Physical processes and zooplankton distribution in the Great South Channel : observational and numerical studies
Epstein, Ari W.
MetadataShow full item record
LocationGreat South Channel
Gulf of Maine
KeywordMarine zooplankton; Marine phytoplankton; Copepoda; Food chains; Marlin (Ship) Cruise; Endeavor (Ship: 1976-) Cruise EN237
This thesis addresses the question, "How do small-scale physics and biology combine to produce dense aggregations of certain species of zooplankton in the Great South Channel (GSC) of the Gulf of Maine?" The thesis consists of three relatively independent parts: an observational study made while following two right whales as they fed on dense patches of the copepod Galanus finmarchicus in the northern GSC; a detailed description of a tightly integrated set of biological and physical observations made in the GSC by means of a new instrument, the Video Plankton Recorder (VPR); and a two-dimensional Eulerian numerical model that simulates one way in which a physical flow field, combined with a biological behavior pattern, may produce dense plankton patches at a convergent front. Part I: Data from a wide variety of instruments was combined to produce a coherent picture of the physical and biological environment near two feeding right whales observed in June, 1989. Instruments included a CTD (with transmissometer), a MOCNESS net system, a 150-kHz ADCP, and a towed acoustic plankton profiler operating at 120 and 200 kHz. Acoustic data were intercalibrated with net-tow data and with "noise" in the transmissometer signal in order to estimate copepod abundance in the plankton patches on which the whales were feeding. One of the whales was observed to reverse course when copepod abundance dropped below about 1.5- 4.5 x 103 copepods/m3 , which is consistent with independent estimates of the density of copepods necessary for a right whale to gain more energy from the prey it ingests than it loses to the extra hydrodynamic drag it experiences while feeding. Part II: The VPR is a towed underwater microscope designed to image plankton non-invasively with sufficient resolution to obtain information on the spatial distribut ion of organisms on scales ranging from millimeters to hundreds of kilometers. CTD instrumentation mounted on the VPR makes it possible to correlate biological and hydrographic data with great precision. This study reports data from one transect made across the GSC in May, 1992. The data show close correlations between hydrographic features (such as fronts, plumes and water masses) and broad-scale plankton distribution. In addition, it was possible to correlate the fine-scale (order tens of meters) patchiness in plankton distribution with the local stability of the water column (as indicated by gradient Richardson number). In one case, biological data provided an aid in determining the origin of one of the observed water masses. Part III: This chapter presents a two-dimensional Eulerian numerical model that shows how depth-keeping swimming behavior on the part of an organism, combined with a convergent flow field at a surface front , can create dense patches of the organism. In this model a steady-state flow field and vertical diffusivity field are prescribed, along with the initial distribution of the plankton. The plankton swim vertically with speeds that depend only on depth, but the form of that depth-dependence may take into account such factors as the vertical variation in light level or in the concentration of some prey organism. An analysis of various nondimensional parameters associated with the model illustrates the roles played in determining the final structure of the patch by such factors as diffusion, water velocity and details of the animals' swimming behavior. Output from the model is compared with data taken at a dense plankton patch observed near a front in the northern Great South Channel in early June, 1989.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1995
Showing items related by title, author, creator and subject.
The ecology of colonial radiolarians : their colony morphology, trophic interactions and associations, behavior, distribution, and the photosynthesis of their symbionts Swanberg, Neil Ralph (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1979-08)Colonial radiolarians (Spumellaria) are among the most common and abundant large zooplankton, but they have been little studied by modern biologists. Colonies were found on 98% of epipelagic diving stations in the period ...
Limits of Nematoscelis megalops in the northwestern Atlantic in relation to Gulf Stream cold core rings. I, Horizontal and vertical distributions Wiebe, Peter H.; Boyd, Steven H. (Woods Hole Oceanographic Institution, 1979-01)The hydrographic limit of the distribution of Nematoscelis megalops in the Northwestern Atlantic Ocean is usually marked by the abrupt changes in water properties across the Gulf Stream. There are, however, isolated but ...
Zooplankton biomass and related MOCNESS data for tows taken on the 1981-82 warm-core rings cruises Barber, Valerie A.; Wiebe, Peter H. (Woods Hole Oceanographic Institution, 1985-01)Compiled in this report are tables of zooplankton biomass data (displacement volume), carbon equivalents, and associated net tow data (volume filtered, depth, temperature, and salinity) collected with a Multlple ...