MASS BUDGETS : REGIONAL STUDIES 429

MCLAREN, W. A. 1968. A study of the local ice cap near Wilkes, Antarctica.AN ARE Scientific Report No. 103. Melbourne. Antarctic Division, Depart-ment of Supply.

MÄLZER, H. 1964. Das Nivellement über das Grönländische Inlandeis. EG1G1957-1960, Vol. 3, No. 1. Kebenhavn.

MORGAN, P. J. (Unpublished). Photogrammetric and geophysical methods ofdetermining the mass budget of an ice cap. M.Sc. thesis presented to Depart-ment of Meteorology, University of Melbourne.

OESCHGER, H., ALDER, B., LOOSLI, H. and LANGWAY, C. C. 1966. Radiocarbondating of ice. Earth and Planetry Science Vol. 1, 2, p. 49-54.

PFITZNER, L. (Unpublished). Wilkes ice cap project 1966. ANARE ResearchReport, Antarctic Division, Department of Supply (in preparation).

RADOK, U., JENSSEN, M J. D. and BUDD, W. F. 1969. Steady state temperatureprofiles in ice sheets. JSAGE Symposium.

ROBINSON, E. S. 1966. On the relation of ice surface topography to bed topographyon the South Polar Plateau. / . Glaciol., Vol. 6, No. 43, p. 43-54.

SHUMSKY, P. A. 1963. On the therory of glacier variations. WGG-IASH BulletinVIII, Année No. 1, p. 43-56.

WALKER, D. J. 1966. Wilkes geophysical surveys, Antarctica 1962. Record1966/129. Canberra. Bureau of Mineral Resources Geology and Geophysics,Dept. National Development.

The mass balance of a cold glacier: Meserve Glacier, southVictoria Land, Antarctica*

BY

C. BULL and C. R. CARNEINInstitute of Polar Studies and Department of Geology,

The Ohio State University, Columbus, Ohio 43210

ABSTRACT

The mass balance of Meserve Glacier, on the south side of WrightValley, Antarctica, is nearly in equilibrium. During the year November1965-November 1966, the 9-9 km2 glacier lost 60 X 106 kg of ice, equiva-lent of 0-61 g cm"2 over the whole glacier. In that year the snow accumu-lation was less than usual; in "normal" years the balance may be slightlypositive. On the 1 -8 km2 ablation tongue of the glacier the annual lossranges up to about 34 g cm"2, near the snout at 440 m elevation. Of thisamount, 40 per cent occurs during the cold months from mid-Februaryto mid-November. During the summer, a small amount of melting occurson the 15 m-high cliffs around the glacier tongue, and around the marginsof the glacier's upper surface, but only 2 or 3 per cent of the total loss is bymeltwater runoff. Dry calving from the cliffs, which are approximatelyin equilibrium, amounts to about 1-5 per cent of the total mass loss fromthe glacier. Evaporation from a melting surface may account for 40per cent of the total loss. The remaining loss is by sublimation.

•Contribution No. 124 of the Institute of Polar Studies, The Ohio State University,Columbus, Ohio 43210

430 ISAGE

FIG. 1. Map of Wright Valley area of south Victoria Land, Antarctica, simplifiedfrom New Zealand Antarctica 1:250,000 Reconnaissance Series, Ross Island andTaylor Glacier Sheets.

MASS BUDGETS : REGIONAL STUDIES 431

Introduction

Meserve Glacier (77°35'S, 162°23'E) is one of a series of small glacierson the south side of Wright Valley, south Victoria Land, Antarctica (Fig.1). It is about 7-2 km long, with a total area of 9-9 km2. The accumula-tion zone (area 8-1 km2) is a basin in the Asgard Range, between 1200and 1500 m elevation. The general balance line is in a crevassed area atabout 1130 m, on the shoulder of Asgard Range, and from here the glacierextends in a relatively uncrevassed tongue (area 1-8 km2), about 600 m

CONTOUR NTtP\W- 50 MFrtRS

VELOCITY VECTOR

A CONTROL POINT

- < PHOTO CONTROL POINTCREVA3SC5

FIG. 2. Provisional map of Meserve Glacier, Wright Valley, Antarctica. Eleva-tions and contours shown are probably all 38 m too high.

432 ISAGE

wide, for 2 km down the valley wall, which slopes about 12°, to theterminus at 440 m (Figs. 2 and 3).

