Determination of respiratory processes in the Oxygen Deficient Zone of the Eastern Tropical North Pacific using targeted proteomics

Abstract

The majority of the ocean contains sufficient oxygen to support aerobic respiration. However, when oxygen concentrations fall to levels of 10 umol/kg or less, microorganisms utilize alternative electron acceptors such as nitrogen and sulfur during respiration. Regions of the ocean where this occurs are called Oxygen Deficient Zones (ODZ). Bacteria play a pivotal role in cycling nutrients through such anaerobic pathways as denitrification, and the sulfur cycle, as well as through the chemoautotrophic process, anammox, which is an important component of the energy web in ODZs. Suspended particulate organic matter, containing these bacteria, was collected in the Eastern Tropical North Pacific (ETNP). Six samples were analyzed, using targeted proteomics, to establish the presence and relative magnitudes of each of these processes. Denitrification, anammox, and sulfur cycling occur simultaneously at all six depths sampled between 50-1200m, as opposed to occurring in single process dominated zones. Despite this overlap in zonation, the relative proportions of one process over another does change with depth. This research also provides insight into the expanding concept of anoxic microzones within particles suspended in low oxygen regions of the ocean.