Antarctic saline lakes—stable isotopic ratios, chemical compositions and evolution

0016.7037 79/n1n1-000760?00/0

Geochmica et Cosmochimicn Acta. Vol. 43. pp. 7 lo 25 0 Pergamon Press Ltd. IY7Y. Printed in Gren[ Britain

Antarctic saline lakes-stable isotopic ratios, chemical compositions and evolution OSAMLJ

MATSUBAYA,*

HITOSHI

SAKAI,*

TETSUYA

TORII,?

HARRY BURTON~ and KNOWLES KERRY~ (Received 17

February

1978: accepted

in recked form

18 Auyust

1978)

Abstract-About 90 saline and fresh water lakes as well as glaciers and their melt waters from the ice-free areas of the Soya Coast, the Vestfold Hills and the Southern Victoria Land of Antarctica have been analyzed for hydrogen and oxygen isotopic ratios. These results and the chemical compositions so far published indicate four types of saline lakes. (1) Three saline lakes on the beaches of the first two areas which still are receiving sea water as the major inflow. (2) Other lakes of these two areas which are isolated from sea water inflow. The isotopic ratios of their waters are higher and are plotted farther to the right of the meteoric water line, on the bD vs 6lsO diagram, with increasing salinity. This is because the higher the salinity of a lake, the lake is ice free for a longer period of year, and thus the lake water is more significantly affected by the isotopic effect of evaporation from liquid water. (3) Lake Bonney in the Taylor Valley of the Southern Victoria Land. The west and east lobes of this lake chemically are stratified but only the east lobe shows stratification in the isotopic ratios. Both lobes started as shallow saline lakes similar to some of the saline lakes classified in (2). Fresh water flooding into the lakes and subsequent diffusion mixing formed the present features. By solving diffusion equations under certain assumptions the evolutionary history of Lake Bonney was modeled. (4) Lake Vanda and Don Juan Pond in the Wright Valley of the Southern Victoria Land. Lake Vanda is strongly stratified in both the salinity and isotopic ratios and seems to have a similar evolution history to east lobe of Lake Bonney. Chemical composition of the lakes in (2) and (3) differs variqusly from that of sea water but can be interpreted by different degrees of low temperature concentration of sea water by evaporation or freeze-drying. On the other hand, the high concentration of Ca*+ relative to Mg2+ and Na+ in the lakes of the Wright Valley cannot be interpreted by this way.

INTRODUCT!ON THE SOUTHERN Victoria Land, the Soya Coast and the Vestfold Hills (Fig. 1) are spotted by many icefree, dry areas or the Antarctic oases, where many saline lakes and ponds exist, some containing as much as 450g/kg of dissolved salts. The ice-free area of the Southern Victoria Land is situated in the Transantarctic Mountains to the west of McMurdo Sound in Ross Sea. This area is divided into three east-west trending valleys as shown in Fig. 2. Lake Vanda, 5.6 km long, 1.4 km wide and 68 m deep at the maximum, is situated at the lowest part of the Wright Valley. Lake Bonney in front of the Taylor Glacier is composed of west and east lobes which are connected by a shallow, narrow channel. The west lobe is 2.6 km long, 0.8 km wide and 32.7 m deep, while the east lobe is 4.8 km long, 0.8 km wide and 36 m deep. Lake Vanda and Lake Bonney contain perennially unfrozen water under their surface ice cover. D&ing summer seasons, melt waters from outlet and alpine glaciers in the area flow into the lakes and the ice along the shore melt away. Dissolved salt in

* Institute for Thermal Spring Research, Okayama University, Misasa, Tottori-ken 682-02, Japan. t Chiba Institute of Technology, Narashino, Chiba-ken 275, Japan. t Antarctic Division, Melbourne, Victoria 3004, Australia.

Lake Vanda is predominantly CaCI,, whereas in Lake Bonney, NaCl and MgCl, are the major salts. These lakes are noted for the strong stratification in salinity. Don Juan Pond is in the south fork of the Wright Valley. It was 400m long, 120m wide and about 1Ocm deep on December of 1968. The size of the pond, however, varies with time depending on water balance between inflow and evaporation. The pond water is extremely enriched in CaCI, and sometimes saturated with antarcticite (CaCl,.6Hz0) (TORII and OSSAKA,1965). The ice-free, dry areas at the Soya Coast and the Vestfold Hills are situated along the eastern coast of the Antarctica (Fig. 1) and bounded at the west by the East Antarctic icesheet. These two areas are geographically similar to each other and climatically milder than those in &he Southern Victoria Land. Many lakes, ranging in size up to several kilometers, exist in these areas (MCLEOD, 1964; MURAYAMA, 1977). Lakes situated near the East Antarctic icesheet receive its melt water at the major water input, while those isolated from the icesheet are fed only by snowfall into their catchment areas. Although the Cl- contents of the latter are mostly low fi&lOOOmg/kg), saline lakes having 8 to 170 g/kg of Cl- have been found. Their chemical composition is similar to that of sea water, although some highly saline lakes are richer in to Mg ‘+ than sea water in its relative composition other cations.

8

SO0 E

1 SO*

When sea water is concentrated by freeze-concensaturated with mirabilite tration. it becomes (Na2S0,~ IOH at about 4 times concentration and. thereafter. the SOico~centratiou decreases rapidly accompanying a slight decrease of Na’ content (T~OMBO~J and NELSON. 1956). At slightly before 8 times concentration, hydrohalite begins to precipitate, and the Mg’” content starts to increase with decreasing Na* content (THOMPSON and NELSON. 1956). The salinity and chemical composition of the saline lakes at the Soya Coast and the Vestfold Hills are similar to those of the brines obtained by various degrees of freeze-concentration of sea water. From

Don Juan’Pond Lake

/ Vanda

these results and from geographic features, these lakes have been considered to be of sea water origin (~RAITSCH, 1962; M~Leoo, 1964: YOSHID.4, 1970). However. the lakes in the Southern Victoria Land. are enriched in Mg” and/or Ca” more than expected from the experimental results of THOMPSON and NELSON f 1956). The isotopic ratios of these lakes. on the other hand, are similar to those of snow, ice and glaciers of these areas. implying meteoric origin of the lake waters (RAGOTZKIE and FRIEDMAN.196% AMES% 1966. i974:NAKAI et of.,197%.CRAG (19&S), however, argued that the present isotopic ratios of these lakes

Antarctic saline lakes

woufd no longer be the same as the original ones, because they should have been modified by inflow and isotope exchange with atmospheric moisture. In the present study, the hydrogen and oxygen isotopic ratios of saline and fresh water lakes and glaciers in the above three areas were measured in detail. The

dard waters from the Interna~ionai Atomic Energy Agency at Vienna, Vienna-SMOW, NBS-IA and SLAP were measured to be - 1.0 and - 0.0, - 181.2 and - 24.4 and -419 and - 55.5”;,,,respectively. The average of 45 laboratories for 6D and 6’sO values of NBS-IA and SLAP relative to Vienna-SMOW were - I83 and -24.3, and -427 and - 55.3”:,,, respectively (GONFIANTINL 1977).

isotopic results combined with the chemical and geographic info~ation obtained by ourselves as well as by other investigators will be used to discuss factors

controlling the isotopic ratios of these lakes. The origins and the evolutionary history of these saline lakes, especially of Lake Vanda and Lake Bonney, are discussed based on a new diffusion model.

9

RESULTS The isotopic ratios and chloride concentrations of lakes, melt waters and glaciers are summarized in Tables I and 2 and plotted in Figs. 3 to 9.

