In-stream uptake and retention of C, N and P in a supraglacial stream

AbstractSupraglacial streams form annually during the melt season, transporting dissolved solutes from the melting ice and snowpack to subglacial flow paths and the glacier terminus. Although nutrient and carbon processing has been documented in other supraglacial environments (cryoconite holes, snowpack), little work has examined the potential for in-stream nutrient retention in supraglacial streams. Here we carried out a solute nutrient injection experiment to quantify NH3+, PO43−and labile dissolved organic carbon (DOC) retention in a supraglacial stream. The experiment was performed on a 100 m stream reach on Mendenhall Glacier, an outlet glacier on the Juneau Icefield, southeastern Alaska, USA. The study stream contained two distinct reaches of equal length. The first reach had a lower velocity (0.04 ms−1) and contained abundant gravel sediment lining the ice–water interface, while the second reach was devoid of bedload sediment and had an order-of-magnitude higher velocity. At the end of the second reach, the stream emptied into a moulin, which is typical of supraglacial streams on this and other temperate glaciers. We found that N and P were transported largely conservatively, although NO3−increased along the reach, suggestive of nitrification. Labile DOC was retained slightly within the stream, although rates were low relative to the travel times observed within the supraglacial stream. Although our findings show that these streams have low processing rates, measurable in-stream nitrification and dissolved organic matter uptake within this biologically unfavorable environment suggests that supraglacial streams with longer residence times and abundant fine substrate have the potential to modify and retain nutrients during transport to the glacier terminus.

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Discharge of debris from ice at the margin of the Greenland ice sheet

Journal of Glaciology ◽

10.3189/172756502781831359 ◽

2002 ◽

Vol 48 (161) ◽

pp. 192-198 ◽

Cited By ~ 21

Author(s):

Peter G. Knight ◽

Richard I. Waller ◽

Carrie J. Patterson ◽

Alison P. Jones ◽

Zoe P. Robinson

Keyword(s):

Ice Sheet ◽

Greenland Ice Sheet ◽

High Rate ◽

Outlet Glacier ◽

Tidewater Glaciers ◽

Sediment Production ◽

Basal Ice ◽

Order Of Magnitude ◽

Sediment Transfer ◽

A Minor

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

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Evidence for subglacial ponding across Taylor Glacier, Dry Valleys, Antarctica

Annals of Glaciology ◽

10.3189/172756404781813970 ◽

2004 ◽

Vol 39 ◽

pp. 79-84 ◽

Cited By ~ 34

Author(s):

Alun Hubbard ◽

Wendy Lawson ◽

Brian Anderson ◽

Bryn Hubbard ◽

Heinz Blatter

Keyword(s):

Equipotential Surface ◽

Dry Valleys ◽

Flow Paths ◽

Dielectric Contrast ◽

Pressure Melting ◽

Reflective Power ◽

Taylor Glacier ◽

High Dielectric ◽

Ice Water ◽

Modelling Data

AbstractIce-penetrating radar and modelling data are presented suggesting the presence of a zone of temperate ice, water ponding or saturated sediment beneath the tongue of Taylor Glacier, Dry Valleys, Antarctica. The proposed subglacial zone lies 3–6 km up-glacier of the terminus and is 400– 1000m across. The zone coincides with an extensive topographic overdeepening to 80m below sea level. High values of residual bed reflective power across this zone compared to other regions and the margins of the glacier require a high dielectric contrast between the ice and the bed and are strongly indicative of the presence of basal water or saturated sediment. Analysis of the hydraulic equipotential surface also indicates strong convergence into this zone of subglacial water flow paths. However, thermodynamic modelling reveals that basal temperatures in this region could not exceed –7˚C relative to the pressure-melting point. Such a result is at odds with the radar observations unless the subglacial water is a hypersaline brine.

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TermPicks: A century of Greenland glacier terminus data for use in machine learning applications

10.5194/tc-2021-311 ◽

2021 ◽

Author(s):

Sophie Goliber ◽

Taryn Black ◽

Ginny Catania ◽

James M. Lea ◽

Helene Olsen ◽

...

