Reconstructing ENSO: the influence of method, proxy data, climate forcing and teleconnections

Abstract

In this study we compare three newly developed independent NINO3.4 sea surface temperature (SST) reconstructions using data from (1) the central Pacific (corals), (2) the TexMex region of the USA (tree rings) and (3) other regions in the Tropics (corals and an ice core) which are teleconnected with central Pacific SSTs in the 20th century. Although these three reconstructions are strongly calibrated and well verified, inter-proxy comparison shows a significant weakening in interproxy coherence in the 19th century. This breakdown in common signal could be related to insufficient data, dating errors in some of the proxy records or a breakdown in El Niñ o-Southern Oscillation's (ENSO's) influence on other regions. However, spectral analysis indicates that each reconstruction portrays ENSO-like spectral properties. Superposed epoch analysis also shows that each reconstruction shows a generally consistent 'El Niñ o-like' response to major volcanic events in the following year, while during years T þ 4 to T þ 7 'La Niñ a-like' conditions prevail. These results suggest that each of the series expresses ENSO-like 'behaviour', but this 'behaviour' does not appear to be spatially or temporally consistent. This result may reflect published observations that there appear to be distinct 'types' of ENSO variability depending on location within the tropical Pacific. Future work must address potential dating issues within some proxies (i.e. sampling of multiple coral heads for one location) as well as assessing the time stability of local climate relationships with central Pacific SSTs. More emphasis is needed on sampling new and extending old coral proxy records from the crucial central and eastern tropical Pacific region. y The contribution of R. Allan was written in the course of his employment at the Met Office, UK and is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland.

A probabilistic model of chronological errors in layer-counted climate proxies: applications to annually banded coral archives

“…2 demonstrates how miscounting errors may produce an apparent amplitude modulation of otherwise stationary signals, producing spurious trends in the average derived from them. Because climate reconstruction methods rely in some fashion on a weighted average of observations assumed to be contemporaneous, this may partially explain why many ENSO reconstructions (e.g., Mann et al, 2000;Wilson et al, 2010;McGregor et al, 2010;Li et al, 2011; display increasing trends in ENSO variance over time (McGregor et al, 2013). As pointed out in the latter study, computing ENSO variance on individual records prior to averaging them together is more robust to chronological errors.…”

Reconstructing El Niño Southern Oscillation using data from ships’ logbooks, 1815–1854. Part II: Comparisons with existing ENSO reconstructions and implications for reconstructing ENSO diversity

“…Similar to the need for increased logbook digitisation, there is also large scope for an increased coverage of proxy networks. An increase in the number of corals from the Pacific Ocean would help to improve the reconstruction of the different flavours of ENSO (Wilson et al 2010). Recent work has looked at using proxies from regions where the EP and CP signals are distinctly different, in order to distinguish between ENSO flavours (Schollaen et al 2015).…”

“…S1. Wilson et al (2010) provide a normalised NINO3.4 reconstructions which uses proxy data from teleconnection (TEL) regions. Annually resolved proxies were used from teleconnection regions within the tropics.…”

“…Annually resolved proxies were used from teleconnection regions within the tropics. Eleven coral proxies and one tropical ice core record were used for their TEL reconstruction which spans from 1540 to 1998 (Wilson et al 2010). Therefore, a smaller number of proxies are used compared to McGregor et al (2010), however the focus on tropical teleconnections only suggests that there may be less noise in the ENSO signals from the proxies used in this reconstruction.…”

Paleoclimate Data–Model Comparison and the Role of Climate Forcings over the Past 1500 Years*

“…Multiproxy networks comprise data from multiple archives and multiple sites. Such networks are used to reconstruct climatic variables from the regional to global scale, generating spatial averages (e.g., Mann et al 2008), gridded spatial fields (e.g., Mann et al 2009), or indices of largescale modes of variability such as El Niño-Southern Oscillation (e.g., Wilson et al 2010).…”