Carbon isotopic evidence for methane hydrate instability during quaternary interstadials

Area of Science:

• Paleoceanography
• Marine geochemistry
• Climate science

Background:

• Millennial-scale carbon isotopic oscillations observed in benthic foraminifera from the Santa Barbara Basin.
• These oscillations suggest changes in sedimentary methane gradients and gas hydrate dissociation over the last 60,000 years.

Purpose of the Study:

• To investigate the causes of millennial-scale carbon isotopic oscillations in the Santa Barbara Basin.
• To understand the role of gas hydrate dissociation in these oscillations and their potential impact on atmospheric methane.

Main Methods:

• Analysis of benthic and planktonic foraminiferal carbon isotopes over the last 60,000 years.
• Correlation of isotopic data with paleoceanographic proxies and climate records.

Main Results:

• Large millennial-scale carbon isotopic oscillations (approx. 5 per mil) reflect methane outgassing from gas hydrate dissociation during interstadials.
• Brief, negative excursions (up to -6 per mil) indicate massive methane releases from basin sediments.
• Gas hydrate stability was influenced by intermediate-water temperature changes linked to thermohaline circulation shifts.

Conclusions:

• Methane hydrate dissociation and subsequent methane release significantly impacted millennial-scale carbon cycles.
• These processes likely contributed to widespread atmospheric methane oscillations along the California margin and potentially globally.
• Thermohaline circulation played a key role in modulating gas hydrate stability.