Red Sea Surface Waters Research Articles

Relationship of the Warming of Red Sea Surface Water over 140 Years with External Heat Elements

Using historic data, variations in the sea surface temperature (SST), sea surface air temperature, and air–sea heat flux of the Red Sea and its adjacent seas over 140 years (1876–2019) as well as correlations of these variations were statistically analyzed. The results show that the SST of the Red Sea increased at a mean rate of 0.043 °C/decade in these years with an accelerated rate in recent decades, and the SST anomalies of the sea had significant positive correlations and high synchronisms with those of adjacent seas as well as air temperature anomalies. In this period, the Red Sea lost more heat to the air via evaporation due to water warming and gained more heat from the Gulf of Aden. The analysis revealed that the temperature rise in the Red Sea surface water was directly caused by the horizontal heat input from the upper warming water of the Gulf of Aden under the circumstance of global ocean warming, rather than by the rise in local air temperature. However, in recent decades, the accelerated rise in air temperature over the sea has decreased the sensible heat flux, which might contribute to the Red Sea warming.

The impact of Red Sea and topography on the atmospheric kinetic energy budget of a cyclonic system

The main objective of this paper is to assess the impact of the features (topography and surface water) of the Red Sea on the Kinetic Energy Budget (KEB) of a case of cyclogenesis occurred on November 15–19, 2015, over the eastern Mediterranean. This case of cyclogenesis was simulated using the weather research and forecasting model (WRF). This case study included one WRF control run (WRF-CR) and three sensitivity studies. The WRF-CR experiment was carried out with the physical presence of the Red Sea features, while the other three sensitivity experiments were executed as (i) No Red Sea Topography (NRST), (ii) No Red Sea surface Water (NRSW), and (iii) No Red Sea Topography and surface Water (NRSTW). The analysis of KEB terms from WRF-CR revealed that the persistence of the subtropical jet stream and its activity represent the main source of kinetic energy throughout the study period. Also, the most critical energy source is the generation of kinetic energy throughout the study period except from 18Z18 to 00Z19, while the major energy sink is the kinetic energy dissipation from grid scales to sub-grid during the study period except from 12Z18 to 00Z19. Furthermore, the horizontal flux convergence functions as an energy source during the first (15 November) and second (16–17 November) stages, whereas it acts as the principal energy sink in the final stage (18 November). It's also found that the KEB terms computed from WRF-CR behave similarly to those calculated from the other three studies, but with significant variances in absolute values.

Diversity and Sources of Airborne Eukaryotic Communities (AEC) in the Global Dust Belt over the Red Sea

Airborne eukaryotic communities (AEC), rank among the least studied aerobiological components, despite their adverse impacts on human health and the environment. Here, we describe the AECs in the global dust belt, the area between the west coast of North Africa and Central Asia, which supports the highest dust fluxes on the planet. We sampled atmospheric dust over 14 months (fall 2015–fall 2016) from onshore and offshore locations of the Red Sea, the only waterbody that entirely encompassed in the global dust belt. We also sampled surface water samples to determine the potential transfer of taxa across the air-sea interface. To target the eukaryotes, we performed Miseq sequencing of atmospheric dust and surface water samples. Analysis of amplicon sequencing indicates a total pool of 18,816 sequence variants (SVs). Among 33 unique eukaryotic phyla in the AEC over the Red Sea, the most dominant taxa were Streptophyta, Apicomplexa, and Ascomycota. Aerosol eukaryotes originated from various sources and formed more diverse communities than eukaryotic communities of the Red Sea surface water. AECs were dominated by phylotypes released from plant material and soils, and including taxa reported to be harmful to human health. The AEC composition was significantly influenced by sampling locations and seasonal conditions but not by the origin of the air masses nor dust loads. This work is original and uses state-of-the-art methods and very powerful NGS- bioinformatics and statistical approaches. The selected study site has high interest and it has been well chosen because of the unique combination of high loads of dust deposition, being the only fully contained seawater body in the area acting as a sink for the atmospheric dust, and the lack of riverine inputs and watershed effects empathizing the role of atmospheric inputs in the ecology of the system.

Aeolian Prokaryotic Communities of the Global Dust Belt Over the Red Sea.