The Souf~er~ Victoria tnnd The dD and S’s0 values of alpine glaciers, their melt waters and lakes from the Southern Victoria Land are EXPERIMENTAL summarized in Fig. 3. The alpine glaciers and their melt The D/H and 1*0/160 ratios of water were measured waters mostly range from -210 to - 26C1’7~, in 6D and by means of the uranium-reduction method (FRIEDMAN, -26 to -34’:i,,, in 6’sO, in accord with those reported 1953) and the H20-CO2 equilibration method (EPSTEIN for snow and ice at other coastal areas of Antarctica, that and MAYEDA, 19.531,respectively. is, - 150 to -250’%,, in 6D and -20 to -3&xX, in Sir’0 The 6180 values of saline waters were corrected for the (GONFIA~~N~and PK~IOTTO, 1959: PKXIOTTOef uf., 1960; hydration effect of dissolved salts after TAUBE (1954) and EPSTEINet af., 1963; LORIUSer al., 1969). SOFER and GAT (1972). Highly saline waters from Don The Taylor Glacier flowing out from the East Antarctic Juan Pond, however, were distilled in vacuum before the icesheet has lower isotopic ratios (aD = -330& HZO-C02 equilibration, because they require equilib6’sO = -42.5’Q than those of the alpine glaciers in this ration time significantly longer (about 2 weeks) than dilute area. The 6D and h’s0 values of snow and ice at the water (half a day). The results are reported in the delta South Pole or the central part of East Antarctica are values relative to SMOW standard (CRAIG, 1961): -4OOY&,and -S@,, on the average, respectively (EPSTEIN ei a!., 1965; LORIUSer al., 1969). Thus. the Taylor Glacier isotopically reflects inland snow and ice, whereas alpine dx=(!5--+ IO’, glaciers reflect the coastal or in situ precipitation. Figures 4, 5 and 6 show the vertical isotopic profiles of Lake Bonney and Lake Vanda. Figure 6 also includes where X is D or IsO and R is D/H or 18O/‘6O. The the groundwaters of Lake Vanda obtained by the Dry Valanalytical errors are +3”, for hydrogen and &0.2”:,,, for ley Drilling Project (DVDP) (CARTWRIGHTet al., 1974). oxygen. 6D and 6’*0 values of the three reference stan-

._

@*0,+/O* __ 150

Wright Valley 0 :glacier i meit water l :&ah Vanda c. ground

Taylor Valley 0 :glacier I

melt 0 : Lake Fryxell l : L&e Bonney, , ditto 0: , ditto 8:

*

Miers Valley A: Lake Miers

Water

water

200 Common Wealth 01.

West Lobe Ch8nnel East Lobe

Surface

ice

4 -250 O_ P c@

-300

-350 Fig. 3. Relationship between 6D and fi”O values in lakes and glaciers at the Southern Victoria Land.

0. MATSUBAYA rf 01.

10 Table

I.

lsotoplc

and

chemical

compositions Victoria

Southern Victoria Wright VallJ?_y

9 10 11 12 13 14 15 16 17 18 19 :: :: 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 :; 41 :: 44 45 46 41 48 49 50 51 52 53 54

of Land

lake and

waters, the

Soya

meltwaters

and

glaciers

of the

Southern

Coast”’

Land

MeSerYe Gl.z.CLBS (l-2-75) -250 -251 Bartley Glacier (l-2-75) Bull fake U-2-75) -230 Onyx River, at weir(unknown I-220 ditto (l-2-75) -229 -230 Pond iunnamedl 11-3-551 fanapus Pcnd (X-3-751 -237 Lake vanda am Cl- x-731 -246 Point x, ditto -247 em ditto ditto IUm ditto -246 ditto 30m ditto -248 ditto 44m ditto -252 ditto 48m ditto -256 ditto 52m ( ditto ) -245 ditto 56m [ ditto I -248 ditto 60m f ditto ) -241 ditto 64n ( ditto > -237 ditto 65.5m i ditto 1 -248 4m (12-x -733 -242 Point R, ditto 8m ( ditto ) -242 ditto L2m ditto 1 -242 ditto 16m ditto -245 ditto 2Qm ditto 1 -245 ditto -247 4Om f ditto dotto 44m ( ditto -246 ditto 5011%( ditto > -248 ditto ssnl -246 ditto 60n f ditto 1 -247 ditto 65rn i ditto 1 -2*6 ditto -244 6831si ditto 1

( ( ( ( (

) ) ) ) 1

( ( (

) ) 1 f ditto !

Groundwatex4' 70.9%71.6rn (11-17-731 -239 72.2m ditto -236 75.7%76"7m ditto -240 79.7%80.6m ditto -242 North fork. No.3 (IZ-14-741-136 Pond ditto No.4 ( ditto ) -162 No.5 f ditto ! -172 ditto DAD JUB~ Pond 112-30-53) -193 ( l- 6-65) -186 ditto ditto (12-28-681 -*El3 111-U-69) ditto -214 ( l- 7-71) ditto -161 ditto l-15-71) -156 ditto (12-10-71) -195 ditto (11-17-73) -209 (12- 3-73) ditto -197 ( 4-25-741 ditto -206 ( 7- V-74) ditto -206 ditto (1% 7-74) -ia3 ditto 112-14-74) -180 ditto i l- 9-751 -170 Surface ice, upper (10-28-74) -130 ditto middle ditto ) -159 ditto lower ditto -154

( ( (

) 1 )

(

( (

1

-32.4

-

-32.4 -29.2 -27.4 -29.8 -26.1 -28.2

0.1 c0.i

-30.4 -31.3 -31.5 -32.0 -31.9 -31.7 -31.5 -31.4 -30.3 -29.1 -24.2 -31.3 -31.3 -31.8 -32.0 -31.7 -31.9 -31.8 -31.5 -30.7 -29.5 -29.4

0.2 0.2 0.3 0.6 0.9 1.6 14.2 33.3 53.5 60.9 74.L 0.28 i-J.2 0.2 0.5 0.5 0.6 1.1 5.3 28.4 54.1 70.0 73.5

-29.3 -28.2 -27.0 -26.8

73.7 93.2 109 114

-33.2

- 7.a -10.0 -14.6 -13.5

-13.V -10.8 -17.4

-

8.3

- 9.4 -14.4 -16.6 -11.8 -19.5 -20.2 -13.6 -12.4 -10.3

3.4 74.2 0.7 247 251 236 209 197 15L 2Ol 216 244 158 148 163 156 182

-13.9

_

-14.3 -14.6

-

-2L.O -16.1 -16.3 -13.4 -13-V

139 87.3 91.0 0.8 0.E

-10.7

246

-216 -222 -226 -244 -258 -235

-28.4 -29.4 -30.0 -32.1 -33.6 -24.8

_ -

-233 -231. -330

-30.1

-

-30.1 -42.5

" *

-296 -312 -325 -323 -315 -321 -313 -321 -316 -300 -299 -304 -312

-39.5 -41.0 -42.0

3,811x(12-Z-731-211 5.5 Ground water'! ditto 6) 6.lmf ditto J-179 56 ditto 61 9.4m( ditto j-176 53 Inflow from west il-11-751 -155 58 1nf1o.s from southweetiditto)-158 59 Puddle beside 60 Don Juan Pond (l-9-75) -202

valley common wealth Glacier

_ _” _ _ ^ _ _ I

_ -

-

_

I

_

r

-

_

-

_

-

_

_

-

-

-

-

-

_

”

.

-

_

-

L

-

-

-

_

_

-

-

I 0.025 0.028 0.120 0.123 0.111

I

-

^

_

_

-

-

_ 0.034

0.042 0.059 0.098 0.127 0.192 1.25 3.46 4.29 5.l2 1.96 o.oa3 0.045

0.049 0.090

0.097 0.150 0.15l 0.554 2.39 4.37 6.34 6.98

-

.

_ _

0.463

0.284 -

_ 7.82 8.75 -

0.0 0.5 0.0 0.00 0.0 0.02 0.0 0.00 a.00 0.03 0.03 0.01 8.03

I

(7.4) (8.8) 0.011 0.019 0.019 0.029 0.144 0,351 0.334 0,402 0.604 I:::; O.OLO !"E 0:0x9 0.026 0.067 0.247 Ci.Ul5 0.551 0.586

0.98 1.08 I

2.16 1.63 3.52 16.0 19.6 I -

I

0.047 0.061 0.096 0.174 0.276 0.496 4.88 14.8 19.4 19.2 33.1 0.056 0.060 0.070 0.165 0.180 0.195 0.314 0.702 10.7 19.9 24.5 25.6

28.9

33.2 -_

a.012

0.034

0.022 0.045 0.066 0.132 1.35 4.19 5.52 5.31 8.70 0.015 0.016 0.017 0.034 0.042 0.043 0.088 0.472 3.02 5.60 7.05

1.046

1.067 1.075 1,046

1.039 1.071 1.094 1.095 1.093 1.122 L.142 1.150

I

9.03 10.5

0.23 0.26 0.20 " O.L4 '. I -

_

1.156

132.2 137.1 127.1 107.2 99.3 76.4 102.5 112.7

2.6 1.8 1.8 1.6 1.5 0.45 1.27 1.6

BL.1

1.1 1.1

1,380 1.386 1.361 1.298 1.283 1.216 1.288 L.324 1.370 1.224 1.208 1.233 1.255 1.265

-

74.1 -

_

_ _

-

_

Taylor

61

(12-26-74) Canada Glacier (12-27-74) Suese Glacier 112- S-74) Lacroix Glacier (12-19-741 Rhcrne Glacier 1l2-22-741 SoIlas Glacier (X2-23-141 ditto finelt water> (12-19-74) (12-23-74) Hughes GlaCler 68 Taylor glacier (U-22-74) 69 Lake Bonney, 70 West Lobe, %I (l-5-72) ditto 8.5~ ( ditto 7k ditto 1Om i ditto ) 72 ditto 13m ( ditto i 73 15m i ditto 1 Y4 ditto ditto 1% ( ditto ) 75 ditto 22m I ditto 1 76 ditto 26m f ditto ditto 29.W ditto 1 :;: East Lobe, Sin (l-9-72) ditto 8.5m ditto z ditto lUm ditto 81 ditto 82 13m ditto ) 62 63 64 65 66 67

1

( ( ( (

1

) 1

-42.4 -42.0 -41.5 -40.3 -*0.5 -40.5 -39.8 -40.2 -40.0 -40.2

“.

