Sea surface temperature and stable isotopes from 9 cores of the Northeastern Atlantic

Temporal and spatial patterns in eastern North Atlantic sea-surface temperatures (SST) were reconstructed for marine isotope stage (MIS) 11c using a submeridional transect of five sediment cores. The SST reconstructions are based on planktic foraminiferal abundances and alkenone indices, and are supported by benthic and planktic stable isotope measurements, as well as by ice-rafted debris content in polar and middle latitudes. Additionally, the larger-scale dynamics of the precipitation regime over northern Africa and the western Mediterranean region was evaluated from iron concentrations in marine sediments off NW Africa and planktic d13C in combination with analysis of planktic foraminiferal abundances down to the species level in the Mediterranean Sea. Compared to the modern situation, it is revealed that during entire MIS 11c sensu stricto (ss), i.e., between 420 and 398 ka according to our age models, a cold SST anomaly in the Nordic seas co-existed with a warm SST anomaly in the middle latitudes and the subtropics, resulting in steeper meridional SST gradients than during the Holocene. Such a SST pattern correlates well with a prevalence of a negative mode of the modern North Atlantic Oscillation. We suggest that our scenario might partly explain the longer duration of wet conditions in the northern Africa during MIS 11c compared to the Holocene.

Stable isotopes and XRF data over the Paleocene-Eocene Thermal Maximum from IODP Sites U1403 and U1409

During the Paleocene-Eocene Thermal Maximum (PETM) about 56 million years ago, thousands of petagrams of carbon were released into the atmosphere and ocean in just a few thousand years, followed by a gradual sequestration over approximately 200,000 years. If silicate weathering is one of the key negative feedbacks that removed this carbon, a period of seawater calcium carbonate saturation greater than pre-event levels is expected during the event's recovery phase. In marine sediments, this should be recorded as a temporary deepening of the depth below which no calcite is preserved - the calcite compensation depth (CCD). Previous and new sedimentary records from sites that were above the pre-PETM calcite compensation depth show enhanced carbonate accumulation following the PETM. A new record from an abyssal site in the North Atlantic that lay below the pre-PETM calcite compensation depth shows a period of carbonate preservation beginning about 70,000 years after the onset of the PETM, providing the first direct evidence for an over-deepening of the calcite compensation depth. This record confirms an overshoot in ocean carbonate saturation during the PETM recovery. Simulations with two earth system models support scenarios for the PETM that involve both a large initial carbon release followed by prolonged low-level emissions, consistent with the timing of CCD deepening in our record. Our findings indicate that sequestration of these carbon emissions was most likely the result of both globally enhanced calcite burial above the calcite compensation depth and, at least in the North Atlantic, by a temporary over-deepening of the calcite compensation depth.

Stable isotopic composition and carbonate concentrations of sediments of the Cretaceous/Paleogene boundary in the Antarctic

Stable isotopic records across the Cretaceous/Paleogene (K/P) boundary in Maud Rise Holes 689B and 690C indicate that significant climatic changes occurred during the latest Cretaceous, beginning approximately 500 k.y. prior to the mass extinction event and the enrichment of iridium at the K/P boundary (66.4 Ma). An oxygen isotopic decrease of ~0.7 per mil - ~1.0 per mil is recorded in the Late Cretaceous planktonic and benthic foraminifers between 66.9 and 66.6 Ma. The negative isotope excursion was followed by a positive excursion of similar magnitude between 66.6 Ma (latest Cretaceous) and ~66.3 Ma (earliest Paleocene). No other isotopic excursions of this magnitude are recorded in the planktonic and benthic microfossil records 1.0 m.y prior to, and for 2.0 m.y following the mass extinction event at the K/P boundary. The magnitude and duration of these isotopic excursions were similar to those at the Paleocene/Eocene and Eocene/Oligocene boundaries. A major d13C excursion occurred 200 k.y. prior to the boundary, involving a positive shift in planktonic and benthic d13C of ~0.5 per mil - 0.75 per mil. Similar changes observed in other deep-sea sequences indicate that this reflected a global change in d13C of the oceanic total dissolved carbon (TDC) reservoir. The magnitude of this inferred carbon reservoir change and its association with high latitude surface-water temperature changes recorded in the d18O records implies that it was linked to global climate change through feedback loops in the carbon cycle. At the K/P boundary, the surface-to-deep water d13C gradient is reduced by approximately 0.6 per mil - ~0.2 per mil. However, unlike sequences elsewhere, the planktonic-benthic d13C gradient (Delta d13C) was not eliminated in the Antarctic. The surface-to-deep water gradient was re-established gradually during the 400 k.y. following the mass extinction. Full recovery of the Delta d13C occurred by ~60.0 Ma. In addition to the reduced vertical d13C gradient across the K/P boundary, there was a negative excursion in both planktonic and benthic d13C beginning approximately 100 k.y. after the boundary (66.3 Ma). This excursion resulted in benthic d13C values in the early Paleogene that were similar to those in the pre-K/P boundary intervals. This negative shift appears to reflect a change in the d13C of the oceanic TDC reservoir shift that may have resulted from reduced carbon burial and/or increased carbon flux to the oceans. Any model that attempts to explain the demise of the oceanic plankton at the end of the Cretaceous should consider the oceanic environmental changes that were occurring prior to the massive extinction event.

