Here we report the discovery of the Afifi brine pool, which is named after one of our co-authors for his dedication to scientific research on the Red Sea. Yet, it ranks amongst the saltiest of all known brine pools.
We characterize its location, size, oceanographic setting and general geochemical conditions, as well as the microbial communities associated with this brine pool. The Afifi brine pool was discovered by observing a perfectly flat water column reflection from the top of the brine surface detected by the Simrad EK60 echosounder Fig. The maximum depth of the seafloor under the brine pool is It is consistent with elevated salinity levels registered in the other Red Sea brine basins 5 , The salinity of the brine is mainly contributed by NaCl Table 1 which is characteristic of a thalassohaline brine.
When less mobile anions or cations, involved in biological processes or oxidation-reduction processes, are discarded, we observe that the major ions Cl, Na, Ca, Mg, SO 4 , and Sr are concentrated in the brine 5. Additionally, the concentration values reported for the Afifi brine pool are in agreement with a chemical evolution preceding gypsum precipitation The concentrations of Mg Whereas a differential dissolution of evaporites may help explain these values, the observations that sulphate concentration in the Afifi brine pool is 5.
This is in contrast to the Atlantic II Deep, which experiences a significant accumulation of metal sulphides The temperature of the brine pool is The pH in the Afifi brine body drops to 5.
The acidification of pH in the brine bodies is a trend recorded in all the Red Sea brine pools, but a pH value below 6. Temperature and depth profiles from the Afifi brine pool along the brine seawater interface A and all the water column B.
This trend is similar to what was observed in other brines around the world 26 , Quantitative estimates of the 16S rRNA gene copy numbers of Archaea and Bacteria confirmed the flow cytometry estimates with values of 1.
Prokaryote communities of the Afifi brine body and the oxic sea water above the brine. A Abundance of total prokaryote cells measured by flow cytometry left histograms and of bacterial and archaeal 16S rRNA gene copies measured by quantitative Real Time PCR central and right histograms. B Bacterial taxonomic classes. C Archaeal taxonomic classes. After quality filtering and noise-removal we obtained a total of , and , paired-end 16S rRNA genes sequences that allowed us to identify and OTUs of Archaea and Bacteria , respectively.
Eighty-nine OTUs of Archaea and of Bacteria are shared between the brine and the overlying seawater. Bacteria species diversity Shannon index is nearly twice higher than Archaea whereas the two domains have similar species evenness.
Hierarchical clustering of all samples based on the normalized abundance for each bacterial class indicates a clear separation between the communities associated to the anaerobic and highly saline brine water and the overlying oxic seawater. Furthermore, the presence of KB1 bacteria only in the brine body can be explained by the metabolic adaptation of these bacteria to the high salinity encountered in this environment B Vertical profile of oxygen and nitrogen to argon ratios in the Afifi brine pool and overlaying Red Sea water.
The icon, representing an echosounder profile of the Afifi brine pool, shows the depth where the interface between overlaying Red Sea waters and the brine pool waters is located. Similarly to bacterial classes, the two environments are clearly separated based on the normalized abundance for each archaeal classes. The Thaumarchaeota class composes nearly all the archaeal community in the oxic sea water The relative abundance of some archaeal taxa also shifts between the Red Sea water and the brine.
With the notable exception of the MSBL1 archaeal group absent in Afifi, most of the taxa abundant in the brine body were also found in other brines of the Red Sea, including the KB1 clades 28 , Functional assignments deduced from the bacterial and archaeal taxonomy indicates that methanogenesis and respiration of sulfur compounds are significantly higher in the brine than in the overlying seawater Fig.
This relatively low abundance of functional assignment is probably due to relatively unstudied brines environments with many new microorganisms belonging the so-called microbial dark matter. In the seawater overlying the brine, most of Thaumarchaeota members were associated to nitrification whereas bacteria of the Gammaproteobacteria class were predicted to be phototrophs.
The presence of phototrophs bacteria in the seawater and in the brine waters communities can be explained by the shallow depth of the Afifi basin and the fact that they belong to the Ectothiorhodospiraceae family which are purple sulfur bacteria capable of photosynthesis In the brine, members of the Deltaproteobacteria class resulted associated to sulfur or sulfate respiration, while the Methanobacteria class to methanogenesis.
