Northernmost Red Sea Research Articles

Observations of the First Documented Indian Ocean Humpback Dolphin (Sousa plumbea) in the Northernmost Red Sea Gulf of Aqaba

Observations of the First Documented Indian Ocean Humpback Dolphin (Sousa plumbea) in the Northernmost Red Sea Gulf of Aqaba

Tiran Straits: The transfer zone between the Red Sea and the Gulf of Elat and its tectonic significance

Abstract A precipitous submarine horst is located between Sinai Peninsula and Tiran Island, but also between Hume Deep (1400 m) in northernmost Red Sea and Tiran Deep (1400 m), in the southernmost Gulf of Elat. The horst outcrops above sealevel in places, where corals built small reefs, trending NNE-SSW. The horst forms a structural transfer zone trending NNE-SSW and constrained by series of normal faults on both flanks. Transfer zones were repeatedly encountered to separate between axial grabens along regional rifts in East Africa and elsewhere while similar structures were observed in analog models. Transfer zones between grabens along axial rifts were attributed to oblique extension, consequently the occurrence of the Tiran transfer zone could indicate that geodynamic regime of oblique extension prevails in the northern Red Sea and exists also in Elat Rift. Tiran horst is structurally associated with the arcuate system of grabens and elongated salt diapirs that were encountered in the bathyal northern Red Sea, which swings from the Red Sea NW-SE orientation to the N-S trend of Elat Rift. The age of the initiation of the rifting and the contemporaneous ascent of its margin was attributed to late Miocene – early Pliocene, as indicated by extensive series of coralline terraces and by non-branching fluvial system on Tiran Island. The research did not encounter supporting evidence that the Elat Rift is a transform fault that branched off the Red Sea during the early-middle Miocene nor that Tiran Deep is a pull-apart basin.

Microcopepod community structure in the Gulf of Aqaba and northern Red Sea, with special reference to Oncaeidae

The abundance and vertical distribution of microcopepods sampled by nets with 55 μm mesh size was compared for two neighbouring but hydrographically different areas, the Gulf of Aqaba and the northernmost Red Sea, during spring 1999. The vertical structure of the total microcopepod communities differed considerably between the two regimes: In the stratified waters of the Red Sea, calanoids outnumbered oncaeids as well as oithonids at 0–100 m, whereas oncaeids dominated in all meso- and bathypelagic layers below 100 m deep. In the unusually deep vertically mixed waters of the Gulf of Aqaba, calanoids outnumbered each of the non-calanoid taxa as deep as 250 or 350 m, whereas the oncaeid dominated deep water community was restricted to depth ranges below 400 m. Dominant non-calanoid species in both areas were Oncaea bispinosa, Paroithona pacifica, Oithona simplex, Spinoncaea ivlevi, O. tregoubovi and O. cristata. O. scottodicarloi occurred in exceptionally high numbers in the northern Gulf. Pronounced differences between the two areas were found in the vertical distribution of poecilostomatoid species. By comparing the present results with published data from the central and southern Red Sea and other tropical and warm-temperate oceanic areas, intra- and inter-oceanic differences in the structure of microcopepod communities in oligotrophic areas are discussed. The high abundance and vertically extended range of calanoid copepods during spring appears to be a specific feature of the Gulf of Aqaba, indicating an unusual vertical succession in the trophodynamic structure of the copepod fauna in this area.

Population structure and fecundity of the microcopepod Oncaea bispinosa in the Red Sea—a challenge to general concepts for the scaling of fecundity

General concepts of reproductive traits in pelagic marine copepods have been developed largely without data from the microcopepod family Oncaeidae. For a very abundant oncaeid species in the Red Sea, Oncaea bispinosa Bottger-Schnack, reproductive parameters are provided and used for testing how the copepod family Oncaeidae may fit into these concepts. Total number and vertical distribution of eggs of this species have been calculated for populations in the northernmost Red Sea and the Gulf of Aqaba during spring, based on counts of detached egg sacs retained in fine mesh net samples. Reproduction is indicated to take place in the meso- and bathypelagic zones, with maximum abundances of eggs occurring within the deep population centres of females at 250 to 450 m depth. The epipelagic population appeared to be non-reproductive. By calculating the biomass of the eggs and the females using published data on size/weight relationships, a first estimate of the reproductive potential of O. bispinosa was obtained and compared with various other oncaeid species. The presently available data for Oncaeidae in total suggest a relationship between single egg (Ec) and female (Fc) carbon weight (Ec = 0.012 × Fc0.48) that differs from corresponding regressions reported in the literature for other marine pelagic copepods. In addition, regressions are given for minimum and maximum clutch carbon related to female carbon weight. Potential egg production rates of O. bispinosa have been calculated from the observed fractions of egg-bearing females and published data on egg developmental times, as available for larger oncaeids. These production rates appear to be lower than have been observed in experimental studies for different pelagic microcopepod taxa. Remaining uncertainties in generalizing concepts for the scaling of fecundity in pelagic marine copepods are discussed, and the need for more comparable data, especially for the numerically abundant oncaeids, is emphasized.

