What question did this study set out to answer?

This research aims to investigate how oxygen minimum zones (OMZs) in the Eastern Tropical North Pacific changed during the last deglaciation.

April 30, 2026

Expansion of the Eastern Tropical North Pacific Oxygen Minimum Zone During the Last Deglaciation Recorded by Planktic Foraminifera

Key Points

This research aims to investigate how oxygen minimum zones (OMZs) in the Eastern Tropical North Pacific changed during the last deglaciation.
Analyzed planktic foraminiferal assemblages and geochemical records from core MAZ‐1E‐04.
Utilized radiocarbon ventilation ages and isotopic data (δ 18 O, δ 13 C, and δ 15 N) to assess OMZ responses.
Considered bottom water ventilation shifts and habitat depth changes of foraminifera.
OMZ intensified during the mid-deglaciation compared to the Last Glacial Maximum, with potential shifts in bottom water ventilation.
Evidence of OMZ shallowing around 14 ka with expansions near the thermocline.
No consistent productivity shifts were found, indicating ventilation as the primary restructuring driver.

Abstract

Abstract Climate change is currently driving the expansion of oxygen minimum zones (OMZs), areas of the open ocean with consistently low oxygen levels. Changes in temperature, productivity and consequent respiration, and water mass ventilation drive OMZ expansion and contraction with implications for ecosystem function and biogeochemical cycling. However, there is uncertainty in how OMZs respond to climatic change on longer timescales. The structure and drivers of OMZ change in the Eastern Tropical North Pacific (ETNP) are investigated through the most recent period of rapid warming (∼20.7–10 ka) using planktic foraminiferal assemblages, radiocarbon ventilation ages, foraminiferal δ 18 O, δ 13 C, I/Ca records, and bulk sediment δ 15 N. Evidence from core MAZ‐1E‐04 (22°54.29′N, 106°54.59′W; 1,463 m depth) from the Mexican Margin shows the OMZ intensified during the mid‐deglaciation relative to the Last Glacial Maximum (LGM) with potential shifts in bottom water ventilation. Oxygen isotopes from planktic foraminifera at multiple depth habitats, including OMZ dweller Globorotaloides hexagonus , indicate shallowing of the OMZ ∼14 ka with continued expansion near the thermocline through the mid‐deglaciation. No systematic shifts in productivity are captured by the records, suggesting ventilation as the primary driver of OMZ restructuring at this site. Radiocarbon ventilation ages provide evidence for a potential decoupling of intermediate and shallower waters with a boundary ∼1–1.5 km; however, open questions about radiocarbon ventilation ages near Baja California warrant a careful interpretation of this record.

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