RADIOLARIAN FLUXES, STOCKS, AND POPULATION RESIDENCE TIMES IN SURFACEWATERS OF THE CENTRAL EQUATORIAL PACIFIC

Radiolarian settling fluxes and standing stocks from the central equat orial Pacific are more indicative of physical process than the living environment of the organism. Polycystine radiolaria were collected fro m plankton and in moored sediment traps along longitude 140 degrees W during both warm and cold phases of the 1992 ENSO as part of the US JG OFS Equatorial Pacific program (EqPac). Highest shell fluxes occurred at the 5 degrees N and 5 degrees S trapsites, roughly the boundary bet ween equatorial and subtropical environments. The sediment trap sample s collected at these sites were composites of different living assembl ages that live equatorward, poleward and, in some cases, directly with in the overlying water. Stock to flux ratios indicate an average radio larian residence time of around one week within the 5 degrees N to 5 d egrees S equatorial band. The population residence time for Didymocyrt is tetrathalamus, which dominated the plankton during El Nino, is 3 we eks. Key indicator species of the cold tongue;period, Tetrapyle octaca ntha (subtropical) and Lophophaena hispida (equatorial), have residenc e times slightly less than one week. This suggests environmental forci ng can fundamentally alter community composition by limiting which spe cies populations can be maintained under certain advective and mixing regimes. In this way, seasonal to interannual oscillations in the meri dional current can control the composition of radiolarian communities. T. octacantha exhibited the highest stocks and fluxes of any radiolar ia, which implies high sediment abundance of this species reflects hig h input versus preferential preservation. Correlations between fluxes of radiolaria and organic carbon indicate the radiolaria play a larger role in the plankton community within the gyre margin environment tha n at the lower latitude sites. (C) 1998 Elsevier Science B.V. All righ ts reserved.