Dynamics and historical changes of the Petersen , , Canada Adrienne White1 ([email protected]), Luke Copland1, Derek Mueller2 (1)Laboratory for Cryospheric Research, Department of Geography, University of Ottawa; (2)Geography and Environmental Studies, Carleton University

Background Definitions (Fig.2) The recent break up of ice shelves on ice shelf: An ice mass of (Fig.1) has been linked to climate warming and to the loss of considerable thickness (>20 m) and multiyear landfast (MLSI) (4). The importance of extent, that typically has an undulating MLSI as a protective barrier for ice shelves was apparent in surface that is afloat on the ocean but 2005, when the Petersen Ice Shelf lost 20% of its area within attached to the coast…. (1). days of break out of 1020 km² of MLSI from Yelverton Bay (4). Since then the MLSI has only reformed occasionally as a Multiyear landfast sea ice: Sea ice that is fringe in front of ice shelf. These changes are of concern for attached to land, that has survived at the stability of the remaining Petersen Ice Shelf, yet no prior least one complete melt season (2). studies regarding this ice mass exist. This limits the ability to understand how the ice shelf is changing and to predict how Epishelf lake: ‘…an ecosystem type that it will react to climatic forcing in the future. occurs where ice shelves block the head of fiords and embayment’s, retaining a Objective layer of freshwater (that has flowed in To conduct the first comprehensive survey of the Petersen from terrestrial sources) over the Ice Shelf, which includes: marine water below.’(3)

1. Historical changes in ice shelf area Fig.2 Diagram that illustrates the relationship between ice shelves, epishelf lakes and MLSI. Dominant sources of 2. Ice shelf thickness mass gain (accumulation) and loss for ice shelves are shown. (Image modified, source: D. Mueller)

Fig.1 Map of the study area showing the Petersen Ice Shelf (ASTER, July 16, 2009). Inset map of 3. Surface mass balance Ellesmere Island (MODIS, August 22, 2010) showing the location of Petersen Ice Shelf with a red box. 4. Epishelf lake analysis

Methods Current thickness Radarsat‐2 Ultrafine Image: Apr 1, 2011 Temporal area changes In May 2011 a Pulse EKKO Pro 250 MHz ground penetrating Air photos and satellite imagery (Fig.3) will be loaded into ArcGIS software to measure the extent of the Petersen Ice radar (GPR) system was used to measure ice shelf thickness Shelf and its adjacent features (i.e. epishelf lake, MLSI and tributary glaciers). For each image a polygon shapefile will be (Fig.4-6). The GPR was mounted into a sled and towed by created to manually trace the extent of the features and calculate the area of each feature for every time period. snowmobile (~20 km hr-1). The GPR parameters were set based on the velocity of ice (obtained with a CMP survey) and Air Photo MODIS ASTER Radarsat‐2 Ultrafine expected ice depths based on past studies (5). The GPR system used a built-in GPS (global positioning system) that recorded the unique position of each GPR trace along each transect. A handheld GPS unit was used to navigate in a grid pattern.

Fig.5 GPR transects collected in May 2011 across Petersen Ice Shelf. Transect in pink represents the transect in the radargram shown in Fig.6.

Battery supply Fig.3 To measure the change in area through time a variety of aerial photographs, and optical and synthetic aperture radar (SAR) satellite imagery will be used including: (from left to right) vertical aerial photographs form the National Air Photo Library (Ottawa), MODIS, ASTER and Radarsat.

Receiver Surface mass balance An ablation stake network was installed on the surface of the ice shelf and tributary glacier in May 2011 (Fig.7-9). The height of these ablation stakes above the ice surface will be re-measured in May 2012 to determine the rate of annual Transmitter surface lowering. Vertical density profiling and stratigraphy was conducted at each site to derive the snow water equivalent (Fig.7).

GPR control unit

dGPS receiver and battery supply

Fig.4 Field set-up: 250 MHz Pulse EKKO Pro Fig.6 Radargram for a ~4 km long transect collected in May 2011 (shown in pink on Fig.5). These dGPS antenna GPR system custom fit into sled. preliminary results show shallow depths (~8 m) closer to the outer shelf becoming much deeper Ablation stake (~58 m) towards the inner area (going from west to east in Fig.5).

Fig.8 Differential GPS measurements were collected in May 2011 at each ablation stake site to record the Epishelf Lake Status horizontal and vertical position. To determine the current status of the epishelf lake, measurements were collected in May 2011 (Fig.11). In the field, a CTD (conductivity-temperature-depth) profiler was lowered into a hole drilled into the epishelf ice cover (Fig.12). These measurements, along with CTD profiles collected in the same area in 2008 and 2009, will be used to determine if a freshwater lake exists and how it has changed.

Fig.7 Ultrafine Radarsat-2 image (Apr 1, 2011) that shows the location of each ablation stake site (shown as a green cross). The different types of ice including the ice shelf, lake ice, MLSI, old sea ice and first year ice (FYI) are shown. Fig.9 Density profiling and stratigraphy was conducted at each ablation stake to derive snow water equivalent.

