time as the data fusion key, this surface-mapping method enables us to examine the relationship between the meltwater field of the iceberg to the larger-scale marine ecosystem of the Southern Ocean. Through geospatial data fusion, we are able to combine very fine-scale maps of dynamic processes with more synoptic but lower-resolution data from satellite systems. Our results illustrate the importance of spatial cyberinfrastructure in the overall scientific enterprise and identify key interfaces and sources of error that require improved controls for the development of future Earth observing systems as we move into an era of peta- and exascale, data-intensive computing. PMID:21444769

  14. The water fluxes of the Yellow River to the sea in the past 50 years, in response to climate change and human activities.

    PubMed

    Jiongxin, Xu

    2005-05-01

    Since the 1970s, the water fluxes to the sea of the Yellow River have declined significantly. Based on data of precipitation, air temperature, the measured and "natural" river flow, the water diversion and consumption, and the areas of erosion and sediment control measures over the drainage basin, water fluxes to the sea of the Yellow River are studied in relation with the influences of changing climate and human activities. The Yellow River basin can be divided into different water source areas; multiple regression indicates that the variation in precipitation over different water source areas has different effect on water fluxes to the sea. In the period between 1970 and 1997, averaged air temperature over the whole Yellow River increased by about 1.0 degree C, from 16.5 degrees C to 17.5 degrees C, a factor that is negatively correlated with the water yield of the Yellow River. Water diversion and consumption has sharply increased and resulted in a significant decline in the water fluxes to the sea. Since the 1960s, erosion and sediment control measures have been practiced over the drainage basin. This factor, to a lesser degree, is also responsible for the decrease in water fluxes to the sea. A multiple regression equation has been established to estimate the change in water fluxes to the sea caused by the changes in precipitation, air temperature, water diversion and consumption, erosion, and sediment control measures, indicating that the contribution of water diversion and consumption to the variation in annual water flux to the sea is 41.3%, that of precipitation is 40.8%, that of temperature is 11.4%, and that of erosion and sediment control measures is 6.5%. PMID:15924206

  15. Overview of gas flux measurements from volcanoes of the global Network for Observation of Volcanic and Atmospheric Change (NOVAC)

    NASA Astrophysics Data System (ADS)

    Galle, Bo; Arellano, Santiago; Conde, Vladimir

    2015-04-01

    NOVAC, the Network for Observation of Volcanic and Atmospheric Change, was initiated in 2005 as a 5-years-long project financed by the European Union. Its main purpose is to create a global network for the study of volcanic atmospheric plumes and related geophysical phenomena by using state-of-the-art spectroscopic remote sensing technology. Up to 2014, 67 instruments have been installed at 25 volcanoes in 13 countries of Latin America, Italy, Democratic Republic of Congo, Reunion, Iceland, and Philippines, and efforts are being done to expand the network to other active volcanic zones. NOVAC has been a pioneer initiative in the community of volcanologists and embraces the objectives of the Word Organization of Volcano Observatories (WOVO) and the Global Earth Observation System of Systems (GEOSS). In this contribution, we present the results of the measurements of SO2 gas fluxes carried out within NOVAC, which for some volcanoes represent a record of more than 8 years of semi-continuous monitoring. The network comprises some of the most strongly degassing volcanoes in the world, covering a broad range of tectonic settings, levels of unrest, and potential risk. Examples of correlations with seismicity and other geophysical phenomena, environmental impact studies and comparisons with previous global estimates will be discussed as well as the significance of the database for further studies in volcanology and other geosciences.

  16. Simulation of potential impacts of land use/cover changes on surface water fluxes in the Chaophraya river basin, Thailand

    NASA Astrophysics Data System (ADS)

    Kim, Wonsik; Kanae, Shinjiro; Agata, Yasushi; Oki, Taikan

    2005-04-01

    The Chaophraya river basin in Thailand is one of the most significant land use/cover change (LUCC) regions where clearing of natural vegetation to cropland or secondary forest has occurred over several decades. The LUCC affects surface water fluxes (SWF), including transpiration, interception loss, evaporation, and runoff, because the SWF components are controlled by aerodynamic characteristics, soil moisture content, and potential photosynthetic activities according to vegetation type. Therefore, to understand the potential impacts of LUCC on SWF in the Chaophraya river basin, the simple biosphere model 2 (SiB2) with paddy scheme was run in uncoupled mode with forcing in keeping with the International Satellite Land Surface Climatology Project Initiative I data set. The simulation results revealed the following: (1) The absorbed radiation energy of forest was larger than other vegetation types although the Bowen ratios are similar. (2) The characteristics of SWF for each vegetation type were significantly controlled by soil water content, photosynthetic activity, and leaf area index. (3) The SWF index (W) and the relative SWF index (RW) were suggested as scaling parameters to estimate the seasonality of SWF as follows (definitions are given in section 3.4): Wi = ??i) and RWi = ?. (4) The WS were divided into two groups: the low seasonality SWF type (WS ≤ 0.5) consisting of forest or paddy field and the high seasonality SWF type (WS > 0.5) consisting of grassland or crop. (5) Runoff of the Chaophraya river basin decreased because of expanding crop area and paddy fields, an increase in the evaporation during the rainy season caused by changes in various vegetation types to paddy fields, and an increase in transpiration during the dry season caused by an expanding crop area.

  17. Composition and fluxes of freshwater through Davis Strait using multiple chemical tracers

    NASA Astrophysics Data System (ADS)

    Azetsu-Scott, Kumiko; Petrie, Brian; Yeats, Philip; Lee, Craig

    2012-12-01

    Freshwater transport through Davis Strait can supply additional buoyancy to the deep convection region of the Labrador Sea which influences the strength of the meridional overturning circulation and consequently the global climate. The freshwater contribution from local sea ice meltwater, meteoric water (fluvial, glaciofluvial and precipitation) and the Arctic outflow were quantified using oxygen isotope composition (δ18O), salinity and nutrient relationships in September-October, 2004. Freshwater transported by the Arctic outflow was isolated using a modified nutrient relationship method and further deconvoluted into sea ice meltwater, meteoric water and Pacific water. For the first time, fluxes of individual freshwater components were estimated using observations of the velocity field derived from mooring arrays and geostrophic currents from hydrography. The Arctic outflow dominated in western Davis Strait (>60%) and its influence extended eastward close to the Greenland Slope. The sea ice meltwater fraction was small (<2%) and limited to the surface layer of the central and western Strait. The meteoric water fraction was highest on the Greenland Shelf (>6%) and attributed to glacial meltwater. The freshwater inventory of the 0-100 m layer was equivalent to 7.4 m in western Davis Strait: 8 m from the Arctic outflow and -0.6 m from brine rejection. In eastern Davis Strait, the freshwater inventory was 4 m: 3 m from meteoric water and 1 m from sea ice meltwater. The Arctic outflow contributed 82-99 mSv to the southward freshwater transport about 67-81% of the total; glacial meltwater contributed the largest northward transport of 10-30 mSv.

  18. The Brunhes/Matuyama polarity transition recorded as Be-10 flux changes in deep-sea sediments

    NASA Astrophysics Data System (ADS)

    Suganuma, Y.; Yokoyama, Y.; Yamazaki, T.

    2008-12-01

    Fluxes of meteoric cosmogenic radionuclide, Be-10, is thought to be varied due to changes of incoming comic-ray flux modulated by geomagnetic field intensity variation. Enhanced production rate of the nuclides during a geomagnetic polarity transition period is expected as a result of the low dipole field strength. We therefore measured Be-10 concentrations in deep-sea sediments including the Brunhes/Matuyama geomagnetic polarity transition to reconstruct the detailed structures of the geomagnetic field behavior. A piston core, MD982187 was taken from the West Caroline Basin, the western equatorial Pacific Ocean, during the IMAGES IV campaign. The water depth of the site of MD982187 core is about 4600 m, which is close to the carbonate compensation depth (CCD) in this area at present (Berger et al., 1976). Measurement of Be-10 was conducted using the accelerator mass spectrometry (AMS) of the University of Tokyo, Japan. The result shows significant increase of Be-10 concentration during the polarity transition, indicating that the geomagnetic field intensity was low during this interval. In detail, well-defined double highs of Be-10 concentration are recognized. These highs are thought to correspond to the B/M polarity boundary and the "precursor" event, 15 kyr before the M/B boundary (e.g., Hartl and Tauxe, 1996; Singer et al., 2005), respectively. This feature is very similar to the relative paleointensity record of MR982187 core by Yamazaki and Oda (2005) and other published relative paleointensity records of the Brunhes/Matuyama geomagnetic polarity transition, indicating that Be-10 concentration of the deep-sea sedimentary sequence well records the variation of the geomagnetic field intensity. However, ca. 18 cm of clear depth offset between the Be-10 concentration and the relative paleointensity record was observed from the same sedimentary sequence of MR982187 core. This indicates that the relative paleointensity record of MR982187 core is offset by ca. 18 cm

  19. Water and carbon fluxes in rain fed agricultural sites under a changing climate: The role of stomata

    NASA Astrophysics Data System (ADS)

    Hosseini, A.; Gayler, S.; Streck, T.; Katul, G. G.

    2014-12-01

    were derived from eddy-covariance measurements of latent heat flux and net ecosystem exchange. To place those results in the broader context of climate change and food security issues, a sensitivity analyses on water and carbon fluxes with respect to climatic variables, soil texture, and root-density distribution is also presented.

  20. Uncertainties in vertical groundwater fluxes from 1-D steady state heat transport analyses caused by heterogeneity, multidimensional flow, and climate change

    NASA Astrophysics Data System (ADS)

    Irvine, Dylan J.; Cartwright, Ian; Post, Vincent E. A.; Simmons, Craig T.; Banks, Eddie W.

    2016-02-01

    Steady state 1-D analytical solutions to estimate groundwater fluxes from temperature profiles are an attractive option because they are simple to apply, with no complex boundary or initial conditions. Steady state solutions have been applied to estimate both aquifer scale fluxes as well as to estimate groundwater discharge to streams. This study explores the sources of uncertainty in flux estimates from regional scale aquifers caused by sensor precision, aquifer heterogeneity, multidimensional flow and variations in surface temperature due to climate change. Synthetic temperature profiles were generated using 2-D groundwater flow and heat transport models with homogeneous and heterogeneous hydraulic and thermal properties. Temperature profiles were analyzed assuming temperature can be determined with a precision between 0.1°C and 0.001°C. Analysis of synthetic temperature profiles show that the Bredehoeft and Papadopulos (1965) method can provide good estimates of the mean vertical Darcy flux over the length of the temperature profile. Reliable flux estimates were obtained when the ratio of vertical to horizontal flux was as low as 0.1, and in heterogeneous media, providing that temperature at the upper boundary was constant in time. However, temporal increases in surface temperature led to over-estimation of fluxes. Overestimates increased with time since the onset of, and with the rate of surface warming. Overall, the Bredehoeft and Papadopulos (1965) method may be more robust for the conditions with constant temperature distributions than previously thought, but that transient methods that account for surface warming should be used to determine fluxes in shallow aquifers.

  1. MODELING THE IMPACTS OF DECADAL CHANGES IN RIVERINE NUTRIENT FLUXES ON COASTAL EUTROPHICATION NEAR THE MISSISSIPPI RIVER DELTA. (R827785E02)

    EPA Science Inventory

    A mathematical model was used to link decadal changes in the Mississippi River nutrient flux to coastal eutrophication near the Mississippi River Delta. Model simulations suggest that bottom water hypoxia intensified about 30 years ago, as a probable consequence of increased n...

  2. Subglacial lake and meltwater flow predictions of the last North American and European Ice Sheets

    NASA Astrophysics Data System (ADS)

    Livingstone, S. J.; Clark, C. D.; Tarasov, L.

    2012-04-01

    There is increasing recognition that subglacial lakes act as key components within the ice sheet system, capable of influencing ice-sheet topography, ice volume and ice flow. The subglacial water systems themselves are recognised as being both active and dynamic, with large discharges of meltwater capable of flowing down hydrological pathways both between lakes and to the ice-sheet margins. At present, much glaciological research is concerned with the role of modern subglacial lake systems in Antarctica. Another approach to the exploration of subglacial lakes involves identification of the geological record of subglacial lakes that once existed beneath ice sheets of the last glaciation. Investigation of such palaeo-subglacial lakes offers significant advantages because we have comprehensive information about the bed properties, they are much more accessible and we can examine and sample the sediments with ease. If we can find palaeo-subglacial lakes then we have the potential to advance understanding with regard to the topographic context and hydrological pathways that the phenomena form a part of; essentially we gain spatial and sedimentological information in relation to investigations of contemporary subglacial lakes and lose out on the short-time dynamics. In this work we present predictions of palaeo-subglacial lakes and meltwater drainage pathways under the former European and North American ice sheets during the last glaciation. We utilise data on the current topography and seafloor bathymetry, and elevation models of the ice and ground surface topography (interpolated to a 5 km grid) to calculate the hydraulic potential surface at the ice-sheet bed. Meltwater routing algorithms and the flooding of local hydraulic minima allow us to predict subglacial channels and lakes respectively. Given that specific ice-surface and bed topographies are only known from modelled outputs, and thus contain significant uncertainty, we utilise many such outputs to examine

  3. Aquifers in melt-water channels along the southwest flank of the Des Moines Lobe, Lyon County, Minnesota

    USGS Publications Warehouse

    Schneider, Robert; Rodis, Harry G.

    1961-01-01

    The melt-water channels in Lyon County trend southeastward because the flank of the ice sheet was confined by a landmass that sloped to the northeast. Similar buried channels may be present elsewhere along the southwest flank of the Des Moines lobe. If so, they probably can be located by the methods described.

  4. Regional Glacier Sensitivity to Climate Change in the Monsoonal Himalaya: Implications for Water Resources

    NASA Astrophysics Data System (ADS)

    Rupper, S.; Maurer, J. M.; Schaefer, J. M.; Tsering, K.; Rinzin, T.; Dorji, C.; Johnson, E. S.; Cook, E. R.

    2014-12-01

    The rapid retreat of many glaciers in the monsoonal Himalaya is of potential societal concern. However, the retreat pattern in the region has been very heterogeneous, likely due in part to the inherent heterogeneity of climate and glaciers within the region. Assessing the impacts of glacier change on water resources, hydroelectric power, and hazard potential requires a detailed understanding of this potentially complex spatial pattern of glacier sensitivity to climate change. Here we quantify glacier surface-mass balance and meltwater flux across the entire glacierized region of the Bhutanese watershed using a full surface-energy and -mass balance model validated with field data. We then test the sensitivity of the glaciers to climatic change and compare the results to a thirty-year record of glacier volume changes. Bhutan is chosen because it (1) sits in the bulls-eye of the monsoon, (2) has >600 glaciers that exhibit the extreme glacier heterogeneity typical of the Himalayas, and (3) faces many of the economic and hazard challenges associated with glacier changes in the Himalaya. Therefore, the methods and results from this study should be broadly applicable to other regions of the monsoonal Himalaya. Our modeling results show a complex spatial pattern of glacier sensitivity to changes in climate across the Bhutanese Himalaya. However, our results also show that <15% of the glaciers in Bhutan account for >90% of the total meltwater flux, and that these glaciers are uniformly the glaciers most sensitive to changes in temperature (and less sensitive to other climate variables). We compare these results to a thirty-year record of glacier volume changes over the same region. In particular, we extract DEMs and orthorectified imagery from 1976 historical spy satellite images and 2006 ASTER images. DEM differencing shows that the glaciers that have changed most over the past thirty years also have the highest modeled temperature sensitivity. These results suggest that

  5. Evidence for electron neutrino flavor change through measurement of the (8)B solar neutrino flux at the Sudbury Neutrino Observatory

    NASA Astrophysics Data System (ADS)

    Neubauer, Mark Stephen

    2001-11-01

    The Sudbury Neutrino Observatory (SNO) is a water Cerenkov detector designed to study solar neutrinos. Using 1 kiloton of heavy water as the target and detection medium, SNO is able to separately determine the flux of electron neutrinos (νe) and the flux of all active neutrinos from the Sun by measuring the rate of charged current (CC) and neutral current (NC) interactions with deuterons. A comparison of these interaction rates allows for direct observation of solar neutrino oscillations. SNO can also search for oscillations by comparing the rate of CC and neutrino- electron elastic scattering (ES) events, since ES has both charged current and neutral current sensitivity. In this thesis, we present measurement of the 8B solar ν e flux of 1.78+0.13-0.14 (stat+syst) × 106cm-2s -1 (35% BP2000 SSM) through measurement of the CC rate over 169.3 days of livetime. We have also measured the 8B flux from the ES reaction to be 2.56+0.48-0.45 (stat+syst), consistent with measurements by previous water Cerenkov experiments. A flavor analysis comparing the CC measured flux with that determined through ES by SuperKamiokande yields a non- νe active neutrino flux from 8B of 3.62+1.06-1.08 × 106cm-2s-1 , providing evidence for νe --> ν μ,τ oscillations as a solution to the solar neutrino problem. This result excludes pure solar νe --> ν s oscillations at greater than the 99.7% C.I. The total active 8B neutrino flux has been measured to be 5.39+1.07-1.09 × 106cm-2s-1 , consistent with BP2000 SSM predictions. First analyses of the CC (NHit) spectrum and hep flux in SNO are presented. The CC spectrum is found to be a good fit to expectations from an undistorted 8B spectrum, and global best fit vacuum oscillation solutions are disfavored over the other solutions by the data. Through observations near the 8B endpoint with consideration of energy systematics, hep flux limits of 4.1 (90% C.I.) and 6.9 (99% C.I.) times SSM expectations are obtained. A statistical fit for the

  6. Regional Approaches to Climate Change (REACCH) in the Inland Pacific Northwest: Micrometeorological Measurements of Nitrous Oxide Fluxes over a Wheat Cropping System

    NASA Astrophysics Data System (ADS)

    Lamb, B. K.; Waldo, S.; Chi, J.; Pressley, S. N.; Allwine, G.; O'Keeffe, P.; Huggins, D. R.; Pan, W.; Stockle, C.; Uberuaga, D.

    2012-12-01

    It is becoming increasingly important to investigate the relationship between global climate and agriculture in the face of ongoing climate change and the need to feed a growing global population. The REgional Approaches to Climate CHange (REACCH) USDA project is focused on Inland Pacific Northwest cereal cropping systems with an overarching goal to develop strategies for regional agriculture to mitigate and adapt to climate change. An important component of REACCH is to establish a baseline of greenhouse gas (GHG) fluxes for current and alternate management practices. While cropping systems have the potential to sequester carbon in the soils, they are a net source of nitrous oxide (N2O), a greenhouse gas with three hundred times the warming potential of CO2. We report here initial micrometeorological flux measurements of N2O over a high rainfall, annual cropping system under no-tillage management. The measurements were collected from three-meter eddy covariance towers. Each tower is equipped with a sonic anemometer and peripheral meteorological instruments. Closed-path cavity ring down spectroscopy instruments were used to measure N2O fluxes via two techniques: eddy covariance and the modified Bowen ratio gradient method. The flux data from the two techniques are compared to each other and also to enclosure chamber measurements to determine viability and the range of uncertainty in the measurements. They are also analyzed for patterns associated with management events and meteorological conditions.

