Mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments, which are organic poor. Sapropels occur (quasi-) periodically in sedimentary ...sequences of the last 13.5 million years, and exist both in the eastern and western Mediterranean sub-basins. They have been the subject of extensive study, based on records from both short (conventional) and long (Ocean Drilling Program) sediment cores, and from a wide variety of uplifted marine sediment sequences on the basin margins and islands. Previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep-sea anoxia, enhanced export productivity, or a combination of these effects. However, a wealth of new evidence and insights has emerged during the past 1–2 decades, based on traditional and novel proxy data as well as modelling, which has revealed intriguing new aspects and nuances to the reconstructed conditions. Hence, it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels, which have over the past decade also become a matter of commercial interest in sub-salt hydrocarbon exploration. In this review, we present a context of modern Mediterranean climate and oceanography, followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition. We find that sapropels predominantly formed during (astronomically timed) episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition. There is strong correspondence with times of monsoon intensification, fuelling runoff from North Africa into the Mediterranean Sea, while preconditioning due to sea-level rise, and regional precipitation and runoff may have contributed as well. Within these broad episodes of surface buoyancy gain and resultant decline in deep-water ventilation, specific deposition under dysoxic, anoxic, or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth-dependent patterns/gradients, with distinct temporal variability on (at least) decadal to centennial–millennial timescales. In the final section, we evaluate the implications of different modes of deep-water removal from silled basins, to investigate why sapropels are more frequently and often more intensely developed in the eastern Mediterranean than in the western Mediterranean.
In the present study we applied online transcranial magnetic stimulation (TMS) bursts at 10Hz to the supplementary motor area (SMA) and primary motor cortex to test whether these regions are causally ...involved in mental rotation. Furthermore, in order to investigate what is the specific role played by SMA and primary motor cortex, two mental rotation tasks were used, which included pictures of hands and abstract objects, respectively.
While primary motor cortex stimulation did not affect mental rotation performance, SMA stimulation improved the performance in the task with object stimuli, and only for the pairs of stimuli that had higher angular disparity between each other (i.e., 100° and 150°).
The finding that the effect of SMA stimulation was modulated by the amount of spatial orientation information indicates that SMA is causally involved in the very act of mental rotation. More specifically, we propose that SMA mediates domain-general sequence processes, likely required to accumulate and integrate information that are, in this context, spatial. The possible physiological mechanisms underlying the facilitation of performance due to SMA stimulation are discussed.
•Online TMS was applied over SMA and M1 during the performance of mental rotation tasks.•TMS of the SMA improves the performance for stimuli with higher angular disparity.•SMA mediates domain-general sequence processes and acts as an accumulator.•M1 does not play a causal role in mental rotation tasks.
Glutamatergic hyperactivity in the nucleus striatum, the main basal ganglia input, has been involved in the progression of Parkinson's disease (PD) and the onset of L-Dopa-induced dyskinesias (LIDs). ...Abnormalities in the spiny projection neurons excitability and firing, and in the overactivity of glutamate transmission found in animal models of PD, pointed to the synaptic dysfunctions as a primary target to counteract alterations before overt neurodegeneration, conferring a key role to striatal glutamatergic transmission in the early phases of the disease. The present paper provides an overview of the evidence that glutamatergic overactivity is a critical mechanism underlying different PD-associated striatal alterations in early and advanced symptomatic stages of the disease. These aberrant changes, under L-Dopa therapy, lead to a more complex synaptopathy that involves other neurotransmitter systems and persistent modifications to generate LIDs. The review discusses the main changes in glutamatergic functions found in PD preclinical models and clinical studies and an update of the current pharmacological strategies to modulate the glutamatergic systems at the pre- and postsynaptic levels will be provided.
•Glutamate-mediated excitatory signals play a key role in the basal ganglia circuitry.•Excessive glutamatergic transmission in the striatum is implicated in the progression of PD and in the emergence of LIDs.•DA levels reduction leads to alterations in firing activity patterns in tPD striatum of experimental models and patients.•Blunting excessive glutamate transmission is a therapeutic strategy to normalize neurotransmitter synaptic levels.
