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Glacier Retreat and Melt-Lake Expansion at Stephenson Glacier

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Glacier Retreat and Melt-Lake Expansion at Stephenson Glacier Polar Record 38 (207): 297-308 (2002). Printed in the United Kingdom. 297 Glacier retreat and melt-lake expansion at Stephenson Glacier, Heard Island World Heritage Area Kevin Kiernan and Anne McConnell School of Geography and Environmental Studies, University of Tasmania, Hobart, Tasmania 7005, Australia Received September 2001 ABSTRACT. Historical records, recent observations, and geomorphological evidence indicate that rates of retreat and downwasting of the tidewater Stephenson Glacier, and concurrent expansion of ice-marginal melt-lakes, has increased by an order of magnitude since 1987. Melt-lake expansion is partly the product of greatly accelerated ablation of older, ice-cored twentieth-century moraines. The timing of these changes broadly coincides with reported increases in atmospheric and sea-surface temperatures around other sub-Antarctic islands, but correlates less well with changes along the northern Antarctic Peninsula, where warming has been more rapid. These recent changes in landscape character and geomorphological processes have implications for geodiversity, biodiversity, and cultural heritage values in this World Heritage Area. Ifthe causal climatic warming is anthropogenic, it reinforces the fact that even the most remote and little­ visited nature conservation reserves may be compromised by off-site human impacts, confronting management authorities with difficult philosophical and practical issues. Contents local climate. A smaller volcanic complex, Laurens Pe­ Introduction 297 ninsula, extends westwards from Big Ben, and Elephant Physical environment 297 Spit extends -10 km downdrift from the eastern side of the Methods 298 mountain. The mean annual temperature (MAT) recorded Results 298 between 1948 and 1954 when a permanent base was Interpretation of results 304 maintained at Atlas Cove, between Laurens Peninsula and Discussion 305 Big Ben, was 1.3°C, with a seasonal variation in tempera­ Conclusions 307 ture at sea level of -4°C. The maximum recorded tempera­ Acknow ledgements 307 tures are 15.8°C at Atlas Cove and 21°C at Spit Camp on References 307 the north coast at the inner end of Elephant Spit, and the Introduction lowest recorded temperature is -9°C. Recorded annual Widespread glacier retreat in the sub-Antarctic since 1950, average precipitation at Atlas Cove is 1350 mm. Snow and retreat and ice-shelf decay in the Antarctic Peninsula falls to sea level throughout the year (Allison 1980; Aus­ since the early 1980s, has occurred coincident with signifi­ tralian Antarctic Division 1995). Steep and rapidly flow­ cant warming of atmospheric and sea-surface tempera­ ing glaciers descend to tidewater from Big Ben. Their tures (Smith and Steencamp 1990; Doake and Vaughan equilibrium line altitude (ELA) lies close to sea level, and 1991; Gordon and Timmis 1992; Vaughan and Doake they are sensitive indicators of climate change (Ruddell 1996; Cosimo 2000; Alley and Bindschadler 2001). This and Allison 1997). Laurens Peninsula has also been paper records and interprets glacier retreat and landscape glaciated to sea level in historical time, but its glaciers are changes at Stephenson Glacier on Heard Island (72°32'E, now confined above 400 m altitude. 53°06'S), a sub-Antarctic wilderness reserve and World Stephenson Glacier descends -11 km down the eastern Heritage Area in the southern Indian Ocean (Fig. 1). Heard flank of Big Ben between the glacially abraded Graham Island occurs in a region from which there have been few Ridge and the youthful volcanic construct of Scarlett Hill, detailed studies of recent glacier retreat or of the terrestrial then broadens to form a piedmont lobe up to -3 km wide record and impact of climate change. Such climate change (Fig. 2). East of its present terminus lies the large Dovers may have important implications for geomorphological Moraine complex, which stretches north-south across the processes in some conservation reserves, and for manage­ apex of Elephant Spit and now deflects the glacier into ment of their natural and cultural values (Bridgewater lobes that flow northeast and southeast. A smaller lateral 1996; Stone 1996; Galloway and others 1998). If glacier moraine complex has formed west of Stephenson Lagoon f recession on Heard Island is due to anthropogenic climate below Scarlett Hill, while in the south an interlobate drift i) change (Green 2000), it provides further evidence of the complex -1 km wide has formed between Stephenson potential for even the most remote of nature conservation Glacier and an icestream thatformerly descended southwest preserves to be compromised by human impacts. of Graham Ridge (Fig. 1). Little ground-based geomorphological data have pre­ Physical environment viously been available to aid in studies of glacier recession Heard Island is dominated by Big Ben, a strato-volcano 20 and geomorphic change on Heard Island. Historical and km in diameter that rises 2745 m into the stormy sub­ photographic records suggest that