& %? mmmFIG. 3. Oblique aerial photograph of Meservc Glacier. Photograph by U.S.Navy for U.S. Geological Survey.

The glacier terminates in a 20-m cliff which extends, with decreasingheight, for 1200 and 2400 m along the east and west sides of the tongue,respectively. The surface of the tongue, along transverse lines, rises about40 m from the cliff edge to the centreline. Gravity measurements indicateice thicknesses of 40 to 60 m, with maximum values of 80 m, in each offour transverse profiles, the bed remaining at almost the same elevation.In one profile in the accumulation zone, the glacier is much thicker(350 m) on the eastern side than on the west, and it does occupy a signifi-cant depression.

Meserve Glacier has been the site for glaciological investigations,including the flow law of cold ice (Holdsworth and Bull, 1970), and themechanisms of formation of transverse crevasses (Holdsworth, 1969).

MASS BUDGETS : REGIONAL STUDIES 433

Investigations are being made (Everett and Behling, 1969) of the chemicaland physical weathering characteristics of the prominent lateral morainesaround the tongue in an attempt to obtain reliable indices of the relativeages of these and other glacial deposits in the ice-free areas of southVictoria Land.

A necessary part of these studies is the assessment of the mass balanceof Meserve Glacier. Field investigations were carried out during the1965-66 and 1966-67 Antarctic field seasons. A detailed report on partsof the analysis is given by Carnein (1967).

Measurement of mass balance parameters

Climate of the area

Temperatures. The mean annual air temperature at valley floor level(250 m) is about — 16°C. In boreholes in Meserve Glacier at 480 melevation the temperature below 8 m averages — 18°C (Holdsworth andBull, 1970).

During the two summers, air temperatures were recorded at two sites,one, Moraine Station, on a flat part of the moraine 50 m east of the icecliff, at about 450 m elevation, the other, Glacier Station, on the glaciersurface, 90 m west of the moraine site, at 490 m elevation. About half ofthe temperature difference, 1°C, between these two stations is due to theelevation difference. The 1965-66 temperature data are summarized inTable 1.

TABLE 1MONTHLY MEAN AND EXTREME TEMPERATURES (°C), SUMMER 1965-66, MESERVEGLACIER. THE FIRST NUMBER IN EACH PAIR REFERS TO MORAINE STATION; THE

SECOND TO GLACIER STATION

. Nov. 1965I (11-30 Nov.) Jan. 1966

Feb. 1966(1-13 Feb.)

Mean monthlyMean maximumMean minimumAbsolute maximumAbsolute minimum

—4-9, —5-8—0-9, —2-3—7-5, —8-3+ 1-5, -fl-5

—11-4, —12-2

—61, —6-7—2-2, —2-6—8-5, —9-2—0-3, —11

—12-7, —13-3

The minimum temperature during the 1966 winter at the MoraineStation was —40-5°C. During the summer, the temperatures in theice-free valleys average about 0°C, the daily maxima occasionally reach7 or 8°C, and a maximum of 12-3°C has been recorded (Bull, 1966). Inthese conditions, some melting occurs on the lower parts of glaciers,including Meserve Glacier and especially on the low-lying Wright Lowerand Wilson Piedmont Glaciers, from which the Onyx River flows inlandto Lake Vanda.

Precipitation and winds. In Wright Valley the precipitation decreaseswestward: probably the annual precipitation does not exceed 5 g cm~2

434 ISAGE

of water (all falling as snow) except on Wilson Piedmont Glacier. Almostall of the snowfall is associated with moist easterly winds from theMcMurdo Sound area. During summer 1965-66 snow fell at MeserveGlacier on 8 out of 91 days, totalling about 1-2 g cm-2.

The direction of surface winds in Wright Valley is controlled to a largeextent by the topography. At Meserve Glacier site summer winds arepredominantly from the north-east. The frequencies are given in Table 2.

TABLE 2FREQUENCIES OF SURFACE WINDS AT MESERVE GLACIER FROM 6-HOURLY READINGS.THE FIRST NUMBER IN EACH PAIR REFERS TO MORAINE STATION (21 NOVEMBER 1965-13 FEBRUARY 1966); THE SECOND TO GLACIER STATION (25 NOVEMBER 1965-13

FEBRUARY 1966)

Speedm sec"1

0-12-34-56-78-9

10-1213 +Total0/

/o

N

1,46, 12 , -] —3 —

13,54 ,1

NE

4 ,830,1530,2842,33

103, 846, 10

10,37225,21567,66

E

1 , -1 , -—, —— _

— —

2,01,0

SE

6,712, 1916,152, 11,3— —1,3

38,4811,15

S

3,39,82 , -

4 , 2

2 , -20,136,4

SW

6,813,1610,82 , 2-, 1

31,359,11

W

211

-

41

-2

_.

