Tuatara: Volume 15, Issue 3, December 1967
Mummified Seal Carcases in a Deglaciated Region of South Victoria Land, Antarctica
Mummified Seal Carcases in a Deglaciated Region of South Victoria Land, Antarctica
* Dept. of Zoology, The Australian National University, Canberra A.C.T., Australia
** Dept. of Zoology, Victoria University of Wellington, New Zealand
THE PRESENCE OF mummified seal carcases in both glaciated and ice-free regions of McMurdo Sound was first reported by early British expeditions (Scott, 1905; Wilson, 1907). Dead crabeater seals (Lobodon carcinophagus) were found as much as 35 miles inland on the surface of a glacier more than 3000 feet above sea level. Similarly, Weddell seals (Leptonychotes weddellii) were found 20 miles inland at heights of 2400 feet (Wilson, 1907) and one Weddell seal was found at 5000 feet (Scott, 1905).
More recently Péwé, Rivard and Llano (1959), Bull (1959), Balham (1960), Caughley (1960), and Claridge (1961) have reported the presence of carcases inland in the McMurdo Sound region. Several Russian authors including Evteev and Arseniev (1960) have discussed the discovery of seal remains on the Scott Glacier and Bunger Hills on the Knox Coast and also 800 km. west of Mirny in the Larseman and Vestfold Hills.
During the summers of 1957-8, 1958-9 and 1959-60 three small expeditions from the Victoria University of Wellington, New Zealand, investigated about 2500 square miles of ice-free lowland valleys and mountain divides forming part of the deglaciated area lying to the west of McMurdo Sound. A variety of geological and geophysical studies were carried out by these exploratory parties (Bull (1959), Bull, McKelvey and Webb (1962), etc.). The ice-free terrain bounded on the north by the Miller, Cotton and Debenham Glaciers and in the south by the Taylor Glacier which was investigated by the Victoria University of Wellington parties was an area unknown to previous expeditions, although adjacent ice-free areas were visited by field parties from Scott's expeditions of 1901-4 and 1910-13, by Shackleton's expedition of 1907-9, and by numerous parties from more recent expeditions.
Bull, McKelvey and Webb (1962) have described the general area as follows:
* Dept. of Zoology, The Australian National University, Canberra A.C.T., Australia
** Dept. of Zoology, Victoria University of Wellington, New Zealand
The high ice plateau of eastern Antarctica … is bounded at approximately long. 16° E. by a coastal mountain chain extending from lat. 70° S. to 85° S. North of lat. 79° S. this chain lies within Victoria Land.
The greater part of Victoria Land is completely glacierized; major glaciers flow eastwards from the inland ice plateau through the coastal ranges to the Ross Sea. Extensive névé fields in the coastal ranges feed alpine glaciers which flow to join the main valley glaciers.
However, in the area between the Miller, Cotton, and Debenham Glaciers (lat. 77° S.) and the Taylor and Ferrar Glaciers (lat. 77° 45' S.), similar east-west trunk glaciers have retreated, leaving approximately 4000 km.2 of lowland valleys and separating ranges almost entirely free of ice …'
Westwards this ice-free area is bounded by the inland ice plateau, which rises from 6500-8000 feet to 9800 feet at long. 150° E. To the east for about 36 miles north of Cape Bernacchi the piedmont of the Victoria Land mountain range is covered by the Wilson Piedmont Glacier, which forms the coastal boundary of the ice-free area.
The mummified seals described here were found in the ice-free valleys lying between the Asgaard. Olympus, and St. John's Ranges which form units of the Victoria Land mountain chain. These ranges extend eastwards for 35 miles from the inland ice plateau, traversing the deglaciated region in an east-west direction, to meet the coastal plateau. The Wright Valley and the Victoria Valley System form the major valleys of this area and both have a general east-west trend, extending for 25-30 miles towards the inland ice plateau (Fig. 1).
