Holocene hydroclimatic variability in the tropical Pacific explained by changing ENSO diversity

Abstract

Understanding El Niño-Southern Oscillation (ENSO) response to past climate forcings is hindered by conflicting paleoclimate evidence. Records from the eastern Pacific show an intensification of ENSO variability from early to late Holocene, while records from the central Pacific show highly variable ENSO throughout the Holocene without an obvious relation to insolation forcing, which is the main climate driver during this interval. Here, we show via climate model simulations that conflicting Holocene records can be reconciled by considering changes in the relative frequency of the three preferred spatial patterns in which El Niño events occur (Eastern Pacific, Central Pacific, and Coastal) and in the strength of their hydroclimatic impacts. The relationship between ENSO diversity and variance is not only crucial for interpreting paleo-ENSO records and understanding ENSO response to external forcings but can also be used across climate model simulations to help evaluate the realism of ENSO projections in a changing climate.

Extreme coastal El Niño events are tightly linked to the development of the Pacific Meridional Modes

“…Our results also have implications for the interpretation of climate simulations and long-term reconstructions of ENSO diversity (e.g., [21,56]). In particular, the link of extreme coastal El Niño events with PMMs established here calls to contrasting proxies of El Niño impacts in the far eastern Pacific (high temperatures, flooding, impacts on marine ecosystems) with proxies from the PMMs regions (e.g., off Southern California coast, where the NPMM has a strong loading) in order to reconcile information in a range of proxy records and for testing models of future El Niño behavior under climate change.…”

Borneo Stalagmite Evidence of Significantly Reduced El Niño‐Southern Oscillation Variability at 4.1 kyBP

“…A collection of corals from the northern South China Sea (SCS) grew within the 4.1–4.5 kyBP window and indicate cooler and possibly wetter conditions at this time (Dang et al., 2020; X. Chen et al., 2023). One study hypothesizes that the SCS coral records indicate weak ENSO intensity (Dang et al., 2020), while a second study suggests the SCS data, combined with the Line Island coral records, indicates more frequent Central Pacific (CP) El Niño events relative to East Pacific (EP) El Niño events (X. Chen et al., 2023), citing the Community Earth System Model v1 (CESM1) simulation results from Karamperidou and DiNezio (2022). From the 2006–2018 Mulu rainwater δ 18 O monitoring alone, it is not yet clear if CP and EP El Niño events influence Mulu rainwater δ 18 O differently.…”

Coral Paleoclimate Perspectives Support the Role of Low‐Latitude Forcing on the 4.2 ka BP Event

“…A recent study indicates that ENSO diversity, for example, CP El Niño versus EP El Niño, modulates ENSO variance during the Holocene (Karamperidou & DiNezio, 2022). Accordingly, a decrease in the ratio of EP/CP El Niño leads to a reduction in ENSO variability (Karamperidou & DiNezio, 2022). If this hypothesis holds, a decrease in ENSO variability during the transition from the mid‐ to late‐Holocene would indicate either a decrease in EP El Niño or an increase in CP El Niño.…”

“…This is consistent with the sediment record from El Junco in the Eastern Pacific (EP) (Z. Zhang et al., 2014) (Figure S8 in Supporting Information ), which also supports a muted ENSO variance around the 4.2 ka BP period. A recent study indicates that ENSO diversity, for example, CP El Niño versus EP El Niño, modulates ENSO variance during the Holocene (Karamperidou & DiNezio, 2022). Accordingly, a decrease in the ratio of EP/CP El Niño leads to a reduction in ENSO variability (Karamperidou & DiNezio, 2022).…”