0.7 (361 28.2 0,135 48.7 0.226 _60.3 0.284 __ 34.4 0.360 __78.1 0.375 0.8 (3.9) 8.7 0.058 9.1 n.055 _ _

_ -

-

-

I

-

-

I

_

-

-

-

I

-

-

4.52 4.33 4.45 0.11 0.29 0.53 -

_ I

-

-

_

0.11 2.75 4.06

-

-

0.376 8.25 21.8 28.2 33.0 32.1 0.298 3.87 3.85 -

-

0.014 0.456 0,813 0.996 _ 1.26 _ 1.47 0.018 a.134 O.Lr,Z _

_

_

-

0.056 0.926 1.18 I.56 1.46 _ 1.48 0.119 0.323 0.566 -_

-

_I

0,068 3.19 5.05 6.27 _ 7.97 8.34 0.067 0.948 0.914

1.001 1.037 1,063 1.078 1.09A

1.102 1.001 1.011 1.011

(continued)

Antarctic Table Sample locality (Date "f sampli"gj2)

NO.

"Do,.."

"0

11

saline lakes

1. (continued) Cl-

Br-

SO:g/kg

(

I

-2%

I )

-281 -261 -251 -251 -252 -307

-38.3 -31.7 -26.5 -25.0 -25.2 -25.2 -40.8

-301

-38.3

-256

-33.2

-214

-26.4

-236 -236 -254 -243

-30.4 -31.3 -31.8 -31.2

-210

-27.3

-200

-25.0

-212 -236

-27.1 -29.5

-212 -210 -210 -208 -211

-26.4 -27.0 -27.0 -26.8 -27.1

(3.5) (5.6) (5.5) (6.3) (6.5)

-132

-14.1

3.8

-143

-16.9

1.1

-174

-20.3

1.6

-186

-23.1

2.8

-162

-18.0

6.0

-147 -146 -150 -147 -148 -151 -157 -154 -150 -149

-18.0 -18.2 -18.3 -17.3 -18.3 -18.1 -18.4 -18.6 -17.9 -17.5

0.087 0.100 0.077 0.102 0.073 0.098 0.086 0.110 0.078 0.086

-154

- 74 - 74 -140

-11.3 -11.0 -15.1 -15.2 -16.4 - 7.9 - 3.8 - 4.2 - 9.1

ditto 15m ditto ditto 19m ( ditto ) ditto 22m ( ditto ) ditto 26m ditto :: ditto 29.5m ( ditto ) 88 ditto 32.5m ( ditto chnnel, 9.5m (unknown) :z Inflow to West Lobe, from Taylor Glacier (1-5-73) Inflow to West Lobe, fr"m 91 Rhone Glacier (l-9-73) Inflow t" East Lobe, 92 from east (unknown) Lake Pryxell, 93 Point S, 4m (12-20-72) 94 ditto Em ( ditto ) ditto 12m ( ditto ) ditto 9': 16m ditto ) 97 Lake Frvxell. Surface ice. upper section (unknowni 98 ditto middle section (unknown) 99 ditto lower section (unknown) 100 Lake Chad (12-5-74)

::

85

(

(

_

_ -

Miers

K+

Ca*+

Mg2+

Sf;;;:;

(mg/kg)3)

79.3 114

0.775 1.11

2.51 2.51

21.6 34.3

1.36 2.01 -_

0.737 0.990

15.25 22.37

1.100 1.143

143 141 162 9.0

1.34 1.24 3.16

2.75 2.85 2.94 -

43.9 43.5 56.9 3.75

2.74 2.69 2.30 O.lB9

1.35 1.11 1.22 0.384

27.27 23.70 21.71 1.28

1.181 1.177 1.203

_

-

-

-

_ _

-

_

(0.4) (4.3) (8.4) 0.011

(27) 0.17 0.24 0.25

0.085 1.11 1.95 2.98

0.013 0.091 0.172 0.203

0.025 0.032 0.031 0.027

0.016 0.124 0.248 0.331

108 116 7.7

3.2 3.5 1.6

:;"8 29.2 51.1 51.1 171

::; 3.2 7.9 7.8 12

49 53 4.3 4.3 11 16 31 32 39

2.1 2.2 0.20 0.18 0.41 0.55

1.3 2.2 0.48 0.40 0.41 0.58

::: 0.82

::: 0.2

7.1 7.3 0.65 0.70 1.3 1.5 3.4 3.3 39

(0.4)

(2.2)

0.18 1.43 2.80 3.70

-_

co.1

Valley

102 103 104 105

Miers Glacier (melt water) (l-12-651 Lake Miers, Em (l-12-65) ditto 12m ( ditto ) ditto 16m ( ditto ditto 20m ( ditto

106

Cape

101

Aa+ or

1 )

RossIsland 107 108

Royds, ditto

Cape

Evans,

109

ditto

110

ditto

S"ya 111 112 113 114 115 116

Lake

ditto ditto ditto ditto

118 119 120

Lang 121 122 123 124 125 126 127 128 129 130 131 132

Lake Lake Lake Lake Lake Lake

Lake

135

Lake

)

,

st.19 P""J1-y-64) ( ditto ) Pond, st.20 ditto )

(

Ongul

Island

(4- 2-67) (4-23-67) (5-26-67) (6-13-67) (7-11-67) (7-12-671 i8-11~67j (Y-11-67) (l-23-68) (l- 7-701

Hovde

Zakuro, l.Om (10-6-72) ditto 4.lm ditto Akebi, 2.Om (10-7-72) ditto 5.0m ( ditto Nurume, 1.5m ditto ) ditto 16.0~1~ ( ditto Oyayubi, 1.5m(lO-5-72) ditto 5.0m( ditto ) Itiziku. 0.2m (2-8-73)

(

) -137 -141 ) -143 -144 1 - 83

(

Naka"ota"i7' 2.Sm 110-4-72) ditto 17.0m ditto Higasi-Yukidori, 2.5m (11-23-72) ditto 15.5m ditto Kami-Kama, 2.0~" (11-24-72) Hioasi-Ham"=. 3.0m (11-25-72) ditto 22.0m ditto ) Nisi-Hamna, 2.5m (10-4-72) ditto 15.5m ditto

(

Lake

-238

-30.8

(25)

(4.01

(18)

(0.8)

1

-237

-30.6

(42)

(5.5)

(241

(2.1)

(0.9)

(3.0)

)

-161 -162

-19.6 -19.5

(52) (53)

(6.0) (6.5)

(401 (43)

(2.6) (2.7)

(8.6) (11)

(9.2) (9.3)

-167

-21.5

(23)

(20)

(13)

(1.5)

(11)

(6.3)

-234 -245

-31.4 -32.7

(2.2) (2.7)

(2.0) (2.2)

(1.01 (1.1)

(0.5) (0.5)

(CO.4) (0.4)

(0.9) (0.9)

-266 -264

-34.8 -34.7

(7.8) (6.8)

(2.0) (1.6)

(4.2) (3.7)

(0.6) (0.5)

;;.;,'

ii.;;

Tankobu, *.5m(ll-14-72)-303 -305 ditto 13.0m ( ditto -289 Lake BOZU, 3.5m (11-15-72) ditto 17.0m ( ditto ) -288

-39.7 -40.0 -37.7 -37.7

(2.1) (2.1) (2.2) (1.31

I:.:; 11:0, (0.6)

(CO.4) (CO.4) (<0.4) NO.4)

(0.4) (0.5) (0.4) (0.2)

-10.0 -10.0

121 127

(

Lake

(

138

0

By-rag

139 140 141 142

(

(

133 134

136 137

Coast

0-ike ditto ditto ditto Wz

Pond, St.26 (l-14-64) Home Lake ditto Pond, St.15

I

1.132 1.142 1.008 1.008 1.022 1.036 1.068 1.070 1.223

D

Asane

Laae

)

(0.6) (0.5) I:::;

I:*:; co:1, (0.1)

Skarvsnes 143 144

Lake

Hunazoko, l.Om .Om

ditto

(10-27-72) ditto

(

)

-143 -143

3.0 3.4

56 70

2.3. 2.8

2.0 5.4

8.0 9.3

1.148 1.150

(continued)

0. MATSUBAYA

12

Table NO.

Sample locality (Date Of sampllnql*)

I'%

60

rl ul.

