An Inconsistent ENSO Response to Northern Hemisphere Stadials Over the Last Deglaciation

• Published in: Geophysical research letters 2024-06, Vol.51 (12), p.n/a
• Main Authors: Glaubke, Ryan H., Schmidt, Matthew W., Hertzberg, Jennifer E., Ward, Lenzie G., Marcantonio, Franco, Schimmenti, Danielle, Thirumalai, Kaustubh
• Format: Article
• Language: English
• Subjects: abrupt climate change; Atmospheric circulation; Chemical composition; Climate change; Climatic conditions; Deglaciation; eastern Pacific; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; ENSO; Foraminifera; Future climates; Glacial periods; Glacier ice; Glacier melting; Global weather; Holocene; La Nina; Marine sediments; Meltwater; Northern Hemisphere; ocean circulation; Sediments; Southern Oscillation; Temperature variability; Variability; Weather patterns; Wind speed; Younger Dryas; Zooplankton
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL107634

The dynamics shaping the El Niño‐Southern Oscillation's (ENSO) response to present and future climate change remain unclear, partly due to limited paleo‐ENSO records spanning past abrupt climate events. Here, we measure Mg/Ca ratios on individual foraminifera to reconstruct east Pacific subsurface temperature variability, a proxy for ENSO variability, across the last 25,000 years, including the millennial‐scale events of the last deglaciation. Combining these data with proxy system model output reveals divergent ENSO responses to Northern Hemisphere stadials: enhanced variability during Heinrich Stadial 1 (H1) and reduced variability during the Younger Dryas (YD), relative to the Holocene. H1 ENSO likely intensified through meltwater‐induced changes to ocean/atmospheric circulation, a response observed in models, but the lack of a similar response during the YD challenges model simulations. We suggest the tropical Pacific mean state during H1 primed ENSO for larger fluctuations under meltwater forcing, whereas the YD mean state likely buffered against it. Plain Language Summary The El Niño‐Southern Oscillation (ENSO) is one of the planet's largest and most influential recurring climate patterns. The fluctuation between warm (El Niño) and cold events (La Niña) every several years has a substantial impact on global weather patterns that carry important socioeconomic consequences. How the frequency and severity of ENSO events may change in response to present and future climate change is largely uncertain, although lessons from past abrupt climate events can help inform our projections of future ENSO. To that end, we analyzed the chemical composition of small, individual zooplankton shells buried in marine sediments to reconstruct “snapshots” of subsurface temperature variability in the eastern Pacific, a feature closely linked to ENSO, over the last 25,000 years. During this time, two abrupt climate events induced by melting glacial ice (“Heinrich Stadial 1” and the “Younger Dryas”) were characterized by different ENSO responses (stronger and weaker, respectively). We suggest that the average climate conditions in the tropical Pacific (temperature, wind strength, etc.) played an important role by either priming the ENSO system for disruption by meltwater (Heinrich Stadial 1) or buffering against it (Younger Dryas). Key Points Single‐shell foraminiferal trace element ratios reveal a deglacial history of El Niño‐Southern Oscillation's (ENSO) variability from t