Mapping plankton biomass in the deep-ocean: an ecological provinces approach

Abstract

The distribution of epipelagic plankton biomass by size-fractions was studied during Malaspina-2010 expedition across the Indian, Pacific and Atlantic oceans. The objective was to characterize plankton biomass structure at large spatial scales in poorly explored areas of the ocean. Samples from 95 stations, representative of 3 of major ocean biomes and 12 ecological provinces, were fractionated in 5 size-classes (40 to 5000 μm) and biomass determined as dry weight. Mean plankton biomass was similar for all oceans and major biomes but varied significantly between provinces, being particularly high in the N Pacific Equatorial Countercurrent and in the Caribbean provinces. The differences were mainly due to increases in medium-sized plankton, while for most provinces the biomass was uniformly distributed across logarithmic size-classes. Total and size-class plankton biomass was negatively and non-linearly correlated with the mixing layer depth and with the depth of the chlorophyll maximum across provinces. In contrast only the biomass of the smaller plankton was positively and linearly correlated with sea surface temperature, while the biomass of other size-classes was positively affected by the thermal stratification gradient in the upper layer. The obtained relationships will improve our ability to monitor and model the ocean response to global change