  7. Changes in dissolved organic carbon and total dissolved nitrogen fluxes across subtropical forest ecosystems at different successional stages

    NASA Astrophysics Data System (ADS)

    Yan, Junhua; Li, Kun; Wang, Wantong; Zhang, Deqiang; Zhou, Guoyi

    2015-05-01

    Lateral transports of carbon and nitrogen are important processes linking terrestrial ecosystems and aquatic systems. Most previous studies made in temperate forests found that fluxes of carbon and nitrogen by runoff water varied in different forests, but few studies have been made in subtropical forests. This study was to investigate dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) fluxes at the catchment scale along a subtropical forest succession gradient from pine forest (pioneer) to coniferous and broadleaved mixed forest (transitional) to broadleaved forest (mature). Our results showed that DOC concentration significantly decreased (p<0.001) while TDN concentration significantly increased (p<0.001) in runoff water from pioneer to mature forests, which in turn resulted in a decrease in DOC flux and an increase in TDN flux, as mean annual runoff did not vary significantly among three succession forest catchments. The mean (±standard deviation) annual DOC flux was 118.1±43.6, 88.3±16.7 and 77.2±11.7 kg ha-1 yr-1for pioneer, transitional and mature forest catchments, respectively; and the mean annual TDN flux was 9.9 ±2.7, 18.2±3.0 and 21.2 ±4.5 kg ha-1 yr-1for pioneer, transitional and mature forest catchments, respectively. The mature forest reduced DOC flux by increased soil chemical adsorption and physical protection. An increase in TDN flux from pioneer to mature forests was consistent with the previous finding that mature forest was nitrogen saturated while pioneer forest was nitrogen limited. Therefore large-scale conversion of pioneer forests to transitional or mature forests in subtropical China will reduce DOC concentration and increase TDN concentration in the down-stream water, which may have significant impact on its water quality and aquatic biological activities.

  8. Changes in interannual climate sensitivities of terrestrial carbon fluxes during the 21st century predicted by CMIP5 Earth System Models

    NASA Astrophysics Data System (ADS)

    Liu, Yongwen; Wang, Tao; Huang, Mengtian; Yao, Yitong; Ciais, Philippe; Piao, Shilong

    2016-03-01

    Terrestrial carbon fluxes are sensitive to climate change, but the interannual climate sensitivity of the land carbon cycle can also change with time. We analyzed the changes in responses of net biome production (NBP), net primary production (NPP), and heterotrophic respiration (Rh) to interannual climate variations over the 21st century in the Earth System Models (ESMs) from the Coupled Model Intercomparison Project 5. Under Representative Concentration Pathway (RCP) 4.5, interannual temperature sensitivities of NBP (γTempNBP), NPP (γTempNPP), and Rh (γTempRh) remain relatively stable at global scale, yet with large differences among ESMs and spatial heterogeneity. Modeled γTempNPP and γTempRh appear to increase in parallel in boreal regions, resulting in unchanged γTempNBP. Tropical γTempNBP decreases in most models, due to decreasing γTempNPP and relatively stable γTempRh. Across models, the changes in γTempNBP can be mainly explained by changes in γTempNPP rather than changes in γTempRh, at both global and regional scales. Interannual precipitation sensitivities of global NBP (γPrecNBP), NPP (γPrecNPP), and Rh (γPrecRh) are predicted not to change significantly, with large differences among ESMs. Across models, the changes in γPrecNBP can be mainly explained by changes in γPrecNPP rather than changes in γPrecRh in temperate regions, but not in other regions. Changes in the interannual climate sensitivities of carbon fluxes are consistent across RCPs 4.5, 6.0, and 8.5 but larger in more intensive scenarios. More effort should be considered to improve terrestrial carbon flux responses to interannual climate variability, e.g., incorporating biogeochemical processes of nutrient limitation, permafrost dynamics, and microbial decomposition.

  9. Marine sedimentary record of Meltwater Pulse 1a along the NW Barents Sea continental margin

    NASA Astrophysics Data System (ADS)

    Giulia Lucchi, Renata; Sagnotti, Leonardo; Camerlenghi, Angelo; Macrì, Patrizia; Rebesco, Michele; Pedrosa, Maria Teresa; Giorgetti, Giovanna

    2016-04-01

    The upper continental slope of the Storfjorden-Kveithola Trough Mouth Fans (NW Barents Sea) contains a several m-thick late Pleistocene sequence of plumites composed of laminated mud interbedded with sand/silt layers. Radiocarbon ages revealed that deposition occurred during about 130 years at a very high sedimentation rate of 3.4 cm a-1, at about 7 km from the present shelf break. Palaeomagnetic and rock magnetic analyses confirm the existence of a prominent, short-living sedimentary event. The plumites appear laterally continuous and were correlated with the sedimentary sequences described west of Svalbard and neighbouring glacial depositional systems representing a major event at regional scale appointed to correspond to the deep-sea sedimentary record of Meltwater Pulse-1a. We also present new sedimentological and geochemical insights, and multi-beam data adding information on the palaeoenvironmental characteristics during MWP-1a and ice sheet decay in the NW Barents Sea.

  10. Sediment/Aqueous Partitioning of Fecal Indicator Bacteria in Spring Meltwater

    NASA Astrophysics Data System (ADS)

    Schnabel, W.; Mutter, E.; Myerchin, G.

    2009-12-01

    This study was designed to elucidate the partitioning behavior of fecal indicator bacteria Enterococcus and E. coli in spring snowmelt. Two snowmelt lysimeters were constructed and inoculated with agriculturally-derived manure prior to the first snowfall. After approximately six months, the lysimeter runoff was collected daily and transported to the lab for analysis. Particle-attached and disassociated bacteria were separated via centrifugation, and quantified via the most probable number technique. Results revealed significant differences between the behaviors of Enterococcus compared to E. coli. First, Enterococcus exhibited a significantly higher survival rate over the winter months compared to E. coli. Second, Enterococcus partitioned almost exclusively with the sediment in the meltwater, whereas E. coli partitioned variably between the aqueous and particulate phases. These results demonstrated that water quality managers must understand the specific partitioning behavior of the indicator organisms tested in order to effectively interpret water quality monitoring results.

  11. Meltwater and tidal currents: Controls on circulation in a small glacial fjord

    NASA Astrophysics Data System (ADS)

    Cowan, Ellen A.

    1992-04-01

    McBride Inlet is a small glacial fjord that receives freshwater from a submarine tunnel at the base of a tidewater glacier at its head. The upwelling buoyant plume mixes with basin water, lowering the salinity throughout the ice-proximal basin. Freshwater also upwells from the melting ice face but the effects are only important in winter when discharge is low. Deep water renewal occurs in summer because the water mass crossing the sill inward is denser than the deep basin water. The thick, low velocity surface layer is affected by tides and wind, producing a slow moving gyre near the glacier. Meltwater discharge from a submarine position and the resultant circulation in McBride Inlet result in extremely high ice-proximal sedimentation rates.

  12. Antarctic climate cooling and response of diatoms in glacial meltwater streams

    USGS Publications Warehouse

    Esposito, R.M.M.; Horn, S.L.; McKnight, Diane M.; Cox, M.J.; Grant, M.C.; Spaulding, S.A.; Doran, P.T.; Cozzetto, K.D.

    2006-01-01

    To understand biotic responses to an Antarctic cooling trend diatom samples from glacial meltwater streams in the McMurdo Dry Valleys, the largest ice-free area in Antarctica. Diatoms are abundant in these streams, and 24 of 40 species have only been found in the Antarctic. The percentage of these Antarctic diatom species increased with decreasing annual stream flow and increasing harshness of the stream habitat. The species diversity of assemblages reached a maximum when the Antarctic species accounted for 40-60% of relative diatom abundance. Decreased solar radiation and air-temperatures reduce annual stream flow, raising the dominance of these Antarctic species to levels above 60%. Thus, cooling favors the Antarctic species, and lowers diatom species diversity in this region. Copyright 2006 by the American Geophysical Union.

  13. Cystobasidiomycetes yeasts from Patagonia (Argentina): description of Rhodotorula meli sp. nov. from glacial meltwater.

    PubMed

    Libkind, Diego; Sampaio, José Paulo; van Broock, Maria

    2010-09-01

    A basidiomycetous yeast, strain CRUB 1032(T), which formed salmon-pink colonies, was isolated from glacial meltwater in Patagonia, Argentina. Morphological, physiological and biochemical characterization indicated that this strain belonged to the genus Rhodotorula. Molecular taxonomic analysis based on the 26S rDNA D1/D2 domain and internal transcribed spacer region sequences showed that strain CRUB 1032(T) represents an undescribed yeast species, for which the name Rhodotorula meli sp. nov. is proposed (type strain is CRUB 1032(T)=CBS 10797(T)=JCM 15319(T)). Phylogenetic analysis showed that Rhodotorula lamellibrachii was the closest known species, which, together with R. meli, formed a separate cluster related to the Sakaguchia clade within the Cystobasidiomycetes. Additional Patagonian yeast isolates of the class Cystobasidiomycetes are also investigated in the present work. PMID:19880630

  14. The influence of stream thermal regimes and preferential flow paths on hyporheic exchange in a glacial meltwater stream

    NASA Astrophysics Data System (ADS)

    Cozzetto, Karen D.; Bencala, Kenneth E.; Gooseff, Michael N.; McKnight, Diane M.

    2013-09-01

    Given projected increases in stream temperatures attributable to global change, improved understanding of relationships between stream temperatures and hyporheic exchange would be useful. We conducted two conservative tracer injection experiments in a glacial meltwater stream, to evaluate the effects of hyporheic thermal gradients on exchange processes, including preferential flow paths (PFPs). The experiments were conducted on the same day, the first (a stream injection) during a cool, morning period and the second (dual stream and hyporheic injections) during a warm, afternoon period. In the morning, the hyporheic zone was thermally uniform at 4°C, whereas by the afternoon the upper 10 cm had warmed to 6-12°C and exhibited greater temperature heterogeneity. Solute transport modeling showed that hyporheic cross-sectional areas (As) at two downstream sites were two and seven times lower during the warm experiment. Exchange metrics indicated that the hyporheic zone had less influence on downstream solute transport during the warm, afternoon experiment. Calculated hyporheic depths were less than 5 cm, contrasting with tracer detection at 10 and 25 cm depths. The hyporheic tracer arrival at one downstream site was rapid, comparable to the in-stream tracer arrival, providing evidence for PFPs. We thus propose a conceptual view of the hyporheic zone in this reach as being dominated by discrete PFPs weaving through hydraulically isolated areas. One explanation for the simultaneous increase in temperature heterogeneity and As decrease in a warmer hyporheic zone may be a flow path preferentiality feedback mechanism resulting from a combination of temperature-related viscosity decreases and streambed heterogeneity.

  15. Estimation of annual suspended-sediment fluxes, 1931-95, and evaluation of geomorphic changes, 1950-2010, in the Arkansas River near Tulsa, Oklahoma

    USGS Publications Warehouse

    Lewis, Jason M.; Smith, S. Jerrod; Buck, Stephanie D.; Strong, Scott A.

    2011-01-01

    An understanding of fluvial sediment transport and changing channel morphology can assist planners in making responsible decisions with future riverine development or restoration projects. Sediment rating curves can serve as simple models and can provide predictive tools to estimate annual sediment fluxes. Sediment flux models can aid in the design of river projects by providing insight to past and potential future sediment fluxes. Historical U.S. Geological Survey suspended-sediment and discharge data were evaluated to estimate annual suspended-sediment fluxes for two stations on the Arkansas River located downstream from Keystone Dam in Tulsa County. Annual suspended-sediment fluxes were estimated from 1931-95 for the Arkansas River at Tulsa streamflow-gaging station (07164500) and from 1973-82 for the Arkansas River near Haskell streamflow-gaging station (07165570). The annual flow-weighted suspended-sediment concentration decreased from 1,970 milligrams per liter to 350 milligrams per liter after the completion of Keystone Dam at the Tulsa station. The streambed elevation at the Arkansas River at Tulsa station has changed less than 1 foot from 1970 to 2005, but the thalweg has shifted from a location near the right bank to a position near the left bank. There was little change in the position of most of the banks of the Arkansas River channel from 1950 to 2009. The most substantial change evident from visual inspection of aerial photographs was an apparent decrease in sediment storage in the form of mid-channel and meander bars. The Arkansas River channel between Keystone Dam and the Tulsa-Wagoner County line showed a narrowing and lengthening (increase in sinuosity) over the transition period 1950-77 followed by a steady widening and shortening of the river channel (decrease in sinuosity) during the post-dam (Keystone) periods 1977-85, 1985-2003, and 2003-10.

  16. Subtropical iceberg scours: Tracking the path of meltwater in the deglacial North Atlantic

    NASA Astrophysics Data System (ADS)

    Hill, J. C.; Condron, A.

    2015-12-01

    Over 700 individual iceberg scours have been identified in seafloor bathymetry spanning the southern U.S. Atlantic margin, from Cape Hatteras, North Carolina to the Florida Keys, in water depths from 170-380m. These iceberg scours represent the plowing path of iceberg keels transported southward along the margin in a cold, coastal boundary current derived from the Laurentide Ice Sheet. Despite limited regional multibeam bathymetry data, the scours are traceable along the seafloor for >30 km and exhibit characteristic morphology of iceberg keel marks documented along glaciated continental margins. Many of the scours are flanked by lateral berms that are several meters high and often terminate in semi-circular pits ringed by several meter high ridges (i.e. grounding pits or iceberg plow ridges). The scours decrease in size and abundance moving southward, in accordance with increased iceberg melting farther from the ice calving margin. For example, the scours offshore of South Carolina (~32.5°N) are ~10-100m wide and incised 10-20m into the sediment, whereas scours off the Florida margin (31°N- 24.5°N) are narrower (10-50m wide) and incised 2-5m into the sea floor. Icebergs at these subtropical latitudes would likely have been comparable in size (up 300 m thick) to those calving from the modern-day Greenland Ice Sheet margin. Results from numerical simulations using MITgcm, a high-resolution, eddy-permitting, coupled ice-ocean model configured for the LGM suggest that cold, freshwater and small (≤90m thick) icebergs could have seasonally drifted to South Carolina, but iceberg transport to southern Florida requires much larger (5Sv) meltwater floods to overcome the northward flowing Gulf Stream. These meltwater flood events would most likely have been short-lived (<1 yr), but may have diverted a significant volume of freshwater away from the subpolar regions into the subtropical North Atlantic.

  17. Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    NASA Astrophysics Data System (ADS)

    Livingstone, S. J.; Clark, C. D.; Woodward, J.; Kingslake, J.

    2013-11-01

    We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.

  18. Oxygen Isotopes and Meltwater: Younger Dryas and 8.2 ka Event

    NASA Astrophysics Data System (ADS)

    Keigwin, L. D.

    2015-12-01

    Delta 18-O is one of our most powerful and widely used proxies, with, arguably, the fewest likely unknown unknowns. Here I will consider the d18-O evidence for the two best-known floods of mostly liquid water to the ocean, the Younger Dryas (YD) and the 8.2 ka event. The first d18-O signal of a meltwater flood in the ocean was reported 40 years ago by Kennett and Shackleton (1975) and that paper led directly to the meltwater diversion hypothesis for the origin of the YD cooling. It was later suggested by Rooth (1982) that such a flood could interrupt Nordic seas convection and trigger the YD cold episode. It was reported at this meeting last year that a candidate flood has been found in the Mackenzie River region of the western Arctic based on low d18-O and multiple other lines of evidence. The 8.2 ka event was about one-tenth the duration of the YD but with possibly higher transport, and is more difficult to detect in open marine sediments. As with the YD, it has been modeled by hosing and low salinities have been derived by temperature correcting the d18-O. The resulting low salinity was shown not to follow the prediction of the highest resolution modeling, and theory, that the fresh water would be transported mostly equatorward along the continental shelf. However, I report here that the low d18-O signal of the 8.2 ka flooding is present in new cores from near Logan Canyon on the Scotian shelf break, and in Jordan Basin, Gulf of Maine. These results substantially validate the modeling of Condron and Winsor that fresh water transport must have been along the continental shelf.

  19. Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet.

    PubMed

    Smith, Laurence C; Chu, Vena W; Yang, Kang; Gleason, Colin J; Pitcher, Lincoln H; Rennermalm, Asa K; Legleiter, Carl J; Behar, Alberto E; Overstreet, Brandon T; Moustafa, Samiah E; Tedesco, Marco; Forster, Richard R; LeWinter, Adam L; Finnegan, David C; Sheng, Yongwei; Balog, James

    2015-01-27

    Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km(2) of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54-2.81 cm⋅d(-1)) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41-98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056-0.112 km(3)⋅d(-1) vs. ∼0.103 km(3)⋅d(-1)), and when integrated over the melt season, totaled just 37-75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean. PMID:25583477

  20. Meltwater chemistry and solute export from a Greenland Ice Sheet catchment, Watson River, West Greenland

    NASA Astrophysics Data System (ADS)

    Yde, Jacob C.; Knudsen, N. Tvis; Hasholt, Bent; Mikkelsen, Andreas B.

    2014-11-01

    Solute export from the Greenland Ice Sheet (GrIS) to coastal regions around Greenland is likely to increase in the future as a consequence of increasing icemelt production. Here, we present hydrochemical characteristics, solute and major ion exports and chemical denudation rates for 2007-2010 for the Watson River sector of the GrIS that drains into the fjord Kangerlussuaq. The hydrochemistry is dominated by Ca2+ and HCO3- with a relatively high molar K+/Na+ ratio of 0.6 ± 0.1, typical for meltwaters draining a gneissic lithology. Low molar Ca2+/Na+ and Mg2+/Na+ ratios indicate that weathering of disseminated carbonates contributes less than silicate weathering to the chemical composition. The solute export varied between 33 × 103 (2009) and 61 × 103 tons (2010), showing that increasing discharge leads to increasing solute export at the catchment scale. Deviations between ion yield estimates derived from use of discharge-weighted and mean daily concentrations methods were generally less than 5%, indicating that the choice of method is of less importance. The chemical denudation rates ranged between 36 and 56 Σ∗ meq+ m-2 per year, which are lower than previous records from glacierized catchments. However, when normalized by discharge the denudation rates are comparable to other Arctic sites. When extrapolating the results from the Watson River catchment to the entire Greenland for 2007-2010, the solute export from Greenland meltwater varied between 7.1 × 106 and 7.8 × 106 tons, whilst the major ion export was between 6.4 × 106 and 7.3 × 106 tons. Dissolved Fe, a potential biolimiting nutrient for primary productivity in the North Atlantic, had annual export rates from Greenland between 15 × 103 and 52 × 103 tons.

