1,721,074 research outputs found
A Malthusian curb on spatial structure in micro-organism populations
No full textThat all organisms are born in the company of a parent but die alone is a fundamental biological asymmetry. It has been suggested that this provides a deep-rooted source of spatial pattern formation for microorganisms even at the scale of the population. Such a theory, however, neglects the strong influence in nature of the limited and spatially variable availability of food. The tendency, first recognized by Thomas Malthus in the 18th century, of a population to out-strip its food resources will eventually lead, through local starvation, to the suppression of a heterogeneity growing within a population. Using a generic model it is demonstrated that including local food limitation of breeding strongly dampens spatial structure otherwise resulting from birth and death. The extent of this damping is shown to be a function of the strength of the coupling between organisms and their food and of the total abundance of organic material. Moreover, this work provides an example of a density-dependent process acting to diminish spatial structure rather than to create it and highlights the rich variety of behaviour that is missed by continuum models which fail to represent such local dynamics
Phytoplankton patchiness: the role of lateral stirring and mixing
No full textExplanations for the patchy distribution of marine phytoplankton are critically reviewed with the focus on the role played by lateral advection and mixing. Generating mechanisms for what is increasingly seen as a ubiquitous feature of the oceans have been sought in biology, behaviour, population dynamics, physics and various combinations thereof. As the mesoscale and sub-mesoscale (1-500 km) contain the "weather" of the ocean--eddies and fronts capable of strong stirring and mixing of any tracers advected by them--the physical circulation in this regime may have a strong role in the generation of patchiness. As a consequence, the focus here is on the ways the turbulent currents at these scales can interact with other processes to produce the complex spatial structures in phytoplankton distributions seen in countless satellite images and cruise data. The mechanisms reviewed include patch formation (KiSS theory), filamentation, Turing and related instabilities, diffusion waves, shear effects and turbulent stirring. Parallel to this is a discussion of observations and of the techniques that have been used to analyse them, particularly spectral analysis. It will be seen that many of the limitations in extant theories stem from a paucity of data and ambiguity in its interpretation. A synthesis of recent developments in sampling, instrumentation, image analysis and turbulence theory is used to suggest alternatives to conventional approaches, to highlight important work in related fields and to motivate new lines of research
Plankton distribution spectra: inter-size class variability and the relative slopes for phytoplankton and zooplankton
No full textThe use of gliders for oceanographic science: the data processing gap
Full text linkAutonomous gliders represent a step change in the way oceanographic data can be collected and as such they are increasingly seen as valuable tools in the oceanographer’s arsenal. However, their increase in use has left a gap regarding the conversion of the signals that their sensors collect into scientifically useable data.At present the novelty of gliders means that only a few research groups within the UK are capable of processing glider data whilst the wider oceanographic community is often unaware that requesting deployment of a glider by MARS does not mean that they will be provided with fully processed and calibrated data following the deployment. This is not a failing of MARS – it is not in their remit – but it does mean that a solution is needed at the UK community level. The solution is also needed quickly given the rapidly growing glider fleet and requests to use it.To illustrate the far from trivial resources and issues needed to solve this problem at a community level, this document briefly summarises the resources and steps involved in carrying glider data through from collection to final product, for the glider owning research groups within the UK which have the capability.This report does not provide a recommendation on whether such a community facility should be the responsibility of NOC, BODC or MARS but does provide information on possible protocols and available software that could be part of a solution.This report does, however, recommend that, to support the growing use of the MARS gliders, a permanently staffed group is needed as a priority, to provide data processing and calibration necessary to allow the translation of glider missions into high impact scientific publications
Mechanisms for vertical nutrient transport within a North Atlantic mesoscale eddy
No full textPrompted by observational evidence for an enhanced source of surface nutrients within an anticyclonic eddy in the NE Atlantic, we investigate vertical transport processes that may produce such a phenomenon. For the eddy investigated, the dominant mechanism is found to be ageostrophic circulation resulting from a perturbation of the circular flow of the eddy. This can produce upwelling velocities of order 10 md?1. Ekman pumping due to wind stress on the eddy also produces upwelling within, but on a smaller scale of ~0.5 md?1. There is no evidence that self-propagation of the eddy leads to an enhanced nutrient flux by displacement upwards of nutrient-laden deeper isopycnals over the core of the eddy. Deeper winter mixing within the eddy relative to the surroundings, however, may contribute to the elevated nutrient levels
The sustained observatory over the Porcupine Abyssal Plain (PAP): Insights from time series observations and process studies (preface)
No full textOceanographic research in the past 20 years has highlighted the importance of understanding decadal-scale variation in the oceans in order to predict how the ocean will respond to climate change. Climate factors control many of the processes that regulate the input of nutrients to the euphotic zone, primary productivity, zooplankton responses, the downward flux of organic matter, the biomass and composition of seabed communities and, ultimately, the burial of carbon in deep-sea sediments. A critical part of our understanding of the interdependence of these many elements comes from long-term Eulerian observations, such as the Hawaii Ocean Time series (HOT) (Karl et al., 2003), the Bermuda Atlantic Time Series (BATS) (Steinberg et al., 2001), the NE Pacific Station M (Smith and Druffel, 1998) and the NE Atlantic Porcupine Abyssal Plain site (PAP) ([Billett and Rice, 2001] and [Lampitt et al., 2001]). Each time series site is considered as representing a different oceanic setting and each has a different suite of observations and history. However, the unifying theme of them all is to understand the time varying properties and processes of the oceanic environment. Only at Station M and PAP have water column and seabed observations been integrated, a feature of some considerable advantage. This special issue presents the latest work at PAP
On the role of biological dynamics in plankton patchiness at the mesoscale: an example from the north east Atlantic (abstract of poster to be presented at: AGU Ocean Sciences Meeting, 26-30 January 2004, Portland, Oregon)
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