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 Earth's 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.

Mediterranean moisture source for an early-Holocene humid period in the northern Red Sea.

Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about 3 per thousand reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff, which thereafter decreased to modern values. The northern Red Sea humid interval is best explained by enhancement and southward extension of rainfall from Mediterranean sources, possibly involving strengthened early-Holocene Arctic Oscillation patterns and a regional monsoon-type circulation induced by increased land-sea temperature contrasts. We conclude that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene.

The microcopepod fauna in the Gulf of Aqaba, northern Red Sea: species diversity and distribution of Oncaeidae (Poecilostomatoida)

A total of 23 species and three groups of form variants of oncaeid copepods have been identified, which were collected in small mesh net samples taken along a transect from the northernmost Red Sea (>27°N) to the Gulf of Aqaba down to a maximum depth of 800 m. Two of the species were present only in the Red Sea main basin, but were not recorded in the Gulf. By comparing the present results with previously published data from the central and southern Red Sea a first assessment of the zoogeographical distribution of Oncaeidae in the entire Red Sea has been achieved. The species diversity of Oncaeidae in the Gulf of Aqaba appears to be considerably lower compared to the southern Red Sea, where 31 oncaeid species and four groups of form variants have been found. The observed latitudinal gradient in species numbers of Oncaeidae generally corresponds to the gradients observed for various other zooplankton taxa in the Red Sea. First data on the vertical distribution of oncaeid species in the Gulf are provided.

The rotation of Arabia and the Levant fault system

We establish the kinematics of the rotation of Arabia with respect to Africa and show that the rotation rate of Africa increased by a factor of about four in late Serravallian time, about 12–13 Ma ago. We discuss evidence that oceanic accretion started simultaneously in the Gulf of Aden and in the Red Sea at this time. It is also at this time that the Levant and Anatolian fault systems were initiated. Our initial reconstruction of the Red Sea Rift in Late Oligocene-Early Miocene time approximately superposes the present shore lines which coincide with the mid-point of the zones of rapid crustal thinning, the future continental slopes. The amount of extension during the early phase of continental rifting is obtained by assuming that the total volume of continental crust is conserved during extension, and by checking these estimates through closure around the Sinaï triple junction. In the Late Miocene, the Southern evant fault zone was a zone of distributed shear deformation, through counterclockwise block rotation, extending soul h ward within the northernmost Red Sea. Since the Early Pliocene, the shear motion has been localized within the Gulf of Aqaba, changing the tectonic pattern in the northern Red Sea.

Problems concerning the evolution of oceanic lithosphere in the northern Red Sea

The pole of rotation for the opening of the Red Sea at 36.5°N, 18.0°E (Arabia from Africa) implies the fastest spreading rates are in the south and are about 50% less in the north. Various studies show the spreading rate in the south to be about 1 cm/yr over the last 4–5 Ma. Problems arise as to the nature of the lithosphere beneath the northernmost Red Sea. The problem is further complicated by the fact that the Red Sea may have evolved in three phases. The first is the Gulf of Suez phase (mainly Oligocene), the second corresponds to the first (62 km) movement along the Aqaba-Dead Sea shear (?latest Oligocene-early Miocene) and the third to the second (45 km) movement along the Aqaba-Dead Sea shear (Plio-Pleistocene). These motions and their implications for the northernmost Red Sea are assessed. The northern Red Sea differs from the central and southern Red Sea in having no clear magnetic lineations. Only a few isolated circular anomalies are observed. There are two possible explanations: 1. (1) there is extremely thinned continental lithosphere occasionally pierced by strongly magnetised volcanic centres, or, 2. (2) the oceanic lithosphere is present but without magnetic anomalies. It is suggested that the first explanation applies to the first (Gulf of Suez) phase and the second explanation to the two later (Aqaba-Dead Sea) phases. It is further suggested that the lack of magnetic anomalies may be due to a combination of large thicknesses of unstable sediments (salt), high temperatures and low sea floor spreading rates. These lead to the evolution of oceanic lithosphere with slow cooling, inhibiting the acquisition of strong magnetisation and giving subdued magnetic anomalies.

