Calcification rates in the equatorial Pacific along 140°W

The calcite standing stock, calcification rate, concentrations of detached coccoliths and plated coccolithophore cells were determined in the equatorial Pacific along 140°W, between 12°N and 12°S latitude, during August and September 1992. Continuous surface optical and fluorescence measurements were also taken along this transect. Integrated calcification ranged between 3 and 12% of the total carbon fixed into particulate matter. Calcification exceeded 50% of the total fixed carbon (per unit volume) at specific depths from the northern-most oligotrophic stations. A pronounced subsurface peak in suspended calcite was noted near the equator. Calcification was considerably more patchy than photosynthesis. Normalizing the calcification rates to the surface area of calcite-producing species provided an estimate of the extracellular calcite flux rates. These results showed that the populations from the equator to 3°N at 60 m depth, and near the surface from the equator to 9°S were the most active calcite producers. Underway estimates of light scattering showed the importance of upwelling for bringing cold, clear, relatively particle-free water to the surface, followed by growth and calcite production as the water warmed. When temperatures reached their upper range (about 28.8°C), light scattering decreased again, presumably as growth slowed and particles sank. Integrated calcification estimates averaged over the equatorial region were compared to sediment trap data: the results suggest significant disappearance of calcite particles in the top 1000 m, above the lysocline. One hypothesis to explain this is that dissolution occurred in microzones where decomposition of reduced organic matter lowered the pH sufficiently to dissolve calcite.