  1. Greenland ice-sheet contribution to sea-level rise buffered by meltwater storage in firn.

    PubMed

    Harper, J; Humphrey, N; Pfeffer, W T; Brown, J; Fettweis, X

    2012-11-01

    Surface melt on the Greenland ice sheet has shown increasing trends in areal extent and duration since the beginning of the satellite era. Records for melt were broken in 2005, 2007, 2010 and 2012. Much of the increased surface melt is occurring in the percolation zone, a region of the accumulation area that is perennially covered by snow and firn (partly compacted snow). The fate of melt water in the percolation zone is poorly constrained: some may travel away from its point of origin and eventually influence the ice sheet's flow dynamics and mass balance and the global sea level, whereas some may simply infiltrate into cold snow or firn and refreeze with none of these effects. Here we quantify the existing water storage capacity of the percolation zone of the Greenland ice sheet and show the potential for hundreds of gigatonnes of meltwater storage. We collected in situ observations of firn structure and meltwater retention along a roughly 85-kilometre-long transect of the melting accumulation area. Our data show that repeated infiltration events in which melt water penetrates deeply (more than 10 metres) eventually fill all pore space with water. As future surface melt intensifies under Arctic warming, a fraction of melt water that would otherwise contribute to sea-level rise will fill existing pore space of the percolation zone. We estimate the lower and upper bounds of this storage sink to be 322 ± 44 gigatonnes and  1,289(+388)(-252) gigatonnes, respectively. Furthermore, we find that decades are required to fill this pore space under a range of plausible future climate conditions. Hence, routing of surface melt water into filling the pore space of the firn column will delay expansion of the area contributing to sea-level rise, although once the pore space is filled it cannot quickly be regenerated. PMID:23135470

  2. Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet

    PubMed Central

    Smith, Laurence C.; Chu, Vena W.; Yang, Kang; Gleason, Colin J.; Pitcher, Lincoln H.; Rennermalm, Asa K.; Legleiter, Carl J.; Behar, Alberto E.; Overstreet, Brandon T.; Moustafa, Samiah E.; Tedesco, Marco; Forster, Richard R.; LeWinter, Adam L.; Finnegan, David C.; Sheng, Yongwei; Balog, James

    2015-01-01

    Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km2 of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54–2.81 cm⋅d−1) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41–98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056–0.112 km3⋅d−1 vs. ∼0.103 km3⋅d−1), and when integrated over the melt season, totaled just 37–75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean. PMID:25583477

  3. Changes in opal fluxes along the northwest African margin during the last glacial period; linking high and low latitude patterns of productivity

    NASA Astrophysics Data System (ADS)

    Bradtmiller, L. I.; Galgay, M.; McGee, D.; Kinsley, C. W.; Anderson, R. F.

    2014-12-01

    Recent studies have proposed competing hypotheses to explain increased opal fluxes in high and low latitudes during the most recent deglaciation. Anderson et al. (2009) rely on increased wind-driven upwelling in the Southern Ocean to explain the increased availability of Si in both the Southern Ocean and tropical thermoclines, leading to increased opal fluxes in both regions coincident with the deglacial rise in CO2. Meckler et al. (2013) suggest that a decrease in the presence of North Atlantic intermediate water (GNAIW) during the deglaciation allowed Si-rich southern-sourced waters to fill the tropical Atlantic leading to increased opal burial. We attempt to distinguish between these two mechanisms by reconstructing opal fluxes and fluxes of windblown dust over the past ~65ka at four sites along the northwest African margin. The records include the deglaciation, including Heinrich Event 1 (H1) and the Younger Dryas (YD), as well as several earlier Heinrich events. We find that opal and dust fluxes increase simultaneously during the deglaciation, and more highly resolved cores record H1 and the YD as distinct peaks within the deglaciation. Furthermore, opal and dust fluxes scale approximately linearly with one another during these events. We observe opal peaks associated with most Heinrich Events through H6. Finally, we observe a strong similarity between patterns of opal flux in the Southern Ocean and along the African Margin. This suggests that the pattern of diatom productivity and opal flux along the African Margin reflects a combination of changes in wind strength due to shifting temperature gradients, and changes in the export of silica-rich water from the Southern Ocean, both as a result of the global scale climate changes associated with Heinrich Events. Anderson, R. F., S. Ali, L. I. Bradtmiller, S. H. H. Nielsen, M. Q. Fleisher, B. E. Anderson and L. H. Burckle. Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2

  4. Assessing the impacts of land cover change on energy fluxes and evapotranspiration in the middle reach of the Yellow River Basin

    NASA Astrophysics Data System (ADS)

    Gong, T.; Lei, H.; Jiao, Y.; Yang, D.

    2013-12-01

    Land cover change has been generally considered a local environmental issue. Our study focuses on the impacts of land cover change on the energy and water balance using field observation approach. The study site is at Yulin (38.45N, 109.47E) which is in the middle reach of the Yellow River Basin. A flux tower was built in June 2011, and exchange of water vapor and energy between atmosphere and canopy was measured by the eddy covariance (EC) technique. Soil water content and soil temperature were measured at depths of 5, 10, 20, 40, 60, 80, 120, 160cm, under bare soil region and vegetation region, respectively. Before June 2012, the vegetation in this site was typical desert plants, Salix psammophila and Artemisia ordosica. After June 2012, nearly half of the natural vegetation that around the flux tower were cut off by the farmers, which converted half of the land cover to bare soil. Two contrastive periods are selected: the first year (before land cover change) is from July 1st 2011 to June 30th 2012, the second year (transient period) is from July 1st 2012 to June 30th 2013. We will evaluate and compare the datasets of this two periods to explore the impacts of land cover change on: (1) energy balance, including latent heat flux (LE), sensible heat flux (H), net radiation (Rn), and bowen ratio (B0); (2) water balance, including soil water content (SWC) of different depths in unsaturated zone, especially after a long-durated-rainfall, and evapotranspiration. According to the comparative approach, we aim to get insights into how agricultural cultivation impacts on the local water balance (i.e., what is the most sensitive variable to the land cover change, how the groundwater and subsurface water interact, and further, their responses to the land cover change). Moreover, we try to discuss whether this agricultural cultivation can lead to environmental problems.

  5. Isotopic composition of ice cores and meltwater from upper fremont glacier and Galena Creek rock glacier, Wyoming

    USGS Publications Warehouse

    DeWayne, Cecil L.; Green, J.R.; Vogt, S.; Michel, R.; Cottrell, G.

    1998-01-01

    Meltwater runoff from glaciers can result from various sources, including recent precipitation and melted glacial ice. Determining the origin of the meltwater from glaciers through isotopic analysis can provide information about such things as the character and distribution of ablation on glaciers. A 9.4 m ice core and meltwater were collected in 1995 and 1996 at the glacigenic Galena Creek rock glacier in Wyoming's Absaroka Mountains. Measurements of chlorine-36 (36Cl), tritium (3H), sulphur-35 (35S), and delta oxygen-18 (??18O) were compared to similar measurements from an ice core taken from the Upper Fremont Glacier in the Wind River Range of Wyoming collected in 1991-95. Meltwater samples from three sites on the rock glacier yielded 36Cl concentrations that ranged from 2.1 ?? 1.0 X 106 to 5.8??0.3 X 106 atoms/l. The ice-core 36Cl concentrations from Galena Creek ranged from 3.4??0.3 X 105 to 1.0??0.1 X 106 atoms/l. Analysis of an ice core from the Upper Fremont Glacier yielded 36Cl concentrations of 1.2??0.2 X 106 and 5.2??0.2 X 106 atoms/l for pre- 1940 ice and between 2 X 106 and 3 X 106 atoms/l for post-1980 ice. Purdue's PRIME Lab analyzed the ice from the Upper Fremont Glacier. The highest concentration of 36Cl in the ice was 77 ?? 2 X 106 atoms/l and was deposited during the peak of atmospheric nuclear weapons testing in the late 1950s. This is an order of magnitude greater than the largest measured concentration from both the Upper Fremont Glacier ice core that was not affected by weapons testing fallout and the ice core collected from the Galena Creek rock glacier. Tritium concentrations from the rock glacier ranged from 9.2??0.6 to 13.2??0.8 tritium units (TU) in the meltwater to -1.3??1.3 TU in the ice core. Concentrations of 3H in the Upper Fremont Glacier ice core ranged from 0 TU in the ice older than 50 years to 6-12 TU in the ice deposited in the last 10 years. The maximum 3H concentration in ice from the Upper Fremont Glacier deposited in the

  6. LAND-USE CHANGE AND CARBON FLUX BETWEEN 1970S AND 1990S IN CENTRAL HIGHLANDS OF CHIAPAS, MEXICO

    EPA Science Inventory

    We present results of a study in an intensively impacted and highly fragmented landscape in which we apply field-measured carbon (C) density values to land-use/land-cover (LU/LC) statistics to estimate the flux of C between terrestrial ecosystems and the atmosphere from the 1970s...

  7. Effects land surface type, land use, and land use change on aquatic-atmosphere fluxes of carbon dioxide from tropical forests and peat lands of Borneo

    NASA Astrophysics Data System (ADS)

    Oechel, W. C.; Abelleira Martínez, O.; Anshari, G.; Ikawa, H.; Lawrence, W. T.; Metz, M.; Neteler, M.; Nuriman, M.; Rocchini, D.; Zona, D.

    2011-12-01

    Tropical peat lands appear to be loosing huge amounts of carbon dioxide to the atmosphere due to patterns of land use and land use change including conversion of tropical forest peat lands to palm oil production and other agricultural endeavors and forest exploitation. Here, we look at the effect of land use patterns on the export of carbon to tropical river systems and the efflux from tropical rivers to the atmosphere. Levels of pcarbon dioxide, DOC and POC were measured in the Kapuas River, the longest river in Borneo. Patterns of land use and land use change were correlated with export rates of organic matter to the river as well as the vertical fluxes of carbon dioxide from the river and delta to the atmosphere. Land conversion of tropical forests on peat land soils to agriculture, including palm oil production, had some of the highest rates of lateral fluxes of organic carbon to the river system, and among the highest fluxes of carbon dioxide from the river to the atmosphere. This approach illustrates the utility of using a combination of methods: pcarbon dioxide measurement, water chemistry, temporal remote sensing, and modeling to understand and quantify the impact of land use change on GHG emissions from tropical peat lands. Boat based eddy covariance, developed and tested in the coastal zones of the Pacific Ocean, promises to provide a powerful addition to these approaches.

  8. Quantifying fluxes and characterizing compositional changes of dissolved organic matter in aquatic systems in situ using combined acoustic and optical measurements

    USGS Publications Warehouse

    Downing, B.D.; Boss, E.; Bergamaschi, B.A.; Fleck, J.A.; Lionberger, M.A.; Ganju, N.K.; Schoellhamer, D.H.; Fujii, R.

    2009-01-01

    Studying the dynamics and geochemical behavior of dissolved and particulate organic material is difficult because concentration and composition may rapidly change in response to aperiodic as well as periodic physical and biological forcing. Here we describe a method useful for quantifying fluxes and analyzing dissolved organic matter (DOM) dynamics. The method uses coupled optical and acoustic measurements that provide robust quantitative estimates of concentrations and constituent characteristics needed to investigate processes and calculate fluxes of DOM in tidal and other lotic environments. Data were collected several times per hour for 2 weeks or more, with the frequency and duration limited only by power consumption and data storage capacity. We assessed the capabilities and limitations of the method using data from a winter deployment in a natural tidal wetland of the San Francisco Bay estuary. We used statistical correlation of in situ optical data with traditional laboratory analyses of discrete water samples to calibrate optical properties suited as proxies for DOM concentrations and characterizations. Coupled with measurements of flow velocity, we calculated long-term residual horizontal fluxes of DOC into and out from a tidal wetland. Subsampling the dataset provides an estimate for the maximum sampling interval beyond which the error in flux estimate is significantly increased.?? 2009, by the American Society of Limnology and Oceanography, Inc.

  9. Modeling secular changes in seawater chemistry accurately requires inclusion of environmental controls on low-temperature, off-axis, hydrothermal fluxes

    NASA Astrophysics Data System (ADS)

    Coogan, L. A.; Dosso, S. E.; Higgins, J. A.

    2014-12-01

    There are sharp rises in the Sr- and Li-isotopic composition of seawater at the Eocene-Oligocene boundary that are generally thought to be associated with Himalayan uplift and associated climatic changes and continental weathering variability. In modeling such data the norm is to hold the chemical fluxes associated with off-axis hydrothermal circulation through the oceanic crust constant while varying the river fluxes (and/or isotopic ratios). There is, however, no a priori reason to assume the chemical fluxes (or isotopic compositions) associated with off-axis hydrothermal systems should stay constant. Instead, changing environmental conditions (e.g. seawater composition and bottom water temperature) will lead to changes in these fluxes. An alternative model to explain the sharp rise in the Sr- and Li-isotopic composition of seawater at the Eocene-Oligocene boundary is cooling of the deep ocean. Decreased reaction rates in the oceanic crust, due to decreasing temperature, can be shown to lead to a decrease in the flux of unradiogenic Sr into the ocean. The magnitude matches, within uncertainty, that required to explain the increase in seawater Sr-isotopic composition [Coogan and Dosso, in review]. The story for Li is more uncertain. Two factors may lead to smaller effective fractionation factors between seawater and the (large) Li sink in the oceanic crust when bottom water is warmer: (i) higher temperature will decrease the isotopic fractionation factor; (ii) the more extensive fluid-rock reaction in the ocean crust when bottom water is warmer will make Li uptake by the oceanic crust more efficient. All other things being equal this will lead to a lower Li content of seawater. In turn, a lower Li content in seawater will mean that for a given Li-uptake rate by the crust the effective fractionation factor is smaller, due to Rayleigh distillation of Li-isotopes during fluid-rock reaction in the oceanic crust. In combination these factors predict a significant (many

  10. Small Valleys Networks on Mars: The Glacial Meltwater Channel Networks of Devon Island, Nunavut Territory, Arctic Canada, as Possible Analogs

    NASA Technical Reports Server (NTRS)

    Lee, Pascal; Rice, James W., Jr.

    1999-01-01

    Small valley networks are perhaps the clearest evidence for episodes of sustained fluid erosion by water on Mars. While small valley formation has occurred even in Amazonian times, notably on the flanks of some volcanoes, most small valley networks on Mars are associated with the heavily cratered Noachian terrains and are thought to be as old as these terrains. We discuss here the recent identification of glacial meltwater channel networks on Devon Island, Nunavut Territory, Arctic Canada, as possible analogs for many small valley networks seen on Mars. A meltwater channel network interpretation for the martian networks may help solve critical problems plaguing more classical interpretations of their origin such as surface runoff following precipitation or groundwater release, including the need for warm climatic conditions. Additional information is contained in the original extended abstract.

  11. Short-term changes in anaerobic oxidation of methane in response to varying methane and sulfate fluxes

    NASA Astrophysics Data System (ADS)

    Wegener, G.; Boetius, A.

    2008-08-01

    A major role in global methane fluxes has been attributed to the process of anaerobic oxidation of methane, which is performed by consortia of methanotrophic archaea and sulfate reducing bacteria. An important question remains how these very slow growing microorganisms with generation times of 3 7 months respond to natural variations in methane fluxes at cold seeps. Here, we used an experimental flow-through column system filled with cold seep sediments naturally enriched in methanotrophic communities, to test their response to short-term variations in methane and sulfate fluxes. At stable methane and sulfate concentrations of ~2 mM and 28 mM, respectively, we measured constant rates of anaerobic oxidation of methane (AOM) and sulfide production (SR) for up to 160 days of incubation. When percolated with methane-free medium, the anaerobic methanotrophs ceased to oxidize methane and to produce sulfide. After a starvation phase of 40 days, the addition of methane restored former AOM and SR rates immediately. At methane concentrations between 0 2.3 mM we measured a linear correlation between methane availability, AOM and SR. At constant fluid flow rates of 30 m yr-1, ca. 50% of the methane was consumed by the ANME population at all concentrations tested. Reducing the sulfate concentration from 28 to 1 mM, a decrease in AOM and SR by 35% was observed. Hence, the marine anaerobic methanotrophs (ANME) are capable to consume substantial amounts of methane rising from the subsurface seabed to the hydrosphere over a wide range of fluxes of methane and sulfate.

  12. Meltwater history inferred from authigenic carbonates and fine grained glaciomarine sediments from the Mendeleev Ridge in the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Nam, Seung-Il; Woo, Kyung Sik; Ji, Hyo Seon; Stein, Ruediger; Mackensen, Andreas; Matthiessen, Jens

    2015-04-01

    Authigenic carbonates and mud fractions of the glaciomarine sediments were investigated texturally and geochemically. The sediment core (PS72/410-1) was retrieved using a giant box corer from the central Mendeleev Ridge of the western Arctic Ocean (Station location= Lat. 80°30.37"N, Long. 175°44.38"W) during the Polarstern Arctic expedition (PS72) in 2008. The core is 39 cm long with age of ca. 76 ka BP and was collected from the water depth of 1,802 meters. The sediments show various colours from grey to brown as previously reported in other Arctic deep sea sediments, reflecting glacial-interglacial and/or stadial-interstadial cycles. Authigenic carbonate minerals are present through the whole sequence except for a few centimetres. These authigenic carbonates are composed of high Mg-calcite, low Mg-calcite and aragonite. Various crystal shapes of aragonite and calcite together with clear growth shapes of the crystals suggest that they are inorganic in origin. Highly enriched carbon isotope compositions (δ13C = 0 ~ +5‰ vs. PDB) strongly indicate that they formed in methanogenic zone below sediment/water interface by the reaction between anoxic pore fluids and host sediments induced by methanogenic bacteria. However, a wide range of oxygen isotope values (δ18O = -5 ~ +5‰ vs. PDB) may indicate that porewater has been changed due to reaction between residual seawater and volcanic sediments. Relatively higher contents of K, Al, Fe and Be values from muddy sediments as well as low δ18O compositions of authigenic carbonates may imply strong input of meltwater from volcanic region (Eastern Arctic region) whereas higher oxygen isotope compositions of authigenic carbonates and higher Sr and K contents of mud sediments may reflect stronger influence from carbonate-rich region (Canadian Arctic region). Mineralogical changes form low to high Mg-calcite together with decrease in Mg, Sr and Fe contents strongly support less freshwater input from glacial mode to

  13. Morphological changes of tungsten surfaces by low-flux helium plasma treatment and helium incorporation via magnetron sputtering.