21

NW

4,5j _-, 1—;_

_ ' _5,62,2

Total

27,3573,5961, 5447,36

111,906,10

13,40338, 324

%

8,1121,1818,1714,1133,282 ,34,12——

During the summer, the differences in frequencies of winds from differ-ent directions from month to month are not significant. The north-easterly winds usually decrease during the late evening; light south-westerly winds often blow between 0200 and 0900. At Lake Vanda,15 km west of Meserve Glacier, easterly winds occur about two-thirds ofthe time, and westerlies for the remainder (Bull, 1966). The westerlywinds are partly katabatic from the Antarctic ice sheet, warmed andreduced in relative humidity in their descent into Wright Valley. Theyare thin and frequently do not blow as far along the valley as MeserveGlacier. Strong westerly winds are probably much more common duringthe winter (Bull, 1966).

Clouds and radiation. During the summer, low-level clouds, associatedwith the easterly and north-easterly winds, decrease in amount westwardalong Wright Valley. High-level clouds (cumulus and cirrus) usuallycome from the west and south-west. Cloud amounts at Meserve Glacierfor summer 1965-66 are given in Table 3. Except for February, they aresimilar to those recorded at Lake Vanda in 1958-59.

From the cloud amounts in 1958-59, compared with those at theneighbouring Scott Base, where radiation measurements have been made,the radiation balance for the ice-free parts of Wright Valley has beenestimated as a gain between 6000 and 29,000 cal cm-2 yr"1 (Bull, 1966).During the 1965-66 season measurements were made of the incoming

MASS BUDGETS : REGIONAL STUDIES 435

TABLE 3MEAN CLOUD AMOUNTS (IN PER CENT) AT MORAINE STATION, MESERVE GLACIER,

Month

11-30 November1-31 December1-31 January5-13 February

SUMMER 1965-66

Time

0700

60474385

1300

58524486

1900

64545695

Meantotal clouds

61514889

Estimatedlow cloud

35242470

3 C 13 20 25 -SO ( i 3 C

ß 15 20 23 50,1 5 C S 20 a » , l 3 I Û I S 2 O 2 3 M 1 3 10

s o 2 0 n x , i j " ' • « > • • " ô ' ' • • » " " ' » •

MESEftVE GLACIER ANTARCTICAI •-— 6AS£ ST*TOJ I

20 13 30

HUMCITY

» Xi«63 I

FIG. 4. Meteorological parameters at Base (Moraine) and Glacier Stations,Meserve Glacier, November 1965-February 1966.

436 ISAGE

short-wave radiation. Outgoing long-wave radiation has been calculatedby the methods of Ambach (1960), assuming values for the constantsobtained by Andrews (1964) and Keeler (1964) at comparable latitudes inthe northern hemisphere. The net flux of radiation on the glacier isplotted, with other weather parameters, in Fig. 4.

Stake measurements of ablation and accumulation

Twenty-five stakes in four lines across the ablation area, between 470and 607 m elevation (Fig. 2), were measured weekly from late November1965 to 13 February 1966. A denser line of stakes covered the 60 mclosest to the eastern edge, over the tunnel excavated along the glacierbase (Holdsworth and Bull, 1969); others were implanted in the cliff nearthe tunnel entrance. Most of the stakes were also measured during the1966-67 summer.

Twenty stakes in the accumulation area (Fig. 2) were measured on 4and 17 December 1965 and 29 January 1966. Seventeen of them wereremeasured on 29 November 1966.

These stakes are not well distributed for accurate assessment of the massbalance, but the glacier shape is so simple that the necessary extrapolationsshould not introduce large errors.

In the ablation zone, very little surface snow was present at the beginningof either field season. Most of the small winter snow accumulation isremoved immediately by the strong winds. Table 4 gives the surfacelowering at the stakes on the tongue. Those concentrated at the easternedge are considered later. An ice density of 0-88 g cm"3, measured atseveral surface sites, is assumed throughout.