Stable carbon and oxygen isotope ratios of bulk sediment from DSDP Hole 62-463 (Appendix A)

In order to elucidate early Aptian marine paleotemperature evolution across the period of enhanced organic carbon (Corg)-burial [Oceanic Anoxic Event (OAE) 1a], stable isotope analyses were performed on pelagic limestones at Deep Sea Drilling Project Site 463, central Pacific Ocean. The delta18O data exhibit a distinct anomaly by ~-2? spanning the OAE 1a interval (i.e., a ~6 m-thick, phytoplanktonic Corg-rich unit constrained by magneto-, bio- and delta13C stratigraphy). Elucidation of paleotemperature significance of the delta18O shift is made by taking account of recent Sr/Ca evidence at the same section, which revealed that geochemical signals in carbonate-poor lithologies are relatively unaltered against burial diagenesis. By discriminating delta18O values from carbonate-poor samples (CaCO3 contents=5-30 wt.%), it appears that an abrupt rise in seasurface temperatures (SSTs) by 8 °C (=-1.7? shift in delta18O) occurred immediately before OAE 1a, whereas a cooling mode likely prevailed during the peak Corg-burial. In terms of its stratigraphic relationship as to the Corg-rich interval and to a pronounced negative delta13C excursion, as well as its timescale, the observed SST rise resembles those associated with the Paleocene-Eocene thermal maximum and, more strikingly, Jurassic Toarcian OAE. This observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism, which was likely initiated by the greenhouse effect via massive release of CH4 or CO2 from the isotopically-light carbon reservoir and terminated by a negative productivity feedback.

Negative regulation of prophenoloxidase (proPO) activation by a clip-domain serine proteinase homolog (SPH) from endoparasitoid venom

Most parasitic wasps inject maternal factors into the host hemocoel to suppress the host immune system and ensure successful development of their progeny. Melanization is one of the insect defence mechanisms against intruding pathogens or parasites. We previously isolated from the venom of Cotesia rubecula a 50 kDa protein that blocked melanization in the hemolymph of its host, Pieris rapae [Insect Biochem. Mol. Biol. 33 (2003) 1017]. This protein, designated Vn50, is a serine proteinase homolog (SPH) containing an amino-terminal clip domain. In this work, we demonstrated that recombinant Vn50 bound P. rapae hemolymph components that were recognized by antisera to Tenebrio molitor prophenoloxidase (proPO) and Manduca sexta proPO-activating proteinase (PAP). Vn50 is stable in the host hemolymph-it remained intact for at least 72 It after parasitization. Using M. sexta as a model system, we found that Vn50 efficiently down-regulated proPO activation mediated by M. sexta PAP-1, SPH-1, and SPH-2. Vn50 did not inhibit active phenoloxidase (PO) or PAP-1, but it significantly reduced the proteolysis of proPO. If recombinant Vn50 binds P. rapae proPO and PAP (as suggested by the antibody reactions), it is likely that the molecular interactions among M. sexta proPO, PAP-1, and SPHs were impaired by this venom protein. A similar strategy might be employed by C rubecula to negatively impact the proPO activation reaction in its natural host. (C) 2004 Elsevier Ltd. All rights reserved.

