Saber Al-Rousan

Increased seasonality in Middle East temperatures during the last interglacial period

The last interglacial period (about 125,000 years ago) is thought to have been at least as warm as the present climate. Owing to changes in the Earths orbit around the Sun, it is thought that insolation in the Northern Hemisphere varied more strongly than today on seasonal timescales, which would have led to corresponding changes in the seasonal temperature cycle. Here we present seasonally resolved proxy records using corals from the northernmost Red Sea, which record climate during the last interglacial period, the late Holocene epoch and the present. We find an increased seasonality in the temperature recorded in the last interglacial coral. Today, climate in the northern Red Sea is sensitive to the North Atlantic Oscillation, a climate oscillation that strongly influences winter temperatures and precipitation in the North Atlantic region. From our coral records and simulations with a coupled atmosphere–ocean circulation model, we conclude that a tendency towards the high-index state of the North Atlantic Oscillation during the last interglacial period, which is consistent with European proxy records, contributed to the larger amplitude of the seasonal cycle in the Middle East.

Ecological and geochemical characteristics of bottom habitats at the northern Jordanian coast of the Gulf of Aqaba

A detailed study to assess the environmental conditions of the benthic habitats at the northern tip of the Gulf of Aqaba has been carried out during the summer of 2003. The texture, geochemical, and biogenic characteristics of bottom sediments as well as a description and distribution of corals, seagrass, fish species, and fish assemblages have been investigated. Results showed that the sea bottom at the study site is mainly a non-coralline sandy bottom covered with seagrass. Well-developed seagrass beds covered about 70–98% of the bottom. No coral cover was recorded. This is to be expected because of the absence of hard substrate and because of high loads of suspended matter. The seagrass habitat in the area serves as important nursery grounds for the fish larvae and hosts sea urchins and sea cucumbers. The bottom sand in the area was undisturbed, animal tracks were rare, but bioturbated holes and mounds were abundant. Bottom surface sediments were fine-grained, black with high quartz, feldspar, and mica, and low in mud content. Chemically, these sediments had low calcium carbonate, organic nitrogen, and high total phosphorus concentrations, suggesting that the sediment mineral composition is derived from existing metamorphic rocks, by weathering and erosion. The biogenous part of the sediments was mainly calcium carbonate, consisting of shells or coverings of some micro- and macro-organisms. The number and diversity of fish species inhabiting the survey site are typical of seagrass-bed sandy-bottom habitats. Some of the fish species observed are characteristic of this site and very rarely found elsewhere on the Jordanian coast. About half the fish population in the area belong to six families: Labridae (12%), Pomacentridae (7%), Mullidae (7.%), Apoginidae (6%), Chaetodontidae (6%), and Gobiidae (6%).

Effects of pollution on the geochemical properties of marine sediments across the fringing reef of Aqaba, Red Sea.

The Gulf of Aqaba is of significant strategic and economic value to all gulf-bordering states, particularly to Jordan, where it provides Jordan with its only marine outlet. The Gulf is subject to a variety of impacts posing imminent ecological risk to its unique marine ecosystem. We attempted to investigate the status of metal pollution in the coastal sediments of the Jordanian Gulf of Aqaba. The distribution of Cd, Cr, Zn, Cu, Pb, Al, Fe, and Mn concentrations were determined in trapped and bottom-surface sediments at three selected sites at different depths. In addition, monthly sedimentation rates at varying water depths were also estimated at each sampling site using sediment traps. The high concentrations of Cd, Cr, Zn were recorded at the Phosphate Loading Birth (PLB) site followed by the Industrial Complex (IC) site indicating their dominant anthropogenic source (i.e., the contribution of industrial activities). However, Fe, Al, and Mn contents were related to inputs from the terrigenous (crustal) origin. Except for Al, Fe and Mn at the PLB site, the concentrations of metals exhibited a decreasing trend with increasing water depth (distance from the shoreline). The PLB site also showed the highest sedimentation rate which decreased with increasing water depth. The Enrichment factors (EFs) showed that Cd was the most enriched element in the sediment (indicating that Cd pollution is widespread), whereas the least enriched metal in sediments was Cu. EF values suggested that the coastal area is impacted by a combination of human and natural sources of metals, where the anthropogenic sources are intense in the PLB site (north of Gulf of Aqaba). The MSS area is potentially the least polluted, consistent with being a marine reserve. The IC sediments have been found to be impacted by human activities but less intensely compared to the PLB area. These results suggested that there are two sources of metals in sediments; the primary source is likely closer to PLB, while the secondary is nearby the IC.

