Sökning: "geokemi"

Visar resultat 6 - 10 av 285 avhandlingar innehållade ordet geokemi.

  1. 6. 231Pa and Th isotopes as tracers of deep water ventilation and scavenging in the Mediterranean Sea

    Författare :Sandra Gdaniec; Per Anerson; Carl-Magnus Mörth; Matthieu Roy-Barman; Helen Coxall; Per Roos; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Protactinium; Thorium; particle transport; deep water circulation; geokemi; Geochemistry;

    Sammanfattning : The naturally occurring isotopes 231Pa and 230Th are used as tracers of marine biogeochemical processes. They are both produced from the radioactive decay of their uniformly distributed uranium parents (235U and 234U) in seawater. LÄS MER

  3. 7. A surface approach to understanding the dissolution of fluorite type materials : Implications for mineral dissolution kinetic models

    Författare :José Ricardo Assunção Godinho; Sandra Piazolo; Andreas Lüttge; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; dissolution; topography; fluorite; surface; geokemi; Geochemistry;

    Sammanfattning : Traditional dissolution models are based in the analyses of bulk solution compositions and ignore the fact that different sites of a surface dissolve at different rates. Consequently, the variation of surface area and surface reactivity during dissolution are not considered for the calculation of the overall dissolution rate, which is expected to remain constant with time. LÄS MER

  4. 8. Ocean chemistry and the evolution of multicellularity

    Författare :Emma U. Hammarlund; Stefan Bengtson; Donald Canfield; Nils Holm; Graham Budd; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Geochemistry; biology; paleontology; evolution; multicellularity; geokemi; Geochemistry;

    Sammanfattning : Oxygen has been assumed to be a vital trigger for the evolution of multicellular life forms on Earth, partly based on its power to promote substantial energy flux in cell respiration and partly as biosynthesis of compounds like collagen require oxygen. However, the co-evolution of large life and the Earth’s chemical environment is not well understood at present, and there is particular disagreement in the field about whether the Cambrian explosion of animal life forms was a chemical or biological event. LÄS MER

  5. 9. Phosphate and Arsenic Cycling under Experimental Early Proterozoic Marine Conditions

    Författare :Christoffer Hemmingsson; Iain Pitcairn; Ernest Chi Fru; Per Andersson; Christophe Dupraz; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; DIP; Early Proterozoic; coprecipitation; adsorption; Iron formations; BIF; geokemi; Geochemistry;

    Sammanfattning : Nutrient dynamics in the Archean-Paleoproterozoic oceans strongly influenced primary productivity and the rise of atmospheric O2. Reconstructing the cycling of key nutrients such as dissolved inorganic phosphate (DIP) at this time is important for our understanding of the timing, rate and extent of atmospheric oxygenation at this time. LÄS MER

  7. 10. Carbon trace gas dynamics in subarctic lakes

    Författare :Joachim Jansen; Patrick Crill; Andreas Lorke; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; lakes; methane; carbon dioxide; fluxes; gas transfer; proxy; climate change; geokemi; Geochemistry;

    Sammanfattning : Northern lakes are important sources of greenhouse gases carbon dioxide and methane to the atmosphere. Emissions are expected to increase as the climate continues to warm. Even so, lake carbon budgets are currently poorly constrained. This is in part because of a limited understanding of the processes that govern the flux. LÄS MER