DEEP-SEA BENTHIC FORAMINIFERA: BENTHO-PELAGIC COUPLING?

Over the lifetime of the Cushman Foundation for Foraminiferal Research the interpretation of deep-sea benthic foraminiferal assemblages has undergone fundamental changes. Deep-sea benthic foraminifera are the most abundant organisms recording life on the deep-sea floor, an extremely oligotrophic habitat receiving less than ~1% of photosynthetically produced organic matter. In the Foundation's early years, benthic foraminiferal assemblages were mainly used as paleobathymetric proxies (Bandy, 1953), though Pflum & Frerichs (1976) noted the importance of riverine organic flux. Low-diversity faunas were recognized as typical for low-oxygen environments in basins off California (Smith, 1964), their morphology recognized in the 1980s (Bernhard, 1986). The early 1970s saw development of the concept that oceanic water masses with a specific temperature, nutrient content, salinity and pH are inhabited by characteristic faunas (Streeter, 1973), thus used to track deep-sea circulation patterns. Further research did not confirm this concept; work off NW Africa (Lutze, 1980) may have led to the understanding that organic flux is most important in controlling benthic life in deep oceanic ecosystems (but see Pflum & Frerichs, 1976). In the TROX model (Jorissen et al., 1995), foraminiferal microhabitats are limited by food-availability in oligotrophic ecosystems, by critical oxygen levels in eutrophic systems. Benthic Foraminiferal Accumulation Rates are used as a proxy for primary productivity in surface waters (Herguera & Berger, 1991), and the abundance of some species reflects episodic phytodetritus falls (Gooday, 1988). However, the organic flux to the sea floor is highly determined by the structure of the biological pump, an important component of the global carbon cycle which influences oceanic storage of dissolved inorganic and organic carbon, thus global climate. Comparison of benthic foraminiferal proxies for arrival of food to the sea floor with proxies for others component parts of the biological pump (e.g., calcareous nannoplankton productivity, biogenic Ba estimates of remineralization) may open new ways to understand the functioning of the whole biological pump across climate changes of the past, from Pleistocene glacial-interglacial cycles to hyperthermal events in a Greenhouse World.