Isotopic and magnetic provenance characterization of distal IRD in the Galicia Interior Basin (NW Iberia)

The sediments of the Galicia Interior Basin in NW Iberia Margin are of particular palaeoclimatic interest as they are located at the boundary where the climatic oscillations of the glacial interval were interrupted by extreme events such as Heinrich events. These events are well characterized in Northern North Atlantic areas, but little is known about their occurrence beyond the Ruddiman belt. This study presents a combined environmagnetic and geochemical approach to the provenance and characterization of distal ice-rafted detritus (IRD) that occurred during the last glacial period in core CI12PC3 from the Galicia Interior Basin. The last six Heinrich Layers were identified by their magneto-mineralogical and geochemical properties. Their Sr and Nd isotopic signatures indicated that the Laurentide Ice Sheet was the major source for HL1, HL2, HL4 and HL5. However, the European ice sheets also influenced the initial development stages of HL1, HL2, HL4. HL3, HL6 and partially HL1, HL2 and HL4 were influenced by more juvenile provinces, such as Iceland/Faroes sheets and/or by the Fram Strait/East Greenland nearby areas. Separate provenance analyses of the coarse and fine fractions in the studied Heinrich Layers also indicated that IRDs and glacial flour sources might not always be the same. Our results shed unequivocal evidence that Canadian-sourced distal IRD are preceded by European-sourced IRD, at least from the H4. In our view, LIS and EIS instabilities registered in the Iberian Margin respond to the same climate forcing at different velocities

IRD characterization, provenance and age in the Galician Interior Basin

The Galician Interior Basin sediments have a particular palaeoclimatic interest, as they are located in the boundary where the climatic oscillations of the glacial interval were interrupted by extreme events such as Heinrich events (HE). The sedimentary expression of these events is characterized by the presence of distal Ice Rafted Detritus (IRD). IRD layers can be identified by the rapid increase in magnetic susceptibility values (κ) up to 400x10-6SI, from background values lower than 100x10-6 SI providing key information on climatically forced events and allowing a tighter chronostratigraphic control. However, the mixing of these materials with local/regional components may difficult their depiction, and also the occurrence of diagenetic processes that alter their original magnetic composition, to the point of under detection by standard magnetic analysis (susceptibility). The aim of this paper is the environmagnetic and geochemical characterization of these distal IRD occurring in the area and the study of their age and provenance related to the last six HE. In order to achieve these goals we measured their magnetic properties, their chemical and mineralogical composition and performed the analyses of Sr and Nd isotope ratios measured in the detrital fraction of one of the cores. This study explores the potential of magnetic properties as a tool to discriminate Heinrich layers provenance in base to differences in their magnetic mineralogy assemblages

Magnetic properties contribution to the identification and provenance of marine sediments: distal IRD in the Galicia Interior Basin (NW Spain)

This paper discusses the advantages of using a combined environmagnetic and geochemical approach to the provenance and characterization of distal IRDs occurring during the Last Glacial Period in core CI12PC3 from the Galicia Interior Basin (GIB). Six Heinrich layers (HL1-6) have been identified in the area in base to the detection of distinct populations of exotic magnetic mineral assemblages alien to the local/regional sedimentation environment. Their extension has been determined by Ca/Sr and Si/Sr ratios and their provenance by 143Nd/144Nd and 87Sr/86Sr isotopic ratios and FORCs. The sedimentary expression of HL is characterized by the presence of distal Ice Rafted Detritus (IRD). Distal IRD magnetic signatures in the GIB consist of (i) an increase of one order of magnitude in the peak amplitude of magnetic susceptibility from background values, (ii) a general coarsening of the magnetic grain size in a mineral assemblage dominated by titano-magnetites, (iii) FORC distributions pushing towards the coarse MD or PSD component, and (iv) thermomagnetic curves depicting the occurrence of several magnetite phases. These four features are very different from the fine-grained biogenic magnetic assemblages characterized by the combination of lower MS and higher coercivity values that dominate the predominant mixtures of the non-interacting SSD and PSD components in the non-IRD influenced background sedimentation. Our results show that the last 70.000 yr of sedimentation in the GIB were controlled by the relative contribution of local detrital material derived from the Iberian Variscan Chain and IRD alien material from the iceberg melting during the Heinrich Events. They also show two main IRD provenance fields: Europe and Canada. And that the later is more important for for HL1, HL2, HL4 and HL5. FORCs analysis complemented the isotopic information and provided a very unique information, indicating that glacial flour may not always have the same provenance as IRD and that ice-melted derived suspended sediment has its own dynamics and may reach further and/or persists longer than IRD

Sedimentary climatic record in the Galician Internal Basin: sediment provenance, transport time and hydrodynamics over the last 60.000 years