I. (continued) Cl-

Br-

143 146 147 148 149

dxtt* 7.om i ditto 1 -144 ditto 8.5~1 I ditto ) -137 Lake Oyako, 2.0m (10-27-721 -136 ditto 7.5m ( ditto ) -134 Lake Nagaike'),

150 151

ditto Lake

152 133 154 155

156 157 158

2.0m 9.0m

Hyotan'). 2.0m 9.5m

Kobati7) 2:om ditto 8.5m Lake Suribati, 1.5m

- 9.9

Ca*+

Mq'+

-

3.2

5.4

&: (56)

65 57 0.22 0.23

2.8

-

(?i?

(22;:

(11)

(26)

::4" (35) (37)

-130 -128

-12.8 -13.1

0.74 0.78

-

(17) (16)

0.41 0.44

(211 (22)

(12) (9.8)

(77) (84)

(10-26-72) ( ditto

I

-141 -135

-x4.1 -14.1

0.97 0.85

-

(21) (191

0.53 0.48

1251 123)

(121 110)

(97) (86)

~10-26-721 ditto )

(

-139 -148

-14.3 -13.8

14.5 14.6

-

0.42 0.39

7.5 7.4

0.29 0.29

0.085 0.086

:::

(10-26-72)

-130

-12.2

80.7

-

2.7

44

1.5

0.79

5.4

-10.9

113

60

2.2

1.1

7.4

-35.9

-36.0

13.7) (1.3)

(1.61 (3.3)

(2.1) (0.6)

(0.41 (0.7)

10.4) (CO.41

(1.0) (O.dj

-19.6 -20.2 -20.2

_

_

(25) (23)

(5.0)

-154 -153

-19.3 -19.8 -19.5

(4;) (26)

-133 -138 -137

-14.7 -15.4 -15.4

(85) (86)

Specific ravity

take

Lake Suribatl, 17.0m -146 110-26-72) Lake Ka!nlnoike7', 2.01~(10-23-721 -277 ditto ll.Om ( ditto i -278

surface (2-3-721 ditto 2.0~1 (11-7-721 ditto 7.5~1 ditto 1

(

Lake

surface ditto *.om ditto 8.5m

-153 -157 -156

( Z-3-72) -15i

x-ik;:;;ace

163 ditto 2.Om (11-6-72) 164 ditto 7.h ( ditto t 165 fake Skallen Oike, 166 167

K+

126 127 0.37 0.40

7.1

Skallen 159 l.akeKoike'), 160 161 162

??a+

- 9.9 -15.3 -15.4

;l~yW;7;' L

ditto

so:-

g/kg or hw‘kg)3)

"I,,

(2-4-72) (11-7-72) ditto

(

1

_

(13) (4.3) (111

(0.9) (4.6) " (4.7) (0.8) (4.2) (4.6)

_ (7.21 (10) (11)

_

(20) 113)

(1.21 (1.0)

rs:o, 19.71

(5.31 (4.9)

132) (48) 149)

12.21 (3.4) (2.9)

(6.3) (9.4) (121

(6.0) (9.5) (9.51

(1) All the isotopic data are by this work. Chemical data for Nos. X-37 are by S. NAKAYA (unpublished), for Nos. 38-45 and 47-51 by TORII et ul. (1977). for Nos. 7W39 and 93-96 by TORH et CT/.(1975). for Nos. 1?1-167 by H. MURAYAMA (unpublished) and all others by the present authors. Salt contents of the lakes for which no chemical data are available are mostly lower than 1 @‘kg. (2) Date of sampling (month-day-year) (x = unknown date). (3) Figures in bracket are in mg/kg. (4) Obtained by the Dry Valley Drilling Project 4 (DVDP). (5) Obtained by DVDP 5. (6) Obtained by DVDP 13. (7) Temporary name.

-300

- 350

- 250

-40

-45

-35

50

0

100

1

I

60, %o 6”o t y 00 Cl-,

g/kg

L. Bonney

A

West

Lobe

W - 1 (Jan. 1973)

Fig. 4. Vertical

distributions

of isotopic

ratios

and Cl-

content

in the weal lobe of Lake

Bonney

Antarctic saline lakes

13

Table 2. Isotopic ratios, chloride concentration and specific and glaciers in the Vestfold Hills Sample

NO.

(Date

of

locality 1) sampling)

gravity

$82 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221. 222 223 224 22.5 226 227 228 229 230 231 232 233 234 235

Lake Rookery (10-29-74) Lake C ( ditto ) Ace Lake ( ditto ) ditto , 5m (11-29-74) ditto , 10m 111-14-74) ditto , 15m (11-29-74) Lake H (11-7-74) Lake I ( ditto ) Lake A (10-29-74) Lake J (11-7-74) Lake F (11-4-74) Lake E ( ditto ) Lake G (11-5-74) Lake K (11-8-741 Lake L ( ditto ) Lake M f ditto ) Lake L (11-29-74) Collerson Lake (9-17-74) Split Lake, north (S-l-74) ditto middled ditto ) Echo Lake (4-30-74) 5m (S-26-74) Badge Lake, ditto 33m ( ditto ) Oval Lake (4-30-74) Lake -2 ( ditto ) Lake -3 ( ditto ) Lake d (12-2-74) Lake $I ( ditto f Lake E ( ditto 1 Lake oi ( ditto 1 Lake 8 ( ditto ) Lake 0 (11-29-743 Lake 2 (12-l-74) Lake p (11-30-74) Braunsteffel Lake ( ditto ) Veretno Lake (11-29-74) Cowan Lake (11-30-74) Lake Diagle (8-8-74) Lake Stinear, lm (12-2-74) ditto 20m ( ditto f Deep Lake, Im (11-26-74) ditto 15m f ditto ) ditto 20m C ditto ) ditto 34m ( ditto } Club Lake (4-27-74) Lake Jabs f ditto ) Lake T (11-30-74) Lake S ( ditto ) Lake iJ ( ditto 1 Lake V f ditto 1 Lake W (12-l-74) Lake X ( ditto f Lake Y f ditto 1 Lake Next-4 (4-24-74) Lake -4 ( ditto ) Clear Lake, 1Om (U-27-741 ditto 2% ( ditto 1 McCallum Lake, 2m (4-21-74) ditto 25m t ditto 1 Anderson Lake (7-18-74) Watts Lake (4-13-74) Lebed Lake (Z-25-74) Crooked Lake (2-19-74) Glacier ice, 1 ditto ditto 32 ditto ditto

waters

’b

Cl-

- 51 -156 -152 -154 -147 -145 -149 - 28 -141 -142 -168 -156 -164 -218 -176 -171 -134 -156 -133 -130 -142 -152 -135 -141 -151 -127 -140 -153 -148 -154 -150 -163 -146 -152 -153 -151 -144 -136 -141 -142 -143 -143 -142 -141 -147 -140 -160 -139 -143 -213

- 3.5 -18.0 -18.4 -18.3 -17.3 -17.3 -17.8 - 2.8 -15.6 -15.7 -20.7 -18.4 -20.2 -28.5 -21.6 -21.2 - 9.8 -18.7 -12.4 -11.6 -15.0 -16.0 -13.0 -14.2 -17.2 -11.3 -13.6 -15.2 -15.2 -16.6 -15.5 -16.4 -15.x -14.6 -17.2 -15.0 -13.9 -13.1 -13.5 -13.6 -13.1 -13.1 -13.2 -12.7 -13.9 -13.7 -18.9 -14.9 -14.3 -26.L

73.9 39.7 15.8 15.6 17.8 18.1 3.6 32.9 10.0 64.8

1.096 1.049

48.9 6.2 82.2 82.5 24.9 59.7 91.0 70.0

1.064

64.8

1.085

-155 -216 -213 -133 -132 -155 -154 -156 -160 -159 -166 -146 -244 -380 -185 -580 -170 -214

-16.4 -25.8 -26.2 -13.1 -12.0 -18.1 -18.2 -19.3. -18.8 -17.5 -19.L -13.2 -30.8 -23.2 -23.7 -22.8 -22.2 -27.3.

6D

6 "/..a

168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203

of lake

Specific gravity

1.044 1.082

1.102 1.104 1.078 1.128 1.087

4-5 ::z

;t:: 1.9

I

109 119 I.18 139 140 139 141 339 85.1 3.5

1.135 1.150 1.150 1.179 1.181 1.181 1.182 1.180 1.107

120 I.07 6.9

1.152 1.139

E 13:5 45.4 1.1 126

1.06X 1.160

(1) Date is month-day-year, results have been reported by AMBE (1974), RAGOTZKIEand FRIEDMAN (1965)* and NAKAI et al., (197.5) for these lakes. TAUBE (1954) and SOFIB and GAT (1972, 1975) demonstrate that, in Ca*+- and Mg2+-rich brines,

Similar *The results by Ragotzkie and Friedman are actually by about 30:& lower than our results. This difference, however, may

be

attributed

to

the

systematic

difference

between the two laboratories, because Friedman reported lower 6D values by 13.8X for NBS-IA and 34.19, for SLAP than our laboratory (~O~~~lN~ 1977).

the activity ratios of the isotopic water species significantly deviate from the concentration ratio. Figures 7A and B are 6D vs 6’aO plots of Don Juan Pond waters based

0.