Enzyme Electrochemistry - Biocatalysis on an electrode

Oxidoreductase enzymes catalyze single- or multi-electron reduction/oxidation reactions of small molecule inorganic or organic substrates, and they are integral to a wide variety of biological processes including respiration, energy production, biosynthesis, metabolism, and detoxification. All redox enzymes require a natural redox partner such as an electron-transfer protein ( e. g. cytochrome, ferredoxin, flavoprotein) or a small molecule cosubstrate ( e. g. NAD(P)H, dioxygen) to sustain catalysis, in effect to balance the substrate/product redox half-reaction. In principle, the natural electron-transfer partner may be replaced by an electrochemical working electrode. One of the great strengths of this approach is that the rate of catalysis ( equivalent to the observed electrochemical current) may be probed as a function of applied potential through linear sweep and cyclic voltammetry, and insight to the overall catalytic mechanism may be gained by a systematic electrochemical study coupled with theoretical analysis. In this review, the various approaches to enzyme electrochemistry will be discussed, including direct and indirect ( mediated) experiments, and a brief coverage of the theory relevant to these techniques will be presented. The importance of immobilizing enzymes on the electrode surface will be presented and the variety of ways that this may be done will be reviewed. The importance of chemical modification of the electrode surface in ensuring an environment conducive to a stable and active enzyme capable of functioning natively will be illustrated. Fundamental research into electrochemically driven enzyme catalysis has led to some remarkable practical applications. The glucose oxidase enzyme electrode is a spectacularly successful application of enzyme electrochemistry. Biosensors based on this technology are used worldwide by sufferers of diabetes to provide rapid and accurate analysis of blood glucose concentrations. Other applications of enzyme electrochemistry are in the sensing of macromolecular complexation events such as antigen - antibody binding and DNA hybridization. The review will include a selection of enzymes that have been successfully investigated by electrochemistry and, where appropriate, discuss their development towards practical biotechnological applications.

Environmentally stable high-power soliton fiber lasers that use chirped fiber Bragg gratings

Environmentally stable high-power erbium fiber soliton lasers are constructed by Kerr or carrier-type mode locking. We obtain high-energy pulses by using relatively short fiber lengths and providing large amounts of negative dispersion with chirped fiber Bragg gratings. The pulse energies and widths generated with both types of soliton laser are found to scale with the square root of the cavity dispersion. Kerr mode locking requires pulses with an approximately three times higher nonlinear phase shift in the cavity than carrier mode locking, which leads to the generation of slightly shorter pulses with as much as seven times higher pulse energies at the mode-locking threshold.

Two-dimensional viscoelastic discrete triangular system with negative-stiffness components

Potential applications of high-damping and high-stiffness composites have motivated extensive research on the effects of negative-stiffness inclusions on the overall properties of composites. Recent theoretical advances have been based on the Hashin-Shtrikman composite models, one-dimensional discrete viscoelastic systems and a two-dimensional nested triangular viscoelastic network. In this paper, we further analyze the two-dimensional triangular structure containing pre-selected negative-stiffness components to study its underlying deformation mechanisms and stability. Major new findings are structure-deformation evolution with respect to the magnitude of negative stiffness under shear loading and the phenomena related to dissipation-induced destabilization and inertia-induced stabilization, according to Lyapunov stability analysis. The evolution shows strong correlations between stiffness anomalies and deformation modes. Our stability results reveal that stable damping peaks, i.e. stably extreme effective damping properties, are achievable under hydrostatic loading when the inertia is greater than a critical value. Moreover, destabilization induced by elemental damping is observed with the critical inertia. Regardless of elemental damping, when the inertia is less than the critical value, a weaker system instability is identified.

Environmentally stable high-power soliton fiber lasers that use chirped fiber Bragg gratings

Environmentally stable high-power erbium fiber soliton lasers are constructed by Kerr or carrier-type mode locking. We obtain high-energy pulses by using relatively short fiber lengths and providing large amounts of negative dispersion with chirped fiber Bragg gratings. The pulse energies and widths generated with both types of soliton laser are found to scale with the square root of the cavity dispersion. Kerr mode locking requires pulses with an approximately three times higher nonlinear phase shift in the cavity than carrier mode locking, which leads to the generation of slightly shorter pulses with as much as seven times higher pulse energies at the mode-locking threshold.

Multi-Tissue Stable Isotope Analysis and Acoustic Telemetry Reveal Seasonal Variability in the Trophic Interactions of Juvenile Bull Sharks in a Coastal Estuary

Understanding how natural and anthropogenic drivers affect extant food webs is critical to predicting the impacts of climate change and habitat alterations on ecosystem dynamics. In the Florida Everglades, seasonal reductions in freshwater flow and precipitation lead to annual migrations of aquatic taxa from marsh habitats to deep-water refugia in estuaries. The timing and intensity of freshwater reductions, however, will be modified by ongoing ecosystem restoration and predicted climate change. Understanding the importance of seasonally pulsed resources to predators is critical to predicting the impacts of management and climate change on their populations. As with many large predators, however, it is difficult to determine to what extent predators like bull sharks (Carcharhinus leucas) in the coastal Everglades make use of prey pulses currently. We used passive acoustic telemetry to determine whether shark movements responded to the pulse of marsh prey. To investigate the possibility that sharks fed on marsh prey, we modelled the predicted dynamics of stable isotope values in bull shark blood and plasma under different assumptions of temporal variability in shark diets and physiological dynamics of tissue turnover and isotopic discrimination. Bull sharks increased their use of upstream channels during the late dry season, and although our previous work shows long-term specialization in the diets of sharks, stable isotope values suggested that some individuals adjusted their diets to take advantage of prey entering the system from the marsh, and as such this may be an important resource for the nursery. Restoration efforts are predicted to increase hydroperiods and marsh water levels, likely shifting the timing, duration and intensity of prey pulses, which could have negative consequences for the bull shark population and/or induce shifts in behaviour. Understanding the factors influencing the propensity to specialize or adopt more flexible trophic interactions will be an important step in fully understanding the ecological role of predators and how ecological roles may vary with environmental and anthropogenic changes.

