Ahuva Almogi-Labin

Global climate instability reflected by Eastern Mediterranean marine records during the late Holocene

Abstract Extremely high sediment accumulation rates in the southeastern (SE) Mediterranean off Israel make this region ideal for high-resolution paleoceanographic reconstructions. Two cores were examined and foraminiferal oxygen and carbon isotope composition as well as physical and geochemical properties of the sediments were used to reconstruct the climatic and environmental changes of the SE Mediterranean Basin during the late Holocene (3.6 ka). The δ18O values of Globigerinoides ruber suggest that the freshwater balance changed several times during this time interval. Humid phases took place between 3.5–3.0 ka BP and 1.7–1.0 ka BP. The later was accompanied by enhanced preservation of terrestrial organic matter within the sediment (ORS event). Relatively more arid conditions prevailed in this area between 3.0 and 1.7 ka BP. During the last millennia at ca. 0.8 and 0.27 ka two climatic events occurred which are probably correlative to both the Medieval Warm Period and the cooling global event known as the Little Ice Age, respectively. A long-term slight increase in planktonic foraminiferal δ18O values occurs together with a gradual decrease in the δ13C values of both G. ruber and the benthic foraminifera Uvigerina mediterranea. This trend is associated with an increase in sedimentation rates, Ti/Al ratio, magnetic susceptibility, and color index of the sediments. We suggest that this trend shown by various independent proxies seems to be related to the aridification process that started ca. 7.0 ka in the mid–low latitude desert belt and the SE Mediterranean region and continuous until the present. The long-term δ13C decrease shown by surface and bottom water foraminifera reflects a gradual change in the δ13C of the dissolved CO2 of the entire SE Mediterranean water column. This follows the global CO2 rise in the late Holocene as a result of the terrestrial biomass destruction during the aridification process. Moreover the gradual reduction of the vegetation cover in East Africa led to an increased erratic flood-related sediment flux via the Nile River up to the present. This is reflected by the general change in the local sediment composition. At 3.6 ka, the Saharan eolian input reached 65% whereas at about 0.3 ka 70% of the SE Mediterranean sediment was composed of Nile particulate matter.

Late Cretaceous upwelling system along the Southern Tethys Margin (Israel): Interrelationship between productivity, bottom water environments, and organic matter preservation

Organic-rich Upper Cretaceous sequences in Israel were deposited in an extensive, highly productive upwelling-linked system which prevailed along the southern Tethys margin, and lasted for ∼19 m.y. (Santonian to late Maastrichtian). An understanding of the spatial and temporal characteristics of this system was gained through detailed paleontological and geochemical analyses of subsurface sequences in two basins in Israel, representing an outer (Shefela) and an inner (Zin) facies belt. The nature of the upwelling system, and its effect on the sedimentary record, is related to two basic environmental parameters, namely paleoproductivity intensity and oxygen levels at the bottom. The assessment of these parameters and their interrelationship has been performed through the development of paleontological (foraminiferal) criteria, which are independent of the organic matter content. Following the establishment of these criteria, it is concluded that the productivity reached its maximum intensity during the late Campanian, which was also the time of most notable differentiation between the center of the upwelling system in the inner belt and the less intense conditions in the outer basin. This distribution is expressed in varied lithology (organic-rich carbonates, phosphorites, and siliceous rocks) at the core of upwelling and a uniform lithology (organic-rich carbonates) at the margin of this system. The uniform lithology of the Maastrichtian in both basins, composed of organic-rich carbonates, is ascribed to a gradual weakening of productivity. The bottom conditions in the inner belt during the late Campanian (the time of maximum surface productivity) were near anoxic, changing to more aerated (dysaerobic) conditions during the early Maastrichtian. In the outer belt a more aerated bottom (dysaerobic) prevailed throughout the late Campanian to late Maastrichtian. The elevated organic matter content in both basins reflects the overall environment of high productivity; its actual variations, however, seem to be unrelated to changes in surface productivity and bottom oxygen levels.

Three hundred eighty thousand year long stable isotope and faunal records from the Red Sea: Influence of global sea level change on hydrography

Stable isotope and faunal records from the central Red Sea show high-amplitude oscillations for the past 380,000 years. Positive δ18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53‰ and 55‰ are inferred from pteropod and benthic foraminifera δ18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic δ18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically - driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates.