The sediments of the Galician Interior Basin are influenced by the Atlantic Meridional Overturning Circulation (AMOC) and by their proximity to the Western Iberia continental landmass, and thus provide an adequate archive to study the peculiarities of the last glacial‐interglacial dynamics and the transition into present day conditions. The aim of this study has been to analyse the sedimentary expression of climatic processes and forcings derived from the relation between the last North Atlantic glacial cycle and the local regional components -including abrupt climate changes and local events- since the end of the last glacial period in this area. We have attempted to establish the rates and magnitudes of change of this system to understand its climate dynamics, processes and feedbacks, and hence its role on a local to sub‐regional scale from a palaeoclimatic proxies perspective. The inference of these climatic mechanisms encrypted in the deep-sea sedimentary record needs to constrain the spatial and temporal scales of the sedimentary processes involved, in particular the identification of source areas, pathways and transport, storage times and hydrodynamic conditions. In order to achieve these goals we have used a twofold approach; an initial effort to constrain the current sedimentary conditions to their associated local hydrography conditions by means of a mooring, which will be used to later infer the palaeoenvironmental conditions from sediment cores. The location of the mooring and the 5 coring locations has been based on the acquisition of new geophysical data: a precise 20 x 20 m bathymetry covering an area of 9860 km2 and 690 km of high-resolution seismic profiles distributed in 10 transects that allow to investigate the main sedimentary units in the region. The mooring comprised 2 sediment traps located at 500 and 1400 m below the sea surface. These depths are under the influence of the Eastern North Atlantic Central Water (ENACW) and Mediterranean Water (MW). The sediment traps also target sediments from the shelf and the upper slope. Sediments were collected monthly for a 9 month period, whilst hydrographic conditions such as current speed, salinity, oxygen and turbidity were continuously recorded in associated instruments at the same depths. Finally, a multidisciplinary study combining resolution scans, including geochemistry (ITRAX), physical properties (GEOTEK) and enviromagnetic properties (2G cryogenic magnetometer), has been constrained using a very robust geochronology framework. Further analyses comprised grain size distributions, S͞S, SEM, XRD, stable and high-precision radioactive isotopes. The area consists mostly of generally autochthonous hemipelagic and terrigenous muds and sandy to silty muds with high clay content, showing abundant bioturbation and early diagenesis. Allochthonous material of different provenances (characterized by 143Nd/144Nd and 87Sr/ 86Sr isotopic ratios) occurs interbedded within the hemipelagic sediments associated to Heinrich Stadials HS1 to HS6. The sediments also show significant changes in the vigour of bottom-currents (based on the S͞S proxy) both within and between the HS. The combination of these sedimentological, geochemical and geophysical data has provided a new insight into the role of current strength, circulation and sediment provenance changes in the area, and allowed to establish across vs. along margin transport balances in the sedimentary record of the Galician Internal basin over the last 60 Ky

Electronic and Magnetic Properties of Partially-Open Carbon Nanotubes

On the basis of the spin-polarized density functional theory calculations, we demonstrate that partially-open carbon nanotubes (CNTs) observed in recent experiments have rich electronic and magnetic properties which depend on the degree of the opening. A partially-open armchair CNT is converted from a metal to a semiconductor, and then to a spin-polarized semiconductor by increasing the length of the opening on the wall. Spin-polarized states become increasingly more stable than nonmagnetic states as the length of the opening is further increased. In addition, external electric fields or chemical modifications are usable to control the electronic and magnetic properties of the system. We show that half-metallicity may be achieved and the spin current may be controlled by external electric fields or by asymmetric functionalization of the edges of the opening. Our findings suggest that partially-open CNTs may offer unique opportunities for the future development of nanoscale electronics and spintronics.Comment: 6 figures, to appear in J. Am. Chem. So

Southernmost indications of large freshwater discharges during the Heinrich Stadials (Galicia Interior Basin, Northwest Iberian Continental Margin)

The reconstruction of circum-Atlantic ice-sheet instabilities is of great importance to understanding the mechanisms that force abrupt climate changes. We have used enviromagnetic and geochemical data to explore these issues, providing a continuous and well-dated record of the evolution of glacial/interglacial sedimentation in the Galician Interior Basin (GIB) during the last glacial period covering the last six Heinrich Stadials. Our results show sediments of European provenance that have been related to meltwater pre-events during the initial stages of HS1, HS2, and HS4 corroborating the Channel River depositional history. Therefore, this study provides insight into one of the potential forcing mechanisms for Heinrich Events and, by inference, for Heinrich Stadials. The GIB records are an important element in the discussion of EIS–LIS–AMOC dynamics. Their significant distance from these ice-sheets is such that they have only recorded the most catastrophic ice shelves collapse events and/or meltwater discharges, acting as a low-amplitude filter to the interrelated dynamics and instabilities of the North Atlantic ice sheets. Our results demonstrate that European-sourced sediments arrived earlier at this site than Laurentide-sourced icebergs. This implies greater EIS freshwater discharges resulting from the deglacial activation of EIS palaeorivers for HS1 and from glacial instabilities during the course of the EIS’ progression to its LGM position for HS2 and HS4. This supports the idea of synchronous collapse of the EIS and LIS. The data also suggest that these discharges acted as a positive feedback mechanism that further weakened the AMOC, accelerating LIS and EIS collapse

