Benthic foraminiferal response to major paleoceanographic changes - A view of the deep-sea restaurant menu

Relative and absolute abundances of fossil benthic foraminifera are widely used in attempts to understand the deep-sea environment and its variability in space and time. Recent studies in the present-day ocean have demonstrated that a strong bentho-pelagic coupling exists even in deep water because the fluxes of organic matter from primary producers in the photic zone are the main supply of food (energy) to benthic communities in the severely food-limited deep sea. In the present oceans, these fluxes vary not only in magnitude but also in pattern: 1) Mainly seasonal accumulations on the sea floor of fresh, little degraded, fluffy aggregates, resulting from massive phytoplankton blooms. 2) Fecal pellets produced by zooplankton, which deliver more degraded organic matter to the sea floor with a less obvious seasonal pattern. 3) Constant delivery of particulate organic matter (POM) in the dilute "marine snow". 4) Lateral supply of particulate organic matter by bottom currents. Benthic foraminiferal faunas reflect these patterns in their species composition. In this study, we used observations of biological oceanographers in an attempt to increase understanding of benthic foraminiferal faunal structure and accumulation rates over the last 150 kyr in cores from the northern North Atlantic and Southwest Pacific. Over this period of major climatic changes, faunas at these two widely separated regions show time-successive changes as a result of change in the mode and magnitude of the food supply from the surface waters The faunal changes are interpreted as resulting from different direct causes in the two regions: changes in productivity linked to ice-edge fluctuations in the northern North Atlantic, frontal movements in the Southwest Pacific.