Grounding line migration through the calving season at Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry

Abstract. Ice velocity variations near the terminus of Jakobshavn Isbræ, Greenland, were observed with a terrestrial radar interferometer (TRI) during three summer campaigns in 2012, 2015, and 2016. We estimate a ∼  1 km wide floating zone near the calving front in early summer of 2015 and 2016, where ice moves in phase with ocean tides. Digital elevation models (DEMs) generated by the TRI show that the glacier front here was much thinner (within 1 km of the glacier front, average ice surface is ∼  100 and ∼  110 m above local sea level in 2015 and 2016, respectively) than ice upstream (average ice surface is >  150 m above local sea level at 2–3 km to the glacier front in 2015 and 2016). However, in late summer 2012, there is no evidence of a floating ice tongue in the TRI observations. Average ice surface elevation near the glacier front was also higher, ∼  125 m above local sea level within 1 km of the glacier front. We hypothesize that during Jakobshavn Isbræ's recent calving seasons the ice front advances ∼  3 km from winter to spring, forming a >  1 km long floating ice tongue. During the subsequent calving season in mid- and late summer, the glacier retreats by losing its floating portion through a sequence of calving events. By late summer, the entire glacier is likely grounded. In addition to ice velocity variation driven by tides, we also observed a velocity variation in the mélange and floating ice front that is non-parallel to long-term ice flow motion. This cross-flow-line signal is in phase with the first time derivative of tidal height and is likely associated with tidal currents or bed topography.

Download Full-text

Grounding line migration through the calving season of Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry

10.5194/tc-2017-231 ◽

2018 ◽

Author(s):

Surui Xie ◽

Timothy H. Dixon ◽

Denis Voytenko ◽

Fanghui Deng ◽

David M. Holland

Keyword(s):

Early Summer ◽

Floating Zone ◽

Ocean Tides ◽

Ice Surface ◽

Digital Elevation ◽

Grounding Line ◽

Glacier Front ◽

Ice Velocity ◽

Velocity Variations ◽

Calving Season

Abstract. Ice velocity variations near the terminus of Jakobshavn Isbræ, Greenland were observed with a terrestrial radar interferometer (TRI) during three summer campaigns in 2012, 2015, and 2016. Ice velocity variations appear to be largely modulated by ocean tides. We estimate a ∼ 1 km wide floating zone near the calving front in early summer of 2015 and 2016, where ice moves in phase with ocean tides. Digital Elevation Models (DEMs) generated by the TRI show that the glacier front here is thin (ice surface is 140 m above local sea level within a very short distance (

Download Full-text

Inversion for basal friction coefficients with a two-dimensional flow line model using Tikhonov regularization

Research in Geophysics ◽

10.4081/rg.2012.e11 ◽

2012 ◽

Vol 2 (2) ◽

pp. 11 ◽

Cited By ~ 8

Author(s):

Yuri V. Konovalov

Keyword(s):

Inverse Problem ◽

Friction Coefficient ◽

Sea Level ◽

Flow Line ◽

Regularization Parameter ◽

Surface Velocity ◽

Line Model ◽

Basal Friction ◽

Ice Surface ◽

Level Shifts

We present results of basal friction coefficient inversion. The inversion was performed by a 2D flow line model for one of the four fast flowing ice streams on the southern side of the Academy of Sciences Ice Cap in the Komsomolets Island, Severnaya Zemlya archipelago. The input data for the performance of both the forward and the inverse problems included synthetic aperture radar interferometry ice surface velocities, ice surface elevations and ice thicknesses obtained by airborne measurements (all were taken from Dowdeswell <em>et al.</em>, 2002). Numerical experiments with: i) different sea level shifts; and ii) randomly perturbed friction coefficient have been carried out in the forward problem. The impact of sea level changes on vertical distribution of horizontal velocity and on shear stress distribution near the ice front has been investigated in experiments with different sea level shifts. The experiments with randomly perturbed friction coefficient have revealed that the modeled surface velocity is weakly sensitive to the perturbations and, therefore, the inverse problem should be considered ill posed. To mitigate ill posedness of the inverse problem, Tikhonov’s regularization was applied. The regularization parameter was determined from the relation of the discrepancy between observed and modeled velocities to the regularization parameter. The inversion was performed for both linear and non-linear sliding laws. The inverted spatial distributions of the basal friction coefficient are similar for both sliding laws. The similarity between these inverted distributions suggests that the changes in the friction coefficient are accompanied by appropriate water content variations at the glacier base.

