Microbialitic structures in Storr's Lake, San Salvador Island, Bahama Islands

The water level in two-meter-deep Storr's Lake, San Salvador Island, fluctuates annually in response to rainfall, groundwater recharge, and evaporation. Although sea water flows in through conduits at high tide and lake waterflows out at low tide, daily lake-level fluctuations have not been observed. Lake water salinity of as little as 38,500 ppm to as great as 93,500 ppm has been measured; water in the lake is density-stratified. Several different microbialitic structures exist in Storr's Lake in well-established zones that apparently are controlled, in large part, by water depth. Thrombolitic microbialites around the lake margin are exposed annually above temporary water levels for intervals of many weeks or months. Crumbly stromatolitic microbialites up to 15 cm tall form an adjacent zone lakeward from the thrombolites; they may be partially emergent above water for extended periods. Next lakeward is a zone of flat-topped, irregular, hard stromatolitic microbialites developed on hard substrates of varying depth but whose tops are impressive in their uniform depth; these structures apparently are never emergent. In deepest water throughout much, but not all, of the central portion of Storr's Lake are columnal stromatolitic structures ranging from 10 to at least 70 cm in height whose tops are consistently 40-50 cm beneath the inferred minimum lake level. Between these columnal structures and ubiquitous throughout the lake beneath water depths of 20-30 cm is an organic ooze as much as 1 m thick that is covered by a soft but coherent alga layer. INTRODUCTION