Influence of seaway changes during the Pliocene on tropical Pacific climate in the Kiel climate model: mean state, annual cycle, ENSO, and their interactions
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The El Niño/Southern Oscillation (ENSO) is the leading mode of tropical Pacific interannual variability in the present-day climate. Available proxy evidence suggests that ENSO also existed during past climates, for example during the Pliocene extending from about 5.3 million to about 2.6 million years BP. Here we investigate the influences of the Panama Seaway closing and Indonesian Passages narrowing, and also of atmospheric carbon dioxide (CO2) on the tropical Pacific mean climate and annual cycle, and their combined impact on ENSO during the Pliocene. To this end the Kiel Climate Model), a global climate model, is employed to study the influences of the changing geometry and CO2-concentration. We find that ENSO is sensitive to the closing of the Panama Seaway, with ENSO amplitude being reduced by about 15–20 %. The narrowing of the Indonesian Passages enhances ENSO strength but only by about 6 %. ENSO period changes are modest and the spectral ENSO peak stays rather broad. Annual cycle changes are more prominent. An intensification of the annual cycle by about 50 % is simulated in response to the closing of the Panama Seaway, which is largely attributed to the strengthening of meridional wind stress. In comparison to the closing of the Panama Seaway, the narrowing of the Indonesian Passages only drives relatively weak changes in the annual cycle. A robust relationship is found such that ENSO amplitude strengthens when the annual cycle amplitude weakens.
KeywordsGateway Panama Seaway Indonesian Passages Paleoclimate modeling Annual cycle ENSO
This study was supported by the Excellence Cluster “The Future Ocean” at Kiel University and the SFB 754 “Climate-Biogeochemistry Interactions in the Tropical Ocean”, which both are sponsored by the German Science Foundation (DFG). The model simulations were conducted at the Computing Center of Kiel University. Zhaoyang Song is a Ph.D. student, sponsored by the Chinese Scholarship Council (CSC).
- Latif M, Roeckner E, Botzet M, Esch M, Haak H, Hagemann S, Jungclaus J, Legutke S, Marsland S, Mikolajewicz U, Mitchell J (2004) Reconstructing, monitoring, and predicting multidecadal-scale changes in the North Atlantic thermohaline circulation with sea surface temperature. J Clim 17:1605–1614. doi: 10.1175/1520-0442(2004)017<1605:RMAPMC>2.0.CO;2 CrossRefGoogle Scholar
- Madec G (2008) NEMO ocean engine. Note du Pole de modélisation 27, Institut Pierre-Simon Laplace, p 193Google Scholar
- Roeckner E, Bäuml G, Bonaventura L, Brokopf R, Esch M, Giorgetta M, Manzini E (2003) The atmospheric general circulation model ECHAM5. Part I: model description. Max Planck Institute for Meteorology, Hamburg, Germany, Report No. 349, p 127Google Scholar
- Valcke S (ed) (2006) OASIS3 user guide. PRISM Tech. Rep. 3. http://www.prism.enes.org/Publications/Reports/oasis3_UserGuide_T3.pdf