Expression of NES-hTERT in Cancer Cells Delays Cell Cycle Progression and Increases Sensitivity to Genotoxic Stress

Telomerase is a reverse transcriptase associated with cellular immortality through telomere maintenance. This enzyme is activated in 90% of human cancers, and inhibitors of telomerase are currently in clinical trials to counteract tumor growth. Many aspects of telomerase biology have been investigated for therapy, particularly inhibition of the enzyme, but little was done regarding its subcellular shuttling. We have recently shown that mutations in the nuclear export signal of hTERT, the catalytic component of telomerase, led to a mutant (NES-hTERT) that failed to immortalize cells despite nuclear localization and catalytic activity. Expression of NES-hTERT in primary fibroblast resulted in telomere-based premature senescence and mitochondrial dysfunction. Here we show that expression of NES-hTERT in LNCaP, SQ20B and HeLa cells rapidly and significantly decreases their proliferation rate and ability to form colonies in soft agar while not interfering with endogenous telomerase activity. The cancer cells showed increased DNA damage at telomeric and extra-telomeric sites, and became sensitive to ionizing radiation and hydrogen peroxide exposures. Our data show that expression of NES-hTERT efficiently counteracts cancer cell growth in vitro in at least two different ways, and suggest manipulation with the NES of hTERT or its subcellular shuttling as a new strategy for cancer treatment

Nitrogen uptake and internal recycling in Zostera marina exposed to oyster farming: eelgrass potential as a natural biofilter

Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 (+) uptake capacities by pulse labeling with (NH4)-N-15 (+) and plant photosynthesis and respiration. The internal N-15 resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 (+) uptake rate (33.1 mmol NH4 (+) m(-2) day(-1)) relative to those not exposed to oyster cultures (25.6 mmol NH4 (+) m(-2) day(-1)). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 (+) excreted by oysters (similar to 5.2 x 10(6) mmol NH4 (+) day(-1)). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 (+) produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal N-15 into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 (+) uptake and less negative delta C-13 values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients

Activation of Type 1 Cannabinoid Receptor (CB1R) promotes neurogenesis in murine subventricular zone cell cultures

The endocannabinoid system has been implicated in the modulation of adult neurogenesis. Here, we describe the effect of type 1 cannabinoid receptor (CB1R) activation on self-renewal, proliferation and neuronal differentiation in mouse neonatal subventricular zone (SVZ) stem/progenitor cell cultures. Expression of CB1R was detected in SVZ-derived immature cells (Nestin-positive), neurons and astrocytes. Stimulation of the CB1R by (R)-(+)-Methanandamide (R-m-AEA) increased self-renewal of SVZ cells, as assessed by counting the number of secondary neurospheres and the number of Sox2+/+ cell pairs, an effect blocked by Notch pathway inhibition. Moreover, R-m-AEA treatment for 48 h, increased proliferation as assessed by BrdU incorporation assay, an effect mediated by activation of MAPK-ERK and AKT pathways. Surprisingly, stimulation of CB1R by R-m-AEA also promoted neuronal differentiation (without affecting glial differentiation), at 7 days, as shown by counting the number of NeuN-positive neurons in the cultures. Moreover, by monitoring intracellular calcium concentrations ([Ca2+](i)) in single cells following KCl and histamine stimuli, a method that allows the functional evaluation of neuronal differentiation, we observed an increase in neuronal-like cells. This proneurogenic effect was blocked when SVZ cells were co-incubated with R-m-AEA and the CB1R antagonist AM 251, for 7 days, thus indicating that this effect involves CB1R activation. In accordance with an effect on neuronal differentiation and maturation, R-m-AEA also increased neurite growth, as evaluated by quantifying and measuring the number of MAP2-positive processes. Taken together, these results demonstrate that CB1R activation induces proliferation, self-renewal and neuronal differentiation from mouse neonatal SVZ cell cultures.Fundacao para a Ciencia e a Tecnologia - Portugal [POCTI/SAU-NEU/68465/2006, PTDC/SAU-NEU/104415/2008, PTDC/SAU-NEU/101783/2008, POCTI/SAU-NEU/110838/2009]; Fundacao Calouste Gulbenkian [96542]; Fundacao para a Ciencia e Tecnologiainfo:eu-repo/semantics/publishedVersio