California Association of Chemistry Teachers D. A. House,
'
R. A. Hoare, K. 6. Popplewell, R. A. Henderson, W. M. Prebble, ond A. T. Wilson Victoria University of Wellington
Wellington, New Zeoland Antarctic Expedition No. 8
Ihe Antarctic continent (1)is about one and a half times as large as the United States and is covered with a true continental ice sheet six million cubic miles in volume and up to two miles thick. Because of its sub-zero climate, the Antarctic is looked upon as a natural low temperature laboratory, and many strange phenomena exist because of the prevailing cold temperatures and low precipitation. Thus the highest forms of native life on the land are insectsticks, lice, mites, and springtails ( B ) , and almost all of the 5.5 million square mile continent is devoid of vegetation. There are, however, small areas of ice-free land or 'Loases"-the Vestfold Hills, Garfield Hills, and Bunger Hills in East Antarctica, and the Dry Valley region in McMurdo Sound. All these areas contain saline lakes (3, 4); those in the Dry Valleys (Fig. 1) Based on a. lecture resented hv D. A. House at the seventh .4nnual Summer ~oniereneeof the California ~ssoeiationof Chemistry Teachers, August, 1965. 'Address from Sept,ember, 1966: Department of Chemistry, University of Canterbury, Christchureh, New Zealand.
Figure 1. M a p showing loker of tho MrMurdo Dry Valley system. Sea ice, snowfields, ond glacier ice white stippled Ice and mow-free oreor -
-
Aeknowlsdgment: Aher U.S.G.S. Victoria Land.
1:i00,000 mop of Ice Free volley^
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are permanently covered with 12 to 22 ft. of ice. There is also one small lake (Don Juan) in the Wright Valley containing saturated calcium chloride solution and crystallizing CaC12.6Hz0 as a new mineral (5), hydrophilite (6),which is not found anywhere else in the world. The lakes in the Dry Valley area are of major interest t o the geochemist, geophysicist, and limnologist. They are quite numerous and in various stages of existence: dried up salt beds, frozen ice blocks, and permanently ice-covered water. All occupy inland drainage basins (i.e., have no outlet) and are either fed by glacial melt water, or are gradually drying up. As a result of a preliminary reconnaissance of the area (7-9),we had decided to make field investigations on chemical composition, temperature, in situ density, conductivity, and light transmission of the lake waters; we also collected water samples for detailed chemical analysis on our return to New Zealand. To obtain water samples, we first had to penetrate the ice cover. This was done with a hand Sipre ice auger and took two men about an hour, when things went well. In some lakes it took more then three hours to drill through the 12-ft ice cover, because the surface melt water flowing into the hole tended to make the drill stick and to make lifting the ice core difficult. We then "pumped" the 4-in. diameter hole for water samples at 2.5 ft intervals. A semirotary hand pump was used and the depth located as shown in Figure 2. First the hose had to be filled with water (primed), and this was the most difficult job because ice would form in the tube and create a blockage if exposed to the surface for too long. At each depth the hose had to be cleared of water from the previous depth before a sample could be taken. This required pumping two full buckets between each sample, and it took two men 10 hr to "pump" a 110-ft-deep lake by this method. Water samples were stored in one-pint or half-gallon plastlc bottles. The chemists then determined the chloride ion concentration by Mohr titration (using potassium chromate indicator) with silver nitrate, the bicarbonate ion concentration with standard acid using methyl orange indicator, and the magnesium plus calcium ion concentration (total hardness) with standard EDTA. The analyses had to he performed in a heated tent to prevent solutions in burets and bottles from freezing. We logged only one hole in each lake for water samples, but to get the bathymetry (shape of lake bottom),
we drilled several holes and measured the depth and conductivity and temperature profiles. Temperature was carefully measured using a copper-constantan thermocouple and a Tinsley potentiometer with 0°C water/ice mixture for the reference junction. Conductivity was obtained with a special remote control conductivity probe on a long flex. Large correction factors had to be applied to the conductivity readings at depth because of the high ionic concentration of the water. To measure solar radiation penetrating the ice, we used a selenium photo-electric cell and a bolometer, which measured the heating effectof the radiation being adsorbed on one side of a thermopile. PUMPING AND
DENSITY
OPERATIONS
abnormally high geothermal gradient under the lake, and radiant energy from the sun penetrating the ice cover and being absorbed. Lake Temperatures in the Dry Valley Region, McMurdo Sound, Antarctica
Max. temp.