14 -350 -45

MATSUBAYA

er ul.

-300

-250

-200

-150

-40

-35

-30

-25

~

lpo

‘I”

oi

SD,%,

6180,0/oo

2po

cl-.g/kg

L. Bonney East E-l

Love (Jan.1973)

30

I

6~ Fig. 5. Vertical

distributions

of isotopic

Cl-

ratios

and

on the concentration ratios and the activity ratios. respectively. The latter plot was constructed after SOFER and GAT (1972. 1975). The chemical composition of all these waters were reported by TORII et al. (1977) (see Table I). 7‘1~ Soya Coast and the Vesrfold Hills The areas water from

results are summarized in Fig. 8. The lakes may be divided into three groups from the flowing into them: the lakes receiving melt the Antarctic icesheet, those Isolated from

-350

type of

waters the ice-

content

in the east

-250

- 200

-150

-40

-35

-30

-25

1

lobe

of Lake

100

150

1

200

,

6D,%o 6”0,

%o

Cl-.g/lw

L. Vanda

20

0

0

0

@

8

8

: K (Jan. 1973) : R (Nov. (973) : DVDP 4 (Nov.19731

E r x 40 d

60

Sediment 66

Fig. 6. Vertical

distributions

of isotopic

Bonney

sheet melt waters. and those located close to a beach and probably fed by sea water. The isotopic ratios of the first group vary widely from - 150 to - 300”<,,, in 6D and from -20 to -4o”,,,, in (i’s0 but closely lie on the meteoric water line. This wide variation may be interpreted as a result of mixing between melt waters from the coastal snow and those from the icesheet. On the other hand. the cSD values of the second type lakes are within a narrow range from - 125 to - 170’:,,,. while the 6‘sO values show a wide spread from -9 to

-300 50

0

at these

Cl-

6”O

ratios

and Cl _ content

in Lake Vanda

Antarctic saline lakes

6

J

6D=86'aO+10

0:

Don

0:

Ground

-20

Juan

Pond

water

@:

Inflow

0:

Pond

and at

@B

surface

North

-20

-10

ice

-240

Fork

-fO

8’80, Yo. Fig. 7. Relationship between SD and 5t80 values in the Don Juan Pond and the ponds at the north fork of the Wright Valley, are based on concentration ratios (A) and activity ratios (Et). The date of collection and Cl- content (g/kg, in parentheses) are, respectively: 1, Dec. 30 1963(247): 2, Jan. 6 1965(251): 3, Dec. 28 1968(236): 4, Nov. II 1969(209): 5, Jan. 7 1971(197): 6, Jan. I5 1971(151): 7, Dec. 10 1971(201); 8, Nov. 17 1973(216): 9, Dec. 3 1973(244): IO, Apr. 25 1974(158): It, Jul. 9 1974(14X): 12, Dec. 7 1974(163): 13, Dec. I4 197ql76); 14, Jan. 9 1975(182).

- 21”<,,. Figure 8 indicates that these waters are rather similar in 6D, but higher in 6’*0 than precipitation (6D = - lSO*,,,6t80 = - 20’:,,) at coastal areas. In Fig. 9, the 6”O values of lake waters are plotted against Clcontent. It should be noted that in both areas, the enrichment of “0 becomes more pronounced with increasing Cl- content or salinity until the former reaches about 100 g/kg. The 6D values of water having Cl- content higher than lOOg/kg are within a range of - 140 f IS”,,,,in both areas and 6’*0 values are stabilized at - 10 + I’:,,, at the Soya Coast and at - 13 LET I”,,, at the Vestfold Hills. The four lakes of exceptionally high isotopic ratios in Fig. 8 are located close to beaches and belong to the third type.

0 : soya 0

: Vsstfold

coast Hills

DISCUSSlON Factors

controlling

the

isotopic

ratios

of

Antarctic

lakes

According to CRAIG et af. (1963), GOMIANTINI (1965),CRAIG and GORDON(1965) and SOFERand GAT

(1972, 1975), the net isotopic effect in the evaporation of lake water depends on surface temperature of water, humidity of overlying atmosphere, the isotopic ratios of atmospheric moisture, salinity and chemical composition of lake water. Summar~ing these

6 D~8t3’~0+10

L. Nurume

Fig. 8. Relationship between 6D and 6t*O values in the lakes at the Soya Coast and the Vestfold Hills.

16

0. MATSUBAYA et ui authors, the isotopic ratio of water vapor evaporating from a lake is expressed as follows:

0 l

L.8

0 ‘.

-5

0

0

L.Rookery

OYIlYUbi

I’.,

L N”,“rn#!

0

L Hunaroha

where &+ 6,. and 6,, are the fiD or ~5~~0 values multiplied by 10m3 of the evaporating water vapor, lake water and atmospheric moisture. respectively: a the activity of lake water: h the relative humidity of air normalized to the surface temperature of lake water: x the isotopic fractionation factor between water and vapor under equilibrium: f- the correction factor for the hydration effect of dissolved salts and p. p,. and pit. are the transport resistance of the light and heavy isotopic species in the,atmosphere, and of the heavy isotopic species in water, respectively. When a lake is under a steady-state balance between loss of water by evaporation and gain by inflow, the isotopic ratios of evaporating water vapor. (SF, must be equal to those of the inflow, 6,. fntroducing various sets of data into the parameters of equation (1) (see figure caption lo Fig. 10 for these parameters), the isotopic ratios of lake water under

L. ltixiku

-II 34 0 _d ‘p -l! i

1

-210 0

soya coa3t

.

Vesttold

Hills

i

I 0

50

150

100

Cl-, g/Kg Fig. 9. Relationship between fi’*O value and Cl- content in the lakes at the Soya Coast and the Vestfold Hills.

S’“O,%, -50

-10

-20

-30

-40

!!

fin-a8”0+10 Soya

Coast

k Vertfotd

Hills /

100

Don Juan PO

4 0

ci co 200

moisture

for

300

400 Fig. 10. Result of calculations on the isotopic ratios of lake waters in the steady state balance between inflow gain and evaporation loss. Except for A. B and C, all the model lakes have the same salinity anti composition as the brine obtained by 25 times low-temperature concentration of sea water. Lake water of A, B and C is fresh water. 4 and 8 times concentrated sea water, respectively. For all the calculations. pit/p = 0.2 (SOFERand GAT. 1975); p,/p= 1.025 [average of CRAIG et Q/. (1963), GONFIANTINI(1965) and SOFER and GAT (1975)]; big = 1.107, Q, = 1.0013 [PUPEZIN et Q/. (1972)]; r after SOFERand GAT (1975, 1977). Unless otherwise indicated or stated below, h = 0.60 and 6D and 6**0 of inflow = -250 and - 32’:,,,#(shown by open square). 6, = - 110 and - 15 for solid triangle (I), - 230 and - 30 for solid square (II), - 350 and - 45 (shown by open triangle) for five solid circles and four circles designated as A, B, C and E and - 470 and - 60 for solid rhombus (IV). Inflow to E is -200 atid -25:,,.

Antarctic saline lakes various steady state balances were calculated and plotted in Fig. 10. Four points in Fig. 10 designated as I, II, D of III and IV (III is a group of circles A, B, C, D, E) indicate how the steady state lakes isotopically are affected by change in 6D and 6i*O values of atmos: pheric moisture while the 6D and a’*0 values of inflow and the humidity are kept constant. The isotopic ratios of atmospheric moisture for I and IV roughly represent water vapors evaporating from sea water and polar ice, respectively. This indicates that inland lakes would isotopically be much lighter than coastal ones. Also note that all the four steady-state lakes are balanced on the right of the meteoric water line and are shifted from the inflow (shown by open square) to varying extents and directions, depending on the isotopic ratios of the atmospheric moisture. The five solid circles (one of which is D of III) demonstrate that significant changes occur to the 6D and S’*O values of the steady-state lakes when air humidity is varied from 30 to 707s. An inspection of equation (1) with & being read as 6, reveals that the isotopic ratios of moisture affect S, in proportion to h, while those of inflow in proportion to (a - h). Therefore, with increasing humidity, the former will become more important in controlling 6, and the steady-state lake would approach the equilibrium with atmospheric moisture (shown by open triangle in Fig. 10). The reverse would be the case when h decreases. The effect of the isotopic ratios of inflow at h = 60”/, is demonstrated by a shift from D to E which corresponds to the isotopic shift of inflow from -250 and -32”,,, to -200 and -25’:,, Among the lakes grouped in III of Fig. 10, circle A represents the isotopic ratios of a fresh water lake under the same steady state condition as in D. Circles B and C are the steady state lakes in which the salinity and composition are such that sea water attained at 4 and 8 times concentration by freeze-concentration, respectively, with other conditions being the same as in D. These points indicate that the isotopic ratios of a lake water are lowered by an increase in salinity just as they are by humidity increase. This is because the vapor pressure of water becomes lower with increasing salinity and thus the effect of increasing salinity is eventually the same as that of increasing the humidity of the air. The sharp change in the variation trend at point C is due to the fact that from C to D the concentration of Mg*+ and Ca2+ increases whereas Na+ decreases as a result of the precipitation of hydrohalite and that the activity of isotopic water molecules is affected by the change in cationic composition of water (SOFER and GAT, 1972,1975). In natural lakes, such change occurs at much lower temperatures than 0°C. However, the trend is approximately the same as depicted here. When a lake is covered by ice all year round, evaporation of water would occur in layer by layer at the outermost surface of ice and, therefore, the isotopic effect in evaporation would not be significant. G.T.A. 43 I--s

