Remineralization of particulate organic carbon in an ocean oxygen minimum zone

E L Cavan,M Trimmer,F Shelley,R Sanders

doi:10.1038/ncomms14847

Abstract

Biological oceanic processes, principally the surface production, sinking and interior remineralization of organic particles, keep atmospheric CO2 lower than if the ocean was abiotic. The remineralization length scale (RLS, the vertical distance over which organic particle flux declines by 63%, affected by particle respiration, fragmentation and sinking rates) controls the size of this effect and is anomalously high in oxygen minimum zones (OMZ). Here we show in the Eastern Tropical North Pacific OMZ 70% of POC remineralization is due to microbial respiration, indicating that the high RLS is the result of lower particle fragmentation by zooplankton, likely due to the almost complete absence of zooplankton particle interactions in OMZ waters. Hence, the sensitivity of zooplankton to ocean oxygen concentrations can have direct implications for atmospheric carbon sequestration. Future expansion of OMZs is likely to increase biological ocean carbon storage and act as a negative feedback on climate change.

Highlights

Biological oceanic processes, principally the surface production, sinking and interior remineralization of organic particles, keep atmospheric CO2 lower than if the ocean was abiotic
Determining what controls remineralization length scales (RLS), understanding the processes which control on the fate of organic particles in oxygen minimum zones (OMZ) is important[16]
To determine whether microbial turnover of particulate organic carbon (POC) is reduced in OMZs, giving rise to the large RLS consistently observed, we collected fast and slow-sinking particles from the Eastern Tropical North Pacific (ETNP) OMZ, along a transect from the coast to the open ocean

Summary

Introduction

Biological oceanic processes, principally the surface production, sinking and interior remineralization of organic particles, keep atmospheric CO2 lower than if the ocean was abiotic. We measured bulk POC content and direct measurements of sinking rates to estimate POC flux profiles and RLSs. We measured microbial oxygen consumption under non-limiting oxygen conditions on both fast and slow-sinking particles, together with their organic carbon content, to estimate their relative reactivity or carbon-specific turnover (k). We measured microbial oxygen consumption under non-limiting oxygen conditions on both fast and slow-sinking particles, together with their organic carbon content, to estimate their relative reactivity or carbon-specific turnover (k) Taking these k values and coupling them to our measured sinking rates we can estimate the RLS of particles sinking through the OMZ assuming microbial respiration, and remineralization, either aerobic or anaerobic[22], was the only process involved in reducing organic carbon flux. Our primary results show when the observed RLS was high, microbes were responsible for B 70% of the POC turnover

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