| Summary: | Interactions between currents and oceanic islands may underly biological enhancement in circuminsular waters (island mass effect). It is often assumed, although demonstrated only in a few cases, that eddy-shedding in the island wake is the dominant physical process involved in this effect. Due to dominance of the Earth's rotation over frictional and advective effects, vortex-shedding events are not likely to occur around Southern Ocean islands. Nevertheless, enhanced biological productivity around these islands is well documented, and is thought to support the large local populations of seabirds and pinnipeds. Thus, this study addresses the question: "How is the island mass effect generated in a Southern Ocean archipelago, and how does it contribute to the energy source that supports the biomass build-up of the land-based predators?" Analysis of data and samples, obtained during eight cruises to the Prince Edward Archipelago (47$\sp\circ$S, 38$\sp\circ$E), showed the occurrence of anticyclonic anomalies in the island seas and the doming of isotherms and isopycnals over the plateau. These observations and the results of dimensional analysis indicate that appropriate conditions exist for the formation of closed streamline, stratified Taylor columns. Variations in mixed layer depth, vertical stability and reduced nitrogen accounted for up to 80% of the variability associated with phytoplankton photosynthetic capacity ($P\sbsp{m}{B}$). It is suggested that high rainfall ($\approx250\ mm\ month\sp{-1}$) and guano excretion ($\approx1.2 \times 10\sp6 mol\ N\ d\sp{-1}$) on the archipelago result in nitrogen-rich freshwater run-off. Phytoplankton blooms (1.5-2.5 mg Chl-a $m\sp{-3}$) may develop in the island seas when this freshwater run-off is retained by anticyclonic eddies for a sufficient period of time (several days). Estimates of in situ zooplankton grazing rates showed that only 10-20% of daily primary production is consumed by pelagic herbivores. A great portion of the phytoplankton standing stock appears to be transferred to the benthic subsystem, thus explaining the high biomass of suspensoid feeders observed ($\approx$50% of total epibenthic biomass). This resource is largely exploited by the benthic shrimp Nauticaris marionis which, in turn, represents the staple food item of bottom-feeding seabirds. On the other hand, much of the food requirements of the community of surface-feeding predators may be met by nighttime, surface migration of allochthonous zooplankton. This process could account for a carbon supply equivalent to the local maximum phytoplankton production. Thesis (Ph.D.)--Dalhousie University (Canada), 1990.
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