Keyword(s):

Machine Learning ◽

Greenland Ice Sheet ◽

Median Number ◽

Google Earth ◽

Training Data ◽

Machine Learning Techniques ◽

Data Set ◽

Outlet Glacier ◽

Glacier Terminus ◽

Median Error

Abstract. Marine-terminating outlet glacier terminus traces, mapped from satellite and aerial imagery, have been used extensively in understanding how outlet glaciers adjust to climate change variability over a range of time scales. Numerous studies have digitized termini manually, but this process is labor-intensive, and no consistent approach exists. A lack of coordination leads to duplication of efforts, particularly for Greenland, which is a major scientific research focus. At the same time, machine learning techniques are rapidly making progress in their ability to automate accurate extraction of glacier termini, with promising developments across a number of optical and SAR satellite sensors. These techniques rely on high quality, manually digitized terminus traces to be used as training data for robust automatic traces. Here we present a database of manually digitized terminus traces for machine learning and scientific applications. These data have been collected, cleaned, assigned with appropriate metadata including image scenes, and compiled so they can be easily accessed by scientists. The TermPicks data set includes 39,060 individual terminus traces for 278 glaciers with a mean and median number of traces per glacier of 136 ± 190 and 93, respectively. Across all glaciers, 32,567 dates have been picked, of which 4,467 have traces from more than one author (duplication of 14 %). We find a median error of ∼100 m among manually-traced termini. Most traces are obtained after 1999, when Landsat 7 was launched. We also provide an overview of an updated version of The Google Earth Engine Digitization Tool (GEEDiT), which has been developed specifically for future manual picking of the Greenland Ice Sheet.

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Effect of hypothermia on ventilatory response to carbon dioxide inhalation and carbon dioxide infusion in dogs

Journal of Applied Physiology ◽

10.1152/jappl.1960.15.3.397 ◽

1960 ◽

Vol 15 (3) ◽

pp. 397-401 ◽

Cited By ~ 11

Author(s):

John Salzano ◽

F. G. Hall

Keyword(s):

Carbon Dioxide ◽

Body Temperature ◽

Lower Order ◽

Ventilatory Response ◽

Water Immersion ◽

Carbon Dioxide Tension ◽

Order Of Magnitude ◽

Gaseous Carbon Dioxide ◽

Ice Water ◽

Immersion Hypothermia

Some respiratory and circulatory responses to carbon dioxide stress during ice-water immersion hypothermia were studied in 13 dogs. Stresses were imposed by increasing the carbon dioxide tension of the inspired gas in eight animals and by intravenous infusion of gaseous carbon dioxide in five other animals. It was found that when compensation is made for the depressed ventilation exhibited at low body temperature, animals responded to the carbon dioxide stresses in essentially the same manner in the hypothermic as in the normothermia state. However, the responses are of a lower order of magnitude. Submitted on November 19, 1959

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Quantification of the total ion transport in the near-Earth plasma sheet

Annales Geophysicae ◽

10.5194/angeo-35-869-2017 ◽

2017 ◽

Vol 35 (4) ◽

pp. 869-877 ◽

Cited By ~ 6

Author(s):

Rikard Slapak ◽

Maria Hamrin ◽

Timo Pitkänen ◽

Masatoshi Yamauchi ◽

Hans Nilsson ◽

...

Keyword(s):

Plasma Sheet ◽

Low Energy ◽

Auroral Region ◽

Ion Dynamics ◽

Lower Velocity ◽

Order Of Magnitude ◽

Using Data ◽

Open Question ◽

Atmospheric Loss ◽

Net Fluxes

Abstract. Recent studies strongly suggest that a majority of the observed O+ cusp outflows will eventually escape into the solar wind, rather than be transported to the plasma sheet. Therefore, an investigation of plasma sheet flows will add to these studies and give a more complete picture of magnetospheric ion dynamics. Specifically, it will provide a greater understanding of atmospheric loss. We have used Cluster spacecraft 4 to quantify the H+ and O+ total transports in the near-Earth plasma sheet, using data covering 2001–2005. The results show that both H+ and O+ have earthward net fluxes of the orders of 1026 and 1024 s−1, respectively. The O+ plasma sheet return flux is 1 order of magnitude smaller than the O+ outflows observed in the cusps, strengthening the view that most ionospheric O+ outflows do escape. The H+ return flux is approximately the same as the ionospheric outflow, suggesting a stable budget of H+ in the magnetosphere. However, low-energy H+, not detectable by the ion spectrometer, is not considered in our study, leaving the complete magnetospheric H+ circulation an open question. Studying tailward flows separately reveals a total tailward O+ flux of about 0. 5 × 1025 s−1, which can be considered as a lower limit of the nightside auroral region O+ outflow. Lower velocity flows ( < 100 km s−1) contribute most to the total transports, whereas the high-velocity flows contribute very little, suggesting that bursty bulk flows are not dominant in plasma sheet mass transport.

