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...

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

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

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...

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...

Time Evolution of Surface Chlorophyll Patterns From Cross-Spectrum Analysis of Satellite Color Images

Sequences of coastal zone color scanner (CZCS) images from the offshore region adjacent to Vancouver Island, Canada, have been analyzed to estimate the time rate of decorrelation of surface phytoplankton chlorophyll pigment patterns. In these high-latitude, high-pigment areas, CZCS-derived pigment estimates were lower than those obtained from ship samples by about a factor of 3, their frequency distributions were skewed in opposite directions, and subareas of the images often showed a discontinuity in the frequency distribution at a concentration of 1.5 mg m–3, where the algorithm changes CZCS bands. We selected cloud-free subareas that were common to several images separated in time by 1–17 days. Image pairs were subjected to two-dimensional auto spectrum and cross-spectrum analysis in an array processor, and spectra of squared coherence were formed. The squared coherence estimates for several wave bands were plotted against time separation, in analogy with a time-lagged cross correlation function. Threshold levels for significant random uncorrelated fields with specified power law behavior K–1.5, near the observed range K–1.5–K–2. For wavelengths of 50–150 km, significant coherence is lost after 7–10 days, and for wavelengths of 25–50 km, significant coherence is lost after 5–7 days; in both cases offshore regions maintain coherence longer than coastal regions. For wavelengths of 12.5–25 km, only the offshore regions maintained coherence after 1 day, but that was clearly lost after the next time separation of 6 days. The implication for the formation of monthly average large-scale surface maps to estimate open ocean productivity (e.g., Esaias et al., 1986) is that all mesoscale patterns (<150-km length scale) will not be resolved

Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder

A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping Experiment) is currently being commissioned at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical interferometer designed to measure the large scale neutral hydrogen power spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used to measure the baryon acoustic oscillation (BAO) scale across this poorly probed redshift range where dark energy becomes a significant contributor to the evolution of the Universe. The instrument revives the cylinder design in radio astronomy with a wide field survey as a primary goal. Modern low-noise amplifiers and digital processing remove the necessity for the analog beamforming that characterized previous designs. The Pathfinder consists of two cylinders 37\,m long by 20\,m wide oriented north-south for a total collecting area of 1,500 square meters. The cylinders are stationary with no moving parts, and form a transit instrument with an instantaneous field of view of $\sim$100\,degrees by 1-2\,degrees. Each CHIME Pathfinder cylinder has a feedline with 64 dual polarization feeds placed every $\sim$30\,cm which Nyquist sample the north-south sky over much of the frequency band. The signals from each dual-polarization feed are independently amplified, filtered to 400-800\,MHz, and directly sampled at 800\,MSps using 8 bits. The correlator is an FX design, where the Fourier transform channelization is performed in FPGAs, which are interfaced to a set of GPUs that compute the correlation matrix. The CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed to detect the BAO feature and constrain the distance-redshift relation.Comment: 20 pages, 12 figures. submitted to Proc. SPIE, Astronomical Telescopes + Instrumentation (2014

Couplings between changes in the climate system and biogeochemistry

The Earth's climate is determined by a number of complex connected physical, chemical and biological processes occurring in the atmosphere, land and ocean. The radiative properties of the atmosphere, a major controlling factor of the Earth's climate, are strongly affected by the biophysical state of the Earth's surface and by the atmospheric abundance of a variety of trace constituents. These constituents include long-lived greenhouse gases (LLGHGs) such as carbon dioxide (CO{sub 2}), methane (CH{sub 4}) and nitrous oxide (N{sub 2}O), as well as other radiatively active constituents such as ozone and different types of aerosol particles. The composition of the atmosphere is determined by processes such as natural and anthropogenic emissions of gases and aerosols, transport at a variety of scales, chemical and microphysical transformations, wet scavenging and surface uptake by the land and terrestrial ecosystems, and by the ocean and its ecosystems. These processes and, more generally the rates of biogeochemical cycling, are affected by climate change, and involve interactions between and within the different components of the Earth system. These interactions are generally nonlinear and may produce negative or positive feedbacks to the climate system. An important aspect of climate research is to identify potential feedbacks and assess if such feedbacks could produce large and undesired responses to perturbations resulting from human activities. Studies of past climate evolution on different time scales can elucidate mechanisms that could trigger nonlinear responses to external forcing. The purpose of this chapter is to identify the major biogeochemical feedbacks of significance to the climate system, and to assess current knowledge of their magnitudes and trends. Specifically, this chapter will examine the relationships between the physical climate system and the land surface, the carbon cycle, chemically reactive atmospheric gases and aerosol particles. It also presents the current state of knowledge on budgets of important trace gases. Large uncertainties remain in many issues discussed in this chapter, so that quantitative estimates of the importance of the coupling mechanisms discussed in the following sections are not always available. In addition, regional differences in the role of some cycles and the complex interactions between them limit our present ability to provide a simple quantitative description of the interactions between biogeochemical processes and climate change