Stable-isotope ratios and accumulation rates of four firn cores from the Dronning Maud Land, Antarctica

Four firn cores were retrieved in 2007 at two ridges in the area of the Ekström Ice Shelf, Dronning Maud Land, coastal East Antarctica, in order to investigate the recent regional climate variability and the potential for future extraction of an intermediate-depth core. Stable water-isotope analysis, tritium content and electrical conductivity were used to date the cores. For the period 1981-2006 a strong and significant correlation between the stable-isotope composition of firn cores in the hinterland and mean monthly air temperatures at Neumayer station was (r=0.54-0.71). No atmospheric warming or cooling trend is inferred from our stable-isotope data for the period 1962-2006. The stable-isotope record of the ice/firn cores could expand well beyond the meteorological record of the region. No significant temporal variation of accumulation rates was detected. However, decreasing accumulation rates were found from coast to hinterland, as well as from east (Halvfarryggen) to west (Søråsen). The deuterium excess (d) exhibits similar differences (higher d at Søråsen, lower d at Halvfarryggen), with a weak negative temporal trend on Halvfarryggen (0.04 per mil/a), probably implying increasing oceanic input. We conclude that Halvfarryggen acts as a natural barrier for moisture-carrying air masses circulating in the region from east to west.

Chemistry and stable isotope record of sediment core GeoB4905-4

Evidence of rapid climatic oscillations like those observed in the Greenland ice cores and sediments from high latitudes of the northern Atlantic have been recognized in the pulses of terrigenous material to continental margin sediments off Cameroon. Fe/Ca ratios used as a parameter to quantify the relative proportions of terrigenous fluxes versus marine carbonate monitor the variability of the west African monsoon. They reveal the history of abrupt changes in precipitation over western and central Africa during the past 52 kyr. These rapid changes are particularly pronounced during the last glacial period and occur at timescales of a few thousand years. Stable oxygen isotope (delta18O) records of Globigerinoides ruber (pink) show high negative values reflecting periods of high monsoon precipitation. The Fe/Ca pattern is very similar to the Dansgaard-Oeschger cycles from the Greenland ice cores. The good correspondence between the warm interstadials of the Dansgaard-Oeschger cycles from the GISP2 ice core records and the high pulses of Fe/Ca sedimentation in our core suggest a strong teleconnection between the low-latitude African climate and the high-latitude northern hemisphere climate oscillations during the last glacial. This climatic link is probably vested in the west African monsoonal fluctuation that alters tropical sea surface temperatures, thermohaline circulations and in turn net export of heat from the south to the north Atlantic, coupled with the variability of the low-latitude southeast trade winds.

Mineralogical (bulk rock and clay fraction) and stable isotope composition (d13C, d18O) of Aptian deposits of the Bir Oum Ali succession, central Tunisia

Alternations between siliciclastic, carbonate and evaporitic sedimentary systems, as recorded in the Aptian mixed succession of southern Tunisia, reflect profound palaeoceanographic and palaeoclimatic changes in this area of the southern Tethyan margin. The evolution from Urgonian-type carbonates (Berrani Formation, lower Aptian) at the base of the series, to intervals dominated by gypsum or detrital deposits in the remainder of the Aptian is thought to result from the interplay between climate change and tectonic activity that affected North Africa. Based on the evolution of clay mineral assemblages, the early Aptian is interpreted as having been dominated by slightly humid conditions, since smectitic minerals are observed. Near the early to late Aptian boundary, the onset of a gypsiferous sedimentation is associated with the appearance of palygorskite and sepiolite, which supports the installation of arid conditions in this area of the southern Tethyan margin. The evaporitic sedimentation may have also been promoted by the peculiar tectonic setting of the Bir Oum Ali area during the Aptian, where local subsidence may have been tectonically enhanced linked to the opening of northern and central Atlantic. Stress associated with the west and central African rift systems may have triggered the development of NW-SE, hemi-graben structures. Uplifted areas may have constituted potential new sources for clastic material that has been subsequently deposited during the late Aptian. Chemostratigraphic (d13C) correlation of the Bir Oum Ali succession with other peri-Tethyan regions complements biostratigraphic findings, and indicates that a potential expression of the Oceanic Anoxic Event (OAE) 1a may be preserved in this area of Tunisia. Although the characteristic negative spike at the base of this event is not recognized in the present study, a subsequent, large positive excursion with d13C values is of similar amplitude and absolute values to that reported from other peri-Tethyan regions, thus supporting the identification of isotopic segments C4-C7 of the OAE1a. The absence of the negative spike may be linked to either non preservation or non deposition: the OAE1a occurred in a global transgressive context, and since the Bir Oum Ali region was located in the innermost part of the southern Tethyan margin during most of the Aptian, stratigraphic hiatuses may have been longer than in other regions of the Tethys. This emphasizes the importance of integrating several stratigraphic disciplines (bio-, chemo- and sequence stratigraphy) when performing long-distance correlation.

