1. IntroductionThe Greenland ice sheet has been experiencing increasing surface melt (Bhattacharya et al., 2009; Box, 2013; Fettweis et al., 2011).. Most of the surface melt goes through supraglacial streams and lake systems that drain through moulins. Moulins are circular, near-vertical sinkholes in ice sheet and glacier systems in which water enters from the surface. This drainage of water by moulins provides an increase in meltwater to supraglacial and subglacial environments, thus increasing basal sliding of outlet glaciers. It is important to understand the spatial distribution and seasonal progression of these hydrologic feature by mapping with fine resolution and great spatial coverage, allowing for a broader understanding of sheet-wide reactions to increased melting (Chu, 2013). This projects seeks to glimpse into the spatial changes of moulins on the Greenland Ice sheet from 2012 to 2015 by using satellite imagery and GIS.

Research questions:

● How do surface and bedrock topography affect moulin density?● Does velocity affect the movement of moulin migration?

2. Materials and MethodsSatellite Imagery● Worldview-1, Worldview-2, and Worldview-3 satellite imagery between the

dates of 2015-17-7 and 2015-31-7 were used for the collection of moulin data for the 2015 dataset. Each moulin was manually digitized in ArcMap using visual evidence from the images. Some streams had several moulins that were grouped into one moulin, known as the main moulin. The 2015 main moulins were linked to 2012 main moulins. The 2012 dataset was provided by Chu et al. (in prep).

Digital Elevation Model● Morlighem, M., E. Rignot, J. Mouginot, H. Seroussi, and E. Larour. 2015.

IceBridge BedMachine Greenland, Version 2. [surface, bedrock, thickness]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/AD7B0HQNSJ29. [04/2017-06/2017]○ Bedrock and surface slope, bedrock ruggedness, and bedrock

roughness were derived from this DEM using GIS. Principal Strain Rate● Principal strain rate data were provided by Poinar et al. (2015) at a 250m

resolution. This data was derived from RADARSAT-12 average velocity data from the years 2007-2010.

Velocity● Velocity data provided by Nagler et al. (2015) are produced from

Sentinel-1. This ice velocity map was produced at a 500x500 m resolution and represents the average magnitude of velocity from 2016-23-12 to 2017-27-02.

Ordinary Least Squares Regression● An ordinary least squares regression model was used to find out which

attributes of bedrock and surface topography explained moulin density. Explanatory variables include: bedrock DEM; surface DEM; bedrock slope; surface slope; ice thickness; velocity; principal strain rate; bedrock roughness, and bedrock ruggedness.

5. AcknowledgmentsWe would like to thank Professor Vena Chu for her guidance throughout the process of this project.

3. Results 4. ConclusionsBased on the results most new moulins form in elevations below 1300 meters. Although 27.02% of 2015 main moulins were seen as unlinked to the 2012 main moulins, there may be some that are connected that are not seen through the satellite images, possibly because of human error resolution, distance, etc. There does not seem to be a correlation between velocity and moulin travel distance.

Surface and bedrock elevation, ice thickness, and bed slope were not statistically significant in determining moulin density for both the 2012 and 2015 sites. However, surface slope, principal strain rate, velocity, bedrock roughness, and bedrock ruggedness were indeed significant. One way in which this study can be built upon is by utilizing other forms of regression modeling other than ordinary least squares. Further, more explanatory variables may be used in order to have a more well-rounded understanding of the causes of moulin density.

6. Literature CitedBhattacharya, I., Jezek, K. C., Wang, L., & Liu, H. (2009). Surface

melt area variability of the Greenland ice sheet: 1979–2008. Geophysical Research Letters, 36(20).

Chu, V. W. (2013). Greenland ice sheet hydrology: A review. hjklProgress in Physical Geography, 38(1), 19-54.

Chu, V.W., Smith, L.C., Gleason, C.J., Yang, K., and Pitcher. L.H., hjjjjPoinar, K., and Joughin, I.R. (in prep). Assessing southwestern hjjjjGreenland ice sheet moulin distribution and formation from hjjjjhigh-resolution WorldView-1/2 remote sensing.

Morlighem, M., E. Rignot, J. Mouginot, H. Seroussi, and E. Larour. hjjjj2015. Deeply Incised Submarine Glacial Valleys Beneath the hjjjjGreenland Ice Sheet, Nature Geoscience. 7. 418-422.