Paleoenvironmental events during the last 13,000 years in the central Red Sea as recorded by pteropoda

A high-resolution record was obtained by investigating a sedimentary sequence from two cores taken in the central Red Sea (R/V Meteor cruise 5, leg 2). The numerical variations between nonmigratory and migratory pteropods and their stable isotopic record were studied together with variations in the carbonate and total organic carbon content in order to estimate changes in the structure of the water column during the last 13 kyr. The results indicate the existence of a highly stratified water column during deglaciation and early Holocene (13–8.5 ka). During this period the depth of the mixed layer varied between less than 50–100 m at most, and productivity was markedly reduced in comparison to the recent situation. The intermediate and deep water were constantly highly depleted in oxygen. A pronounced Younger Dryas event was recognized at 10.4 ka which coincides with an arid phase on the border land. The oxygenation of the intermediate water improved remarkably after 7.5 ka and peaked during the period between 4.6 and 2.0 ka. During this period the mixed layer reached its present depth and the productivity which was maximal during middle Holocene attained present level during the last 4.6 kyr.

Decline of the Maastrichtian pelagic ecosystem based on planktic foraminifera assemblage change: Implication for the terminal Cretaceous faunal crisis

An outer shelf–upper slope tropical Tethyan pelagic environment existed over southern Israel during Maastrichtian time. Planktic foraminifera in the >63 and >149 µm size fractions from four sections in this area were studied quantitatively for a high-resolution ecostratigraphic analysis of the pre–Cretaceous-Tertiary (K-T) paleoenvironment. During the Maastrichtian, 41% of the planktic foraminifera species became extinct, mostly keeled Globotruncanidae , which also became quantitatively reduced near the end of the Maastrichtian from as much as 35% to only 5% of the planktic foraminifera population. Evolutionary replacement of extinct species by new forms nearly ceased in that interval. Two major opportunistic blooms of Guembelitria took place, associated with reduced abundances of keeled forms and the dominant species Heterohelix globulosa . The first bloom occurred within the upper Gansserina gansseri to lower Abathomphalus mayaroensis Zones and the second within the Plummerita hantkeninoides Zone. The extinctions, concomitant changes in faunal dominance, and opportunist blooms indicate that the pelagic ecosystem in the Negev area experienced multiple stresses during the Maastrichtian. The planktic foraminiferal assemblages were taxonomically impoverished and in decline prior to the K-T boundary crisis.

Dinoflagellate cysts, paleoproductivity and upwelling systems: A Late Cretaceous example from Israel

Abstract Diverse assemblages of dinoflagellate cysts occur in Coniacian-Maastrichtian sedimentary sequences in Israel, which represent the inner (shallower) and outer (deeper, seaward) belt of a Late Cretaceous upwelling system along the margin of the southern Tethys. The assemblages are composed mainly of peridinioid (P) and gonyaulacoid (G) cysts in varying concentrations. It is suggested that the observed fluctuations in the numerical peridinioid/gonyaulacoid (P/G) cyst ratio reflect mainly changes in upwelling intensity and productivity in the studied area: high P/G values represent a higher productivity and vice versa. TheP/G curve indicates a generally high productivity during the Campanian, followed by a decrease during the Maastrichtian. The inner part of the upwelling region is characterized by higherP/G values, representing a higher productivity. The similarity between theP/G ratio curve and the foraminiferal-based paleoproductivity curve from the same sections supports the utility of theP/G ratio as a reliable productivity indicator, applied here for the first time to Upper Cretaceous sediments.

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

Abstract 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.

Quaternary paleo-oceanography, pteropod preservation and stable-isotope record of the Red Sea

