Science.gov

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

    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

  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

    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.

  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 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.

  12. 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.

  13. 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

  14. 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

  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. 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.

  6. 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

  7. 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.

  8. 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.

  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. 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.

  7. 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.

  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. 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.

  19. 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.

  20. 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.

  1. 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.

  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. 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

  5. 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

  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. 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

  9. 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

  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. 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

  16. 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.

  17. 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

  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. 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).

  20. 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

  1. 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

  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. 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

  16. 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.

  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. 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

  19. 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

  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. 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.

  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. 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).

  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. 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.

  9. 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

  10. 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

  11. 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

  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. 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

  15. 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

  16. 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

  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. 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

  20. 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.

  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. 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.

  7. 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.

  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. 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

  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. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. 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.

  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. 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

  8. 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.

  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. 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

  11. 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.

  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. 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

  1. 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

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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%.

  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. 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

  10. 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.

  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. 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.

  19. 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

  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. 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.