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Coastal Studies at Heard Island 1992/93: Changes in Sea Surface Temperature and Coastal Landforms

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Coastal Studies at Heard Island 1992/93: Changes in Sea Surface Temperature and Coastal Landforms Papers and Proceedings Royal of VfJZume 133(2), 2000 27 COASTAL STUDIES AT HEARD ISLAND 1992/93: CHANGES IN SEA SURFACE TEMPERATURE AND COASTAL LANDFORMS by Ken Green (with one table and five text-figures) GREEN, K., 2000 (,30:vi): Coastal studies at Heard Island 1992/93: Changes in sea surface temperature and coastal landforms. In Banks, M.R. & Brown, M.J. (Eds): HE'ARD ISLAND PAPERS. Pap. Proc. R. Soc. Tasm. 133(2): 27~32. ISSN OORO-4703. Australian Institute of Alpine Studies, PO Box 2228, Jindabyne, NSV/, Australia 2627. Sea temperature was measured weekly at Spit Bay, Heard Island, from April 1992 to March 1993. Temperatures were generally than those recorded in 1949 (at Atlas Cove), but these sites are not strictly comparable. Sea temperatures around Heard Island were stable from the 1920s to the 1940s, with a general increase in sea surface temperatures in the region being a recent phenomenon accompanied by widespread glacial retreat and the accelerated erosion of coastal features since the early 19 50s. There is an area of active erosion by both water and wind in an arc from Winston Lagoon on the southeastern coast through to the northeastern coast at Compton Lagoon. This is most likely an effect of the loss of glaciers allowing strong erosive water movement along the coast. Movements of this dynamic coastline have important implications for long-term monitoring studies and for fhe management of the island. Key Words: global warming, glaciers, erosion, Heard Island. INTRODUCTION immediate impact upon rates of coastal erosion; hence, glacial retreat will only be covered insofar as it affects the Those researchers looking for evidence of, or a visible result coastal morphology. Therefore, this paper is concerned of climate change on land look preferentially to glaciers. with evidence of warming in the Heard Island area and the However, the retreat or mass diminution of glaciers also has impact this is having on the coastal morphology. a flow-on effect, the retreat of tidewater glaciers in particular altering coastal dynamics. Changes in coastal morphology a1 Heard Island (53 °06' S, 73 °32 'E) have always been ofgreatest METHODS interest to those whose mode of transport on the island has been foot. Ledingham (1987), for example, included a map Sea temperature was measured weekly at Spit Bay camp and accompanying text describing access by foot around the from April 1992 to March 1993. Water was collected in a island in 1986/87. Most observed changes to the coast since plastic bucket from the sea within 1 m of the cobble beach. human occupation of Heard Island have glacial retreat as Temperature was measured in the morning to avoid any their proximate cause, with climate warming as the ultimate confounding effect of diurnal variation. The temperature cause (Allison & Keage 1986). was recorded to the nearest O.l°C with a standard The impact of glacial retreat on the coastal morphology meteorological thermometer (Dobbie -20°C to +60°C). of the northwestern end of Heard Island has been negligible. Sea temperatures taken from the RSV Aurora Australis at Jacka Glacier, for example, prevented travel to Red Island Spit Bay and in Atlas Cove on 23 January 1992 were from Atlas Cove in the early ANARE days (1947-54), but compared. Temperatures taken from the shore of Spit Bay its retreat, while making travel possible by foot, has not were compared with those taken from the MV Icebird on altered the coastline of the Laurens Peninsula (fig. 1). The 11 and 12 March 1993, whilst it was anchored off Spit Bay. beach in front of the Vahsel Glacier was considered Meteorological observations began at Spit Bay on 1 March uncrossable in 1985, with ice falls and waves to the snout with temporary housing for the instruments. The screen (Burton & Williams 1985), and was reported in the 1986/ and raingauge were set up on 7 March and instruments 87 expedition to be passable at low tide but dangerous, due zeroed at 0000 GMT the following morning, so official to large ice falls (Ledingham 1987). The 1987/88 expedition observations began on 9 March. Standard meteorological made several crossings at low tide (E.]