Modeling the Mutualistic Interactions between Tubeworms and Microbial Consortia

The deep-sea vestimentiferan tubeworm Lamellibrachia luymesi forms large aggregations at hydrocarbon seeps in the Gulf of Mexico that may persist for over 250 y. Here, we present the results of a diagenetic model in which tubeworm aggregation persistence is achieved through augmentation of the supply of sulfate to hydrocarbon seep sediments. In the model, L. luymesi releases the sulfate generated by its internal, chemoautotrophic, sulfide-oxidizing symbionts through posterior root-like extensions of its body. The sulfate fuels sulfate reduction, commonly coupled to anaerobic methane oxidation and hydrocarbon degradation by bacterial–archaeal consortia. If sulfate is released by the tubeworms, sulfide generation mainly by hydrocarbon degradation is sufficient to support moderate-sized aggregations of L. luymesi for hundreds of years. The results of this model expand our concept of the potential benefits derived from complex interspecific relationships, in this case involving members of all three domains of life

System and method of fluid exposure and data acquisition

An apparatus has a data acquisition device, an environmental cell in a spatial registration relative to the data acquisition device, the environmental cell being configured to support a sample, and a fluid management system configured to initiate and discontinue exposure of the sample to a reaction fluid while the spatial registration is maintained. A method of performing data acquisition for a sample includes spatially registering the sample relative to a data acquisition device, at least partially exposing the sample to a reaction fluid while substantially maintaining the spatial registration of the sample relative to the data acquisition device, at least partially discontinuing exposing the sample to the reaction fluid while substantially maintaining the spatial registration of the sample relative to the data acquisition device, and acquiring data about the sample while substantially maintaining the spatial registration of the sample relative to the data acquisition device

The dissolution kinetics of major sedimentary carbonate minerals.

Among the most important set of chemical reactions occurring under near Earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals. These minerals comprise about 20% of Phanerozoic sedimentary rocks. Calcite and, to a significantly lesser extent, dolomite are the major carbonate minerals in sedimentary rocks. In modern sediments, aragonite and high-magnesian calcites dominate in shallow water environments. However, calcite is by far the most abundant carbonate mineral in deep sea sediments. An understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel CO2 on climate, diagenesis of sediments and sedimentary rocks. It also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs, and the preservation of buildings and monuments constructed from limestone and marble. In this paper, we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century. Our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions. We will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments. Such complex topics are clearly worthy of review papers on their own merits. Calcite has been by far the most studied mineral over a wide range of conditions and solution compositions. In recent years, there has been a substantial shift in emphasis from measuring changes in solution composition, to determine “batch” reaction rates, to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy (AFM). However, there remain major challenges in integrating these two very different approaches. A general theory of surfac

Dissolution rate spectra data of calcite single crystal and micrite material

The large discrepancy between field and laboratory measurements of mineral reaction rates is a long-standing problem in earth sciences, often attributed to factors extrinsic to the mineral itself. Nevertheless, differences in reaction rate are also observed within laboratory measurements, raising the possibility of intrinsic variations as well. Critical insight is available from analysis of the relationship between the reaction rate and its distribution over the mineral surface. This analysis recognizes the fundamental variance of the rate. The resulting anisotropic rate distributions are completely obscured by the common practice of surface area normalization. In a simple experiment using a single crystal and its polycrystalline counterpart, we demonstrate the sensitivity of dissolution rate to grain size, results that undermine the use of "classical" rate constants. Comparison of selected published crystal surface step retreat velocities (Jordan and Rammensee, 1998) as well as large single crystal dissolution data (Busenberg and Plummer, 1986) provide further evidence of this fundamental variability. Our key finding highlights the unsubstantiated use of a single-valued "mean" rate or rate constant as a function of environmental conditions. Reactivity predictions and long-term reservoir stability calculations based on laboratory measurements are thus not directly applicable to natural settings without a probabilistic approach. Such a probabilistic approach must incorporate both the variation of surface energy as a general range (intrinsic variation) as well as constraints to this variation owing to the heterogeneity of complex material (e.g., density of domain borders). We suggest the introduction of surface energy spectra (or the resulting rate spectra) containing information about the probability of existing rate ranges and the critical modes of surface energy

Temporal Evolution of Calcite Surface Dissolution Kinetics

This brief paper presents a rare dataset: a set of quantitative, topographic measurements of a dissolving calcite crystal over a relatively large and fixed field of view (~400 μm2) and long total reaction time (>6 h). Using a vertical scanning interferometer and patented fluid flow cell, surface height maps of a dissolving calcite crystal were produced by periodically and repetitively removing reactant fluid, rapidly acquiring a height dataset, and returning the sample to a wetted, reacting state. These reaction-measurement cycles were accomplished without changing the crystal surface position relative to the instrument’s optic axis, with an approximate frequency of one data acquisition per six minutes’ reaction (~10/h). In the standard fashion, computed differences in surface height over time yield a detailed velocity map of the retreating surface as a function of time. This dataset thus constitutes a near-continuous record of reaction, and can be used to both understand the relationship between changes in the overall dissolution rate of the surface and the morphology of the surface itself, particularly the relationship of (a) large, persistent features (e.g., etch pits related to screw dislocations; (b) small, short-lived features (e.g., so-called pancake pits probably related to point defects); (c) complex features that reflect organization on a large scale over a long period of time (i.e., coalescent “super” steps), to surface normal retreat and step wave formation. Although roughly similar in frequency of observation to an in situ atomic force microscopy (AFM) fluid cell, this vertical scanning interferometry (VSI) method reveals details of the interaction of surface features over a significantly larger scale, yielding insight into the role of various components in terms of their contribution to the cumulative dissolution rate as a function of space and time

Advances in dissolution understanding and their implications for cement hydration

Recent advances in bridging kinetics and thermodynamics of mineral dissolution have opened new horizons in our understanding of the role of dissolution in cement hydration. Indeed most hydration kinetic regimes of alite can be rationally envisioned from a dissolution perspective. This short note reviews some key findings on dissolution mechanisms and their implication for cementitious systems