    PubMed

    Iyyakkunnel, Santhosh; Marot, Laurent; Eren, Baran; Steiner, Roland; Moser, Lucas; Mathys, Daniel; Düggelin, Marcel; Chapon, Patrick; Meyer, Ernst

    2014-07-23

    The effect of helium on the tungsten microstructure was investigated first by exposure to a radio frequency driven helium plasma with fluxes of the order of 1 × 10(19) m(-2) s(-1) and second by helium incorporation via magnetron sputtering. Roughening of the surface and the creation of pinholes were observed when exposing poly- and nanocrystalline tungsten samples to low-flux plasma. A coating process using an excess of helium besides argon in the process gas mixture leads to a porous thin film and a granular surface structure whereas gas mixture ratios of up to 50% He/Ar (in terms of their partial pressures) lead to a dense structure. The presence of helium in the deposited film was confirmed with glow-discharge optical emission spectroscopy and thermal desorption measurements. Latter revealed that the highest fraction of the embedded helium atoms desorb at approximately 1500 K. Identical plasma treatments at various temperatures showed strongest modifications of the surface at 1500 K, which is attributed to the massive activation of helium singly bond to a single vacancy inside the film. Thus, an efficient way of preparing nanostructured tungsten surfaces and porous tungsten films at low fluxes was found. PMID:24960311

  14. Changes in the energy response of a dedicated gamma camera after exposure to a high-flux irradiation.

    PubMed

    Matheoud, R; Zito, F; Canzi, C; Voltini, F; Gerundini, P

    1999-06-01

    This work reports the effects of the gain variation of the photomultiplier tubes (PMTs) observed on a cardiac dedicated gamma camera after accidental high-flux irradiation. One detector of this dual-headed 90 degrees-fixed gamma camera was accidentally left uncollimated during a quality assurance procedure on the other detector with a 57Co flood source (259 MBq) and received a non-uniform high flux of 1.9-0.6 Mcps over 25000 mm2 areas for about 30 min. To evaluate the severity and the duration of the perturbation effect on the energy response of the detector, the photopeak position was monitored for about 1 month with a 99mTc point source. The 140 keV photopeak shifted to 158 keV soon after irradiation, reached the correct position after 9 days and moved to a stable value of 132 keV after 15 days. Afterwards, a new energy calibration reset the photopeak position at 140 keV and the correct energy response of the gamma camera. This experience suggests that particular care should be taken to avoid exposures to high radiation fluxes that induce persistent gain shifts on the PMTs of this system. PMID:10498509

  15. Marine Palynological Records From the Eastern Canadian Margin Suggest Multiple Meltwater Sources at the Time of the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Levac, E.; Lewis, M. C. F. M.

    2015-12-01

    The sources and paths of meltwater drainage into the North Atlantic Ocean at the time of the Younger Dryas (YD) are still debated. The eastern route implied drainage from glacial Lake Agassiz and predecessor lakes along the southeastern edge of the Laurentide Ice Sheet to the North Atlantic Ocean, via the St. Lawrence River. A northern drainage route, along which meltwater reached the North Atlantic via the Arctic Ocean, is presently favoured, but alternate sources of freshwater (icebergs etc.) are also possible. We present evidence for meltwater drainage via the St. Lawrence valley from 8 sediment cores from Cabot Strait, Laurentian Channel, and from the Scotian, Northeast Newfoundland and Labrador Shelves at the time of the YD. Distinct dinoflagellate cyst assemblages are identified during the YD interval and we propose new biostratigraphic markers for the event. Dinoflagellage cysts are also used to reconstruct sea surface conditions. Reconstructions from cores along the eastern route contain strong evidence of lowered salinity within the YD interval, thereby re-establishing the St. Lawrence drainage system as a significant route for inflow of YD meltwater to the North Atlantic. This prompted us to re-examine original data and paleoceanographic interpretation of surface water conditions based on new analysis of dinoflagellate cyst zonation combined with an updated chronology supported by new radiocarbon dates and refined calibrations. Evidence for lowered salinity is also recorded in cores from the NE Newfoundland and Labrador Shelves. Geographical differences in the duration of cold, low salinity conditions associated with the YD event, west and east of Laurentian Channel, suggests another source of freshwater, possibly via the Labrador Current.

  16. Water Fluxes from Leaf to Ecosystem Scales in a Seasonal Mexican Cloud Forest: Implications for Climate Change Impacts and Future Research Priorities

    NASA Astrophysics Data System (ADS)

    Asbjornsen, H.; Gotsch, S. G.; Goldsmith, G. R.; Alvarado-Barrientos, M. S.; Holwerda, F.; Bruijnzeel, L. A.; Dawson, T. E.

    2014-12-01

    The ecohydrological functioning of cloud forests is intricately linked to unique plant ecophysiological traits and processes that influence water fluxes at the plot to ecosystem scales. However, despite substantial gains in our understanding of cloud forest plant ecophysiology over the past decade, integration of water flux information from the leaf to the watershed scale is still lacking. We present a synthesis of research aimed at revealing the linkages between plant ecophysiology and forest ecohydrological functioning, conducted in a seasonal cloud forest in Veracruz, Mexico. A variety of species-specific leaf-level water flux behaviors were found to influence various aspects of plant water relations, which in turn, scaled up to impact stand water balance. For example, foliar fog absorption compensated for approximately 9.3 ± 1.2% of transpiration, and nocturnal transpiration for dominant tree species during the dry-season accounted for 22% to 30% of daytime transpiration. Further, the presence of dense fog, light fog, and cloud cover was shown to reduce transpiration such that annual transpiration may increase up to 17% in the case that all fog occurrence is replaced by clear sky conditions. We discuss how these processes affect whole-plant and stand water balances, as well as the potential feedbacks of vegetation controls on hydrologic fluxes under future climate change. After placing our findings within a global context we present a conceptual model of the links between plant ecophysiological and ecosystem hydrological functioning in cloud forest settings. Finally, critical areas for future research are highlighted to further improve our understanding of the linkages between leaf- and ecosystem-level processes and fluxes.

  17. Carbon Management In the Post-Cap-and-Trade Carbon Economy: An Economic Model for Limiting Climate Change by Managing Anthropogenic Carbon Flux

    NASA Astrophysics Data System (ADS)

    DeGroff, F. A.

    2013-05-01

    In this paper, we discuss an economic model for comprehensive carbon management that focuses on changes in carbon flux in the biosphere due to anthropogenic activity. The two unique features of the model include: 1. A shift in emphasis from primarily carbon emissions, toward changes in carbon flux, mainly carbon extraction, and 2. A carbon price vector (CPV) to express the value of changes in carbon flux, measured in changes in carbon sequestration, or carbon residence time. The key focus with the economic model is the degree to which carbon flux changes due to anthropogenic activity. The economic model has three steps: 1. The CPV metric is used to value all forms of carbon associated with any anthropogenic activity. In this paper, the CPV used is a logarithmic chronological scale to gauge expected carbon residence (or sequestration) time. In future economic models, the CPV may be expanded to include other factors to value carbon. 2. Whenever carbon changes form (and CPV) due to anthropogenic activity, a carbon toll is assessed as determined by the change in the CPV. The standard monetary unit for carbon tolls are carbon toll units, or CTUs. The CTUs multiplied by the quantity of carbon converted (QCC) provides the total carbon toll, or CT. For example, CT = (CTU /mole carbon) x (QCC moles carbon). 3. Whenever embodied carbon (EC) attributable to a good or service moves via trade to a jurisdiction with a different CPV metric, a carbon toll (CT) is assessed representing the CPV difference between the two jurisdictions. This economic model has three clear advantages. First, the carbon pricing and cost scheme use existing and generally accepted accounting methodologies to ensure the veracity and verifiability of carbon management efforts with minimal effort and expense using standard, existing auditing protocols. Implementing this economic model will not require any new, special, unique, or additional training, tools, or systems for any entity to achieve their minimum

  18. Influence of glacial meltwater on water balance processes of two Tibetan lakes indicated by δ18O

    NASA Astrophysics Data System (ADS)

    Gao, J.; Itpcas

    2011-12-01

    δ18O measurements based on systematic sampling and isotopic modeling have been adopted to study the affects of glacial meltwater in two lake basins (Lakes Yamdrok-tso and Puma Yum-tso) at two different elevations on the southern Tibetan Plateau. Temporally, δ18O values in precipitation and lake water display a seasonal fluctuation in both lakes. Spatially, δ18O values in the two lake basins increase by 10% from the termini of glaciers to the lake shores, by about 1% from the lakeshores to the lake center, by 0.4% from the water surface to depth in these lakes. The obvious annual δ18O variations indicate that lake water mixes sufficiently in a short time. Model results show that glacial meltwater is an important factor on lake water balance process. Equilibrium δ18O values decrease 0.8% for Yamdrok-tso Lake and 0.6% for Puma Yum-tso Lake when contributions of glacial meltwater to these lakes shrink by 60%. δ18O ratios increase rapidly during the initial stages and take a relatively longer time to approach the equilibrium value. The modeled results also show that the surface lake water temperature has a minimal impact on this process.
    Dr. Jing Gao

  19. Catastrophic meltwater discharge down the Hudson Valley: A potential trigger for the Intra-Allerød cold period

    NASA Astrophysics Data System (ADS)

    Donnelly, Jeffrey P.; Driscoll, Neal W.; Uchupi, Elazar; Keigwin, Lloyd D.; Schwab, William C.; Thieler, E. Robert; Swift, Stephen A.

    2005-02-01

    Glacial freshwater discharge to the Atlantic Ocean during deglaciation may have inhibited oceanic thermohaline circulation, and is often postulated to have driven climatic fluctuations. Yet attributing meltwater-discharge events to particular climate oscillations is problematic, because the location, timing, and amount of meltwater discharge are often poorly constrained. We present evidence from the Hudson Valley and the northeastern U.S. continental margin that establishes the timing of the catastrophic draining of Glacial Lake Iroquois, which breached the moraine dam at the Narrows in New York City, eroded glacial lake sediments in the Hudson Valley, and deposited large sediment lobes on the New York and New Jersey continental shelf ca. 13,350 yr B.P. Excess 14C in Cariaco Basin sediments indicates a slowing in thermohaline circulation and heat transport to the North Atlantic at that time, and both marine and terrestrial paleoclimate proxy records around the North Atlantic show a short-lived (<400 yr) cold event (Intra-Allerød cold period) that began ca. 13,350 yr B.P. The meltwater discharge out the Hudson Valley may have played an important role in triggering the Intra-Allerød cold period by diminishing thermohaline circulation.

  20. Catastrophic meltwater discharge down the Hudson Valley: a potential trigger for the Intra-Allerød cold period

    USGS Publications Warehouse

    Donnelly, Jeffrey P.; Driscoll, Neal W.; Uchupi, Elazar; Keigwin, Loyd D.; Schwab, William C.; Thieler, E. Robert; Swift, Stephen A.

    2005-01-01

    Glacial freshwater discharge to the Atlantic Ocean during deglaciation may have inhibited oceanic thermohaline circulation, and is often postulated to have driven climatic fluctuations. Yet attributing meltwater-discharge events to particular climate oscillations is problematic, because the location, timing, and amount of meltwater discharge are often poorly constrained. We present evidence from the Hudson Valley and the northeastern U.S. continental margin that establishes the timing of the catastrophic draining of Glacial Lake Iroquois, which breached the moraine dam at the Narrows in New York City, eroded glacial lake sediments in the Hudson Valley, and deposited large sediment lobes on the New York and New Jersey continental shelf ca. 13,350 yr B.P. Excess 14C in Cariaco Basin sediments indicates a slowing in thermohaline circulation and heat transport to the North Atlantic at that time, and both marine and terrestrial paleoclimate proxy records around the North Atlantic show a short-lived (<400 yr) cold event (Intra-Aller??d cold period) that began ca. 13,350 yr B.P. The meltwater discharge out the Hudson Valley may have played an important role in triggering the Intra-Aller??d cold period by diminishing thermohaline circulation. ?? 2005 Geological Society of America.

  1. Biodiversity of cold-adapted yeasts from glacial meltwater rivers in Patagonia, Argentina.

    PubMed

    de García, Virginia; Brizzio, Silvia; Libkind, Diego; Buzzini, Pietro; van Broock, María

    2007-02-01

    The occurrence of culturable yeasts in glacial meltwater from the Frías, Castaño Overo and Río Manso glaciers, located on Mount Tronador in the Nahuel Huapi National Park (Northwestern Patagonia, Argentina) is presented. Subsurface water samples were filtered for colony counting and yeast isolation. The total yeast count ranged between 6 and 360 CFU L(-1). Physiologic and molecular methods were employed to identify 86 yeast isolates. In agreement with yeast diversity data from studies for Antarctic and Alpine glaciers, the genera Cryptococcus, Leucosporidiella, Dioszegia, Rhodotorula, Rhodosporidium, Mrakia, Sporobolomyces, Udeniomyces and Candida were found. Cryptococcus and Leucosporidiella accounted for 50% and 20% of the total number of strains, respectively. Among 21 identified yeast species, Cryptococcus sp. 1 and Leucosporidiella fragaria were the most frequent. The typically psychrophilic Mrakia yeast strain and three new yeast species, yet to be described, were also isolated. All yeast strains were able to grow at 5, 10, and 15 degrees C. Among yeast strains expressing extracellular enzymatic activity, higher proteolytic and lipolytic activities were obtained at 4 degrees C than at 20 degrees C. PMID:17313582

  2. Efficient removal of meltwater runoff through supraglacial streams and rivers on the southwestern Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Smith, L. C.; Yang, K.; Pitcher, L. H.; Overstreet, B. T.; Rennermalm, A. K.; Chu, V. W.; Ryan, J.; Hubbard, A.; Cooper, M. G.; Tedesco, M.; Mote, T. L.; Young, K.; Behar, A.

    2015-12-01

    Supraglacial streams and rivers flowing on the Greenland Ice Sheet have received little physical study. We present remotely sensed (UAV, WorldView) and in situ (Acoustic Doppler Current Profiler, Lagrangian drifters) measurements of supraglacial river drainage pattern, hydraulic properties, and discharge in the Kangerlussuaq region. This area of the ice sheet is characterized by large, well-organized supraglacial stream/river networks that efficiently drain the ice surface with minimal retention of surface water, with river moulins being the the dominant physical mechanism by which surface meltwater enters the ice sheet. An intensive 2015 field campaign acquired novel datasets of watershed extent, drainage pattern, ablation rate, albedo and discharge for a ~70 km2 mid-elevation ice catchment ("Rio Behar"), including a continuous 72-hour record of discharge and water temperature in a supraglacial river upstream of its terminal moulin. We conclude that this area of the ice sheet is efficiently drained by supraglacial stream/river networks, that ice-surface DEMs alone cannot fully describe supraglacial drainage and its connection to subglacial systems; and that in situ measurements of supraglacial river discharge offer a unique opportunity to test runoff predictions of regional climate models.

  3. Fundamentals of Melt-Water Interfacial Transport Phenomena: Improved Understanding for Innovative Safety Technologies in ALWRs

    SciTech Connect

    M. Anderson; M. Corradini; K.Y. Bank; R. Bonazza; D. Cho

    2005-04-26

    The interaction and mixing of high-temperature melt and water is the important technical issue in the safety assessment of water-cooled reactors to achieve ultimate core coolability. For specific advanced light water reactor (ALWR) designs, deliberate mixing of the core-melt and water is being considered as a mitigative measure, to assure ex-vessel core coolability. The goal of this work is to provide the fundamental understanding needed for melt-water interfacial transport phenomena, thus enabling the development of innovative safety technologies for advanced LWRs that will assure ex-vessel core coolability. The work considers the ex-vessel coolability phenomena in two stages. The first stage is the melt quenching process and is being addressed by Argonne National Lab and University of Wisconsin in modified test facilities. Given a quenched melt in the form of solidified debris, the second stage is to characterize the long-term debris cooling process and is being addressed by Korean Maritime University in via test and analyses. We then address the appropriate scaling and design methodologies for reactor applications.

  4. Meltwater production due to strain heating in Storglaciären, Sweden

    NASA Astrophysics Data System (ADS)

    Aschwanden, Andy; Blatter, Heinz

    2005-12-01

    Storglaciären, northern Sweden, is temperate in most parts except for a cold surface layer in the ablation zone. One of four possible sources for liquid water in temperate ice is melting due to strain heating. Velocity fields are calculated with an ice flow model, so that calculated and observed surface velocities agree. Meltwater accumulation is computed by integrating strain heating along trajectories starting at the surface in the accumulation area and ending at the cold-temperate transition surface in the ablation zone. The distribution of moisture content due to strain heating alone is mapped in a longitudinal section of Storglaciären. Values reach more than 10 g of water per kilogram ice-water mixture in the lowest parts of the temperate domain. For this moisture content the rate factor is more than 3 times higher than for water-free ice, and therefore water production by strain heating is important for the modeling of temperate and polythermal glaciers.

  5. Drowning of the - 150 m reef off Hawaii: A casualty of global meltwater pulse 1A?

    USGS Publications Warehouse

    Webster, J.M.; Clague, D.A.; Riker-Coleman, K.; Gallup, C.; Braga, J.C.; Potts, D.; Moore, J.G.; Winterer, E.L.; Paull, C.K.

    2004-01-01

    We present evidence that the drowning of the - 150 m coral reef around Hawaii was caused by rapid sea-level rise associated with meltwater pulse 1A (MWP-1A) during the last deglaciation. New U/Th and 14C accelerator mass spectrometry dates, combined with reinterpretation of existing radiometric dates, constrain the age of the coral reef to 15.2-14.7 ka (U/Th age), indicating that reef growth persisted for 4.3 k.y. following the end of the Last Glacial Maximum at 19 ka. The drowning age of the reef is roughly synchronous with the onset of MWP-1A between 14.7 and 14.2 ka. Dates from coralline algal material range from 14 to 10 cal ka (calibrated radiocarbon age), 1-4 k.y. younger than the coral ages. A paleoenvironmental reconstruction incorporating all available radiometric dates, high-resolution bathymetry, dive observations, and coralgal paleobathymetry data indicates a dramatic rise in sea level around Hawaii ca. 14.7 ka. Paleowater depths over the reef crest increased rapidly above a critical depth (30-40 m), drowning the shallow reef-building Porites corals and causing a shift to deepwater coralline algal growth, preserved as a crust on the drowned reef crest. ?? 2004 Geological Society of America.

  6. Extensive liquid meltwater storage in firn within the Greenland ice sheet

    NASA Astrophysics Data System (ADS)

    Forster, Richard R.; Box, Jason E.; van den Broeke, Michiel R.; Miège, Clément; Burgess, Evan W.; van Angelen, Jan H.; Lenaerts, Jan T. M.; Koenig, Lora S.; Paden, John; Lewis, Cameron; Gogineni, S. Prasad; Leuschen, Carl; McConnell, Joseph R.

