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Abstract El Niño–Southern Oscillation (ENSO) dominates interannual climate variability; thus, understanding its response to climate forcing is critical. ENSO's sensitivity to changing insolation is poorly understood, due to contrasting interpretations of Holocene proxy records. Some records show dampened ENSO during the early to mid‐Holocene, consistent with insolation forcing of ENSO amplitude, but other records emphasize decadal‐centennial fluctuations in ENSO strength, with no clear trend. To clarify Holocene ENSO behavior, we collected proxy data spanning the last ~12 kyr and find relatively low El Niño amplitude during the early to mid‐Holocene. Our data, together with published work, indicate both a long‐term trend in ENSO strength due to June insolation forcing and high‐amplitude decadal‐centennial fluctuations; both behaviors are shown in models. The best supported mechanism for insolation‐driven dampening of ENSO is weakening of the upwelling feedback by insolation‐forced warming/deepening of thermocline source waters. Elucidating the thermocline's role will help predict future ENSO change.
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Pacific warm pool subsurface heat sequestration modulated Walker circulation and ENSO activity during the Holocene
Dynamics driving the El Niño–Southern Oscillation (ENSO) over longer-than-interannual time scales are poorly understood. Here, we compile thermocline temperature records of the Indo-Pacific warm pool over the past 25,000 years, which reveal a major warming in the Early Holocene and a secondary warming in the Middle Holocene. We suggest that the first thermocline warming corresponds to heat transport of southern Pacific shallow overturning circulation driven by June (austral winter) insolation maximum. The second thermocline warming follows equatorial September insolation maximum, which may have caused a steeper west-east upper-ocean thermal gradient and an intensified Walker circulation in the equatorial Pacific. We propose that the warm pool thermocline warming ultimately reduced the interannual ENSO activity in the Early to Middle Holocene. Thus, a substantially increased oceanic heat content of the warm pool, acting as a negative feedback for ENSO in the past, may play its role in the ongoing global warming.
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- Award ID(s):
- 1834208
- PAR ID:
- 10377344
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 6
- Issue:
- 42
- ISSN:
- 2375-2548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1126/sciadv.abc0402
