Microbialites and hydrochemistry of the crater lake of Satonda

Abstract

The Satonda crater lake is up to now the only known "marine" lake with an increased alkalinity compared to seawater. Therefore, the lake contains a decreased amount of Ca2 +. Its pH values about 8.5-8.6. The lake was originally filled with freshwater, which is evident from peat deposits (3,150 14C_yrs BP). Shortly after the lake was rapidly filled with seawater and a marine fauna had established. Large input of organic matter has caused an intense oxygen consumption and, as a result, the bottom water of the lake became anaerobic. Thus, an intense sulfate reduction occurred producing high amounts of bicarbonate ions. The lake became stratified into three water bodies with various salinities separated by two pycnoclines. The surfaces water body is oxygenated and exhibits brackish conditions. The algae/microbialite reefs exhibit avertical development which started with a serpulid framework, followed by loose crusts of the calcified red alga Peyssonnelia and thalli of the green alga Cladophoropsis calcified by cyanobacteria (microstromatolites). The top calcified layer is formed by a network of Lithoporella, Peyssonnelia and microbialites. On the top layer the living reef community is located.