Download Full-text

Rapid retreat, acceleration and thinning of Glaciar Upsala, Southern Patagonia Icefield, initiated in 2008

Annals of Glaciology ◽

10.3189/2013aog63a236 ◽

2013 ◽

Vol 54 (63) ◽

pp. 131-138 ◽

Cited By ~ 31

Author(s):

Daiki Sakakibara ◽

Shin Sugiyama ◽

Takanobu Sawagaki ◽

Sebastián Marinsek ◽

Pedro Skvarca

Keyword(s):

Satellite Images ◽

Surface Elevation ◽

Stable Phase ◽

Tidewater Glaciers ◽

Ice Surface ◽

Research Activities ◽

Front Position ◽

Southern Patagonia ◽

Glacier Front ◽

Ice Velocity

AbstractThe Patagonia Icefields are characterized by a large number of outlet glaciers calving into lakes and the ocean. In contrast to the recent intensive research activities on tidewater glaciers in other regions, very few observations have been made on calving glaciers in Patagonia. We analysed satellite images of Glaciar Upsala, the third largest freshwater calving glacier in the Southern Patagonia Icefield, to investigate changes in its front position, ice velocity and surface elevation from 2000 to 2011. Our analyses revealed a clear transition from a relatively stable phase to a rapidly retreating and fast-flowing condition in 2008. The glacier front receded by 2.9 km, and the ice velocity increased by 20–50%, over the 2008–11 period. We also found that the ice surface lowered at a rate of up to 39 m a−1 from 2006 to 2010. This magnitude and the rate of changes in the glacier front position, ice velocity and surface elevation are greater than previously reported for Glaciar Upsala, and comparable to recent observations of large tidewater glaciers in Greenland. Our data illustrate details of a rapidly retreating calving glacier in Patagonia that have been scarcely reported despite their importance to the mass budget of the Patagonia Icefields.

Download Full-text

Influence of wolf predation on population momentum of the Nushagak Peninsula caribou herd, southwestern Alaska

Rangifer ◽

10.7557/2.39.1.4455 ◽

2019 ◽

Vol 39 (1) ◽

pp. 1-10

Author(s):

Patrick Walsh

Keyword(s):

Population Change ◽

Late Summer ◽

Early Summer ◽

Time Budgets ◽

Direct Response ◽

Wolf Predation ◽

Calving Season ◽

Southwestern Alaska

We investigated wolf predation as a potential driver of population change in the Nushagak Peninsula caribou herd, southwestern Alaska. We investigated the time budgets of three wolf packs using the peninsula from 2007 through 2012, and thus potentially preying on caribou there, in order to make inferences on their likelihood of serving as an important population modifier for the Nushagak Peninsula caribou herd. We found that only one pack regularly used the peninsula. The pack using the peninsula spent an average of 35% of its time there. Its use of the peninsula was disproportionately high in late summer and fall, disproportionately low in winter, and proportional during the caribou calving season in early summer. Overall wolf use of the Nushagak Peninsula increased in direct response to increasing caribou abundance but was not a primary population driver.

Download Full-text

Effects of Dried Distillers’ Grains Cube Supplementation for Steers Grazing Introduced Pastures on Animal Performance and Forage Production

Journal of Animal Science ◽

10.1093/jas/skab096.020 ◽

2021 ◽

Vol 99 (Supplement_2) ◽

pp. 12-13

Author(s):

Jordan Adams ◽

Rodney Farris ◽

Scott Clawson ◽

Earl Ward ◽

Paul Beck

Keyword(s):