there was no significant Antarctic atmosphere and exerts a major influence on the change in the extent of the glaciers between 1874 and 298 KIERNAN AND McCONNELL Fig. 1. Principal land­ forms as at November 2000, and localities ~ moraine ridge/hummocks mentioned in the text. Scarlett HiII­ - ....., meltwater channel ....... beach ridge CIT) water body vegetation -<1_­ <;>"10--­ _ ~._---- ~ -------,,/ ~----/ o 1 2 ~--!:U I I I w ~---~ Ln .". o kiliometres o M M "" "" 1929, but that there was minor recession by 1955 and November 2000 were derived from oblique aerial photog­ major recession of most glaciers had occurred by 1963 raphy and ground-level inspection of the entire Dovers (Budd 1964a, 1964b, 2000; Budd and Stephenson 1970). Moraine complex, GPS control points, and reference to Some asynchronous retreat and advance of different gla­ new vertical aerial photographs of part of the area (Fig. 3). ciers took place during the following decade (Budd 1973, Moraines and outwash channels were mapped from 2000), after which continuing recession occurred (Allison aerial photographs and ground survey. Generalised topo­ and Keage 1986; Garvin and others 1999; Kiernan and graphic profiles over Dovers Moraine were compiled McConnell 1999; Green 2000). using a clinometer, staff, and fibreglass tape. Compari­ sons of soil development across different parts of the Methods Dovers Moraine complex were used as an aid to determin­ Changes in glacier margins and the extent of melt-lakes ing the likely relative age of moraine ridges. The altitudes prior to 1997 have been determined from historical and of melt-lake palaeo-shorelines were measured to deter­ recent photographs, published reports and maps, unpub­ mine the minimum altitude of the glacier margin that lished data obtained by Australian National Antarctic impounded the lakes. Research Expeditions (ANARE), communication with early ANAREexpeditioners, SPOT images, and geomorph­ Results ological observations made in March 1997 and November Review and interpretation of historical records 2000. Delineation of ice limits and melt-lake extent in 1850s-1960 March 1997 is based on observations from the air, oblique An historical sketch produced during the sealing days on aerial photographs, and partial ground-level inspection. Heard Island (1850s-70s) depicted high ice cliffs on the Approximations of the glacier and lake margins as at southern coast between Doppler Hill and Paddick Valley GLACIER RETREAT AND MELT-LAKE EXPANSION AT STEPHENSON GLACIER 299 Fig. 2. Oblique aerial photograph of the northern margin of Stephenson Glacier. Graham Ridge is on the left and Scarlet Hill on the right. (Downes 1996: 87, fig. 14). Oblique aerial photographs In 1954 ice-cored moraine still formed cliffs 3-4 m taken in 1947 recorded heavily ridged, debris-mantled ice high along the south coast between Doppler Hill and reaching the south coast, and a major meltwater stream Paddick Valley, inland of a beach that was too narrow to discharging eastwards between Doppler Hill and the main be traversed safely by ground parties (G. Budd, personal part of Dovers Moraine (ANARE ref 515-635,639). In communication, 26 April 2001). Coastal ice cliffs 15 m 1949 Ealey, Chittleborough, and Paddick encountered high persisted on the northern margin of the glacier. The overhanging ice cliffs on the south coast, inland of a Stephenson Glacier still reached close to the crest of narrow beach (ANARE log 1949, AAD Library Heard Dovers Moraine in at least some areas. Island collection, microfiche sheet 59; Paddick 1993). A 1960-1980 hydrographic chart produced in 1949 similarly depicted By 1963 the Stephenson Glacier had retreated -1 km from ice to the coast (Hydrographic Branch 1949), as did a 1951 the south coast and Graham Ridge had emerged more ANARE map bound with Downes and others (1959). On prominently through the downwasting ice. The northern the basis of these records the 1947 ice edge depicted in ice margin lay 100 m inland behind a beach and lagoon Figure 3 follows Budd and Stephenson (1970), who indi­ (Budd and Stephenson 1970) and the ice surface lay -20 m cated the Stephenson Glacier as having reached the coast below the northeastern crest ofDovers Moraine. Observa­ at that time. However, an alternative interpretation has tions in 1965, 1969, and 1971 indicated generally continu­ been presented by Allison and Keage (1986) who depicted ing retreat, although some re-advance occurred between the glacier proper as having terminated several hundred 1963 and 1971 (Budd 1970; Budd and Stephenson 1970; metres inland, and who apparently regarded the ice-cored Allison and Keage 1986). In 1971 a lake several hundred moraine closer to the coast as being older. metres wide was present between the ice edge and north­ In 1947 the northern margin of the glacier reached the eastern Dovers Moraine, from which a large stream flowed coast, where steep ice cliffs were being undercut by the down a meltwater channel to the coast beside the present­ sea. The 1947 photographs suggest that the glacier reached day ANARE Spit Camp (Budd 2000; G. Budd, personal high up the western slopes of Dovers Moraine.
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