The variance spectrum of phytoplankton in a turbulent ocean

Spatial heterogeneity of ecological variables is recognized as an important stabilizing factor for ecosystem function, but has proved to be a difficult concept to characterize in quantitative, operational terms. In the sea, however, chlorophyll concentration can be estimated by a continuous in vivo measurement, and used to describe the spatial structure of phytoplankton populations in terms of a variance spectrum in either wavenumber or frequency space...

Phytoplankton patchiness: inferences from particle statistics

We examine the influence of mesoscale turbulence and random growth rate fields upon phytoplankton patchiness, on length scales from 1 km to 100 km and time scales from 1 day to 100 days. We consider phytoplankton concentrations with quite general nonlinear growth rate functions, such that the concentration is bounded for all time. We use, and justify the use of, particle separation statistics to deduce variance spectra of nonlinearly transformed concentration. Two growth rate models are examined: an advected field, and a locally specified field. Both lead to initial patchiness in the concentration, correlated with the growth rate field. The advected growth rate field leads to a temporal peak in the patchiness before the mesoscale turbulence causes the concentration variance to cascade to a noisy spatial distribution that retains no correlation with either the motion field, or the growth rate field. We outline numerical experiments to test these results, in particular the occurrence of the peak in patchiness and the time scales associated with its formation and decay

Correlation scales, objective mapping and a statistical test of geostrophy over the continental shelf

We have constructed spatial structure functions for oceanographic variables, collected during 15 cruises off the coast of Vancouver Island, Canada over a 3 year period (1979–81), to determine the appropriate correlation function and unresolved noise level for objective mapping according to the Gauss-Markov theorem. The assumption of quasigeostrophic flow has been tested by comparing the longitudinal and transverse velocity shear structure functions derived from geopotential height fields with those derived from 6 current meter moorings. In addition objective maps of geopotential height imply current shears similar to the directly observed shear vectors, as would be expected under geostrophic control. Structure functions of geopotential height, temperature, salinity, and log-transformed phytoplankton chlorophyll a pigment concentration all have a broad maximum near a separation of 30 km, consistent with a dominant eddy wavelength of ≃60 km, also the estimated wavelength of the most unstable baroclinic disturbance. The sensitivity of the objective maps generated using the Gauss-Markov theorem to different correlation functions, length scales and noise levels was tested: where the sampling was well distributed, the patterns changed little.Temporal structure functions (for data from 25 cruises) of geopotential height, temperature and salinity are roughly cyclic with minima at time lags of 1 and 2 years. The structure functions increase monotonically with lags up to at least 90 days indicating that temporal changes during a ship survey (several days) are sufficiently small that the maps can be regarded as synoptic. Finally, a composite kinetic energy spectrum from a long term (≃3 years) current meter mooring at the edge of the continental shelf has well defined peaks in a band with 10–50 day periods (which we believe represents the mesoscale eddies with ≃60km wavelength), and at the annual and the major tidal and inertial periods

A topographically controlled upwelling center off southern Vancouver Island

From January 1979 to June 1981 an oceanographic experiment off the west coast of Canada provided a unique view of a large annual upwelling event. The upwelling is driven by an interaction between the large scale coastal current systems and a narrow canyon that cuts the continental shelf. This interaction allows water to be raised from depths much greater than those normally expected from the classical wind-driven upwelling mechanisms...

Multiple thermoclines are barriers to vertical exchange in the subarctic Pacific during SUPER, May 1984

As part of the Subarctic Pacific Ecosystem Research program, we made observations of upper ocean physical and biological properties at 50N; 145W during 12–21 May 1984 from a drifting buoy, instrumented with a thermistor chain and meteorological sensors; a CTD/rosette bottle profiler; a shipboard solar radiometer; and a microstructure profiler equipped with a fast response thermistor and two airfoil velocity probes. At that time, the ocean above the seasonal thermocline was divided by a shallow thermocline step (∼0.5°C) into two layers with different turbulence characteristics and dynamics. The surface layer thermal structure (even in wind speeds up to 14 m s–1) underwent a clear diurnal cycle down to at least 20 m, but the rate of dissipation of turbulent kinetic energy ε did not display day/night differences and was negatively or not correlated with the buoyancy frequency N. Below the shallow thermocline step, ε and N covaried, both reaching maximum values in the permanent pycnocline at 80–90 m. Bio-optical properties of the phytoplankton showed different responses to the different physical environments in the two layers. The initial slope of the relationship between photosynthetic rate and irradiance differed significantly between the two layers; and the phytoplankton in the surface layer displayed strong midday inhibition of fluorescence yield down to 30 m. On the one calm day, both the diurnal thermal signal and the fluorescence inhibition were confined to the top few meters, indicating that the deeper penetration on other days was due to near-surface effects being redistributed throughout the upper layer by wind mixing. The turbulence within the permanent pycnocline appeared to be anisotropic down to viscous scales, effectively eliminating vertical turbulent exchange. Such anisotropy in highly stable layers may favor persistence of “microzones” of enriched nutrients but it precludes calculation from microstructure measurements of accurate estimates of the vertical coefficient of turbulent diffusion Kz, required to estimate the vertical flux of dissolved nitrate through the permanent pycnocline

