Award: OCE-1533501

The activities undertaken as part of this project resulted in the first comprehensive dataset of dissolved oxygen isotopologues--rare isotopic variants of O₂ such as ¹⁶O¹⁸O, ¹⁷O¹⁸O, and ¹⁸O¹⁸O--in the open ocean, and a demonstration of the utility of such data for future oceanographic questions. To inform interpretations of this dataset, laboratory experiments constrained the isotopic "signatures" of respiratory oxygen consumption and air-sea gas exchange.

The key question at the outset of the project was: What controls dissolved oxygen in the Southern California Bight (SCB), a region where oxygen concentrations have been decreasing steadily for over a decade? To answer this question, isotopologue depth profiles were taken both in the target region and in the NE Pacific between Hawaii and Alaska--a hypothesized source region for low-oxygen waters in the SCB. Importantly, oxygen isotopologues can distinguish between local respiration and water-mass mixing influences. Regional variations in oxygen isotopologues were identified, with NE Pacific waters showing a "fingerprint" that is apparent in the low-oxygen waters of the SCB. In other words, the isotopologue data support the hypothesis that the low-oxygen waters of the NE Pacific strongly influence dissolved oxygen concentrations in the SCB through ocean circulation. The general isotopologue approach may be used in other oceanographic settings as well to answer questions about the factors impacting the size of oxygen-minimum zones in the ocean.

Some technical innovations also arose from this project as well. In addition to developing automated sample preparation techniques for isotopologue analysis, careful calibration procedures were developed for measurements of the ¹⁶O¹⁸O and ¹⁶O¹⁷O isotopologues of oxygen that brought previously unrecognized analytical errors to light, and presented ways to correct for them. These calibration procedures were especially important for "fingerprinting" waters with low oxygen content, and will be useful moving forward for a variety of isotopic measurements.

An undergraduate student, graduate student, and postdoctoral scholar were trained as part of this grant, and public outreach during field sampling trips was conducted through a group social media account that had a sizeable following. The results have been disseminated to the scientific community through conference presentations, university talks, peer-reviewed publications, and book chapters.

Last Modified: 11/30/2018
Modified by: Laurence Y Yeung