Expanded subsurface ocean anoxia in the Atlantic during the Paleocene-Eocene Thermal Maximum

Area of Science:

• Paleoceanography
• Marine Biogeochemistry
• Climate Change Science

Background:

• The ocean is losing oxygen, impacting marine life and fisheries.
• Hyperthermal events like the Paleocene-Eocene Thermal Maximum (PETM) provide analogs for future ocean deoxygenation.
• Understanding past deoxygenation events is crucial for predicting future ocean dynamics.

Purpose of the Study:

• To investigate ocean deoxygenation dynamics during the PETM.
• To understand the biogeochemical processes driving oxygen loss in ancient oceans.
• To assess the spatial variability of deoxygenation during past warming events.

Main Methods:

• Analysis of sediment cores from the South Atlantic.
• Measurement of foraminifera-bound δ¹⁵N and marine barite δ³⁴S.
• Oceanographic model simulations to investigate ODZ formation and drivers.

Main Results:

• Evidence of declining foraminifera-bound δ¹⁵N and increasing marine barite δ³⁴S during the PETM.
• Indication of enhanced ocean productivity and expansion of oxygen-deficient zones (ODZs) from suboxia to anoxia in the Atlantic thermocline.
• Model simulations identified Southern Ocean warming and high productivity as drivers of 'ammonium-type' ODZs.

Conclusions:

• The PETM led to anoxic conditions in parts of the Atlantic thermocline, characterized by ammonium and sulfide accumulation.
• Intense nitrogen loss and increased phosphorus likely stimulated N₂ fixation.
• Ocean deoxygenation during warming events can exhibit significant spatial variability, as suggested by potential differences in the Pacific.