Input from glaciers Speckle tracking estimates surface motion between pairs of repeat orbit SLC (single-look complex) SAR (synthetic aperture radar) satellite imagery by Fig.11 CTD profile measurements collected in May 2011 in the Fig.12 An RBR CTD profiler was lowered ~51 m into the epishelf lake. Results epishelf lake area along the south edge of the Petersen Ice Shelf. later showed that evidence for the freshwater layer was not detected. tracking the offset of SAR speckle Results show a brine layer in the first 2 m transitioning to saline (Fig.10). The surface motion derived levels by 19 m. over tributary glaciers can be used in combination with GPR thickness measurements to quantify glacier influx. Epishelf Lake Changes These results will be verified against High resolution SAR images will be used to monitor the epishelf lake ice during the past decade. Epishelf lakes across northern ground-based measurements. Ellesmere Island typically have a higher backscatter (>-6.0 dB) compared to sea ice which appears dark (Fig.13-15)(6). Extracting the backscatter values from Radarsat-1 and 2 imagery will be used to observe the changes in the lake ice of epishelf lakes. Ground-based velocity measurements Feb. 2002 were collected in May 2011, with a differential GPS (dGPS). A Trimble R7 dGPS receiver was used to measure the Epishelf lake position of each ablation stake with sub- Sea ice

Ice decimeter accuracy (Fig.8). The position shelf Salt of the ablation stakes will be resurveyed absorbs Fig.13 Radarsat image from February 2002: strong Fig.14 Radarsat image from March 2009: low backscatter shows radar Freshwater ice Fig.10 Preliminary speckle tracking results processed with Fine Radarsat-2 imagery (overlain on a volume in May 2012 to determine annual surface that areas once covered by freshwater ice (Fig.11) are now scattering & -1 backscatter confirms the presence of several epishelf lakes MODIS image). Velocities up to 50 m yr were derived over tributary glaciers flowing into Petersen reflection across Northern Ellesmere Island (green). (Reproduced from covered in sea ice (red). The last epishelf lake appears in Milne motion. A precise point positioning Ice Shelf. Jeffries 2002) Ice Shelf (green). (Reproduced from Jeffries 2002) Fig.15 Backscatter differences (PPP) method will be used to process the between sea ice and lake ice. dGPS data. (Source: D. Mueller)

Anticipated Results and Significance References Acknowledgements This study aims to produce the first survey of the Petersen Ice Shelf, which includes measurements for (1) Copland, L., Mueller, D. R., & Weir, L. (2007). Rapid loss of the Ayles Ice Shelf, Ellesmere Island, Canada. Geophysical ƒ Royal Canadian Geographical Society’s Northern Studentship Research Letters, 34, 1-6. doi: 10.1029/2007GL031809. Award thickness, area changes, epishelf lake changes and surface mass balance. In doing so, this study will use (2) Dowdeswell, J. A., & Jeffries, M. O. (2011). Arctic ice shelves: An introduction. In L. Copland & D. R. Mueller (Eds.), Arctic ƒ ACUNS (W. Garfield Weston Award) advanced geophysical measurements (e.g., GPR, dGPS, speckle tracking) to improve our knowledge of Ice Shelves and Ice Islands. Dordrecht: Springer SBM. ƒ University of Ottawa Admission Scholarship the response of the Petersen Ice Shelf to current and future climate forcing. This will contribute to (3) Jungblut, A. D., Mueller, D. R., & Vincent, W. F. (2011). Arctic Ice Shelf Ecosystems. In L. Copland & D. R. Mueller (Eds.), ƒ Northern Scientific Training Program improving our understanding of ice shelf dynamics and the conditions leading to ice shelf collapse Arctic Ice Shelves and Ice Islands. Dordrecht: Springer SBM. ƒ NSERC Discovery Award along the northern coast of Ellesmere Island. Since any further ice shelf break-up will produce (4) Mortimer, C. A. (2011). Quantification of changes for the Milne Ice Shelf, Nunavut, Canada, 1950-2009. University of ƒ Canada Foundation for Innovation Fig.16 Oil rig in the . Ottawa. (http://www.cbc.ca/news/canada/north/story/ ƒ ArcticNet Funding potentially hazardous ice islands (which can be tens of sq. km in size), this information is highly (5) Pope, S. G. (2010). Changes in Multiyear Landfast Sea Ice in the Northern Canadian Arctic Archipelago. University of 2011/05/02/shell-drilling-beaufort.html) ƒ relevant to downstream petroleum exploration and extraction in the Beaufort Sea (Fig.16). Ottawa. Polar Continental Shelf Program for logistical support ƒ (6) Veillette, J., Mueller, D. R., Antoniades, D., & Vincent, W. F. (2008). Arctic epishelf lakes as sentinel ecosystems: Past, Andrew Hamilton (UBC) for providing field assistance