Large spatial variations in the flux balance along the front of a Greenland tidewater glacier

Abstract. The frontal flux balance of a medium-sized tidewater glacier in western Greenland in the summer is assessed by quantifying the individual components (ice flux, retreat, calving, and submarine melting) through a combination of data and models. Ice flux and retreat are obtained from satellite data. Submarine melting is derived using a high-resolution ocean model informed by near-ice observations, and calving is estimated using a record of calving events along the ice front. All terms exhibit large spatial variability along the ∼5 km wide ice front. It is found that submarine melting accounts for much of the frontal ablation in small regions where two subglacial discharge plumes emerge at the ice front. Away from the subglacial plumes, the estimated melting accounts for a small fraction of frontal ablation. Glacier-wide, these estimates suggest that mass loss is largely controlled by calving. This result, however, is at odds with the limited presence of icebergs at this calving front – suggesting that melt rates in regions outside of the subglacial plumes may be underestimated. Finally, we argue that localized melt incisions into the glacier front can be significant drivers of calving. Our results suggest a complex interplay of melting and calving marked by high spatial variability along the glacier front.

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Calving controlled by melt-under-cutting: detailed calving styles revealed through time-lapse observations

Annals of Glaciology ◽

10.1017/aog.2018.28 ◽

2019 ◽

Vol 60 (78) ◽

pp. 20-31 ◽

Cited By ~ 15

Author(s):

Penelope How ◽

Kristin M. Schild ◽

Douglas I. Benn ◽

Riko Noormets ◽

Nina Kirchner ◽

...

Keyword(s):

Tidal Cycle ◽

Time Lapse ◽

Prognostic Models ◽

Small Scale ◽

Cycle Plays ◽

Tidewater Glacier ◽

Glacier Front ◽

Detailed Record ◽

Frontal Ablation

AbstractWe present a highly detailed study of calving dynamics at Tunabreen, a tidewater glacier in Svalbard. A time-lapse camera was trained on the terminus and programmed to capture images every 3 seconds over a 28-hour period in August 2015, producing a highly detailed record of 34 117 images from which 358 individual calving events were distinguished. Calving activity is characterised by frequent events (12.8 events h−1) that are small relative to the spectrum of calving events observed, demonstrating the prevalence of small-scale calving mechanisms. Five calving styles were observed, with a high proportion of calving events (82%) originating at, or above, the waterline. The tidal cycle plays a key role in the timing of calving events, with 68% occurring on the falling limb of the tide. Calving activity is concentrated where meltwater plumes surface at the glacier front, and a ~ 5 m undercut at the base of the glacier suggests that meltwater plumes encourage melt-under-cutting. We conclude that frontal ablation at Tunabreen may be paced by submarine melt rates, as suggested from similar observations at glaciers in Svalbard and Alaska. Using submarine melt rate to calculate frontal ablation would greatly simplify estimations of tidewater glacier losses in prognostic models.

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AMOC Evolution at 47°N in the Last Decades in Observations and a High-Resolution Ocean Model

10.5194/egusphere-egu21-5071 ◽

2021 ◽

Author(s):

Simon Wett ◽

Monika Rhein ◽

Arne Biastoch ◽

Claus Böning ◽

Klaus Getzlaff

Keyword(s):

High Resolution ◽

Model Simulation ◽

Saline Water ◽

Ocean Model ◽

Meridional Overturning Circulation ◽

The Arctic ◽

Model Simulations ◽

Improve Model ◽

Meridional Overturning ◽

The Individual

The Atlantic Meridional Overturning Circulation (AMOC) plays an important role for the climate system of Europe and the Arctic. It is responsible for the northward transport of warm and saline water in the upper water column and the southward transport of cold and fresh water in the deep.Since the early 2000s, observations from ship-based measurements and moorings are available which allow estimates of the individual components of the AMOC. However, the spatial resolution of mooring measurements is coarse and ship-based surveys are mostly done only once a year, adding to the uncertainty of these measurements. Earlier observational studies in the subpolar North Atlantic have found decadal trends of individual AMOC components. However, whether the entirety of the AMOC exhibits a trend remains unclear. Due to the observational limitations, most knowledge about the recent AMOC development is based on model simulations. Comparing these model simulations with observations remains an important task to understand the changes in the AMOC strength in the last decades and improve model representations of the AMOC.We analyze a realization of the high-resolution VIKING20X ocean model from 1980 to 2019 offering a large overlap with the available observations. We compare it to measurements of the NOAC array at 47&#176;N and sections obtained from repeated ship surveys. We aim to merge observations and model simulation to better estimate recent AMOC changes and increase our understanding of the underlying processes.

