Sedimentation of planktonic foraminifera; seasonal changes in species flux in the Panama Basin

Seasonal changes in the flux of individual planktonic foraminiferal species to the sea floor have been studied in the Panama Basin using material collected in one year by an array of automated sediment traps. The traps were placed at three depths in the water column, at 890, 2590, and 3560 m, with each designed to collect a time-series of six consecutive two-month samples. In general, two basic seasonal flux patterns were recognized from these records of each species. One group of species is marked by a distinct maximum in flux during February and March, in association with the period of most extensive upwelling in the Panama Basin. The species that display this flux pattern are typically nonspinose and live predominantly at or below the thermocline, then migrate toward the surface as upwelling intensities. The second group displays more of a bimodal seasonal flux pattern, with maximum values during June through August and a secondary peak in February and March. This group consists primarily of the spinose species that live above the thermocline in the mixed zone and possess symbiotic zooxanthellae. The increase in flux of these species during the summer occurs when the mixed zone is relatively deep and is associated with a phytoplankton bloom, while the winter increase occurs during the upwelling of nutrient-rich waters.