El Nino Events: Literature Review

downloadDownload
  • Words 898
  • Pages 2
Download PDF

The article by Tudhope et al. (2001) uses oxygen isotope δ18O composition of coralline aragonite to reconstruct past ENSO activity in Papua New Guinea where they believe that ENSO existed 130,000 years ago. Tudhope et al. (2001) also believes that during the 20th century ENSO has been stronger where they hypothesise that this may be due to the ‘effects of ENSO dampening during cool glacial conditions and ENSO forcing by precessional orbital variations’. They began sampling by collecting cores from in situ fossil Porites corals from 3 locations (Huon Peninsula, Madang and Laing Island) which represented phases of reef growth over the last glacial-interglacial cycle.

Fig 1. Fossil coral skeletal δ18O time series for comparison with modern coral records. Shading represents paleo-El Nino events. Source: (Tudhope et al., 2001).

Click to get a unique essay

Our writers can write you a new plagiarism-free essay on any topic

Tudhope et al. (2001) graph ENSO variability in records from fossil corals in figure 1 above. Tudhope et al. (2001) found proxy evidence that surface equatorial pacific was 3°C cooler at the Last Glacial Maximum (LGM) (~20ka) and very similar to present during the last interglacial (~118-128ka). Tudhope et al. (2001) also found that Sea Surface Temperature (SST) was similar to present 2-3ka and about 2-4°C cooler around ~112ka. Tudhope et al. (2001) and Clement et al. (1999) found that orbital precession would cause major changes in ENSO variability through the last glacial-interglacial cycle. In the paper, by Tudhope et al. (2001) they confirmed their hypothesis by stating that a dual control for ENSO exists consisting of a ‘glacial dampening component and an orbital precession component’ which correlated with their paleo-ENSO data.

Similarly, a more recent article by Pena et al. (2008) studied ENSO in their paper titled ‘El Nino – Southern Oscillation – like variability during glacial terminations and interlatitudinal teleconnections’. In the paper of Pena et al. (2008) they hypothesise that ‘oceanic tunnelling has reinforced orbitally induced changes in ENSO-like variability, composing a complex high and low latitude feedback during glacial terminations’. In their paper they begin sampling by taking δ18O, δ13O and Mg/Ca trace element measurements on two planktonic foraminifera species (Globigerinoides ruber and Neogloboquadrina dutertrei) in the Panama basin, where they modelled changes from the last 275,000 ka. They modelled precession and deep thermocline δ18O against the Gaussian precession band-pass filter from the past 275,000 ka as seen in figure 2.

Fig 2. Precession forcing and deep thermocline δ18O modelled against Gaussian precession band-pass filter from the last 275,000 ka. Yellow shading corresponds to major deep thermocline δ18O saltwater excursions, whereas the grey shadings relate to minor events. Source: (Pena at al., 2008).

Pena at al. (2008) concluded their paper by confirming their hypothesis by stating that precession was the dominant force that controlled past changes in the eastern equatorial pacific. Similar to the paper by Tudhope et al. (2001) this paper by Pena at al. (2008) shares the idea of precession being the dominant force in the eastern equatorial pacific and on ENSO however, unlike the paper by Tudhope et al. (2001) the paper of Pena at al. (2008) doesn’t mention if the amplitude of ENSO is increasing or decreasing.

The paper by Otto-Bliesner et al. (2003) studied El Nino and its tropical teleconnections during the last glacial-interglacial cycle. Otto-Bliesner et al. (2003) carried out simulations using climate system models (CSM) based on data derived from alkenones and Mg/Ca ratios. In their CSM for the LGM their model predicted a 20% increase in ENSO variability compared to the present as they state that large warm events and large cold events are much more frequent during the LGM compared to records of the present day. Unlike the papers by Tudhope et al. (2001) and Pena et al. (2008) this paper doesn’t believe that precession forces are the main drivers behind ENSO variability however, their climate models predict that changes in zonal and vertical gradients of ocean temperature are responsible for being the main driver behind ENSO variability. This paper differs in hypotheses to what causes these changes in ENSO variability compared to the papers of Tudhope et al. (2001) and Pena et al. (2008) which shows how hypotheses can change over time.

A more recent paper by Grelaud et al. (2009) studied glacial to interglacial primary production and ENSO dynamics. They sampled using coccolithophore assemblages of the Santa Barbara Basin from a sedimentary sequence that goes back as much as 35ka. By studying many different species of coccolithophores Grelaud et al. (2009) were able to interpret past conditions. They believed that El Nino has continued to exist for the last 28 ka which follows a precession cycle and much like other papers previously mentioned in this article they believe that the Holocene exhibits a decrease in El Nino’s frequency. By observing the stratigraphic sequence Grelaud et al. (2009) found a high relative abundance of Gephyrocapsa oceanica indicating warm waters which is indicative of strong El Nino episodes (Grelaud et al., 2009 and De Bernardi et al., 2005). However, Grelaud et al. (2009) mentions that the evolution of periodicities recorded from coccolithophore assemblages follows precession cycles and that El Nino events are less recurrent when precession is minimal further providing evidence to the precession forcing ENSO variability hypothesis. In the closing remarks of their paper Grelaud et al. (2009) states that “precession has influenced the evolution of El Nino by changing the frequency of the phenomenon and probably its intensity” which is in accordance with a paper by Clement et al. (1999).

image

We use cookies to give you the best experience possible. By continuing we’ll assume you board with our cookie policy.