Environmental control on phytoplankton size-fractionated primary production in the tropical and subtropical Atlantic, Indian and Pacific oceans

Abstract

Phytoplankton primary production and its distribution amongst different size classes play a critical role in the functioning of pelagic marine ecosystems both from an ecological and biogeochemical point of view. Around a quarter of global marine primary production occurs in tropical and subtropical latitudes of the world’s oceans. Current knowledge about the variability of size-fractionated primary production in the open ocean is constrained because the limited number of cruises covering large temporal and spatial scales and using the same methodological approaches. Here we report estimates of pico-, nano- and microphytoplankton primary production obtained during the 2010 Malaspina circumnavigation Expedition. Size-fractionated carbon fixation rates were estimated with the 14C-uptake technique at 5 depths in 147 stations sampled along the tropical and subtropical Atlantic, Pacific and Indian oceans. The estimates carried out in the Indian and South Pacific oceans highlight because, as far as we know, not many direct observations of the size structure and metabolism of phytoplankton communities have been done before in these oceanic regions. The patterns obtained in phytoplankton size-fractionated primary production were related to changes in environmental forcings, including the input of nutrients into the euphotic zone through vertical diffusion. These results provide new insights about how nutrient supply dynamics to the upper ocean controls marine primary production and therefore influences global biogeochemical cycles