Stratigraphic and paleoceanographic significance of Late Quaternary pteropods from deep-sea cores in the Gulf of Aqaba (Elat) and northernmost Red Sea

The quantitative distribution of 16 thecosomatous pteropod species from four deep-sea cores recovered from the Gulf of Aqaba (Elat) and northernmost Red Sea is summarized. The distribution facilitates a relatively high resolution stratigraphic subdivision of the 6–8 m long core sequences and their correlation. The sequences of pteropod assemblages can be related to oxygen isotope curves and thus dated beyond the radiocarbon-range. The oldest strata penetrated are dated at about 150,000 yr B.P. Considering the present-day distribution of the species recognized, the core assemblages are of a tropical-subtropical character throughout the Late Quaternary. On the basis of the composition of the living pteropod populations in the hypersaline (41%.), moderately oligotrophic and desert-enclosed Gulf of Aqaba, the pteropod core assemblages, associated foraminiferal assemblages, and the oxygen isotope values determined on both groups, a sequence of paleoceanographic changes during the Late Quaternary is derived. These changes are primarily influenced by productivity of the waters and pertain less to temperature and salinity. The glacial periods (isotope stages 2,3,4 and upper 6) were characterized by lower temperature than at present, higher salinity and greater fertility of the waters. During the glacial maxima monospecific Creseis acicula assemblages characterize periods of metahaline (more than 50%. salinity) conditions in highly productive waters. Although not identical in detail, the last interglacial (stage 5) assemblages are similar to the Holocene warm-water oligotrophic ones. Between 8000 and 3000 yr B.P. a short period of slightly higher productivity is indicated.

Paleoecological Relations of Foraminifera in a Desert-Enclosed Sea -The Gulf of Aqaba (Elat), Red Sea

Abstract. Planktonic and benthonic foraminifera live in the desert-enclosed, hypersaline and oligotrophic Gulf of Aqaba and northernmost Red Sea near the edge of their ecological tolerance. Marked changes in foraminiferal abundance patterns in the past, resulting from hydrological shifts related to global climatic fluctuations, facilitate a high-resolution ecostratigraphic subdivision of deep-sea records covering the last 150,000 years. Of particular significance are the foraminiferal plankton/benthos ratios, the presence/absence pattern of such species as Globigerinoides sacculifer, as well as the frequency variation of Globigerina bulloules-falconensis, Buliminacea, Miiiolacea and various “rotaliform” species. Paleoceanographic interpretation of the shifts in assemblage composition and of stable oxygen isotope data obtained on planktonic foraminifera and pteropods indicates that during glacial intervals - because of global cooling, lowered sea-level and reduced water exchange at the straits of Bab-el-Mandeb - the temperature of the upper waters fell by about 4–6 oC (to 15–17 oC), salinity rose by about 10%o to more than 50%0 while residence time of the water became longer and the input/output ratio of nutrients became higher. As a consequence, fertility of the photic zone was higher, the organic content of the sediments increased and oxygen levels in the deep basin became reduced. Thus, sea level-oscillations and strait-dynamics played a major role in the foraminiferal paleoecology of the Red Sea.

Late Quaternary Paleoceanography of the Gulf of Aqaba (Elat), Red Sea

The quantitative distribution of planktonic foraminifera, pteropods, and coccolithophorids, as well as oxygen-isotope variations were analyzed in four deep-sea cores from the Gulf of Aqaba (Elat) and the northernmost Red Sea. The core record covers about 150,000 yr. Detailed stratigraphic subdivision is facilitated by combining all calcareous plankton groups. Time-stratigraphic correlation and dating beyond the radiocarbon range are possible by comparison of the oxygen-isotope curves. During the glacial maximum salinity rose to more than 50‰, while winter temperature of the upper waters fell by at least 4°C compared to the present. The rise in salinity can be accounted for by sea-strait dynamics and lowering of sea level. The Gulf of Aqaba and the Red Sea were continuously connected through the Straits of Tiran, and there is no indication of desiccation during the glacial maximum.