Chlorine concentrations and stable isotope ratios in Izu Bonin tephra

d37Cl values were determined for Izu Bonin arc magmas erupted 0-44 Ma in order to better understand the time-dependent processing of volatiles in subduction zones. Pristine ash-sized particles (glass, pumice, scoria, and rock fragments) were handpicked from tephra drilled at ODP Site 782. d37Cl values for these particles span a large range from -2.1 to +1.7 per mil (error = ± 0.3 per mil) vs. SMOC (Standard Mean Ocean Chloride, defined as 0 per mil). The temporal data extend the previously reported range of d37Cl values of -2.6 to 0.4 per mil (bulk ash) and -5.4 to -0.1 per mil (volcanic gases) from the Quaternary Izu Bonin-Mariana volcanic front to more positive values. Overall, the temporal data indicate a time-progressive evolution, from isotopically negative Eocene and Oligocene magmas (-0.7 ± 1.1 per mil, n = 10) to Neogene magmas that have higher ?37Cl values on average (+0.3 ± 1.1 per mil; n = 13). The increase is due to the emergence of positive d37Cl values in the Neogene, while minimum d37Cl values are similar through time. The range in d37Cl values cannot be attributed to fractionation during melt formation and differentiation, and must reflect the diversity of Cl present in the arc magma sources. Cl clearly derives from the slab (> 96% Cl in arc magmas), but d37Cl values do not correlate with isotope tracers (e.g. 207Pb/204Pb and 87Sr/86Sr) that are indicative of the flux from subducting sedimentary and igneous crust. Given the steady, high Cl flux since at least 42 Ma, the temporal variability of d37Cl values is best explained by a flux from subducting isotopically positive and negative serpentinite formed in the ocean basins that mingles with and possibly overprints the isotopically negative flux from sediment and igneous crust at arc front depths. The change in the d37Cl values before and after backarc spreading may reflect either a tectonically induced change in the mechanism of serpentinite formation on the oceanic plate, or possibly the integration of isotopically positive wedge serpentinite as arc fluid source during the Neogene. Our study suggests that serpentinites are important fluid sources at arc front depth, and implies the return of isotopically positive and negative Cl from the Earth surface to the mantle.

Stable isotopes, radionuclides, and calculated sea surface temperature of two sediment cores in the Sicily Channel

The Eastern Mediterranean Transient (EMT) occurred in the Aegean Sea from 1988 to 1995 and is the most significant intermediate-to-deep Mediterranean overturning perturbation reported by instrumental records. The EMT was likely caused by accumulation of high salinity waters in the Levantine and enhanced heat loss in the Aegean Sea, coupled with surface water freshening in the Sicily Channel. It is still unknown whether similar transients occurred in the past and, if so, what their forcing processes were. In this study, sediments from the Sicily Channel document surface water freshening (SCFR) at 1910±12, 1812±18, 1725±25 and 1580±30 CE. A regional ocean hindcast links SCFR to enhanced deep-water production and in turn to strengthened Mediterranean thermohaline circulation. Independent evidence collected in the Aegean Sea supports this reconstruction, showing that enhanced bottom water ventilation in the Eastern Mediterranean was associated with each SCFR event. Comparison between the records and multi-decadal atmospheric circulation patterns and climatic external forcings indicates that Mediterranean circulation destabilisation occurs during positive North Atlantic Oscillation (NAO) and negative Atlantic Multidecadal Oscillation (AMO) phases, reduced solar activity and strong tropical volcanic eruptions. They may have recurrently produced favourable deep-water formation conditions, both increasing salinity and reducing temperature on multi-decadal time scales.