Frequency and spatial selectivity in nuclear magnetic resonance spectroscopy

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Early Maastrichtian stable isotopes: Changing deep water sources in the North Atlantic?

We propose that the observed short-term stable isotope fluctuations reflect changes in high- and low-latitude intermediate to deep water sources, based on a high-resolution stable isotope record of planktic and benthic foraminifera from the Early Maastrichtian (71.3 to 69.6 Ma) of Blake Nose (DSDP Site 390A, North Atlantic). Sources of these waters may have been the low-latitude eastern Tethys and high-latitude North Atlantic. Changes in intermediate to deep water sources were probably steered by eccentricity-controlled insolation fluctuations. Lower insolation favored the formation of high-latitude deep waters due to positive feedback mechanisms resulting in high-latitude cooling. This led to a displacement of low-latitude deep waters at Blake Nose. Higher insolation reduced intermediate to deep-water formation in high latitudes, yielding a more northern flow of low-latitude deep waters. <br/

Short-term environmental changes in the Cretaceous Tethyan Ocean: micropaleontological evidence from the Early Albian Oceanic Anoxic Event 1b

To better understand the linkage between climate and ocean circulation under greenhouse conditions we have studied calcareous nannofossils, palynomorphs and benthic foraminifera from the Early Albian Oceanic Anoxic Event 1b black shale (OAE 1b) in the Vocontian Basin (SE France). We propose that monsoonal activity resulting from precessional forcing and modulated by eccentricity-driven temperature changes represents the driving factor of OAE 1b formation in low latitudes. With the onset of OAE 1b, increasingly warm and humid conditions, stronger winds and enhanced terrestrial input led to higher surface water productivity. Therefore, increased productivity is an important factor for OAE 1b formation in the Vocontian Basin. However, monsoonally forced productivity changes are a regional climate signal only. The supraregional occurrence of the OAE 1b is probably due to a reduction of deep water formation in the low latitudes under extremely warm and humid conditions, leading to enhanced preservation of organic matter.<br/

High-resolution carbon isotope records of the Aptian to Lower Albian from SE France and the Mazagan Plateau (DSDP Site 545): a stratigraphic tool for paleoceanographic and paleobiologic reconstruction

High-resolution carbon isotope stratigraphy is established for the Aptian to Lower Albian of the Vocontian Basin (SE France), and correlated to the carbon isotope record of the Mazagan Plateau (DSDP Site 545). The carbon isotope stratigraphy of the Vocontian Basin is proposed as a standard reference curve for the Aptian to Lower Albian, due to the completeness and high temporal resolution of the stratigraphic succession, the good biostratigraphical time control, and the frequent occurrence of regional to global black shale horizons including Oceanic Anoxic Events 1a (OAE 1a) of the Lower Aptian and OAE 1b of the Lower Albian. The carbon isotope record appears better suited for long-distance short-term correlation of different marine and terrestrial environments than biostratigraphy because of the synchroneity of carbon isotope signals in a range of sediment types. However, the combination of both biostratigraphy and carbon isotope stratigraphy provides an effective tool to reconstruct biotic change and paleoceanography, and to correlate regional to global black shale horizons in different marine environments. This combined approach allows us to ascertain the synchroneities or diachroneities of first and last appearances of biostratigraphic marker species. Based on the demonstrated diachroneity of important biostratigraphic markers of the Aptian/Albian boundary, the globally observed break point between the end of the uppermost Aptian positive carbon isotope excursion and the onset of the pronounced negative shift of 13C values, is an alternative criterion. The distinctive structure and amplitudes of the carbon isotope record are observed in both the inorganic and organic carbon and can therefore be recognized in all marine and terrestrial environments of the Aptian to Lower Albian

Forcing mechanisms for mid-Cretaceous black shale formation: evidence from the Upper Aptian and Lower Albian of the Vocontian Basin (SE France)

