Expansion of Ocean Anoxia During Glacial Periods Recorded in the Cobalt Flux to Pelagic Sediments

• Published in: Geophysical research letters 2023-10, Vol.50 (19), p.n/a
• Main Authors: Hawco, Nicholas J., Foreman, Rhea K.
• Format: Article
• Language: English
• Subjects: Anoxia; Anthropogenic climate changes; Anthropogenic factors; Climate change; Cobalt; Deoxygenation; Diagenesis; Fish; GEOTRACES; glacial cycles; Glacial periods; Heavy metals; Holocene; Ice ages; Last Glacial Maximum; manganese oxides; Oceans; Oxygen; oxygen deficient zone; Oxygen enrichment; Pelagic sediments; Plumes; Sediments; Transient response
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL105135

The expansion of oxygen deficient zones (ODZs) within the ocean's interior is anticipated to be a major consequence of anthropogenic climate change, but past changes in ODZs are poorly defined. Recent mapping efforts have revealed plumes of the redox‐active metal cobalt within ODZs, driving a basin‐scale correlation between high cobalt and low O2. Here, we investigate the cobalt flux to Equatorial Pacific sediments along the Line Islands Ridge as a novel record of basin‐scale fluctuations in ODZ extent. After accounting for remobilization by diagenesis, we document a ∼40% increase in cobalt accumulation over the last glacial period, with a more pronounced peak during the Last Glacial Maximum, indicative of larger ODZs compared to the Holocene. Our results link ODZ expansion with colder climates and lend support to model‐based assertions that ongoing deoxygenation may reflect a transient response to warming. Plain Language Summary Climate change is linked to a decline in ocean oxygen levels, impacting fish and other organisms that need oxygen to breathe. Knowledge of past changes in ocean oxygen would help put ongoing deoxygenation trends into context. In this study, we investigated changes in oxygen in the Pacific Ocean over the past 145,000 years. Because low‐oxygen waters are enriched in the metal cobalt, we reconstructed the cobalt abundance of the past oceans as a proxy for oxygen. During the past two Ice Ages, when Earth was colder than today, we find evidence for higher cobalt, and therefore an expansion of oxygen‐poor waters. Key Points The cobalt flux to pelagic sediments reflects heightened sources associated with Oxygen Deficient Zones In Equatorial Pacific sediments, cobalt flux increased by ∼40% during the Last Glacial Period, compared to the Holocene Oxygen Deficient Zones likely expanded during the previous two glacial periods