Stable oxygen isotope record of Globigerinoides sacculifer and age determination of sediment cores from teh Somali Basin

This study documents the biological signatures impressed upon the sedimentary record underlying both the 5°N upwelling system of the Somali Current and the equatorial area of the Somali Basin out of the upwelling influence. The evolution of these two distinct hydrographic systems is compared for the last 160 kyr. Correspondence and cluster analyses are performed on combined radiolarian and planktonic foraminiferal quantitative data in order to study the changes of the planktonic assemblages through time and space. The Upwelling Radiolarian Index (URI) is used as a productivity proxy. The water temperature and hydrographic structure of the upper water masses appear to be the major factors controlling the distribution patterns of the fauna. The relative abundances of three groups of foraminifera, cold water form (dextral N. pachyderma), mixed layer dwellers (G. trilobus, G. ruber, G. sacculifer, G. conglobatus, and G. glutinata), and thermocline dwellers (G. menardii, G. tumida, N. dutertrei, G. crassaformis, and P. obliquiloculata), follow distinct evolutionary patterns at the two sites during the last 160 kyr. At the equatorial site (core MD 85668), downcore fluctuations in the relative abundances of the three groups are closely related to the glacial/interglacial cyclicity and provide some insights into the interpretation of hydrographic changes. The dominance of the mixed layer foraminifera at the transition intervals between isotope stages 6/5 and 2/1, combined with weak URI values, is thought to reflect the reorganization of the oceanographic circulation. These short-term events (with a duration of < 5000 year) could be related to the rapid inflow of oxygen-depleted water through the Indonesian straits as a result of sea level rise during deglaciation. Underneath the 5°N gyre (core MD 85674), the response to global climatic changes is overprinted by the regional effect of the Somalian upwelling, which has been persistent over the last 160 kyr.

Changes in calcareous nannofossil assemblages across the Paleocene/Eocene transition from the paleo-equatorial Pacific Ocean

Quantitative analyses of selected calcareous nannofossils in deep-sea sections recovered from the paleo-equatorial Pacific (ODP Leg 199) provide new information about biostratigraphy, biochronology and the evolutionary history of calcareous nannofossils across the Paleocene/Eocene transition interval. The sediment cores from ODP Leg 199 represent the first continuous Paleocene/Eocene boundary sections ever to be sampled in the central equatorial Pacific Ocean. Calcareous nannofossil assemblages are studied to document the distribution of biostratigraphically useful taxa such as Ericsonia, Discoaster, Fasciculithus, Rhomboaster and Tribrachiatus. Focus is given to the evolution of the Rhomboaster-Tribrachiatus lineage in the lower Eocene interval at Site 1215, and on the stratigraphic relationship of these taxa relative to species in the genus Fasciculithus. Critical intervals of North Atlantic DSDP Site 550 have also been re-examined. The Tribrachiatus digitalis morphotype was described at Site 550 from an interval affected by down-hole contamination, partly originating from within the Tribrachiatus orthostylus range. The T. digitalis morphotype represents an evolutionary transitional form between T. contortus and T. orthostylus, entering the stratigraphic record within the range of the former species and disappearing within the lower part of the range of the latter species. The subzonal subdivision of Zone NP10 hence collapses. Lithological and colour variability reflecting orbital cyclicity occur in the lower Eocene of Site 1215, permitting a relative astronomical age calibration of the Tribrachiatus taxa. The distinct Rhomboaster spp.-Discoaster araneus association also occurs in the paleo-equatorial Pacific Ocean, together with a marked decrease in diversity of Fasciculithus spp. Site 1220 reveals a short peak abundance of Thoracosphaera spp. just above the P/E boundary interval, which probably reflects a stressed surface water environment.

Magnetic susceptibility and electric conductivity of marine surficial sediments by benthic electromagnetic profiling

