A well-oxygenated eastern tropical Pacific during the warm Miocene

Area of Science:

• Paleoceanography
• Climate Science
• Marine Biogeochemistry

Background:

• Ocean oxygen content is declining due to climate change, particularly in oxygen-deficient zones (ODZs).
• Earth-system models predict ODZ expansion until 2100, but long-term responses remain uncertain.

Purpose of the Study:

• Investigate ocean oxygenation changes during the warmer-than-present Miocene Climatic Optimum (MCO).
• Understand the long-term response of ocean oxygenation to warming events.

Main Methods:

• Analyzed planktic foraminifera I/Ca and δ15N data as proxies for ODZ extent and intensity.
• Used Mg/Ca data to reconstruct sea surface temperatures.
• Compared paleoceanographic data with Earth-system model simulations.

Main Results:

• Dissolved-oxygen concentrations in the eastern tropical Pacific (ETP) exceeded 100 µmol kg−1 during the MCO.
• An ODZ developed due to increased west-to-east temperature gradients and shoaling of the ETP thermocline.
• Weaker trade winds during warm periods may reduce ETP upwelling, concentrating productivity and oxygen demand eastward.

Conclusions:

• Warm climate states, like the MCO, influence ocean oxygenation patterns.
• Findings support models suggesting a potential reversal of recent deoxygenation trends and ETP ODZ expansion under future warming scenarios.