Table 4 shows that nearly 40 per cent of the annual loss occurred duringthe winter, from mid-February to mid-November. Ablation is largestclose to the glacier edges: for the three stakes in each line nearest theglacier centreline, the summer lowering is 88 per cent of the mean at allstakes, and for the whole year is 90 per cent of the overall mean.

The ablation rates on Meserve Glacier, about 1-4 g cm"2* per weekduring the summer, at air temperatures averaging — 5°C, may be comparedwith others in Antarctica. On a blue-ice lobe of Reedy Glacier (86°S,126°W), exposed to strong, dry winds, Mercer (1968,a) measured sublima-tion rates of about 0-7 g cm~2 per week with air temperatures averaging—20°C. Much lower rates are found on blue-ice fields in Dronning MaudLand (72°S, 3°W) (Schytt, 1961) and in the Ser Rondane mountains (72°S,25°E) (Autenboer, 1964), despite much higher summer temperatures thanin the Reedy Glacier area. Strong dry winds are much more importantthan "high" temperatures in producing sublimation at sub-zero tempera-tures.

* All budget values given in water equivalent.

MASS BUDGETS : REGIONAL STUDIES 437

TABLE 4SURFACE LOWERING OF STAKES DISTRIBUTED OVER THE GLACIER TONGUE

Stake

G 111-2101-31-4

G 212-22-3202-42-52-6

G 3 13-23-3303-43-53-6

G 414-2404-34-44-5

Mean

Elevationm

583595607598591

536544561579565557542

501506525544531525517

475489509497485471

—

from edge(E or W )

m

45 E143 E242 E211 W118 W

10 E40 E139 E238 E224 W106 W55 W

16 E35 E133 E230 E228 W130 W62 W

16 E108 E198 E196 W99 W33 W

Surface lowering (g cm"2)

27 Nov. 65to

13 Feb. 66

— 150—17-2—8-7—7-3—141

—32-3—150— 150—11-3—11-4— 110—16 2

—20-9—191— 15-4—9-6—13-3—15 4—14-7

—21-8—20 5—16 2—15 9— 11-7—14-3

—15-3

13 Feb. 66 27 Nov. 65to to

21 Nov. 66 21 Nov. 66

—11-3 —26-3—8-2 —25-4—6-2 —149—6-4 ; —13-7—11-0 —25-1

—5-8 —381—8-9 —23-9—8-6 —23-6—5-7 —17-0—8-7 i —201—8-7 —19-7—16 8

—10 I—8-8

—330

—310—27-9

— 11-6 —270—11-3 —20-9—10-5 —23-8—9-9 ; —25-3— 106 —25-3

—13-7 —35-5—9-9 —30-4—11-7 —27-9— 10-4 i —26-3—9-3 —210— 110

—9-9

—25-3

—25-2

The observed variation of surface lowering with elevation has beenextrapolated to cover the entire ablation zone. Average annual loweringnear the terminus, at 460 m elevation, is about 34 g cm"2, and is zero atthe general balance line at 1130 m. The negative balance of the surfaceof the tongue totals 216-7 x 106 kg.

Attempts to measure the ablation (not including dry calving) on the icecliffs have not been very successful. Only four markers on the easterncliff were maintained for the entire 12-month period, November 1965-November 1966. The annual losses are given in Table 5, where they arecompared with those on the upper surface nearby.

The annual negative balance on the eastern cliff here is thus about 1-6times that near the centreline. Assuming this same ratio holds all roundthe tongue, the annual loss by ablation from the cliff, not including drycalving, is about 9-5 X 106 kg.

438 ISAGE

TABLE 5ABLATION AT MARKERS ON AND NEAR THE EASTERN CLIFF, MESERVE GLACIER,

27 NOVEMBER 1965-21 NOVEMBER 1966

Marker

DlD2CS1CS2

TS1TS3TS5TS6G4-0

Position

2 m above base of cliff2 m above base of cliff12 m above base of cliff14 m above base of cliff

On surface, 5 m from cliff edgeOn surface, 25 m from cliff edgeOn surface, 45 m from cliff edgeOn surface, 55 m from cliff edgeOn surface, 198 m from cliff edge

Elevationin m

~460~460

472-5474-5

475-2481-64870487-8508-9

Surface loweringg cm~2

44-1140-9 I Mean52-4 f 45-143-1J

31040-832-631-227-9

In the névé basin during the period 4 December 1965-29 January 1966,surface lowering occurred at all stakes in the A' and B lines (elevationsbelow 1350 m) except at A'l and B4. On the two higher traverses, C andD lines, summer accumulation occurred, except at the east side of the Cline. Over the year to December 1966 positive balance was recorded atonly 7 of the 16 stakes. Apart from B2 and C2, all stakes on the east sideof the basin showed accumulation; the central stakes showed ablation;on the west side, four stakes showed negative and three showed positivebalance (Table 6).