. Woehler, pers. observations were made at 0000 GMT which was 0500 comm.). Such differences in opinion may be due more to local Heard Island time. the state of the tides than large-scale changes in the beach. Observations of coastal changes were obtained from A cursory examination of the coast of the northwestern end photographs, previous expedition reports and direct of Heard Island over a period of a month in early 1992 observations in 1990 and 1992/93. Surface water was showed no great differences from the situation documented collected from Stephenson Lagoon and from the sea off in 1987/88 by Kirkwood (1989a). Spit Bay in March 1993. Density values of these samples This paper is mainly concerned with the area of active were determined with an Anton Paar OJ\1A 55 density erosion along the coastline of Heard Island in an arc from meter, with salinity values calculated after Whitfield & Winston Lagoon on the southeastern coast around to the Jagner (1981). northeastern coast at Compton Lagoon. Changes to the glaciers themselves have been dealt with by Allison & Keage (1986). Loss of mass in a glacier will not have an 28 K Green • Sail Rock T l - 52°55'S " Shag Rock • DruryRock -I Red Island I Jacka Glacier HEARD ISLAND II A.N.A.R.E. STATION Corinthilm Bay / Compton Lagoon Brown Lagoon SlruaBeach Stepheruron Glacier Stephenson Lagoon Oil BII.11"eI Point Spit Bay Camp Elephant Spit Glacial Stream Paddick Valley Winston Lagoon o 5 10 Cape Lockyer IIIIIII_WJ Lambeth Bluff Kilometres 73"20'E 73°40'E L....-53_o1--L5IS_____ ---1I ____--'-I. ________ ~ ____L FIG.1 - Heard Island, showing places refirred to in the text. RESULTS AND DISCUSSION 7.8°C respectively (Bureau of Meteorology 1953). Both the average maximum and the average minimum air temperatures Sea Surface Temperature over the period covered by Ealey & Chittleborough (1956) were lower than at Spit Bay in 1992/93. Air temperatures at The Spit Bay site was not strictly comparable to that used by Spit Bay in 1992 fell to a minimum of -7.2°C, with Ealey & Chittleborough (1956) in 1949 (their station II), Stephenson Lagoon freezing to a depth of at least 0.5 m which was about 400 m offshore over 9 m of water in the through the winter. However, unlike the waters of Atlas comparative calm of Atlas Cove. Temperatures recorded at Cove in 1949, the calm saline waters of Compton Lagoon Spit Bay in 1992/93 were similar to those given for Antarctic did not freeze in winter 1992. Temperatures recorded from surface waters at the Antarctic Convergence in summer and the RSV Aurora Australis on 23 January 1992 were similar winter respectively (Deacon 1933). By contrast, Ealey & at Spit Bay at 1100 h (2.6°C) and at Atlas Cove at 1230 h Chitdeborough (1956) found that air temperatures lowered (3 .O°C). These factors together would indicate that, although the water temperature in 1949, with the effect being greater the two sites are not strictly comparable, the higher sea closer to shore. The relationship with conditions on shore, temperatures recorded in 1992 compared with those in which are dependent upon the surrounding Antarctic water 1949 may well be indicative of a general warming of the mass (Allison & Keage 1986), and how this relationship, in turn, affects the temperature of nearshore waters is difficult to unravel. However, the 3 .4°C recorded from the shore of Spit Bay on 8 March 1993 was similar to the 3.2°-3.4°C r~. Spit Bay 1992=931 L--<>- Atlas Cove ~~ recorded from the MV Icebird off Spit Bay on 11 and 12 March 1993. Sea temperature at Spit Bay dropped by about 2°C from April to late June 1992 and then fluctuated around 1°C throughout the winter (reaching a low ofOAoC on 19 October 1992) before rising from late November (fig. 2). Surface water temperatures recorded in Atlas Cove were generally lower in 1949 and fell to below zero, with sea ice recorded on two occasions (Ealey & Chittleborough 1956). The photograph in Ealey & Chittleborough (1956) showed that the ice was not just a skin on the water but quite robust pancake ice. Minimum temperatures at Adas Cove in 1949 for 8/9 July and 2/3 August (the days before and FIG. 2 - Sea surfoce temperature recorded at Spit Bay Camp during ice formation) were -8.9°/--8.9°C and --10.6°/- in 1992/93 and at Atlas Cove in 1949/50. Coastal studies at Heard lsland 1992193 29 l'ABLE 1 Monthly summary of C";UHJiV>:.',",,' data for Atlas Cove 1949--54 and Spit Bay 1992~93 -.-.----------------------~---.------------~--.---~-----.------------.- Month Mean Mean Range of Mean Mean Range of Lowest Lowest maximum maximum mean rnlnlInurn m1l11mUm mean ffil1111TIUlll ffillllIT1Urtl 1992/93 1949/50 maxima 1992193 1949/50 IUlnHnd 1992/93 1949-50 1949-54 1949-54 --- ~----.------------------- - _.----------------- -------------------_." Jan and Feb' 52 1.3 -0.5 March 6.5 5.3 3.7 to 5.8 0.8 1.2 0.6 to 2.0 -1.5 -1.9 April 7.0 4.9 2.9 to 5.4 1.3 0.6 0.6 to 1.3 -0.5 -3.3 .May 4.3 3.1 2.6 to 4.4 -0.4 -0.8 -0.8 to 0.9 -2.8 -5.5 June 4.4 0.7 0.6 to 2.7 -1.6 -3.8 -3.8 to -0.3 -4.5 -8_5 July 2.0 -0.5 -0.5 to 2.6 -2.3 -4.8 -4.8 to --0.8 -5.5 -9.1 August 2.0 0.4 0.4 to 2.7 -2.7 -3.8 --3.8 to-·1.0 -6.5 -10.6 September 4.9 0.1 0.1 to 1.8 -2.5 -4.6 -4.6 to-2.3 -7.2 -8.8 October 4.0 1.2 0.9 to 2.2 -2.4 -2.5 -2.5 to-1.1 -6.0 -7.3 November 6.8 1.4 1.4 to 3.3 -0.1 -1.7 -1.7 to 0.0 2.8 -3.5 December 6.7 (5.1) 3.6 3.6 to 4.4 1.1 (1.4) 0.::1 0.3 to 0.9 -0.8 --1.8 January 6.6 5.0 4.7 to 5.5 1.3 1.2 1.1 to 1.9 -0.5 0.1 February 9.8 4.7 4.6 to 6.0 1.7 1.3 1.3 to 2.4 -1.5 -0.8 Marchi 6.9 0.6 0.3 March to Feb 5.4 -0.5 -7.2 * 23 days only at Atlas Cove t Records taken for the first ten days of March 1993.
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