    2014-02-01

    Mass loss from the Greenland ice sheet contributes significantly to present sea level rise. High meltwater runoff is responsible for half of Greenland's mass loss. Surface melt has been spreading and intensifying in Greenland, with the highest ever surface area melt and runoff recorded in 2012. However, how surface melt water reaches the ocean, and how fast it does so, is poorly understood. Firn--partially compacted snow from previous years--potentially has the capacity to store significant amounts of melt water in liquid or frozen form, and thus delay its contribution to sea level. Here we present direct observations from ground and airborne radar, as well as ice cores, of liquid water within firn in the southern Greenland ice sheet. We find a substantial amount of water in this firn aquifer that persists throughout the winter, when snow accumulation and melt rates are high. This represents a previously unknown storage mode for water within the ice sheet. We estimate, using a regional climate model, aquifer area at about 70,000km2 and the depth to the top of the water table as 5-50m. The perennial firn aquifer could be important for estimates of ice sheet mass and energy budget.

  7. Short-term groundwater fluxes in the hyporheic zone as a consequence of changing river stages; numerical simulation by HYDRUS 2D/3D.

    NASA Astrophysics Data System (ADS)

    Wyseure, Guido; Chou, Po-Yi

    2010-05-01

    All hydrological handbooks contain methods for direct runoff and base-flow separation. The semi-log separation method is the most classical one. One can, however, question the physical base for such method. In addition, the water fluxes in the riverbed are important for ecology and water quality. In our study an 2-D cross-section including the river and the surrounding aquifer was set-up in HYDRUS 2D/3D. Initial conditions were a steady-state subsurface flow feeding the river with a recharge from the soil surface. A surface runoff event was simulated by a rise and recession of the water level in the river. Differences between summer and winter situation were explored by given representative temperatures to the different components of the river-aquifer system. The simulations show that the fluxes are very different along the riverbed. Even during steady state baseflow we see that the fluxes through the bottom were 2 to 3 times smaller as compared to the side banks. During the hydrographs the proportion can become up to 5 times. Another interesting result is that within the time frame of the hydrograph and its immediate recession relatively little water, which pentetrated in the aquifer, returns to the river. Most of the water replenishes the aquifer and there is only a very small rise of baseflow. In our simulation we returned to the original level as before the hydrograph, so in reality even less or no rise in baseflow may occur immediately after a hydrograph. Of course, in a longer time-frame the recharge of the aquifer will give a rise to the actual subsurface drainage. The change in seasonal temperatures within the river-aquifer system has a substantial effect. For identical river stage hydrograph changes the hyporheic exchange fluxes are more intense in summer than in winter. If we define the hyporheic zone as the extedn to which the water fluxes from the river can penetrate, then we see that this zone is wider on the sides as compared to the bottom of the

  8. Responses of CO(2), N(2)O and CH(4) fluxes between atmosphere and forest soil to changes in multiple environmental conditions.

    PubMed

    Yan, Junhua; Zhang, Wei; Wang, Keya; Qin, Fen; Wang, Wantong; Dai, Huitang; Li, Peixue

    2014-01-01

    To investigate the effects of multiple environmental conditions on greenhouse gas (CO2 , N2 O, CH4 ) fluxes, we transferred three soil monoliths from Masson pine forest (PF) or coniferous and broadleaved mixed forest (MF) at Jigongshan to corresponding forest type at Dinghushan. Greenhouse gas fluxes at the in situ (Jigongshan), transported and ambient (Dinghushan) soil monoliths were measured using static chambers. When the transported soil monoliths experienced the external environmental factors (temperature, precipitation and nitrogen deposition) at Dinghushan, its annual soil CO2 emissions were 54% in PF and 60% in MF higher than those from the respective in situ treatment. Annual soil N2 O emissions were 45% in PF and 44% in MF higher than those from the respective in situ treatment. There were no significant differences in annual soil CO2 or N2 O emissions between the transported and ambient treatments. However, annual CH4 uptake by the transported soil monoliths in PF or MF was not significantly different from that at the respective in situ treatment, and was significantly lower than that at the respective ambient treatment. Therefore, external environmental factors were the major drivers of soil CO2 and N2 O emissions, while soil was the dominant controller of soil CH4 uptake. We further tested the results by developing simple empirical models using the observed fluxes of CO2 and N2 O from the in situ treatment and found that the empirical models can explain about 90% for CO2 and 40% for N2 O of the observed variations at the transported treatment. Results from this study suggest that the different responses of soil CO2 , N2 O, CH4 fluxes to changes in multiple environmental conditions need to be considered in global change study. PMID:23868392

  9. Anthropogenically derived changes in the sedimentary flux of Mg, Cr, Ni, Cu, Zn, Hg, Pb, and P in Lough Neagh, Northern Ireland

    SciTech Connect

    Rippey, B.; Murphy, R.J.; Kyle, S.W.

    1982-01-01

    The concentration-depth behavior of Mg, Cr, Ni, Cu, Zn, Hg, Pb, and P in three sediment cores from a central site in Lough Neagh, Northern Ireland, was examined for changes in the sedimentary flux of these elements. Two main periods of change were found. A change in the catchment erosion-leaching regime in the 17th century, caused by widespread and comprehensive woodland clearance, produced increased sedimentary Mg, Cu, and Pb concentrations. A second and larger change occurred after about 1880 A.D. Cr, Cu, Zn, Hg, Pb, and P, and , to a lesser extent, Ni concentrations increase toward the sediment surface. Differing P and trace-metal profiles, a comparison of the estimated anthropogenic sedimentary flux with background atmospheric contributions, and a general comparison with other situations all suggest that background atmospheric sources make a substantial contribution to the more recent Cu, Zn, Hg, and Pb sedimentary contamination. The trace-metal contamination of Lough Neagh is part of a global pattern.

  10. Large increase in dissolved inorganic carbon flux from the Mississippi River to Gulf of Mexico due to climatic and anthropogenic changes over the 21st century

    NASA Astrophysics Data System (ADS)

    Ren, Wei; Tian, Hanqin; Tao, Bo; Yang, Jia; Pan, Shufen; Cai, Wei-Jun; Lohrenz, Steven E.; He, Ruoying; Hopkinson, Charles S.

    2015-04-01

    It is recognized that anthropogenic factors have had a major impact on carbon fluxes from land to the ocean during the past two centuries. However, little is known about how future changes in climate, atmospheric CO2, and land use may affect riverine carbon fluxes over the 21st century. Using a coupled hydrological-biogeochemical model, the Dynamic Land Ecosystem Model, this study examines potential changes in dissolved inorganic carbon (DIC) export from the Mississippi River basin to the Gulf of Mexico during 2010-2099 attributable to climate-related conditions (temperature and precipitation), atmospheric CO2, and land use change. Rates of annual DIC export are projected to increase by 65% under the high emission scenario (A2) and 35% under the low emission scenario (B1) between the 2000s and the 2090s. Climate-related changes along with rising atmospheric CO2 together would account for over 90% of the total increase in DIC export throughout the 21st century. The predicted increase in DIC export from the Mississippi River basin would alter chemistry of the coastal ocean unless appropriate climate mitigation actions are taken in the near future.

  11. Changes in water, carbon, and nitrogen fluxes with the addition of biochar to soils: lessons learned from laboratory and greenhouse experiments

    NASA Astrophysics Data System (ADS)

    Barnes, R. T.; Gallagher, M. E.; Masiello, C. A.; Liu, Z.; Dugan, B.; Rudgers, J. A.

    2011-12-01

    The addition of biochar to agricultural soils has the potential to provide a number of ecosystem services, ranging from carbon (C) sequestration to increased soil fertility and crop production. It is estimated that 0.5 to 0.9 Pg of C yr-1 can be sequestered through the addition of biochar to soils, significantly increasing the charcoal flux to the biosphere over natural inputs from fire (0.05 to 0.20 Pg C yr-1). There remain large uncertainties about biochar mobility within the environment, making it a challenge to assess the ecosystem residence time of biochar. We conducted laboratory and greenhouse experiments to understand how soil amendment with laboratory-produced biochar changes water, C, and nitrogen (N) fluxes from soils. We used column experiments to assess how biochar amendment to three types of soils (sand, organic, clay-rich) affected hydraulic conductivity and dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) fluxes. Results varied with soil type; biochar significantly decreased the hydraulic conductivity of the sand and organic soils by a factor of 10.6 and 2.7, respectively. While not statistically significant, biochar addition increased the hydraulic conductivity of the clay-rich soil by 50% on average. The addition of biochar significantly increased the DOC fluxes from the C-poor sand and clay soils while it significantly decreased the DOC flux from the organic-rich soil. In contrast, TDN fluxes decreased with biochar additions from all soil types, though the results were not statistically significant from the clay-rich soil. These laboratory experiments suggest that changes in the hydraulic conductivity of soil due to biochar amendments could play a significant role in understanding how biochar additions to agricultural fields will change watershed C and N dynamics. We additionally conducted a 28-day greenhouse experiment with sorghum plants using a three-way factorial treatment (water availability x biochar x mycorrhizae) to

  12. Directed flux motor

    NASA Technical Reports Server (NTRS)

    Wilson, Andrew (Inventor); Punnoose, Andrew (Inventor); Strausser, Katherine (Inventor); Parikh, Neil (Inventor)

    2011-01-01

    A directed flux motor described utilizes the directed magnetic flux of at least one magnet through ferrous material to drive different planetary gear sets to achieve capabilities in six actuated shafts that are grouped three to a side of the motor. The flux motor also utilizes an interwoven magnet configuration which reduces the overall size of the motor. The motor allows for simple changes to modify the torque to speed ratio of the gearing contained within the motor as well as simple configurations for any number of output shafts up to six. The changes allow for improved manufacturability and reliability within the design.

  13. Flux variations and vertical distributions of siliceous Rhizaria (Radiolaria and Phaeodaria) in the western Arctic Ocean: indices of environmental changes

    NASA Astrophysics Data System (ADS)

    Ikenoue, T.; Bjørklund, K. R.; Kruglikova, S. B.; Onodera, J.; Kimoto, K.; Harada, N.

    2015-03-01

    The vertical distribution of radiolarians was investigated using a vertical multiple plankton sampler (100-0, 250-100, 500-250, and 1000-500 m water depths, 62 μm mesh size) at the Northwind Abyssal Plain and southwestern Canada Basin in September 2013. To investigate seasonal variations in the flux of radiolarians in relation to sea ice and water masses, a time-series sediment trap system was moored at Station NAP (75°00´ N, 162°00´ W; bottom depth 1975 m) in the western Arctic Ocean during October 2010-September 2012. The radiolarian flux was comparable to that in the North Pacific Ocean. Amphimelissa setosa was dominant during the season with open water as well as at the beginning and end of the seasons with sea-ice cover. During the sea-ice-cover season, however, oligotrophic and cold-water-tolerant actinommids were dominant, productivity of Radiolaria was lower, and species diversity was greater. These suggest that the dynamics of sea ice are a major factor affecting the productivity, distribution, and composition of the radiolarian fauna.

  14. Aerosol-Induced Radiative Flux Changes Off the United States Mid-Atlantic Coast: Comparison of Values Calculated from Sunphotometer and In Situ Data with Those Measured by Airborne Pyranometer

    NASA Technical Reports Server (NTRS)

    Russell, P. B.; Livingston, J. M.; Hignett, P.; Kinne, S.; Wong, J.; Chien, A.; Bergstrom, R.; Durkee, P.; Hobbs, P. V.

    2000-01-01

    The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) measured a variety of aerosol radiative effects (including flux changes) while simultaneously measuring the chemical, physical, and optical properties of the responsible aerosol particles. Here we use TARFOX-determined aerosol and surface properties to compute shortwave radiative flux changes for a variety of aerosol situations, with midvisible optical depths ranging from 0.06 to 0.55. We calculate flux changes by several techniques with varying degrees of sophistication, in part to investigate the sensitivity of results to computational approach. We then compare computed flux changes to those determined from aircraft measurements. Calculations using several approaches yield downward and upward flux changes that agree with measurements. The agreement demonstrates closure (i.e. consistency) among the TARFOX-derived aerosol properties, modeling techniques, and radiative flux measurements. Agreement between calculated and measured downward flux changes is best when the aerosols are modeled as moderately absorbing (midvisible single-scattering albedos between about 0.89 and 0.93), in accord with independent measurements of the TARPOX aerosol. The calculated values for instantaneous daytime upwelling flux changes are in the range +14 to +48 W/sq m for midvisible optical depths between 0.2 and 0.55. These values are about 30 to 100 times the global-average direct forcing expected for the global-average sulfate aerosol optical depth of 0.04. The reasons for the larger flux changes in TARFOX include the relatively large optical depths and the focus on cloud-free, daytime conditions over the dark ocean surface. These are the conditions that produce major aerosol radiative forcing events and contribute to any global-average climate effect.

  15. Metabolic Changes in Klebsiella oxytoca in Response to Low Oxidoreduction Potential, as Revealed by Comparative Proteomic Profiling Integrated with Flux Balance Analysis

    PubMed Central

    Zhu, Yan; Li, Dan; Bao, Guanhui; Wang, Shaohua; Mao, Shaoming; Song, Jiangning; Li, Yin

    2014-01-01

    Oxidoreduction potential (ORP) is an important physiological parameter for biochemical production in anaerobic or microaerobic processes. However, the effect of ORP on cellular physiology remains largely unknown, which hampers the design of engineering strategies targeting proteins associated with ORP response. Here we characterized the effect of altering ORP in a 1,3-propanediol producer, Klebsiella oxytoca, by comparative proteomic profiling combined with flux balance analysis. Decreasing the extracellular ORP from −150 to −240 mV retarded cell growth and enhanced 1,3-propanediol production. Comparative proteomic analysis identified 61 differentially expressed proteins, mainly involved in carbohydrate catabolism, cellular constituent biosynthesis, and reductive stress response. A hypothetical oxidoreductase (HOR) that catalyzes 1,3-propanediol production was markedly upregulated, while proteins involved in biomass precursor synthesis were downregulated. As revealed by subsequent flux balance analysis, low ORP induced a metabolic shift from glycerol oxidation to reduction and rebalancing of redox and energy metabolism. From the integrated protein expression profiles and flux distributions, we can construct a rational analytic framework that elucidates how (facultative) anaerobes respond to extracellular ORP changes. PMID:24584239

  16. Lava heating and loading of ice sheets on early Mars: Predictions for meltwater generation, groundwater recharge, and resulting landforms

    NASA Astrophysics Data System (ADS)

    Cassanelli, James P.; Head, James W.

    2016-06-01

    Recent modeling studies of the early Mars climate predict a predominantly cold climate, characterized by the formation of regional ice sheets across the highland areas of Mars. Formation of the predicted "icy highlands" ice sheets is coincident with a peak in the volcanic flux of Mars involving the emplacement of the Late Noachian - Early Hesperian ridged plains unit. We explore the relationship between the predicted early Mars "icy highlands" ice sheets, and the extensive early flood volcanism to gain insight into the surface conditions prevalent during the Late Noachian to Early Hesperian transition period. Using Hesperia Planum as a type area, we develop an ice sheet lava heating and loading model. We quantitatively assess the thermal and melting processes involved in the lava heating and loading process following the chronological sequence of lava emplacement. We test a broad range of parameters to thoroughly constrain the lava heating and loading process and outline predictions for the formation of resulting geological features. We apply the theoretical model to a study area within the Hesperia Planum region and assess the observed geology against predictions derived from the ice sheet lava heating and loading model. Due to the highly cratered nature of the Noachian highlands terrain onto which the volcanic plains were emplaced, we predict highly asymmetrical lava loading conditions. Crater interiors are predicted to accumulate greater thicknesses of lava over more rapid timescales, while in the intercrater plains, lava accumulation occurs over longer timescales and does not reach great thicknesses. We find that top-down melting due to conductive heat transfer from supraglacial lava flows is generally limited when the emplaced lava flows are less than ∼10 m thick, but is very significant at lava flow thicknesses of ∼100 m or greater. We find that bottom-up cryosphere and ice sheet melting is most likely to occur within crater interiors where lavas

  17. The impact of warming on greenhouse gas fluxes: an experimental comparison which reveals the varied response of ecosystems to climate change.

    NASA Astrophysics Data System (ADS)

    Stockdale, James; Ineson, Philip

    2016-04-01

    Modelled predictions of the response of terrestrial systems to climate change are highly variable, yet the response of net ecosystem exchange (NEE) is a vital ecosystem behaviour to understand due to its inherent feedback to the carbon cycle. The establishment and subsequent monitoring of replicated experimental manipulations are a direct method to reveal these responses, yet are difficult to achieve as they typically resource-heavy and labour intensive. We actively manipulated the temperature at three agricultural grasslands in southern England and deployed novel 'SkyLine' systems, recently developed at the University of York, to continuously monitor GHG fluxes. Each 'SkyLine' is a low-cost and fully autonomous technology yet produces fluxes at a near-continuous temporal frequency and across a wide spatial area. The results produced by 'SkyLine' enable the detail response of each system to increased temperature over diurnal and seasonal timescales. Unexpected differences in NEE are shown between superficially similar ecosystems which, upon investigation, suggest that interactions between a variety of environmental variables are key and that knowledge of pre-existing environmental conditions help to predict a systems response to future climate. For example, the prevailing hydrological conditions at each site appear to affect its response to changing temperature. The high-frequency data shown here, combined with the fully-replicated experimental design reveal complex interactions which must be understood to improve predictions of ecosystem response to a changing climate.

  18. Land-use changes alter radiative energy and water vapor fluxes of a tall-grass Andropogon field and a savanna-woodland continuum in the Orinoco lowlands.

    PubMed

    San José, José; Montes, Rubén; Grace, John; Nikonova, Nina; Osío, Anaís

    2008-03-01

    Changes in land use in the Orinoco lowlands affect the daily trends of energy and water vapor fluxes. We analyzed these fluxes along a disturbance gradient beginning from a cultivated tall-grass Andropogon field (S1) and extending over three savanna sites with increasing woody cover over herbaceous vegetation. The savanna sites encompass a herbaceous savanna (S2), a tree savanna (S3) and a woodland savanna (S4). In the wet season, there were differences in the radiation budget: seasonally averaged albedo for S1 (0.17) exceeded that of S2-S4 (0.13-0.14). Eddy covariance fluxes indicate that the partitioning of the daily net radiation (Rn) into sensible and latent heat (lambda E) fluxes depends on land use. During the wet season, evapotranspiration (i.e., lambda E) over the S1-S4 sites accounted for a variable fraction of Rn (i.e., 0.75, 0.52, 0.67 and 0.68, respectively). Therefore, the Bowen ratio was typically below 1. As the dry season progressed, the lambda E/Rn ratio decreased markedly with increasing air and canopy temperatures and air humidity mole fraction deficit. The maximum evaporation rate over the S1-S4 sites was 3.2, 2.5, 3.5 and 4.1 mm day(-1), respectively, and the annual values were 721, 538, 771 and 732 mm year(-1), respectively, equivalent to 49, 65, 52 and 88% of the rainfall. Soil water content fell from a maximum above 0.28 in the wet season to 0.030, 0.026, 0.030 and 0.028 m(3) m(-3) at sites S1-S4, respectively, in the dry season. Leaf area index was greatly reduced as herbaceous vegetation dried out. PMID:18171666

  19. Sediment and Particular Organic Carbon (POC) fluxes changes over the past decades in the Yellow River system

    NASA Astrophysics Data System (ADS)

    Lu, Xixi; Ran, Lishan

    2015-04-01

    The Yellow River system used to have very high sediment export to ocean (around 1.5 Gt/yr in the 1950s) because of severe soil erosion on the Loess Plateau. However, its sediment export has declined to <0.25 Gt/yr in recent years (in the 2000s), mainly due to human activities like construction of reservoirs and check dams and other soil and water conservations such as construction of terraces and vegetation restoration. Such drastic reduction in soil erosion and sediment flux and subsequently in associated Particular Organic Carbon (POC) transport can potentially play a significant role in carbon cycling. Through the sediment flux budget we examined POC budget and carbon sequestration through vegetation restoration and various soil and water conservations including reservoirs construction over the past decades in the Yellow River system. Landsat imageries were used to delineate the reservoirs and check dams for estimating the sediment trapping. The reservoirs and check dams trapped a total amount of sediment 0.94 Gt/yr, equivalent to 6.5 Mt C. Soil erosion controls through vegetation restoration and terrace construction reduced soil erosion 1.82 Gt/yr, equivalent to 12 Mt C. The annual NPP increased from 0.150 Gt C in 2000 to 0.1889 Gt C in 2010 with an average increment rate of 3.4 Mt C per year over the recent decade (from 2000 to 2010) through vegetation restoration. The total carbon stabilized on slope systems through soil erosion controls (12 Mt C per year) was much higher than the direct carbon sequestration via vegetation restoration (3.4 Mt C per year), indicating the importance of horizontal carbon mobilization in carbon cycling, albeit a high estimate uncertainty.