The increasing in abundance of Deltaproteobacteria associate to sulphur and sulphate respiration and Methanobacteria involved in the methanogenesis, confirmed the variability of metabolism adopted by microorganisms to thrive in the harsh brine environment and how these microbes are adapted to the anoxic conditions of the brine waters. The respiration of sulphur compounds has been widely detected in different brines where high sulfate reduction rate has been observed, both in sulphidic brine like Kebrit, and in non sulfidic brine such as Atlantis II, Discovery, Nereus and Erba, where it was also hypothesized the presence of specific sulfate reducing bacteria adapted to the condition of the brines These values are higher in the Afifi Brine Pool, ranging between Winckler et al.
Hence, isotopic balance calculations show that a mantle gaseous contribution of about 0. The negative TIC isotopic values requires a very negative source of TIC, compatible with that expected to be produced by respiration of oil oxidation or methane oxidation.
The Afifi brine pool is anoxic with oxygen concentrations ranging from below detection limit in the brine pool interior to 5. This isotopic balance explains the increase in 18 O and 17 O in the dissolved oxygen in the waters at the interface above the brine pool Table 3 , Fig.
The decrease of dissolved oxygen concentration in the brine waters explains why in this layer there is an enrichment of microbes with anaerobic metabolisms that are not present in the overlaying seawater. Note that that no isotopic oxygen data is reported inside the brine, since the concentration was too low to resolve this.
However, in the brine layer of the Afifi Brine, members of the Planctomycetes phylum that are anammox bacteria were only found in very low abundance 1. Vertical profiles of A nitrate concentration, B the isotopic composition o nitrogen in nitrate, C the isotopic composition of oxygen in nitrate in the Afifi brine pool waters and the overlaying Red Sea water, and D the relationship between the isotopic composition of oxygen and nitrogen in nitrate in the water column of the Afifi brine pool.
Vertical profiles of A nitrogen to argon ratios, and B the isotopic composition of nitrogen N 2 in the gasses dissolved in the waters of the Afifi brine pool. However, the Afifi brine pool has waters with high isotopic values in both oxygen and hydrogen Fig.
A hydrothermal system would justify the high values of oxygen, but not those of hydrogen The slope of this relationship is similar to that of evaporation experiments reported by Craig et al. Likewise, the slope of this relationship represents intermediate values between low temperatures and high temperatures of crater lakes 54 , The brine pool waters, therefore, have an isotopic footprint of the typical enrichment in 18 O and D expected from evaporative processes 56 , possibly derived from seepage of fossil brines from evaporitic sediments, to yield brine pool waters 5.
The relationship between oxygen and deuterium isotopes in waters of the Afifi brine pool red symbols and overlaying Red Sea waters open symbols , and the corresponding vertical profiles of these isotopes in the waters of the Afifi brine pool.
The solid line shows the relationship expected under evaporation MWL and the dotted line shows the fitted regression line, corresponding to the equation shown. The geological setting of the Afifi pool is between Plio-Pleistocene reef platforms underlain by Miocene layered evaporites, including salt 9. Salt tectonic processes formed diapirs that flowed on the seafloor 52 , and the dissolution of salt may have formed the brines that accumulated in the Afifi bathymetric depression.
We suggest that the water in the Afifi brine pool was derived from seawater trapped in the pores of the underlying evaporitic sediments, which would have undergone important isotopic fractionation due to evaporation intrinsic to the genesis of evaporites A mixture of normal waters of the Red Sea and these waters trapped in the evaporites formation or diagenetic water , could give rise to these isotopic and salinity values. This last hypothesis explains both the chemical and isotopic composition aspects of the waters of Afifi brine pools.
Other diagenetic waters are related to alteration of volcanic rock to clay minerals, which generates water impoverished in 18 O, but enriched in D, because the mineral phase is enriched in 18 O and impoverished in D 50 , 59 , 60 , 61 , This process may be common since bottom sediments are rich in montmorillonite Accordingly, our results indicate that the Afifi brine pool water is not hydrothermal in origin.