Festuca Arundinacea ◽

Statistical Power ◽

Cynodon Dactylon ◽

Animal Health ◽

Late Summer ◽

Early Summer ◽

Distillers Grains ◽

Forage Production ◽

Trenbolone Acetate ◽

Dried Distillers Grains

Abstract We evaluated the effects of supplementing dried distillers’ grains cubes (DDGS) and re-implantation of steers (n = 149; BW = 238 ± 13.8 kg) grazing tall fescue (Festuca arundinacea)/bermudagrass (Cynodon dactylon) pastures (n = 9 pastures, 7.2 ± 2.90 ha) from 14 April to 17 September 2020 (n = 155 d) in a split-plot design on steer performance and forage production. Main plot supplemental treatments (n = 3 pastures/treatment) included 1) Fertilized Control (FC), no supplementation on fertilized pastures (112 kg N/ha); 2) Fertilized Supplement (FS), supplemental DDGS fed at 2.9 kg 3-d/wk on fertilized pastures; and 3) Supplement (S), supplemented DDGS at 0.75% BW/d on unfertilized pastures prorated for 5-d/wk feeding. Steers were previously implanted during receiving with 40 mg trenbolone acetate and 8 mg estradiol (REV-G; Revalor G, Merck Animal Health). On July 7, steers in each pasture were randomly assigned to one of three re-implant treatments: 1) no re-implant; 2) REV-G; or 3) 200 mg progesterone and 20 mg estradiol (Synovex S, Zoetis Animal Health). Steers in FS and S gained more (P < 0.01) than FC throughout the trial and final BW was greater (P < 0.01) for FS and S compared with FC. Unexpectedly, re-implanting had no effect on ADG (P = 0.57) or BW (P = 0.34), but statistical power may be lacking. Supplemental efficiency was greater in the late summer for FS (P = 0.05) compared to S. Fertilizing pastures in FS and FC did not affect biomass (P = 0.39), however, CP was increased (P = 0.01) and acid and neutral detergent fibers tended to decrease (P = 0.06) relative to S in the early summer (April, May, June, and July), but did not differ in late summer (August and September). Based upon our analysis, DDGS is a suitable supplement and can replace N fertilizer for steers grazing introduced pastures.

Download Full-text

179 Using a 100% Dried Distillers Grains Cube as a Supplement for Steers Grazing Mixed Grass Prairie in Oklahoma

Journal of Animal Science ◽

10.1093/jas/skz397.105 ◽

2020 ◽

Vol 98 (Supplement_2) ◽

pp. 46-46

Author(s):

Zane N Grigsby ◽

Paul A Beck ◽

Stacey A Gunter

Keyword(s):

Animal Health ◽

Late Summer ◽

Estradiol Benzoate ◽

Positive Control ◽

Negative Control ◽

Early Summer ◽

Trenbolone Acetate ◽

Mixed Grass Prairie ◽

Mixed Grass ◽

Main Plot

Abstract This research was conducted to determine effects of supplementation and implanting on BW gain by steers grazing mixed grass prairie (n = 12 pastures, 19.9 ± 0.7 ha) in northwest Oklahoma. Three main plot treatments were: 1) Negative Control (NC), no supplementation, 2) Positive Control (PC), supplemented with DDGS cubes, 1.8 kg/steer on alternate days in late summer, 3) High Supplement (HS), 1/3 increase in stocking rate with 0.75% BW supplemental DDGS cubes all season. Steers (n = 125, BW = 223.1 ± 23.2 kg) were stocked at 2.2 ha/steer for PC and NC, 1.3 ha/steer for HS. Grazing was from May 17 – September 27 (132 d). All steers were implanted with 200 mg progesterone and 20 mg estradiol benzoate (SYN, Synonvex S, Zoetis Animal Health) on May 17. On July 18 three reimplant treatments were applied: 1) no reimplant; 2) SYN; or 3) 40 mg trenbolone acetate and 8 mg estradiol (Revalor G, Merck Animal Health). Data were analyzed using the PROC MIXED in SAS as a split-plot experimental design. In early summer HS had 0.26 kg greater (P < 0.01) ADG than NC and PC. Late summer gains of PC were 0.33 kg/d more (P ≤ 0.01) than NC; and HS gained 0.49 and 0.16 kg/day more (P ≤ 0.04) than NC and PC, respectively. Gain per hectare for PC (46 kg/ha) were greater (P < 0.01) than NC (35 kg/ha) and more than doubled (P < 0.01) with HS (89 kg/ha). Reimplanting had no effect on ADG (P ≥ 0.28). Late season supplementation with PC resulted in supplemental efficiency of 2.7 kg supplement/kg added gain compared with NC. Increased stocking rates with season long supplementation in HS resulted in supplemental efficiency of 3.8 kg supplement/kg added gain per hectare. Based on these data, a 100% DDGS cube is an effective supplement option to increase BW gain during the late summer or increase carrying capacity and gain during the summer grazing period in northwestern Oklahoma.