17

On the other hand, the ice should be enriched by 20yX, in D and 3’%,,in “0 (C)‘NEIL, 1968; SUZUOKI and KWURA, 1973) compared to underlying lake water. Therefore, when the steady-state is established in a lake between inflow and evaporation from surface ice, the inflow isotopically. should be equal to the ice. In other words, the lake water should isotopitally be lighter than the inflow by the amounts of isotope fractionation between ice and water. Because the ratio of the hydrogen to the oxygen isotopic fractionation factors is 2013 = 6.7 and because the amount of fractionation is small, the lake water tends to remain close to the meteoric water line. In lakes which are frozen only for a certain period of a year, the isotopic ratios of the lake waters are controlled by a combination of the two processes discussed above. So far, we have assumed that no outflow from lakes exists. When x% of inflow flows out from a lake, the steady state isotope balance may be expressed as follows : 1OOU + 6,) = (100-x)(1 + 6,) + x(1 + 6,),

(2)

where (1 + 6,) is given by equation (1). Equation (2) indicates that a fresh water lake under the conditions set for III of Fig. 10 would shift from the inflow shown by open square to A along the line connecting the two extremes, while x changes from 100 to 0.

Lakes in Southern Victoria Land Lake Fryxell, Lake Vanda and Lake Bonney are covered by 3-4 m of ice at all the seasons, although narrow open surface appears along coasts in summer. Fresh waters underlying the surface ice of these lakes lie close to the meteoric water line as are expected from the above model (Fig. 3). The isotopic ratios of ice of Lake Fryxell are higher by 25%,, in 6D and 4”/,,,,in 6180 than those of the lake water just beneath the ice (Fig. 3). The fractionation factors are similar to those between ice and water in isotopic equilibrium at 0°C. The strongly stratified distribution of salts in Lake Vanda and Lake Bonney has been interpreted as a result of mixing by the cross-diffusion of bottom saline water body and overlying fresh water layer (e.g. WILSON, 1964; SHIRTCLIFFE,1964). According to the model described in the previous section, the characteristic isotopic ratios of the saline bottom waters from the east lobe of Lake Bonney and those from Lake Vanda indicate that these lakes had been shallow saline lakes with open surface before they were covered by fresh water and the diffusive mixing started. On the other hand, the saline bottom waters of the west lobe of Lake Bonney are not stratified isotopically but are similar to the present melt water from the Taylor Glacier. This suggests that the saline bottom water of the west lobe has never been exposed to air for long enough to be isotopically shifted. In later sections, we will speculate possible histories of

18

0. MATSUBAYA et crl

Lake Bonney and Lake Vanda which take account of the different isotopic profiles between these lakes. The close correlation between the isotopic ratios The isotopic and water balances of Don Juan Pond and salinity of lake water observed for the second are the most extreme among the Antarctic saline lakes type of lake (Figs. 8 and 9) can now be interpreted studied. The isotopic ratios as well as the salinity are as follows. The most important effect of dissolved higher in summer than in winter (e.g. from November salts in the Antarctic saline lakes is to lower the freez1973 to January 1975) (Fig. 7), implying that the pond ing tem~rature of lake water. Thus, the higher the water is concentrated by evaporation during a sumsalinity of a lake, the longer it would be subjected mer season and then diluted by fresh water inhow to evaporation from liquid water. Consequently. a throughout the year (HARRIS and CARTWRIGHT, 1978). lake would become isotopicaily heaver and more However, the pond waters collected during the sumshifted to the right from the meteoric water line with mer seasons show that waters of higher salinities tend increasing salinity. The lake water having Cl- higher to have the lower SD and 6% values than the waters than lOOg/kg is ice-free almost all year round and of lower salinities. Furthermore, two summer melt is eventually stabilized at the values controlled by water inflows having Cl- content of 80 to 140 mg/l focal climatic and hydrological conditions. The isotopically are heavier than the most of the pond 6Db’*0_Clcorrelation is the unique feature waters. These facts are in accord with the predicted obtainable under rather mild climate at the Antarctic isotopic change with saiinity of steady state lakes. A, coasts where surface ice melts away for a certain B. C, D, in III of Fig. 10. This implies that the period of year depending on the salinity of lake water. isotopic ratios of the pond water were controlled by Lake Oyayubi and Lake Nurume at the Soya Coast the steady-state balance between evaporation and and Lake Rookery and Lake J at the Vestfold Hills infiow. have exceptionally high isotopic ratios (Figs. 8 and 9). The melt water inflows to the pond in the summer Except for Lake Nurume, these lakes are situated season cited above have already been enriched in the close to a beach. The isotopic ratios of these four heavy waters by evaporation. The isotopic ratios of lakes can be satisfactorily reproduced by equation (1). true inflow to this pond may be represented by those ~suming that sea water flows into them and using of snow faIIs into this area of the Dry VaIIey which the same parameters as those used to reproduce the are -230°t,, in dD and - 30”,,, in 6180. The isotopic isotopic ratios of other saline waters of these areas. ratios of atmospheric moisture of this area should An important implication of this is that the salinity be equal to or even lower than those shown by an of such lakes would increase with time and highly apen triangle of Fig. 10. Taking these values into saline lakes could form by this way. A significant account. Fig. 10 indicates that Don Juan Pond is in amount of salts, especially mirabilite, may precipitate a steady-state balance under much drier climate than during such a process. If such a lake is blocked from Lake Vanda and Lake Bonney. As a matter of fact, sea water inflow as a result of the uplift of coastal water activity in the pond water is about 0.48 when land and starts to receive inflow from melt waters. the salinity reaches SO?
19

Antarctic saline lakes

10/

-

0

L.

n

Dingle

0

6

Deep

Na* NIg++

L.

Club L.

4)

0 29.5

L. Bonncy,

west

mI

52 .5

: n

29.5 \

L. Bonney,

East

L. ltiriku 0

100

200 Cl’,

Q/K0

Fig. 11. Relationship between Na+/Mg’+ ratio and Cl- content in the lakes from the Soya Coast (open circles) and the Vestfold Hills (solid circles) and in Lake Bonney. For explanation, see text. The data for the four lakes from the Vestfold Hills are after MCLEOD (1964). Their Cl- contents in g/kg were recalculated from his data in g/l and a linear relationship between the density and Cl- content empirically obtained’for the saline lake waters of the Soya Coast and the Vestfold Hills. Other data are from Tables 1 and 2.

the lake was evolved from sea water. The Na+/Mg*+ ratio is more useful than the Na+ concentration, because the ratio would remain unaffected even if an evolved lake is later diluted by fresh water. In Fig. 11 the Na+/Mg*+ ratios of various saline lakes are plotted against their Cl- contents. Curve I in this figure is the estimated change of Na+/Mg*+ ratio in the freeze-concentration based on the experimental results of THOMPSONand NELSON (1956). The rapid drop of the Na+/Mg’+ ratios above Cl- = 140 g/kg is due to the onset of crystallization of sodium chloride, whereas the gentle slope below that point is due to the precipitation of mirabilite. Curve II in Fig. 11 represents the similar change in Na+/Mg2+ ratio when sea water is concentrated by evaporation at 0°C. It was calculated from the solubility data of sodium chloride (SEIDELL, 1953, pp. 290, 770, and 965). The precipitation of sodium chloride begins at somewhat higher Cl- content than in the case of freeze-concentration. This is due to the difference in temperature for the two processes. Figure 11 indicates that the relationship between ratio and Cl- content of saline lakes the Na+/Mg’+ at the Soya Coast (open circle) and the Vestfold Hills (solid circle) is in general accord with that predicted from curve I or II. The low Na+/Mg’+ ratio in Lake Itiziku, for instance, is compatible with the fact that

the lake is nearly dried up and that the lake water has been saturated with sodium chloride at about 0°C. At the Vestfold Hills, Lake Dingle and Lake Stinear are on curve I, being saturated with mirabilite, but not with sodium chloride. Deep Lake and Club Lake are saturated with sodium chloride and close to curve I. The chemical compositions of these lakes were recalculated after the data given by MCLEOD (1964) (see the caption to Fig. 11). Similarly, the Cl-/Brratio of lake water serves as a useful means to deduce the evolution history of lake water. In Fig. 12, the estimated changes of Cl-/Brratio with increasing Cl- content are shown by curve I for the case of freeze-concentration and by curve II for evaporation at O”C, respectively. In both cases, the partition coefficient, (Cl-/Br-) in NaCl/(Cl-/Br-) in water, was assumed to be 10, although it varies from 6 to 14 depending on the temperature and composition of water (BRAITSCH and HERRMANN, 1963). Although the amount of available data on Br- content is much less than that on Na+ and Mg2+ contents, the observed trend of variation in Cl-/Brratio agrees with that in Na+/Mg’+ ratio. Note that Deep Lake and Club Lake are on the saturation line of sodium chloride in both Na+/Mg2+ vs Cl- and Cl-/Brvs Cl- plots. The data for the lakes in the Vestfold Hills are from MCLEOD (1964).