Distribution, accumulation and diagenesis of surficial sediments in coastal and continental shelf systems follow complex chains of localized processes and form deposits of great spatial variability. Given the environmental and economic relevance of ocean margins, there is growing need for innovative geophysical exploration methods to characterize seafloor sediments by more than acoustic properties. A newly conceptualized benthic profiling and data processing approach based on controlled source electromagnetic (CSEM) imaging permits to coevally quantify the magnetic susceptibility and the electric conductivity of shallow marine deposits. The two physical properties differ fundamentally insofar as magnetic susceptibility mostly assesses solid particle characteristics such as terrigenous or iron mineral content, redox state and contamination level, while electric conductivity primarily relates to the fluid-filled pore space and detects salinity, porosity and grain-size variations. We develop and validate a layered half-space inversion algorithm for submarine multifrequency CSEM with concentric sensor configuration. Guided by results of modeling, we modified a commercial land CSEM sensor for submarine application, which was mounted into a nonconductive and nonmagnetic bottom-towed sled. This benthic EM profiler Neridis II achieves 25 soundings/second at 3-4 knots over continuous profiles of up to hundred kilometers. Magnetic susceptibility is determined from the 75 Hz in-phase response (90% signal originates from the top 50 cm), while electric conductivity is derived from the 5 kHz out-of-phase (quadrature) component (90% signal from the top 92 cm). Exemplary survey data from the north-west Iberian margin underline the excellent sensitivity, functionality and robustness of the system in littoral (~0-50 m) and neritic (~50-300 m) environments. Susceptibility vs. porosity cross-plots successfully identify known lithofacies units and their transitions. All presently available data indicate an eminent potential of CSEM profiling for assessing the complex distribution of shallow marine surficial sediments and for revealing climatic, hydrodynamic, diagenetic and anthropogenic factors governing their formation.

Simulated agricultural subsistence, timing of transition, and percentage of immigrant farmers

Farming and herding were introduced to Europe from the Near East and Anatolia; there are, however, considerable arguments about the mechanisms of this transition. Were it the people who moved and either outplaced, or admixed with, the indigenous hunter-gatherer groups? Or was it material and information that moved---the Neolithic Package---consisting of domesticated plants and animals and the knowledge of their use? The latter process is commonly referred to as cultural diffusion and the former as demic diffusion. Despite continuous and partly combined efforts by archaeologists, anthropologists, linguists, palaeontologists and geneticists, a final resolution of the debate has not yet been reached. In the present contribution we interpret results from the Global Land Use and technological Evolution Simulator (GLUES). GLUES is a mathematical model for regional sociocultural development, embedded in the geoenvironmental context, during the Holocene. We demonstrate that the model is able to realistically hindcast the expansion speed and the inhomogeneous space-time evolution of the transition to agropastoralism in western Eurasia. In contrast to models that do not resolve endogenous sociocultural dynamics, our model describes and explains how and why the Neolithic advanced in stages. We uncouple the mechanisms of migration and information exchange and also of migration and the spread of agropastoralism. We find that: (1) An indigenous form of agropastoralism could well have arisen in certain Mediterranean landscapes, but not in Northern and Central Europe, where it depended on imported technology and material. (2) Both demic diffusion by migration and cultural diffusion by trade may explain the western European transition equally well. (3) Migrating farmers apparently contribute less than local adopters to the establishment of agropastoralism. Our study thus underlines the importance of adoption of introduced technologies and economies by resident foragers.

Sedimentation and mineral analysis on sediment cores from the Lena Delta

Core and outcrop analysis from Lena mouth deposits have been used to reconstruct the Late Quaternary sedimentation history of the Lena Delta. Sediment properties (heavy mineral composition, grain size characteristics, organic carbon content) and age determinations (14C AMS and IR-OSL) are applied to discriminate the main sedimentary units of the three major geomorphic terraces, which form the delta. The development of the terraces is controlled by complex interactions among the following four factors: (1) Channel migration. According to the distribution of 14C and IR-OSL age determinations of Lena mouth sediments, the major river runoff direction shifted from the west during marine isotope stages 5-3 (third terrace deposits) towards the northwest during marine isotope stage 2 and transition to stage 1 (second terrace), to the northeast and east during the Holocene (first terrace deposits). (2) Eustasy. Sea level rise from Last Glacial lowstand to the modern sea level position, reached at 6-5 ka BP, resulted in back-filling and flooding of the palaeovalleys. (3) Neotectonics. The extension of the Arctic Mid-Ocean Ridge into the Laptev Sea shelf acted as a halfgraben, showing dilatation movements with different subsidence rates. From the continent side, differential neotectonics with uplift and transpression in the Siberian coast ridges are active. Both likely have influenced river behavior by providing sites for preservation, with uplift, in particular, allowing accumulation of deposits in the second terrace in the western sector. The actual delta setting comprises only the eastern sector of the Lena Delta. (4) Peat formation. Polygenetic formation of ice-rich peaty sand (''Ice Complex'') was most extensive (7-11 m in thickness) in the southern part of the delta area between 43 and 14 ka BP (third terrace deposits). In recent times, alluvial peat (5-6 m in thickness) is accumulated on top of the deltaic sequences in the eastern sector (first terrace).

