Sea surface temperature reconstruction for the middle Pleistocene from sediment core MD03-2699

Past sea surface water conditions of the western Iberian Margin were reconstructed based on biomarker analyses of a marine deep sea core MD03-2699 from the Estremadura Spur north off Lisbon, providing new insights into orbital and suborbital-scale climate variability between marine isotope stage (MIS) 15 to MIS 9 (580 to 300 ka). We use biomarker-based proxy records such as the alkenone unsaturated index to estimate sea surface temperature (SST), the total alkenone concentration to reconstruct phytoplankton productivity, and terrestrial biomarkers to evaluate the continental input. The results extend the existing biomarker record, namely the SST for the Iberian Margin, back to the sixth climatic cycle (580 ka). A general trend of stable interglacials contrasts with glacial periods and glacial inceptions which are marked by high-frequency variability. Thus, several short-lived climatic coolings were identified by large SST decreases, the occurrence of ice-rafted detritus and high percentages of the tetraunsaturated alkenone C 37:4. Some of these events were extremely cold and similar in their general trends to the well-known Heinrich events of the last glaciation. We identified eight Heinrich-type events between 580 and 300 ka. The general deglaciation pattern detected between MIS 15 and MIS 9 is similar in their general trends to that characterizing the more recent climatic cycles, i.e., marked by two coolings separated by a short warming episode which may reflect the southward, northward, and southward migration of the Polar Front.

Planktic foraminifera isotopes, temperature and d18O of seawater at the central Walvis Ridge for Termination II (MIS 6 to 5), sediment core 64PE-174P13

Salty and warm Indian Ocean waters enter the South Atlantic via the Agulhas leakage, south of Africa. Model simulations and proxy evidence of Agulhas leakage strengthening during glacial terminations led to the hypothesis that it was an important modulator of the Atlantic Ocean circulation. Yet, the fate of the leakage salinity and temperature anomalies remains undocumented beyond the southern tip of Africa. Downstream of the leakage, new paleoceanographic evidence from the central Walvis Ridge (southeast Atlantic) shows that salinity increased at the thermocline, and less so at the surface, during glacial termination II. Thermocline salinity change coincided with higher frequency of Agulhas rings passage at the core location and with salinity maxima in the Agulhas leakage area, suggesting that leakage waters were incorporated in the Atlantic circulation through the thermocline. Hydrographic changes at the Walvis Ridge and in the leakage area display a distinct two-step structure, with a reversal at ca. 134 ka. This matched a wet interlude within the East Asia weak monsoon interval of termination II, and a short-lived North Atlantic warming. Such concurrence points to a Bølling-Allerød-like recovery of the Atlantic circulation amidst termination II, with a northward shift of the Intertropical Convergence Zone and Southern Hemisphere westerlies, and attendant curtailment of the interocean connection south of Africa.

Sea-surface temperature and salinity reconstruction for sediment core GeoB5844-2

We present high-resolution paleoceanographic records of surface and deep water conditions within the northern Red Sea covering the last glacial maximum and termination I using alkenone paleothermometry, stable oxygen isotopes, and sediment compositional data. Paleoceanographic records in the restricted desert-surrounded northern Red Sea are strongly affected by the stepwise sea level rise and appear to record and amplify well-known millennial-scale climate events from the North Atlantic realm. During the last glacial maximum (LGM), sea surface temperatures were about 4°C cooler than the late Holocene. Pronounced coolings associated with Heinrich event 1 (~2°C below the LGM level) and the Younger Dryas imply strong atmospheric teleconnections to the North Atlantic. Owing to the restricted exchange with the Indian Ocean, Red Sea salinity is particularly sensitive to changes in global sea level. Paleosalinities exceeded 50 psu during the LGM. A pronounced freshening of the surface waters is associated with the meltwater peaks MWP1a and MWP1b owing to an increased surface-near inflow of "normal" saline water from the Indian Ocean. Vertical delta18O gradients are also increased during these phases, indicating stronger surface water stratification. The combined effect of deglacial changes in sea surface temperature and salinity on water column stratification initiated the formation of two sapropel layers, which were deposited under almost anoxic condition in a stagnant water body.

Age and alkenone-derived Holocene sea-surface temperature records of sediment core M40-4-SL78

This Special Issue of The Holocene contains 16 research papers based on a symposium at the 11th International Meeting of the European Union of Geosciences held in Strasbourg in April 2001. The aim of the symposium was a state-of-the-art assessment of empirical studies of postglacial marine and terrestrial climatic archives and their integration with numerical climate models. This editorial places the individual papers in the broader context of natural climate variability and anthropogenic impacts on the global climate system, regional differences in climate between maritime and continental areas, and the need for an improved theoretical basis for understanding the underlying causes of environmental change. The focus of the Special Issue is the dynamic and relatively well-understood climate of the North Atlantic and the European realm, where, in relation to the steepest offshore temperature gradient on Earth, observational data are abundant and many recent advances have been made in climate reconstruction from proxy archives. The editorial also contains a summary and overview of the papers included in the four main sections of the Special Issue, which emphasize: (1) numerical modelling experiments; (2) models of glacier buildup and equilibrium-line altitude; (3) marine and terrestrial proxy records of climatic change; and (4) multiproxy palaeoenvironmental reconstruction of a Portuguese lagoonal system.