  20. Characteristics of the meltwater field from a large Antarctic iceberg using δ18O

    NASA Astrophysics Data System (ADS)

    Helly, John J.; Vernet, Maria; Murray, Alison E.; Stephenson, Gordon R.

    2015-03-01

    Large tabular icebergs represent a disruptive influence on a stable water column when drifting in the open ocean. This is a study of one iceberg, C18A, encountered in the Powell Basin in the Weddell Sea in March 2009, formed from iceberg C18 (76×7 km) originating from the Ross Ice Shelf in May 2002. C18A was lunate in shape with longest dimensions of 31 km×7 km×184 m. The meltwater field from C18A was characterized using δ18O from water samples collected near C18A (Near-field, 0.4-2 km) and contrasted with a Far-field comprised of samples from an Away site (19 km from C18A), a Control site (70 km away), and a region populated with small icebergs (Iceberg Alley, 175 km away). The in-sample fractions of meteoric water were calculated relative δ18O in iceberg ice and Weddell Deep Water and converted to meteoric water height (m) and a percentage within 100 m depth bins. The Near-field and Far-field difference from surface to 200 m was 0.51±0.28%. The concentration of meteoric water dropped to approximately half that value below 200 m, approximate keel depth of the iceberg, although detectable to 600 m. From surface to 600 m, the overall difference was statistically significant (P<0.0001). From this, we estimate the Near-field volume astern of the iceberg (0.16 km3d-1) as a continuous source of meteoric water.

  1. New sedimentological evidence supporting a catastrophic meltwater discharge event along the Beaufort margin, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Klotsko, S.; Driscoll, N. W.; Keigwin, L. D.; Mendenhall, B.

    2015-12-01

    In 2013, a cruise on the USCGC Healy mapped the Beaufort margin from Barrow, AK into the Amundsen Gulf using a towed CHIRP subbottom profiler and a hull-mounted Knudsen CHIRP subbottom profiler to study the deglaciation of the margin. Sediment cores were also acquired. New grain size analyses for three sediment cores will be presented. These records help constrain the flooding events captured in the existing grain size data from JPC 15, just east of the Mackenzie trough. This core shows evidence of multiple ice rafted debris events that were likely sourced from the retreat of the Amundsen ice stream. These layers have peaks in grain size around ~20 microns compared to the ~5 micron average for the rest of the core. The grain size peaks correlate to the high amplitude reflectors observed in the seismic CHIRP data. Similar reflectors are observed in the seismic data from two of the new core locations, one in the Mackenzie trough and one east of the trough. The seismic data from these stations also record a thick sediment package that is ~7 meters thick at its depocenter. This layer is interpreted to record a massive meltwater discharge event that entered the Arctic via the Mackenzie River. Oxygen isotope data from JPC 15 support an event at this location based on the covarying benthic and planktonic records. In our conceptual model, the pulses of freshwater from the Amundsen Gulf likely freshened the margin sufficiently that the major discharge event was then able to push the system over the edge. This catastrophic glacial lake draining out the Mackenzie River into the Beaufort Sea and export out of the Arctic into the North Atlantic caused diminished meridional overturning circulation - slowing of the conveyor belt thermohaline circulation - which, in turn, potentially caused the Younger Dryas cold period.

  2. Denitrification and hydrologic transient storage in a glacial meltwater stream, McMurdo Dry Valleys, Antarctica

    USGS Publications Warehouse

    Gooseff, M.N.; McKnight, Diane M.; Runkel, R.L.; Duff, J.H.

    2004-01-01

    In extreme environments, retention of nutrients within stream ecosystems contributes to the persistence of aquatic biota and continuity of ecosystem function. In the McMurdo Dry Valleys, Antarctica, many glacial meltwater streams flow for only 5-12 weeks a year and yet support extensive benthic microbial communities. We investigated NO3- uptake and denitrification in Green Creek by analyzing small-scale microbial mat dynamics in mesocosms and reach-scale nutrient cycling in two whole-stream NO 3- enrichment experiments. Nitrate uptake results indicated that microbial mats were nitrogen (N)-limited, with NO 3- uptake rates as high as 16 nmol N cm-2 h-1. Denitrification potentials associated with microbial mats were also as high as 16 nmol N cm-2 h-1. During two whole-stream NO3--enrichment experiments, a simultaneous pulse of NO2- was observed in the stream water. The one-dimensional solute transport model with inflow and storage was modified to simulate two storage zones: one to account for short time scale hydrologic exchange of stream water into and out of the benthic microbial mat, the other to account for longer time scale hydrologic exchange with the hyporheic zone. Simulations indicate that injected NO3- was removed both in the microbial mat and in the hyporheic zone and that as much as 20% of the NO3- that entered the microbial mat and hyporheic zone was transformed to NO2- by dissimilatory reduction. Because of the rapid hydrologic exchange in microbial mats, it is likely that denitrification is limited either by biotic assimilation, reductase limitation, or transport limitation (reduced NO2- is transported away from reducing microbes).

  3. Meltwater runoff from Haig Glacier, Canadian Rocky Mountains, 2002-2013

    NASA Astrophysics Data System (ADS)

    Marshall, S. J.

    2014-07-01

    Observations of high-elevation meteorological conditions, glacier mass balance, and glacier runoff are sparse in western Canada and the Canadian Rocky Mountains, leading to uncertainty about the importance of glaciers to regional water resources. This needs to be quantified so that the impacts of ongoing glacier recession can be evaluated with respect to alpine ecology, hydroelectric operations, and water resource management. I assess the seasonal evolution of glacier runoff in an alpine watershed on the continental divide in the Canadian Rocky Mountains. Analysis is based on meteorological, snowpack and surface energy balance data collected at Haig Glacier from 2002-2013. The study area is one of several glacierized headwaters catchments of the Bow River, which flows eastward to provide an important supply of water to the Canadian prairies. Annual specific discharge from snow- and ice-melt on Haig Glacier averaged 2350 mm water equivalent (w.e.) from 2002-2013, with 42% of the runoff derived from melting of glacier ice and firn, i.e. water stored in the glacier reservoir. This is an order of magnitude greater than the annual specific discharge from non-glacierized parts of the Bow River basin. From 2002-2013, meltwater derived from the glacier storage was equivalent to 5-6% of the flow of the Bow River in Calgary in late summer and 2-3% of annual discharge. The basin is typical of most glacier-fed mountains rivers, where the modest and declining extent of glacierized area in the catchment limits the glacier contribution to annual runoff.

  4. Meltwater run-off from Haig Glacier, Canadian Rocky Mountains, 2002-2013

    NASA Astrophysics Data System (ADS)

    Marshall, S. J.

    2014-12-01

    Observations of high-elevation meteorological conditions, glacier mass balance, and glacier run-off are sparse in western Canada and the Canadian Rocky Mountains, leading to uncertainty about the importance of glaciers to regional water resources. This needs to be quantified so that the impacts of ongoing glacier recession can be evaluated with respect to alpine ecology, hydroelectric operations, and water resource management. In this manuscript the seasonal evolution of glacier run-off is assessed for an alpine watershed on the continental divide in the Canadian Rocky Mountains. The study area is a headwaters catchment of the Bow River, which flows eastward to provide an important supply of water to the Canadian prairies. Meteorological, snowpack, and surface energy balance data collected at Haig Glacier from 2002 to 2013 were analysed to evaluate glacier mass balance and run-off. Annual specific discharge from snow- and ice-melt on Haig Glacier averaged 2350 mm water equivalent from 2002 to 2013, with 42% of the run-off derived from melting of glacier ice and firn, i.e. water stored in the glacier reservoir. This is an order of magnitude greater than the annual specific discharge from non-glacierized parts of the Bow River basin. From 2002 to 2013, meltwater derived from the glacier storage was equivalent to 5-6% of the flow of the Bow River in Calgary in late summer and 2-3% of annual discharge. The basin is typical of most glacier-fed mountain rivers, where the modest and declining extent of glacierized area in the catchment limits the glacier contribution to annual run-off.

  5. The distribution of glacial meltwater in the Amundsen Sea, Antarctica, revealed by dissolved helium and neon

    NASA Astrophysics Data System (ADS)

    Kim, Intae; Hahm, Doshik; Rhee, Tae Siek; Kim, Tae Wan; Kim, Chang-Sin; Lee, SangHoon

    2016-03-01

    The light noble gases, helium (He) and neon (Ne), dissolved in seawater, can be useful tracers of freshwater input from glacial melting because the dissolution of air bubbles trapped in glacial ice results in an approximately tenfold supersaturation. Using He and Ne measurements, we determined, for the first time, the distribution of glacial meltwater (GMW) within the water columns of the Dotson Trough (DT) and in front of the Dotson and Getz Ice Shelves (DIS and GIS, respectively) in the western Amundsen Sea, Antarctica, in the austral summers of 2011 and 2012. The measured saturation anomalies of He and Ne (ΔHe and ΔNe) were in the range of 3-35% and 2-12%, respectively, indicating a significant presence of GMW. Throughout the DT, the highest values of ΔHe (21%) were observed at depths of 400-500 m, corresponding to the layer between the incoming warm Circumpolar Deep Water and the overlying Winter Water. The high ΔHe (and ΔNe) area extended outside of the shelf break, suggesting that GMW is transported more than 300 km offshore. The ΔHe was substantially higher in front of the DIS than the GIS, and the highest ΔHe (31%) was observed in the western part of the DIS, where concentrated outflow from the shelf to the offshore was observed. In 2012, the calculated GMW fraction in seawater based on excess He and Ne decreased by 30-40% compared with that in 2011 in both ice shelves, indicating strong temporal variability in glacial melting.

  6. Excavation of Tunnel Valleys and Inner Gorges by Subglacial Meltwater Erosion

    NASA Astrophysics Data System (ADS)

    Beaud, F.; Flowers, G. E.; Venditti, J. G.; Koppes, M. N.

    2015-12-01

    Subglacial meltwater erosion (SME) is thought to contribute to the excavation of tunnel valleys and inner gorges, yet the underpinnings of the formation of these landforms remain obscure. Tunnel valleys are large channel-like features (100s of metres to few kilometres wide and up to 10s of kilometres in length) commonly found in the vicinity of former continental ice-sheet margins. The main question concerning their formation is: does SME excavate them gradually or by large subglacial floods? Inner gorges are V-shaped incisions in an otherwise glacially overprinted landscape. The initial assertion of their fluvial origin has recently been disputed, as they have been shown to persist through multiple glaciations and SME has been invoked to explain some inner gorges in Scandinavia and the Alps. The question is therefore: can SME explain the excavation of an inner gorge? In order to test these hypotheses related to the genesis of tunnel valleys and inner gorges, we use a 1-D model of subglacial hydrology to drive a model of bedrock erosion by total sediment load based on the tools and cover effect. Calculated values of subglacial transport stage in response to ordinary seasonal processes are comparable to those during large floods in rivers. Subglacial floods therefore limit bedrock erosion by transporting sediment farther from the bed, thus inhibiting impacts. Consequently, we find that gradual SME is likely to produce more incision over a glacial cycle. When we simulate the total SME that occurs through a glacial cycle under a synthetic ice-sheet margin, we are able to produce tunnel valleys or inner gorges over the timespan of a glaciation. Based on these results, we propose that (1) tunnel valleys and inner gorges can both be the result of SME, (2) tunnel valleys in bedrock can be formed through gradual processes rather than floods, and (3) SME enhances inner gorge relief.

  7. Last Deglacial Arctic to Pacific Transgressions via the Bering Strait: Implications for Climate, Meltwater Source, Ecosystems and Southern Ocean Wind Strength

    NASA Astrophysics Data System (ADS)

    Nwaodua, Emmanuel C.

    The main goal of this research is to provide physical evidence of reverse flow(s), from the Arctic to the North Pacific Ocean, after the Last Glacial Maximum (LGM). This is primarily essential to studies concerned with understanding how the fluctuations in strength of the Southern Ocean Wind (SOW), in conjunction with an open Bering Strait, alter the direction of water flow through the Bering Strait. Visible and Near Infrared (VNIR) derivative spectroscopy; quotient normalization and varimax rotated principal component analysis of diffuse spectral reflectance (DSR) measurements from 234 surface core samples and 2 piston cores, in addition to the USGS spectral library, were used to extract and identify these lithological compositions (in order of importance) within the study location. These compositions are chlorite + muscovite; goethite + phycoerythrin + phycocyanin; smectite; calcite+dolomite; and illite + Chlorophyll a. The Geostatistical tool, kriging, was utilized in creating the sedimentary maps of all the components. These maps were used to determine these components' modern spatial patterns. This aided in the evaluation and downcore interpretation of the component most suited for this study. The illite in illite + Chlorophyll a assemblage was deemed to be the appropriate water mass tracer for a reverse flow from the Arctic into the North Pacific; this is because of its prominence and abundance in the Mackenzie River drainage basin and on the west Arctic Sea shelf. The illite denotes these periods of meltwater pulses (MWP): MWP 1A, ˜14,600 and 13,800 Cal yrs. BP, separated by the Older Dryas; MWP 1B, ˜11,000--9,200 Cal yrs. BP; and MWP 1C, ˜8,000 Cal yrs. BP. The timing of these pulses along with previously published data on the Bering Sea shelf and the North Pacific Ocean enabled these deductions: 1) the initial opening of the Bering Strait and the flow direction after the LGM; 2) the source of these meltwater pulses and the mechanism that might drive

  8. HISTORICAL CHANGES IN GLOBAL SCALE CIRCULATION PATTERNS, MID-ATLANTIC CLIMATE STREAM FLOW AND NUTRIENT FLUXES TO THE CHESAPEAKE BAY

    EPA Science Inventory

    The rate of change in Northern Hemisphere temperature in the past century strongly suggests that we are now in a period of rapid global climate change. Also, the climate in the mid-Atlantic is quite sensitive to larger scale climate variation, which affects the frequency and seve...

  9. Rising Mean Annual Temperature Increases Carbon Flux and Alters Partitioning, but Does Not Change Ecosystem Carbon Storage in Hawaiian Tropical Montane Wet Forest

    NASA Astrophysics Data System (ADS)

    Litton, C. M.; Giardina, C. P.; Selmants, P.

    2014-12-01

    Terrestrial ecosystem carbon (C) storage exceeds that in the atmosphere by a factor of four, and represents a dynamic balance among C input, allocation, and loss. This balance is likely being altered by climate change, but the response of terrestrial C cycling to warming remains poorly quantified, particularly in tropical forests which play a disproportionately large role in the global C cycle. Over the past five years, we have quantified above- and belowground C pools and fluxes in nine permanent plots spanning a 5.2°C mean annual temperature (MAT) gradient (13-18.2°C) in Hawaiian tropical montane wet forest. This elevation gradient is unique in that substrate type and age, soil type, soil water balance, canopy vegetation, and disturbance history are constant, allowing us to isolate the impact of long-term, whole ecosystem warming on C input, allocation, loss and storage. Across the gradient, soil respiration, litterfall, litter decomposition, total belowground C flux, aboveground net primary productivity, and estimates of gross primary production (GPP) all increase linearly and positively with MAT. Carbon partitioning is dynamic, shifting from below- to aboveground with warming, likely in response to a warming-induced increase in the cycling and availability of soil nutrients. In contrast to observed patterns in C flux, live biomass C, soil C, and total ecosystem C pools remained remarkably constant with MAT. There was also no difference in soil bacterial taxon richness, phylogenetic diversity, or community composition with MAT. Taken together these results indicate that in tropical montane wet forests, increased temperatures in the absence of water limitation or disturbance will accelerate C cycling, will not alter ecosystem C storage, and will shift the products of photosynthesis from below- to aboveground. These results agree with an increasing number of studies, and collectively provide a unique insight into anticipated warming-induced changes in tropical

  10. The role of meltwater variability in modulating diurnal to inter-annual ice-sheet flow: New insights from a ~decade of high-temporal resolution GPS observations on the western Greenland margin

    NASA Astrophysics Data System (ADS)

    Stevens, L. A.; Behn, M. D.; Das, S. B.; Joughin, I.; van den Broeke, M.; Herring, T.; McGuire, J. J.

    2015-12-01

    Meltwater-driven processes across the ablation zone of the Greenland Ice Sheet are controlled by seasonal fluxes as well as shorter-term variability in surface melt. Few high-temporal resolution GPS observations of ice-sheet flow extend for longer than a couple years, limiting multiyear analyses of seasonal variability in ice-sheet flow. Using a small GPS network installed at ~1000-m above sea level (m a.s.l.) operating from 2006-2014, and supplemented with a larger array of 20 GPS stations installed from 2011­-2014, we observe nine years of ice-sheet surface motion on the western margin of the Greenland Ice Sheet. The GPS array spans a horizontal distance of 30 km across an elevation range of 700-1250 m a.s.l., and captures the ice-sheet's velocity response to the seasonal melt cycle. By combining the GPS array measurements with temperature, precipitation, and runoff estimates from the Regional Atmospheric Climate Model (RACMO), we examine the relationship between ice-sheet flow and surface melt variability both at the seasonal scale (i.e., during melt onset, summer melt season and melt cessation) as well as during transient high melt periods such as precipitation events, anomalously high melt episodes, and supraglacial lake drainages. We observe varying surface motion following early versus late summer extended melt events, with early-season extended melt events inducing longer sustained speed-up than late summer events. We also examine differences in the timing of melt onset and magnitude, comparing the anomalously high runoff observed across the ice sheet in 2010 and 2012 against the average to low runoff observed in the years comprising the remainder of the record. This nearly decadal record improves our understanding of the role of meltwater variability in modulating ice-sheet flow on diurnal to inter-annual timescales.