About 1-2 km2 of the glacier above the general balance line showednegative balance for the year; the remaining 6-9 km2 showed a positivebalance. The year 1965-66, however, was probably not a "normal"year, the accumulation being much less than in the preceding years, asshown by the pit studies described below. Normally ablation exceedsaccumulation only in the three small areas marked A in Fig. 2.

The accumulation pattern in the névé basin is largely controlled bystrong westerly winds in winter, which cause deflation in the western halfand redeposition on the eastern half of the basin. The snowfall is so smallthat a single storm can cause large local areal variability of accumulation.For example, in one storm, on 6 December 1965, when southerly windsof more than 16 m sec"1 were recorded at Moraine Station, 14-8 g cm"2

was lost at stake C and more than 4-4 g cm"2 at four other stakes on theeastern ends of B and C lines.

Snow pit studiesDuring the 1965-66 summer, snow stratigraphy studies were made in

seven pits in the névé basin. Because the snowfall in the area is so smalland so greatly reworked by strong winds, no reliable criteria could bedeveloped for distinguishing annual units.

In each of five of the pits (near stakes A, A', C, B and B2) a prominent,12 cm-thick, fine-grained layer, probably wind slab, occurs at depths

MASS BUDGETS : REGIONAL STUDIES 439

between 80 and 120 cm. In these profiles loads above the slab are 35-0,33-5, 41-0, 33-5, and 34-0 g cm-2, so that if the slab were formed simultane-ously at these five sites, the average accumulation since then has beenareally uniform. Three of these sites showed loss during the 1965-66year ranging from 0-2 to 9-5 g cm"2; for the other two, data are notavailable.

TABLE 6CHANGES IN SNOW SURFACE LEVEL AT STAKES IN NÉVÉ BASIN, MESERVE GLACIER,

1965-66

Stake

A'lA'2A'A'3A'4

BlB2BB3B4

ClC2CC3C4

DlD2DD3

Elevation*m

12521227121712071202

12921273126312521247

13421332132213021292

1402137313621342

4 December 1965-29 January 1966

g cm"2

+ 0-4—0-9—

0—11

—6-3—6-7

0—0-7+ 1-1

— 2 0—6-8

—14-8+ 0-4+ 1-9

+ 0-4+ 3-0+ 2-2+ 0-7

December 1965-December 1966

g cm"2

-f 10-8+ 1-1—0-2—0-4+ 3-2

+ 9-2+ 9-5

—5 0+ 3-7

—3-6—2-6—2-2—1-1

+ 70+ 3-1

+ 2-0

* Elevations are approximate, pending corrections to preliminary surveycalculations.

In some of the profiles alternations of density are discernible. Ifsuccessive dense layers mark annual layers, the accumulation at B insome recent year was 17 g o r r 2 . It is noteworthy that in pits dug in areasshowing surface lowering in 1965-66 (B2 and C), no ice or high densitysnow layer was found to depths of 2 m. Attempts to determine theannual accumulation from the increase with depth of the grain size, usingdata from Little America (Vickers, 1966) and the McMurdo-South Poletraverse (Giovinetto, 1963) suggest that in the accumulation zone thepositive balance normally averages between 3 and 7 g cm"2 yr"1.

For the year 1965-66, an average gain of 3-0 g cm-2 is estimated forthe 6-9 km2 area of the névé basin showing positive balance. In the 1-2km2 showing negative balance the average loss was about 3-1 g cm"2.

440 ISAGE

Dry calving

Dry calving from the cliff occurs all around the ablation tongue,forming an apron of broken ice, averaging 2 m thick and extending 12mfrom the cliff. The total mass of ice in this apron is about 30-0 x 106 kg,almost all avalanche debris.

For the 12-month period January 1966-January 1967, the total naturalcalving along the western and eastern cliffs were 1-06 x 10G kg, and2-11 x 106 kg, respectively. In November 1966, 0-47 X 106 kg wasblasted from the eastern cliff, above the tunnel entrance. As this materialwould probably have calved naturally during the summer, it is includedin the annual mass lost by calving, 3-64 x 106 kg.