Abstract An abundance of pteropod species, their mode of preservation, and stable isotope ratios of carbon and oxygen in benthic and planktic foraminifera have been determined in core MD76-140 from the northern Red Sea. Isotopic data and benthic foraminiferal species indicate changes in O2 concentration in the bottom sediments. The glacial stages are characterized by an almost anoxic bottom, while the interglacial bottom was generally well ventilated. In general very well preserved pteropod shells occur in glacial oxygen-depleted intervals, and also on recent well ventilated bottoms. In the interglacial stages the preservation deteriorates, and in the most extreme cases there is a complete dissolution of the aragonitic shells. In these cases most of the assemblage is lost and the only traces of the original shells are their internal molds. These are cemented with high magnesium calcite (HMC) which is a more stable carbonate phase in bottom sediments of the interglacial. Dissolution of aragonite discriminates between large and small shells, the latter tend to be removed completely, while the larger ones may be preserved as internal HMC molds. Limacina inflata is more readily molded than L. trochiformis, and thus its relative abundance increases in poorly preserved assemblages. The state of aragonitic shell preservation depends on the degree of organic matter combustion in the sediments. Well preserved shells occur in sediments where the supply of organic matter is limited and O2 levels are high. Preservation deteriorates with increasing supply of organic carbon, O2 consumption and increasing production of CO2. In this case the dissolved carbonate is reprecipitated as HMC cement. With further increase in organic matter supply and reduced ventilation, nearly all oxygen is consumed and NO3− and subsequently SO42− become the oxidizing agents. This is followed by an increasing carbonate alkalinity and excellent aragonitic shell preservation.

Sea-land paleoclimate correlation in the Eastern Mediterranean region during the late Holocene

18 O) of the epipelagic foraminifera Globigerinoides ruber (G. ruber) and of carbonate cave deposits (speleothems) from the Eastern Mediterranean (EM) region, Israel, are linked through the hydrological cycle. The Soreq speleothem δ 18 O record matches the marine δ 18 OG. ruber record for the EM Sea during the last 3600 years, with an almost constant ∆δ 18 OG.ruber-speleothems of 5.54 ± 0.26‰, similar to the present-day offset. Thus, a link between land and marine isotopic records is established. Both of these can be considered reliable recorders of the climatic conditions that prevailed in the land-locked EM region during the late Holocene. Several climatic events are documented during the Holocene, superimposed on a general aridity trend that started ~8000 yr BP. Among these climatic events are three humid events, at ~3200, ~1300, and ~700 yr BP, the last one being associated with the global Medieval Warm Period humid event. Three dry events occurred, at 2100, 900, and 300 yr BP, the last one coinciding with the Little Ice Age.

Carbonate preservation and climatic changes in the central Red Sea during the last 380 kyr as recorded by pteropods

Numerical abundances of pteropods and planktic foraminifera, and the mode of pteropod preservation, were determined in core KL 11 taken from the central part of the Red Sea. The abundance of pteropods (shells/g dry sediment) was compared to that of planktic foraminifera (% Pt/Pf + Pt) — a technique that permits detection of changes in carbonate preservation for the last 380 kyr. The numerical abundance of pteropods is influenced by the properties of the water column, and preservation is influenced by the bottom water. During the last ∼ 200 kyr (except during isotope stage 5.5) carbonates are in general well preserved. During this period the abundance pattern of the pteropods and planktic foraminifera is very similar and follows the climatic signal of the Red Sea with high numbers during the interglacial stages, changing to very low numbers during glacial maximum conditions. The similar abundance trends of the two groups, and between them and the δ18O curve, indicates abundance is strongly linked to salinity. From isotope stage 6 to the bottom of the core the pteropods occur in low numbers, unlike the planktic foraminifera, which continue to display the high-amplitude glacial-interglacial cyclicity. The deviations, mainly during interglacial stages, between the abundance pattern of the two groups and the low % Pt/Pf + Pt values, indicate a significant change in carbonate preservation. Distinctive carbonate dissolution intervals are recognized in the Red Sea, correlating to large scale deep water dissolution events of the ‘mid-Brunhes dissolution cycle’ in the Indian Ocean. The anti-estuarine circulation pattern of the Red Sea prevents a direct connection between the deep water masses of the two oceans and rules out the likelihood that changes in the deep water circulation caused these carbonate dissolution events. The numerical variations between nonmigratory epipelagic and migratory mesopelagic pteropods were used to evaluate changes in the structure of the water column. Abundance maxima of mesopelagic pteropods, as in the recent Red Sea, indicate an aerated water column with ≥0.5 ml O2/l oxygen concentrations at the minimum zone. Mesopelagic abundance maxima coincide commonly with negative monsoonal index values indicating a more aerated water column connected to increasing aridity in the Red Sea region. Abundance maxima of epipelagic pteropods indicate a strongly stratified water column, at times causing severe depletion in oxygen at intermediate water depths. Epipelagic peak events coincide often with positive monsoon index values implying an overall milder and more humid climate in the Red Sea, probably associated with enhanced precessional-controlled southwest monsoon activity.