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Temporal and Spatial Variability of Near‐Inertial Waves in the East/Japan Sea From a High‐Resolution Wind‐Forced Ocean Model

Journal of Geophysical Research Oceans ◽

10.1029/2018jc014802 ◽

2019 ◽

Vol 124 (8) ◽

pp. 6015-6029 ◽

Cited By ~ 2

Author(s):

Chanhyung Jeon ◽

Jae‐Hun Park ◽

Young‐Gyu Park

Keyword(s):

High Resolution ◽

Spatial Variability ◽

Japan Sea ◽

Ocean Model ◽

Inertial Waves ◽

Temporal And Spatial Variability ◽

Temporal And Spatial

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Large spatial variations in the frontal mass budget of a Greenland tidewater glacier

10.5194/tc-2018-143 ◽

2018 ◽

Author(s):

Till J. W. Wagner ◽

Fiamma Straneo ◽

Clark G. Richards ◽

Donald A. Slater ◽

Laura A. Stevens ◽

...

Keyword(s):

Spatial Variability ◽

Ice Dynamics ◽

Tidewater Glaciers ◽

Mass Budget ◽

Tidewater Glacier ◽

Glacier Front ◽

In Situ Observations ◽

The Impact ◽

Local Variability

Abstract. We investigate the frontal mass budget of a medium-sized tidewater glacier in western Greenland. This is done by comparing the seasonal retreat of the glacier to ice advection and ablation along the front. Frontal ablation is partitioned into calving and submarine melting, both of which are estimated from in situ observations. We observe large spatial variability in all mass budget terms along the glacier front. In particular, we find that the ablation of the glacier front is characterized by two main regimes: melting dominated versus calving dominated. While melting-dominated segments appear to be associated with subglacial discharge plumes, calving-dominated regions occur outside such plumes. The melting-dominated segments are rather localized, and the majority of ablation is estimated to occur in the form of calving. However, we stress the large uncertainty in melt rate estimates and consider the possibility that current parameterizations substantially underestimate melting. Finally, we argue that localized melt incisions into the glacier front can be significant drivers of calving. Our results suggest a complex interplay of melting and calving marked by high spatial variability along the glacier front. Understanding the impact of such local variability on larger scale ice dynamics may help guide future mass balance projections for tidewater glaciers.

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Algorithms for automated montage synthesis of images from laser-scanning confocal microscopes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100139627 ◽

1995 ◽

Vol 53 ◽

pp. 650-651

Author(s):

D. E. Becker

Keyword(s):

Image Analysis ◽

High Resolution ◽

Laser Scanning ◽

Cell Counting ◽

Wide Area ◽

Data Set ◽

Computational Synthesis ◽

Automated Cell Counting ◽

Partial View ◽

The Individual

An efficient, robust, and widely-applicable technique is presented for computational synthesis of high-resolution, wide-area images of a specimen from a series of overlapping partial views. This technique can also be used to combine the results of various forms of image analysis, such as segmentation, automated cell counting, deblurring, and neuron tracing, to generate representations that are equivalent to processing the large wide-area image, rather than the individual partial views. This can be a first step towards quantitation of the higher-level tissue architecture. The computational approach overcomes mechanical limitations, such as hysterisis and backlash, of microscope stages. It also automates a procedure that is currently done manually. One application is the high-resolution visualization and/or quantitation of large batches of specimens that are much wider than the field of view of the microscope.The automated montage synthesis begins by computing a concise set of landmark points for each partial view. The type of landmarks used can vary greatly depending on the images of interest. In many cases, image analysis performed on each data set can provide useful landmarks. Even when no such “natural” landmarks are available, image processing can often provide useful landmarks.