TABLE 7MASS BALANCE OF MESERVE GLACIER, NOVEMBER 1965-NOVEMBER 1966

I Mass x 10" kg

Negative balance of surface below general balance line ; 216-8Negative balance of cliff, excluding dry calving : 9-5Dry calving from cliff : 3-6Negative balance in névé basin (1-2 km2)

Total lossesPositive balance in névé basin (6-9 km2)

For whole glacier, loss

37-2267-12070

601

This is equivalent to an average loss of 0-61 g cm"1 over the whole glacier area.

Estimate of mass balance

For the year 1965-66 the quantities in the mass balance equation aregiven in Table 7.

In "normal" years the positive balance in the névé basin is probablybetween 3 and 7 g cm-2. Assuming that the 1965-66 loss on the tongue,230 X 106 kg, also applies to that "normal" year, the glacier would have apositive balance between 13 and 237 x 106 kg, with the smaller figurebeing the more likely. As the total mass of the glacier is about 1-5 X 1010

kg, none of these estimated values of the mass balance represents a signi-ficant departure from equilibrium.

Consideration of some of the mechanisms of ablationMelting

On clear summer days, even when air temperatures are as low as —7°C,some melting does occur on the glacier surface, the ice cliff and the apron,forming meltwater streams on both sides of the glacier.

The total runoff in the stream near the tunnel entrance, for the period14 November 1965-13 February 1966, was about 60,000 m3 (Carnein,1967). Most of this flow was due to melting of the relatively dirtyavalanche debris apron. On one day the total runoff over the easterncliff, measured directly, was 60 to 100 m3, only 4 per cent of the runoff in

MASS BUDGETS." REGIONAL STUDIES 441

the stream near the tunnel entrance. The total whole summer runofffrom the east side of the glacier surface was about 2400 m3, giving anaverage loss of about 4 g cm-2 over the ice cliff and the 100 m-wide stripat the edge of the glacier, below about 700 m elevation, where melting wasobserved. Meltwater thus constitutes only 2 or 3 per cent of the mass lostfrom the glacier tongue.

Evaporation and sublimation

At Glacier Station measurements were made during the summer of airtemperature, relative humidity and wind velocity and direction at oneheight, 170 cm. The evaporation that would occur, assuming an ice-surface temperature = 0°C, vapour pressure = 6-11 mbar and windvelocity = 0, has been estimated, using the formulae of Lister and Taylor(1961) and Keeler (1964). For three representative two-day periods inearly, middle and late summer, evaporations were calculated from meanhourly values of the parameters; for the rest of the summer, evaporationrates have so far been calculated only from mean daily values. Thecalculated evaporation for the summer is 8-36 g cm"2, 50 per cent of themeasured loss of 16-4 g cm"2 at five stakes about 5 m from the meteoro-logical station. Here the meltwater runoff is about 3-3 g cm"2, 20 percent of the total summer loss. The remaining 30 per cent is unexplainedat present.

From 13 February to 21 November 1966 the loss at these five stakesaveraged 12-8 g cm"2. A very small part of this loss may have been byevaporation after 13 February, but most of it is due to sublimation causedby the strong, dry, westerly winds.

The stability of the ice cliff

Along 450 m of the eastern margin between the G4 and Gl lines, theice flow over the line of the cliff has been calculated, assuming that thevariation of velocity with depth is everywhere of the same form as inborehole Ml, close to stake Gl (Holdsworth and Bull, 1969), and that thevelocity at depth is in the same direction as at the surface.

The balance for the 450 m-long cliff section is as follows:Throughflow of ice past line of cliff = 2-84 x 106 kgLoss of ice by dry-calving = 0-97 x 106 kgLoss of ice by other ablation =2-14 x 106 kg

Net loss = 0-27 x 106 kgThis loss, if real, would produce an annual cliff retreat of about 4-9 cm,

comparable with the errors in the various estimates. It can be said onlythat the cliff is approximately in equilibrium.

The stability of the glacier surface

The equilibrium state of the glacier may also be assessed from the massbalance of a section of the ablation zone. The annual flow of ice through.