Lake Fryxell
("C)
Depth of mau. (ft)
Mi. temp. ("c)
Depth of min. (ft)
2.25
27
0
13V)
0.25 27. 0 0.65 50" 0 9 inches of brine s t -0.55'C
15(T) under 15.75
Hoar*
(Esst lobe) (West lobe) Chad
-..--
f t nf i,.o
Bonney (East lobe) (West lobe) Joyce Vanda Canoms
-2.6 -5.35 -0.15 0 0
" N o t steady state. Varies with time and position. B = Bottom T = loe caver/water interface
Chemical or radioactive heating (12) and biological activity (IS) can be shown to be quantitatively insufficient to maintain the observed temperatures, and hot springs would show nonuniform heat characteristics, whereas the observed temperature profiles in these lakes are markedly uniform. A detailed analysi.; of the temperature profiles for Lake Bonney shows that the heat supplied via solar radiation through the ice can he considered as the major source (14-16), and this method of heating has been assumed to operate in the other warm saline lakes (17). However, it should be noted that other workers have postulated hot springs in Lake Bonney (18) and a high geothermal gradient (19) or volcan~cactivtty (20, 21) as the heat source for Lake Vanda. Let us consider the quantitative aspects of solar radiation and, assuming that the radiation through the water is attenuated exponentially, we have Q = Qoe---* Figure 2. Method of woter rompling ond density meawrernent through the ice cover.
We made in situ density measurements with a simple swing balance and a perspex cylinder (Fig. 2). We weighed the cylinder in air, then lowered it into the water on a nylon line and reweighed it a t the appropriate depth. Knowing the weight per unit length of the nylon line and the density of the perspex, we could calculate the water density. H o w A r e the Lakes Heated?
The results for the temperature measurements are shown in the table. It should he noted that, although the mean annual temperature of this region is about -20°C (10, 11) the temperatures of the lake waters, in some parts, are well above O°C and in one case (Vanda), up to 25°C. Five major sources can he considered possible to supply the heat input (12): biological activity within or a t the base of the lake, chemical heating, hot springs,
where Q is the amount of euergy/unit area/unit time, being radiated down past a horizontal plane at some distance x below some arbitary zero depth; Qo is the energy reaching the depth x = 0; and a = 0.693/xL/,, where X Lis~ the , distance in which the radiation intensity is reduced to half its value at Q0. The radiation Q is converted into heat by being absorbed either in the lake water below depth x or on reaching the bottom. Assuming no convection (because of strong density stratification), the amount of radiant energy passing downward past a depth z,plus the amount of heat conducted through the lake water, must equal the amount of heat conducted out the bottom of the lake ( C ) .
which integrates to:
Volume 43, Number 9, September 1966
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503
I
100
102
1.04
1.06
1
1.0
I
DENSITY (glcm') O " " * CHWRIDE iodnl Flgure 3. Temperature ond chloride ion concentration profiles for Lake Fryxell.
where T is the temperature, k the thermal conductivity of water, and D and F are constants. a is ohtained by bolometry. Fitting the appropriate plot of equation (1) to give dT/& = 0 at the right depth and to give the right temperature gradient and temperature a t x = 0, a calculated curve such as that in Figure 3 is obtained. Results from the Chemical Analyses
All the lakes studied (except Lake Chad) were chemicaUy stratified, i.e., had almost pure water a t the icewater interface and became increasingly saline with depth. The water a t the bottom of Lake Bonney contained 185,000 ppm chloride ion, more than twelve times that of sea water. Chloride ion concentration profiles are shown in Figures 3 and 4. Many limnologists have tried t o use the data from the chemical analyses of the lake waters to determine the origin of the water (9, 18, 91, 99), in particular to distinguish between a marine origin or a mineral spring source, but without any marked success. The ratios between various cations and anions do not seem to resemble either source. We believe that the water has always come from melting ice, and that the salts have come from the sea, via sea spray and snow, and slowly accumulated over long periods. If this is so, knowing the present salt content, we can calculate a salt age for the lakes. This, however, involves several dubious assumptions, the most unreliable being that of constant inflow of water, at the present rate and concentration, since the lake was formed. Nevertheless, making the calculation gives a figure of 30,000-50,000 years for the 504
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Journal of Chemical Education
000
Figure 4. Temperature, demity, and chloride ion concentration profiler far loke Vonda.