Download Full-text

Replacing synthetic N with clovers or alfalfa in bermudagrass pastures. 1. Herbage mass and pasture carrying capacity

Animal Production Science ◽

10.1071/an15045 ◽

2017 ◽

Vol 57 (3) ◽

pp. 539 ◽

Cited By ~ 4

Author(s):

P. Beck ◽

T. Hess ◽

D. Hubbell ◽

M. S. Gadberry ◽

J. Jennings ◽

...

Keyword(s):

Medicago Sativa ◽

Trifolium Repens ◽

Carrying Capacity ◽

Nutritive Value ◽

Cynodon Dactylon ◽

Late Summer ◽

Early Summer ◽

Fertilisation Rate ◽

Medicago Sativa L ◽

Trifolium Repens L

The objective of this study was to evaluate the effects of including alfalfa (ALF, Medicago sativa L.) or a combination of white (Trifolium repens L.) and red (Trifolium pretense L.) clovers (CLVR) inter-seeded into bermudagrass (Cynodon dactylon L. Pers.) on herbage nutritive value compared with monocultures of bermudagrass fertilised with 0 (0N), 56 (56N), or 112 (112N) kg nitrogen (N)/ha over four grazing seasons. In autumn, at the end of the fourth year and in the spring before the fifth grazing season, alfalfa and clover plants were killed and the carryover N benefit of CLVR or ALF was compared with N fertilisation rates during the fifth year. Across years, N fertilisation rate increased herbage mass and carrying capacity linearly; whereas herbage production from CLVR and ALF swards was equivalent to 56N, were greater than 0N and less than 112N. Herbage mass in CLVR and ALF swards was greater than fertilised bermudagrass swards in the spring and did not differ from fertilised bermudagrass in the early summer. In late summer herbage accumulation of CLVR and ALF swards appeared to decrease, limiting the herbage mass in the legume pastures compared with 56N and 112N. Carrying capacity of CLVR and ALF swards was greater than fertilised bermudagrass in the spring and early summer, but did not differ from fertilised swards in the late summer. The N benefit of including legumes in bermudagrass swards can alleviate the reliance on synthetic N fertilisation with little overall effect on pasture carrying capacity.

Download Full-text

Effects of Environmental Temperature onCapnodis tenebrionisAdult Phenology

Psyche A Journal of Entomology ◽

10.1155/2012/586491 ◽

2012 ◽

Vol 2012 ◽

pp. 1-8 ◽

Cited By ~ 3

Author(s):

Carmelo Peter Bonsignore

Keyword(s):

Late Summer ◽

Early Summer ◽

Adult Density ◽

Degree Days ◽

Continuous Increase ◽

Climate Conditions ◽

Average Annual Temperature ◽

Activity Temperature ◽

The Difference ◽

New Generation

The phenology ofCapnodis tenebrionisadults was presented with reference to two different climate conditions. In a temperate moderate-warm climate, adult density showed two separate peaks during the year: one in early summer of the overwintering generation and one with beetles emerging in the late summer. In a warmer semiarid climate, the overwintering adults and the new generation overlapped during summer with a continuous increase of adult density. The difference in the average annual temperature between areas during the study period was almost3∘C, and, in the warmer area, the new generation ofC. tenebrionisemerged at least one month earlier. To make a prediction of adult presence, a model utilizing degree-days was developed from data collected over a five-year period. Models obtained from equations (Logistic 4-parameter,y(x)=yo+a/(1+(x/xo)b)) of each year were developed to describe the relationship between degree-day accumulation (with a minimal threshold activity temperature of14.21∘Ccalculated in the laboratory) and the cumulative percentage of adult presence. According to the overall model, the 50% of overwintering beetles occurred at 726 degree-days (Biofix: 1st March) and the emerging beetles occurred at 801 degree-days (Biofix: 1st July). The results show that a change in temperature is an important aspect that highlights the adaptability of this species.

