The low-productivity South Pacific Gyre (SPG) is Earth's largest oceanic province. Its sediment accumulates extraordinarily slowly (0.1–1 m per million years). This sediment contains a living community that is characterized by very low biomass and very low metabolic activity. At every depth in cored SPG sediment, mean cell abundances are 3 to 4 orders of magnitude lower than at the same depths in all previously explored subseafloor communities. The net rate of respiration by the subseafloor sedimentary community at each SPG site is 1 to 3 orders of magnitude lower than the rates at previously explored sites. Because of the low respiration rates and the thinness of the sediment, interstitial waters are oxic throughout the sediment column in most of this region. Consequently, the sedimentary community of the SPG is predominantly aerobic, unlike previously explored subseafloor communities. Generation of H ₂ by radiolysis of water is a significant electron-donor source for this community. The per-cell respiration rates of this community are about 2 orders of magnitude higher (in oxidation/reduction equivalents) than in previously explored anaerobic subseafloor communities. Respiration rates and cell concentrations in subseafloor sediment throughout almost half of the world ocean may approach those in SPG sediment.

A high-resolution record of Eocene paleo-temperature variation is preserved within the high southern latitude, marine shelf succession of the La Meseta Formation on Seymour Island, off the NE side of the Antarctic Peninsula. ⁸⁷Sr/⁸⁶Sr ratios of bivalve shell carbonate indicate that the La Meseta Formation spans virtually the entire Eocene, and suggest the presence of an early middle Eocene unconformity. Paleoclimatic and paleoceanographic inferences are based on the stable oxygen and carbon isotope values of two genera of bivalves collected with a high degree of stratigraphic resolution within the formation, and with multiple replicate samples from each horizon. δ¹⁸O data indicate roughly 10 °C of cooling from the early Eocene climatic optimum (~15 °C) through the end of the Eocene (minimum ~5 °C), much of which took place in two comparatively short intervals at ca. 52 and ca. 41 Ma. Many features of the isotope curves generated from this Eocene shelf section are apparent in δ¹⁸O and δ¹³C data from the Southern and global oceans, including warm intervals that likely correspond to the early and middle Eocene climatic optima (EECO and MECO). A rapid middle Eocene shift to much more positive values is the most significant in the section and reflects a drop to universally cooler temperatures in the late middle and late Eocene that might also be associated with a short-lived glacial advance. However, even using a somewhat depleted value for δ¹⁸O of seawater in the Antarctic peninsular region, average Seymour Island shelf-water paleotemperatures did not reach freezing before the end of the Eocene. δ¹³C data similarly reflect the documented middle Eocene surface ocean enrichment followed by more negative values, but depletion is much more pronounced on Seymour Island and persists for the remainder of the Eocene, suggesting a combination of upwelling, metabolic effects, and/or atypical carbon cycling on the shelf in this region. Isotope data capture information about changes in the paleoenvironment that also had consequences for the biota, as published paleontological records document marked change in the nature of terrestrial and marine biota at this time. The fact that middle Eocene cooling and biotic turnover in the Peninsular region correspond well in time to the proposed initial opening of Drake Passage suggests that the formation of gateways, in addition to changes in pCO₂, had significant consequences for the Earth's climate system during the Paleogene.

: Microporosity is recognized as a significant concern in Phanerozoic-age limestone reservoirs throughout the world because its presence can severely complicate hydrocarbon evaluation and production. Numerous studies have documented the occurrence and abundance of micropores, their physical appearance, and diagenetic origins in specific reservoirs, but no published study has been systematic and global in its approach. Presented here is a global assessment of limestone microporosity that is based on scanning electron microscope, crystal size distributions, helium porosimetry, and mercury-injection capillary-pressure data collected from 12 microporous limestone reservoirs spanning a broad range of geologic ages, depositional facies, and burial depths. Results indicate that the vast majority of limestone microporosity is hosted within a framework of low-magnesium calcite microcrystals. In general, crystal size distributions are narrow and positively skewed. Compiled data indicate that > 99% of all microcrystals measure between 0.5 and 9.0 µm in diameter with a mode at ca. 2.0 µm. Based on microcrystal shape, packing, and edge density, microporous limestones can be classified into three major textural classes, which we term granular, clustered, and fitted. Granular textures, which include subhedral and euhedral subclasses, are characterized by a framework of unconsolidated rhombic to polyhedral microcrystals that exhibit straight to curvilinear boundaries and intermediate crystal edge densities. Clustered textures, which include loose and fused subclasses, are characterized by a framework of irregularly shaped microcrystals with relatively high densities of discontinuous, curvilinear crystal edges. Fitted textures, which include partial and fused subclasses, are characterized by a dense mosaic of slightly larger microcrystals with mostly curvilinear boundaries and relatively low edge densities. These textural classes have unique mean crystal sizes, average pore-throat radii, bulk porosities, and permeabilities. Furthermore, textural classes and their characteristic pore-throat radii fall along a single log-normal transform in porosity–permeability space. Based on these relationships, three petrophysical microporosity “types” are distinguished. Type 1 is associated with granular subhedral crystal fabrics and typically exhibit relatively large average pore throat radii (ca. 0.7 µm) as well as high porosity (> 20%) and permeability (1–20 mD). Type 2 includes granular euhedral and clustered fabrics, which most commonly exhibit intermediate average pore-throat radii (ca. 0.2 µm), porosity (10–20%), and permeability (0.1–1 mD). Type 3 includes fitted crystal fabrics, which are generally characterized by smaller average pore-throat radii (ca. 0.06 µm), and relatively low porosity (< 10%) and permeability (< 0.1 mD).

The petroleum industry requires new technologies to improve the economics of exploration and production. Digital rock physics is a methodology that seeks to revolutionize reservoir characterization, an essential step in reservoir assessment, using computational methods. A combination of X-ray computed microtomography, digital pore network modeling, and 3D printing technology represents a novel workflow for transferring digital rock models into tangible samples that can be manufactured in a variety of materials and tested with standard laboratory equipment. Accurate replication of pore networks depends on the resolution of tomographic images, rock sample size, statistical algorithms for digital modeling, and the resolution of 3D printing. We performed this integrated approach on a sample of Idaho Gray Sandstone with an estimated porosity of 29% and permeability of 2200 mD. Tomographic images were collected at resolutions of 30 and $7\mathrm{\mu m}$ per voxel. This allowed the creation of digital porosity models segmented into grains and pores. Surfaces separating pores from grains were extracted from the digital rock volume and 3D printed in plastic as upscaled tangible models. Two model types, normal (with pores as voids) and inverse (with pores as solid), allowed visualization of the geometry of the grain matrix and topology of pores, while allowing characterization of pore connectivity. The current resolution of commodity 3D printers with a plastic filament ($30\mathrm{\mu m}$ for pore space and $16\mathrm{\mu m}$ for grain matrix) is too low to precisely reproduce the Idaho Gray Sandstone at its original scale. However, the workflow described here also applies to advanced high-resolution 3D printers, which have been becoming more affordable with time. In summary, with its scale flexibility and fast manufacturing time, 3D printing has the potential to become a powerful tool for reservoir characterization.