CALCIFICATION RATES IN THE EQUATORIAL PACIFIC ALONG 140-DEGREES-W

The calcite standing stock, calcification rate, concentrations of deta ched coccoliths and plated coccolithophore cells were determined in th e equatorial Pacific along 140 degrees W, between 12 degrees N and 12 degrees S latitude, during August and September 1992. Continuous surfa ce optical and fluorescence measurements were also taken along this tr ansect. Integrated calcification ranged between 3 and 12% of the total carbon fixed into particulate matter. Calcification exceeded 50% of t he total fixed carbon (per unit volume) at specific depths from the no rthern-most oligotrophic stations. A pronounced subsurface peak in sus pended calcite was noted near the equator. Calcification was considera bly more patchy than photosynthesis. Normalizing the calcification rat es to the surface area of calcite-producing species provided an estima te of the extracellular calcite flux rates. These results showed that the populations from the equator to 3 degrees N at 60 m depth, and nea r the surface from the equator to 9 degrees S were the most active cal cite producers. Underway estimates of light scattering showed the impo rtance of upwelling for bringing cold, clear, relatively particle-free water to the surface, followed by growth and calcite production as th e water warmed. When temperatures reached their upper range (about 28. 8 degrees C), light scattering decreased again, presumably as growth s lowed and particles sank. Integrated calcification estimates averaged over the equatorial region were compared to sediment trap data; the re sults suggest significant disappearance of calcite particles in the to p 1000 m, above the lysocline. One hypothesis to explain this is that dissolution occurred in microzones where decomposition of reduced orga nic matter lowered the pH sufficiently to dissolve calcite. Copyright (C) 1996 Elsevier Science Ltd.