Abstract
Abstract. A complete understanding of past El Niño–Southern Oscillation (ENSO) fluctuations is important for the future predictions of regional climate using climate models. One approach to reconstructing past ENSO dynamics uses planktonic foraminifera as recorders of past climate to assess past spatio-temporal changes in upper ocean conditions. In this paper, we utilise a model of planktonic foraminifera populations, Foraminifera as Modelled Entities (FAME), to forward model the potential monthly average δ18Oc and temperature signal proxy values for Globigerinoides ruber, Globigerinoides sacculifer, and Neogloboquadrina dutertrei from input variables covering the period of the instrumental record. We test whether the modelled foraminifera population δ18Oc and Tc associated with El Niño events statistically differ from the values associated with other climate states. Provided the assumptions of the model are correct, our results indicate that the values of El Niño events can be differentiated from other climate states using these species. Our model computes the proxy values of foraminifera in the water, suggesting that, in theory, water locations for a large portion of the tropical Pacific should be suitable for differentiating El Niño events from other climate states. However, in practice it may not be possible to differentiate climate states in the sediment record. Specifically, comparison of our model results with the sedimentological features of the Pacific Ocean shows that a large portion of the hydrographically/ecologically suitable water regions coincide with low sediment accumulation rate at the sea floor and/or of sea floor that lie below threshold water depths for calcite preservation.
Highlights
1.1 El Niño–Southern Oscillation (ENSO)Predictions of short-term, abrupt changes in regional climate are imperative for improving spatio-temporal precision and accuracy when forecasting future climate
We utilise a model of planktonic foraminifera populations, Foraminifera as Modelled Entities (FAME), to forward model the potential monthly average δ18Oc and temperature signal proxy values for Globigerinoides ruber, Globigerinoides sacculifer, and Neogloboquadrina dutertrei from input variables covering the period of the instrumental record
Our model computes the proxy values of foraminifera in the water, suggesting that, in theory, water locations for a large portion of the tropical Pacific should be suitable for differentiating El Niño events from other climate states
Summary
Predictions of short-term, abrupt changes in regional climate are imperative for improving spatio-temporal precision and accuracy when forecasting future climate. Coupled ocean– atmosphere interactions (wind circulation and sea surface temperature) in the tropical Pacific, collectively known as the El Niño–Southern Oscillation (ENSO) on interannual timescales and the Pacific Decadal Oscillation on decadal timescales, represent largest source of interannual climate variability in global climate (Wang et al, 2017). The instrumental record of the past century provides important information (that can be translated into the Southern Oscillation Index; SOI); detailed oceanographic observations of the components of ENSO (both the El Niño and Southern Oscillation), such as the Tropical Oceans Global Atmosphere (TOGA; 1985– 1994) experiment only provide information from the latter half of the twentieth century (Wang et al, 2017). An integrated approach combining palaeoclimate proxies (Ford et al, 2015; de GaridelThoron et al, 2007; Koutavas et al, 2006; Koutavas and Joanides, 2012; Koutavas and Lynch-Stieglitz, 2003; Leduc et al, 2009; White et al, 2018) and computer models (Zhu et al, 2017) can help shed light on the triggers of past ENSO events, their magnitude, and their spatio-temporal distribution
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