Rapid deoxygenation of the Southern California Oxygen Minimum Zone during the Little Ice Age

Abstract:

Recent oxygen minimum zone (OMZ) intensification has been ascribed to warming oceans, yet the extent of natural oceanic dissolved oxygen (DO) variability remains poorly understood. Here we present a high-resolution (4–9 years) redox-sensitive metal record from the Santa Barbara Basin that reconstructs the Southern California OMZ through the Common Era. Rapid OMZ intensification on multidecadal to centennial timescales is generally associated with warmer climate and reveals greater DO variability than observed in instrumental records. However, an anomalous interval of low-DO SBB bottom water during the Little Ice Age (1600–1750 CE) contradicts the expectation of better-ventilated mid-depth North Pacific during cool climate. We attribute this OMZ intensification to declining Sea of Okhotsk ice formation under a weakened Siberian High and Aleutian Low that reduced North Pacific Intermediate Water (NPIW) ventilation. Thus, NPIW ventilation appears very sensitive to atmospheric circulation changes that could amplify future OMZ variability under anthropogenic influences.