0. MATSUBAYA

2Q

Figures I1 and 12 indicate that in the west and east lobes of Lake Bonney, the Cl- contents of the saline waters are lower than those expected from the Na+/Mg2+ and Cl-/Brratios. It should be noted, however, that the Cl- content increases with increasing depth without change in Na*/Mg’+ and especially Cl-/Brratios. This strongly suggests that the saline bottom waters in the two lobes were once located on curve I or 11 with almost the same Na+/Mg” and Cl-,/Brratios as the present, when they were the shallow saline lakes as mentioned before. The present Cl- contents may be the result of dilution of the saline waters with the overlying fresh waters. Such dilution should have occurred through cross-diffusion between the two layers as is discussed in a later section. If the above model is correct, the Cl- content of the original brine of the west lobe may be estimated to be 166g/kg by extrapolating the data points on Figs. 11 and 12 to right until they hit curve II. This implies that the extent of evaporation-concentration of sea water in the west lobe was such that 30516of Na+ in the original sea water was crystallized as mirabilite and sodium chloride. In the east lobe, the Clcontent quickly increases at the bottom and the Na+/Mg*+ and Cl-/Brratios likewise increase. The lowermost brine of the east lobe lies close to curve II in both Figs. 11 and 12 and is nearly saturated with sodium chloride at the present bottom tempera-

et (11

ture (about -3°C). This may be due to the dissolution of sodium chloride in the sediment into the lowermost brines. Sodium chloride in the sediment was reported by YAMACATA et a/. (1967) and WILSON and HENDY (1974). If the Na+/Mg2+ and Cl-/Brratios between 20 and 29Sm depths are taken to be the original values not affected by this effect, the original Cl- content is estimated to be 172 g/kg by the same method as applied to the west lobe. The 70’?:, of sodium ion has to be removed in order to produce this brine by the evaporation-concentration of sea water. WILSON and HENDY (1974) estimated that the amount of sodium chloride in the sediment is at least 7 x 10’ ton. This is only about 1.59:, of the sodium chloride left in the present lake water of East Lobe and cannot account for the inferred amount of sodium chloride crystallized from sea water. Dissolved cations in Don Juan Pond are predominantly Ca2 +. Na+ and Mg’ + are minor cations (Table 1). The Na+/Ca2’ ratio varies from 0.19 to 0.02 (in mole ratio) in the cycle of summer concentration and winter dilution as mentioned previously. As shown in Fig. 13, when the Cl- contents are lower than 210 g/kg, the NacKa2’ ratios are fairly constant (0.1%0.17). To the contrary, for the brines of Cl- higher than 210 g/kg, the Na+/Ca’+ ratios decrease along the saturation curve of sodium chloride in the calcium chloride solution at 0°C. Thus, Don Juan Pond should be precipitating sodium chloride

800 L. Stinear

x0Water

Sea

0

.a L. Dingle

0

II

600 Club

L.

Deep L. 400 CliG=

\ 32.5 1 200

yf

!

\

\

0

Cl-, g/Kg ratio and Cl- content in the lakes at the Soya Coast (open Fig. 12. Relationship between Cl-/Brcircles) and the Vestfold Hills (filled circles) and in Lake Bonney. Data sources are the same as in Fig. 11.

Antarctic

when concentrated beyond Cl- = 210gJkg in summer. The leftward shift of the lake water point in Fig. 13 when it is diluted below the above Cl- concentration, is similar to that observed for the bottom saline waters in the east and west lobes of Lake Bonney (Figs. 11 and 12) and supports the previous interpretation of the data. In Lake Vanda, the Na+/(Ca’+ + Mg’+) ratio is about 0.3 and similar to that in Don Juan Pond, although the Mg2+/Ca2+ ratio in the former is about 20 times that in the latter (Mg2+/Ca2+ = 0.50 in Lake Vanda). On a similar basis to that discussed above, the Cl- content of the original saline water of Lake Vanda should have been about 197 g/kg (see Fig. 13), if it was saturated with sodium chloride. Otherwise, the Cl- content may have been lower than 197 g/kg, but would not have been much lower than the value estimated for the east lobe of Lake Bonney (172 g/kg), because the bottom saline waters of these two lakes are isotopically similar to each other and should have been formed under similar climatic conditions. The ground waters from the bore hole of DVDP 4 which penetrated into the central part of the lake floor have Cl- contents ranging from 74 to 114 g/kg. They may be the original saline water which remained in the lake sedmiments and were diluted by meteoric ground waters. The Mg2+/Ca2+ ratios in Lake Vanda and Don Juan Pond are considerably larger than those obtainable by simple freeze-concentration of sea water. The Cl-/Brratios in Lake Vanda and Don Juan Pond are 8000 and 12,000, respectively (TORII et al., 1975,

saline lakes

21

1977). more than 10 times higher than sea water. These facts strongly stand against the view that the calcium-rich salts in Lake Vanda and Don Juan Pond directly came from sea water. On the other hand, the stable isotopic ratios of dissolved sulfates in Lake Vanda (RAFTER and MIZUTANI, 1967; NAKAI et al., 1975; SAKAI, MATSUBAYA and TORI], unpublished data) and geological evidence (CARTWRIGHT et al., 1974) strongly indicate that the salts are marine in their ultimate origin. Evidently, some mechanism(s) other than simple freeze- or evaporation-concentration of sea water is needed to interpret the unusual enrichment of Ca2+ over Mgzt in the Wright Valley (BOWSER et al., 1970).

History of Lake Bonney and Lake Van& As mentioned in the former two sections, Lake Bonney and Lake Vanda once had been shallow saline lakes and then overlain by fresh water. WILSON (1964) and SHIRTCLIFFE(1964) derived diffusion equations which describe the vertical distribution of salts in Lake Vanda and in Lake Bonney, respectively. Under certain assumptions, they were able to obtain the age of the lake as the time elapsed since the diffusion commenced. In this section, it will be shown that a similar diffusion equation can be solved for the age and thickness of the initial saline water layer by using the parameters estimated independently in the foregoing sections. Then, based on these and other information so far obtained, we will deduce an acceptable history of Lake Bonney and Lake Vanda.

0.4

Saturation of NaCl

0.3

curve at

0 OC

Nat ca++

Fig. 13. Relationship spond

to those

between Na+/Ca*+ ratio and Cl- content in Don Juan Pond. of Fig. 7. Data sources are TORI] et al. (1977) and their unpublished

Numbers corredata (Table 1).

0. MATSUBAYA er ~1.

22

If a saline water layer of a thickness of h m is covered at time f = 0 by a fresh water layer of an infinite thickness. the concentration profile of a given ionic specie-s along the vertical water column at time f since the beginning of diffusion may be expressed as follows (CRANK, 1975. p. 15):

5

erf P(t+

$,

+

erf Pf%-Rt]

p= h/2(Dt)‘h

4

3

%

where C is the content of an ion in water at a distance of .Y m above the bottom, C, is the content of the ion in the initial saline water. and D is the diffusion coefficient of the ion. Equation (3) reduces to

2

L

1

h (C/C& =0 = erf _____ Z(Dt)’ .? at .Y = 0. The dilution

ratio at the bottom. (C/C,),,,, is equal to the ratio of the present concentration of Cl- at the bottom water to the Cl- concentration in the originai saline waters before the start of diffusion. The latter values for Lake Vanda and Lake Bonney have been estimated from Figs. 11, 12 and 13 as mentioned earlier. From these values, we first obtained the value of the scaling factor. h/2(Dt)“‘. for each lake. Then, the value of h was estimated for each lake which gives the best agreement between the observed and calculated vertical distributions. The results of such fitting are shown in Fig. 14. Finally, by using appropriate diffusion constant, the age of each lake was estimated. The results of such calculation and the parameters used are summarized in Table 3. In these calculations, we assumed that vertical molecular diffusion only is the important process of material transport. This is justified because the temperature distribution in these lakes are satisfactorily explained by the model that heat is transported only by molecular diffusion of water (SHIRT~LIFFE, 1964: YUSA. 19751. YUSA (1977) also suggested that absorption of solar energy by the bottom saline water would not cause any significant convection in the saline layer. On the other hand, CRAIG (1966) emphasized uniform chemical composition along the vertical water column of Lake Vanda and Lake Bonney. He pointed out that upward convective diffusion is more important than molecular diffusion. because other-

