SUPPLEMENTARY INFORMATION Supplementary information DOI: 10.1038/NGEO1481 An aerial view of 80 years of climate-related glacier fluctuations in southeast Greenland Anders A. Bjørk1*, Kurt H. Kjær1, Niels J. Korsgaard1, Shfaqat A. Khan2, Kristian K. Kjeldsen1, Camilla S. Andresen3, Jason E. Box4,5, Nicolaj K. Larsen6 and Svend Funder1 1Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark 2DTU Space - National Space Institute, Technical University of Denmark, Department of Geodesy, Copenhagen, Denmark. 3Geological Survey of Denmark and Greenland, Department of Marine Geology and Glaciology, Copenhagen, Denmark. 4Department of Geography, The Ohio State University, Columbus, Ohio, USA 5Byrd Polar Research Center, The Ohio State University, Columbus, Ohio, USA 6Department of Geocience, Aarhus University, Aarhus, Denmark *e-mail: [email protected] 1. Data 2. Methods 2.1 Image selection strategy 2.2 1981/1985 Digital Elevation Models and ortho-mosaics 2.3 Ortho-mosaics from 1981 and 1985 aerial photos 2.4 Control of the imagery 2.5 Digitization and error assessment 2.6 Glacier length measurements 2.7 Land-terminating elevation change 2.8 Regional differentiation and glacier subdivision 3. Additional climate data 4. Results 4.1 List of measured glaciers 4.2 Supplementary regional changes 4.3 Mid-Century advance 4.4 Unknown time of exposure for “1943” images 5. Supplementary information references 1 NATURE GEOSCIENCE | www.nature.com/naturegeoscience 1 © 2012 Macmillan Publishers Limited. All rights reserved. 1. Data 1932/1933 Imagery Images were recorded primarily for cartography during the 7th Thule Expedition to southeast Greenland, led by the Danish/Greenlandic scientist and explorer Knud Rasmussen. After topographic maps were produced, the images were classified and archived in a citadel on the outskirts of Copenhagen. Some of the aerial images had been published after the expedition25 and in the official report of the expedition26. Besides these images, the data have remained unexplored until recently rediscovered in Copenhagen. Figure S1. Photo positions and examples of aerial oblique images recorded during the 7th Thule Expedition. Image A is taken from the side of the aircraft with a low shooting angle at an altitude of 3700 meters. Image B is a tail-shot from 3300 meters with a higher shooting angle – the glacier depicted is the Thrym Glacier (1700 m wide) in the inner part of Skjoldungen Fjord (63°33’N; 41°45’W).The markings on the upper image are from geodesists generating the maps from the original images. The aerial images recorded during the 7th Thule Expedition (Fig. S1) fall into two categories: a series of flight lines recorded at 4,000 meters altitude off the coast towards land, and a series of tail images shot 2 © 2012 Macmillan Publishers Limited. All rights reserved. backwards relative to the direction of flight altitudes between 2,500 – 3,500 m. The set of tail flight lines are shot with a larger inclination, thereby more applicable for mapping purposes. The images are of varying quality, with the earliest recordings generally being the poorest. Many images were discarded due to poor quality. During the first year of flying in 1932 the technology and environment was new to the operators, and many film rolls are useless due to over exposure25. We have used images from the 1932 series, which are of high contrast, and the remaining images are from the 1933 campaign. Contact prints of the images have been scanned at 600 DPI; this resolution has proven sufficient to recognize all details from the prints. 1933 Terrestrial Imagery Due to the rough ice - and sailing conditions off the southeast coast of Greenland - very few historical terrestrial oblique images are available. From the historic expeditions few photographs were recorded and even fewer containing glaciers which can be geo located today. Five glaciers in the northern part of the study area have had their 1933 positions established based on terrestrial images recorded during The 7th Thule Expedition by Knud Rasmussen (Fig. S2). The work was an independent project carried out by the geologist Keld Milthers25, who’s results were not published. Five Land-terminating glaciers were recorded with a high precision photogrammetric camera for the purpose of measuring summer ablation. The glacier margins have been reestablished after revisiting the glaciers during the summer of 2010. Figure S2. Terrestrial images recorded in 1933 (left) and 2010 (right) from a Land-terminating glacier northeast of Tasiilaq (65°58’N; 35°51’W). During the 77 year period the glacier has retreated 1.7 km. Photo: Kjeld Milthers & Niels J. Korsgaard. From the exact 1933 camera positions new images were recorded (Fig. S2, right). This work was primarily done in order to create new 2010 digital elevation models and measure mass loss. In this study only results from the front positions have been used. Other examples of terrestrial images exist, however, at these sites aerial images from the same period and with a better resolution have been used instead. 