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Stability in hypolimnion of Deep Rift Lakes, East Africa

东非深裂湖低水位的稳定性

基本信息

批准号：
03041012
负责人：
NAKAO Kinshiro
金额：
$ 11.2万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-03041012/
关键词：
Rift lake Meromictic lake Dissolved gases of Carbon dioxide Stable stagnant layer Last glaciation Equatorial climate Trade-wind climate Climatic change 深水層メロミクティック構造溶存メタン熱帯湖熱塩対流リフトバレ-

项目摘要

Lake Kive is situated in the equatorial region of the Rift Valley, East Africa, at latitude 2ﾟS and longitude 29ﾟE ; It discharges from the south end of the lake by the Ruzizi River into Lake Tanganyika located 150km downstream.The lake basin was formed by the tectonic activity in 50X10^4yr.B.P. or 100X10^4yr.B.P., newer than the Tanganyika Lake in about 2000X10^4yr.B.P., The lake-level had been fell down to 300 meters lower than present one, during the last glaciation from 7X10^4yr.B.P. to 1X10^4yr.B.P., then the Kivu Lake was a closed lake in this time,Its morphometric features are : 2,300km^2 in area of lake surface, 7,300km^2 in basin area including the lake surface, 485m in maximum depth and 240m in mean depth. The sounding results of water temperature indicate significant tendency of increasing from the depth of 90m to the bottom at all sites, it is characterized that the density of lake water is increased by a dissolved matter and is meromictic. The water of lake Kivu has been stabilized by the increase on the amounts of dissolved gases of carbon dioxide and methane and the salinity contents of CaCO_3, K and Na discharged from the bottom floor through a thin sediments cover.On the other hand, the Tanganyika Lake is oldest rift lake, covered by thick sediments of 2,000m and then is not meromictic and the morphonetric features are : 32,000km^2 in area of lake surface, 238,700km^2 in basin area including the lake surface.From the results of water budget for the both lakes, it became clear that the annual precipitation in the Kivu basin of equatorial climate incleased from 790mm to 1,500mm after the last glaciation, but was not changeable in the Tanganyika basin of trade-water climate. During the last glaciation, the both lakes became a closed lake and the zone of trade-wind climate spread over the several hundreds kilometer to the north.

基夫湖位于东非大裂谷的赤道地区，南纬2 ° S，东经29 ° E，湖的南端经鲁齐齐河注入下游150公里处的坦噶尼喀湖，湖盆形成于50 × 10 ^4 yr. B. P.或100 × 10 ^4 yr. B. P.的构造活动，比坦噶尼喀湖更新约2000 × 10 ^4年B. P.，在末次冰期（7 × 10 ^4 ~ 1 × 10 ^4 yr. B. P.），湖平面下降到现在的300米以下，基伍湖是一个封闭的湖泊，其地貌特征是：湖面面积2,300平方公里，包括湖面在内的盆地面积7,300平方公里，最大水深485米，平均水深240米。水温测深结果表明，各测点从90 m深度到底部水温有明显的上升趋势，表现为溶解物使湖水密度增加，湖水呈半混溶状态。Kivu湖的湖水已经稳定，因为溶解的二氧化碳和甲烷气体的量增加，CaCO_3、K和Na的盐度含量通过薄的沉积物覆盖层从湖底排出。另一方面，坦噶尼喀湖是最古老的裂谷湖，被2,000米厚的沉积物覆盖，因此不是部分混合的，其形态特征是：湖泊面积32,000 km^2，流域面积238,700 km^2，从两湖的水量平衡结果可以看出，赤道气候的基伍湖流域末次冰期后年降水量增加了790 ~ 1500 mm，而贸易水气候的坦噶尼喀湖流域年降水量变化不大。末次冰期时，两湖成为封闭湖泊，信风气候带向北延伸数百公里。