Enhanced Mediterranean water cycle explains increased humidity during MIS 3 in North Africa

We report a new fluid inclusion dataset from northeastern Libyan speleothem SC-06-01, which is the largest speleothem fluid inclusion dataset for North Africa to date. The stalagmite was sampled in Susah Cave, a low-altitude coastal site, in Cyrenaica, on the northern slope of the Jebel Al-Akhdar. Speleothem fluid inclusions from the latest Marine Isotope Stage (MIS) 4 and throughout MIS 3 (∼67 to ∼30 kyr BP) confirm the hypothesis that past humid periods in this region reflect westerly rainfall advected through the Atlantic storm track. However, most of this moisture was sourced from the western Mediterranean, with little direct admixture of water evaporated from the Atlantic. Moreover, we identify a second moisture source likely associated with enhanced convective rainfall within the eastern Mediterranean. The relative importance of the western and eastern moisture sources seems to differ between the humid phases recorded in SC-06-01. During humid phases forced by precession, fluid inclusions record compositions consistent with both sources, but the 52.5–50.5 kyr interval forced by obliquity reveals only a western source. This is a key result, showing that although the amount of atmospheric moisture advections changes, the structure of the atmospheric circulation over the Mediterranean does not fundamentally change during orbital cycles. Consequently, an arid belt must have been retained between the Intertropical Convergence Zone and the midlatitude winter storm corridor during MIS 3 pluvials

Gross nitrogen transformation rates do not support previously described BNI capacities of selected Brachiaria genotypes

Nitrification is one of the key processes leading to water contamination and greenhouse gas emissions (N2O) in pasture systems. As vast areas of tropical pastures are nitrogen (N) limited, grasses from the Brachiaria genus have adapted to reduce N losses and increase N use efficiency by releasing substances capable of biological nitrification inhibition (BNI) in the rhizosphere. Although the release of BNI compounds and its impact on N2O emissions and net nitrification rates in soil have been studied, the impact of BNI on gross nitrogen transformation rates has not been addressed, despite its relevance to mechanistic understanding of this phenomena

Cryogenic cave carbonates from the Ural Mountains (Russia)

Coarsely crystalline cryogenic cave carbonates (CCCcoarse) are widely used indicators of past permafrost conditions. Nevertheless, details of their formation with respect to macroscopic morphology, stable isotope evolution and potential metastable precursor phases are poorly understood. CCCcoarse were found in 5 caves located along a north-south transect of the Ural Mountains, Russia. A comprehensive data set was generated including results of carbonate stable isotope composition, stable isotopic composition of fluid inclusion water, stable oxygen isotope thermometry, trace element composition, X-ray diffraction and transmission properties and U/Th disequilibrium dating. Detailed petrographic characterization of the samples allows for the proposal of a morphological classification scheme for CCCcoarse. Non-crystallographic branching of crystallites, also referred to as crystal splitting, is identified as the mechanism enabling morphological variety in CCCcoarse. Splitting propensity is likely related to physico-chemical properties of the mineral forming solution such as Mg++ concentration and supersaturation with respect to carbonate minerals. Numerical modelling of C and O stable isotope evolution shows that open system style degassing of CO2 during CCCcoarse formation accounts for 10 20% of the observed isotopic trends. These results support a model of slow and continuous degassing of CO2 via nucleation of gas bubbles in co-precipitating ice in compliance to freezing experiments. Fluid inclusion analyses suggest that early stages of CCCcoarse formation take place at isotopic equilibrium between carbonate minerals and the parent solution. However, oxygen isotope fractionation (()18=1.0318 0.0005) appears to be smaller than expected from literature values extrapolated to 0C. Diffraction properties of a CCCcoarse specimen indicate that it formed via non-classical crystallisation pathways. Crystallisation by particle attachment (CPA) of poorly crystalline, or even amorphous precursor phases can explain diffraction data.Töchterle, Paul, BScUniversität Innsbruck, Masterarbeit, 2018(VLID)253269

Fluid inclusion oxygen and hydrogen stable isotopes in a speleothem from Susah Cave, Libya

Fluid inclusion isotopes for a speleothem from Liby

Gross nitrogen transformations in tropical pasture soils as affected by Urochloa genotypes differing in biological nitrification inhibition (BNI) capacity

This is a post-print, peer-reviewed version of an article published in Soil Biology and Biochemistry. The final authenticated version is available online at: https://doi.org/10.1016/j.soilbio.2020.10805

Cave discoveries and speleogenetic features in northeast Greenland

Solution caves situated in the Centrumsø region of northeast Greenland (80°N) were first documented in 1960. Since then, there have been three dedicated caving expeditions to the area that have increased the numbers of cave observations and discoveries substantially. Here, the larger caves, as documented by the Greenland Caves Project during 2015 and 2019, are presented, including surveys and summaries of their key features. Additionally, smaller caves and potential leads, as documented during 2019, are also presented