Earth system instability explains redox paradox during late Cambrian SPICE event

Area of Science:

• Geochemistry
• Paleoceanography
• Biogeochemical Cycles

Background:

• The late Neoproterozoic-early Paleozoic experienced shifts from ocean oxygenation events (OOEs) to ocean anoxic events (OAEs).
• The Cambrian SPICE event is a significant early Paleozoic OAE, but its causes are debated.
• Understanding these redox changes is key to early animal evolution.

Purpose of the Study:

• Investigate the drivers and dynamics of the Cambrian SPICE event.
• Reconstruct the ocean redox conditions during the SPICE event.
• Reconcile the pre-SPICE redox paradox using biogeochemical modeling.

Main Methods:

• Analysis of carbonate uranium isotope (δ238Ucarb) data from North and South China.
• Utilizing refined COPSE (Carbon, Oxygen, Phosphorus, Sulphur, and Evolution) biogeochemical modeling.
• Integrating isotopic data with paleoclimate and paleoceanographic proxies.

Main Results:

• A sharp decrease in δ238Ucarb values at the SPICE onset indicates rapid global ocean anoxia.
• Subsequent return to pre-excursion values suggests a transition to oxic conditions.
• COPSE modeling reconciles low atmospheric pO2 with limited seafloor anoxia before SPICE.

Conclusions:

• The SPICE event reflects non-steady-state Earth system behavior with oscillating biogeochemical cycles.
• Coupled phosphorus-oxygen-carbon-sulfur and uranium cycles played a critical role.
• Redox-dependent biodiversity filters influenced early animal evolution during these events.