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Sub-decadal variations in outlet glacier terminus positions in Victoria Land, Oates Land and George V Land, East Antarctica (1972–2013)

Antarctic Science ◽

10.1017/s0954102017000074 ◽

2017 ◽

Vol 29 (5) ◽

pp. 468-483 ◽

Cited By ~ 8

Author(s):

A.M. Lovell ◽

C.R. Stokes ◽

S.S.R. Jamieson

Keyword(s):

Antarctic Peninsula ◽

East Antarctica ◽

West Antarctica ◽

Position Change ◽

Outlet Glacier ◽

Glacier Terminus ◽

Victoria Land ◽

Decadal Scale ◽

Decadal Variations ◽

The Antarctic

AbstractRecent work has highlighted the sensitivity of marine-terminating glaciers to decadal-scale changes in the ocean–climate system in parts of East Antarctica. However, compared to Greenland, West Antarctica and the Antarctic Peninsula, little is known about recent glacier change and potential cause(s), with several regions yet to be studied in detail. In this paper, we map the terminus positions of 135 glaciers along the coastline of Victoria Land, Oates Land and George V Land from 1972–2013 at a higher temporal resolution (sub-decadal intervals) than in previous research. These three regions span a range of climatic and oceanic conditions and contain a variety of glacier types. Overall, from 1972–2013, 36% of glaciers advanced, 25% retreated and the remainder showed no discernible change. On sub-decadal timescales, there were no clear trends in glacier terminus position change. However, marine-terminating glaciers experienced larger terminus position changes compared with terrestrial glaciers, and those with an unconstrained floating tongue exhibited the largest variations. We conclude that, unlike in Greenland, West Antarctica and the Antarctic Peninsula, there is no clear glacier retreat in the study area and that most of the variations are more closely linked to glacier size and terminus type.

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On the Use of Asymptotic Solutions to Plane Ice—Water Problems

Journal of Glaciology ◽

10.1017/s0022143000031269 ◽

1969 ◽

Vol 8 (53) ◽

pp. 285-300 ◽

Cited By ~ 14

Author(s):

G. S. H. Lock

Keyword(s):

Boundary Conditions ◽

Asymptotic Solutions ◽

Variable Properties ◽

Governing Equations ◽

Freezing And Thawing ◽

One Dimensional ◽

Wide Range ◽

Order Of Magnitude ◽

Water Problems ◽

Ice Water

The paper considers one-dimensional freezing and thawing of ice–water systems for the conditions first examined by Stefan. An order-of-magnitude analysis applied to the governing equations and boundary conditions quantifies the error resulting from the neglect of various factors. Principal among these are density difference, initial superheat and variable properties.Asymptotic solutions for the temperature distribution and interface history are developed for a wide range of boundary conditions: prescribed temperature or heat flux, prescribed convection and prescribed radiation. Comparison with known results reveals the general adequacy of the asymptotic solutions and an estimate of the error incurred.

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Change Points Detected in Decadal and Seasonal Trends of Outlet Glacier Terminus Positions across West Greenland

Remote Sensing ◽

10.3390/rs12213651 ◽

2020 ◽

Vol 12 (21) ◽

pp. 3651

Author(s):

Ashley V. York ◽

Karen E. Frey ◽

Sadegh Jamali ◽

Sarah B. Das

Keyword(s):

Sea Surface ◽

Change Points ◽

Change Point Analysis ◽

Landsat Images ◽

Sea Ice Concentration ◽

Outlet Glacier ◽

West Greenland ◽

Glacier Terminus ◽

Point Analysis ◽

Ice Concentration

We investigated the change in terminus position between 1985 and 2015 of 17 marine-terminating glaciers that drain into Disko and Uummannaq Bays, West Greenland, by manually digitizing over 5000 individual frontal positions from over 1200 Landsat images. We find that 15 of 17 glacier termini retreated over the study period, with ~80% of this retreat occurring since 2000. Increased frequency of Landsat observations since 2000 allowed for further investigation of the seasonal variability in terminus position. We identified 10 actively retreating glaciers based on a significant positive relationship between glaciers with cumulative retreat >300 m since 2000 and their average annual amplitude (seasonal range) in terminus position. Finally, using the Detecting Breakpoints and Estimating Segments in Trend (DBEST) program, we investigated whether the 2000–2015 trends in terminus position were explained by the occurrence of change points (significant trend transitions). Based on the change point analysis, we found that nine of 10 glaciers identified as actively retreating also underwent two or three periods of change, during which their terminus positions were characterized by increases in cumulative retreat. Previous literature suggests potential relationships between our identified change dates with anomalous ocean conditions, such as low sea ice concentration and high sea surface temperatures, and our change durations with individual fjord geometry.

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