A Southwest Pacific Coral Perspective on ENSO Variability: Precessional Forcing vs. Internal Variability

Abstract:

ENSO variability is manifest in the western Pacific through heat and moisture exchanges associated with the Western Pacific Warm Pool (WPWP) and the South Pacific Convergence Zone (SPCZ). Forward modeling (pseudoproxy analysis) results and published coral proxy records from the tropical Pacific indicate that in addition to the central and eastern Pacific regions, corals from the WPWP and SPCZ regions skillfully record ENSO variability. Some studies suggest that precessional forcing directly reduces/enhances ENSO variability. Other studies suggest that internal variability is the primary control on Holocene ENSO changes. Herein, we use coral proxy records from the tropical Pacific and numerical simulations to better understand the response of ENSO to precessional forcing and internal variability.

We extend the coral record of ENSO variability using a new modern coral record from the Solomon Islands (1716-2008 CE) and a select suite of Holocene fossil coral records from the WPWP. The new modern coral record captures large ENSO events with considerable skill, providing new evidence for potential large ENSO events during the early 18^th and 19^th centuries, events that are not represented in current coral and/or multi-proxy reconstructions. We also note that long periods of reduced ENSO activity can occur during intervals with near constant precessional forcing at modern values. The fossil coral records provide discrete time windows into ENSO variability over the Holocene. These records provide evidence of similar patterns of ENSO activity during intervals with different precessional configurations. The modern and fossil coral records imply a strong influence of internal variability in the modulation of ENSO, which may make it difficult to establish a direct control of precessional forcing on ENSO variability over the Holocene.