  11. Can ipids in lake sediments help to reconstruct changes in methane availability and methane fluxes in boreal and temperate lakes?

    NASA Astrophysics Data System (ADS)

    Stoetter, T.; van Hardenbroek, M.; Rinta, P.; Schilder, J.; Schubert, C. J.; Heiri, O.

    2013-12-01

    Methane (CH4) is a major greenhouse gas and lakes are an important but poorly studied source of CH4 to the atmosphere. Lipid analysis was used before to identify and quantify CH4 oxidizing bacteria (MOB), giving insight into CH4 oxidation and production in lakes. However, few studies are available that examine how closely the distribution and the carbon isotopic signature (δ13C) of lipids are related to CH4 concentrations and fluxes in different lake ecosystems. In a multi-lake survey we quantified the relationship between lipids, mainly fatty acids (FAs), and CH4 concentrations or fluxes, with the aim of assessing whether FA analysis of lake sediment samples can provide information on past CH4 abundance and production in lakes. The study sites include small lakes in Sweden, Finland, the Netherlands, and Switzerland. Surface sediments collected in the deepest point of the lakes were examined using gas chromatography with flame ionization for determining FA concentrations, gas chromatography mass spectrometry (GC-MS) for identification of individual FAs, and isotope ratio mass spectrometry (IRMS) for determining compound specific δ13C values. Since CH4 is significantly more depleted in 13C than other carbon sources, δ13C is a good tracer for CH4 related processes. The analysis of the acid fraction in the sediments showed that mainly three FAs, identified as C16:1ω7, C16:1ω5 and C18:1ω7, were more depleted in 13C than the others, suggesting that they may originate from MOB. Comparison with literature sources indicated that these FAs are produced by MOB, however, not exclusively. The relative abundance of these depleted FAs showed clear relations to CH4 parameters. For example, increasing abundances were observed with increasing CH4 concentrations in the sediment or with increasing CH4 flux measured at the lake surface. An explanation for these relations would be an increase in MOB biomass with increasing CH4 availability, as they use CH4 as energy and carbon

  12. The ERK signaling target RNF126 regulates anoikis resistance in cancer cells by changing the mitochondrial metabolic flux

    PubMed Central

    Yoshino, Seiko; Hara, Toshiro; Nakaoka, Hiroki J; Kanamori, Akane; Murakami, Yoshinori; Seiki, Motoharu; Sakamoto, Takeharu

    2016-01-01

    Loss of anchorage to the extracellular matrix leads to apoptosis (anoikis) in normal cells, but cancerous cells are usually resistant to such stress. Here we report the pivotal role of an E3 ubiquitin ligase, ring-finger protein 126 (RNF126), in the resistance of cancer cells to the stress associated with non-adherent conditions. Non-adherent cancer cells exhibited increased flux through the tricarboxylic acid cycle via increased conversion of pyruvate to acetyl-CoA. RNF126 was found to act as a ubiquitin ligase for pyruvate dehydrogenase kinases (PDKs), resulting in their proteasomal degradation. This decrease in PDK levels allowed pyruvate dehydrogenases to catalyze the conversion of pyruvate to acetyl-CoA. Moreover, depletion of RNF126 or increased expression of PDK1 in cancer cells suppressed colony formation in soft agar as well as tumorigenicity in mice. RNF126 expression in cancer cells was found to be under the control of the extracellular signal-regulated kinase signaling pathway, which is essential for anoikis resistance. Thus, RNF126 is an attractive molecule for treating cancer by selectively targeting anchorage-independent growth. PMID:27462466

  13. Effects of glacial meltwater inflows and moat freezing on mixing in an ice-covered antarctic lake as interpreted from stable isotope and tritium distributions

    USGS Publications Warehouse

    Miller, L.G.; Aiken, G.R.

    1996-01-01

    Perennially ice-covered lakes in the McMurdo Dry Valleys have risen several meters over the past two decades due to climatic warming and increased glacial meltwater inflow. To elucidate the hydrologic responses to changing climate and the effects on lake mixing processes we measured the stable isotope (??18O and ??D) and tritium concentrations of water and ice samples collected in the Lake Fryxell watershed from 1987 through 1990. Stable isotope enrichment resulted from evaporation in stream and moat samples and from sublimation in surface lake-ice samples. Tritium enrichment resulted from exchange with the postnuclear atmosphere in stream and moat samples. Rapid injection of tritiated water into the upper water column of the make and incorporation of this water into the ice cover resulted in uniformly elevated tritium contents (> 3.0 TU) in these reservoirs. Tritium was also present in deep water, suggesting that a component of bottom water was recently at the surface. During summer, melted lake ice and stream water forms the moat. Water excluded from ice formation during fall moat freezing (enriched in solutes and tritium, and depleted in 18O and 2H relative to water below 15-m depth) may sink as density currents to the bottom of the lake. Seasonal lake circulation, in response to climate-driven surface inflow, is therefore responsible for the distribution of both water isotopes and dissolved solutes in Lake Fryxell.

  14. Meltwater palaeohydrology of the Baker River basin (Chile/Argentina) during Late Pleistocene deglaciation of the Northern Patagonia Icefield

    NASA Astrophysics Data System (ADS)

    Thorndycraft, Varyl; Bendle, Jacob; Benito, Gerardo; Sancho, Carlos; Palmer, Adrian; Rodríguez, Xavier

    2016-04-01

    The Late Pleistocene deglaciation of the Northern Patagonia Icefield (NPI) was characterised by rapid ice sheet thinning and retreat, and the development of large proglacial lake systems characterised by continental scale drainage reversals. In this region, research has focused primarily on the identification of former ice-limits (e.g. moraine ridges) for geochronological analyses, with little attention given to the meltwater palaeohydrology of major river valleys. The Baker River catchment drains the majority of the eastern ice shed of the NPI, with a basin area of 29,000 km2 that includes the large transboundary lakes of General Carrera/Buenos Aires and Cochrane/Puerreydón. The Baker River valley is aligned north to south, crossing the east-west valleys of the main NPI outflow glaciers, and thus represents an important aspect of regional Late Pleistocene palaeogeography. The Baker River valley therefore has the potential to refine regional models of deglaciation through better understanding of relationships between glacier dynamics, ice dammed lakes and meltwater pathways. Here we present geomorphological mapping from the Atlantic-Pacific drainage divide (over 150 km east of the Cordillera) to the lower Baker valley, in order to reconstruct Late Pleistocene palaeohydrology. We provide new mapping of palaeolake shoreline elevations and evidence for glacial lake outburst flood (GLOF) pathways that require a re-evaluation of the currently accepted palaeogeographic models. For example, the palaeohydrological evidence does not support existing models of a unified Buenos Aires/Puerreydón mega-lake at ca. 400m elevation. We propose a relative chronology of palaeohydrological events that help refine the published moraine chronology derived from cosmogenic nuclide exposure dating. Controls on Late Pleistocene meltwater palaeohydrology of the Baker catchment are discussed, including the interplay of glacial processes and regional tectonics, in particular, dynamic

  15. Responses of carbon dioxide flux and plant biomass to water table drawdown in a treed peatland in northern Alberta: a climate change perspective

    NASA Astrophysics Data System (ADS)

    Munir, T. M.; Xu, B.; Perkins, M.; Strack, M.

    2014-02-01

    Northern peatland ecosystems represent large carbon (C) stocks that are susceptible to changes such as accelerated mineralization due to water table lowering expected under a climate change scenario. During the growing seasons (1 May to 31 October) of 2011 and 2012 we monitored CO2 fluxes and plant biomass along a microtopographic gradient (hummocks-hollows) in an undisturbed dry continental boreal treed bog (control) and a nearby site that was drained (drained) in 2001. Ten years of drainage in the bog significantly increased coverage of shrubs at hummocks and lichens at hollows. Considering measured hummock coverage and including tree incremental growth, we estimate that the control site was a sink of -92 in 2011 and -70 g C m-2 in 2012, while the drained site was a source of 27 and 23 g C m-2 over the same years. We infer that, drainage-induced changes in vegetation growth led to increased biomass to counteract a portion of soil carbon losses. These results suggest that spatial variability (microtopography) and changes in vegetation community in boreal peatlands will affect how these ecosystems respond to lowered water table potentially induced by climate change.

  16. The Response of a Global Circuit Model with Stratospheric and Tropospheric Aerosol to Cosmic Ray Flux Changes

    NASA Astrophysics Data System (ADS)

    Zhou, L.; Tinsley, B. A.

    2005-12-01

    The global circuit is a key intermediate between solar activity and the Earth's climate by controlling the downward current density Jz which can affect cloud microphysics by electroscavenging and electrofreezing process. Atmospheric ionization due to the cosmic ray flux (CRF) dominates the ion production in the troposphere and stratosphere except close to the surface. We have constructed a new model with improved fidelity, in which the ion production rate due to cosmic ray flux is consistent with the 1954-1965 observations by Neher. These include the ionization decreases and geomagnetic cutoff latitude variations due to solar activity. Production of ionization close to the surface over land is controlled by the distribution of radon (Dentener et al., 1999), with different scale heights of the radon vertical distribution for the different seasons. Tropospheric aerosol concentration is from the GADS data base (Hess et al., 1998) providing detailed global aerosol concentrations that also have seasonal variations. Volcanic eruptions increase the atmosphere resistance by increasing the aerosol concentration in the stratosphere and the upper troposphere. We model additional ultrafine aerosol condensed from the volcanic sulfuric acid vapor in the upper troposphere and the stratosphere, that is transported there by the Brewer-Dobson circulation, as discussed by Tinsley (2005). We calculate the columnar resistance distribution over the world and the total global load resistance. We find that the effects of the seasonal variations on the columnar resistance and total load resistance are small. Solar activity increases the global resistance because the reduced CRF decreases the ion pair production rate. Column resistance shows a strong variability at high geomagnetic latitudes because of the solar/geomagnetic modulation of the lower energy CRF. This is reflected in strong variations of Jz. There is a 7~12 percent enhancement of global load resistance on the solar cycle and

  17. Climate Change and Biogeochemical Cycling in Green Lakes Valley, Colorado Front Range, USA

    NASA Astrophysics Data System (ADS)

    Barnes, R. T.; Parman, J.; Williams, M. W.

    2010-12-01

    Alpine ecosystems are particularly susceptible to disturbance due to their short growing seasons, sparse vegetation, thin soils, and a harsh climate. Warming temperatures and atmospheric nitrogen deposition, two drivers of global change, are currently affecting the Green Lakes Valley within the Colorado Front Range. At the top of Green Lakes Valley is Arikaree glacier, a 9 ha cirque glacier which has steady decreased in size since 2000. The watershed continues to receive elevated amounts of nitrogen deposition; however the atmospheric flux of inorganic nitrogen has decreased by 0.56 kg ha-1yr-1 since 2000, due to several years of low rainfall. Despite this decrease N deposition, the alpine watershed’s yield of nitrate has increased by 40% over the same time period relative to 1990-1999, at an approximate rate of 0.47 kg ha-1yr-1 since 2000. Concurrent with increases in nitrate were large increases in sulfate (1.13 kg ha-1yr-1), calcium (0.63 kg ha-1yr-1) and silica (0.22 kg ha-1yr-1) yields. The source of these increased yields appears to be meltwater from Arikaree and thawing permafrost. Mass balance models indicate that high ammonium loads within Arikaree’s meltwater are rapidly nitrified; contributing approximately 0.45 kg yr-1 to the NO3- flux within the upper reaches of the watershed. The chemistry of melting permafrost (as indicated by rock glacial meltwater) is rich in geochemical weathering products suggesting that it is the source of increased sulfate, calcium, and silica as well as providing sustained water contributions late into the growing season. Downstream within the subalpine, there was no increase in nitrate yield and relatively small increases in weathering products, suggesting that the subalpine serves as a sink for excess nitrogen and weathering products. Finally, there were no long term increases in nitrate, sulfate, silica, or calcium at a nearby watershed devoid of glacial and permafrost features; providing further evidence that the

  18. Changes in acral blood flux under local application of ropivacaine and lidocaine with and without an adrenaline additive: a double-blind, randomized, placebo-controlled study.

    PubMed

    Häfner, Hans-Martin; Schmid, Ute; Moehrle, Matthias; Strölin, Anke; Breuninger, Helmut

    2008-01-01

    Vascular effects of local anesthetics are especially important in dermatological surgery. In particular, adequate perfusion must be ensured in order to offset surgical manipulations during surgical interventions at the acra. However, the use of adrenaline additives appears fraught with problems when anesthesia affects the terminal vascular system, particularly during interventions at the fingers, toes, penis, outer ears, and tip of the nose. We studied skin blood flux at the fingerpads via laser Doppler flowmetry over the course of 24 hours in a prospective, double-blind, randomized, placebo-controlled study with 20 vascularly healthy test persons following Oberst's-method anesthetic blocks. In each case, 6 ml ropivacaine (7.5 mg/ml) (A), lidocaine 1% without an additive (B), and lidocaine 1% with an adrenaline additive (1:200,000) (C) was used respectively as a verum. Isotonic saline solution was injected as a placebo (D). Measurements were carried out with the aid of a computer simultaneously at D II and D IV on both hands. Administration of (A) led to increased blood flux (+155.2%); of (B) initially to a decrease of 27%; of (C) to a reduction of 55% which was reversible after 40 minutes and of (D) to no change.(A) resulted in sustained vasodilatation which was still demonstrable after 24 h. (B) had notably less vasodilative effect, although comparison with (D) clearly showed that (B) is indeed vasodilative. (C) resulted in only a passing decrease in perfusion; this was no longer measurable when checked after 6 and 24 h. This transient inadequacy of blood flux also appeared after administration of (D). These tests show that adrenaline additive in local anesthesia does not decrease blood flow more than 55% for a period of 16 min. Following these results an adrenaline additive can be safely used for anesthetic blocks at the acra in healthy persons. PMID:18334782

  19. A 125 year record of fluvial calcium flux from a temperate catchment: Interplay of climate, land-use change and atmospheric deposition

    NASA Astrophysics Data System (ADS)

    Worrall, F.; Howden, N. J. K.; Burt, T. P.

    2012-10-01

    SummaryThis paper analyses the world's longest fluvial record of water hardness and calcium (Ca) concentration. We used records of permanent and temporary hardness and river flow for the UK's River Thames (catchment area 9998 km2) to estimate annual Ca flux from the river since 1883. The Thames catchment has a mix of agricultural and urban land use; it is dominated by mineral soils with groundwater contributing around 60% of river flow. Since the late 1800s, the catchment has undergone widespread urbanisation and climate warming, but has also been subjected to large-scale land-use change, especially during World War II and agricultural intensification in the 1960s. Here, we use a range of time series methods to explore the relative importance of these drivers in determining catchment-scale biogeochemical response. Ca concentrations in the Thames rose to a peak in the late 1980s (106 mg Ca/l). The flux of Ca peaked in 1916 at 385 ktonnes Ca/yr; the minimum was in 1888 at 34 ktonnes Ca/yr. For both the annual average Ca concentration and the annual flux of Ca, there were significant increases with time; a significant positive memory effect relative to the previous year; and significant correlation with annual water yield. No significant correlation was found with either temperature or land use, but sulphate deposition was found to be significant. It was also possible, for a shorter time series, to show a significant relationship with inorganic nitrogen inputs into the catchment. We suggest that ionic inputs did not acidify the mineral soils of the catchment but did cause the leaching of metals, so we conclude that the decline in river Ca concentrations is caused by the decline in both S and N inputs.

  20. Characterizing supraglacial meltwater channel hydraulics on the Greenland Ice Sheet from in situ observations

    USGS Publications Warehouse

    Gleason, Colin J.; Smith, Laurence C.; Chu, Vena W.; Legleiter, Carl; Pitcher, Lincoln H.; Overstreet, Brandon T.; Rennermalm, Asa K.; Forster, Richard R.; Yang, Kang

    2016-01-01

    Supraglacial rivers on the Greenland ice sheet (GrIS) transport large volumes of surface meltwater toward the ocean, yet have received relatively little direct research. This study presents field observations of channel width, depth, velocity, and water surface slope for nine supraglacial channels on the southwestern GrIS collected between 23 July and 20 August, 2012. Field sites are located up to 74 km inland and span 494-1485 m elevation, and contain measured discharges larger than any previous in situ study: from 0.006 to 23.12 m3/s in channels 0.20 to 20.62 m wide. All channels were deeply incised with near vertical banks, and hydraulic geometry results indicate that supraglacial channels primarily accommodate greater discharges by increasing velocity. Smaller streams had steeper water surface slopes (0.74-8.83%) than typical in terrestrial settings, yielding correspondingly high velocities (0.40-2.60 m/s) and Froude numbers (0.45-3.11) with supercritical flow observed in 54% of measurements. Derived Manning's n values were larger and more variable than anticipated from channels of uniform substrate, ranging from 0.009 to 0.154 with a mean value of 0.035 +/- 0.027 despite the absence of sediment, debris, or other roughness elements. Ubiquitous micro-depressions in shallow sections of the channel bed may explain some of these roughness values. However, we find that other, unobserved sources of flow resistance likely contributed to these elevated n values: future work should explicitly consider additional sources of flow resistance beyond bed roughness in supraglacial channels. We conclude that hydraulic modelling for these channels must allow for both sub- and supercritical flow, and most importantly must refrain from assuming that all ice-substrate channels exhibit similar hydraulic behavior, especially for Froude numbers and Manning's n. Finally, this study highlights that further theoretical and empirical work on supraglacial channel hydraulics is

  1. Polyoxymethylene passive samplers to monitor changes in bioavailability and flux of PCBs after activated carbon amendment to sediment in the field.

    PubMed

    Beckingham, B; Ghosh, U

    2013-06-01

    Field and laboratory exposures of polyoxymethylene passive samplers to sediments and the water column were applied to monitor changes in bioavailability and flux of polychlorinated biphenyls (PCBs) following a pilot-scale amendment of activated carbon in Grasse River. Following amendment, reductions in passive sampler uptake tracked reductions in bioaccumulation in a freshwater invertebrate, which supports a biological basis for utilizing passive samplers for in situ site investigations following a remediation. Freely dissolved concentrations of PCBs were reduced in sediment pore waters compared to untreated sediments indicating reduced bioavailability of PCBs after activated carbon amendment. Freely dissolved PCB concentrations in sediment pore water in treated sites were also lower than overlying water concentrations indicating a reversal of the sediment from being a source to a sink of PCBs from the water column. These observations indicate that activated carbon amendment to sediment limits contaminant exposure to both the benthic and pelagic food webs through reductions in bioavailability and flux of PCBs into the water column. PMID:23415491

  2. Dynamic modeling of the Ganga river system: impacts of future climate and socio-economic change on flows and nitrogen fluxes in India and Bangladesh.

