Oxygen Isotopes Unravel the Role of Microorganisms in Phosphate Cycling in Soils

2012 ◽  
Vol 46 (11) ◽  
pp. 5956-5962 ◽  
Author(s):  
Federica Tamburini ◽  
Verena Pfahler ◽  
Else K. Bünemann ◽  
Kathi Guelland ◽  
Stefano M. Bernasconi ◽  
...  
Keyword(s):  
Oxygen Isotopes

scholarly journals Cumulated insolation: a simple explanation of Milankovitch's forcing on climate changes

2013 ◽  
Vol 9 (5) ◽  
pp. 5553-5568 ◽  
Author(s):  
F. Marra
Keyword(s):  
Northern Hemisphere ◽  
Oxygen Isotopes ◽  
Climate Changes ◽  
Ice Sheets ◽  
Simple Explanation ◽  
Glacial Cycle ◽  
Conditioning Factor ◽  
Summer Insolation ◽  
Satisfactory Answer

Abstract. The occurrence of the sudden melting of the ice sheets during the glacial terminations is explained in this paper as the consequence of the combined role of the minima and the maxima of mean summer insolation on the Northern Hemisphere, providing a new contribution to understand the mechanisms ruling glacial forcing. Indeed, no satisfactory answer has been provided so far to the question why one specific maximum, after a series of consecutive maxima of insolation, has the potentiality to trigger a deglaciation. The explanation proposed in this paper accounts for a pre-conditioning factor, represented by "mild" (warmer) minimum, followed by a sufficiently warm maximum as the conditions that cause the end of a glacial cycle. These conditions are realized whenever the sum of the values of each consecutive minima and maxima ("cumulated insolation") on the curve of mean summer insolation at 65° N exceeds 742 Watt m−2. The comparison of the succession of these cumulated insolation values with the astronomically tuned Oxygen isotopes record provides a satisfactory match with the occurrence of all the glacial terminations in the last 800 ka.

The role of contamination in the tightrope of Gran Canaria felsic magma differentiation

2020 ◽  
Author(s):  
Edgar Alejandro Cortes Calderon ◽  
Ben Ellis ◽  
Julia Neukampf ◽  
Chris Harris ◽  
Darren Mark ◽  
...  
Keyword(s):  
Oxygen Isotopes ◽  
Major And Trace Elements ◽  
Crustal Assimilation ◽  
Gran Canaria ◽  
Liquid Line ◽  
Ar Geochronology ◽  
Liquid Line Of Descent ◽  
Differentiation Trend ◽  
Alkali Feldspars

<p>Peralkaline magmatism is mostly sustained by extensive feldspar fractionation from mafic parents at shallow depths in intraplate settings. In this case, silica saturation is critical as it controls the differentiation trend that a peralkaline magma follows. SiO<sub>2</sub>-oversaturated parents fractionate towards rhyolites, and SiO<sub>2</sub>-undersaturated towards phonolitic compositions. The Miocene post-shield stage of Gran Canaria records both differentiation trends, which has previously been ascribed to changes in the mantle source. Such stage has been divided in the Mogan and Fataga Group based on silica saturation. Here, we propose that contamination plays a key role in the differentiation of Gran Canaria volcanics. This assumption is supported with new <sup>40</sup>Ar/<sup>39</sup>Ar geochronology, mineral, glass and juvenile clast chemistry (oxygen isotopes, major and trace elements) merged with a detailed stratigraphy. Two types of contaminants were identified, one being cogenetic feldspar-dominated cumulates and the second one being sediments within the island crust. We propose that barium-rich trachytic magmas with positive europium anomalies are linked to melting of the feldspar cumulates left after extensive fractional crystallisation. The chemistry of such trachytes does not follow a liquid line of descent and contains reverse-zoned alkali-feldspars. The shift in silica saturation took less than 1 Ma and is marked by an increase in peralkalinity from 0.9 to 1.5 and a decrease in oxygen isotopes ratio from 7.0 to 5.0 ‰. We interpret these observations as the consequence of maturation of the shallow magma reservoir towards less sediment contamination. Such assimilation of sediments is limited thermally, and compositionally because the system should remain alumina deficient. Crustal assimilation in Gran Canaria did not produce voluminous silicic melts by itself but allowed the deviation of the differentiation trend of a more primitive, initially SiO<sub>2</sub>-undersaturated magma. The tightrope of differentiation is represented by the thermal divide between the granite and phonolite minima (i.e. feldspar join in petrogeny’s residua system). Contamination by sediments produces a transient SiO<sub>2</sub>-oversaturated system (Mogan Group). Cogenetic assimilation of cumulates by thermal rejuvenation of the reservoir attracts the magma towards the thermal divide (ubiquitous during the peralkaline stage). Armouring against sediment assimilation through time relaxes the system back to the initial SiO<sub>2</sub>-undersaturated conditions (Fataga Group).</p>

scholarly journals Volatile abundances and oxygen isotopes in basaltic to dacitic lavas on mid-ocean ridges: The role of assimilation at spreading centers

2011 ◽  
Vol 287 (1-2) ◽  
pp. 54-65 ◽  
Author(s):  
V.D. Wanless ◽  
M.R. Perfit ◽  
W.I. Ridley ◽  
P.J. Wallace ◽  
C.B. Grimes ◽  
...  
Keyword(s):  
Oxygen Isotopes ◽  
Ocean Ridges ◽  
Spreading Centers

Increased drought events in southwest China revealed by tree ring oxygen isotopes and potential role of Indian Ocean Dipole

2019 ◽  
Vol 661 ◽  
pp. 645-653 ◽  
Author(s):  
Chenxi Xu ◽  
Wenling An ◽  
S.-Y. Simon Wang ◽  
Liang Yi ◽  
Junyi Ge ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Tree Ring ◽  
Oxygen Isotopes ◽  
Indian Ocean Dipole ◽  
Potential Role ◽  
Southwest China

Role of dactinomycin in the improved survival of children with Wilms' tumor

JAMA ◽  
1966 ◽  
Vol 195 (12) ◽  
pp. 1005-1009 ◽  
Author(s):  
D. J. Fernbach
Keyword(s):  
Wilms Tumor
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