Ocean Deoxygenation Conference | Kiel 2018

Marine oxygen minimum zones (OMZs) harbor diverse microbial communities that play a major role in global biogeochemical cycles. The Eastern Tropical South Pacific designates a dynamic yet persistent OMZ driven by strong upwelling that replenishes the surface nutrient supply and fuels primary production. A rapid flux of detrital organic matter from the surface drives strong vertical chemical gradients as well as changes in redox conditions through the water column. These gradients have been associated with significant restructuring of extant microbial communities in addition to indications of physiological responses to changing conditions. Microbial dynamics are relevant to understanding the trophic states of broad expanses of oxygen deficient waters, in addition to the cycling of biologically relevant elements such as nitrogen and carbon. The taxonomic composition of microbial communities can be described through analysis of the composition, distribution, and structural characteristics of cell membrane lipids also known as intact polar lipids (IPLs; a form of biomarker) in suspended particulate organic matter. In this study, we present the vertical distribution of IPLs through water columns experiencing varying chemical gradients associated with the OMZ off the coast of Iquique, northern Chile. Our analysis shows a great diversity in membrane lipid production and denotes transitions in IPL distributions between distinct microbial assemblages in relation to increasing oxygen deficiency and varying nutrient availability from two nearshore sites along the Humboldt Current system. We discuss the implications of these results in the study of microbial communities of modern OMZs using gene-independent techniques, as well as the potential application of these biomarkers to study microbial processes in the past as preserved in sedimentary records.