Pyrite sulfur isotopes reveal glacial-interglacial environmental changes

Area of Science:

• Geochemistry
• Biogeochemistry
• Paleoclimatology

Background:

• The sulfur biogeochemical cycle influences Earth's redox state via various reactions with distinct isotopic fractionations.
• Sulfur isotopic composition (δ34S) in sedimentary sulfate and sulfide phases tracks Earth's environmental changes, including atmospheric oxygenation.
• Interpreting pyrite-based δ34S records requires understanding depositional controls, as they may not solely reflect global sulfur cycle changes.

Purpose of the Study:

• Investigate alternative controls on the sedimentary sulfur isotopic composition of marine pyrite.
• Examine δ34S variations in pyrite over the past 500,000 years, spanning five glacial-interglacial periods.

Main Methods:

• Analyzed a 300-m drill core of Mediterranean sediments.
• Examined stratigraphic variations in the sulfur isotopic composition of pyrite (δ34Spyr).

Main Results:

• Observed significant stratigraphic variations (>76‰) in δ34Spyr, synchronized with glacial-interglacial sea level and temperature changes.
• Identified glacial-interglacial variations in sedimentation rates as the dominant control on sedimentary pyrite's sulfur isotopic composition.
• Demonstrated that pyrite δ34S records can reflect local environmental changes, especially during periods of significant sea-level fluctuation.

Conclusions:

• Depositional factors, particularly sedimentation rates during sea-level changes, significantly influence sedimentary sulfur isotope records.
• Pyrite δ34S records provide valuable paleoenvironmental information, reflecting local rather than solely global sulfur cycle dynamics.
• Revises the interpretation of sedimentary sulfur isotope records, highlighting the importance of depositional context.