salt age of Lake Bonney, and, if this is correct, it would he the age of the retreat of the last major glaciation filling the Taylor Valley. Ages from Diffusion
Let us consider another aspect of the salt concentration versus depth-profile, especially for Lake Vanda, where the details have been worked out ($3, 94). Let us assume that the lake was once similar to Don Juan, i.e., a lake of concentrated calcium chloride with the margining moraine enriched with sodium chloride. Assume also that a climatic change permitted a considerable body of fresh glacial melt water to flow in. The lake would then consist of an ice cover, a layer of fresh water, and a layer of salt water. With no convective mixing, the salt would start to diffuse into the fresh water. The concentration profile in such a system at any time has an equation of the form:
where C = concentration of CaC12; D = diffusion coefficient of CaClz; h = distance above bottom; t = time elapsed; M = total mass of CaClr/unit area. Figure 5 shows the observed concentration profile for Lake Vanda, along with concentration profiles calculated at various times. Thus, a time of 1200 years for the occurrence of a climatic change fits very well with the observed data. Lake Vanda also has a very pronounced shore line 185 ft above its present level (90, 91,96) (Fig. 6) and algae found under rocks at that level have been carbon-14 dated a t 3000 years ($67,so
Antarctica are very sparce, but the geochemical studies on Lakes Bonney and Vanda suggest that the last major glacial retreat was ahout 50,000 years ago ($9),and this has led to the theory (30) that the Antarctic contains the key to the origin of ice ages. The diiusion dates also indicate more recent paleoclimatic changes that would otherwise be di5cult to obtain. It should also he mentioned that installations for the trapping of solar energy using density-stratified "solar pools" (31, 32) have been developed in Israel and these ice-covered Antarctic lakes seem to be natural examples of this heat storage process. Literature Cited Figure 5. Consentrotion profiles cdcuioted from the diffurion equation compared with the experimental data for Loke Vanda.
Vanda has had a complicated history, being 400 ft deep 3000 years ago, a drying CaCL lake 1200 years ago, and now a chemically stratified lake 200 ft deep. The chloride ion concentration profile of Lake Vanda at higher levels is also very interesting (Fig. 4). The regions 11-55 ft have a salt gradient, and thus show a weak density stratification. However, the 55-125 ft, region has uniform composition and temperature, and thus must be convecting. Radioactive 1-131 has been used to show a current of 1.2 fpm in this region. The isotope was released from one hole at a depth of 65 fk, and the time taken for activity to reach a scintillation counter lowered through another hole 33 f t away was measured (19).
(1) CARY,A. P., "The Antarctic,'' Scimti& American, 207, September, 1962. (2) Llano, G. A,, "The Terrestrial Life of the Antarctic," Scienti@ American, 207, September, 1962. (3) KOROTKEVICH, V. S., Concerning the Population of Water Bodies in the Oases of East Antarctica, in "Soviet Antarctic Research." Elsevier Pub. Co., N. Y., 1964, Vol. I, p. 154.
