Bücher der Reihe Elements in Geochemical Tracers in Earth System Science

Uranium isotopes have emerged as a proxy to reconstruct the redox conditions of the Earth's oceans and atmosphere. This Element covers the background, methods, and case studies of this promising tool for understanding Earth's environmental transitions, as rapid development continues to refine the accuracy of interpretations of 238U/235U records.

In the marine environment barium isotope ( 138Ba) variations are driven by barite cycling. This Element examines these variations; evaluates their global, regional, local, and geological controls; and explores how 138Ba can be exploited to constrain the origin of enigmatic sedimentary sulfates and study marine biogeochemistry over Earth's history.

In this Element, we propose a refinement of molybdenum (Mo) geochemistry within aquatic systems, ancient rocks, and modern sediments through molecular geochemistry. Specifically, to intermediate sulfide concentrations governing Mo behavior below the "switch-point" and dominant sequestration pathways in low oxygen conditions.

Magnesium is a major constituent in silicate and carbonate minerals, the hydrosphere and the biosphere. Magnesium is constantly cycled between these reservoirs. This review summarises some of the key motivations, successes and challenges facing the use of magnesium isotopes to construct a budget of seawater magnesium, present and past.

Over million-year timescales, the geologic cycling of carbon controls long-term climate and the oxidation of Earth's surface. Inferences about the carbon cycle can be made from time series of carbon isotopic ratios measured from sedimentary rocks.

Diverse and abundant lipid biomarker assemblages have been reported from a variety of Proterozoic marine environments from the careful analysis of well-preserved rocks and oils. These molecular biosignatures have provided unique insights into the communities and the environmental conditions which characterized the Proterozoic marine biosphere. We summarize some of the major temporal patterns evident in Proterozoic lipid biomarkers found to date, whilst emphasizing the scale of local heterogeneity found within Neoproterozoic oceans from region to region, and their relationship with the evolving ecological, climatic and ocean/atmospheric redox conditions. Short commentaries on a selection of papers published from the last 15 years of biomarker literature are given. The focus here is on key studies, highlighted for further reading, which have helped to better constrain the timing of the ecological expansion of eukaryotes in Proterozoic oceans or which have impacted on our knowledge of the biological sources of Proterozoic biomarkers.

Lithium isotopes are a relatively novel tracer of present and past silicate weathering processes. Given that silicate weathering is the primary long-term method by which CO2 is removed from the atmosphere, Li isotope research is going through an exciting phase. We show the weathering processes that fractionate dissolved and sedimentary Li isotope ratios, focusing on weathering intensity and clay formation. We then discuss the carbonate and silicate archive potential of past seawater I 7Li. These archives have been used to examine Li isotope changes across both short and long timescales. The former can demonstrate the rates at which the climate is stabilised from perturbations via weathering, a fundamental piece of the puzzle of the long-term carbon cycle.