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Ocean Science An interactive open-access journal of the European Geosciences Union

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Ocean Sci., 12, 861-873, 2016
http://www.ocean-sci.net/12/861/2016/
doi:10.5194/os-12-861-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
04 Jul 2016
Observed El Niño conditions in the eastern tropical Pacific in October 2015
Lothar Stramma1, Tim Fischer1, Damian S. Grundle1,a, Gerd Krahmann1, Hermann W. Bange1, and Christa A. Marandino1 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
anow at: Bermuda Institute of Ocean Sciences (BIOS), 17 Biological Station, St George's GE 01, Bermuda
Abstract. A strong El Niño developed in early 2015. Measurements from a research cruise on the R/V Sonne in October 2015 near the Equator east of the Galapagos Islands and off the shelf of Peru are used to investigate changes related to El Niño in the upper ocean in comparison with earlier cruises in this region. At the Equator at 85°30′ W, a clear temperature increase leading to lower densities in the upper 350 m had developed in October 2015, despite a concurrent salinity increase from 40 to 350 m. Lower nutrient concentrations were also present in the upper 200 m, and higher oxygen concentrations were observed between 40 and 130 m. In the equatorial current field, the Equatorial Undercurrent (EUC) east of the Galapagos Islands almost disappeared in October 2015, with a transport of only 0.02 Sv in the equatorial channel between 1° S and 1° N, and a weak current band of 0.78 Sv located between 1 and 2°30′ S. Such near-disappearances of the EUC in the eastern Pacific seem to occur only during strong El Niño events. Off the Peruvian shelf at  ∼  9° S, characteristics of upwelling were different as warm, saline, and oxygen-rich water was upwelled. At  ∼  12,  ∼  14, and  ∼  16° S, the upwelling of cold, low-salinity, and oxygen-poor water was still active at the easternmost stations of these three sections, while further west on these sections a transition to El Niño conditions appeared. Although from early 2015 the El Niño was strong, the October measurements in the eastern tropical Pacific only showed developing El Niño water mass distributions. In particular, the oxygen distribution indicated the ongoing transition from “typical” to El Niño conditions progressing southward along the Peruvian shelf.

Citation: Stramma, L., Fischer, T., Grundle, D. S., Krahmann, G., Bange, H. W., and Marandino, C. A.: Observed El Niño conditions in the eastern tropical Pacific in October 2015, Ocean Sci., 12, 861-873, doi:10.5194/os-12-861-2016, 2016.
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Short summary
Results from a research cruise on R/V Sonne to the eastern tropical Pacific in October 2015 during the 2015–2016 El Niño show the transition of current, hydrographic, and nutrient conditions to El Niño conditions in the eastern tropical Pacific in October 2015. Although in early 2015 the El Niño was strong and in October 2015 showed a clear El Niño influence on the EUC, in the eastern tropical Pacific the measurements only showed developing El Niño water mass distributions.
Results from a research cruise on R/V Sonne to the eastern tropical Pacific in October 2015...
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