03-054-448-636-00-83-0

39-84-0

XXXXXXXX

109

109

109

106

106

106

106

106

cmcmcmkgkgkgkgkg

3

3

s = 43-8 x

yr-i

442 1SAGE

the glacier sections along the G2 and G4 lines has been calculated fromthe components of the surface velocities perpendicular to the lines,multiplied by the ice thickness and a factor between 0-83 and 0-92. Thisfactor is obtained by extrapolating over a small range of depths the ratioof the throughflow to the surface velocity times depth, in holes Ml and M2(Fig. 2), where the ice thicknesses are 22-9 and 34-8 m, and the values ofthis factor are 0-83 and 0-86, respectively. The throughflow (cm3 cm"1

yr"1) at each of the movement stakes was plotted against position, and thetotal throughflow for the two sections was calculated by a graphicalmethod.

Similarly the surface lowerings at the stakes in the G2, G3 and G4 lineswere used to estimate the mass loss from the glacier between the G2 andG4 lines.

The values obtained for the one-year period are as follows:Ice flowing through G2 section = 103-0Ice flowing through G4 section =

Difference = 48-6 X 109 cm3 = 43-8 x 10« kgNegative balance, top surface =Dry calving, cliff =Other ablation, cliff =

Total losses =Overall gain =

Over the 14-6 x 108 cm2 area, this gain is equivalent to an annualincrease in surface elevation of 3-1 cm, about the same as errors in theestimates of surface lowering and cliff loss. Again it may be concludedonly that this part of the glacier is approximately in equilibrium.

DiscussionThe examination of the mass balance for the entire glacier, the stability

of the cliffs and of the surface elevation of the tongue, all indicate that theMeserve Glacier is very nearly in equilibrium, at least for this very limitedperiod of observation. With such a glacier, on which the accumulationis so low, however, small changes in the accumulation or ablation canproduce very large changes in the glacier. An increase of only 3 g cm"2

yr - 1 in the mean accumulation in the névé basin, with unchanged ablation,would, if maintained for several hundred years, extend the tongue about0-7 km downslope and laterally to a position between the innermost andmiddle prominent lateral moraines shown in Fig. 3.

Similarly, a reduction in the accumulation by 2 g cm"2 yr"1 could causethe tongue to retreat 1 km, leaving only a short tongue, as now occurs inthe unnamed glacier, 4 km west of Meserve Glacier. Farther west, theglaciers, all originating in basins similar to that of Meserve Glacier,become progressively smaller, and near the head of the Wright Valley,25 to 40 km west of Meserve Glacier, the cirques are almost empty (Bullet ai, 1962). Measurements of annual accumulation in other névé basinsalong Asgard Range would be very valuable. At present the only

MASS BUDGETS : REGIONAL STUDIES 4 4 3

measurements from the area are those on Meserve Glacier, values of &and 6 g cm"2 yr - 1 on Wilson Piedmont Glacier, within 12 km of the coast(Bull, 1966), and 5 to 7 g cm-2 at 800 to 1000 m elevation on PackardGlacier, Victoria Valley, 30 km from the coast (Calkin, 1963; reported;in Bull, 1966). On the névé basins of Commonwealth and CanadaGlaciers, which flow south from Asgard Range into Taylor Valley, 12and 20 km from the coast respectively, Henderson et al. (1966) estimatemean positive balances of about 2-8 nd 4-6 g cm~2 yr"1, assuming thatthe glaciers are in equilibrium.

The near-equilibrium state of Meserve Glacier does not permit anyprofitable calculation of the rate of lateral recession of the tongue, or ofthe age of the innermost of the lateral moraines, on which Everett andBehling (1969) have been studying chemical and physical weathering. Inthese moraines, in the ice-cemented debris under Meserve Glacier, and inmost of the surface deposits in the ice-free regions, are accumulations ofsalts, many of them soluble. The possible origin of these salts includetrapped sea water, hot-spring activity associated with the volcanism,leaching of evaporite beds in sedimentary rocks, wind-transported marinesalts, and chemical weathering of local bedrock and soil. Jones and Faure(1967) find that although the Sr87:Sr88 ratio in surface snow of MeserveGlacier is nearly identical with that of Ross Sea water, the ratio for waterfrom Onyx River and Lake Vanda and for valley soils is similar to thatof the major bedrock units. They conclude that as no local evaporitebeds have been found, the strontium in Lake Vanda has been derivedlargely by chemical weathering of bedrock.