A long distance migration of continental brines to the Red Sea deeps has been proposed by other authors 66 , which we consider highly unlikely. However, the basin containing the relatively shallow Afifi brine pool Fig. In this scenario, the Afifi brine pool could be largely the result of a glacial lowstand evaporative event, accounting for the agreement between the isotopic composition of its waters and a theoretical evaporation line of Gofiantini et al.
For example, seawater evaporation in pools of a natural salt factory Cabo de Gata, SE Spain give similar isotopic values to those found in the Afifi brine pool However, this hypothesis is inconsistent with the ionic composition of Afifi pool waters, which does not provide evidence of precipitation of sulfates or other minerals. Consequently, we believe that the most likely hypothesis explaining the origin of the Afifi brine pool brines are submarine seeps of pore formation waters derived from seawater after diagenetic reactions, and which became concentrated brines from dissolution of the underlying evaporitic sediments.
The Afifi brine pool reported and named here is the shallowest and southern-most brine pool yet known in the Red Sea, and offers, because of its accessibility, a convenient test bed to study microbial and geochemical processes in brine pool waters. Most importantly, the unique isotopic composition of the Afifi brine waters also suggest an origin different from that of other Red Sea brine pools, dominated by interactions with evaporites without any contribution of hydrothermal fluids, which is different from that of the hot brine pools in the Red Sea.
This finding adds to the diversity of environments and processes yielding Red Sea brine pools and calls for a revision of the theories explaining their origins. A grid acoustic survey was conducted to map the brine, and based on the echosounders bottom and brine surface detections, a 3D model of the brine was created in Matlab.
From this model brine area and volume were calculated. To make a high resolution bathymetry map Fig. Sampling of the Afifi Brine The salinity and pH were further controlled when the samples were onboard using a portable multi-parameter detector YSI.
Once on the deck, we filtered five liters of the recovered seawater or brine on 0. Triplicate seawater and brine samples of 1. The pH was adjusted at 7. Sterile deionized water was used to clean the instrument after each measurement. The well-plate was shacked before each measure for one cycle, and after each well, the flow cytometer was washed for three cycles.
We started to record the events after 30 secs. Two negative samples for the Red Sea water and the brine water were run to gate possible false events: one non-filtered and non-stained sample and one filtered 0.
For the exact gating strategy, please refer to Figs. S1 and S2. The final cell counts were multiplied by 1. The phenol-chloroform extraction protocol was used to extract total DNA from the different filters. The phenol:chloroform:isoamyl alcohol step was repeated a second time. We ran all the standards and samples in triplicates.
R 2 values and amplification efficiency for Bacteria were 0. Statistical analyses were performed using the R packages phyloseq and vegan 77 , Hierarchical clustering using the Euclidean distance metric and average linkage was used to cluster all samples based on the normalized abundance for each domain.
Functional annotations of prokaryotic clades was done using the FAPROTAX software which uses current literature on cultured strains to assess metabolic functions 31 , Brine mining is the extraction of any desirable compounds or elements from a naturally occurring salt solution , such as brackish groundwater, seawater, and surface water e.
Brine mining operations may extract numerous materials from the same deposit, and production may include lithium as well as a variety of other elemental substances and compounds. The actual process for recovering lithium from brine varies depending upon the source of the brine.
The three main types of lithium brine deposits include continental, geothermal, and oil field deposits, as outlined below:. Continental brine deposits are found in underground reservoirs, typically in locations with arid climates. The brines are contained within a closed basin, with the surrounding rock formations being the source of the dissolved constituents in the brine. In conventional lithium brine extraction, the brine is first pumped to the surface, where it undergoes a number of steps to ultimately produce a saleable lithium salt, such as lithium carbonate.
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Press Inquiries. Email: kjeanbap MIT. Phone: Caption : Illustration depicts the potential of the suggested process. Brine, which could be obtained from the waste stream of reverse osmosis RO desalination plants, or from industrial plants or salt mining operations, can be processed to yield useful chemicals such as sodium hydroxide NaOH or hydrochloric acid HCl.
Credits : Illustration courtesy of the researchers. Caption :. Credits :. Related Articles. Toward cheaper water treatment. Getting the salt out. A brighter future for filtered seawater.
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