Reorganized atmospheric circulation during the little ice age leads to rapid Southern California deoxygenation

Abstract

The magnitude of natural oceanic dissolved oxygen (DO) variability remains poorly understood due to the short duration of the observational record. Here we present a high-resolution (4–9 years) reconstruction of the Southern California oxygen minimum zone (OMZ) through the Common Era using redox-sensitive metals. Rapid OMZ intensification on multidecadal timescales reveals greater DO variability than observed in instrumental records. An anomalous interval of intensified OMZ between 1600–1750 CE contradicts the expectation of better-ventilated mid-depth North Pacific during cool climates. Although the influence of low-DO Equatorial Pacific Intermediate Water on the Southern California Margin was likely weaker during this interval, we attribute the observed rapid deoxygenation to reduced North Pacific Intermediate Water (NPIW) ventilation. NPIW ventilation thus appears very sensitive to atmospheric circulation reorganization (e.g., a weakened Siberian High and Aleutian Low). In addition to temperature-induced gas solubility, atmospheric forcing under future anthropogenic influences could amplify OMZ variability.