Table 3. Ape. Cl- content

Lakes _- .._.._L&SO banda ditto Lake Bonney West Lobe ditto East Lobe

Cl-,

0

0.2

II

a.4

C/CO

Thickness,

197 170

4.2 4.9

166 145 172

11.9 14.2 17.0

m

0.8

1.0

Fig. 14. Vertical distribution of Clcontent in Lake Vanda and Lake Bonney. Solid curves are the best fits of diffusion equation (3) to the observed values (see text). Dotted lines show the progressive change of distribution with change in scaling factor P = h/2(Z)t)“’ in equation (3) or time since the start of diffusion.

wise the chemical composition would show a systematic variation along depth. However, large fluctuations in the compositional data reported so far make it rather difficult to decide whether or not the chemical composition is actually uniform along the depth profile. The molecular diffusion coefficient of an ion varies with the temperature of water and the concentration of other ions as well as its own concentration (ERDEYGR~~z, 1974, pp. 186203). Therefore, it must vary with time and depth. However, in these lake waters, chloride predominates over other anions and its diffusion coefficient is almost equal to the average of those of cations. Therefore, only the diffusion of chloride ions was considered in the following calculation and its diffusion coefficient was assumed to be 1.0 x 10e5 cm*/sec. As shown in Fig. 14, the calculated distribution of Cl- in the east lobe of Lake Bonney does not fit satisfactorily to the observed one. This may be due

and thickness of the initial saline water layers of Lake Vanda estimated by the new diffusion model g/kg

0.6

Age,

yrs 1,200

1,200 5,800 5,800 2,600

b.p.

and Lake Bonney

Remarks saturated with undersaturated

NaCl with NaCl

evaporation-concentration freeze-concentration

Antarctic saline lakes to the fact that the Cl- distribution in this lobe has been disturbed by dissolution of sodium chloride from the lake sediments. SHIRTCLIFFE(1964) estimated the age of the east lobe to be only 60 yr by solving a diffusion equation in which the saline water below 26 m depth was taken to be original. Sodium chloride deposits exist in the lake sediment (YAMAGATAet al., 1967; WILSON and HENDY, 1974). Therefore, the original saline water should be saturated with sodium chloride, whereas the present water below 26 m depth is not. This contradicts his assumption. If the Clcontent of the original saline water is made higher, the age must be longer than his estimation. For the west lobe of Lake Bonney, two ages were listed in Table 3; one was based on the original Clcontent estimated by freeze-concentration (Curve I in Figs. 11 and 12) and the other by evaporation-concentration (Curve II in Figs. 11 and 12). The good agreement between the two calculations indicates that the Cl- content of the original brine does not sensitively affect the results. Similar examples are given in Table 3 for Lake Vanda, too. The estimated ages of Lake Vanda are consistent with the age of 1200 yr estimated by WILSON (1964) who assumed that all the salts initially were on the lake floor in an infinitely thin layer. Combining these ages and taking into account the isotopic and chemical data discussed so far, the evolution of Lake Bonney and Lake Vanda may be speculated as follows; we assume that at the initial stage both lakes were dried-up with their salts being deposited on the lower parts of the basins. At about 6000 yr B.P., melt water from the Taylor Glacier started to feed the west lobe of Lake Bonney, forming a shallow saline lake by dissolving the salt deposits. Because the saline waters of the west lobe isotopically are not shifted from the inflow, the saline lake must have been covered by ice soon after its formation. This would be possible if the rate of inflow was faster than the rate of dissolution of the bottom salts. In such a case, the lake at first would be covered by melt water and then the saline water would form at the bottom as the salts dissolve into the bottom layer. The lake would have been covered by ice soon after its formation and, thereafter, the isotopic and water balances in this lake have been kept between water inflow and evaporation from ice. On the other hand, by some later stage of this event, a shallow saline pond formed at the bottom of the present east lobe of Lake Bonney and probably at the bottom of Lake Vanda. The saline lakes would easily have formed and remained unstratified if the inflow rates into the lakes were smaller than the rate of salt dissolution. The isotopic ratios of these lakes must have undergone the significant shifts from those of inflow and must have acquired the present values soon after its formation. At about 120&26OO yr B.P., certain climatic changes increased the rate of melt water inflow into Lake Bonney and Lake Vanda. In Lake Bonney, the

23

melt water from the Taylor Glacier started to overflow into the east lobe, causing the stratification of the east lobe. Lake Vanda also was stratified by this event. However, because the age of the east lobe of Lake Bonney is not as certain as that of Lake Vanda, the difference in the estimated age of this event for Lake Bonney and Lake Vanda should not be taken to be significant. Apart from the current advance of the Taylor Glacier (Taylor I) (DENTON et al., 1971), the last glaciation to affect the McMurdo Sound area was the Ross Sea I Glaciation (DENTON et al., 1971). It flowed into the valleys from the seaward end and caused deep (up to 340 m) ice-dammed lakes to be formed. In the Taylor Valley, this lake, which extended from the present Lake Fryxell to several kilometers beyond Lake Bonney, was at its maximum by 18,OOOyr B.P. and finally drained about 9000yr B.P. (DENTON, personal communication) as the rising sea refloated the ROSS Ice Shelf. Therefore, the series of events speculated above should have taken place soon after the recession of the Ross Sea I Glaciation. SUMMARY (1) Three saline lakes on the beaches of the Soya Coast and the Vestfold Hills are still receiving sea water as the major inflow and maintain exceptionally high 6D and 6180 values. (2) Other lakes of these two areas are isolated from sea water. They show wide ranges of variation in the isotopic and chemical compositions and in salinity, depending on whether they are fed by melt water from the East Antarctic icesheet or from local precipitation. The lakes of Cl- content greater than lOOg/kg are ice-free for more than half a year and have unique steady state isotopic ratios (6D = approx - 125 to - 155”,,,,, 6’*0 = approx -9 to - 14”;J which are determined by climatic conditions prevailing at the coastal areas. The lakes of the lower Cl- content than lOOg/kg are covered by ice for a longer fraction of a year and the isotopic ratios lie between those of the precipitation of these areas and those of the lakes of Cl- > lOOg/kg. (3) The west and east lobes of Lake Bonney in the, Taylor Valley of the Southern Victoria Land started as shallow saline lakes formed at about 6OOOyr B.P. by flooding of fresh water on to dried salt deposits. The west lobe was covered by fresh water soon after the formation and the isotopic ratios of the saline bottom water were not modified by evaporation from those of the icesheet melt water. On the other hand, the saline lake of the east lobe remained ice-free and acquired the similar isotopic shifts as observed in the present-day saline lakes at the Soya Coast and the Vestfold Hills until at about 2600yr B.P. At that time, melt water from the Taylor Glacier started to flood over the saline water and formed stratified lake of the present feature. Lake Vanda seems to have a similar history to that of Lake Bonney.

0.

24

(4) The chemical and (2) and in Lake

MATSUBAYA ef ul

compositions of the lakes in (1) variously differ from that

Bonney

of sea water but can be explained by different degrees of concentration of sea water at near freezing temperature of sea water, However, the chemical composition of Lake Vanda as well as that of Don Juan Pond cannot be explained by simple concentration of sea water at low temperature.

A~l\nc~~l~(!qt~m;,nrs--Thewater samples

from the Southern

Victoria Land were collected mostly by members of Japanese summer parties of the Dry Valley Drilling Project from 1972 to 1974. those from the Soya Coast by members of the 13th Japanese National Antarctic Research Expedition (1972), and those from the Vestfold Hills by members of the Australian National Antarctic Research Expedition (1974). We are indebted to these individuals. especially to H. MURAYAMA, Yokohama National University and S. NAKAYA. Hokkaido University who gave us the hydrological information from the field observations and also permitted us to use unpublished data on the chemical compositions of lake waters. We are indebted to C. J. BOWSER, University of Wisconsin. for his constructive criticism as a referee of this journal and C. H. HENDY. University of Waikato for his critical reading of the manuscript. We also thank S. TAKAMI and T. Noot of the institute for Thermal Spring Research. Okayama University. for their technical assistance.

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Antarctic saline lakes SOFERZ. and GAT J. R. (1975) The isotope composition of evaporating brines: Effect of the isotopic activity ratio in saline solutions. Earth Planet. Sci. Left. 26,

25

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