Atmospheric CO2 fluctuations over glacial-interglacial cycles remain a major challenge to our understanding of the carbon cycle and the climate system. Leading hypotheses put forward to explain ...glacial-interglacial atmospheric CO2 variations invoke changes in deep-ocean carbon storage, probably modulated by processes in the Southern Ocean, where much of the deep ocean is ventilated. A central aspect of such models is that, during deglaciations, an isolated glacial deep-ocean carbon reservoir is reconnected with the atmosphere, driving the atmospheric CO2 rise observed in ice-core records. However, direct documentation of changes in surface ocean carbon content and the associated transfer of carbon to the atmosphere during deglaciations has been hindered by the lack of proxy reconstructions that unambiguously reflect the oceanic carbonate system. Radiocarbon activity tracks changes in ocean ventilation, but not in ocean carbon content, whereas proxies that record increased deglacial upwelling do not constrain the proportion of upwelled carbon that is degassed relative to that which is taken up by the biological pump. Here we apply the boron isotope pH proxy in planktic foraminifera to two sediment cores from the sub-Antarctic Atlantic and the eastern equatorial Pacific as a more direct tracer of oceanic CO2 outgassing. We show that surface waters at both locations, which partly derive from deep water upwelled in the Southern Ocean, became a significant source of carbon to the atmosphere during the last deglaciation, when the concentration of atmospheric CO2 was increasing. This oceanic CO2 outgassing supports the view that the ventilation of a deep-ocean carbon reservoir in the Southern Ocean had a key role in the deglacial CO2 rise, although our results allow for the possibility that processes operating in other regions may also have been important for the glacial-interglacial ocean-atmosphere exchange of carbon.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Transport of water and anions (OH super(-), HCO sub(3) super(-), F super(-), Cl super(-), Br super(-), and I super(-)) in a model poly(arylene ether) anion exchange membrane (AEM) with quaternary ...ammonium (QA) functional groups is studied for water volume fractions of Phi sub(water)=5-99.9% Phi water=5-99.9%. At elevated water content, OH super(-) conductivity recorded under CO sub(2) free conditions occurs mainly through structural diffusion, approaching half of the H super(+) conductivities of Nafion. Severe conductivity decrease at low hydration suggests incomplete dissociation of NR sub(4) super(+) OH super(-) and inferior percolation within the aqueous domain of the AEM compared to Nafion. Further conductivity decrease result from CO sub(2) contamination, forming carbonates which are less mobile, less hydrated and also less dissociated from the QA compared to OH super(-) at a given relative humidity (RH). For other anions, conductivity decreases in the order F super(-)>Cl super(-)>Br super(-)>I super(-)F->Cl->Br->I- for a given RH and also for the same hydration number lambda =H sub(2)O/QA. These trends correlate with both decreasing water uptake and degree of dissociation, which is incomplete for some anions even at very high levels of hydration. Consequently, the functional groups in their halide forms display weak electrolyte behavior in contrast to the corresponding salts. Varying degrees of dissociation of different anions are held responsible for distinct variations of the nano-morphology of hydrated membranes.
Ice volume (and hence sea level) and deep-sea temperature are key measures of global climate change. Sea level has been documented using several independent methods over the past 0.5 million years ...(Myr). Older periods, however, lack such independent validation; all existing records are related to deep-sea oxygen isotope (δ(18)O) data that are influenced by processes unrelated to sea level. For deep-sea temperature, only one continuous high-resolution (Mg/Ca-based) record exists, with related sea-level estimates, spanning the past 1.5 Myr. Here we present a novel sea-level reconstruction, with associated estimates of deep-sea temperature, which independently validates the previous 0-1.5 Myr reconstruction and extends it back to 5.3 Myr ago. We find that deep-sea temperature and sea level generally decreased through time, but distinctly out of synchrony, which is remarkable given the importance of ice-albedo feedbacks on the radiative forcing of climate. In particular, we observe a large temporal offset during the onset of Plio-Pleistocene ice ages, between a marked cooling step at 2.73 Myr ago and the first major glaciation at 2.15 Myr ago. Last, we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep-sea temperature.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
: Microalgae have the potential to become a novel source of bioactive molecules, especially for those who might wish to enhance the nutritional and functional quality of foods. Spirulina, one of the ...most popular microalgae, has been described by the World Health Organization as one of the greatest superfoods on earth serving as an example of the potential of microalgae. This review provides background on current and future uses of microalgae in the human diet, lists the most common species of microalgae used to this end, and describes some production methods used in research and industrial production and recovery. The review also discusses some of the difficulties so far encountered such as low productivities and recovery rates, as well as challenges in the production of compounds of interest. Many scientists and engineers in research centers around the globe are currently dedicated to solve these problems as the various capabilities of microalgae have caught the attention of the energy, environmental, and agricultural industries, we propose that the food industry should as well evaluate the potential of microalgae as a novel source of “health promoting” compounds.