Aeolian prokaryotic communities (APC) are important components of bioaerosols that are transported freely or attached to dust particles suspended in the atmosphere. Terrestrial and marine ecosystems are known to release and receive significant prokaryote loads into and from the surrounded atmospheric air. However, compared to terrestrial systems, there is a lack of microbial characterization of atmospheric dust over marine systems, such as the Red Sea, which receives significant terrestrial dust loads and is centrally located within the Global Dust Belt. Prokaryotic communities are likely to be particularly important in the Global Dust Belt, the area between the west coast of North Africa and Central Asia that supports the highest dust fluxes on the planet. Here we characterize the diversity and richness of the APC over the Red Sea ecosystem, the only sea fully contained within the Global Dust Belt. MiSeq sequencing was used to target 16S ribosomal DNA of two hundred and forty aeolian dust samples. These samples were collected at ∼7.5 m high above the sea level at coastal and offshore sampling sites over a 2-year period (2015–2017). The sequencing outcomes revealed that the APC in the atmospheric dust is dominated by Proteobacteria (42.69%), Firmicutes (41.11%), Actinobacteria, (7.69%), and Bacteroidetes (3.49%). The dust-associated prokaryotes were transported from different geographical sources and found to be more diverse than prokaryotic communities of the Red Sea surface water. Marine and soil originated prokaryotes were detected in APC. Hence, depending on the season, these groups may have traveled from other distant sources during storm events in the Red Sea region, where the APC structure is influenced by the origin and the concentration of aeolian dust particles. Accordingly, further studies of the impact of atmospheric organic aerosols on the recipient environments are required.

Adhesion to coral surface as a potential sink for marine microplastics

Only 1% of plastic entering the ocean is found floating on its surface, with high loads in ocean accumulation zones and semi-enclosed seas, except for the Red Sea, which supports one of the lowest floating plastic loads worldwide. Given the extension of reefs in the Red Sea, we hypothesize a major role of scleractinian corals as sinks, through suspension-feeding, and assessed microplastic removal rates by three Red Sea coral species. Experimental evidence showed removal rates ranging from 0.25 × 10−3 to 14.8 × 10−3 microplastic particles polyp−1 hour−1, among species. However, this was only 2.2 ± 0.6% of the total removal rate, with passive removal through adhesion to the coral surface being 40 times higher than active removal through suspension-feeding. These results point at adhesion of plastic to coral reef structures as a major sink for microplastics suspended in the water column after sinking, helping explain low concentrations in Red Sea surface waters.

Taphonomic and Ontogenetic Effects on Na/Ca and Mg/Ca in Spinose Planktonic Foraminifera From the Red Sea

AbstractAs a recorder of the hydrological cycle and ocean circulation, salinity is one of the most wanted parameters in paleoceanography. Current paleosalinity reconstructions mostly rely on the interpretation of stable oxygen isotope signals combined with an independent paleotemperature proxy. Due to error propagation, this indirect approach is associated with large uncertainties. Recent culture studies and a Red Sea field study have shown that incorporation of Na in foraminiferal shell calcite depends on salinity, providing a potential direct proxy for salinity. However, application of a Na/Ca‐based salinity proxy requires further calibration, which should also consider settling of foraminifera through the water column and burial in the sediment. Here we compare Na/Ca in living specimens from Red Sea surface waters with specimens collected from 0‐ to 500‐m water depth and sedimentary specimens from core‐tops. This shows that Na/Ca in Globigerinoides ruber and Trilobatus sacculifer shells decrease with increasing water depth and until the sediment surface. For both species, laser‐ablation‐ICP‐Q‐MS measurements combined with electron‐probe microanalysis show that Na is enriched in the spines. Loss of spines during settling of foraminifera through the water column hence provides a mechanistic explanation for the observed Na decrease in bulk specimens with water depth. In contrast, average Mg/Ca values increase toward the seafloor in both species, coinciding with deposition of gametogenic calcite, which is enriched in Mg but has Na/Ca values similar to that in lamellar calcite. Both spine shedding and gametogenic calcite addition hence affect the average minor/trace element composition of foraminiferal calcite.

Water chemistry reveals a significant decline in coral calcification rates in the southern Red Sea

Experimental and field evidence support the assumption that global warming and ocean acidification is decreasing rates of calcification in the oceans. Local measurements of coral growth rates in reefs from various locations have suggested a decline of ~6–10% per decade since the late 1990's. Here, by measuring open water strontium-to-alkalinity ratios along the Red Sea, we show that the net contribution of hermatypic corals to the CaCO3 budget of the southern and central Red Sea declined by ~100% between 1998 and 2015 and remained low between 2015 and 2018. Measured differences in total alkalinity of the Red Sea surface water indicate a 26 ± 16% decline in total CaCO3 deposition rates along the basin. These findings suggest that coral reefs of the southern Red Sea are under severe stress and demonstrate the strength of geochemical measurements as cost-effective indicators for calcification trends on regional scales.

