ALBERT

Description: Shallow gas occurs between 0 and 1000 m below the sea floor. It consists mainly of microbial-formed or thermogenic methane or a combination of both, sometimes with a limited admixture of higher hydrocarbons (propane, butane, etc.).

Description: Mass budget calculations, validated with satellite gravity observations [from the Gravity Recovery and Climate Experiment (GRACE) satellites], enable us to quantify the individual components of recent Greenland mass loss. The total 2000–2008 mass loss of ~1500 gigatons, equivalent to 0.46 millimeters per year of global sea level rise, is equally split between surface processes (runoff and precipitation) and ice dynamics. Without the moderating effects of increased snowfall and refreezing, post-1996 Greenland ice sheet mass losses would have been 100% higher. Since 2006, high summer melt rates have increased Greenland ice sheet mass loss to 273 gigatons per year (0.75 millimeters per year of equivalent sea level rise). The seasonal cycle in surface mass balance fully accounts for detrended GRACE mass variations, confirming insignificant subannual variation in ice sheet discharge.

Description: The definition of noise and signal in seismic data will vary widely with the viewer's perspective and methods to process and visualize the data. Thus we begin with our definition from the perspective of presenting structural subsurface information.

Description: A new equation is proposed for the calculation of sound speed in seawater as a function of temperature, salinity, depth, and latitude in all oceans and open seas, including the Baltic and the Black Sea. The proposed equation agrees to better than ±0.2m∕s with two reference complex equations, each fitting the best available data corresponding to existing waters of different salinities. The only exceptions are isolated hot brine spots that may be found at the bottom of some seas. The equation is of polynomial form, with 14 terms and coefficients of between one and three significant figures. This is a substantial reduction in complexity compared to the more complex equations using pressure that need to be calculated according to depth and location. The equation uses the 1990 universal temperature scale (an elementary transformation is given for data based on the 1968 temperature scale). It is hoped that the equation will be useful to those who need to calculate sound speed in applications of marine acoustics.

Description: The seismic trace is a complex aggregate of reflected and scattered signals from subsurface formation interfaces and heterogeneities. Although many varieties of random noise may also be present in the trace, we know from reacquiring the same seismic survey that seismic data are highly repeatable, indicating that significant information about the subsurface is contained in the trace but not yet used by our standard analysis methods. Seismic scattering is a type of signal contained in the data that is generally not utilized.

Description: Proteins containing the PB1 domain, a protein interaction module conserved in animals, fungi, amoebas, and plants, participate in diverse biological processes. The PB1 domains adopt a ubiquitin-like β-grasp fold, containing two α helices and a mixed five-stranded β sheet, and are classified into groups harboring an acidic OPCA motif (type I), the invariant lysine residue on the first β strand (type II), or both (type I/II). The OPCA motif of a type I PB1 domain forms salt bridges with basic residues, especially the conserved lysine, of a type II PB1 domain, thereby mediating a specific PB1-PB1 heterodimerization, whereas additional contacts contribute to high affinity and specificity of the modular interaction. The canonical PB1 dimerization is required for the formation of complexes between p40phox and p67phox (for activation of the NADPH oxidase crucial for mammalian host defense), between the scaffold Bem1 and the guanine nucleotide exchange factor Cdc24 (for polarity establishment in yeasts), and between the polarity protein Par6 and atypical protein kinase C (for cell polarization in animal cells), as well as for the interaction between the mitogen-activated protein kinase kinase kinases MEKK2 or MEKK3 and the downstream target mitogen-activated protein kinase kinase MEK5 (for early cardiovascular development in mammals). PB1 domains can also mediate interactions with other protein domains. For example, an intramolecular interaction between the PB1 and PX domains of p40phox regulates phagosomal targeting of the microbicidal NADPH oxidase; the PB1 domain of MEK5 is likely responsible for binding to the downstream kinase ERK5, which lacks a PB1 domain; and the scaffold protein Nbr1 associates through a PB1-containing region with titin, a sarcomere protein without a PB1 domain. This Review describes various aspects of PB1 domains at the molecular and cellular levels.

Description: Gas-hydrate accumulations located onshore in Arctic permafrost regions are seen as a potential source of natural gas. Surprisingly, most of the gas hydrate found in the Mackenzie Delta and Beaufort Sea areas was indirectly discovered or inferred from conventional hydrocarbon exploration programs. One of these occurrences, the Mallik gas-hydrate field (Figure 1), has received particular attention over the last 10 years. Two internationally partnered research well programs have intersected three intervals of gas hydrates and have allowed successful extraction of subpermafrost core samples with significant gas hydrates. The gas-hydrate intervals are up to 40 m thick and have high gas-hydrate saturation, sometimes exceeding 80% of pore volume of unconsolidated clastic sediments with average porosities from 25–40%. At Mallik, the gas-hydrate intervals are located at depths of 900–1100 m and are localized on the crest of an anticline.

Description: Background Polychaetes assigned as Scoloplos armiger (Orbiniidae) show a cosmopolitan distribution and have been encountered in all zoogeographic regions. Sibling S. armiger-like species have been revealed by recent studies using RAPDs and AFLP genetic data. We sequenced a ~12 kb fragment of the Scoloplos cf. armiger mitochondrial genome and developed primers for variable regions including the 3' end of the cox3 gene, trnQ, and most of nad6. A phylogenetic analysis of this 528-nucleotide fragment was carried out for S. armiger-like individuals from the Eastern North Atlantic as well as Pacific regions. The aim of this study is to test the cosmopolitan status, as well as to clarify the systematics of this species complex in the Eastern North Atlantic, while using a few specimens from the Pacific Ocean for comparision. Results Phylogenetic analysis of the cox3-trnQ-nad6 data set recovered five different clades of Scoloplos cf. armiger. The fragment of the mitochondrial genome of Scoloplos cf. armiger is 12,042 bp long and contains 13 protein coding genes, 15 of the 22 expected tRNAs, and the large ribosomal subunit (rrnl). Conclusion The sequenced cox3-trnQ-nad6 fragment proved to be very useful in phylogenetic analyses of Scoloplos cf. armiger. Due to its larger sampling scale this study goes beyond previous analyses which used RAPD and AFLP markers. The results of this study clearly supports that Scoloplos armiger represents a species complex and not a cosmopolitan species. We find at least two S. armiger-like species within the Pacific region and three different S. armiger-like species in the North Atlantic. Implications for the taxonomy and the impact on ecological studies are discussed.

Description: A bottom-simulating reflection (BSR) is a seismic reflectivity phenomenon that is widely accepted as indicating the base of the gas-hydrate stability zone. The acoustic impedance difference between sediments invaded with gas hydrate above the BSR and sediments without gas hydrate, but commonly with free gas below, are accepted as the conditions that create this reflection. The relationship between BSRs and marine gas hydrate has become so well known since the 1970s that investigators, when asked to define the most important seismic attribute of marine gas-hydrate systems, usually reply, “a BSR event.” Research conducted over the last decade has focused on calibrating seafloor seismic reflectivity across the geology of the northern Gulf of Mexico (GoM) continental slope surface to the seafloor. This research indicates that the presence and character of seafloor bright spots (SBS) can be indicators of gas hydrates in surface and near-surface sediments (Figure 1). It has become apparent that SBSs on the continental slope generally are responses to fluid and gas expulsion processes. Gas-hydrate formation is, in turn, related to these processes. As gas-hydrate research expands around the world, it will be interesting to find if SBS behavior in other deepwater settings is as useful for identifying gas-hydrate sites as in the GoM.