3 © 2012 Macmillan Publishers Limited. All rights reserved. 1931 Images The images from the British Arctic Air Route Expedition (BAARE) from 1931 (Fig. S3) are used to fill in the blanks where no suitable images from the 7th Thule Expedition are available. This is primarily the coastline from Umivik to the beginning of Sermilik Fjord, where no tail-images were acquired during the 7th Thule Expedition. The images from the 1931 survey are all oblique photos recorded with a handheld camera from the airplane. The main objective of the survey was to investigate the area for a potential landing strip, leaving less attention to glacierized areas45. The angle of the recordings and the distance to the ice margin varies greatly from close-ups of glacier fronts to coverage of entire regions. Figure S3. Examples of images recorded during BAARE in 1931. Recorded with a handheld camera, the angle and distance to the ice vary. Left is the inner part of Johan Petersen Fjord (66°00’N; 38°25’W), right is a local ice cap on the southern part of Jens Munks Ø (64°29’N; 40°17’W). Photos are courtesy of Scott Polar Research Institute. The BAARE photos were provided in digital form from the Scott Polar Research Institute, with a resolution of c. 300 DPI. A number of the images have been scanned at 1200 DPI resolution from the negatives with little influence in the final precision. 4 © 2012 Macmillan Publishers Limited. All rights reserved. 1943 Images Figure S4. Position of the photos recorded during World War II, example from Thrym Glacier (1700 m wide) in the inner part of Skjoldungen Fjord (63°33’N; 41°45’W) During the 2nd World War an intensive photo campaign took place by the U.S. military. A large number of aerial photos were recorded throughout the coasts of Greenland (Fig. S4). The vertical photos were recorded in scale 1:40,000. The film rolls were handed over to the Danish National Survey and Cadastre after the war. Records of the photo campaign are elusive on when the flights took place, as the precise dates and camera details are no longer available. The best estimate is that these photos were recorded in the second half of the war. The registration cards at the archive of the Danish National Cadastre and Survey associated with these flight lines have the year “1943” and “1943?” noted on them, hence 1943 has also been the year used in this study. The true age of these images is still being investigated both in Denmark, and in the U.S. The implications of a possible incorrect year for our results and main conclusions are discussed in section 4.4. All 1943 vertical photos were scanned from the contact prints at 600 dpi, resulting in a ground resolution of c. 2 m. 5 © 2012 Macmillan Publishers Limited. All rights reserved. 1965 Images Recently unclassified US intelligence satellite images from the Corona program covering the southeast Greenland coast line have been used (Fig. S5). The images were provided in digital form scanned on a photogrammetric precision-scanner at 7 µm from the original negatives from the U.S. Geological Survey. The camera model used for all images was the J-1 stereo photogrammetric camera with a ground resolution of less than 0.61 m46. Figure S5. Detail from the declassified Corona satellite recorded in 1965, with the Fenris Glacier in the inner part of Sermilik Fjord (66°21’N; 37°30W). 6 © 2012 Macmillan Publishers Limited. All rights reserved. 1981 and 1985 photos Figure S6. The compilation of aerial imagery from 1981 and 1985 presented as blocks of ortho-rectified mosaics. The 650 km coastline is divided into sections to make file sizes manageable. Cut-out from Ikertivaq Bay (65°32’N; 39°56’W) comprised of six different vertical aerial photos. Vertical aerial photos from 1981 and 1985 (Fig. S6) covering the entire coast have been used. Flights were conducted in summer from late June to early August, and mages were recorded from an altitude of 13,000 meters to a scale of 1:150,000. The photos are part of a larger collection of images covering the entire ice-free parts of Greenland 1978-1987, processed at the Palaeoclimate-Quaternary Group of the Centre for GeoGenetics, Natural History Museum of Denmark. The 1981 and 1985 scale 1:150,000 photos have been aero-triangulated to the GR96 reference system, and have been used to produce a DEM which is the basis for a series of orthorectified mosaics (Fig. S6). These ortho-mosaics with a 4 m ground resolution are used as the 1981/85-data and serve as the horizontal reference for rectification of all other imagery in this study.