The Wright Valley
Victoria Valley System
The Lower Victoria Valley is formed by the convergence of the Upper Victoria, Barwick and McKelvey Valleys and extends eastward to the Lower Victoria Glacier, a lobe of the Wilson Piedmont Glacier. The floors of these valleys are thickly covered with moraine deposits and are higher than the floor of the Wright Valley east of Dais. The ice-covered Lake Vida occupies the lowest point of the valley system, extending for about 3 miles at an altitude of approximately 1150 feet. The lake collects melt water from both the Upper and Lower Victoria Glaciers and from adjacent glaciated cirques.
The Victoria Valley system and the Wright Valley are connected by a high level pass, Bull Pass, with an entrance some 2000 feet above the adjacent floor of Wright Valley. The northern entrance of Bull Pass slopes gently to join McKelvey Valley, whose floor lies above that of the Wright Valley.
The Wilson Piedmont
The Wilson Piedmont blocks the entrances to the major ice-free valleys of the area and in the north merges with the Debenham Glacier. The piedmont glacier is from 3 to 10 miles wide and is almost 1000 feet thick east of the Wright Valley (Bull, 1959). The coastal edge of the Wilson Piedmont Glacier is fringed by a band of moraine deposits (about 2 miles wide) between Gneiss Point and Cape Bernacchi. For the greater part of its length the Wilson Piedmont has steep ice cliffs on the seaward side. However, access to the piedmont can be gained north of Gneiss Point and near Hogback to the south. The Wilson Piedmont Glacier rises steeply to about 1800 feet, then falls gradually to 1300 feet at the entrance to Wright Valley. The piedmont ice approaches to the Wright Valley are less severe than those of the Victoria Valley, for the Lower Victoria Glacier is steep, rough, and narrower than the Lower Wright Glacier, presenting a formidable barrier to access from the coast.
The seal carcasses described here were found by the various field parties of the Victoria University of Wellington Expeditions. A proportion of the carcases found were examined in detail during the summers of 1957-58 and 1958-59 by Barwick, and by Balham in 1957-58 and 1959-60 seasons.
The geographical location, altitude and situation of each seal carcase were recorded together with detailed biological observations. Routine photographs were made and samples for radiocarbon dating were collected from a number of carcases. The position page 169 of 121 carcases was plotted; 72 of these were studied in detail, the remaining 49 being noted by expedition members engaged in geological and geophysical surveys. Radiocarbon age determinations have since been made on two of these samples by the Institute of Nuclear Sciences, Lower Hutt, New Zealand.
Distribution of Seal Carcases
Seal carcases were found throughout the two valley systems, and were encountered by all field parties engaged in traverses. During the three summers of 1957-58, 1958-59 and 1959-60 the area was travelled by field parties who moved on foot along the valley floors, across the mountain ranges and to mountain summits within the area. The journeys of the various parties comprise about 1000 miles of unduplicated traverses through the region; since the light-coloured seal carcases can be seen for several hundred yards across the moraine-covered valley floors, it is likely that the seals recorded represent a high proportion of the more complete remains to be found in the area.
The majority of carcases were found in the lower parts of the valley floors: this was particularly true of the Wright Valley carcases. Two-thirds of the carcases examined in detail were pointing either up-valley or down-valley, while the remainder showed a random heading in relation to topography. The approximate position of each carcase found is indicated on the map (Fig. 1), which also shows the substrate of each site. Seal remains occurred on both moraine and basement-rock substrates representing all four glaciations distinguished by Bull, McKelvey and Webb (1962).
In general, overall distribution appears to be determined by topography, assuming that the seals migrated inland along the valley floors. The largest concentrations of seals were found in the North Fork of the Wright Valley, the floor of which lies more open to the main valley than that of the South Fork, which is blocked by moraine ridges. In the North Fork 35 seals were found, but only 3 were located in the South Fork. Most of the North Fork seals occurred in two groups (Figures 1 and 2, Group B; Group C). Group B consisted of 12 seal carcases lying within a 150-yard radius of a small saline pool in a large kettle-shaped depression about 150 feet deep. The steep sides would have provided easy entry for seals and the depression formed a natural trap. The second group of 14 seals (Group C) were scattered at the western end of the North Fork at the point where the valley floor joins the steep slopes at the end of the Labyrinth, which forms a natural barrier to the further progress of any seal.