The status of coral reefs on the Jordanian coast of the Gulf of Aqaba, Red Sea

Abstract The Jordanian coast of the Gulf of Aqaba was intensively surveyed during the year 2004 to assess the health of the coral reefs in Jordan. Permanent line transects were laid on the reef flat, at depths of 8 m and 15 m at eight sites, and selected benthos components were studied. It was found that the distribution of hard corals increases gradually from north to south and that the 15 m deep transects had the highest coverage of hard corals. On the other hand, soft corals showed the highest coverage at sites where industrial activities are taking place. Coral death was low along the Jordanian coast and is comparable to surveys made in previous years, though protection measures are needed at the sites where industrial and recreational activities are focused. The hotels area, the phosphate loading berth and the Tala Bay sites had more than 40% seagrass coverage and were classified as seagrass habitats. Giant clams were hardly found on Jordan’s reefs and it is suggested that they should be considered as endangered species. It is concluded that the coral reefs in Jordan are in good condition, although pressure resulting from the rapid development of the tourism, industry and construction sectors along the coast is expected to increase and to represent the major threat to this ecosystem in the future. Continuous monitoring is therefore suggested.

Coral calcification: Use of radioactive isotopes and metabolic inhibitors to study the interactions with photosynthesis and respiration

In order to characterize the process of calcification in scleractinian corals, a series of laboratory experiments were conducted using radioactive isotopes. Labelled calcium, bicarbonate and glucose were used and the fates of the labelled tracers were followed in the skeleton and the tissue fractions of the coral Galaxea fascicularis. In addition, a variety of metabolic inhibitors were used to test the effects of various enzymes and processes on the incorporation rates. The incorporation rate of 45Ca into the coral skeleton decreased to about one-fifth upon inhibition of metabolic respiration by the specific inhibitor NaCN suggesting a major role of metabolic respiration in coral calcification, and decreased to one-half upon inhibition of carbonic anhydrase by the specific inhibitor acetazolamide indicating a role of the enzyme in the process. The results obtained have also shown that corals are able to incorporate carbon from seawater bicarbonate and added glucose in both skeleton and tissue fractions. The process of incorporation was influenced by light conditions, carbonic anhydrase, respiration and photosynthesis. The incorporation rate of 14C-HCO was reduced to about one-tenth in the skeleton, and one-fifth in the tissue, upon inhibition of carbonic anhydrase suggesting a major influence of the enzyme in the incorporation process. The inhibition of photosynthesis had more influence on the tissue incorporation rate of the tracer than the skeleton suggesting that photosynthesis is the main process responsible for tissue use of seawater bicarbonate in the coral. 14C-glucose incorporation into the skeleton was mainly affected by NaCN addition and to a lesser extent by dichlorophenyldimethylurea (DCMU) addition, while the tissue fraction was mainly affected by NaCN addition. It was concluded that respiration and photosynthesis, in addition to the enzyme carbonic anhydrase, are limiting factors for the process of calcification in the coral, and that various forms and sources of carbon can be used in coral calcification and tissue growth.

Heavy metals signature of human activities recorded in coral skeletons along the Jordanian coast of the Gulf of Aqaba, Red Sea

The concentrations of six heavy metals were studied in five living coral species and their fossil counterparts collected along the Jordanian Coast of the Gulf of Aqaba. The study aimed at investigating the validity of using coral skeletons as bioindicators for environmental pollution by heavy metals in the Gulf of Aqaba, Red Sea. The skeletal samples of the collected corals were acid digested and analyzed for Cd, Cu, Fe, Mn, Pb, and Zn content using flame atomic absorption spectrophotometer. The results obtained have shown that higher concentrations of heavy metals were found in coral skeletons from areas hosting intense developments and human activities. The massive Porites sp. coral tended to accumulate the highest metal concentrations among the other species (except for Mn). This was due to interspecific differences or selectivity of heavy metals between different coral species. It was noteworthy that fossil coral species recorded higher average metal concentrations than their living counterparts; this was attributed to surface contamination due to prolonged burial of the fossil corals in sediment over the years. The study concluded that corals (specially the massive Porites species) are vulnerable to the accumulation of high concentrations of heavy metals in their skeletons and therefore can serve as proxies to monitor environmental pollution.

Assessment of seagrass communities along the Jordanian coast of the Gulf of Aqaba, Red Sea

Abstract The distribution and abundance of seagrass communities have been investigated from from three sites along the Jordanian coast of the Gulf of Aqaba. The results showed that the seagrass Halophila stipulacea has the widest distribution in all sites. However, the species Halodule uninervis and Halophila ovalis were less abundant and were found at the Tala Bay site and only at shallow depths. The seagrass distributions increased with increasing depth up to 12 m, and thereafter declined. However, in some shallow areas, seagrass is completely absent due to extensive human activities. On average, the highest seagrass cover from this study was recorded at the Tala Bay site (36.6%), followed by 29.9% and 22.9% at Phosphate Loading Berth and Hotel Area sites, respectively. The mean biomass of leaves for the seagrass species H. stipulacea averaged 104.2 g m−2. The values increase with depth, reaching maximum at 12 m depth and followed by decrease down. Changes in mean leaf density, length, width, number of shoots and shoot length in all sites closely followed changed in biomass. These could be attributed to decreasing irradiance and as an adaptive change response to lower light intensities and lower growth rates at deeper depths.

