LATITUDINAL VARIATIONS IN BENTHIC PROCESSES IN THE ABYSSAL EQUATORIALPACIFIC - CONTROL BY BIOGENIC PARTICLE-FLUX

The equatorial Pacific forms a band of high, globally significant prim ary production. This productivity drops off steeply with distance from equatorial upwelling, yielding large latitudinal gradients in biogeni c particle Aux to the abyssal seafloor. As part of the US JGOFS Progra m, we studied the translation of these particle-flux gradients into th e benthic ecosystem from 12 degrees S to 9 degrees N along 135-140 deg rees W to evaluate their control of key benthic processes, and to eval uate sediment proxies of export production from overlying waters. In O ctober-December 1992 the remineralization rates of organic carbon, cal cium carbonate and biogenic opal roughly matched the rain rates of the se materials into deep sediment traps, exhibiting peak values within 3 degrees of the equator. Rates of bioturbation near the equator were a bout ten-fold greater than at 9 degrees N, and appeared to exhibit sub stantial dependence on particulate-organic-carbon flux, tracer time sc ale (i.e. age-dependent mixing), and pulsed mixing from burrowing urch ins. Organic-carbon degradation within sediments near the equator was dominated by a very labile component (reaction rate constant, k, appro ximately 15 per year) that appeared to be derived from greenish phytod etritus accumulated on the seafloor. Organic-carbon degradation at the highest latitudes was controlled by a less reactive component, with a mean k of approximately 0.075 per year. Where measured, megafaunal an d macrofaunal abundances were strongly correlated with annual particul ate-organic carbon flux; macrofaunal abundance in particular might pot entially serve as a proxy for export production in low-energy abyssal habitats. Sedimentary microbial biomass also was correlated with the r ain rate of organic carbon, but less strongly than larger biota and on shorter time scales (i.e. approximately 100 days). We conclude that t he vertical flux of biogenic particlues exerts tight control on the na ture and rates of benthic biological and chemical processes in the aby ssal equatorial Pacific, and suggest that global changes in productivi ty on decadal or greater time scales could yield profound changes in d eep-sea benthic ecoystems. (C) 1998 Elsevier Science Ltd. All rights r eserved.