ALKALI METAL CONSTRAINTS ON THE ORIGIN OF SALTS IN LAKES AND PONDS FROM THE McMURDO DRY VALLEYS, ANTARCTICA

Alkali metals in lake, pond, and ice samples of the McMurdo Dry Valleys in southern Victoria Land, Antarctica were studied to clarify the origins of dissolved salts and to estimate their evolutional history. The contents of Li, Rb and Cs largely varied ranging from 0.30ppb to 390ppm, 0.06ppb to 514ppb and 0.001ppb to 90.9ppb, respectively. The low rare alkali metal contents with high Ef_m [Ef_m=(m/Cl)_s/(m/Cl)_, m; alkali metal, s; sample, sw; seawater] values of the pond waters and ice samples in the Labyrinth imply that dissolved salts are mainly derived from atmospheric fallout. The decrease of Ef_m values with increasing Cl content of the Labyrinth pond waters suggests that rare alkali metals are removed from waters during freeze and evaporative concentrations. The bottom waters of Lakes Fryxell and Bonney may originate from trapped seawater influenced by water-rock interaction. The extremely high Ef_m values (especially the Ef_, Ef_ values) of Don Juan Pond water and the bottom water in Lake Vanda can be explained by the contribution of deep ground waters

ORIGIN OF DISSOLVED SALTS INFERRED FROM LITHIUM ABUNDANCE IN LAKE AND POND WATERS IN THE ANTARCTIC McMURDO DRY VALLEYS

Lithium and major ionic components in lake, pond and meltstream waters and ice samples in the McMurdo Dry Valleys of southern Victoria Land, Antarctica were determined to elucidate the origin of dissolved salts. The Li concentration of the bottom water in Lake Fryxell (0.13mg/L) was similar to that of seawater (0.178mg/L), but those of Lakes Bonney (5.1-8.8mg/L) and Vanda (27.0mg/L), and Don Juan Pond (390mg/L) were much higher. In contrast, the Li concentrations in the pond waters, glacial meltwaters, pond ice core in the Labyrinth were generally low (less than 88.0μg/L). The enrichment factor for Li [Ef_=(Li/Cl)_/(Li/Cl)_] was used to discuss the origin of dissolved salts in the water bodies. The logEf_ values of the pond waters in the Labyrinth linearly decrease with Cl concentration. Whereas these values in the bottom waters of Lakes Fryxell, Bonney, Vanda and Don Juan Pond were largely deviated from the Labyrinth pond water line, suggesting the difference of sources and/or concentration processes. The result of the dissolution experiment of dolerite in NaCl solution at 40℃ and the high Li concentrations with high Ef_ values of Lake Vanda and Don Juan Pond suggest that their salts are originated from ground waters influenced by hydrothermal activity. Freeze concentration experiment of seawater showed that some Li migrates into the ice phase. The freezing fractionation of Li into the ice phase, therefore, may be a significant elimination mechanism of Li from pond waters in the Labyrinth. The repeated cycles of freezing of the pond waters and subsequent ablation of ice will lead to the saline waters having low Ef_ values

ナンキョク ミナミ ビクトリアランド ノ ラビリンス ニ オケル チスイ チュウ ノ エン キイン リチウム ト ホウソ カラ ノ コウサツ

南極南ビクトリアランド・ドライバレー地域・ラビリンス(77°33′S, 160°50′E)の池水中の塩起因を明らかにするため, LiとB含量を測定した。また, これらと比較するため, ドライバレー地域のバンダ湖, ドンファン池, フリクセル湖およびボニー湖ならびにベストフォールドヒルズのディープ湖とエース湖についても同様の測定を行った。ラビリンスの淡水および塩水中のLiおよびBの濃度および濃縮係数などより, 池水の化学成分は海水や熱水起源ではなく, おもに風送塩に起因するものであることが明らかになった。これらのことはラビリンスの塩水池が風送塩を含む氷河氷や雪の融水が凍結濃縮を繰り返すことによって形成されたとする考えを支持している。塩化物イオン含量の増加とともにB/Cl比が減少することから, Bは凍結過程で氷に移行し, 蒸発によって徐々に揮発していくと考えられる。Lithium and boron contents in pond waters of the Labyrinth (77°33′S, 160°50′E) of the Dry Valleys region in Southern Victoria Land, Antarctica were determined to elucidate the origin of dissolved salts. Also Lakes Vanda, Fryxell and Bonney, and Don Juan Pond in the Dry Valleys region as well as Deep and Ace Lakes in the Vestfold Hills were studied for comparison. The contents and enrichment factors of Li and B in both freshwater and saline ponds in the Labyrinth reveal that major ionic components in the pond waters originate mainly from atmospheric salts, rather than from trapped seawater and/or hydrothermal waters. These results support that the saline pond waters in the Labyrinth can be formed by the successive concentration through evaporation of pond waters supplied from glacial ice and/or snow containing atmospheric salts. The decrease of B/Cl ratios with the increase of chloride ion contents implies strongly that B is transported into ice during freezing of pond water, then volatilizes gradually to the atmosphere under frigid conditions

CHEMICAL CHARACTERISTICS OF POND WATERS IN THE LABYRINTH OF SOUTHERN VICTORIA LAND, ANTARCTICA

A large number of fresh and saline ponds are found in the Labyrinth (77°33\u27S, 160°50\u27E) of the upper Wright Valley in the Dry Valleys region of southern Victoria Land, Antarctica. They are located near the terminus of the Wright Upper Glacier between 800-1000m above sea level. From a limnological point of view, the most interesting problems concerning these saline ponds are the origin of their salts and their evolutional history. Chloride ion contents vary remarkably among the ponds ranging from 0.0049 to 52.4g kg^. Surprisingly, more than a half of the ponds are saline with the highest chloride ion content being 2.7 times greater than that of seawater. The δD and δ^O values of the pond waters indicate a snow and/or glacier melt-water origin, and that the ponds underwent subsequent alteration due to evaporation or freezing. The composition of chemical components reveal no evidence of trapped seawater. Thus the salt concentrations in the Labyrinth pond waters must be explained principally by the accumulation of atmospheric salts and subsequent repeated cycles of evaporation and freezing of the pond waters over a considerable period of time. (This paper is submitted to the special issue of Hydrobiologia.