Salinity controls on Na incorporation in Red Sea planktonic foraminifera

AbstractWhereas several well‐established proxies are available for reconstructing past temperatures, salinity remains challenging to assess. Reconstructions based on the combination of (in)organic temperature proxies and foraminiferal stable oxygen isotopes result in relatively large uncertainties, which may be reduced by application of a direct salinity proxy. Cultured benthic and planktonic foraminifera showed that Na incorporation in foraminiferal shell calcite provides a potential independent proxy for salinity. Here we present the first field calibration of such a potential proxy. Living planktonic foraminiferal specimens from the Red Sea surface waters were collected and analyzed for their Na/Ca content using laser ablation quadrupole inductively coupled plasma mass spectrometry. Using the Red Sea as a natural laboratory, the calibration covers a broad range of salinities over a steep gradient within the same water mass. For both Globigerinoides ruber and Globigerinoides sacculifer calcite Na/Ca increases with salinity, albeit with a relatively large intraspecimen and interspecimen variability. The field‐based calibration is similar for both species from a salinity of ~36.8 up to ~39.6, while values for G. sacculifer deviate from this trend in the northernmost transect. It is hypothesized that the foraminifera in the northernmost part of the Red Sea are (partly) expatriated and hence should be excluded from the Na/Ca‐salinity calibration. Incorporation of Na in foraminiferal calcite therefore provides a potential proxy for salinity, although species‐specific calibrations are still required and more research on the effect of temperature is needed.

Distinct modes of East Asian Winter Monsoon documented by a southern Red Sea coral record

The large-scale boreal winter climatic patterns associated with interannual variability in a coral oxygen isotope (δ18O) record from the southern Red Sea covering most of the last century are investigated. From the early 1930s to the early 1960s, the winter coral δ18O record, reflecting temperature and salinity variations in southern Red Sea surface waters, is associated with global (or large scale) sea surface temperature (SST) and 850 mb geopotential height (Z850) anomalies which project on the corresponding patterns associated with the El Nino-Southern Oscillation (ENSO). In contrast, since the early 1960s the winter coral δ18O record is related to a Z850 pattern that reflects the ENSO-independent part of the East Asian Winter Monsoon (EAWM), which includes the Siberian High, the East Asian through, and the East Asian upper-tropospheric Jet. Our results indicate a weakening of the ENSO control on interannual temperature/salinity variations in southern Red Sea surface waters in the early 1960s, due to the warming of the Indian Ocean, and suggest that information about the nonstationarity in the relationship between ENSO and two distinct modes of EAWM can be documented in southern Red Sea coral δ18O records.

Carbonate recrystallisation and organic matter maturation in heat-affected sediments from the Shaban Deep, Red Sea

Parasound profiles across the Shaban Deep in the Red Sea indicate turbiditic transport of surface sediments from the topographic height (basalt ridge) into the interior of the deep. This is supported by petrographical and (isotope-) geochemical evidence in the East Basin of the Shaban Deep where the presence of variable mixtures of authochtonous and allochthonous sediment compounds had been found. The uppermost 170 cm of both sediment cores 17008-1 and 17009-3 reveal “normal” stable oxygen isotope values for the planktonic foraminifera Globigerinoides ruber near −1‰ which is indicative for carbonate formation in Red Sea surface water around 27 °C. However, below 182 cm in core 17008-1 highly variable δ 18O values for G. ruber between 0.26 and −10.68‰ occur which are not the result of temperature-controlled oxygen isotope fractionation between foraminiferal carbonate and Red Sea surface water. The lowest δ 18O values of −10.68‰ measured for highly-altered foraminifera shells suggests carbonate precipitation higher than 90 °C. Organic petrographical observations show a great diversity of marine-derived macerals and terrigenous organic particles. Based on petrographical investigations sediment core 17008-1 can be subdivided in intervals predominantly of authochtonous character (i.e. 1, 3, 5 corresponding to core depths 0–170 cm, 370–415 cm, 69–136 cm), and allochthonous/thermally altered character (e.g. 2 and 4 corresponding to core depths 189–353 cm and 515–671 cm). Allochthonous/thermally altered material displays a wide to an extremely wide range of maturities (0.38–1.42% R r) and also natural coke particles were found. Similarly, the organic geochemical and pyrolysis data indicate the predominance of well-preserved, immature algal and bacterial remains with a minor contribution of land plant material. Sediments below 170 cm (core 17008-1) contain contributions of re-sedimented pre-heated material most likely from the area of the basaltic ridge. This is documented by individual coke particles reduced hydrogen indices and elevated T max values up to 440 °C. An “oil-type” contribution (evidenced by mature biomarkers, hopene/hopane ratios, elevated background fluorescence, n-alkane distribution) is also present in the sediments which most likely originated at greater depth and impregnated the surface sediments. The heat source responsible for recrystallisation of foraminiferal carbonate and maturation of organic particles in Shaban Deep sediments most likely is attributed to modern basalt extrusions which now separate the Shaban Deep subbasins.