One other concentration of seals was reported in the Wright Valley; a group of 19 seals was found by a geological party at page 170 the terminal snout of the western alpine glacier tongue which reaches the valley floor (Group A, Figures 1 and 2). No explanation for this concentration is offered since the authors had no opportunity to inspect this group. Another concentration of 7 seals was found in the notch formed by the steep sides of the ablating snout of the Lower Wright Glacier and an adjacent hillside. This gully-like formation formed a blind slot which apparently funnelled the animals into a trap.
In the Wright Valley the remains of 88 seals were found, but only 30 seals were located in the Victoria Valley. This difference possibly reflects the relative ease of access to each of the valleys from the coast across the Wilson Piedmont Glacier. The approaches to the Wright Valley are at a lower altitude and are less severe* than those of the Victoria Valley. In both cases the glaciers blocking their entrances have steep, dissected, ablating faces: seals could enter readily, but except at a few points a return would be extremely difficult.
Figure 2: The distance from the sea coast of seal remains, estimated to the nearest half mile, for the most direct route that could be followed by each migrating seal.
* This difference was ascertained by one of us (R.E.B.) during a foot-traverse of the Wilson Piedmont Glacier.
The maximum altitude at which seal remains were encountered was approximately 3000 feet, in the North Fork of the Wright Valley and on the western slopes of the Insel Range in the Victoria system 30 miles from the sea coast.
Condition of the Carcases
The condition of the remains of the 121 seals varied considerably. The climate, essentially desert-like, produces dessication and ultimate mummification; the mummified carcases become eroded and are eventually destroyed by wind-blown granitic sands which are aided by the effects of freeze and thaw and the prolonged periods of summer sun. Almost all of the seals examined were eroded on their exposed surfaces (Plate 1, Figure 1), but the surfaces which were not exposed generally retained a covering of hair (Plate 1, Figure 2), and many of the carcases had a distinct seal odour.
The remains found ranged from complete, uneroded carcases to weathered fragments of skin and bone only a few inches long. No signs of organic decay were found in the better-preserved carcases. Skua gulls (Catharacta antarctica lonnbergi) are occasionally seen in the valleys but only one carcase showed signs of damage by birds, and this was confined to removal of the exposed eye of the seal.
|(a)||Complete carcase. Undamaged by wind erosion, showing no signs of desiccation, ‘fresh’. (Only one animal was found in this condition).|
|(b)||Complete carcase with slight weathering, in the form of erosion of hair in patches, incipient cracking of skin, and bubbling of oils at the skin surface.|
|(c)||Complete carcase. Partial erosion of hair on all exposed surfaces, cracking of skin to expose deeper tissues and some erosion of skin to expose the bones of the flippers and the cranium.page 172|
|(d)||Incomplete carcase. Extensive erosion and exposure of the bones of the uppermost regions—skull, rib cage and fore and hind limbs, with the deeper soft tissues and bony parts visible. Skeleton undamaged, but the soft tissues eroded from between the bony elements.|
|(e)||Incomplete carcase. Very extensive erosion with regional destruction of bone as well as tissues, generally with the vertebral column completely exposed and 40 to 50 per cent of the soft tissue destroyed.|
|(f)||Incomplete carcase. More than 50 per cent of the carcase eroded. Vertebral column and cranium incomplete, destruction of limbs, remnants of the rib cage only. Usually such remains are insufficient to identify the species, sex or size.|
|(g)||Minimal remains consisting of miscellaneous fragments of seals, remote from all other remains.|
Figure 3 shows the number of seals placed in each of these groups and in subgroups intermediate to the more clearly defined erosion stages A to F. Group G, termed ‘minimal remains’ contain the miscellaneous fragments of seals found remote from other remains and considered to be those of seals destroyed by erosive processes.
Species could not be determined in many of the seals examined in detail since the carcases were considerably eroded. The species of 41 seals could be accurately determined, while identification of another 8 is uncertain. Of these 35 were identified as crabeater seals (Lobodon carcinophagus (Jaquinot and Pucheran)), and another 5 are probably of this species; 6 were found to be Weddell seals (Leptonychotes weddelli (Lesson)) and another 3 were tentatively identified as Weddells. Earlier reports also indicate that crabeater seals are the species commonly found in the dry valleys. Péwé, Rivard and Llano (1959) reported that all except one of the identifiable carcases were crabeaters, the exception being a leopard seal (Hydrurga leptonyx). Similarly Caughley (1960) notes that all 28 seals encountered in the Taylor Dry Valley were crabeaters.