Community structure of the family Pomacentridae along the Jordanian coast, Gulf of Aqaba, Red Sea

Abstract The spatial distribution and community structure of the family Pomacentridae were studied at different depths and sites along the coast of the Gulf of Aqaba in seagrass and coral reef habitats. Sixteen coastal sites along the Jordanian coast were studied by the visual census technique. A total of 151,134 pomacentrid fishes representing 23 species were observed during 188 visual censuses at 96 belt transects, and 4 additional species were observed outside the transect lines. Six species accounted for 85% of all individuals. Results from cluster analysis of the studied sites based on percentage of benthic cover revealed two main groups: the seagrass and the coral reef dominated sites. Fishes were most abundant at 12 m depths in the coral dominated sites, while fewer numbers were found at reef flat and seagrass sites. This was attributed to the shelter, structural complexity and food availability in the coral reef sites. Pomacentrus trichourus and Amphiprion bicinctus were the most common pomacentrid fishes. Teixeirichthys jordani was restricted to the northern coast of the Gulf of Aqaba. Multivariate analysis of the pomacentrid community revealed certain associations of fishes with different habitats. Within the large group of coral reef associated fishes we could distinguish the following three groups: a group of species that occur at 12 m deep transects such as Chromis weberi and C. pembae; a group of species that occur only in the reef flat such as Plectroglyphidodon leucozonus and P. lacrymatus; a group of the most dominant and most common species such as Neopomacentrus miryae and Pomacentrus trichourus.

Chemical evaluation of sand material sources for beach replenishment along the coast of the Gulf of Aqaba, Red Sea

Four potential borrow sites (sources of sand) for beach nourishment were selected at the Aqaba terraces and dredged offshore sand along the Jordanian coast of the Gulf of Aqaba, and at Al-Humaimah and Wadi Rum sand dunes north and northeast of Aqaba town. An elution test has been performed on the sand materials of these potential borrow sites to determine the levels of dissolved inorganic phosphorus and dissolved inorganic nitrogen that might be leached from the sand particles when they come into contact with seawater, and examine their suitability for beach replenishment works. The levels of total phosphorus, total nitrogen, organic matter and selected heavy metals were also measured in the sand materials after the elution test and compared with their levels in the same samples before elution and with their levels in the natural beach sand of the study area. The results of the tests show that the concentrations of the measured pollutants are low in the sand materials of the borrow sites, and the amounts of these pollutants that may reach the seawater of the Gulf of Aqaba, if quantities as large as 100,000 tons of the sand materials were used in beach nourishment projects, are very low when compared with their levels in seawater. The results of the tests, as well as organic matter and mud contents of the sand materials, indicate their suitability for use in beach nourishment. However, the Aqaba uplifted terraces would be the most suitable and the lowest cost source because they are common along the shores of the Gulf of Aqaba.

Phosphate enrichment in the northern Gulf of Aqaba: Regulation by carbonate sediments and impact on nitrogen elevation

The effect of carbonate sediment in regulating phosphate concentrations in sea water was investigated by laboratory incubation experiments using different sediment types. Incubation experiments were made with two types of sediments: uncontaminated sediment from a marine reserve and contaminated sediment with deposited phosphate powders. Fluxes of inorganic nitrogen and phosphate were estimated from linear regressions of solute concentrations over incubation periods. Ammonium and phosphate fluxes were about twofold higher in the uncontaminated sediment that had significantly lower organic carbon and total phosphate concentrations than in the phosphate-contaminated sediment. To test the effect of dissolved phosphate on increasing nitrogen fixation, additional incubation experiments were carried out using treated carbonate and silicate sediments with added dissolved phosphate (20 μM). Incubations were made under sterile conditions with HgCl2 added to distinguish between biologically enhanced processes and pure physicochemical processes. The adsorption rate of phosphate onto carbonate sediment was about twice that onto silicate sediments. No nitrogen elevation either as ammonium or as nitrate was observed in the soluble phosphate enrichment incubations. In conclusion, this study demonstrates the importance of the regulation of soluble phosphate concentrations in carbonate sediment environments where the carbonate sediment acts as a buffering system keeping soluble phosphate concentrations at certain steady-state levels. The study also demonstrates the lack of evidence on enhancement of nitrogen concentrations due to the increase phosphate concentrations.