Water masses in the Gulf of Aden

Hydrographic data collected from Gulf of Aden since 1920 have been compiled to identify and refine the definitions of water masses in the Gulf of Aden (GA) and to describe their spatio-temporal variability. Four water masses have been identified based on their θ-S characteristics. The Red Sea Water (RSW) that flows from the Red Sea is the most prominent water in the GA; this occupies about 37% of the total volume of Gulf of Aden. The Gulf of Aden Surface Water (∼3%) forms as a mixture of local water and the water from western Arabian Sea during winter and Red Sea surface water during summer. The intermediate water, identified as Gulf of Aden Intermediate Water (GAIW), occupies about 9% of the total volume of GA; a characteristic salinity minimum is associated with it at σθ=26.50 kg m−3. The northward spread of sub-tropical subsurface water from the south appears to be the major source of GAIW. The bottom water, named Gulf of Aden Bottom Water, showed the least variability. It was formed due to the mixing of Red Sea Water and water of southern origin. Mixing triangles have been used to analyze the composition of water in the GA.

Study of seawater alkalization as a promising RO pretreatment method

Inorganic fouling is a major challenge in seawater RO desalination due to its relatively high SO 4/HCO 3 molar ratios. In most of the recorded cases, if not all, calcium sulfate scale is dominating (>90% wt/ wt) other scale types such as CaCO 3, MgSO 4, MgCO 3, MgSiO 3, SiO 2 and CaPO 4. However, the standard pretreatment practice in RO plants depends on the acidification of seawater in order to remove the minor carbonate and bicarbonate. Meanwhile, solubility of the major sulfate species decreases considerably because of acidification. The present study investigated the application of NaOH alkalization on the Red Sea surface water instead. It was found that the method has many technical and economical advantages, such as removal of hard chemical species (i.e. hard carbonate, bicarbonate, sulfate, silicate, phosphate and iron), removal of suspended solids and colloids, bacterial disinfection, cleaning and wetting of a membrane surface, increasing permeate recovery, lower sludge volume of environmentally chemical nature, and the possibility of instant preparation of NaOH in-line by seawater electrolysis. The alkalization method is fast, clean and economic. The proposed model as well as chemical equations are presented in detail.

Phytoplankton and foraminiferal frequencies in northern Indian Ocean and Red Sea surface waters

This paper describes the distribution patterns of living planktonic foraminifers, coccolithophorids and picocyanobacteria along an east-west traverse in northern Indian Ocean and Red Sea surface waters during the southwestern monsoon. The absolute frequencies of coccolithophorids and foraminifers more or less correlated with temperature in the western Arabian Sea and South of India, where deeper waters well up into the photic zone. The increased frequencies in these upwelling zones were especially accounted for by the coccolithophorids Emiliania huxleyi (Lohmann) Hay & Mohler, Gephyrocapsa oceanica Kamptner and the foraminifer Globigerina bulloides d'Orbigny. The coccolithophorids Umbellosphaera irregularis Paasche and U. tenuis (Kamptner) Paasche showed a preference for warm, oligotrophic waters, and were absent in the upwelling areas. The small, red-pigmented picocyanobacteria in surface waters (depth 0 to 5 m) formed an important part of the primary production. Their relative frequency was more or less constant, on an average of 2·10 7 cells·dm −3 along the entire transect, so their relative contribution to biomass was higher in nutrient-poor environments than in nutrient-rich upwelling waters. Both carbonate producing foraminifers and coccolithoporids increase in number with improved nutrient availability in the upwelling areas. Their relative frequencies in sediments underlying the upwelling zones will reflect the varying upwelling conditions, caused by fluctuations in monsoonal atmospheric circulation, and thus allow for the reconstruction of past climatic change in this area.