Geochemical Study of the Formation Process for the Saline Lakes in the Dry Valleys, South Victoria Land, Antarctica

A simple model is proposed for the present chemical composition of the saline lakes in the Dry Valleys. A diluted water of sea salt whose compositional ratio was that of sea water was concentrated by evaporation to the present chlorinity. During the concentration process, a part of Na^+ and K^+ replaced Ca^ and Mg^ of the sediment or weathering rock, and some part of CaSO_4 deposited from the solution. All the reaction proceeded under an ionic massbalance. This simple idea can beautifully explain the origin of the chemical compositions of Lakes Vanda and Bonney. The salt concentration profiles in these saline lakes can be explained by the molecular diffusion (or ionic diffusion) of dissolved chemical substances from the bottom layer to the surface layer. The vertical transport of salt from the bottom layer is given by a conventional Fickian equation, with a diffusion coefficient (D); [numerical formula] where C is the salt concentration, z is the vertical distance coordinate increasing upward from z=0 at the bottom to z=h at the top of the saline layer, and t is time. For eq. (1), the initial and boundary conditions are [numerical formula] [numerical formula] [numerical formula] The solution of (1), obtained by the Laplace transformation with the boundary conditions (2)-(4) is [numerical formula] whereφ_1 is a function of time (t), height (z), and diffusion coefficient (D), its complete form being [numerical formula] The value of t of these saline lakes in the Dry Valleys is estimated by trial and error computation using eq. (5) and (5a). The age of stratification estimated for the salt diffusion from the bottom layers ranges from 1,000 to 1,250 years

Distribution and origin of some trace metals in Lake Vanda, Antarctica

In 1978-79 field season, water samples were collected vertically at Lake Vanda. The concentrations of Al, Fe, Ni, and Cu were determined. The vertical profile of copper is similar to that of chlorinity. Aluminium has constant value from the surface to the bottom. The concentrations of iron are also constant from the surface to 55m but below this layer iron increases abruptly. In the layer above 55m, iron should be present as trivalent solid form and precipitated to the bottom where iron is reduced and diffused upward. This process could be repeated to account for the iron distribution of the observed profile. Copper shows a good correlation with chlorinity which is not removed significantly in the lake. The copper to sodium ratio of sea water is three orders of magnitude smaller than that of deep water of the lake, which has a similar ratio to Antarctic snow. The data supports that the origin of copper is air-borne particles via glacier and glacial melt water

ドライバレー チイキ ノ エンコ ノ セイセイ カテイ ニ ツイテ

ドライバレー地域に点在する3つの塩湖,バンダ,ボニー,フリクセルの各湖について,底層にみられる高塩分濃度水の生成過程および塩成層生成年代について考察した.高塩分濃度水は,海水組成を有するうすい水,あるいぱ海塩を起源水として,長年月の蒸発,濃縮により現在の底層水濃度まで濃縮された.その過程において,岩石,堆積物等とのイオン交換反応がおこり,Na^+,K^+は溶液から失われ,Ca^,Mg^は溶液へ与えられ,Ca^の一部はCaSO_4として沈積したことで説明できる.底層水の濃度傾斜については,形成期の塩湖はきわめて小さな氷河湖であった.その氷河湖へ大きな気候変動があり,周辺氷河融水が流入し,底層の高塩濃度水中の化学成分は底層から上層へ分子拡散,またはイオン拡散により拡散し,現在のような鉛直分布となった.この考えに基づいて,Fickの式,塩の拡散係数,実測塩濃度を用いて計算,その結果,1,000～1,250年前に気候変動があったと考えられる.A simple model is proposed for the present chemical composition of the saline lakes in the Dry Valleys. A diluted water of sea salt whose compositional ratio was that of sea water was concentrated by evaporation to the present chlorinity. During the concentration process, a part of Na^+ and K^+ replaced Ca^ and Mg^ of the sediment or weathering rock, and some part of CaSO_4 deposited from the solution. All the reaction proceeded under an ionic massbalance. This simple idea can beautifully explain the origin of the chemical compositions of Lakes Vanda and Bonney. The salt concentration profiles in these saline lakes can be explained by the molecular diffusion (or ionic diffusion) of dissolved chemical substances from the bottom layer to the surface layer. The vertical transport of salt from the bottom layer is given by a conventional Fickian equation, with a diffusion coefficient (D); [numerical formula] where C is the salt concentration, z is the vertical distance coordinate increasing upward from z=0 at the bottom to z=h at the top of the saline layer, and t is time. For eq. (1), the initial and boundary conditions are [numerical formula] [numerical formula] [numerical formula] The solution of (1), obtained by the Laplace transformation with the boundary conditions (2)-(4) is [numerical formula] whereφ_1 is a function of time (t), height (z), and diffusion coefficient (D), its complete form being [numerical formula] The value of t of these saline lakes in the Dry Valleys is estimated by trial and error computation using eq. (5) and (5a). The age of stratification estimated for the salt diffusion from the bottom layers ranges from 1,000 to 1,250 years

ナンキョク バンダコ ノ ビリョウ キンゾク ノ ブンプ ト ソノ キゲン

1978-79年のフィールドシーズンに南極バンダ湖(水深68m)で表層から底層まで10層の採水を行い, その微量金属(Al, Fe, Ni, Cu)を定量した。銅は塩素と同様な分布を示した。アルミニウムは水深によらずほぼ一定の値を示した。鉄は55m以浅ではほぼ一定の値を示すが, それ以深で急激な濃度増加が認められた。これは3価の鉄が底付近で還元され上方に拡散し, この過程をくり返したためと考えられる。湖水中で大きな除去過程がない(対塩素比が水深によらずほぼ一定)と考えられる銅を微量金属の代表として, その起源を考察した。湖水のCu/Na比は海水に比べ3桁以上高い値であり, またCu/Na比は南極点などの雪氷の値に近似しており, エーロゾル-降雪-氷河-氷河融水-バンダ湖の径路が微量金属の起源と考えられる。In 1978-79 field season, water samples were collected vertically at Lake Vanda. The concentrations of Al, Fe, Ni, and Cu were determined. The vertical profile of copper is similar to that of chlorinity. Aluminium has constant value from the surface to the bottom. The concentrations of iron are also constant from the surface to 55m but below this layer iron increases abruptly. In the layer above 55m, iron should be present as trivalent solid form and precipitated to the bottom where iron is reduced and diffused upward. This process could be repeated to account for the iron distribution of the observed profile. Copper shows a good correlation with chlorinity which is not removed significantly in the lake. The copper to sodium ratio of sea water is three orders of magnitude smaller than that of deep water of the lake, which has a similar ratio to Antarctic snow. The data supports that the origin of copper is air-borne particles via glacier and glacial melt water