Certain living radiolarian species and taxonomic groups identified in plankton tows from North Atlantic, Gulf of Mexico, Caribbean, Pacific, and Antarctic waters are useful biologic indicators of physical oceanographic parameters. Changes in dominance and diversity of these radiolarians may signal: (1) distance from shore or position on shelf; (2) relative depths (e.g., above and below seasonal and permanent thermoclines); (3) direction, strength, and provenance of currents;

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(4) specific water masses; (5) conditions of preservation; (6) presence and strength of upwelling onto shelves and under boundary currents; (7) eutrophic conditions; and (8) tectonic events (isolating radiolarian populations).

These biologic indicators and their related forms are useful in determining similar parameters in the fossil record. Studies of radiolarians from Neogene Deep Sea Drilling Project and onshore samples indicate: (1) relative distance from continents; (2) relative paleodepths; (3) strengths and directions of paleocurrents; (4) presence and degree of paleo-upwellings; (5) origin, development, and presence of paleowater masses; (6) paleo-eutrophic conditions; and (7) paleotectonic activity. These biologic indicators may provide a framework for paleo-oceanographic interpretations of Mesozoic and perhaps even Paleozoic radiolarian-bearing sediments.

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