Calcareous nannoplankton, palynomorph, benthic foraminifera, and oxygen isotope records from the supraregionally distributed Niveau Paquier (Early Albian age, Oceanic Anoxic Event 1b) and regionally distributed Niveau Kilian (Late Aptian age) black shales in the Vocontian Basin (SE France) exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid-Cretaceous low latitudes. To quantify surface water productivity and temperature changes, nutrient and temperature indices based on calcareous nannofossils were developed. The nutrient index strongly varies in the precessional band, whereas variations of the temperature index reflect eccentricity. Since polar ice caps were not present during the mid-Cretaceous, these variations probably result from feedback mechanisms within a monsoonal climate system of the mid-Cretaceous low latitudes involving warm/humid and cool/dry cycles. A model is proposed that explains the formation of mid-Cretaceous black shales through monsoonally driven changes in temperature and evaporation/precipitation patterns. The Lower Albian Niveau Paquier, which has a supraregional distribution, formed under extremely warm and humid conditions when monsoonal intensity was strongest. Bottom water ventilation in the Vocontian Basin was diminished, probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes. Surface water productivity in the Vocontian Basin was controlled by the strength of monsoonal winds. The Upper Aptian Niveau Kilian, which has a regional distribution only, formed under a less warm and humid climate than the Niveau Paquier. Low-latitude deep water formation was reduced to a lesser extent and/or on regional scale only. The threshold for the formation of a supraregional black shale was not reached. The intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale. At least in the Vocontian Basin, the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity. <br/

Causes for the formation of the Late Aptian Niveau Fallot black shales in the Vocontian Basin (SE France): Evidence from planktic and benthic foraminifera and stable isotopes

We present paleoceanographic models for the formation of the marlstone facies and the most prominent black shale intervals of the Late Aptian Niveau Fallot black shale succession from the Vocontian Basin (SE France). In the lower part of the succession, the composition of benthic foraminiferal assemblages of the Niveau Fallot 2? and 2? black shales suggests an enhanced burial of organic matter due to more eutrophic conditions and resulting low oxygen conditions at the seafloor. In the upper part of the succession (including Niveau Fallot 3 and 4), a third-order sea-level fall, indicated by a decrease in the stable carbon isotope values, may have resulted in a reduced water mass exchange between the Vocontian Basin and the western Tethyan Ocean. This may have led to dysoxic conditions at the seafloor of the Vocontian Basin and may have favored the formation of organic-rich sediments as shown by benthic foraminiferal assemblages. Decreased evaporation, however, is proposed as the most important mechanism causing a restriction of deep water formation within the basin which finally led to the formation of the Niveau Fallot 3 and 4 black shales. Based on our investigations, the formation of the Niveau Fallot black shales was caused by different factors, the most prominent ones include sea-level fluctuations, increasing productivity, and changes in precipitation and evaporation rates. Furthermore, Niveau Fallot 3 can probably be correlated with the Thalmann black shale event in California and a dark horizon at the Mazagan Plateau (DSDP Site 545). <br/

Prone ventilation reduces mortality in patients with acute respiratory failure and severe hypoxemia : systematic review and meta-analysis

BACKGROUND: Prone position ventilation for acute hypoxemic respiratory failure (AHRF) improves oxygenation but not survival, except possibly when AHRF is severe. OBJECTIVE: To determine effects of prone versus supine ventilation in AHRF and severe hypoxemia [partial pressure of arterial oxygen (PaO(2))/inspired fraction of oxygen (FiO(2)) or =100 mmHg (RR 1.07, 95% CI 0.93-1.22; p = 0.36; seven trials, N = 1,169). Risk ratios differed significantly between subgroups (interaction p = 0.012). Post hoc analysis demonstrated statistically significant improved mortality in the more hypoxemic subgroup and significant differences between subgroups using a range of PaO(2)/FiO(2) thresholds up to approximately 140 mmHg. Prone ventilation improved oxygenation by 27-39% over the first 3 days of therapy but increased the risks of pressure ulcers (RR 1.29, 95% CI 1.16-1.44), endotracheal tube obstruction (RR 1.58, 95% CI 1.24-2.01), and chest tube dislodgement (RR 3.14, 95% CI 1.02-9.69). There was no statistical between-trial heterogeneity for most clinical outcomes. CONCLUSIONS: Prone ventilation reduces mortality in patients with severe hypoxemia. Given associated risks, this approach should not be routine in all patients with AHRF, but may be considered for severely hypoxemic patients