Figure 1: Seal carcase in situ on glacial moraine, North Fork, Wright Valley (No. 30, Snout to tail tip: 64 inches). Fig. 2: Underside of seal (No. 30) showing hair remaining on surfaces protected from erosion. Fig. 3: Blood and sand clinging to the lower jaw of a ‘fresh’ carcase, North Fork, Wright Valley (seal No. 46). Note the patch of blood-soaked moraine gravel at lower right where the jaw formerly contacted the surface. Fig. 4: Numerous small sand-encrusted wounds on underside of the seal No. 46. Fig. 5: Carcase from Wright Valley: samples from this seal (No. 7) gave a radiocarbon ‘age’ of 100 years. Fig. 6: ‘Minimal remains’ (seal No. 36), North Fork, Wright Valley; radiocarbon ‘age’ 780 years.
The best preserved carcase was found in the north arm of the Wright Dry Valley some 39 miles from the coast. Before death the animal had bled profusely from the mouth and from wounds on the abdomen (Plate 1, Figure 3). This seal lay on a glacial moraine substratum and the blood-soaked sand beneath the mouth and abdomen suggested that it had died where it was found. On dissection the viscera was found to be suffused with blood and some bleeding had occurred into the abdominal cavity.
The fat layer beneath the skin at mid-abdomen was extremely thin (about 3/16 of an inch thick). Unfortunately the carcase could not be removed for detailed laboratory examination. Bertram (1940) notes that in summer the thickness of blubber over the adult body is 2 to 2 1/2 inches. Evidently there is depletion of blubber through starvation as the animal moves inland. In this animal the stomach was full of sand and gravel typical of the moraine beneath the carcase, and several older carcases were also found to have gravel-filled stomachs. The volume of moraine gravels in these these stomachs appeared to be greater than that noted in the stomachs of animals killed inshore during the summer (Bertram 1940, p. 80).
Several of the better-preserved carcases were scarred and cut in the mid-abdominal region (Plate 1, Figure 4), and there were minor longitudinal or transverse cuts about the anus and beneath the chin. Scars are not usually found on young crabeater seals (Lindsey 1938). There were apparently recent injuries, consistent with travel across rough moraine. Some of these wounds had bled, forming a congealed pad of blood, sand and gravel where the carcases lay on the moraine substratum; suggesting that the animals had also lain undisturbed since death.
Carcases were also found on a moraine-free basement rock in the valley floors; only two of these appeared to have been transported by water-action since death, and one other seal was found partly buried in moraine debris. All others were surface deposits, either on moraine or on basement rock foundations, with no indications that they had been transported since death.
Thus there is strong evidence that the seals have entered the valleys and travelled to their present locations over ice-free moraine.
Radiocarbon Dating of Carcases
Two radiocarbon ages were obtained from material collected in the dry valleys:
1. A sample from a complete carcase found near Lake Vanda (seal No. 7) gave an ‘age’ of 100 years (Plate 1, Figure 5 and Table 1).
Figure 3: Histogram showing numbers of each category of mummified seal remains according to the state of erosion of each carcase. The radiocarbon dates obtained for two carcases (Table 1) are shown in their respective categories.
|I.N.S. Specimen No.||Details||d13C w.r.t. PDB Ch. Lst. Std.||d14C Corr'd for Isot. Effect and Normalised||d14C An'ctic Std. Used||d Difference||14C ‘Age’|
|R. 809/1||Skin from Seal No. 7 Ross Dependency Wright Valley||0/00—24.8||0/00—153||0/00—140||0/00—13||100 yrs|
|R. 809/2||Skin from Seal No. 36 Wright Valley||—24.4*||—233||—140||—93||780 yrs|
|R. 809/3||Penguin Flesh Wright Valley||—24.4||—207||—140||—67||560 yrs|
|R. 536/1||McMurdo Surface Water, Mar. 1959||—0.4||—148|
Claridge (1961) observed some 20 carcases in the Taylor Dry Valley and suggested a rate of one every 100 years.