Nagler, T., Rott, H., Hetzenecker, M., Wuite, J., Potin, P. (2015). The Sentinel-1 Mission: New Opportunities for Ice Sheet Observations. Remote Sensing, 2015, 7, 9371-9389

Poinar, K., Joughin, I., Das, S. B., Behn, M. D., Lenaerts, J. T. M. and Broeke, M. R.: Limits to future expansion of surface-melt-enhanced ice flow into the interior of western Greenland, Geophys. Res. Lett., 1–8, 14 doi:10.1002/2015GL063192, 2015.

Zwally, H. J. (2002). Surface Melt-Induced Acceleration of hjjjjGreenland Ice-Sheet Flow. Science, 297(5579), 218-222.

Characteristics of Moulin Density and Location on the Greenland Ice Sheet 2012 & 2015

Julia Ebert & Lilian Yang – University of California, Santa Barbara

Figure 2: 2014-2015 velocity of the Greenland Ice sheets vs. the distance travelled by the 2015 main moulins from their linked 2012 main moulins. There is almost no change in velocity with increasing distance. The average velocity is 0.236241 m/yr.

There are 282 moulins in the 2012 dataset and 143 moulins in the 2015 dataset. Of the moulins in 2015, there are 111 main moulins to the streams created by the surface melt. 81 of those main moulins were linked to 81 main moulins in the 2012 dataset, but there are 30 new moulins that are not visibly linked to the 2012 satellite images. A majority of the new main moulins formed on the left side of the study area and are under 1300 meters in elevation. 7 new main moulins formed on the right side of the study area and are above 1300 meters in elevation.

Figure 10 (left): 3 moulins (yellow) in the 2012 dataset. The top moulin is the main moulin with 2 submoulins

Figure 9 (right): 1 moulin (green) from the 2015 dataset in

the same location as figure 3.

Scale 1:10,000. Elevation: 1402m

Figure 9 (top left) Bedrock ruggedness with 2012 moulins and study area (grey) and 2015 moulins and study area (black).

Figure 10 (top right). Velocity with 2012 moulins and study area (grey) and 2015 moulins and study area (black).

Moulin Map: 2012 & 2015

Figure 8 (bottom): 2015 moulins (orange) under 2015 satellite imagery. The main moulin has moved 340.2m since 2012.

Figure 7 (top): 2012 moulins (green and cyan) under

2012 satellite imageryElevation: 1382m.

Scale 1:15,000

Figure 5 (top): 2015 moulin (green) under 2015 satellite. Elevation: 1135m Figure 6 (bottom): 2012 moulin (red) under 2012 satellite imagery. Scale 1:8,000

Variable Coefficient Std. Error t-Statistic Probability

Intercept 0.00

0.01

0.00

1.00

Thickness -0.80

108240.3

0.00 1.00

Velocity -0.33 0.01 -35.94 0.00

Strain Rate 0.07 0.01

8.73 0.00

Bed Slope 0.02 0.02

0.82

0.41

Surface Slope

0.09

0.01

9.48

0.00

Bed Elevation

-0.67

70621.81

0.00 1.00

Surface Elevation

0.61

79506.47

0.00

1.00

Bed Ruggedness

-0.05

0.03 -1.99

0.05

Bed Roughness

-0.03 0.01

-4.01

0.00

Variable Coefficient Std. Error t-Statistic Probability

Intercept 0.00

0.00 0.02

0.98

Thickness -105.18

91.05 -1.16

0.25

Velocity 0.15

0.00

39.02

0.00

Strain Rate -105.182

0.00 16.40

0.00

Bed Slope -0.00 0.00

-0.68 0.50

Surface Slope

-0.16 0.00

-33.55

0.00

Bed Elevation

-32.98

28.88 -1.14 0.25

Surface Elevation

90.17 78.47 1.15

0.25

Bed Ruggedness

0.02

0.00

6.54 0.00

Bed Roughness

0.04 0.00 12.21 0.00

297m

340.4m

Table 1 (side left) shows the ordinary least squares regression results for the 2012 moulin dataset.Table 2 (side right) shows the ordinary least squares regression results for the 2015 moulin dataset.

For both datasets, velocity; strain rate; surface slope; bed ruggedness, and bed roughness are all significant in explaining moulin density.

180m

Figure 3 (left): velocity component in the East-West direction. There is almost no change in eastern direction with distance as shown with the trendline. The average easting direction is -0.2337m/yr.Figure 4 (right) velocity component in the North-South direction. The graph shows that the moulins move both in the North and South direction, but increases in the North direction (positive) with increasing distance. The average northings direction is -0.00292 m/yr

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