Stable isotope data and calcification temperature from planktic foraminifera in sediment core BOFS31/1K

Determining the past record of temperature and salinity of ocean surface waters is essential for understanding past changes in climate, such as those which occur across glacial-interglacial transitions. As a useful proxy, the oxygen isotope composition (delta18O) of calcite from planktonic foraminifera has been shown to reflect both surface temperature and seawater delta18O, itself an indicator of global ice volume and salinity (Shackleton, 1974; Rostek et al., 1993, doi:10.1038/364319a0). In addition, magnesium/calcium (Mg/Ca) ratios in foraminiferal calcite show a temperature dependence (Nürnberg, 1995, doi:10.2113/gsjfr.25.4.350; Nürnberg et al., 1996, doi:10.1016/0016-7037(95)00446-7; Lea et al., 1999, doi:10.1016/S0016-7037(99)00197-0) due to the partitioning of Mg during calcification. Here we demonstrate, in a field-based calibration experiment, that the variation of Mg/Ca ratios with temperature is similar for eight species of planktonic foraminifera (when accounting for Mg dissolution effects). Using a multi-species record from the Last Glacial Maximum in the North Atlantic Ocean we found that past temperatures reconstructed from Mg/Ca ratios followed the two other palaeotemperature proxies: faunal abundance (CLIMAP, 1981; Mix et al., 1999, doi:10.1029/1999PA900012) and alkenone saturation (Müller et al., 1998, doi:10.1016/S0016-7037(98)00097-0 ). Moreover, combining Mg/Ca and delta18O data from the same faunal assemblage, we show that reconstructed surface water delta18O from all foraminiferal species record the same glacial-interglacial change-representing changing hydrography and global ice volume. This reinforces the potential of this combined technique in probing past ocean-climate interactions.

Compact Ag@fe3o4 Core-shell Nanoparticles By Means Of Single-step Thermal Decomposition Reaction.

A temperature pause introduced in a simple single-step thermal decomposition of iron, with the presence of silver seeds formed in the same reaction mixture, gives rise to novel compact heterostructures: brick-like Ag@Fe3O4 core-shell nanoparticles. This novel method is relatively easy to implement, and could contribute to overcome the challenge of obtaining a multifunctional heteroparticle in which a noble metal is surrounded by magnetite. Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape. The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature. The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.

In-field Mossbauer study of disordered surface spins in core/shell ferrite nanoparticles

Magnetization and Mossbauer spectroscopy measurements are performed at low temperature under high field, on nanoparticles with a nickel ferrite core and a maghemite shell. These nanoparticles present finite size and surface effects, together with exchange anisotropy. High field magnetization brings the evidences of a monodomain ordered core and surface spins freezing in disorder at low temperature. Mossbauer spectra at 4.2 K present an extra contribution from the disordered surface which is field dependent. Field and size dependences of this latter show a progressive spin alignment along the ferrite core which is size dependent. The weak surface pinning condition of the nanoparticles confirms that the spin disorder is localized in the external shell. The underfield decrease in the mean canting angle in the superficial shell is then directly related to the unidirectional exchange anisotropy through the interface between the ordered core and the disordered shell. The obtained anisotropy field H(Ea) scales as the inverse of the nanoparticle diameter, validating its interfacial origin. The associated anisotropy constant K(Ea) equals 2.5 x 10(-4) J/m(2). (C) 2009 American Institute qf Physics. [doi: 10.1063/1.3245326]

Middle Pleistocene sea surface temperature in the Brazil-Malvinas Confluence Zone: Paleoceanographic implications based on planktonic foraminifera

We reconstructed Middle Pleistocene surface hydrography in the western South Atlantic based on planktonic foraminiferal assemblages, modern analog technique and Globorotalia truncatulinoides isotopic ratios of core SP1251 (38 degrees 29.7`S / 53 degrees 40.7`W / 3400 m water depth). Biostratigraphic analysis suggests that sediments were deposited between 0.3 and 0.12 Ma and therefore correlate to Marine Isotopic Stage 6 or 8. Faunal assemblage-based winter and summer SST estimates suggest that the western South Atlantic at 38 degrees S was 4-6 degrees C colder than at present, within the expected range for a glacial interval. High relative abundances of subantarctic species, particularly the dominance of Neogloboquadrina pachyderma (left), support lower than present SSTs throughout the recorded period. The oxygen isotopic composition of G. truncatulinoides suggests a northward shift of the Brazil-Malvinas Confluence Zone and of the associated mid-latitude frontal system during this Middle Pleistocene cold period, and a stronger than present influence of superficial subantarctic waters and lowering in SSTs at our core site during the recorded Middle Pleistocene glacial.

Continental extension: From core complexes to rigid block faulting

Extension of overthickened continental crust is commonly characterized by an early core complex stage of extension followed by a later stage of crustal-scale rigid block faulting. These two stages are clearly recognized during the extensional destruction of the Alpine orogen in northeast Corsica, where rigid block faulting overprinting core complex formation eventually led to crustal separation and the formation of a new oceanic backarc basin (the Ligurian Sea). Here we investigate the geodynamic evolution of continental extension by using a novel, fully coupled thermomechanical numerical model of the continental crust. We consider that the dynamic evolution is governed by fault weakening, which is generated by the evolution of the natural-state variables (i.e., pressure, deviatoric stress, temperature, and strain rate) and their associated energy fluxes. Our results show the appearance of a detachment layer that controls the initial separation of the brittle crust on characteristic listric faults, and a core complex formation that is exhuming strongly deformed rocks of the detachment zone and relatively undeformed crustal cores. This process is followed by a transitional period, characterized by an apparent tectonic quiescence, in which deformation is not localized and energy stored in the upper crust is transferred downward and causes self-organized mobilization of the lower crust. Eventually, the entire crust ruptures on major crosscutting faults, shifting the tectonic regime from core complex formation to wholesale rigid block faulting.