Document Details
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Document Type |
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Thesis |
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Document Title |
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Modern and late Holocene environmental conditions of Al-Kharrar Lagoon, central Red Sea, Saudi Arabia: Palaeoclimatic inferences الظروف البيئية الحالية والهولوسين المتأخر لبحيرة الخرار، وسط البحر الأحمر،المملكة العربية السعودية: إستنتاجات مناخية قديمة |
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Subject |
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Faculty of Marine Sciences |
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Document Language |
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Arabic |
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Abstract |
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Al-Kharrar Lagoon (KL) is a fossil back-reef, hypersaline small basin situated 10 km northwest of Rabigh City, Saudi Red Sea coast. One-hundred-thirty sediment samples were collected during March 2014, and two cores were recovered from the intertidal zone of the lagoon. Environmental parameters such as bathymetry, temperature, salinity, dissolved oxygen and pH were measured. Sediment samples were analyzed for variables such as benthic foraminifera, organic matter, CaCO₃ and sediment grain-size. This study aims to investigate the present environmental parameters that influence the macro-fauna/flora and, the benthic foraminiferal diversity, abundance and distribution and also to develop a transfer function models to reconstruct past sea-level changes and inference the palaeoenvironmental and palaeoclimatic changes during the late Holocene. The measured vertical profiles of temperature, salinity and density in the lagoon’s water indicated that the water column consists of two layers throughout the year. The results showed also that faunal density and diversity were with averages of 135±300 dead tests/g and 23±10 displaying the highest values (3000 and 44) only at some intertidal areas, respectively. The Q-mode cluster analysis as well as the spatial distribution of benthic foraminifera allowed the division of KL into five environmental biotopes such as the southern tip, the mid-eastern side, the inlet, the intertidal-subtidal and the deep water. These biotopes were dominated by five major assemblages such as the intertidal assemblage (Quinqueloculina seminula-Q. laevigata and Affinetrina quadrilateralis-Neorotalia calcar), the inlet Amphistegina lessonii assemblage, the intertidal-subtidal assemblage (Peneroplis planatus-Coscinospira hemprichii-Sorites orbiculus) and the deep-water assemblage (Spiroloculina communis-Triloculina serrulata-T. trigonula). A foraminifera-based transfer function (TF) has been developed using two models (WA-PLS and PLS) based on a screened training dataset of 75 samples and 111 species obtained from the intertidal-high subtidal area. The relationship between the observed and predicted elevations showed a strong performance for the TF (r²jack= 0.80 in WA-PLS, 0.88 in PLS) with a relatively precise reconstructions where RMSEPjack= 0.12 and 0.10 m for WA-PLS and PLS models, respectively. The basal (225-185cm) interval of the core KHAR2 was deposited under subtidal-intertidal channel environments as indicated by the presence of gravelly lithogenous materials, subtidal species and a slight drop in the palaeo-tidal elevation about 0.5 cm (reconstructed by PLS model) below the present LAT (-36 cm from mean sea level). The relative decrease of the epiphytic species S. orbiculus and P. planatus was in agreement with the reconstructed, low palaeo-tidal elevation, suggesting that this period probably occurred under stable environmental conditions. During 70cm-Recent interval of the core, the high abundance of epiphytic species P. planatus, S. orbiculus and C. hemprichii coincided with rising in the palaeo-tidal elevations up to 0.2m above the LAT, indicating typical intertidal conditions for this interval that could reflect warmer climatic conditions. At 20cm depth, there is a decrease in abundance of epiphytic species and palaeo-tidal elevations that could lead to a decrease in seagrass (the host of S. orbiculus) in the intertidal area. These environmental variations that was recorded in the KHAR2 were also recorded in the sediment core KHAR3. |
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Supervisor |
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Prof. Ramadan H. Abu-Zied |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1440 AH
2019 AD |
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Co-Supervisor |
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Prof. Ali Saeed Basaham |
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Added Date |
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Thursday, July 11, 2019 |
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Researchers
| طلحة أحمد الدبعي | Al-Dubai, Talha Ahmad | Researcher | Doctorate | |
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