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Matchup Characteristics of Sea Surface Salinity Using a High-Resolution Ocean Model

Remote Sensing ◽

10.3390/rs13152995 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2995

Author(s):

Frederick M. Bingham ◽

Severine Fournier ◽

Susannah Brodnitz ◽

Karly Ulfsax ◽

Hong Zhang

Keyword(s):

High Resolution ◽

Time Window ◽

Single Point ◽

Ocean Model ◽

Sea Surface ◽

Sea Surface Salinity ◽

Surface Salinity ◽

Argo Floats ◽

Statistical Measures ◽

Salinity Difference

Sea surface salinity (SSS) satellite measurements are validated using in situ observations usually made by surfacing Argo floats. Validation statistics are computed using matched values of SSS from satellites and floats. This study explores how the matchup process is done using a high-resolution numerical ocean model, the MITgcm. One year of model output is sampled as if the Aquarius and Soil Moisture Active Passive (SMAP) satellites flew over it and Argo floats popped up into it. Statistical measures of mismatch between satellite and float are computed, RMS difference (RMSD) and bias. The bias is small, less than 0.002 in absolute value, but negative with float values being greater than satellites. RMSD is computed using an “all salinity difference” method that averages level 2 satellite observations within a given time and space window for comparison with Argo floats. RMSD values range from 0.08 to 0.18 depending on the space–time window and the satellite. This range gives an estimate of the representation error inherent in comparing single point Argo floats to area-average satellite values. The study has implications for future SSS satellite missions and the need to specify how errors are computed to gauge the total accuracy of retrieved SSS values.

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Factors associated with successful return to work in young heart failure and ischaemic heart disease patients following index hospital admission

European Journal of Preventive Cardiology ◽

10.1093/eurjpc/zwab061.312 ◽

2021 ◽

Vol 28 (Supplement_1) ◽

Author(s):

HV Thakkar ◽

L Hollingsworth ◽

JA Enright ◽

S Sanderson ◽

RJ Macfadyen ◽

...

Keyword(s):

Heart Failure ◽

Return To Work ◽

Decompensated Heart Failure ◽

Individual Factors ◽

P Value ◽

Complex Interplay ◽

Coronary Syndrome ◽

Funding Sources ◽

Financial Benefits ◽

The Individual

Abstract Funding Acknowledgements Type of funding sources: None. Background Factors influencing return to remunerated work following an acute cardiac illness are poorly defined. We wished to compare the factors in our cohorts following first presentation of acute coronary syndrome(ACS) and decompensated heart failure(HF). Methods Prospectively identified subjects, aged 18-65years, from a rehabilitation population for ACS and HF during 2018-2019 underwent a survey. Results Of 133cases meeting inclusion criteria, 84 completed the survey(41 HF, 80% male, mean age 55years; 43 ACS, 86% male, mean age 57years). Socio-economic indexes for Areas(SIEFA) index were similar for HF(900) & ACS(909) groups, which represents 11th and 14th percentile for Australia respectively. Cardiovascular risk factors were similar except hypercholesterolemia(37% v 60%; p = 0.029) was more common in ACS. Many subjects did not continue beyond Yr12, (54% HF v 30% ACS; p = 0.029). A majority of ACS cases returned to work as compared with HF(70% v 44%; p = 0.017)(Figure). On multivariate analysis, male gender[p = 0.031;OR 13.71 (1.28-147.36)]; access to financial benefits[p < 0.001;OR 22.75 (4.31-119.99)] and a desire to return to work [p = 0.014;OR 12.1 (1.67-87.82)] were associated with successful return to work (Table). Limitations Our study has small numbers so will be difficult to generalise to a wider population. We do show a signal towards the complex interplay of the social and individual factors in determining return to work. Further larger studies are required to tease out the differences between the individual factors to help predict return to work in the Australian context. Conclusion Successful return to work for patients with first presentation of ACS or HF could not be reliably predicted. Patients with ACS returned to work more often than HF. In HF patients who do n to return to work, recurrent symptoms, individual motivation, social support and access to financial benefits have a complex interplay. Predictors of return to work Predictor P value OR (95% CI) Diagnosis (heart failure) 0.095 0.29 (0.07, 1.24) Gender (male) 0.031 13.71 (1.28, 147.36) Access to benefit (none) <0.001 22.75 (4.31, 119.99) Desire to RTW (yes) 0.014 12.1 (1.67, 87.82) Abstract Figure. Rates of return to work in the 2 groups