Download Full-text

Impact of extrafloral nectar availability and plant genotype on ant (Hymenoptera: Formicidae) visitation to quaking aspen (Salicaceae)

The Canadian Entomologist ◽

10.4039/tce.2015.38 ◽

2015 ◽

Vol 148 (1) ◽

pp. 36-42 ◽

Cited By ~ 2

Author(s):

Jonathon R. Newman ◽

Diane Wagner ◽

Patricia Doak

Keyword(s):

Populus Tremuloides ◽

Late Summer ◽

Early Summer ◽

Quaking Aspen ◽

Plant Genotype ◽

Free Living ◽

Natural Induction ◽

Formica Fusca ◽

Time Of Year ◽

Nectar Availability

AbstractFor quaking aspen (Populus tremuloides Michaux; Salicaceae) the rate of extrafloral (EF) sugar secretion is increased by defoliation and decreased by drought. Although wholesale blocking of EF nectar has been shown to reduce ant (Hymenoptera: Formicidae) visitation to aspen, the effect of more subtle and realistic variations in nectar availability on ant recruitment is unknown. Working in Alaskan boreal forest (United States of America), we reduced and supplemented EF nectar availability on potted aspen ramets of three genotypes and surveyed visitation by free-living Formica fusca (Linnaeus) (Hymenoptera: Formicidae). Ants were more responsive to a subtle increase in sugar availability than to a decrease. While nectar reduction had no effect on ant visitation, nectar supplementation increased ant visitation to one aspen genotype by 70% during an early summer trial. Average ant visitation to different aspen genotypes varied during the late summer, indicating that aspen genotype can influence attractiveness to ants. We conclude that natural induction of EF secretion in response to herbivory may benefit aspen through improved ant recruitment, though the response is dependent on aspen genotype and time of year. Differences among aspen genets in attractiveness to ants could influence the relative success of genotypes, especially in settings in which aspen regenerates from seed.

Download Full-text

The propagation of a surge front on Bering Glacier, Alaska, 2001–2011

Annals of Glaciology ◽

10.3189/2013aog63a341 ◽

2013 ◽

Vol 54 (63) ◽

pp. 221-228 ◽

Cited By ~ 13

Author(s):

James Turrin ◽

Richard R. Forster ◽

Chris Larsen ◽

Jeanne Sauber

Keyword(s):

Feature Tracking ◽

Average Rate ◽

Surface Velocity ◽

Ablation Zone ◽

Ice Surface ◽

Glacier Terminus ◽

Bering Glacier ◽

Landsat 7 ◽

Ice Velocity ◽

Recent Activity

AbstractBering Glacier, Alaska, USA, has a ∼20 year surge cycle, with its most recent surge reaching the terminus in 2011. To study this most recent activity a time series of ice velocity maps was produced by applying optical feature-tracking methods to Landsat-7 ETM+ imagery spanning 2001-11. The velocity maps show a yearly increase in ice surface velocity associated with the down-glacier movement of a surge front. In 2008/09 the maximum ice surface velocity was 1.5 ±0.017 km a-1 in the mid-ablation zone, which decreased to 1.2 ±0.015 km a-1 in 2009/10 in the lower ablation zone, and then increased to nearly 4.4 ± 0.03 km a-1 in summer 2011 when the surge front reached the glacier terminus. The surge front propagated down-glacier as a kinematic wave at an average rate of 4.4 ±2.0 km a-1 between September 2002 and April 2009, then accelerated to 13.9 ± 2.0 km a-1 as it entered the piedmont lobe between April 2009 and September 2010. The wave seems to have initiated near the confluence of Bering Glacier and Bagley Ice Valley as early as 2001, and the surge was triggered in 2008 further down-glacier in the mid-ablation zone after the wave passed an ice reservoir area.

Download Full-text