The time of formation of the salts by chemical weathering is still un-certain. Everett and Behling (1969) argue that the salts in the morainesaround Meserve Glacier are being formed, in situ, by chemical andphysical weathering. Although meltwater does leach some of the salts,they believe that the salt concentrations can be used at least to indicaterelative age. On the other hand, Faure (oral communication) considersit more likely that the salts are a relict feature of a former warmer and morehumid environment, perhaps in the Tertiary. Part of his argument isbased on the high salt concentrations in the till and in the basal ice exposedin the tunnel under Meserve Glacier (Holdsworth and Bull, 1969). How-ever, the glacier could advance 400 m (the distance from the tunnel to thesnout) very quickly, by a slight change in the annual accumulation. Theprocess of advance, by increasing amounts of dry-calving until the calvedmaterial becomes incorporated into the moving glacier, need not destroyor rework the debris and salts exposed on the surface beyond the end ofthe former glacier.

On the other hand, the ice-free areas of south Victoria Land wereformerly wetter (and therefore probably warmer). For example, Calkin(1964) in Victoria Valley and Bull Pass found many inactive mud-flows,and solifluction lobes much larger than the few now active. One of these;large flows overrode algae that give a radiocarbon age of 9700 years.

444 ISAGE

Everett and Behling's conclusions are supported by Jones (unpublishedstudies). High on the west side of Meserve Glacier the morainal materialis mainly basalt. The Sr87 : Sr86 ratio of the water-soluble salts in the soilshere is about 0-707, indicating the salts are derived largely from the basalts.At lower elevations, where the moraine contains more debris of meta-sedimentary and granitic rocks, the Sr87:Sr86 ratio in the salts increases,reflecting the composition of the moraine, and suggesting that the saltshave formed since the moraines were deposited. At present, however, noreliable method exists of dating the moraines.

It is difficult to explain the size of the lateral moraines of MeserveGlacier: the basal ice layers contain very little debris (Holdsworth andBull, 1969), and, the ice at the contact is not moving, so that little erosionis now taking place. No significant morainal deposits are found immedi-ately adjacent to the cliff although there are small glacier-ice cored"incipient moraines" adjacent to the glacier at the lower end of the accum-ulation zone. The debris is probably being carried to the glacier edgealong discrete planes in the basal ice (Behling, oral communication).

For significant amounts of erosion to occur, the temperature at theglacier bed must be close to the melting point, which, due to the saltcontent, may be below 0°C. For this to occur, however, either the glacierthickness must increase by more than 600 m (assuming an average valuefor geothermal heat flow), or the mean annual air temperature must increaseby about 10°C, or by a combination of these factors. When the outermostmoraines formed, the glacier tongue could have been three times as thickas now, an increase of 200 m. Mercer (1968a) has evidence, from lakesediments and solifluction near Reedy Glacier (86°S, 130°W) of an environ-ment 6 to 10°C warmer than at present. In those conditions the RossIce Shelf and probably most of the West Antarctic Ice Sheet woulddisappear (Mercer, 1968b). Mercer considers that an isotopically-datedhigh sea level about 120,000 years BP, probably during the Sangamoninterglacial, dates the most recent time in which this increased tempera-ture is likely to have occurred. One of the prominent lateral morainesof Meserve Glacier may date from the same time. On the other hand,Dort (1969) suggests that the Hypsithermal period (about 6000 yearsBP) of higher temperatures was the time of the most recent advance,and that the cooling that caused the Little Ice Age in temperate regionsproduced an increased amount of ice in the Ross Sea area, a reductionin the snowfall, and a retreat of the alpine glaciers in southern VictoriaLand.

It is quite apparent that the prime need in studies of the glacial historyof the Wright Valley and the glaciology of the alpine and outlet glaciersis a reliable method of age determination. Everett and Behling's studiesof weathering processes hold promise of a good method of relative agedetermination but absolute ages remain a problem.

MASS BUDGETS : REGIONAL STUDIES 445

Acknowledgements

All the members of the 1965-66 and 1966-67 parties assisted with thedata collection. Thanks are due particularly to Gerald Holdsworth,Principal Investigator of the project, for his painstaking guidance of thefield work, and for his careful estimates of the dry-calving and meltwaterrunoff.

The research on Merserve Glacier has been supported by Grants GA-205and GA-532 awarded to The Ohio State University Research Foundationby the National Science Foundation. The assistance of the personnelof the U.S. Antarctic Research Program and the U.S. Navy is verygratefully acknowledged.

Dr. John Mercer, Robert Behling, and Dr. Lois Jones have criticallyreviewed parts of the manuscript.

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