Memorial University of Newfoundland

About: Memorial University of Newfoundland is a education organization based out in St. John's, Newfoundland and Labrador, Canada. It is known for research contribution in the topics: Population & Gadus. The organization has 13818 authors who have published 27785 publications receiving 743594 citations. The organization is also known as: Memorial University & Memorial University of Newfoundland and Labrador.

Phytoplankton population dynamics at the Bermuda Atlantic Time-series station in the Sargasso Sea

Abstract: Phytoplankton populations were analyzed using flow cytometry in monthly samples at the Bermuda Atlantic Time-series Study (BATS) station in the Sargasso Sea from 1989–1994 for picoplankton ( Synechococcus and Prochlorococcus ) and from 1992–1994 for eukaryotic phytoplankton in order to better understand the mechanisms that dictate seasonal and inter-annual patterns in the phytoplankton community. The eukaryotic phytoplankton were dominated by populations of small nanoplankton (mostly 2–4 μm diameter), though populations of coccolithophores and sometimes pennate diatoms also could be distinguished. Flow cytometric measurements of population abundances, individual cell light scattering (which can be related to cell size), and chlorophyll fluorescence were made. Synechococcus and the eukaryotic phytoplankton reached their greatest concentrations during the spring bloom each year when the water column was deeply mixed and nutrients were detectable in surface waters. The maximum cell concentration for Prochlorococcus was in the summer and fall of each year, with a deeper sub-surface maximum than Synechococcus . Picoplankton chlorophyll fluorescence and estimated cell size were greater at depth than near the surface, and were lowest in midsummer for both Synechococcus and Prochlorococcus . In the summer and fall, Prochlorococcus cells were often smallest at mid-depth, even when fluorescence per cell and cell concentration were lower at the surface. For the eukaryotes (including coccolithophores), cell concentrations were high during the spring in both 1992 and 1993, and in fall 1992. At these times, mean cell size and fluorescence were low. Improved size and carbon estimates were made and it was found that the estimated contribution of phytoplankton carbon to total particulate organic carbon, integrated over the upper 200 m, averaged 33% (range 21–43%) with no pronounced seasonal pattern.

Timescales for radiation belt electron acceleration and loss due to resonant wave-particle interactions: 2. Evaluation for VLF chorus, ELF hiss, and electromagnetic ion cyclotron waves

Abstract: Outer zone radiation belt electrons can undergo gyroresonant interaction with various magnetospheric wave modes including whistler-mode chorus outside the plasmasphere and both whistler-mode hiss and electromagnetic ion cyclotron (EMIC) waves inside the plasmasphere. To evaluate timescales for electron momentum diffusion and pitch angle diffusion, we utilize bounce-averaged quasi-linear diffusion coefficients for field-aligned waves with a Gaussian frequency spectrum in a dipole magnetic field. Timescales for momentum diffusion of MeV electrons due to VLF chorus can be less than a day in the outer radiation belt. Equatorial chorus waves (|λw| < 15 deg) can effectively accelerate MeV electrons. Efficiency of the chorus acceleration mechanism is increased if high-latitude waves (|λw| < 15 deg) are also present. Our calculations confirm that chorus diffusion is a viable mechanism for generating relativistic (MeV) electrons in the outer zone during the recovery phase of a storm or during periods of prolonged substorm activity when chorus amplitudes are enhanced. Radiation belt electrons are subject to precipitation loss to the atmosphere due to resonant pitch angle scattering by plasma waves. The electron precipitation loss timescale due to scattering by each of the wave modes, chorus, hiss, and EMIC waves, can be 1 day or less. These wave modes can separately, or in combination, contribute significantly to the depletion of relativistic (MeV) electrons from the outer zone over the course of a magnetic storm. Efficient pitch angle scattering by whistler-mode chorus or hiss typically requires high latitude waves (|λw| < 30 deg). Timescales for electron acceleration and loss generally depend on the spectral properties of the waves, as well as the background electron number density and magnetic field. Loss timescales due to EMIC wave scattering also depend on the ion (H+, He+, O+) composition of the plasma. Complete models of radiation belt electron transport, acceleration and loss should include, in addition to radial (cross-L) diffusion, resonant diffusion due to gyroresonance with VLF chorus, plasmaspheric hiss, and EMIC waves. Comprehensive observational data on the spectral properties of these waves are required as a function of spatial location (L, MLT, MLAT) and magnetic activity.

Mudstone diversity: Origin and implications for source, seal, and reservoir properties in petroleum systems

Abstract: Mudstone is the most abundant sedimentary rock and variously acts as sources, seals, and shale gas reservoirs in petroleum systems. Many important physicochemical properties of mudstones are strongly influenced by the mineralogy and size of deposited grains, and by diagenetic changes (precompaction and postcompaction); these are commonly predictable. The diverse composition of mudstones reflects input and hydrodynamic segregation of detrital materials to basins, primary production within basins, and diagenetic processes (both precipitation and dissolution) in the sediment. High-magnification observations both in modern and ancient sediments demonstrate that mudstones are texturally and mineralogically heterogeneous; this variability is not always readily apparent. Although some mud is indeed deposited by suspension settling out of low-energy buoyant plumes, textural analyses reveal that it is commonly dispersed by a combination of waves, gravity-driven processes, and unidirectional currents driven variously by storms and tides. Such dispersal mechanisms mean that muddy successions are typically organized into packages that can be interpreted using sequence stratigraphy. Early bioturbation homogenizes mud, whereas early chemical diagenesis can result in highly cemented zones developing, especially at stratal surfaces. The nature of deeper burial diagenesis, which involves compaction, mineral dissolution, recrystallization, mineral reorientation and lithification, and petroleum generation, is preconditioned by depositional and early diagenetic characteristics of the mud. Although the petrophysical properties of homogeneous mudstones are reasonably well known, the quantitative implications of heterogeneity for petroleum expulsion, retention, petroleum migration, seal capacity, acoustic anisotropy, and identification of shale gas reservoir sweet spots are essentially unexplored. Future work should seek to redress this position.