(4) MCLEOD,I. R., The Saline Lakes of the Vestfold Hills, Princess E l k b e t h Land, in "Anta.rotic Geology," Proceedings of the First International Symposium on Antarctic Geology, Cape Town, South Africa, 1963. John Wiley & Sons, Inc., N. Y., 1W4,p. 65. (5) POPPIXWELL,K. B., AND WELLMAN, H. W., unpublished. (6) PLACHE, C., BERMAN, H., AND FRONDEL, C., "Dana's Sy6tern of Mineralogy," 7th ed., John Wiley & Sons, Inc., N. Y., 1951, Vol. 3, pp. 41, 91. (7) CLARK,R. H., "University Antarctio Expeditions" in "South from New Zealand," by QuARmRMArN, L. B., New Zealand Government Printer, Wellington, New Zealand, 1964, p. 72. (8) ARMITAGE, K. B., AND HOUSE,H. B., Limnol. and Oceanog., 7, 36 (1962). (9) ANGINO,E. E., AND ARMITAGE, K. B., J. Geology, 71, 89 (1963). (10) BALL,D. G., AND NICHOLS, R. L., Bull. Geol. Soc. Am., 71, 1703 (1960). D. G.., J. GInn'oloov. 1111 "-,39.. 353 ~ -, N~cnors. - -~~ , R. L.. AND BALL. (1964). H. W., Nature, 196, 1171 (12) WILSON,A. T., A N D WELLMAN, i,-"--,. lOR7.I
E., SISLER,F. D., AND OPPENHEIMER, C. H., J. Sediment. Petrol., 23, 13 (1953). (14) HOARE, R. A., et al., Nature, 202,886 (1964). (15) SKIRTCLIFFE,T. G. L., AND BENGEMAN, R. F., J. Geophys. Res., 69, 3355 (1964). (16) SHIRTCLIFFE, T. G. L., J . Geophys. Res., 69, 5257 (1964). (17) HOARE,R. A,, et al., J . Geophys. Res., 70, 1555 (1965). (18) ANOINO, E. E., ARMITAGE, K. B., AND TASH,J. C., Limnol. and Oceanog., 9, 207 (1964). (19) ~ G O T Z K I ER. , A,, AND LIKENS,G. E., Limnol. andoeeanog., (13) ZOBELL,C.
Figwe 6. Loke Vanda and the Wright Volley. There are pronounced shorelines on the right, indicating o higher lake level in the pmt.
The chemical profile data of Lake Bonney has a]so been analyzed using the diffusion curve (16). Interpretations of its shape suggest that the Iake rose 30 ft only 60 years ago. This is about the time of the earliest explorers. In 1903 the width of the channel in the neck of Lake Bonnev was 17 ft ($7). 1911 it was 100 ft wide and 20 ft deep @8),and today it is 127 ft wide and 30 ft deep. Thus the diffusion calculations are supported by these early measurements. Conclusions
Information on dates of geomorphological changes in
9, 412 (1964). (20) NICHOLS, R. L., Antarctic Res., Geophys. Maovraph, Am. Geophys. Union, 7, 47 (1962). (21) NICHOLS, R. L., J. Glaciology, 40,433 (1965). E., E., ARMITAGE, K. B., AND TASH,J. C., Science, (22) A N G ~ O
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- - - --
1?L -,24 (\1 Q R 7 7,.
(23) WILSON, A. T., Nature, 201, 178 (1964). (24) RODGERS, . C. D., AND WILSON,A. T., Nature, 207, 626 (1Y65). (25) NICHOYR. L., Am. J . Sn'., 261.20 (1963). (26) W I ~ S O N .A. T.. Dersond i27j Scorn, R. F., ;"?he Voyage of the Discovery," MaeMillan and Co., London, 1905, Vol. 2, p. 290. (28) TAYLOR, T. G., "With -r Scott: the Silver Lining," Dodd, Ivleaa ana uo., n . x ., IYIO, p. 134. - r
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.-
.-..
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(29) w ~ L A.~T.,~ ~ ~~ ~, c h e rstudies n i ~ sin~ the Wright Valley, in amss. (30) W ~ S O N , A. T., Natum, 201, 147 (1964). (31) TAP~ROR, H., Large area solar collector; so la^ ponds) for power ~roduction,in U.N. Conf. New Sources of Energy, E/Conf. 35/5/47, (1961). (32) CALDER,R., Nature, 202, 843 (1964). Volume 43, Number 9, September 1966
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