| Physical discontinuities and meridional advection play key roles in radiolarian distribution and abundance in the equatorial Pacific. Plankton samples, collected along 140{dollar}spcirc{dollar}W as part of the US JGOFS Equatorial Pacific program (EqPac), define living ecological assemblages during both warm and cold phases of the 1992 ENSO. Sediment trap samples provide a time series of radiolarian fluxes, establishing the necessary linkage between surface ocean processes and preservation in the sediment record. The data identified the fundamental contrast in this region between warm, subtropical and cool, equatorial environments. Leading indicator species for these two environments are Tetrapyle octacantha and Lophophaena hispida, respectively. Both species had highest standing stocks in association with a convergent tropical instability wave (TIW) front sampled during the cold phase of ENSO. Radiolarian stocks were subducted from the surface of the front near 2{dollar}spcirc{dollar}N to 100 km northward and over 80 meters depth. Comparison of plankton and trap data also demonstrates specific ways in which living assemblages are transformed into sediment death assemblages. "Cold" water end members leaving the system represent a depth integration of surface/equatorial and subsurface/transitional species, while "warm" export assemblages are primarily a mixture of subtropical and western Pacific forms. Meridional recirculation advects radiolaria poleward within the latitudinal band of 5{dollar}spcirc{dollar}S to 5{dollar}spcirc{dollar}N. Redistribution of stocks is most pronounced during the cold phase of ENSO. Calculation of radiolarian residence times further implicate meridional redistribution as important not only to plankton distributions, but suggest fluctuations in the strength of the meridional current might fundamentally alter the composition of the radiolarian community by controlling which species populations can survive. Lifespans of both average radiolaria and important indicator species were longer during El Nino than during the cold tongue period. Sediment death assemblages defined outside the central equatorial Pacific are directly related to assemblages defined in the regional plankton study, while the Tropical sediment assemblage represents a mixture of more than one ecological environment. While lack of certain species in the sediment death assemblages contributed to loss of some ecological information, in some cases this can be compensated for by the broad spatial coverage of the basin-wide sediment data set. |