** In an attempt to obtain some meaning to the dating of Antarctic specimens, T. A. Rafter (pers. comm.) studied the 14C activity of modern penguin and fish flesh collected from McMurdo Sound in December, 1960. These specimens were depleted in 14C activity by approximately 1400/00 with respect to the modern standard used for the aging of terrestrial specimens. He also showed that McMurdo surface sea-water was—1480/00 depleted in 14C activity with respect to this same standard. For this reason it was felt that the only logical assumption to make on the 14C aging of Antarctic specimens was to refer to all ‘ages’ to an Antarctic modern standard of —1400/00 and not to the modern terrestrial standard which, if used, would give results approximately 1,200 too old. Using this assumption 14C results for our specimens are shown in Table 1. (See Rafter (1965) for terminology.)
In Table 1 the d13C values are reported as depletion in parts per thousand (0/00) with respect to PDB Chicago Limestone Standard; d14C values are reported as depletional also in 0/00, after correction for the 14C fractionation effect that takes place in the biological processes as discussed by Rafter (1965); the d14C Antarctic standard used is —1400/00 for which a difference for our Antarctic Specimens can be obtained and an approximate ‘14C Age’.
* Assumed value
In addition to seal remains, the remains of two Adelie penguins (Pygoscelis adeliae) were encountered: one in the South Fork of the Wright Valley, 40 miles from the sea-coast, and the second at the foot of the Lower Wright Glacier 10 miles inland. The South Fork penguin gave a radiocarbon ‘age’ of 560 years.
Crabeater seals pup in the early spring, September to October, well out in the pack-ice far from the coast. Bertram (1940) shows that there is good evidence for an inshore migration of the crabeater seals from the pack-ice to the clear waters about the coast in summer when the pups are 4 to 5 months old. The populations spend the summer months inshore and normally return to the pack ice in autumn. Some crabeater seals, however, have been observed to winter inshore in a similar fashion to the Weddell seal (Bertram). Bertram also notes that the stomachs of four crabeater seals shot inshore in early spring were empty and suggests that they had perhaps been forced to starve beneath the fast ice.
Caughley (1960) states that all 28 seals he examined in Taylor Dry Valley were less than mature size. He regarded the presence of dead seals as the result of the ‘quite normal dispersal’ of seals which were unfortunate enough to have their ‘noses pointed in the wrong direction at the beginning of their journey’.
We suggest that the presence of these crabeater carcases in the dry-valley systems might be the result of the following circumstances: some of the immature seals fail to join the general northward migration in autumn; the random dispersal of these non-oriented young combined with the directive effects of major land features, results in the entry of the seals into the dry valley systems. Death through starvation ensues, and since the seal carcases are not buried by snow or ice they mummify. Thus a proportion of the randomly-dispersed immature animals that have failed to emigrate to pack ice in autumn are preserved to view in the ice-free valleys.
† With regard to the Lamont contemporary wool standard.
|1.||The locations of 121 mummified seal carcases encountered in ice-free Victoria and Wright Valleys of South Victoria Land are described. Seal remains were found up to 40 miles inland and at a maximum altitude of 3000 ft.|
|2.||Seventy-two seals were examined in detail; of these 35 were identified with certainty as crabeaters (Lobodon carcinophagus) and 6 as Weddell seals (Leptonychotes weddelli).|
|3.||The condition of the seals varied from ‘minimal’, represented by small pieces of skin and bone, to one relatively fresh carcase.|
|4.||Samples from two seal carcases gave radiocarbon ‘ages’ of 780 years and 100 years.|
|5.||An average rate of entry into the valley system of one seal every 4-8 years has been calculated using the condition of the seal remains in relation to the radiocarbon ‘ages’ obtained.|
|6.||All the carcases measured were those of immature animals, apparently less than one year old. It is suggested that the mummified remains represent disorientated young that fail to return to the pack-ice at the onset of winter. Some of these seals enter the dry-valley region to die of starvation, and to be preserved to view.|
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