92,575 research outputs found
The last deglaciation in Italy: timing and pattern from a precisely dated stalagmite
No full textThe last deglaciation (Termination I, T-I) was the most recent global-scale climate transition. It involved a drastic temperature increase guiding massive melting of ice sheets, with a concurrent reorganization of inter- and intrahemispherical atmospheric and ocean circulation patterns.
T-I lasted ~3.0 ka (ka = kiloyears before present) in Greenland (NGRIP, 2007), although it was not a linear process. A rapid temperature increase at 14.6±0.3 ka (Bølling-Allerød, BA) was followed by a return towards glacial-like conditions (12.2±0.3 ka, Younger Dryas, YD), before the last warming that led to the Holocene (11.7±0.1 ka). Other secondary climate oscillations characterized T-I too (Cheng et al., 2020). Some of these intra-deglaciation global warmings were particularly rapid, at times occurring at centennial or even decadal timescale. This provides an interesting comparison with the current climate change.
Yet, it is not clear how T-I-related dynamics occurring at the polar regions and/or in the oceans impacted terrestrial environment at mid latitudes, in terms of rainfall and temperature variation and related environmental and ecological changes. This is especially true for the Mediterranean area, considering that its climate is connected – and controlled – by processes occurring in the Atlantic and Arctic. In Italy, T-I records of adequate chronological resolution are virtually absent.
We here present a novel speleothem record from Sant’Angelo Cave (SA1, Ostuni, Apulia) spanning from 47.7±0.1 to 8.9±0.9 ka. In the period from ~20 to ~10 ka, multiple U-Th datings (n=22) resulted in a final age model with an average uncertainty of <0.3 ka and a resolution of ~25 years. Climate proxies (δ18O, n=1045) were anchored to this chronology. The reliability of SA1-δ18O in recording palaeoclimate information was ascertained by a statistically grounded inter-cave replication test with a recently published speleothem record from a nearby site (Columbu et al., 2020). The interpretation of SA1 allows to: 1) accurately and precisely constrain, for the first time in Italy, the timing of the T-I climate pattern; 2) evaluate the impact of BA, YD and Holocene inception in southern Italy, as well as other associated events, especially in terms of rainfall variability; and 3) understand the spatio-temporal relation between the Atlantic/Greenland domain, the Mediterranean realm and monsoonal areas throughout the deglaciation. We discuss this new record within the framework of previous regional studies based on glacial (NGRIP, 2007), marine (Martrat et al., 2007) and continental proxies (Allen et al., 1999; Cheng et al., 2016), with the aim of providing a better comprehension of the timing and structure of T-I in Italy and, by extension, of the central and western Mediterranean area.
Allen J.R.M., Brandt U., Brauer A., Hubbertens H.W., Huntley B., Keller J., Kraml M., Meckeen A., Mingram J., Negendank J.F.W., Nowaczyk N.R., Oberhansli H., Watts W.A., Wulf S. & Zolitschka B. (1999) - Rapid environmental changes in southern Europe during the last glacial period. Science, 400, 740-743.
Cheng H., Edwards R.L., Sinha A., Spötl C., Yi L., Chen S., Kelly M., Kathayat G., Wang X. & Li X. (2016) - The Asian monsoon over the past 640,000 years and ice age terminations. Nature, 534, 640.
Cheng H., Zhang H., Spötl C., Baker J., et al. (2020) - Timing and structure of the Younger Dryas event and its underlying climate dynamics. Proceedings of the National Academy of Sciences, 117, 23408-23417.
Columbu A., Chiarini V., Spötl C., Benazzi S., Hellstrom J., Cheng H. & De Waele J. (2020) - Speleothem record attests to stable environmental conditions during Neanderthal-Modern Human turnover in Southern Italy. Nature Ecology & Evolution, 4, 1188-1195.
Martrat B., Grimalt J.O., Shackleton N.J., de Abreu L., Hutterli M.A. & Stocker T.F. (2007) - Four climate cycles of recurring deep and surface water destabilizations on the Iberian margin. Science, 317, 502-507.
NGRIP, North Greenland Ice Core Project Members. (2004) - High-resolution record of Northern Hemisphere climate extending into the last interglacial period. Nature, 431, 147-151
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Transformation of the endostyle of the anadromous sea lamprey, Petromyzon-marinus L, during metamorphosis .2. Electron-microscopy
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Determining Shear Wave Velocities in Soft Marine Sediments
Full text linkThe inversion technique presented in this volume (Cheng, 1987) that simultaneously
inverts full waveform acoustic logs for shear wave velocity (V[subscript 3]) and compressional wave attenuation (Q[subscript p]) was applied to selected full waveform acoustic logs taken in soft sediments from Deep Sea Drilling Project Site 613.
Besides V[subscript 3] and Q[subscript p], the sensitivity of the inversion to perturbations in the fixed parameters, P-wave velocity (V[subscript p]), fluid velocity (V[[subscript f]), borehole diameter, bulk density (P[subscript b]), and borehole fluid attenuation (Q[subscript f]), were tested. Our study shows that the inversion technique is most sensitive to the estimate of V[subscript p] because the inversion is based
on the P leaky mode energy portion of the spectrum. The Poisson's ratio, however,
which primarily controls the amplitude of the waveforms, is rather stable with different
estimates in V[subscript p]. The inversion technique is less sensitive to small perturbations in borehole diameter, P[subscript b], V[subscript f], and Q[subscript f]
The shear wave velocities inferred from these inversions correlate well with the attendant velocity logs run at Site 613 and the diagenetic changes identified by shipboard stratigraphers. For example, there is an increase in both V[subscript p] and V[subscript 3] at the diagenetic boundary between siliceous nannofossil oozes and porcellanite. This boundary is responsible for a sharp seismic reflector in a USGS. seismic line run nearby. Over the depth interval that we analyzed, from 390.0 to 582.0 meters below sea floor, we determined shear wave velocities ranging from 0.74 to 1.06 km/sec corresponding to compressional wave velocities from 1.70 to 2.20 km/sec.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumNational Science Foundation (U.S.) (Grant OCE84-08761)Chevron (Fellowship
Vapor-liquid equilibrium of carbon dioxide with ethyl caproate, ethyl caprylate and ethyl caprate at elevated pressures
No full textInduction of changes in morphology, reactive nitrogen/oxygen intermediates and apoptosis of duck macrophages by aflatoxin B1
No full textSearch for h(c) -> pi(+)pi(-) J/psi via psi(3686) -> pi(0)pi(+)pi(-) J/psi
No full textUsing a data sample of 448.1 x 10(6) psi(3686) events collected with the BESIII detector operating at the BEPCII, we perform search for the hadronic transition h(c)-> pi(+)pi(-) J/psi via psi (3686) -> pi(0)hc. No signals of the transition are observed, and the upper limit on the product branching fraction B(sigma(3686) -> pi(0)h(c))B(h(c) -> pi(+)pi(-) J/psi) at the 90% confidence level (C. L.) is determined to be 2.0 x 10(-6). This is the most stringent upper limit to date
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