The South East Pacific (SEP) is characterized by very high nutrient concentrations
in the waters adjacent to the Chilean coast, but very low nutrient concentrations (oligotrophic)
in the mid- South Pacific Subtropical Gyre (SPSG), near Easter Island. The steep gradient in
nutrient concentrations across the region affects the level of marine production, the composition
of the microbial community, and the operation of major biogeochemical cycles in ways that are not
fully understood. Despite the remarkable diversity of trophic conditions, strong gradients and
even some unique singularities, the SEP is still the most sparsely sampled oceanic region of the
global ocean from hydrodynamic, biological and biogeochemical points of view. The SPSG is also the
most oligotrophic of all sub-tropical gyres.
Previous expeditions and remote sensing studies have describes the nutrient and
chlorophyll field, but there have been few simultaneous measurements of chemical properties with
microbial community structure and function. This expedition was designed to investigate the impact
of elemental nutrient (nitrogen, phosphorus, iron, silicon, carbon) ratios on marine productivity
and microbial community composition.