    PubMed

    Whitehead, P G; Sarkar, S; Jin, L; Futter, M N; Caesar, J; Barbour, E; Butterfield, D; Sinha, R; Nicholls, R; Hutton, C; Leckie, H D

    2015-06-01

    This study investigates the potential impacts of future climate and socio-economic change on the flow and nitrogen fluxes of the Ganga river system. This is the first basin scale water quality study for the Ganga considering climate change at 25 km resolution together with socio-economic scenarios. The revised dynamic, process-based INCA model was used to simulate hydrology and water quality within the complex multi-branched river basins. All climate realizations utilized in the study predict increases in temperature and rainfall by the 2050s with significant increase by the 2090s. These changes generate associated increases in monsoon flows and increased availability of water for groundwater recharge and irrigation, but also more frequent flooding. Decreased concentrations of nitrate and ammonia are expected due to increased dilution. Different future socio-economic scenarios were found to have a significant impact on water quality at the downstream end of the Ganga. A less sustainable future resulted in a deterioration of water quality due to the pressures from higher population growth, land use change, increased sewage treatment discharges, enhanced atmospheric nitrogen deposition, and water abstraction. However, water quality was found to improve under a more sustainable strategy as envisaged in the Ganga clean-up plan. PMID:25692851

  3. Spring bloom community change modifies carbon pathways and C : N : P : Chl a stoichiometry of coastal material fluxes

    NASA Astrophysics Data System (ADS)

    Spilling, K.; Kremp, A.; Klais, R.; Olli, K.; Tamminen, T.

    2014-08-01

    Diatoms and dinoflagellates are major bloom-forming phytoplankton groups competing for resources in the oceans and coastal seas. Recent evidence suggests that their competition is significantly affected by climatic factors under ongoing change, modifying especially the conditions for cold-water, spring bloom communities in temperate and arctic regions. We investigated the effects of phytoplankton community composition on spring bloom carbon flows and nutrient stoichiometry in multi-year mesocosm experiments. Comparison of differing communities showed that community structure significantly affected C accumulation parameters, with highest particulate organic carbon (POC) build-up and dissolved organic carbon (DOC) release in diatom-dominated communities. In terms of inorganic nutrient drawdown and bloom accumulation phase, the dominating groups behaved as functional surrogates. Dominance patterns, however, significantly affected C : N : P : Chl a ratios over the whole bloom event: when diatoms were dominant, these ratios increased compared to dinoflagellate dominance or mixed communities. Diatom-dominated communities sequestered carbon up to 3.6-fold higher than the expectation based on the Redfield ratio, and 2-fold higher compared to dinoflagellate dominance. To our knowledge, this is the first experimental report of consequences of climatically driven shifts in phytoplankton dominance patterns for carbon sequestration and related biogeochemical cycles in coastal seas. Our results also highlight the need for remote sensing technologies with taxonomical resolution, as the C : Chl a ratio was strongly dependent on community composition and bloom stage. Climate-driven changes in phytoplankton dominance patterns will have far-reaching consequences for major biogeochemical cycles and need to be considered in climate change scenarios for marine systems.

  4. Spring bloom community change modifies carbon pathways and C : N : P : Chl a stoichiometry of coastal material fluxes

    NASA Astrophysics Data System (ADS)

    Spilling, K.; Kremp, A.; Klais, R.; Olli, K.; Tamminen, T.

    2014-12-01

    Diatoms and dinoflagellates are major bloom-forming phytoplankton groups competing for resources in the oceans and coastal seas. Recent evidence suggests that their competition is significantly affected by climatic factors under ongoing change, modifying especially the conditions for cold-water, spring bloom communities in temperate and Arctic regions. We investigated the effects of phytoplankton community composition on spring bloom carbon flows and nutrient stoichiometry in multiyear mesocosm experiments. Comparison of differing communities showed that community structure significantly affected C accumulation parameters, with highest particulate organic carbon (POC) buildup and dissolved organic carbon (DOC) release in diatom-dominated communities. In terms of inorganic nutrient drawdown and bloom accumulation phase, the dominating groups behaved as functional surrogates. Dominance patterns, however, significantly affected C : N : P : Chl a ratios over the whole bloom event: when diatoms were dominant, these ratios increased compared to dinoflagellate dominance or mixed communities. Diatom-dominated communities sequestered carbon up to 3.6-fold higher than the expectation based on the Redfield ratio, and 2-fold higher compared to dinoflagellate dominance. To our knowledge, this is the first experimental report of consequences of climatically driven shifts in phytoplankton dominance patterns for carbon sequestration and related biogeochemical cycles in coastal seas. Our results also highlight the need for remote sensing technologies with taxonomical resolution, as the C : Chl a ratio was strongly dependent on community composition and bloom stage. Climate-driven changes in phytoplankton dominance patterns will have far-reaching consequences for major biogeochemical cycles and need to be considered in climate change scenarios for marine systems.

  5. Geospatial assessment of long-term changes in carbon stocks and fluxes in forests of India (1930-2013)

    NASA Astrophysics Data System (ADS)

    Reddy, C. Sudhakar; Rakesh, F.; Jha, C. S.; Athira, K.; Singh, Sonali; Alekhya, V. V. L. Padma; Rajashekar, G.; Diwakar, P. G.; Dadhwal, V. K.

    2016-08-01

    The present study has estimated spatial distribution of biomass carbon density from satellite remote sensing data, historical archives and collateral data from 1930 to 2013. The spatial forest canopy density datasets for 1930, 1975, 1985, 1995, 2005 and 2013 were analysed to obtain biomass carbon pools at 5 km grid level. The overall loss of forest cover was 28% from 1930 to 2013. Analysis of change in the forest canopy density indicates that the dense forest cover reduced from 419,175 km2 in 1975 to 390,966 km2 in 2013. The total above ground biomass carbon stock of Indian forest was calculated as 3070.27 Tg C in 2013. Standing biomass carbon stocks varied significantly during different steps of time periods. There are a total 67,184 grid cells with loss of carbon stocks during 1930-1975 followed by 55,742 cells during 1975-1985. The annual carbon loss in the above ground biomass showed the highest decrease during the period of 1930 to 1975 and estimated as 2168.50 Tg C while the net annual loss of carbon is 48.19 Tg C. The maximum observed net annual loss of carbon stocks was 53.97 Tg C during 2005 to 2013. Carbon content for various states shows that maximum carbon stocks were stored in the forests of Arunachal Pradesh (11.27%) in 2013. State-wise change analysis indicates the highest loss of carbon stocks in Tripura (80.99%) from 1930 to 2013. Overall reduction in carbon stock in Indian forests has been estimated as 3079.98 Tg C (50.08%) from 1930 to 2013. The spatial characterization of distribution and changes in carbon stocks can provide useful information for planning and strategic management of resources and fulfilling global initiatives to conserve forest biodiversity.

  6. Polychlorinated Biphenyls in a Temperate Alpine Glacier: 1. Effect of Percolating Meltwater on their Distribution in Glacier Ice.

    PubMed

    Pavlova, Pavlina Aneva; Jenk, Theo Manuel; Schmid, Peter; Bogdal, Christian; Steinlin, Christine; Schwikowski, Margit

    2015-12-15

    In Alpine regions, glaciers act as environmental archives and can accumulate significant amounts of atmospherically derived pollutants. Due to the current climate-warming-induced accelerated melting, these pollutants are being released at correspondingly higher rates. To examine the effect of melting on the redistribution of legacy pollutants in Alpine glaciers, we analyzed polychlorinated biphenyls in an ice core from the temperate Silvretta glacier, located in eastern Switzerland. This glacier is affected by surface melting in summer. As a result, liquid water percolates down and particles are enriched in the current annual surface layer. Dating the ice core was a challenge because meltwater percolation also affects the traditionally used parameters. Instead, we counted annual layers of particulate black carbon in the ice core, adding the years with negative glacier mass balance, that is, years with melting and subsequent loss of the entire annual snow accumulation. The analyzed samples cover the time period 1930-2011. The concentration of indicator PCBs (iPCBs) in the Silvretta ice core follows the emission history, peaking in the 1970s (2.5 ng/L). High PCB values in the 1990s and 1930s are attributed to meltwater-induced relocation within the glacier. The total iPCB load at the Silvretta ice core site is 5 ng/cm(2). A significant amount of the total PCB burden in the Silvretta glacier has been released to the environment. PMID:26632967

  7. Coupled stratospheric ozone and temperature responses to short-term changes in solar ultraviolet flux - An analysis of Nimbus 7 SBUV and SAMS data. [stratosphere and mesosphere sounder

    NASA Technical Reports Server (NTRS)

    Hood, L. L.

    1986-01-01

    Earlier studies of solar-induced variations in stratospheric parameters have been mainly concerned with observed ozone responses. In the present investigation, attention is given to temperature responses as well as ozone responses at low latitudes, taking into account 22 months of Nimbus 7 solar backscattered ultraviolet (SBUV) ozone and stratospheric and mesospheric sounder temperature data. A data description is provided, and cross-correlation and regression analyses are conducted. An extension is considered of an analytic model, which was derived by Frederick (1981) for the coupled behavior of ozone and temperature perturbations in the upper stratosphere and lower mesosphere. The extended model is applied to the results of the analyses. The obtained data provide statistical evidence for ozone and temperature responses to changes in solar ultraviolet flux on the time scale of the solar rotation period.

  8. How Population Growth and Land-Use Change Increased Fluvial Dissolved Organic Carbon Fluxes over 130 Years in the Thames Basin (UK)

    NASA Astrophysics Data System (ADS)

    Noacco, V.; Howden, N. J. K.; Wagener, T.; Worrall, F.; Burt, T. P.

    2015-12-01

    This study investigates drivers of changing dissolved organic carbon (DOC) export in the UK's River Thames basin between 1884 and 2014. Specifically, we consider how the impacts of land-use change and population growth drive increases in DOC concentrations and fluxes at the basin outlet. Such key factors for the long-term increase in riverine DOC in temperate, mineral-soil catchments are still widely debated. First, we estimate soil organic carbon (SOC) stocks in the Thames basin for the period. Second, we convert SOC losses due to land-use change into DOC loss to surface waters through runoff. Finally, we combine this input of DOC with an export coefficient model that considers catchment drivers for DOC release to the river. SOC stocks for each year are calculated from a large database of typical SOC levels for land-uses present in the Thames basin and are combined with literature values of transition times for SOC to adjust to a new level following land-use change. We also account for climate change effects on SOC stock due to temperature increases, which reduces SOC stocks as soil organic matter turnover rates increase. Our work shows that the major driver for DOC increase to the river Thames was the rise in the catchment population, where the increase in urban area was used as a proxy. This highlights the role of sewage effluent in contributing to the rise of fluvial DOC, even though wastewater treatments were in place since the early 1990s. Land-use change had significant but short-term impacts in the increase in DOC, mainly due to massive conversion of permanent grassland into arable land during World War II.

  9. Long-term trends in suspended chlorophyll a and vertical particle flux with respect to changing physical conditions in eastern Fram Strait, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Nöthig, Eva-Maria; Bauerfeind, Eduard; Beszczynska-Möller, Agnieszka; Kraft, Angelina; Bracher, Astrid; Cherkasheva, Alexandra; Fahl, Kirsten; Hardge, Kristin; Kaleschke, Lars; Lalande, Catherine; Metfies, Katja; Peeken, Ilka; Klages, Michael; Soltwedel, Thomas

    2014-05-01

    The Fram Strait is the main gateway for water, heat, sea ice and plankton exchanges between the Arctic Ocean and the North Atlantic. The abundance and composition of phyto- and zooplankton communities is governed to a large extent by key physical factors such as water temperature, salinity, currents, stratification of the water column and the presence or absence of sea ice. With our study we aim at tracing effects of environmental changes in pelagic system structure and impacts on the fate of organic matter produced in the upper water column in a region that is anticipated to react rapidly to climate change. Chlorophyll a, an indicator of biomass standing stock of phytoplankton, has been measured in the upper 100 m of the water column since 1991 during several summer cruises (with RV 'Polarstern') across Fram Strait. Chlorophyll a measurements are used to validate productivity estimates by remote sensing from space. The quantity and composition of export fluxes of organic matter including biomarker have been measured since 2000 by annually moored sediment traps deployed at 200-300m at the AWI long-term observatory HAUSGARTEN in eastern Fram Strait (79°/4°E). Along with sinking particles, zooplankton (so-called 'swimmers') was also caught in the traps. Analyses of the material collected by the sediment traps allowed us to track seasonal and inter-annual changes in the surface waters at HAUSGARTEN. We present temporal trends in the chlorophyll a distribution (1991-2012), in swimmer composition in the traps (2000-2009), and in the export of biomarker (2000-2008), particulate organic carbon, particulate biogenic silica, calcium carbonate, and the protist composition (2000-2012), in relation to the changing sea ice cover and water temperature. Whereas chlorophyll a (integrated values 0-100m) showed only a slight increase, the swimmer composition and the composition of the annual particle flux changed after a warm water event occurring from 2005-2007. The warm anomaly

  10. Nutrient load can lead to enhanced CH4 fluxes through changes in vegetation, peat surface elevation and water table depth in ombrotrophic bog

    NASA Astrophysics Data System (ADS)

    Juutinen, Sari; Bubier, Jill; Larmola, Tuula; Humphreys, Elyn; Arnkil, Sini; Roy, Cameron; Moore, Tim

    2016-04-01

    Atmospheric nitrogen (N) deposition has led to nutrient enrichment in wetlands, particularly in temperate areas, affecting plant community composition, carbon (C) cycling, and microbial dynamics. It is vital to understand the temporal scales and mechanisms of the changes, because peatlands are long-term sinks of C, but sources of methane (CH4), an important greenhouse gas. Rainwater fed (ombrotrophic) bogs are considered to be vulnerable to nutrient loading due to their natural nutrient poor status. We fertilized Mer Bleue Bog, a Sphagnum moss and evergreen shrub-dominated ombrotrophic bog near Ottawa, Ontario, now for 11-16 years with N (NO3 NH4) at 0.6, 3.2, and 6.4 g N m-2 y-1 (~5, 10 and 20 times ambient N deposition during summer months) with and without phosphorus (P) and potassium (K). Treatments were applied to triplicate plots (3 x 3 m) from May - August 2000-2015 and control plots received distilled water. We measured CH4 fluxes with static chambers weekly from May to September 2015 and peat samples were incubated in laboratory to measure CH4 production and consumption potentials. Methane fluxes at the site were generally low, but after 16 years, mean CH4 emissions have increased and more than doubled in high nitrogen addition treatments if P and K input was also increased (3.2 and 6.4 g N m-2yr-1 with PK), owing to drastic changes in vegetation and soil moisture. Vegetation changes include a loss of Sphagnum moss and introduction of new species, typical to minerogenic mires, which together with increased decomposition have led to decreased surface elevation and to higher water table level relative to the surface. The trajectories indicate that the N only treatments may result in similar responses, but only over longer time scales. Elevated atmospheric deposition of nutrients to peatlands may increase loss of C not only due to changes in CO2 exchange but also due to enhanced CH4 emissions in peatlands through a complex suite of feedbacks and interactions

  11. Physical mechanism of mind changes and tradeoffs among speed, accuracy, and energy cost in brain decision making: Landscape, flux, and path perspectives

    NASA Astrophysics Data System (ADS)

    Han, Yan; Kun, Zhang; Jin, Wang

    2016-07-01

    Cognitive behaviors are determined by underlying neural networks. Many brain functions, such as learning and memory, have been successfully described by attractor dynamics. For decision making in the brain, a quantitative description of global attractor landscapes has not yet been completely given. Here, we developed a theoretical framework to quantify the landscape associated with the steady state probability distributions and associated steady state curl flux, measuring the degree of non-equilibrium through the degree of detailed balance breaking for decision making. We quantified the decision-making processes with optimal paths from the undecided attractor states to the decided attractor states, which are identified as basins of attractions, on the landscape. Both landscape and flux determine the kinetic paths and speed. The kinetics and global stability of decision making are explored by quantifying the landscape topography through the barrier heights and the mean first passage time. Our theoretical predictions are in agreement with experimental observations: more errors occur under time pressure. We quantitatively explored two mechanisms of the speed-accuracy tradeoff with speed emphasis and further uncovered the tradeoffs among speed, accuracy, and energy cost. Our results imply that there is an optimal balance among speed, accuracy, and the energy cost in decision making. We uncovered the possible mechanisms of changes of mind and how mind changes improve performance in decision processes. Our landscape approach can help facilitate an understanding of the underlying physical mechanisms of cognitive processes and identify the key factors in the corresponding neural networks. Project supported by the National Natural Science Foundation of China (Grant Nos. 21190040, 91430217, and 11305176).

  12. Provenance and flux of detrital materials in Lake Suigetsu sediment (SG12 core) and their temporal changes during the last 20 kyrs based on color and XRF data

    NASA Astrophysics Data System (ADS)

    Suzuki, Y.; Tada, R.; Nakagawa, T.; Gotanda, K.; Haraguchi, T.; Nagashima, K.; Irino, T.; Sugisaki, S.; Kojima, H.; Horiuchi, D.

    2013-12-01

    Lake Suigetsu in Central Japan is known for its annual lamination (varve) starting from 70kys ago. Extremely precise Age-depth model is established for SG06 core based on over 800 14C dates obtained on terrestrial leaf fossils and wiggle-matched to stalagmite 14C records constrained by varve counts (Staff et al., 2013). By projecting this age model to newly drilled core from the same site, we can obtain precisely age-controlled high resolution paleoenvironmental record around the Lake Suigetsu drainage. It is likely that detrital materials in Lake Suigetsu sediments have several different sources such as soil on the slopes around the lake itself, aeolian dust from inland Asia, and suspended particles supplied from Hasu river through lake Mikata, which is located immediately upstream of Lake Suigetsu and trapping most of coarse detrital grains. However, the relative contribution from each detrital source and its temporal changes are poorly known. The lack of knowledge on relative contribution of different detrital sources limits utility of detrital materials as proxies of paleo-environments. In this study, we are aiming to reconstruct the history of precipitation changes in the drainage area of Lake Suigetsu during the Holocene to explore the relationship between precipitation in the Japan Sea side of SW Japan, behavior of Asian monsoon system as an important component of the global climate system. It is well known that flux of suspended particles in rivers increases with precipitation. In order for us to be able to use the Hasu river's flux of suspended particles as the precipitation proxy, however, we first need to establish a simple and swift way to estimate the contribution of detrital materials from Hasu River flowing through Lake Mikata into Lake Suigetsu. We carried out color measurement with 5mm resolution on split half core surface of the sediment drilled in the summer of 2012(SG12), and compared these values to chemical composition data by XRF microscanner

  13. Impact of changes in river fluxe