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    STUDIA BIOLOGIA - Issue no. 1 / 2019  
         
  Article:   WHY WASN’T THE DEAD SEA RED IN THE FIRST HALF OF THE 20TH CENTURY?.

Authors:  AHARON OREN, RAHEL ELEVI BARDAVID, LILY MANA, BOAZ LAZAR, TANYA RIVLIN, ITTAI GAVRIELI.
 
       
         
  Abstract:  During the 19th century and the first decades of the 20th century, the Dead Sea was considered sterile. Only in the 1930s was the lake shown to harbor microbial life. Blooms of unicellular algae (Dunaliella) and halophilic Archaea (Halobacteria) were observed in 1980 and 1992, coloring the lake red (Oren, 1997). The question must be asked why such blooms were never reported earlier, despite the fact that the surface water salinity was sufficiently low for microbial proliferation. Phosphate is the limiting nutrient for primary production in the Dead Sea. We here show that phosphate likely was scavenged by gypsum that during earlier times precipitated from the lake’s water column. Nowadays very little sulfate is left in the Dead Sea (< 5 mM). Significant amounts of gypsum are no longer formed, so that phosphate that enters with floodwaters in rainy years or with the limited base flow remains available and can trigger microbial blooms. Implementation of the planned Red Sea - Dead Sea water conveyance program to restore the shrinking Dead Sea by inflow of massive amounts of water from the Red Sea (Oren et al., 2004; Glausiusz, 2010) will again lead to massive precipitation of gypsum due to the high sulfate content of Red Sea water that will mix in the calcium-rich Dead Sea brine. Despite the expected dilution of the surface water, phosphate scavenging is then expected to deplete the lake of the limiting nutrient, making the chance of dense algal and archaeal blooms much smaller than predicted earlier.

Keywords: Dead Sea, Dunaliella, gypsum, Halobacteria, phosphate.
 
         
     
         
         
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