ABSTRACT
The electrical conductivity of the ocean is a fundamental parameter in the electrodynamics of the Earth System. This parameter is involved in a number of applications ranging from the calibration of in situ ocean flow meters, through extensions of traditional induction studies, and into quite new opportunities involving the remote sensing of ocean flow and properties from space-borne magnetometers such as carried aboard the three satellites of the Swarm mission launched in 2013. Here, the first ocean conductivity data set calculated directly from observed temperature and salinity measurements is provided. These data describe the globally gridded, three-dimensional mean conductivity as well as seasonal variations, and the statistics of spatial and seasonal variations are shown. This "climatology" data set of ocean conductivity is offered as a standard reference similar to the ocean temperature and salinity climatologies that have long been available.
ABSTRACT
Data from recent space missions have added strong support for the idea that there are liquid oceans on several moons of the outer planets, with Jupiter's moon Europa having received the most attention. But given the extremely cold surface temperatures and meagre radiogenic heat sources of these moons, it is still unclear how these oceans remain liquid. The prevailing conjecture is that these oceans are heated by tidal forces that flex the solid moon (rock plus ice) during its eccentric orbit, and that this heat entering the ocean does not rapidly escape because of the insulating layer of ice over the ocean surface. Here, however, I describe strong tidal dissipation (and heating) in the liquid oceans; I show that a subdominant and previously unconsidered tidal force due to obliquity (axial tilt of the moon with respect to its orbital plane) has the right form and frequency to resonantly excite large-amplitude Rossby waves in these oceans. In the specific case of Europa, the minimum kinetic energy of the flow associated with this resonance (7.3 x 10(18) J) is two thousand times larger than that of the flow excited by the dominant tidal forces, and dissipation of this energy seems large enough to be a primary ocean heat source.
ABSTRACT
The ocean is an electrically conducting fluid that generates secondary magnetic fields as it flows through Earth's main magnetic field. Extracting ocean flow signals from remote observations has become possible with the current generation of satellites measuring Earth's magnetic field. Here, we consider the magnetic fields generated by the ocean lunar semidiurnal (M2) tide and demonstrate that magnetic fields of oceanic origin can be clearly identified in satellite observations.
ABSTRACT
Drosophila melanogaster populations that exhibit constrasting life histories as a result of laboratory selection were compared at several potentially relevant enzyme loci. Selection regimes included postponed reproduction, accelerated development, and intermediate generation time. Each selection regime was represented by fivefold replicated populations maintained for between 50 and 500 generations. For each population, allele frequencies were calculated from frequencies of electrophoretically distinguishable allozymes of alcohol dehydrogenase, α-glycerol-3-phosphate dehydrogenase, phosphoglucomutase, and CuZn-superoxide dismutase. Based on allozyme frequency changes consistent across replicate populations, two of the studied loci responded to both selection for postponed reproduction and selection for accelerated development. The responses to contrasting selection regimes were in opposing directions, suggesting antagonistic pleiotropy.
