ALBERT

Description: Seafloor topography is neither spatially homogeneous, nor does it obey Gaussian statistics; deviations from both of these assumptions are important from a geological and acoustic point of view. It has been found that the distribution of topographic slopes can be used as a primary tool for understanding the sources and extent of spatial heterogeneities and patterns on the seafloor. The covariance function has been widely used to characterize seafloor topography, but requires the assumption of Gaussian joint probability statistics to be valid. For heterogeneous topography characterized by large transient signals such as steep scarps and volcanoes, the covariance becomes dominated by the transients; in contrast the family slope distributions can still be used to derive stable descriptors for regions with large transient signals, as well as regions containing asymmetric features, and regions with only limited sampling. Knowledge of slopes is useful because a direct relation exists between the covariance and the slope distributions at different spatial scales. Studies of the slope distribution provide a means of identifying the presence of the non‐Gaussian elements in the topography, and flagging their spatial locations. The methods used here are demonstrated by applying them to three small patches of topography located within 20 km of each other in the Eastern Pacific. It is found that dominant azimuthal directions and dip angles differ widely between the patches. In addition, asymmetries in the cross‐sectional shapes of faulted abyssal hills are documented. [Work supported by ONR.]

Description: High‐frequency bottom acoustic and geoacoustic data from three well‐characterized sites of different bottom composition are compared with scattering models in order to clarify the roles played by interface roughness and sediment volume inhomogeneities. Model fits to backscattering data from two silty sites lead to the conclusion that scattering from volume inhomogeneities was primarily responsible for the observed backscattering. In contrast, measured bottom roughness was sufficient to explain the backscattering seen at a sandy site. Although the sandy site had directional ripples, the model and data agree in their lack of anisotropy.

Description: As offshore petroleum exploration and development move into deeper water, industry must contend increasingly with gas hydrate, a solid compound that binds water and a low-molecular-weight gas (usually methane). Gas hydrate has been long studied in industry from an engineering viewpoint, due to its tendency to clog gas pipelines. However, hydrate also occurs naturally wherever there are high pressures, low temperatures, and sufficient concentrations of gas and water. These conditions prevail in two natural environments, both of which are sites of active exploration: permafrost regions and marine sediments on continental slopes. In this article we discuss seismic detection of gas hydrate in marine sediments. Gas hydrate in deepwater sediments poses both new opportunities and new hazards. An enormous quantity of natural gas, likely far exceeding the global inventory of conventional fossil fuels, is locked up worldwide in hydrates. Ex-traction of this unconventional resource presents unique exploration, engineering, and economic challenges, and several countries, including the United States, Japan, Canada, India, and Korea, have initiated joint industry-academic-governmental programs to begin studying those challenges. Hydrates also constitute a potential drilling hazard. Because hydrates are only stable in a restricted range of pressure and temperature, any activity that sufficiently raises temperature or lowers pressure could destabilize them, releasing potentially large volumes of gas and decreasing the shear strength of the host sediments. Assessment of the opportunities and hazards associated with hydrates requires reliable methods of detecting hydrate and accurate maps of their distribution and concentration. Hydrate may occur only within the upper few hundred meters of deepwater sediment, at any depth between the seafloor and the base of the stability zone, which is controlled by local pressure and temperature. Hydrate is occasionally exposed at the seafloor, where it can be detected either visually or acoustically by strong seismic reflection amplitudes or high backscatter …

Description: The emperor penguin (Aptenodytes forsteri), which feeds only at sea, is restricted to the higher latitudes of the antarctic sea-ice habitat1–3. It breeds on the winter fast ice when temperatures are−30 °C and high winds are frequent3. Assuming entirely the task of incubating the single egg, the male fasts for about 120 days in the most severe conditions. When it is relieved by the female around hatching time, the distance between the colony and the open sea may be 100km or more4,5, but where emperors go to forage at that time or during the summer is unknown. The polynias are areas of open water in sea-ice and during winter, with the under-ice habitats at any time of the year, they are among the most difficult of all Antarctic areas to sample. Here we monitor by satellite the routes taken by emperor penguins for foraging and compare them with satellite images of sea-ice. Winter birds walking over fast ice travelled up to 296 km to feed in polynias, whereas those swimming in light pack-ice travelled as far as 895km from the breeding colony. One record of diving showed that although most dives are to mid-water depths, some are near the bottom. Obtaining such detailed information on foraging in emperor penguins means that this bird now offers a unique opportunity to investigate the Antarctic sea-ice habitat.

Description: Cephalopods are a diverse group of highly derived molluscs, including nautiluses, squids, octopuses and cuttlefish. Evolution of the cephalopod body plan from a monoplacophoran-like ancestor1 entailed the origin of several key morphological innovations contributing to their impressive evolutionary success2. Recruitment of regulatory genes3, or even pre-existing regulatory networks4, may be a common genetic mechanism for generating new structures. Hox genes encode a family of transcriptional regulatory proteins with a highly conserved role in axial patterning in bilaterians5; however, examples highlighting the importance of Hox gene recruitment for new developmental functions are also known6,7. Here we examined developmental expression patterns for eight out of nine Hox genes8 in the Hawaiian bobtail squid Euprymna scolopes, by whole-mount in situ hybridization. Our data show that Hox orthologues have been recruited multiple times and in many ways in the origin of new cephalopod structures. The manner in which these genes have been co-opted during cephalopod evolution provides insight to the nature of the molecular mechanisms driving morphological change in the Lophotrochozoa, a clade exhibiting the greatest diversity of body plans in the Metazoa.