The accurate and precise determination of element concentrations and isotope ratios by mass spectrometry relies on the ability of a geochemist to quantitatively separate target elements, or analytes, from sample matrices. Column chromatography provides a robust and user-friendly method to achieve this for a wide range of elements. The technique utilizes a ‘stationary phase’ of organic resin that shows variable affinities for the elements being studied. In this contribution, we discuss the structure and operation of the two most commonly-used types of resin, namely the traditional cation and anion exchange resins and newer extraction chromatographic materials, such as DGA and LN-spec resin. We then explore their applications to a broad spectrum of elements and sample types. In addition, we present new distribution coefficients for 38 elements utilizing nitric acid solutions with strong cation exchange resin.
Organic matter stores and transfers carbon across the ocean's surface, interior, and sediments, and these processes play a major role in regulating atmospheric CO2 concentrations and governing ecosystem dynamics. Understanding the composition of this carbon is ultimately necessary to determine its sources, transformations, removal, and ecological impacts. This chapter summarizes our current understanding of how the composition (molecular and isotopic) of organic matter relates to its inventory, transformations, and fluxes throughout the ocean as well as the role of organic matter in linking marine ecology, carbon, nutrient, and metal cycling. The present estimates of the inventory of major carbon reservoirs are first discussed along with the major fluxes within and between reservoirs. We then discuss the state of understanding regarding the composition of organic matter, including forms of organic carbon as well as the incorporation of other elements such as nitrogen, phosphorus, sulfur, metals, and halogens which act as important organo-nutrient reservoirs. We present the readers with intriguing new biogeochemical mechanisms that have important implications for organic matter composition and recycling. Finally, we conclude by discussing the predicted changes of organic matter in response to global climate change.
Magma associated mineral deposits are our most important sources of most metals, including most of those considered critical to the global transition to a renewable energy future. This chapter shows that ore deposit formation is ultimately linked to deep Earth tectonic recycling of elements and oxidation state through a range of igneous processes. Through changes in the atmosphere and thus oceans, oceanic crust and deep Earth, the biosphere and Earth co-evolved from being reduced in the Archean to being oxidized in the Phanerozoic, and this appears to be reflected in changes in magma associated ore deposit genesis over time.
Mass extinctions, abrupt losses of many taxonomic groups, are important ecological and evolutionary events typically driven by multiple environmental stressors. There is no consistent pattern of environmental stressors across all events, but many of the traditional five mass extinctions included rapid temperature change, expansion of anoxic and/or euxinic waters, and/or ocean acidification. Important geochemical proxies for temperature include oxygen isotopes (δ18O), clumped isotopes (Δ47), Mg/Ca ratio of carbonates, and the TEX86 index. Anoxia does not have to be ubiquitous to contribute to an extinction, so proxies for the global extent of low-oxygen waters are best, including uranium (δ238U) or molybdenum (δ98Mo) isotope ratios. Paleo-pH and ocean acidification are the most challenging, but have been evaluated with calcium (δ44/40Ca) and boron (δ11B) isotopes. The general picture is understood for most extinctions, but more records and broader geographic coverage would refine the reconstructions. Improving quantitative measures of the magnitude and rate of environmental change are crucial challenges for developing predictions of how environmental perturbations lead to taxonomic losses and extinction selectivity.
The field of marine metal stable isotope geochemistry has expanded dramatically since the last edition of the Treatise on Geochemistry. This chapter examines the marine stable isotope cycling of nine transition metals: V, Cr, Fe, Ni, Cu, Zn, Mo, Cd and W. Classifying the metals according to their oceanic residence time and degree of internal cycling enables comparison between systems and, in each case, to draw out the importance of one or more key controlling processes. Isotopic variability internal to the ocean is driven by a range of biogeochemical processes and their interaction with the physical ocean circulation. Mean whole ocean isotopic compositions are controlled by the isotopic composition of oceanic sources and fractionation into sedimentary sinks. The isotopic oceanic mass balance of each metal is reviewed and, in some cases, updated, providing revised estimates of their oceanic residence times.
Freshwater organic matter acts as a key link between the landscape and the eventual fate of organic carbon in the modern carbon cycle, i.e., remineralization to CO2 or burial in sediments. As freshwater organic matter includes both organic matter fixed in situ and soil and land-plant-derived material, it encompasses a wide range of elemental stoichiometries and molecular formulas (intrinsic variables in terms of organic matter reactivity). The various freshwater systems themselves provide a wide range of environmental (or extrinsic) variables. The combined variations in extrinsic and intrinsic variables influence the reactivity of freshwater organic matter, ultimately driving the balance between organic matter remineralization and organic carbon burial.
Critical Zone processes can mobilize metals from bedrock, or pre-existing ore bodies, to form regolith-hosted (laterites) and supergene deposits of copper, nickel, cobalt, rare earth elements and niobium. Other critical elements such as the platinum group elements and scandium are also an exploration target. Many deposits form under particular climatic and geomorphic conditions in the Cenozoic from coupled physical-chemical-biological processes, however, older examples can be preserved in the rock record. This chapter focusses on economic ore deposits that are formed in the Critical Zone, and specifically, two distinct types of deposits that originate from contrasting parent rocks in diverse tectonic, climatic, biological, and hydrological environments: laterite (Ni, Co, REE, Nb) and supergene (Cu) deposits. We present an overview on a suite of currently economic laterite deposits worldwide, and then we focus on supergene Cu deposits in the Andean Cordillera of South America as a key locality to understand supergene Cu upgrading. These systems exemplify two endmembers that illustrate the range of processes that can lead to metal enrichment in the Earth's surface, and offer the opportunity to assess the nature of element cycles and the effects of changing climate on interactions in the Critical Zone.