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A two-dimensional glacier–fjord coupled model applied to estimate submarine melt rates and front position changes of Hansbreen, Svalbard

Journal of Glaciology ◽

10.1017/jog.2018.61 ◽

2018 ◽

Vol 64 (247) ◽

pp. 745-758 ◽

Cited By ~ 2

Author(s):

E. DE ANDRÉS ◽

J. OTERO ◽

F. NAVARRO ◽

A. PROMIŃSKA ◽

J. LAPAZARAN ◽

...

Keyword(s):

Coupled Model ◽

Small Scale ◽

Two Dimensional ◽

Time Step ◽

Software Packages ◽

Front Position ◽

Circulation Patterns ◽

Glacier Front ◽

Order Of Magnitude ◽

Frontal Ablation

ABSTRACTWe have developed a two-dimensional coupled glacier–fjord model, which runs automatically using Elmer/Ice and MITgcm software packages, to investigate the magnitude of submarine melting along a vertical glacier front and its potential influence on glacier calving and front position changes. We apply this model to simulate the Hansbreen glacier–Hansbukta proglacial–fjord system, Southwestern Svalbard, during the summer of 2010. The limited size of this system allows us to resolve some of the small-scale processes occurring at the ice–ocean interface in the fjord model, using a 0.5 s time step and a 1 m grid resolution near the glacier front. We use a rich set of field data spanning the period April–August 2010 to constrain, calibrate and validate the model. We adjust circulation patterns in the fjord by tuning subglacial discharge inputs that best match observed temperature while maintaining a compromise with observed salinity, suggesting a convectively driven circulation in Hansbukta. The results of our model simulations suggest that both submarine melting and crevasse hydrofracturing exert important controls on seasonal frontal ablation, with submarine melting alone not being sufficient for reproducing the observed patterns of seasonal retreat. Both submarine melt and calving rates accumulated along the entire simulation period are of the same order of magnitude, ~100 m. The model results also indicate that changes in submarine melting lag meltwater production by 4–5 weeks, which suggests that it may take up to a month for meltwater to traverse the englacial and subglacial drainage network.

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High-Resolution Facial Feature Saliency Mapping

Perception ◽

10.1068/p150373 ◽

1986 ◽

Vol 15 (4) ◽

pp. 373-386 ◽

Cited By ~ 20

Author(s):

Nigel D Haig

Keyword(s):

Image Processing ◽

High Resolution ◽

Facial Feature ◽

Human Beings ◽

Comparison Process ◽

Compression Technique ◽

Feature Saliency ◽

Basic Set ◽

Computational Speed ◽

The Individual

For recognition of a target there must be some form of comparison process between the image of that target and a stored representation of that target. In the case of faces there must be a very large number of such stored representations, yet human beings seem able to perform comparisons at phenomenal speed. It is possible that faces are memorised by fitting unusual features or combinations of features onto a bland prototypical face, and such a data-compression technique would help to explain our computational speed. If humans do indeed function in this fashion, it is necessary to ask just what are the features that distinguish one face from another, and also, what are the features that form the basic set of the prototypical face. The distributed apertures technique was further developed in an attempt to answer both questions. Four target faces, stored in an image-processing computer, were each divided up into 162 contiguous squares that could be displayed in their correct positions in any combination of 24 or fewer squares. Each observer was required to judge which of the four target faces was displayed during a 1 s presentation, and the proportion of correct responses for each individual square was computed. The resultant response distributions, displayed as brightness maps, give a vivid impression of the relative saliency of each feature square, both for the individual targets and for all of them combined. The results, while broadly confirming previous work, contain some very interesting and surprising details about the differences between the target faces.

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