Predicting bed form roughness: the influence of lee side angle

Flow transverse bedforms (ripples and dunes) are ubiquitous in rivers and coastal seas. Local hydrodynamics and transport conditions depend on the size and geometry of these bedforms, as they constitute roughness elements at the bed. Bedform influence on flow energy must be considered for the understanding of flow dynamics, and in the development and application of numerical models. Common estimations or predictors of form roughness (friction factors) are based mostly on data of steep bedforms (with angle-of-repose lee slopes), and described by highly simplified bedform dimensions (heights and lengths). However, natural bedforms often are not steep, and differ in form and hydraulic effect relative to idealised bedforms. Based on systematic numerical model experiments, this study shows how the hydraulic effect of bedforms depends on the flow structure behind bedforms, which is determined by the bedform lee side angle, aspect ratio and relative height. Simulations reveal that flow separation behind bedform crests and, thus, a hydraulic effect is induced at lee side angles steeper than 11 to 18° depending on relative height, and that a fully developed flow separation zone exists only over bedforms with a lee side angle steeper than 24°. Furthermore, the hydraulic effect of bedforms with varying lee side angle is evaluated and a reduction function to common friction factors is proposed. A function is also developed for the Nikuradse roughness (k s), and a new equation is proposed which directly relates k s to bedform relative height, aspect ratio and lee side angle.

A sedimentological, faunal, and isotopic record of the middle-to-late Pliocene transition at DSDP Hole 80-548

Hydraulic piston coring at DSDP Site 548, on the upper continental slope southwest of Ireland, recovered a nearly complete Pliocene section spanning 103 m of sediment. The sediments are greenish gray carbonate-rich hemipelagites containing abundant nannofossils and foraminifers. Grain-size analysis demonstrates that the texture of the section is fairly constant, with most of the variation occurring in 63- to 32-µm and < 2-µm fractions. Previous research has shown that the middle-to-late Pliocene transition in the North Atlantic was marked by the appearance of the planktonic foraminiferal species Globorotalia inflata and by the first occurrence of significant quantities of ice-rafted sediment grains in deep-sea sediments. The latter is taken to represent the first important development of Northern Hemisphere glaciation. The first appearance of G. inflata is carefully documented for Site 548 and is demonstrated to be an evolutionary datum at this site, rather than an ecologically controlled first appearance. Surface ocean conditions represented in the sediment section spanning the appearance of G. inflata were strongly cyclic, resulting in large periodic changes in the abundances of Globorotalia puncticulata and N. acostaensis. The benthic foraminiferal population was studied in detail over the middle-to-upper Pliocene transition to establish the nature and behavior of the intermediate-depth water mass in the northeastern Atlantic at the time of ice-sheet growth in the Northern Hemisphere. This water mass is presently warm and saline, having its source in the Mediterranean Sea. The benthic data show that the intermediate-depth water mass was undergoing a series of progressive changes over the interval including the first appearance of G. inflata. These changes are particularly reflected in the relative abundances of Globocassidulina subglobosa (Brady), Uvigerina, and Ehrenbergina. Also, the mean size of individuals in the G. subglobosa populations shows systematic variation, indicating changing intermediate-depth water properties. Oxygen-isotope analyses show that the intermediate-depth water mass was cold during the middle-to-late Pliocene transition. This interpretation is supported by the relative abundances of benthic foraminiferal species. Hence, the intermediate-depth northeastern Atlantic water mass of the middle to late Pliocene was considerably different from the intermediate-depth water mass of the present.

Seawater calcium isotope ratios across the Eocene-Oligocene Transition from Pacific Ocean - Marine Barite

During the Eocene-Oligocene transition (EOT, ca. 34 Ma), Earth's climate cooled significantly from a greenhouse to an icehouse climate, while the calcite (CaCO3) compensation depth (CCD) in the Pacific Ocean increased rapidly. Fluctuations in the CCD could result from various processes that create an imbalance between calcium (Ca) sources to, and sinks from, the ocean (e.g., weathering and CaCO3 deposition), with different effects on the isotopic composition of dissolved Ca in the oceans due to differences in the Ca isotopic composition of various inputs and outputs. We used Ca isotope ratios (d44/40Ca) of coeval pelagic marine barite and bulk carbonate to evaluate changes in the marine Ca cycle across the EOT. We show that the permanent deepening of the CCD was not accompanied by a pronounced change in seawater d44/40Ca, whereas time intervals in the Neogene with smaller carbonate depositional changes are characterized by seawater d44/40Ca shifts. This suggests that the response of seawater d44/40Ca to changes in weathering fluxes and to imbalances in the oceanic alkalinity budget depends on the chemical composition of seawater. A minor and transient fluctuation in the Ca isotope ratio of bulk carbonate may reflect a change in isotopic fractionation associated with CaCO3 precipitation from seawater due to a combination of factors, including changes in temperature and/or in the assemblages of calcifying organisms.