The Mediterranean basin is sensitive to global sea-level changes and African monsoon variability on orbital timescales. Both of these processes are thought to be important to the deposition of ...organic-rich sediment layers or ‘sapropels’ throughout the eastern Mediterranean, yet their relative influences remain ambiguous. A related issue is that an assumed 3-kyr lag between boreal insolation maxima and sapropel mid-points remains to be tested. Here we present new geochemical and ice-volume-corrected planktonic foraminiferal stable isotope records for sapropels S1 (Holocene), S3, S4, and S5 (Marine Isotope Stage 5) in core LC21 from the southern Aegean Sea. The records have a radiometrically constrained chronology that has already been synchronised with the Red Sea relative sea-level record, and this allows detailed examination of the timing of sapropel deposition relative to insolation, sea-level, and African monsoon changes. We find that sapropel onset was near-synchronous with monsoon run-off into the eastern Mediterranean, but that insolation–sapropel/monsoon phasings were not systematic through the last glacial cycle. These latter phasings instead appear to relate to sea-level changes. We propose that persistent meltwater discharges into the North Atlantic (e.g., at glacial terminations) modified the timing of sapropel deposition by delaying the timing of peak African monsoon run-off. These observations may reconcile apparent model–data offsets with respect to the orbital pacing of the African monsoon. Our observations also imply that the previous assumption of a systematic 3-kyr lag between insolation maxima and sapropel midpoints may lead to overestimated insolation–sapropel phasings. Finally, we surmise that both sea-level rise and monsoon run-off contributed to surface-water buoyancy changes at times of sapropel deposition, and their relative influences differed per sapropel case, depending on their magnitudes. Sea-level rise was clearly important for sapropel S1, whereas monsoon forcing was more important for sapropels S3, S4, and S5.
•Chronological framework for sapropels S1–S5, African monsoon, and sea-level change.•Insolation–monsoon/sapropel phasings not systematic over the last glacial cycle.•Meltwater release at glacial terminations delays monsoon and sapropel onset.•Sea-level rise and monsoon run-off both important for sapropel formation.
Hepatocellular carcinomas (HCCs) are not routinely biopsied, resulting in a lack of tumor materials for molecular profiling. Here we sought to determine whether plasma-derived cell-free DNA (cfDNA) ...captures the genetic alterations of HCC in patients who have not undergone systemic therapy.
Frozen biopsies from the primary tumor and plasma were synchronously collected from 30 prospectively recruited, systemic treatment-naïve HCC patients. Deep sequencing of the DNA from the biopsies, plasma-derived cfDNA and matched germline was carried out using a panel targeting 46 coding and non-coding genes frequently altered in HCCs.
In 26/30 patients, at least one somatic mutation was detected in biopsy and/or cfDNA. Somatic mutations in HCC-associated genes were present in the cfDNA of 63% (19/30) of the patients and could be detected ‘de novo’ without prior knowledge of the mutations present in the biopsy in 27% (8/30) of the patients. Mutational load and the variant allele fraction of the mutations detected in the cfDNA positively correlated with tumor size and Edmondson grade. Crucially, among the seven patients in whom the largest tumor was≥5cm or was associated with metastasis, at least one mutation was detected ‘de novo’ in the cfDNA of 86% (6/7) of the cases. In these patients, cfDNA and tumor DNA captured 87% (80/92) and 95% (87/92) of the mutations, suggesting that cfDNA and tumor DNA captured similar proportions of somatic mutations.
In patients with high disease burden, the use of cfDNA for genetic profiling when biopsy is unavailable may be feasible. Our results support further investigations into the clinical utility of cfDNA in a larger cohort of patients.
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