OXYGEN-LIMITED METABOLISM AND THE PERSISTENCE OF OXYGEN DEPENDENT ORGANIC MATTER (ODDOM) IN HYPOXIC MARINE ENVIRONMENTS

In oxygen minimum zones (OMZs), the transition to hypoxia plays a pivotal role in determining the fate of organic matter. The Hypoxic Barrier Hypothesis predicts that as oxygen declines, oxygenase enzymes—which are crucial for the degradation of many organic compounds—become oxygen-limited long before respiration slows. This limitation may partly explain why oxygen declines tend to stall in the hypoxic range without progressing to anoxia. We conducted mesocosm experiments to investigate how controlled hypoxia affects organic matter lability and microbial community metabolism over an extended period. We hypothesized that compounds requiring oxygenase-mediated degradation would accumulate under hypoxic conditions and could be classified as oxygen-dependent dissolved organic matter (ODDOM). The data reveal a shift toward recalcitrant dissolved organic matter (RDOM) in the hypoxic treatment, where compounds resembling ODDOM accumulated. In other experiments, microbial respiration rates were lower in hypoxic conditions when communities were provided with model ODDOM compounds, relative to control experiments with oxygenase-independent carbon sources. Our findings highlight the relationship between oxygen availability, microbial metabolism, and organic matter lability. This research contributes to a better understanding of how OMZs and other low-oxygen environments influence the biogeochemical cycling of carbon. These results offer critical insights into the roles of both biotic and abiotic factors in regulating the transformation and fate of organic matter in aquatic systems.

Presentation Preference: Either

Primary Presenter: Benjamin Daniels, Oregon State University (danieben@oregonstate.edu)

Authors:

Benjamin Daniels, Oregon State University  (danieben@oregonstate.edu)

Sarah Wolf, Oregon State University  (wolfs2@oregonstate.edu)

Qi Chen, Oregon State University  (chenq7@oregonstate.edu)

Kayla Stanley, Oregon State University  (stanlkay@oregonstate.edu)

Gillian St John, Oregon State University  (stjohng@oregonstate.edu)

Abzer Pakkir Shah, University of California Riverside  (abzer.kelmina@gmail.com)

Edward Davis, Oregon State University  (ed@cqls.oregonstate.edu)

Daniel Petras, University of California Riverside  (dpetras@ucr.edu)

Craig Carlson, University of California Santa Barbara  (craig_carlson@ucsb.edu)

Francis Chan, Oregon State University  (Francis.Chan@oregonstate.edu)

Stephen Giovannoni, Oregon State University  (steve.giovannoni@oregonstate.edu)