Space-time structure of a continental shelf ecosystem measured by a towed porpoising vehicle

During August, 1975, an experiment was carried out in the eastern Gulf of Maine with the Batfish, a towed undulating body, on which were mounted an in situ fluorometer and a conductivity-temperature-depth probe. The Batfish cycled between depths of about 4 and 40 m with a cycle length of order 0.6 km...

Advanced engine study program

A design and analysis study was conducted to provide advanced engine descriptions and parametric data for space transfer vehicles. The study was based on an advanced oxygen/hydrogen engine in the 7,500 to 50,000 lbf thrust range. Emphasis was placed on defining requirements for high-performance engines capable of achieving reliable and versatile operation in a space environment. Four variations on the expander cycle were compared, and the advantages and disadvantages of each were assessed. Parametric weight, envelope, and performance data were generated over a range of 7,500 to 50,000 lb thrust and a wide range of chamber pressure and nozzle expansion ratio

Phytophthora taxa associated with cultivated Agathosma, with emphasis on the P. citricola complex and P. capensis sp. nov.

Agathosma species, which are indigenous to South Africa, are also cultivated for commercial use. Recently growers experienced severe plant loss, and symptoms shown by affected plants suggested that a soilborne disease could be the cause of death. A number of Phytophthora taxa were isolated from diseased plants, and this paper reports their identity, mating type, and pathogenicity to young Agathosma plants. Using morphological and sequence data seven Phytophthora taxa were identified: the A1 mating type of P. cinnamomi var. cinnamomi, P. cinnamomi var. parvispora and P. cryptogea, the A2 mating type of P. drechsleri and P. nicotianae, and two homothallic taxa from the P. citricola complex. The identity of isolates in the P. citricola complex was resolved using reference isolates of P. citricola CIT groups 1 to 5 sensu Oudemans et al. (1994) along with multi-locus phylogenies (three nuclear and two mitochondrial regions), isozyme analyses, morphological characteristics and temperature-growth studies. These analyses revealed the isolates from Agathosma to include P. multivora and a putative novel species, P. taxon emzansi. Furthermore, among the P. citricola reference isolates the presence of a new species was revealed, described here as P. capensis. Findings of our study, along with some recent other studies, have contributed to resolving some of the species complexity within the P. citricola complex, resulting in the identification of a number of phylogenetically distinct taxa. The pathogenicity of representative isolates of the taxa from Agathosma was tested on A. betulina seedlings. The putative novel species, P. taxon emzansi, and P. cinnamomi var. parvispora were non-pathogenic, whereas the other species were pathogenic to this host

Sodium fast reactor safety and licensing research plan. Volume I.

This report proposes potential research priorities for the Department of Energy (DOE) with the intent of improving the licensability of the Sodium Fast Reactor (SFR). In support of this project, five panels were tasked with identifying potential safety-related gaps in available information, data, and models needed to support the licensing of a SFR. The areas examined were sodium technology, accident sequences and initiators, source term characterization, codes and methods, and fuels and materials. It is the intent of this report to utilize a structured and transparent process that incorporates feedback from all interested stakeholders to suggest future funding priorities for the SFR research and development. While numerous gaps were identified, two cross-cutting gaps related to knowledge preservation were agreed upon by all panels and should be addressed in the near future. The first gap is a need to re-evaluate the current procedures for removing the Applied Technology designation from old documents. The second cross-cutting gap is the need for a robust Knowledge Management and Preservation system in all SFR research areas. Closure of these and the other identified gaps will require both a reprioritization of funding within DOE as well as a re-evaluation of existing bureaucratic procedures within the DOE associated with Applied Technology and Knowledge Management